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Publisher: Elsevier   (Total: 3162 journals)

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Showing 1 - 200 of 3162 Journals sorted alphabetically
A Practical Logic of Cognitive Systems     Full-text available via subscription   (Followers: 9)
AASRI Procedia     Open Access   (Followers: 15)
Academic Pediatrics     Hybrid Journal   (Followers: 34, SJR: 1.655, CiteScore: 2)
Academic Radiology     Hybrid Journal   (Followers: 23, SJR: 1.015, CiteScore: 2)
Accident Analysis & Prevention     Partially Free   (Followers: 97, SJR: 1.462, CiteScore: 3)
Accounting Forum     Hybrid Journal   (Followers: 26, SJR: 0.932, CiteScore: 2)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 37, SJR: 1.771, CiteScore: 3)
Achievements in the Life Sciences     Open Access   (Followers: 5)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 7)
Acta Astronautica     Hybrid Journal   (Followers: 411, SJR: 0.758, CiteScore: 2)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 2)
Acta Biomaterialia     Hybrid Journal   (Followers: 27, SJR: 1.967, CiteScore: 7)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription   (Followers: 2)
Acta de Investigación Psicológica     Open Access   (Followers: 3)
Acta Ecologica Sinica     Open Access   (Followers: 10, SJR: 0.18, CiteScore: 1)
Acta Haematologica Polonica     Free   (Followers: 1, SJR: 0.128, CiteScore: 0)
Acta Histochemica     Hybrid Journal   (Followers: 3, SJR: 0.661, CiteScore: 2)
Acta Materialia     Hybrid Journal   (Followers: 252, SJR: 3.263, CiteScore: 6)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5, SJR: 0.504, CiteScore: 1)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.542, CiteScore: 1)
Acta Oecologica     Hybrid Journal   (Followers: 12, SJR: 0.834, CiteScore: 2)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription  
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 3, SJR: 0.307, CiteScore: 0)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 1, SJR: 1.793, CiteScore: 6)
Acta Poética     Open Access   (Followers: 4, SJR: 0.101, CiteScore: 0)
Acta Psychologica     Hybrid Journal   (Followers: 28, SJR: 1.331, CiteScore: 2)
Acta Sociológica     Open Access   (Followers: 1)
Acta Tropica     Hybrid Journal   (Followers: 6, SJR: 1.052, CiteScore: 2)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 3, SJR: 0.374, CiteScore: 1)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 2)
Actas Urológicas Españolas     Full-text available via subscription   (Followers: 3, SJR: 0.344, CiteScore: 1)
Actas Urológicas Españolas (English Edition)     Full-text available via subscription   (Followers: 1)
Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 6, SJR: 0.19, CiteScore: 0)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 3)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 6)
Acute Pain     Full-text available via subscription   (Followers: 14, SJR: 2.671, CiteScore: 5)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.53, CiteScore: 4)
Addictive Behaviors     Hybrid Journal   (Followers: 16, SJR: 1.29, CiteScore: 3)
Addictive Behaviors Reports     Open Access   (Followers: 8, SJR: 0.755, CiteScore: 2)
Additive Manufacturing     Hybrid Journal   (Followers: 9, SJR: 2.611, CiteScore: 8)
Additives for Polymers     Full-text available via subscription   (Followers: 22)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 150, SJR: 4.09, CiteScore: 13)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 11, SJR: 1.167, CiteScore: 4)
Advanced Powder Technology     Hybrid Journal   (Followers: 17, SJR: 0.694, CiteScore: 3)
Advances in Accounting     Hybrid Journal   (Followers: 8, SJR: 0.277, CiteScore: 1)
Advances in Agronomy     Full-text available via subscription   (Followers: 14, SJR: 2.384, CiteScore: 5)
Advances in Anesthesia     Full-text available via subscription   (Followers: 28, SJR: 0.126, CiteScore: 0)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 2)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 10, SJR: 0.992, CiteScore: 1)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 11, SJR: 1.551, CiteScore: 4)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 24, SJR: 2.089, CiteScore: 5)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 14, SJR: 0.572, CiteScore: 2)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.61, CiteScore: 7)
Advances in Botanical Research     Full-text available via subscription   (Followers: 2, SJR: 0.686, CiteScore: 2)
Advances in Cancer Research     Full-text available via subscription   (Followers: 33, SJR: 3.043, CiteScore: 6)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 8, SJR: 1.453, CiteScore: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 1.992, CiteScore: 5)
Advances in Cell Aging and Gerontology     Full-text available via subscription   (Followers: 3)
Advances in Cellular and Molecular Biology of Membranes and Organelles     Full-text available via subscription   (Followers: 12)
Advances in Chemical Engineering     Full-text available via subscription   (Followers: 27, SJR: 0.156, CiteScore: 1)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 10, SJR: 0.713, CiteScore: 1)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 10, SJR: 1.316, CiteScore: 2)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 29, SJR: 1.562, CiteScore: 3)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 19, SJR: 1.977, CiteScore: 8)
Advances in Computers     Full-text available via subscription   (Followers: 14, SJR: 0.205, CiteScore: 1)
Advances in Dermatology     Full-text available via subscription   (Followers: 15)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 12)
Advances in Digestive Medicine     Open Access   (Followers: 9)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 5)
Advances in Drug Research     Full-text available via subscription   (Followers: 24)
Advances in Ecological Research     Full-text available via subscription   (Followers: 44, SJR: 2.524, CiteScore: 4)
Advances in Engineering Software     Hybrid Journal   (Followers: 28, SJR: 1.159, CiteScore: 4)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 7)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 46, SJR: 5.39, CiteScore: 8)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 1)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 9)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 58, SJR: 0.591, CiteScore: 2)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 16)
Advances in Genetics     Full-text available via subscription   (Followers: 16, SJR: 1.354, CiteScore: 4)
Advances in Genome Biology     Full-text available via subscription   (Followers: 8, SJR: 12.74, CiteScore: 13)
Advances in Geophysics     Full-text available via subscription   (Followers: 6, SJR: 1.193, CiteScore: 3)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 23, SJR: 0.368, CiteScore: 1)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 12, SJR: 0.749, CiteScore: 3)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 22)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 2, SJR: 0.193, CiteScore: 0)
Advances in Immunology     Full-text available via subscription   (Followers: 36, SJR: 4.433, CiteScore: 6)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 8, SJR: 1.163, CiteScore: 2)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 2, SJR: 1.938, CiteScore: 3)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 7, SJR: 0.176, CiteScore: 0)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 3)
Advances in Life Course Research     Hybrid Journal   (Followers: 8, SJR: 0.682, CiteScore: 2)
Advances in Lipobiology     Full-text available via subscription   (Followers: 1)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 8)
Advances in Marine Biology     Full-text available via subscription   (Followers: 18, SJR: 0.88, CiteScore: 2)
Advances in Mathematics     Full-text available via subscription   (Followers: 11, SJR: 3.027, CiteScore: 2)
Advances in Medical Sciences     Hybrid Journal   (Followers: 6, SJR: 0.694, CiteScore: 2)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 5)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 4, SJR: 1.158, CiteScore: 3)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 23)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 8)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 7, SJR: 0.182, CiteScore: 0)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 3)
Advances in Oncobiology     Full-text available via subscription   (Followers: 1)
Advances in Organ Biology     Full-text available via subscription   (Followers: 1)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 17, SJR: 1.875, CiteScore: 4)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7, SJR: 0.174, CiteScore: 0)
Advances in Parasitology     Full-text available via subscription   (Followers: 5, SJR: 1.579, CiteScore: 4)
Advances in Pediatrics     Full-text available via subscription   (Followers: 24, SJR: 0.461, CiteScore: 1)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 12)
Advances in Pharmacology     Full-text available via subscription   (Followers: 16, SJR: 1.536, CiteScore: 3)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 8, SJR: 0.574, CiteScore: 1)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.109, CiteScore: 1)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 9)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 5)
Advances in Porous Media     Full-text available via subscription   (Followers: 5)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 18)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 20, SJR: 0.791, CiteScore: 2)
Advances in Psychology     Full-text available via subscription   (Followers: 64)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 6, SJR: 0.371, CiteScore: 1)
Advances in Radiation Oncology     Open Access   (Followers: 1, SJR: 0.263, CiteScore: 1)
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 3, SJR: 0.101, CiteScore: 0)
Advances in Space Biology and Medicine     Full-text available via subscription   (Followers: 6)
Advances in Space Research     Full-text available via subscription   (Followers: 397, SJR: 0.569, CiteScore: 2)
Advances in Structural Biology     Full-text available via subscription   (Followers: 5)
Advances in Surgery     Full-text available via subscription   (Followers: 11, SJR: 0.555, CiteScore: 2)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 34, SJR: 2.208, CiteScore: 4)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 17)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 13)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 2.262, CiteScore: 5)
Advances in Water Resources     Hybrid Journal   (Followers: 46, SJR: 1.551, CiteScore: 3)
Aeolian Research     Hybrid Journal   (Followers: 6, SJR: 1.117, CiteScore: 3)
Aerospace Science and Technology     Hybrid Journal   (Followers: 342, SJR: 0.796, CiteScore: 3)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.42, CiteScore: 2)
African J. of Emergency Medicine     Open Access   (Followers: 6, SJR: 0.296, CiteScore: 0)
Ageing Research Reviews     Hybrid Journal   (Followers: 11, SJR: 3.671, CiteScore: 9)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 453, SJR: 1.238, CiteScore: 3)
Agri Gene     Hybrid Journal   (Followers: 1, SJR: 0.13, CiteScore: 0)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 17, SJR: 1.818, CiteScore: 5)
Agricultural Systems     Hybrid Journal   (Followers: 31, SJR: 1.156, CiteScore: 4)
Agricultural Water Management     Hybrid Journal   (Followers: 41, SJR: 1.272, CiteScore: 3)
Agriculture and Agricultural Science Procedia     Open Access   (Followers: 3)
Agriculture and Natural Resources     Open Access   (Followers: 3)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 57, SJR: 1.747, CiteScore: 4)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.589, CiteScore: 3)
Air Medical J.     Hybrid Journal   (Followers: 6, SJR: 0.26, CiteScore: 0)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.19, CiteScore: 0)
Alcohol     Hybrid Journal   (Followers: 11, SJR: 1.153, CiteScore: 3)
Alcoholism and Drug Addiction     Open Access   (Followers: 10)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 1, SJR: 0.604, CiteScore: 3)
Alexandria J. of Medicine     Open Access   (Followers: 1, SJR: 0.191, CiteScore: 1)
Algal Research     Partially Free   (Followers: 11, SJR: 1.142, CiteScore: 4)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 2)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.504, CiteScore: 1)
Allergology Intl.     Open Access   (Followers: 5, SJR: 1.148, CiteScore: 2)
Alpha Omegan     Full-text available via subscription   (SJR: 3.521, CiteScore: 6)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 9, SJR: 0.201, CiteScore: 1)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 51, SJR: 4.66, CiteScore: 10)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 4, SJR: 1.796, CiteScore: 4)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 4, SJR: 1.108, CiteScore: 3)
Ambulatory Pediatrics     Hybrid Journal   (Followers: 6)
American Heart J.     Hybrid Journal   (Followers: 50, SJR: 3.267, CiteScore: 4)
American J. of Cardiology     Hybrid Journal   (Followers: 54, SJR: 1.93, CiteScore: 3)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 45, SJR: 0.604, CiteScore: 1)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 10)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 14, SJR: 1.524, CiteScore: 3)
American J. of Human Genetics     Hybrid Journal   (Followers: 34, SJR: 7.45, CiteScore: 8)
American J. of Infection Control     Hybrid Journal   (Followers: 27, SJR: 1.062, CiteScore: 2)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 35, SJR: 2.973, CiteScore: 4)
American J. of Medicine     Hybrid Journal   (Followers: 47)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3, SJR: 1.967, CiteScore: 2)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 210, SJR: 2.7, CiteScore: 4)
American J. of Ophthalmology     Hybrid Journal   (Followers: 65, SJR: 3.184, CiteScore: 4)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 5, SJR: 0.265, CiteScore: 0)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.289, CiteScore: 1)
American J. of Otolaryngology     Hybrid Journal   (Followers: 25, SJR: 0.59, CiteScore: 1)
American J. of Pathology     Hybrid Journal   (Followers: 28, SJR: 2.139, CiteScore: 4)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 28, SJR: 2.164, CiteScore: 4)
American J. of Surgery     Hybrid Journal   (Followers: 38, SJR: 1.141, CiteScore: 2)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 12, SJR: 0.767, CiteScore: 1)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 7)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.144, CiteScore: 3)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 62, SJR: 0.138, CiteScore: 0)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 17, SJR: 0.411, CiteScore: 1)
Anales de Cirugia Vascular     Full-text available via subscription  
Anales de Pediatría     Full-text available via subscription   (Followers: 3, SJR: 0.277, CiteScore: 0)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription  
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 5, SJR: 4.849, CiteScore: 10)
Analytica Chimica Acta     Hybrid Journal   (Followers: 42, SJR: 1.512, CiteScore: 5)
Analytical Biochemistry     Hybrid Journal   (Followers: 176, SJR: 0.633, CiteScore: 2)
Analytical Chemistry Research     Open Access   (Followers: 11, SJR: 0.411, CiteScore: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 11)
Anesthésie & Réanimation     Full-text available via subscription   (Followers: 2)
Anesthesiology Clinics     Full-text available via subscription   (Followers: 23, SJR: 0.683, CiteScore: 2)
Angiología     Full-text available via subscription   (SJR: 0.121, CiteScore: 0)
Angiologia e Cirurgia Vascular     Open Access   (Followers: 1, SJR: 0.111, CiteScore: 0)
Animal Behaviour     Hybrid Journal   (Followers: 196, SJR: 1.58, CiteScore: 3)

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Journal Cover
Acta Astronautica
Journal Prestige (SJR): 0.758
Citation Impact (citeScore): 2
Number of Followers: 411  
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0094-5765
Published by Elsevier Homepage  [3162 journals]
  • Towards increasing nanosatellite subsystem robustness
    • Abstract: Publication date: Available online 17 November 2018Source: Acta AstronauticaAuthor(s): Carlos Leandro Gomes Batista, Anderson Coelho Weller, Eliane Martins, Fátima Mattiello-Francisco Short development life cycle and low cost of cubesat-based mission have motivated the growing number of nanosatellite launched in the last decade around the world. Fast and cheaper space project do not guarantee success in orbit. The lack of good practices on design, assembly and tests has been pointed out as one of the major causes to nanosatellite mission failures. Efforts on the use of verification and validation techniques are required. Because the increased use of nanosatellites missions for technology qualification of payloads on orbit, faulty behavior of those payloads can be expected. However, such malfunction shall not represent a risk to the whole mission. Robustness is an important property of reactive critical system not addressed properly in the cubesat standardization. Although significant mitigation of the interface failures has been observed at hardware level in the integration phase of the payloads with the nanosatellite platform, behavior aspects of the communicating subsystems on the use of these interfaces shall be verified. The test systematization of CubeSat-based nanosatellites supported by proper tools is necessary to reduce the mission development cycle in terms of the time consumed by the verification & validation activities. In this paper we present a failure emulator mechanism framework, named FEM, for robustness testing of interoperable software-intensive subsystems onboard nanosatellite. FEM acts in the communication channel being part of the integration test workbench in two phases of nanosatellite design: (i) robustness requirement specification using model in the loop (MIL) and (ii) robustness validation using hardware in the loop (HIL). The architectural aspects of the proposed FEM framework support its instantiation to any communication channel of the CubeSat standard. As an example, FEM prototype was instantiated to I2C communication channel to support NanosatC-BR2 testing. NanosatC-BR2 is a Cubesat based scientific mission, under development and integration at Brazilian Institute for Space Research (INPE), which uses I2C communication channel for its payloads interactions with the On-Board Data Handling computer subsystem (OBC). FEM prototype was used to support OBC integration testing with each payload subsystem at MIL scenario aiming at anticipating the robustness requirement verification on the development lifecycle. Moreover, the FEM prototype was also validated at HIL scenario using Test Cases automatically generated. Results of these two scenarios executions are reported demonstrating in a case study the effectiveness of FEM framework in detecting the lack or noncompliance of robustness requirements by the interoperated subsystems under testing.
  • Experimental study on the thermodynamic characteristics of the high
           temperature hydrocarbon fuel in the cooling channel of the hypersonic
    • Abstract: Publication date: Available online 17 November 2018Source: Acta AstronauticaAuthor(s): Haowei Li, Jiang Qin, Yuguang Jiang, Weixing Zhou, Wen Bao, Hongyan Huang Cooling is one of the key technologies for the scramjet considering the enormous thermal load and the demand of reusable long-range mission. In the regenerative cooling process, hydrocarbon fuel flows through the cooling channel, gets heated and experiences severe thermal properties changes. The compressibility of fuel becomes non-negligible and possible dynamic process emerges, which affects both the characteristics of fuel cooling and fuel mass flow control. As a result, the dynamic characteristics of the high temperature hydrocarbon fuel within the cooling channel must be carefully studied. In this work, experiments are conducted at different simulated engine working conditions. The settling time of pipe pressure drop is used to characterize the dynamic process of the outlet fuel mass flow, because the outlet temperature of the fuel is too high to measure the fuel mass flow directly. In conditions of the variation of inlet fuel mass flow and backpressure disturbance, overshoot of the pressure drop is observed and the magnitude of which varies with the working conditions. The settling time of outlet fuel temperature and wall temperature channel firstly increases, then decreases with the increase of the outlet fuel temperature. The settling time of both outlet fuel temperature and wall temperature increases with the increase of the heating heat flux. The experimental results in this work are expected to provide supports to the engine control system design.
  • SiO 2 +crystal+structure+on+the+stability+of+polymer+composites+exposed+to+vacuum+ultraviolet+radiation&rft.title=Acta+Astronautica&rft.issn=0094-5765&">Effect of SiO 2 crystal structure on the stability of polymer composites
           exposed to vacuum ultraviolet radiation
    • Abstract: Publication date: Available online 16 November 2018Source: Acta AstronauticaAuthor(s): V.I. Pavlenko, N.I. Cherkashina Vacuum ultraviolet (VUV) radiation produced by the Sun in the space environment can cause degradation to thermoregulating coatings producing changes in optical, mechanical, and chemical properties. These effects are particularly important for polymers. The purpose of this study was to study the effect of VUV radiation on polymeric composites based on polyalkaneimide. Amorphous and crystalline SiO2 were used as the filler. A comparative characterization of physico-mechanical properties of composites is presented depending on the polymorphic structure of the filler being introduced. According to the microhardness of the surface of composites with amorphous and crystalline SiO2, an optimum filler content of 60–65 wt% is established. The exposure of VUV radiation to polymeric composites with SiO2 leads to a mass loss and a change in their near-surface layers, which leads to a deterioration in the optical properties. At an elevated temperature (125oC), the mass loss of all composites with amorphous crystalline SiO2 does not exceed 1.33%, and with crystalline SiO2, the maximum mass loss is 0.52%. The mass loss of composites with crystalline SiO2 of all compositions did not exceed the allowable value for spacecraft products of 1%. For high-filled (50 wt% filler or more) composites with amorphous SiO2, mass loss after VUV treatment is more than 1%, which does not allow them to be used in outer space. The change in the main optical characteristics of thermoregulating coatings after VUV treatment was studied. The smoothing of the surface of composites after VUV treatment is established.
  • Separation of proteins and DNA by microstructure-changed microfuidic free
           flow electrophoresis chips
    • Abstract: Publication date: Available online 14 November 2018Source: Acta AstronauticaAuthor(s): Wei-Wei Sun, Rong-Ji Dai, Yong-Rui Li, Guo-Xin Dai, Xiu-Jie Liu, Bo Li, Xue-fei Lv, Yu-Lin Deng, Ai-Qing Luo Microfuidic free-flow electrophoresis (μFFE) is a micro-separation analysis technology with continuity, no solid support medium and mild separation conditions. However, the bubble problem has limited its application for a long time. Here, we proposed a μFFE device that isolated the bubbles from the separation chamber with partitioning bars of ∼40 μm wide in ∼5 μm intervals effectively. Compared to the conventional chip form, the change of micro-structure assured the stability of the chips even after working for 150 min. Lysozyme, BSA and pepsin were separated from the μFFE with electric field intensity of 81.82 V/cm, sample flow rate of 3 μL/min and pH 5. The optimized chips successfully separated lysozyme BSA and calf thymus DNA, which demonstrated an excellent baseline-separation of protein and nucleic acid mixtures under milder separation condition. These results showed that optimized μFFE chips based integrated device can be potentially applied to prepare and analyze complex biological samples in the future for deep space exploration.
  • Mixing augmentation mechanism induced by the dual injection concept in
           shcramjet engines
    • Abstract: Publication date: Available online 14 November 2018Source: Acta AstronauticaAuthor(s): Zhao-bo Du, Wei Huang, Li Yan, Zheng Chen, R. Moradi As one of the key techniques, achieving adequate fuel/air mixing before combustion is a task that must be addressed seriously for shock-induced combustion ramjet (shcramjet) engines. In this paper, dual injectors which have been combined by a front hydrogen jet and a rear air jet with different aspect ratios are placed on the second ramp of a shcramjet inlet to promote mixing process between fuel and hypersonic crossflow. At the same time, dual injectors with pure hydrogen injection and the single hydrogen injection with the same injection area are studied as well for comparison. Flow field properties are investigated numerically based on grid independency analysis and code validation. Obtained results predicted by the three-dimensional Reynolds-average Navier-Stokes (RANS) equations coupled with the two equation SST κ-ω turbulence model show that the grid scale makes only a slight difference to wall pressure profiles for all cases studied in this article. The dual transverse injection system with a front hydrogen jet and a rear air jet is beneficial for improvement of the mixing efficiency between hydrogen and air. Mixing efficiency in the near field increases with increase of aspect ratio of the air porthole. The air porthole in dual transverse injections would accelerate mixing process when compared with the single injection strategy irrespective of aspect ratio of the air porthole.
  • Investigation on rat intestinal homeostasis alterations induced by 7-day
           simulated microgravity effect based on a proteomic approach
    • Abstract: Publication date: Available online 14 November 2018Source: Acta AstronauticaAuthor(s): Shibo Wang, Yushi Zhang, Jingjing Guo, Liting Kang, Yulin Deng, Yujuan Li The present study aims at investigating alterations of rat intestinal homeostasis induced by 7-day simulated microgravity (SMG) effect through a proteomic approach. Tail-suspension model was used to simulate microgravity effect and a label-free quantitative proteomic strategy was employed to determine proteins in rat intestine. As a result, 717 differently expressed proteins were identified and 29 proteins were down-regulated while 688 proteins were up-regulated. 283 out of 717 proteins were categorized into 7 clusters with DAVID (version 6.8). The three highest enrichment scores were annotation cluster I about cell-cell adhesion (46 proteins with enrichment score of 16.67), annotation cluster II about carbohydrate metabolism (32 proteins with enrichment score of 6.17) and annotation cluster III about activity of pepdtidase (17 proteins with enrichment score of 4.74). Results of rat intestine proteomics indicate that SMG might disrupt intestinal homeostasis, which possibly resulted in opening of intestinal epithelial barrier (IEB), potentially leading to risk of systemic inflammatory response (SIR) and inflammatory bowel diseases (IBD). The present results also provide some useful information for mechanism and countermeasures of intestine injuries induced by microgravity.
  • Characterization of flow mixing and structural topology in supersonic
           planar mixing layer
    • Abstract: Publication date: Available online 14 November 2018Source: Acta AstronauticaAuthor(s): Dongdong Zhang, Jianguo Tan, Liang Lv, Fei Li The investigations on mixing process and structural topology properties of supersonic planar mixing layer with different inflow conditions are conducted by employing direct numerical simulation. First, the present high-order accuracy numerical methods are validated by comparing the simulation results with the data gained from previous well characterized experimental and numerical cases. Then the high-resolved three-dimensional numerical visualizations of supersonic mixing layer are presented by utilizing Q-criterion. The visualization results show the full development and evolution process of mixing layer, including the shear action, the transition process populated sequentially by Λ-vortices, hairpin vortices and braid structures and the establishment of self-similar turbulence. The effects of density ratio, velocity ratio and convective Mach number between the two parallel streams on mixing layer growth rate are evaluated by examining the indexes including velocity thickness and momentum thickness represented the mixing process. The results indicate that for the only variation of density ratio, the velocity thickness growth rates do not significantly vary, while the momentum thickness becomes larger when the upper and lower streams possess the same density. With the increase of only velocity ratio, the mixing layer becomes more stable and the velocity and momentum thickness are both drastically depressed in the whole flow field. As only convective Mach number increases, the mixing layer growth is inhibited in the near field through the transition delay of the flow, while in the far field, the growth rates are nearly the same for different convective Mach numbers. The spatial correlation analysis of structural topology indicates that the effects of each of the three main flow parameters on vortex topology lead to different mean structure sizes and shapes. The present research is useful for evaluating the effects of different flow parameters on mixing properties, which is important for the future scramjet combustor design and evaluation in engineering.
  • Numerical and experimental study of the thermochemical erosion of a
           graphite nozzle in a hybrid rocket motor with a star grain
    • Abstract: Publication date: Available online 13 November 2018Source: Acta AstronauticaAuthor(s): Tian Hui, Yu Ruipeng, Li Chengen, Zhao Sheng, Zhu Hao Hybrid rocket motors is a promising propulsion system because of its intrinsic advantages over a conventional solid rocket motor and liquid rocket engine. However, serious nozzle erosion is a key problem that prevents hybrid rocket motors from being widely used, especially for propulsion systems with long operating times. In this paper, the erosion of a graphite-based nozzle coupled with a combustion flow field is studied in a hybrid rocket motor with a star grain. As the oxidizer and fuel, 90% hydrogen peroxide and hydroxide-terminated polybutadiene are adopted, respectively. The nozzle erosion was simulated coupled with the flow field in a typical hybrid rocket motor through three-dimensional numerical simulations. The simulations are based on a pure-gas steady numerical model considering turbulence, fuel pyrolysis, oxidizer/fuel reactions, thermal conduction and solid-gas boundary interactions on the fuel and nozzle surfaces. The results indicate that the nozzle erosion is greatly influenced by the inner flow field. The flame near the grain trough is thicker than that near the grain peak. Therefore, the maximum erosion rate (0.042 mm/s) occurs near the nozzle throat corresponding to the grain trough. The OH and H2O contribute 49.8% and 45.5% to the erosion rate, respectively, in this area. Furthermore, 56.6% and 31.9% contributions are made by OH and H2O, respectively, in the area corresponding to the grain peak. The O, CO2 and O2 make much lower contributions to the total erosion. In addition, a firing test is carried out to characterize the graphite nozzle erosion on a full-scale hybrid rocket motor with star grain. The nozzle inner profiles before and after test show that the erosion behavior of the graphite material is strictly related to the fuel shape.
  • Experimental study on combustion characteristics of powder magnesium and
           carbon dioxide in rocket engine
    • Abstract: Publication date: Available online 13 November 2018Source: Acta AstronauticaAuthor(s): Yue Li, Chunbo Hu, Xiaofei Zhu, Jiaming Hu, Xu Hu, Chao Li, Yupeng Cai Mechanisms of powder magnesium and carbon dioxide combustion are required for the concept of Mars propulsion based on the perspective of in-situ resource utilization. Most current characterizations are based on laboratory experiments conducted in stationary or simple flow configuration. However, the chamber condition in most applications of engine is very complicated with high pressure and multi-phase flow environment, and the combustion process in engine-scale has not been established. The burning efficiency, combustion stability and excessive deposition are the mainly primary issues that limit the combustion performance in rocket environment, the experimental study aims at combustion characteristics and the affection mechanism of powder magnesium and carbon dioxide in rocket engine. A new configuration of powder rocket system is established. Meanwhile, a multiple-inlet configuration of CO2 injection is designated to control the CO2 injection positions and parameters, such as global and local oxidant-fuel ratio. Ignition process is studied and an empirical model for ignition judgment is established according to the result of ignition tests. Mechanism for combustion deposition is studied by the analysis of morphology, composition and distribution, characteristics of combustion efficiency are estimated based on test pressure and thermodynamic calculation, and oscillation mechanism of combustion pressure is obtained by frequency domain analysis. The higher concentration of magnesium particle, the cool CO2 injection and the increasing of CO concentration is supposed to be the main reasons for the deposition in different areas along the axis of the combustion chamber. The allocation of gas injection is an important factor that affects the combustion sufficiency associated to the heterogeneous reaction. Raising the O/F ratio in chamber head is an effective way to improve combustion efficiency for rocket engine, and the efficiency is improved firstly and then is decreased with increasing flow rate of fluidization gas. The low frequency oscillation is supposed to be related to flame instability induced by the gas injection in chamber head. The influence caused by primary and secondary gas injection are further analyzed in the frequency domain, the related characteristic bands are classified and the fluctuation tendency is obtained.Graphical abstractImage 1
  • Design-build-launch: A hybrid project-based laboratory course for
           aerospace engineering education
    • Abstract: Publication date: Available online 13 November 2018Source: Acta AstronauticaAuthor(s): R.M. Spearrin, F.A. Bendana A project-based course involving the design, analysis, manufacturing, testing, and launching of mid-power solid-propellant rockets over a ten-week period has been developed and taught as an approach to enhance the education and preparation of aerospace engineers at the university level. The course consists of a sequence of structured laboratory assignments that expose students to common software tools, aerospace materials, manufacturing techniques, and testing methods that directly inform and run parallel to the project. Teams of four to five students complete the project (and portions of the labs) collaboratively within an engineering competition framework. Individual students within each team are assigned specific engineering roles (e.g. design engineer, manufacturing engineer) to create an interdependence that reflects a typical integrated product team in industry and exposes students to realistic social dynamics. Student teams conduct design reviews as progressive milestones for assessment, in addition to laboratory assignments. At a per-student cost on the same order as a textbook, the project-based course combines theoretical content from several subjects with a high-order learning approach (create, evaluate, analyze) to advance the engineering skills of university students.
  • Aluminum agglomeration of AP/HTPB composite propellant
    • Abstract: Publication date: Available online 12 November 2018Source: Acta AstronauticaAuthor(s): Jifei Yuan, Jianzhong Liu, Yunan Zhou, Jianru Wang, Tuanwei Xv Aluminum (Al) powder agglomeration is one of the main reasons for the degradation in the performance of aluminized solid propellant rockets and so, understanding the combustion behavior of aluminum in solid propellants is of great importance. In this work, a laser ignition test bench was used to study the behavior of Al on the burning surface of an aluminum/ammonium perchlorate/hydroxyl-terminated polybutadiene composite propellant, under atmospheric pressure. Based on the images captured by a high-speed camera, the agglomeration process and behavior of the agglomerates were analyzed in detail. The size distribution and speed of motion of the agglomerates away from the burning surface were also considered. Results show that the formation of an agglomerate on the burning surface from multiple aluminum particles include three stages: accumulation, aggregation, and agglomeration. Local ignition promotes the collapse of the aggregate into a spherical agglomerate. Before detachment, the agglomerates often roll around on the burning surface and pick up more aluminum, promoting self-growth. The interesting phenomenon of an agglomerate droplet rupturing and ejecting liquid alumina on the burning surface was clearly captured for the first time. This is believed to indicate the heterogeneous composition characteristics of the agglomerate. The transformation of the polar oxide cap on one part of the agglomerate surface into an alumina shell that fully covers the droplet surface was also captured for the first time. The agglomerates have different shapes, diameters, and velocities when they leave the burning surface. The formation of non-spherical agglomerates consisting of more than one aluminum droplet is ascribed to the propellant microstructure. The 400 agglomerates that were counted had diameters that ranged from 51 μm to 815 μm and the majority of them (nearly 98%) were below 400 μm. The velocities of motion of 176 agglomerates exhibited great dispersion, with the maximum and minimum velocity being 196 cm/s and 13 cm/s, respectively. In general, the moving velocities of the agglomerates decreased with increasing diameter.
  • Multiple-horizon multiple-model predictive control of electromagnetic
           tethered satellite system
    • Abstract: Publication date: Available online 11 November 2018Source: Acta AstronauticaAuthor(s): MohammadAmin AlandiHallaj, Nima Assadian This study aims to investigate the control of the electromagnetic tethered satellite system using a Model Predictive Control (MPC) scheme. The electromagnetic tethered satellite system is actuated by electromagnetic coils to generate controlling forces. The dynamical model of the system is described in high and low levels of accuracy, which are used to design the control framework. Multiple-Horizon Multiple-Model Predictive Control approach is employed to drive the formation to the desired state. Not only does the presented control law satisfy input and output constraints but also has appropriate characteristics in the sense of optimality. The main benefit of using Multiple-Horizon Multiple-Model Predictive Control is having lower computational burden than the classical MPC. The numerical simulation results are presented and compared with sliding mode control to demonstrate the effectiveness of the proposed control method and its advantage over both classical MPC and sliding mode control methods. The obtained results show dramatic reductions in computational time and consumed energy compared to the classical MPC and sliding model control methods, respectively.
  • Effects of fueling distance on combustion stabilization modes in a
           cavity-based scramjet combustor
    • Abstract: Publication date: Available online 10 November 2018Source: Acta AstronauticaAuthor(s): Yanan Wang, Zhenguo Wang, Mingbo Sun, Hongbo Wang, Zun Cai The effects of distance from the injector upstream to the cavity leading edge on combustion stabilization modes were investigated experimentally and numerically. High-speed flame luminosity and schlieren images were utilized to reveal the combustion characteristics. Under a Mach 2.52 supersonic inflow condition with a stagnation temperature of 1629 K, hydrogen was injected with injection distances of 30 mm, 100 mm and 160  mm at global equivalence ratios from 0.20 to 0.32. The flame in cavity stabilized mode is observed at a relatively low equivalence ratio. Increasing the global equivalence ratio, the combustion stabilization mode transfers to the jet-wake stabilized mode with injection distances of 100 mm and 160 mm. It is surprising that the mode transition is the easiest for the medium injection distance of 100 mm. Large eddy simulations were then performed to explain the easiest mode-transition. Mixing characteristics, jet-cavity interactions and the jet-wake features upstream of the cavity for three injection distances were analyzed. With the injection distance of 100 mm, the reflected shock wave impacts on the cavity shear layer, and the interactions of the shock wave structures and the cavity induce the beginning phase of the jet-wake stabilized flame and help the flame propagate upstream around the cavity. Relatively larger amount of the fuel, lower streamwise velocity and lower static pressure was also found in the jet wake upstream of the cavity, which further supports the flame to propagate upstream and stabilize in the jet wake.
  • A new multi-satellite autonomous mission allocation and planning method
    • Abstract: Publication date: Available online 9 November 2018Source: Acta AstronauticaAuthor(s): Bin Du, Shuang Li To overcome the issues of inflexible interactive mode, low negotiation efficiency and poor dynamic response capability of satellite clusters, we propose a new multi-dimensional and multi-Agent clusters collaboration model (MDMA-CCM), including task pre-processing, allocation, scheduling and re-planning under failed conditions. First, the task clustering based pre-processing method is adopted to improve the observation efficiency by combining potential targets. Second, the Contract Net Protocol (CNP) based secondary allocation strategy is developed to effectively increase the observation benefit and reduce the impact of task conflicts through announcement, bidding and awarding. Third, a new Interactively Re-planning Method (IRM) is proposed to effectively reduce the loss by re-inserting tasks in case of failure. Simulation results show that the new planning model not only has obvious advantages in calculation time, but also outperforms the centralized multi-Agent system in terms of benefit value and completion rate.
  • Time-varying state-space model identification of an on-orbit
           rigid-flexible coupling spacecraft using an improved predictor-based
           recursive subspace algorithm
    • Abstract: Publication date: Available online 9 November 2018Source: Acta AstronauticaAuthor(s): Zhiyu Ni, Jinguo Liu, Shunan Wu, Zhigang Wu Spacecraft control problems frequently require the latest model parameters to provide timely updates to the controller parameters. This study investigates the recursive identification problem in a the time-varying state-space model of an on-orbit rigid-flexible coupling spacecraft. An improved recursive predictor-based subspace identification (RPBSID) method is presented to increase on-orbit identification efficiency. Compared with the classical RPBSID and other subspace methods, the improved RPBSID applies the affine projection sign algorithm. Accordingly, the system state variables can be determined directly via recursive computation. Thus, the proposed algorithm does not require constructing the corresponding Hankel matrix or implementing singular value decomposition (SVD) at each time instant. Consequently, the amount of data used in the identification process is reduced, and the computational complexity of the original method is decreased. The time-varying state-space model of the spacecraft is estimated through numerical simulations using the classical RPBSID, improved RPBSID, and SVD-based approaches. The computational efficiency and accuracy of the three methods are compared for different system orders. Computed results of the test response demonstrate that the improved RPBSID algorithm not only achieves sufficient identification accuracy but also exhibits better computational efficiency than the classical methods in identifying the parameters of the spacecraft time-varying state-space model.
  • Proximity scenario design for geostationary rendezvous with collocated
           satellite avoidance
    • Abstract: Publication date: Available online 7 November 2018Source: Acta AstronauticaAuthor(s): Ya-Zhong Luo, Zhen-Jiang Sun, Jin Zhang Proximity operation is one of the prerequisites for in-orbit service or debris removal. Especially for objects in geostationary orbit (GEO), there are certain challenges in rendezvous and proximity operations, such as perturbed relative dynamics and constraints from collocated satellites. In this study, a novel optimization model is built to design the GEO proximity scenario, including the keeping points and durations of each phase. First, as a prerequisite of proximity scenario design, relative dynamics considering solar radiation pressure effects and the corresponding two-point boundary value problem are analytically solved. Second, the concept of passive safety performance is introduced. The safety constraints from both the target satellite and the collocated satellites are considered. The optimization model is then built, and an improved differential evolution optimization algorithm is employed to seek the solution with minimal velocity increment. The numerical examples indicate that a GEO proximity scenario can be stably and effectively designed by the presented method. Moreover, in the scenarios without a collocated satellite, with a static collocated satellite, and with dynamic collocated satellites, the optimized proximity scenarios remain passively safe. If any impulse in the scenario ceases, the resulting free drift trajectory would diverge from the target and the collocated satellites, maintaining the safety index and satisfying the given threshold.
  • Neighboring optimal guidance and constrained attitude control applied to
           three-dimensional lunar ascent and orbit injection
    • Abstract: Publication date: Available online 7 November 2018Source: Acta AstronauticaAuthor(s): Mauro Pontani, Fabio Celani Future human or robotic missions to the Moon will require efficient ascent path and accurate orbit injection maneuvers, because the dynamical conditions at injection affect the subsequent phases of spaceflight. This research is focused on the original combination of two techniques applied to lunar ascent modules, i.e. (i) the recently-introduced variable-time-domain neighboring optimal guidance (VTD-NOG), and (ii) a constrained proportional-derivative (CPD) attitude control algorithm. VTD-NOG belongs to the class of implicit guidance approaches, aimed at finding the corrective control actions capable of maintaining the spacecraft sufficiently close to the reference trajectory. CPD pursues the desired attitude using thrust vector control and side jet system, while constraining the rates of both the thrust deflection angle and the roll control torque. After determining the optimal two-dimensional ascent path, which represents the reference trajectory, VTD-NOG & CPD is applied in the presence of nonnominal flight conditions, namely those due to navigation and actuation errors, incorrect initial position, unpredictable oscillations of the propulsive thrust, and imperfect modeling of the spacecraft mass distribution and variation. These stochastic deviations are simulated in the context of extensive Monte Carlo campaigns, and yield three-dimensional perturbed trajectories. The numerical results obtained in this work unequivocally demonstrate that VTD-NOG & CPD represents an accurate and effective methodology for guidance and control of lunar ascent path and orbit injection.
  • Resonant space tethered system for lunar orbital energy harvesting
    • Abstract: Publication date: Available online 3 November 2018Source: Acta AstronauticaAuthor(s): Jiafu Liu, Colin R. McInnes Using a space tether system attached to the Moon's surface can in principle lead to energy harvesting from the mechanical damping of the tether as it experiences elongational motion due to time-varying tidal forces. It is shown that such a tether system can in principle provide electricity generation for lunar infrastructure, although the power generated is modest relative to the scale of engineering required. First, the dynamics of the coupled planar elongation and librational motion is established for a massless, elastic and damped tether with a large tip-mass in the frame of the elliptic Earth-moon restricted three-body (EEMRTB) system. Equilibria at the natural L2 point are obtained as reference positions to perform the analysis. The method of multiple scales is then used to obtain the steady state amplitude-frequency response by ordering key variables and parameters appropriately. The steady-state power output determined by the elasticity, length and damping of the tether is presented. Specific resonances for peaks of power output, together with corresponding resonance regions, are also investigated along with suggestions for tradeoffs among the key system parameters. Finally, the optimal damping for maximum power output is determined, together with the corresponding natural length and elasticity of the tether.
  • LES of primary breakup of pulsed liquid jet in supersonic crossflow
    • Abstract: Publication date: Available online 1 November 2018Source: Acta AstronauticaAuthor(s): Y.H. Zhu, F. Xiao, Q.L. Li, R. Mo, C. Li, S. Lin The injection of a pulsed liquid jet into supersonic air flow is a promising approach to improving the fuel atomization performance in a Scramjet engine. Therefore, the primary breakup of a pulsed liquid jet in supersonic crossflow is numerically investigated in the present paper. A two-phase flow Large Eddy Simulation (LES) algorithm is developed for simulations of liquid jet atomization in supersonic gas flow. A coupled Level Set and Volume of Fluid (VOF) method is used to track the interface deformation and disintegration. The supersonic gas flow is solved using a compressible flow solver while the liquid phase is solved by an incompressible flow solver. Appropriate boundary conditions are specified at the interface for both solvers to correctly capture the interaction between the gas and liquid phases. The primary atomization of a steady liquid jet with the same average mass flow rate as the pulsed jet is also simulated as a benchmark test case. The liquid velocity pulsation produces a very different primary atomization morphology in comparison with the steady liquid jet, which significantly enhances the primary breakup process. It is observed that Rayleigh-Taylor instability dominates the development of surface waves for the steady liquid jet. For the pulsed liquid jet, the liquid column deformation induced by the liquid velocity pulsation determines the wavelength of the surface waves and thus the liquid jet breakup location. In comparison with the steady liquid jet, the penetration of the pulsed liquid jet increases by 20%, and the width of the wake zone expands by 25%, resulting in improved atomization and mixing performance.
  • Photometric limits on the high resolution imaging of exoplanets using the
           solar gravity lens
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Phil A. Willems We present an analysis of high-resolution imaging of an exoplanet by a meter-class telescope positioned at a real image of the exoplanet created by the solar gravity lens. We assume an exoplanet viewed in full phase and a simple deconvolution method to correct for the intrinsic blur caused by aberrations in the solar gravity lens, and account for the foreground light of the solar corona. We derive equations for the measurement times required for the telescope to produce such a high-resolution image, and find that due to shot noise considerations these times are large compared to human lifespans. We also discuss how measurement times could potentially be significantly shorter for exoplanets with special orbital and rotational parameters.
  • Optimization of scramjet performance with different fuel injection
           techniques and flame holder cavities
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Obula Reddy Kummitha, Krishna Murari Pandey, Rajat Gupta In this research paper an attempt has been made to find out the effect of passive fuel injection and direct fuel injection along with two different cavity flame holders. In this research an innovative cavity flame holder is designed to create more recirculation regions in and around the cavity. Investigation has been extended with an additional cavity flame holder along with direct fuel injection technique. This research has been carried out by solving the compressible flow Favre-averaged equations along with SST k−ω turbulence model, finite rate-eddy dissipation chemistry model and global one step reaction mechanism of fuel and air. From the comparison of numerical results among different combustor configurations, it is identified that the wavy wall cavity design increases the thickness of recirculation region and thereby enhance the growth of shear mixing layer. Consideration of an additional cavity increases the stability of combustion by increasing the residence time of supersonic airstream and also increases the pressure and temperature by creating the more recirculation regions. It is also observed that the combination of both the direct and passive fuel injection techniques enhanced the mixing and combustion efficiency. Finally it is to be concluded that the scramjet combustor with an innovative (wavy wall) cavity design and additional cavity along with direct fuel injection technique is the optimum design to enhance the performance of scramjet.
  • Simulation of pressure oscillations in a combustion chamber under periodic
           inlet disturbances
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Dapeng Wang, Yuzhuo Yang, Weipeng Fan, Xiaochang Li, Ye Gao The working process of a solid rocket motor (SRM) is a transient problem. The burning rate of the propellant is related to several factors, which results in variations in the mass injection rate. To date, the simulation of the flow field in an SRM generally comprises the use of constant inlet boundary conditions, a simulation that does not consider inlet disturbance conditions. This paper is mainly concerned with the influence of periodic disturbances on the pressure oscillation. In this study, a numerical simulation was performed with a periodic disturbance inlet based on the typical Von Karman Institute for Fluid Dynamics subscale motor without an obstacle. It was found that the inlet conditions of the periodic disturbance greatly affect the amplitude and frequency of the pressure oscillation in the combustion chamber. When the mass flow inlet disturbance frequency is close in value to the acoustic modal frequency of the combustion chamber, the amplitude of the pressure oscillations increases. Similarly, when the disturbance frequency is far in value from the acoustic modal frequency, the amplitude of the pressure oscillation decreases. When the inlet disturbance changes from 650 Hz to 400 Hz, the amplitude of the pressure oscillation increases by 451.5%. In addition, at certain frequencies, the inlet disturbance can excite pressure oscillations at acoustic modes near the disturbance frequency in the combustion chamber.
  • Impact of dynamic coupling between relative orbit and attitude on the
           estimation of relative dynamics of spacecraft
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): A. Chaves-Jiménez, J. Guo, E. Gill In this work the extent to which orbit and attitude sensors may cross-support each other in a joint processing to reduce estimation errors of the relative orbital and attitude dynamics is investigated. In order to do this, an engineering dynamic model taking into account the coupling effects between orbit and attitude dynamics is exploited for estimation purposes. A simple yet common configuration of two spacecraft in an along-track formation flying in low Earth Orbit (LEO) is used as case study, where the atmospheric drag perturbation constitutes the source of coupling. An extended Kalman Filter considering the dynamic coupling between orbital and attitude dynamics is used to estimate the absolute and relative dynamics of the system. It is shown that the coupling leads to higher accuracy estimation results.
  • Low-energy transfers to long-term capture in the Earth-Moon system
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Yi Qi, Anton de Ruiter In this paper, low-energy transfers of asteroids to long-term capture (LTC) in the Earth-Moon system (EMS) based on the concept of short-term capture (STC) are constructed and analyzed. Stable LTC orbits distributed in three regions are investigated via the finite-time Lyapunov exponent. Then, five types of low-energy transfers to different target LTC orbits are constructed and discussed. Two kinds of design strategies of low-energy transfers starting from STC orbits and LTC orbits are proposed, respectively. Numerical results indicate that fuel costs of low-energy transfers to stable LTC orbits in the EMS are less than 50 m/s; fuel costs of low-energy transfers to unstable libration point orbits are less than 5 m/s. Taking asteroid 2006 RH120 as an example, a low-energy transfer is constructed in the ephemeris model. The design methods of low-energy transfers we proposed in this paper can be applied to the asteroid redirect missions.
  • A fast trajectory planning framework with task-priority for space robot
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Jianjun Luo, Min Yu, Mingming Wang, Jianping Yuan This paper addresses trajectory planning issue for free-floating space robotic system which is designed to track a prescribed path simultaneously fulfilling imposed constraints such as collision avoidance and minimizing base attitude disturbance. Collision avoidance can be treated as inequality constraints as part of the trajectory planning. To generate smooth trajectory for robot motion, a novel local collision avoidance method considering multiple velocity damper constraints is proposed for non-strictly convex polyhedra. Moreover, we propose a task-priority handling strategy incorporated with a full-fledged Quadratic Programming(QP) procedure to solve the planning problem with sequential tasks. The proposed task-priority handling strategy enables a rapid adaptation of the space manipulators motion, which makes this strategy feasible for real-time planning. The trajectory planning framework with collision avoidance method and task-priority handling strategy were implemented and demonstrated via a kinematically redundant dual-arm space robotic system.
  • Modal analysis and identification of deployable membrane structures
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Jianzheng Wei, Ruiqiang Ma, Yufei Liu, Jianxin Yu, Anders Eriksson, Huifeng Tan The development of ultra-lightweight sails presents many challenges due to their large size and extreme flexibility. One of their key technologies is the design of deployable booms, in particular how to deploy and support the membrane structure. In this paper, a deployable sail with four triangular membranes supported by inflated booms enhanced by four self-supporting thin shells inside and Velcro outside is presented. The feasibility of the folding and unfolding processes is demonstrated, and their modal properties investigated. Firstly, the pressure variation and acceleration time history of a single boom during unfolding process were obtained by dynamic testing system, a finite element model of boom was proposed and structural natural frequencies by simulation were validated by experimental testing. Further, an 8.0 × 8.0 m2 prototype was assembled and stowed in a Φ700 mm by 300 mm container, and the structure was fully deployed with gas control. A finite element model of a combination of inflatable booms and triangular membranes was used to predict the structural overall bending modes. The effect of membrane wrinkling was simulated and controlled to improve membrane precision. This work validated the concept of deployable membrane structural design. The proposed finite element models were verified by experimental testing to be useful for membrane structure analysis.
  • Solar 3D printing of lunar regolith
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): A. Meurisse, A. Makaya, C. Willsch, M. Sperl The authors demonstrated the feasibility of sintering lunar regolith layer-by-layer solely using concentrated sunlight. First trials using actual concentrated sunlight led to an inhomogeneous sintering of individual layers of lunar regolith simulant, due to the significant flux density variations caused by atmospheric fluctuations. Tests focusing Xenon light demonstrated however the concept with the manufacturing of the first solar 3D printed brick made of lunar regolith simulant. The use of artificial light enabled steady illumination conditions over several hours as required to sinter lunar regolith layer-by-layer. Actual compressive strength of the sintered bricks, below 5 MPa, might be currently too low for a direct lunar application. High porosity levels and weak layer-to-layer bonding were observed on the micro-scale, but ways of improving the technology were found by reducing the thermal gradient and the cooling time between consecutive layers, thus showing the potential of the process. Adaptation of the technology on the Moon is presented to illustrate the suitability of solar additive manufacturing on the lunar surface, as a possible technique for shielding habitats and building roads prior to arrival of the astronauts.
  • Conceptual design analysis for a two-stage-to-orbit semi-reusable launch
           system for small satellites
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Christie Alisa Maddock, Lorenzo Ricciardi, Michael West, Joanne West, Konstantinos Kontis, Sriram Rengarajan, David Evans, Andy Milne, Stuart McIntyre This paper presents the conceptual design and performance analysis of a partially reusable space launch vehicle for small payloads. The system employs a multi-stage vehicle powered by rocket engines, with a reusable first stage capable of glided or powered flight, and expendable upper stage(s) to inject 500 kg of payload into low Earth orbits. The space access vehicle is designed to be air-launched from a modified aircraft carrier. The aim of the system design is to develop a commercially viable launch system for near-term operation, thus emphasis is placed on the efficient use of high TRL technologies and on the commercial potential of the technical design. The vehicle design is analysed using a multi-disciplinary design optimisation approach to evaluate the performance, operational capabilities and design trade-offs. Results from two trade-off studies are shown, evaluating the choice wing area and thus aerodynamic characteristics, and the choice of stage masses and engines selection on the mission performance.
  • On-orbit assembly mission planning considering topological constraint and
           attitude disturbance
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Yuchen She, Shuang Li, Bin Du, Kai Cao This paper investigates the on-orbit assembly mission planning problem of a large space antenna structure. The study is significantly important for the construction of large-scale spatial structures. The flexible connection between the antenna pieces and the topological constraint are taken into consideration. Several innovative approaches are presented to realize the mission planning process. First, the mesh model from the fly net dynamics is adopted and modified to create a mapping between the vibrations of the antenna plate during the assembly process and the assembly path. Second, the geometrical model is developed to implement the topological constraint into the system. Finally, a hybrid method combining the branch-and-bound method and the modified ant colony algorithm is proposed to solve the optimization problem. The simulation results show that the proposed algorithm can efficiently obtain a solution which respects the topological constraint and suppresses the vibration disturbance as much as possible.
  • Numerical investigation on behaviors of shock train in a hypersonic inlet
           with translating cowl
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Wen Shi, Juntao Chang, Junlong Zhang, Youyin Wang, Wenxin Hou, Wen Bao In order to extend the range of flight Mach numbers, the variable-geometry inlet equipped with a translating cowl has been proposed. To estimate the effects that the translation of cowl has on the behavior of shock train under constant backpressure in a two-ramp hypersonic inlet, numerical investigations utilizing dynamic mesh method have been conducted. The structures of background waves and trajectories of shock-impact points with variable internal contraction ratios at Mach number 5.9 are obtained. Then, the paths of shock train leading edges have been provided and studied. The results reveal that the shock train leading edge on the bottom wall crosses the shock-impact points abruptly, which forces the shock train to undergo multiple back-and-forth translation motions accompanied with separation mode transition. Severe abrupt motions of shock train occur when it encounters multiple shock-impact points aroused by the separation bubble. Analogously, the shock train interacts with the separation bubble located on the top wall periodically. The probability that the oscillation takes place is increased due to the existence of separation bubble. Therefore, the behavior of shock train is highly associated with the variable background waves.
  • A novel inertial-aided feature detection model for autonomous navigation
           in planetary landing
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Meng Yu, Shuang Li, Xiangyu Huang, Shuquan Wang This paper proposes a novel visual feature detection model for navigation applications in the context of autonomous planetary landing. A novel Hessian marker is developed in the first place, which aims at adapting to the affine distortion between descent image and navigational map, such design is established upon the SURF detection model. Then, an inertial-aided characteristic scale determination method is proposed based upon the proposed Hessian marker, leading to the complete inertial-aided visual feature detection model. Finally, a planet-representative simulation platform is developed for validating the proposed algorithm, the performance of proposed approach in terms of repeatability rate, robustness against the image affine distortion, and navigation accuracy is verified by comparing with the state-of-the-art algorithms under the specifically developed platform.
  • Hydraulic characteristics of high temperature hydrocarbon liquid jets with
           various orifice geometries
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Hyung Ju Lee, Hojin Choi, Dong-Chang Park An experimental study was conducted to investigate the effects of orifice geometry on the hydraulic characteristics of high-temperature aviation fuel jets. Pressurized heated liquid hydrocarbon fuel, simulating fuel used as coolant in the active cooling system of a hypersonic flight vehicle, was injected through a set of plain orifice nozzles of different lengths and diameters. The fuel was heated to close to 573 K (300 °C) using an induction heater at an upstream pressure of up to 1.0 MPa, and discharged to atmospheric downstream pressure conditions. The orifice diameter (D) varies from 0.7 to 1.5 mm and the length (L) from 1.4 to 4.3 mm, which results in length-to-diameter ratios (L/D) from 1.1 to 6.1, and the inlet of the orifice is nominally sharp-edged. Hydraulic characterization in terms of fuel injection temperature (Tinj) was carried out by introducing the discharge coefficient (Cd), and the macroscopic internal flow characteristics were correlated to Reynolds number (Re) and cavitation numbers (K and Ca). The fundamental behaviors of high-temperature liquid fuel jets at the specified operating ranges represented by Cd with respect to Tinj for a given set of injectors revealed that, as Tinj increases above the boiling point, the Cd of the injector with a longer orifice decreases faster than that of a shorter injector of the same orifice diameter, and for injectors of a given orifice length, Cd decreases with Tinj in a similar way irrespective of orifice diameter. Plots of Re vs. Tinj, Cd vs. Re, and Cd vs. K and Ca clearly show the dependence of the cavitation characteristics on the orifice geometry under high temperature injection conditions. In order to quantify the degree of cavitation for various orifice geometries, the Cd vs. Ca curve for each injector configuration has been fitted linearly; the mass flow choking effect in high temperature fuel injection represented by the magnitude of the slope from the linear fit becomes stronger as the orifice is longer in length and/or wider in diameter. This suggests that longer and wider orifices are more susceptible to choked cavitation. It was also found that the geometric effect is maintained for various ΔP, even though the magnitude of the slope increases with ΔP, and the sensitivity of the magnitude to increasing ΔP becomes stronger for longer orifices.
  • An overview of waverider design concept in airframe/inlet integration
           methodology for air-breathing hypersonic vehicles
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Feng Ding, Jun Liu, Chi-bing Shen, Wei Huang, Zhen Liu, Shao-hua Chen A waverider is any supersonic or hypersonic lifting body that is characterized by an attached, or nearly attached, bow shock wave along its leading edge. A waverider can possess high lift-to-drag ratio characteristics as well as an ideal precompression surface of the inlet system, and hence has become one of the most promising designs for air-breathing hypersonic vehicles. Two classes of general methodologies exist for using the waverider concept in the airframe/inlet integration for air-breathing hypersonic vehicles. In the first class, the waverider is used only as the forebody of a vehicle, and behaves as the precompression surface to efficiently provide the inlet system with the required compression flow field. In the second class, and to take advantage of the waverider's high lift-to-drag ratio characteristics as well as the ideal precompression surface for the engine, the waverider design is used as the basis for the design of the entire vehicle, and the engine is generated within the pristine waverider definition while maintaining the bow shock wave attaching to the leading edge. In this paper, waverider applications developed by domestic and overseas scholars in the airframe/inlet integration methodology for air-breathing hypersonic vehicles are reviewed and classified, and the future research and development trends are presented. The idea for the design of a waverider-derived air-breathing hypersonic vehicle can be summarized as follows: the modeling of the basic flow is used to design the waverider in the streamwise direction, and the osculating theory is used to design the waverider in the spanwise direction.
  • Numerical investigation of a rotating detonation engine under
           premixed/non-premixed conditions
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Jian Sun, Jin Zhou, Shijie Liu, Zhiyong Lin Rotating detonation engines are widely studied because of their compact configurations and high thermal cycle efficiency. For briefty, most of the numerical simulations of rotating detonation engines used premixed reactant mixtures. The rotating detonation waves under non-premixed condition are not studied enough. Here, a series of three-dimensional numerical simulations of a rotating detonation engine under both premixed and non-premixed conditions using H2/air mixture are performed. The explicit formulation of density-based solver in ANSYS Fluent is used to perform the simulations. Two total mass flow rates of 272.3 g/s and 500 g/s are selected. When the total mass flow rate is 272.3 g/s, the engine operates at single-wave mode under both premixed and non-premixed conditions. When the total mass flow rate is 500 g/s, the engine operates at single-wave mode under premixed condition. While under non-premixed condition, a spontaneous formation of dual-wave mode is observed. This case agrees well with the phenomenon observed in experiments that as the total mass flow rate increases, the number of rotating detonation waves tends to increase. Pressure waves caused by the high pressure behind the detonation waves can propagate upstream to the H2 and air plenums. The pressure feedback in the H2 plenum is much more obvious than that in the air plenum. Due to the imperfect mixing of H2/air and the more deflagration combustion caused by the hot detonation products, the thrust of the RDE under non-premixed condition is smaller than that under premixed condition.
  • Stable orbital transfer of partial space elevator by tether deployment and
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Gefei Shi, Zhanxia Zhu, Zheng H. Zhu This paper investigates the stable orbital transfer of a climber in a partial space elevator system in circular orbits. The elevator includes a main satellite, an end body, and a climber, which are connected by two straight, inextensible, massless and variable length tethers. Derived from system dynamics, two closed-loop velocity control strategies are proposed to regulate the tethers' deploying and retrieving speeds directly to control the Coriolis forces acting on the climber and the end body directly. The stable region of the control strategies is analyzed, and the effectiveness of the proposed strategies is demonstrated by numerical simulation. Simulation results show that the newly proposed strategies effectively minimize the libration of a partial space elevator system during the orbital transfer of the climber and the system states successfully approach to the desired equilibrium by the end of the orbital transfer. Furthermore, the proposed deployment/retrieval control strategies can be converted to tension control laws easily.
  • Hybrid tension control method for tethered satellite systems during large
           tumbling space debris removal
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Zhongyi Chu, Jingnan Di, Jing Cui Large space debris in the valuable orbit is an inevitable and serious problem which increases the risk of fatal collisions. The use of space tether is a promising method for de-orbiting large debris safely at low cost and low energy consumption. However, the risk of winding is increasing because of variations in sway motion due to underactuativity, high nonlinearity, and the strong coupling of the tethered system. Hence, in this paper, a hybrid tension control method is proposed to stabilise satellite system tethered to large space debris. The dynamic equations of a tethered satellite system are formulated with an analysis of the impact of the variation in sway motion on tether winding. Following this, the optimal commands of sway motion are planned using the Gauss pseudospectral method to preliminarily avoid the tether winding with the target. To further reduce the risk of winding, a fuzzy adaptive proportion differentiation (PD) controller is designed to stabilise the relative attitude of the tether and the large debris. And the control tension is considered as a time-varying parameter and is added using a hierarchical sliding-mode controller (HSMC), which is used to control the in-plane angle and the relative distance to implement the hybrid control of the overall tethered satellite system. Several simulations were implemented to verify the effectiveness of the proposed tension control method.
  • Analysis of artificial gravity paradigms using a mathematical model of
           spatial orientation
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Grant R. Vincent, Jason Gruber, Michael C. Newman, Torin K. Clark Artificial gravity (AG) is a promising approach to reduce the physiological deconditioning experienced by astronauts. Here we propose the linear sled hybrid AG system as an alternative to the typical centrifuge approach to creating AG. In this paradigm, the rider is briefly linearly accelerated towards their head, then rotated 180° around, then decelerated. This sequence is repeated creating footward loading during the linear acceleration and deceleration phases, replicating standing upright on Earth, without any gravity gradient or Coriolis forces. The 180° rotation also produces gradient centripetal acceleration, for a “hybrid” approach. We simulated the well-validated observer model to predict the rider's orientation perception and potential disorientation in response to these two AG paradigms. Particularly, we simulated head tilts to investigate the cross-coupled illusion. For the centrifuge, as expected, we found head tilts caused the cross-coupled illusion and an illusory sense of tilt. As a novel prediction, we found the head tilt angle and centrifuge spin rate to interact non-linearly, producing an inflection point in the peak perceived tilt of the cross-coupled illusion. We found the linear sled paradigm to be well perceived and, as expected, head tilts did not produce the cross-coupled illusion. While the observer model predicted the linear sled paradigm to not be disorienting, future experimental work is necessary for validation. Comfort and motion sickness feasibility, as well as countermeasure efficacy, should be studied experimentally.
  • Investigations on flowfield behavior and resistance backpressure
           characteristics of supersonic cascade with boundary layer suction
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Ziao Wang, Juntao Chang, Junlong Zhang, Jicheng Ma A numerical study aiming at the enhancement of the operating range of supersonic cascade via boundary layer suction is presented. The purpose of this paper is to improve the maximum backpressure ratio of the flowfield by suction control and to learn the flowfield behavior and characteristics with different suction control parameters. An S-shaped supersonic cascade developed and tested at DLR (DLR-PAV-1.5) that operates with a relative entrance Mach number of 1.5 is selected in this paper. A two-dimensional multiblock NS solver has been successfully applied to the cascade flow which is validated using the data of the experiment of Schreiber. An in-deep numerical study has been carried out to investigate the effects of suction locations, widths and angles by comparing the operating range and aerodynamic performance parameters of the supersonic cascade. The results indicate that the maximum backpressure ratio can be enhanced by 17.4% with a loss of 3% mainstream mass flow by suction slot in 60% or 70% length of the axial chord. As the width of the suction slot increases to 7 mm, the maximum backpressure ratio is enhanced by 24%, and the total pressure recovery coefficient is improved to 95.3%. The range of suction slot angle that can effectively improve the maximum backpressure ratio is 60–90° and −90 to −60°. This paper provides guidance for the supersonic cascade to improve its performance parameters through suction control.
  • CUTIE: A cubesats tether-inserted mission for moon exploration
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): C. Bettanini, E.C. Lorenzini, G. Colombatti, A. Aboudan, M. Massironi This paper presents the concept of a dual cubesat mission designed for Moon exploration that enables scientific measurements that are not accessible by high orbital or landed missions thanks to the use of a long passive tether for orbital insertion. Due to the intrinsic characteristic of the Moon environment, low altitude orbiting spacecrafts are in fact requested for mapping key parameters such as plasma, volatiles and magnetic field. Inserting a satellite in such low trajectories from an orbiter has usually a high cost of propellant to achieve the orbit change or requires a long time to finalize the maneuver with electrical propulsive systems. Limitations are even higher for cubesats that have very limited capacity for orbital adjustment, so they cannot perform substantial orbital changes by using classical propulsive techniques. The use of a long passive tether to exchange momentum between two cubesats can eliminate such drawbacks and provide fast, far-reaching and accurate orbital changes with almost no propellant being consumed. A mission scenario is presented with the two mated cubesats released by an orbiter in circular Moon orbit at 500 km altitude. Thanks to the momentum exchanges provided by the swinging tether the upper cubesat will be left in a 520 × 737 km orbit and the lower cubesat into a 460 × 26 km orbit with a low periselenium that provides an ideal altitude for close observation of the lunar surface and monitoring of characteristic parameters of the Moon environment. With a high-inclination orbit, the low-altitude orbital passes will map the entire Moon surface in around 14 days. The upper cubesat will be transferred on a highly predictable and low-perturbation orbit and equipped with laser corner reflectors and a radio link band transponder to allow tracking both from laser stations on Earth (Matera, Italy ASI geodesy station) and from the Lunar Orbiter via radio link. The integrated analysis with radio signals between Cubesats can also be used to improve orbit determination and study perturbation effects on orbital dynamics.
  • Earth analogue testing and analysis of Martian duricrust properties
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): William Lewinger, Francisco Comin, Marcus Matthews, Chakravarthini Saaj Previous and current Mars rover missions have noted a nearly ubiquitous presence of duricrusts on the planet surface. Duricrusts are thin, brittle layers of cemented regolith that cover the underlying terrain. In some cases, the duricrust hides safe or relatively safe underneath the top soil. However, as was observed by both Mars exploration rovers, Spirit and Opportunity, such crusts can also hide loose, untrafficable terrain, leading to Spirit becoming permanently incapacitated in 2009. Whilst several reports of the Martian surface have indicated the presence of duricrusts, none have been able to provide details on the physical properties of the material, which may indicate the level of safe traversability of duricrust terrains. This paper presents the findings of testing terrestrially-created duricrusts with simulated Martian soil properties, in order to determine the properties of such duricrusts and to discover what level of hazard that they may represent (e.g. can vehicles traverse the duricrust surface without penetration to lower sub-surface soils'). Combinations of elements that have been observed in the Martian soil were used as the basis for forming the laboratory-created duricrusts. Variations in duricrust thickness, water content, and the iron oxide compound were investigated. As was observed throughout the testing process, duricrusts behave in a rather brittle fashion and are easily destroyed by low surface pressures. This indicates that duricrusts are not safe for traversing and they present a definite hazard for travelling on the Martian landscape when utilising only visual terrain classification, as the surface appearance is not necessarily representative of what may be lying beneath.
  • Adaptive prediction backstepping attitude control for liquid-filled
           micro-satellite with flexible appendages
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Jun-hai Huo, Tao Meng, Ren-ting Song, Zhong-he Jin In order to study the influence of lightweight flexible appendages vibration (LFAV) and liquid fuel sloshing (LFS) on the micro- and nano-satellite, based on ZDPS-2 satellite of Zhejiang University, this paper develops a kind of attitude dynamics which considers flexible appendages vibration and liquid sloshing. An adaptive prediction backstepping controller (APBC) is designed under the consideration of estimation error of the moment of inertia, the flexible vibration, liquid fuel sloshing and disturbance torques. Also time delay problem is considered in this algorithm. The finite time convergence is performed using Lyapunov stability method. Numerical simulations are carried out to verify the validity of the proposed controller. The results show that compared with the traditional PD controller, under the same attitude measurement error, the APBC has good control performance on eliminating the effect of time delay and provides estimations of moment of inertia parameters online. It can also significantly decrease the magnitude of the flexible appendages vibration and liquid sloshing.
  • The Space Rider Programme: End user's needs and payload applications
           survey as driver for mission and system definition
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Alberto Fedele, Giuseppe Guidotti, Giuseppe Rufolo, Giovanni Malucchi, Angelo Denaro, Federico Massobrio, Stephane Dussy, Salvatore Mancuso, Giorgio Tumino The Space Rider Programme, previously named Pride, is an ESA programme whose objective is to define and develop an affordable reusable European space transportation system to be launched by VEGA-C, to be used as a platform for several types of payload applications. Payloads and related applications strongly drive the definition of Space Rider mission and system, then an analysis of end user's needs has been necessary to adequately feed the design process. This paper reports a survey and an analysis with respect to the following payloads classes: 1- Free-Flyer (Micro-gravity experimentation and Radiation exposure); 2- In-Orbit Demonstrations and Validation for several technologies (Exploration, Orbital infrastructures servicing, Earth observation, Earth science, Telecommunication, Reentry); 3- In-Orbit applications (Earth monitoring and Satellites inspection). In particular, the analysis has been carried out with investigation of the current microgravity platforms and payloads needs, In-Orbit Demonstrations (IOD) flight opportunities status and demand from different stakeholders both on scientific and industrial side. Key assets of the Space Rider platform with respect to payload have been defined and the results of the work has been flow down into the identification of a set of requirements for the Space Rider mission and system focusing on main aspects as operations, mass, power, volume and interfaces.
  • Simulation of supersonic Ethylene–Hydrogen and air auto-ignition flame
           using skeletal mechanism
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Bing Liu, Guo-qiang He, Fei Qin Three ethylene–air combustion mechanisms were validated against detailed mechanism USC-Mech II, and the results showed that the three mechanisms were not appropriate for combustion of ethylene–hydrogen/air. A 38-species skeletal mechanism was developed for ethylene–hydrogen/air based on the detailed mechanism USC-Mech II. A good agreement is found between the skeletal mechanism and the detailed mechanism in terms of the ignition delay time and the laminar flame speed over a wide range of parameters. After the computational methodology was validated with a supersonic hydrogen–air auto-ignition flame, the skeletal mechanism was employed to simulate the auto-ignition of ethylene–hydrogen mixtures in a hot supersonic airflow. The results showed satisfactory agreement with experimental data, which demonstrates that the skeletal mechanism could reasonably predict the ignition position. An analysis of the flame structure was conducted with respect to the distributions of the species, heat release, pressure, and temperature. Investigations into various parameters revealed that auto-ignition occurred in the most reactive mixture fraction with the minimum ignition delay time rather than the stoichiometric mixture fraction during supersonic combustion.
  • Type synthesis of non-holonomic spherical constraint underactuated
           parallel robotics
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Zenggui Gao, Lingbin Zeng, Bin He, Ting Luo, Pengchang Zhang Space robotics is taken as one of the most promising approaches for on-orbit servicing missions. The underactuated non-holonomic parallel mechanism is a new direction of parallel space robotics, with small volume, lightweight, low cost, low energy consumption, and high flexibility. The existing methods on type synthesis could not generate underactuated non-holonomic parallel mechanisms with the introduction of the non-holonomic spherical pairs in parallel mechanisms. This paper is devoted to type synthesis of underactuated parallel mechanisms with spherical motion pattern accompanied by the generation of the non-holonomic spherical pairs in parallel mechanisms with spherical motion pattern. After the introduction of the traditional roller-sphere contact, this paper proposes a novel roller-sphere contact. After this paper provides the type synthesis of parallel mechanisms with spherical motion pattern, it puts forward the generation method of non-holonomic spherical pairs in parallel underactuated mechanisms with spherical motion pattern. The non-holonomic underactuated joint mechanism of a space robot for on-orbit servicing operations is taken as an example to demonstrate the proposed method.
  • Semi-autonomous attitude guidance using relative navigation based on line
           of sight measurements – Aim scenario
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Andrea Pellacani, Francisco Cabral, Aída Alcalde, Pawel Kicman, Jakub Lisowski, Ingo Gerth, Bastian Burmann The Asteroid Impact Mission (AIM) is an ESA small mission of opportunity that intends to travel to the binary asteroid Didymos to assess planetary defence capabilities in the context of the AIDA program, in collaboration with NASA, to demonstrate new technologies for future exploration missions to asteroids and to perform scientific observations.The AIM spacecraft is described in the paper, focusing on the vision-based GNC strategy that reached a high level of maturity at the end of the Consolidation Phase (post B1). Ground navigation analyses pointed out that for close proximity operations (distances under 20 km) a certain degree of autonomy is required.A semi-autonomous attitude guidance has been developed to guarantee that the asteroid will always be kept in the camera Field of View. This algorithm will apply a delta quaternion to the reference attitude profile provided by ground control in order to correct the pointing to the body. This technology has been designed to be easily validated and, at the same time, constrained: the delta quaternion can be limited and in case the thresholds are crossed or any failure occurs, the ground-based reference attitude profile will be used.The AIM GNC prototype was updated to use Line of Sight measurements provided by a centroiding algorithm designed and autocoded in Matlab/Simulink, then validated up to Processor-in-the-loop tests using a flight-representative processor (AT697E LEON2-FT @ 80 MHz). The algorithm is based on the correlation of the image with a Lambertian sphere, taking advantage of the almost spherical shape of Didymain.When relative distance to the binary system is below 8 km, the feature tracking algorithm is used. In this paper a specific case is assessed: the close fly-by for MASCOT-2 delivery (lander included in the payload for AIM's phase B1), tested up to Hardware-in-the-loop with the AIM Framing Camera.
  • A review on exergy analysis of aerospace power systems
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Zeyu Dong, Dapeng Li, Zhenguo Wang, Mingbo Sun Exergy, an integration of the first and second laws of thermodynamics, enriches the traditional analysis method based on energy conservation. It can effectively reveal the causes of the irreversibilities and inefficiencies of the thermodynamic processes, which provides a convenient approach for engineers to design and optimize the components and systems. This paper firstly introduces the development history of exergy and the fundamental mathematics behind exergy analysis in general. Next, the application status of exergy analysis method in turbojet/turbofan engines, scramjet engine, aircraft system and multidisciplinary design optimization is represented in detail. At the end of this review, we put forward the practical needs for further development of exergy analysis and conclude that this method has wide application prospect in the field of aerospace power systems.
  • Time-optimal solar sail heteroclinic-like connections for an Earth-Mars
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Merel Vergaaij, Jeannette Heiligers This paper investigates solar sail Earth-Mars cyclers, in particular cyclers between libration point orbits at the Earth-Moon L2 point and the Sun-Mars L1 point. In order to facilitate cyclers in as few Earth-Mars synodic periods as possible, the overall objective is to minimize the time of flight. These time-optimal cyclers are obtained by using a direct pseudospectral method and exploiting techniques from dynamical systems theory to obtain an initial guess. In particular, heteroclinic connections between the unstable and stable manifolds of the target libration point orbits at the Earth-Moon L2 point and the Sun-Mars L1 point are sought for. While such connections do not exist in the ballistic case, they can be achieved by complementing the dynamics with a solar sail and assuming a constant attitude of the sail with respect to the direction of sunlight. These trajectories are sub-optimal due to the assumed constant sail attitude as well as minor discontinuities in position and velocity at the linkage of the manifolds, which are overcome by transferring the initial guess to the direct pseudospectral optimal control solver. For near- to mid-term sails, results show time-optimal round-trip trajectories that span three synodic Earth-Mars periods, with a few months to one year stay times at the libration point orbits, depending on the time of departure within a five-month window. Through the propellant-less nature of solar sailing, these Earth-Mars cyclers can, in theory, be maintained indefinitely.
  • Contribution of bone micromechanical behavior beyond lamellar length scale
           to the macroscopic bone quality of hind limb unloading rats
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Lian-wen Sun, Shuang Li, Xiao Yang, Fang Pu, Hongyu Qi, Yubo Fan Long duration space flight would cause serious bone loss and bone quality deterioration. For better understanding the underlying mechanism and countermeasures, it is necessary to know the structural-mechanical relationship of the tissue. Bone is a hierarchically structured composite material with up to seven hierarchical levels of organization. At different length scales, it has distinct mechanical behaviors. In a previous study, we studied the effects of microgravity on the nano-indentation properties of bone, showing that microgravity has some effects on the nano-indentation properties of bone. However, this result obtained at nanoscopic length scale is not consistent with the previous observations that microgravity would cause deterioration in the bulk mechanical property of bone at higher structural hierarchies. To address this issue, we used micro-indentation technique in this study to examine the effects of microgravity on the mechanical property of bone at microscopic length scale. After 21 days tail suspension, the elastic modulus (E), hardness (H), and E/H ratio of rat femur were significantly decreased and such changes were different between cortical and trabecular bone. This result was similar with those of three-point bending test, but different from those of nano-indentation test. The results suggest that the decrease of macro-mechanical property under unloading-simulated microgravity (SMG) condition is most likely due to changes at microstructural level (across lamellae) instead of at sub-micron or nanoscopic length scales (within lamellae).Graphical abstractImage 1
  • Numerical investigation on the film cooling performance in a
           multi-elements splash platelet injector
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Liang Yin, Weiqiang Liu, Binxian Shen, Hongpeng Liu A numerical simulation was performed to investigate the film cooling performance of a multi-element splash platelet injector. A 16-species, 41-reaction mechanism and an eddy-dissipation concept model were used for the simulation of turbulent combustion. The effects of typical film cooling parameters, such as injection slot height, slot geometry, mixture ratio, and injection position, were studied. An increase in slot height caused a direct decrease in velocity ratio and film coolant length and an increase in wall temperature in the combustion chamber head. Slot height, slot geometry, and mixture ratio exerted minimal influence on wall temperature. However, changes in slot geometry and injection position remarkably influenced the injector faceplate temperature. The size of the high-temperature zone of the faceplate increased with the change in slot geometry. When the injection position changed, the location and scope of the high-temperature zone also changed. Furthermore, two recirculation zones were observed near the injector post. These recirculation zones considerably affected film cooling performance, and the upper recirculation zone exerted an adverse influence on cooling performance in terms of faceplate temperature. Therefore, an appropriate design of the cooling slot should be selected to improve film cooling performance.
  • Study on the dynamic response of a pressure swirl injector to ramp
           variation of mass flow rate
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Peng Cheng, Qinglian Li, Huiyuan Chen, Zhongtao Kang The response of a pressure swirl injector to ramp variation of mass flow rate is numerically and experimentally investigated. Numerical simulation based on volume of fluid method was conducted to obtain the response of the two-phase flow inside the injector. In experiments, ramp variations of mass flow rate with different slope were introduced into the swirl injector through a throttleable cavitating venturi nozzle. Backlit photography technique and laser diffraction technique were adopted to capture the spray and measure the size distribution of droplets respectively. The relationships between mass flow rate at the injector inlet and transient parameters (such as mass flow rate, air core diameter, axial and tangential velocities) at the injector exit were analyzed. Besides, the effects of throttling rate were discussed. The results indicate that the mass flow rate, air core diameter, velocities at the injector exit, spray angle and the sauter mean diameter vary almost linearly with mass flow rate at the inlet. It is found that the responses of inner flow, spray and size distribution of droplets are delayed. Larger throttling rate results in larger time lag. The numerical results show that the inner flow response quickly and the time delay is small when compared with the external flow. Phenomena, such as anti-regulation and overshoot of the film thickness at the exit, are observed. The anti-regulation was thought to be related with the anti-regulation of combustion which was observed in hot tests.
  • Aerodynamic heating of inflatable aeroshell in orbital reentry
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Yusuke Takahashi, Kazuhiko Yamada The aerodynamic heating of an inflatable reentry vehicle, which is one of the innovative reentry technologies, was numerically investigated using a tightly coupled approach involving computational fluid dynamics and structure analysis. The fundamentals of a high-enthalpy flow around the inflatable reentry vehicle were clarified. It was found that the flow fields in the shock layer formed in front of the vehicle were strongly in a chemical nonequilibrium state owing to its low-ballistic coefficient trajectory. The heat flux tendencies on the surface of the vehicle were comprehensively investigated for various effects of the vehicle shape, surface catalysis, and turbulence via a parametric study of these parameters. In addition, based on the present results of the computational approach, a new heating-rate method was developed to calculate the heat flux of the nonequilibrium flow. It was demonstrated that the method could well-reproduce the heat flux on the inflatable reentry vehicle.
  • Investigations of injection parameters on combustion oscillation in a
           supersonic crossflow
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Guo-Yan Zhao, Ming-Bo Sun, Ya-Nan Wang, Xi-Peng Li, Hong-Bo Wang The influence of injection parameters on combustion oscillation inside an ethylene-fueled scramjet combustor equipped with a cavity flameholder is experimentally investigated for Mach 5.5 flight conditions. Experiments focusing on the influence of the fuel equivalence ratio, the premixing distance, the injection angle, and the number of jets have been carried out. Under certain conditions, high-speed camera and schlieren images show that flame oscillation occurs between the fuel injectors and the leading edge of the cavity. It is also demonstrated that those factors mentioned above can significantly affect the flow-shock interaction which generates low flow speed region and the mixing status which correlates with combustion intensity closely. The strong interaction between combustion and the separated boundary layer downstream of the cavity forms a thermal throat inducing thermal chocking to cause flame flashback. The distributions of the flame front, flame propagation speeds and quasi-periodic oscillation frequencies obtained by the iso-luminosity contour method show distinct differences in different cases. The strong interactions of flow and shock, combustion and separated region can easily trigger flame flashback, and the flame front can be maintained around the injector for long time in cases of deeper penetration depth and longer premixing distance. A simplified combustion opening system model predicts that the flame under sensitive conditions may acquire an exponential amplification once thresholds of the thermal fluctuation are exceeded.
  • Precise time estimation of on-orbit satellite fragmentations
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Yuki Itaya, Koki Fujita, Toshiya Hanada To date, there has been a lot of on-orbit satellite fragmentations since a Thor-Able upper stage exploded in space in 1961. Considering that even sub-millimeter-size debris are a big threat to operational satellites, then it can be said that detailed debris modelling is becoming an urgent task for sustainable space development. For accurate modelling, it is essential to know the accurate time of breakup. However, there is no effective method which can estimate the time precisely. Therefore, this study aims at constructing a new method for estimating the time of breakup precisely. This study focuses on orbital plane as a parameter and derives a new equation. This equation constraints orbital planes of fragments at breakup by using orbital elements of the broken-up object. The advantage of this equation is that the fragments can be evaluated by only inclination and right ascension of the ascending node which can guarantee relatively high accuracy even in a long-term propagation. For the estimation, this study proposes a hybrid method which combines the advantages of the constraint equation and the close approach analysis. As a result, by using officially reported data, it was confirmed that this hybrid method can estimate the time of breakup with an error of 1 min or less. It was also suggested that the difference in the estimated time between the hybrid method and the close approach analysis causes a large difference in predicted fragments.
  • Spaceport and Ground Segment assessment for enabling operations of
           suborbital transportation systems in the Italian territory
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Francesco Santoro, Alberto Del Bianco, Nicole Viola, Roberta Fusaro, Vito Albino, Mario Binetti, Paolo Marzioli Italy, as well as many other countries, has increasing interest in Commercial Space Transportation and in particular, in suborbital flights. A suborbital space transportation system is an opportunity to involve the Italian industry in the development of new technologies, exploit opportunities of microgravity experimentation and pilots/astronauts training, as well as catalyse the national industry. The central position of Italy in the Mediterranean basin, the generically favourable climate condition, the touristic vocation resulting in hospitality at the highest level, pretty much allow year round suborbital operations and unique customer experience. Consequently, Italy appears to be a suitable location to host a Spaceport, even though the density of population has to be factored in as a key aspect, together with a proper environmental assessment.This paper outlines the current Italian approach that, instead of focusing on the development of new Spaceport from scratch, evaluates the capabilities of existing airports and their possible upgrades to achieve the Spaceport license, when a proper regulatory frame is established. Advances in the technical activities that are being conducted to assess various Italian sites of interest are described, including trade off methodologies and ranking criteria. Different aspects are considered, from the availability of civil and military airports, to the identification of the best location between coastline or inland sites but, first of all, in compliance to the safety requirements. Some specific Spaceport infrastructure and operational aspects are described, along with their integration with the already existing ones. These include hangars, propellant storage facilities, ground support equipment, high and low airspace surrounding the airport area, ascent and descent corridors, as well as tracking telemetry station to support specific mission profiles in integrated fashion with the existing airport infrastructure and air traffic. The paper will also describe the approach to the definition of a harmonized cooperative regulatory framework, according to the Aviation Authority, that represents the basis to assess suborbital operations and allows the relevant missions execution. In this activity, basing upon an established Memorandum of Cooperation between FAA, ENAC and the Italian Space Agency, the existing FAA/AST regulatory work frame is considered as reference benchmark and further tailored to the Italian case. Some considerations will also be developed relevant to initial challenges to be faced, by interested stakeholders, in starting commercial spaceflight initiatives as a new ground and emerging business opportunity.
  • Manned lunar landing mission scale analysis and flight scheme selection
           based on mission architecture matrix
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Xiaohui Wang, Liheng Mao, Yuxian Yue, Jianwen Zhao At present, the moon is still an important and preferred destination for human beings to visit due to the abundant resources and its potential to be the stepping-stone and platform of deep space exploration in the future. The manned lunar exploration has very important and profound meaning for leading technology innovation and manifesting comprehensive power of a country. Mission scale analysis and flight scheme selection are key problems for top-level projection and are still remaining to be researched systematically and deeply.This paper focus on the scale analysis of manned lunar landing mission and the optimal selection of flight schemes. At first, the basic configurations and the overall technical specifications of flight vehicle system were presented based on the investigation of traditional vehicles and developing trend of new vehicles. Afterwards, the fundamental elements of flight scheme were defined and the Mission Architecture Matrix was constructed. Based on Mission Architecture Matrix, the scale evaluation method was demonstrated. Finally, the qualitative selection model based on Analytic Hierarchy Process and Gray comprehensive evaluation method were established, the optimal scheme with economic and technical feasibility was given based on these two models. The validity of all models in this paper was tested and verified by different testing examples. The results show that EOR-LOR architecture is the best flight scheme for a short-period manned lunar exploration mission.To the best of our knowledge, it is the very first time that the concept of Mission Architecture Matrix was proposed. The reverse calculating algorithm based on Mission Architecture Matrix could improve the efficiency of mission scale analysis and the presented comprehensive evaluation model could make the selection of flight scheme more objective. These models and methods in this paper could be technical references for preliminary design of manned lunar landing mission.
  • The Breakthrough Starshot system model
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Kevin L.G. Parkin Breakthrough Starshot is an initiative to prove ultra-fast light-driven nanocrafts, and lay the foundations for a first launch to Alpha Centauri within the next generation. Along the way, the project could generate important supplementary benefits to solar system exploration. A number of hard engineering challenges remain to be solved before these missions can become a reality.A system model has been formulated as part of the Starshot systems engineering work. This paper presents the model and describes how it computes cost-optimal point designs. Three point designs are computed: A 0.2 c mission to Alpha Centauri, a 0.01 c solar system precursor mission, and a ground-based test facility based on a vacuum tunnel. All assume that the photon pressure from a 1.06 μm wavelength beam accelerates a circular dielectric sail. The 0.2 c point design assumes $0.01/W lasers, $500/m2 optics, and $50/kWh energy storage to achieve $8.0B capital cost for the ground-based beam director. In contrast, the energy needed to accelerate each sail costs $6M. Beam director capital cost is minimized by a 4.1 m diameter sail that is accelerated for 9 min. The 0.01 c point design assumes $1/W lasers, $10k/m2 optics, and $100/kWh energy storage to achieve $517M capital cost for the beam director and $8k energy cost to accelerate each 19 cm diameter sail. The ground-based test facility assumes $100/W lasers, $1M/m2 optics, $500/kWh energy storage, and $10k/m vacuum tunnel. To reach 20 km s-1, fast enough to escape the solar system from Earth, takes 0.4 km of vacuum tunnel, 22 kW of lasers, and a 0.6 m diameter telescope, all of which costs $5M.The system model predicts that, ultimately, Starshot can scale to propel probes faster than 0.9 c.
  • Resilience evaluation of the environmental control and life support system
           of a spacecraft for deep space travel
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): José Alexandre Matelli, Kai Goebel In deep space manned travels, the crew life will be totally dependent on the environment control and life support system of the spacecraft. A life-support system for manned missions is a set of technologies to regenerate the basic life-support elements, such as oxygen and water, which makes resilience a paramount feature of this system. The resilience of a complex engineered system is the ability of the system to withstand failures, continue operating and recover from those failures with minimum disruption. Resilient design is a new design framework on which the main goal is to quantify system resilience upfront in order to guide the design team during the conceptual design stage. In this article, we present a tool that combines a rule-based approach with a Monte Carlo-based approach to evaluate the resilience of a proposed environment control and life support system designed for deep space travel. Based on the results found, we explore a few design alternatives in order to increase system resilience.
  • An accelerated life test model for solid lubricated bearings used in space
           based on time-varying dependence analysis of different failure modes
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Chao Zhang, Lingfeng Pan, Shaoping Wang, Xingjian Wang, Mileta Tomovic Solid lubricated bearings are crucial mechanical components of spacecraft, and their failures are risky to the integrity of the spacecraft. To assess the reliability measures of solid lubricated bearings, accelerated life tests (ALT) have to be conducted. This paper proposes an ALT model of solid lubricated bearings. Firstly, the reliability function of solid lubricated bearings for each failure mode is derived based on Weibull distribution, and the effect of acceleration stresses is described by the generalized Eyring model. The time-varying copula function is then used to characterize the dependence between the two failure modes and further derive the reliability functions under normal and accelerated conditions. The unknown parameters in this proposed ALT model are estimated via the Bayesian approach. The proposed model is validated by the data collected from an ALT of solid lubricated bearings, and the results show that this model is accurate and effective.
  • Flatness-based trajectory planning for electromagnetic spacecraft
           proximity operations in elliptical orbits
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Yan-wei Zhu, Wei-wei Cai, Le-ping Yang, Huan Huang The inter-craft electromagnetic force, generated by magnetic coils equipped on all neighboring spacecraft, enables a novel propulsion mode without propellant consumption. The paper investigates a trajectory planning algorithm based on differential flatness for spacecraft proximity operations in elliptical orbits using the inter-craft electromagnetic forces. Firstly, the time-energy optimal trajectory planning problem is formulated into the desired electromagnetic control acceleration optimization and magnetic dipoles assignment. Secondly, utilizing the system's differential flatness property, the original trajectory planning problem could be mapped into the flat output space, eliminating the differential equations and reducing the dimensionality of the planning space. Then the resulted flat output planning problem is further parameterized with a mapped Chebyshev pseudospectral method, which is improved by the conformal map and barycentric rational interpolation techniques in order to decrease the side effect of the differentiation matrix's ill-conditioning. Finally, numerical simulations for a three-spacecraft electromagnetic formation reconfiguration mission show that the proposed algorithm is feasible and efficient, compared with the Radau pseudospectral method.
  • Optimization design for shape-transition curved isolator with controllable
           cross-sectional area
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Zewei Meng, Xiaoqiang Fan, Yi Wang, Bing Xiong, Lei Lu In order to obtain a type of variable cross-section curved isolator, a generic method was developed to design a supersonic curved isolator with controllable cross-sectional area by streamline tracing technique based on parameterizing and optimizing basic flow field. Firstly, traditional streamline tracing technique was conducted to design curved isolator. Analysis shows that the traced flow passage presents serious areal throats, which would be detrimental to the unstart performance of inlet and ability of stabilizing shock trains. It is unacceptable in practical applications. Then, the reason, which caused cross-sectional area changing non-monotonously, was analyzed and an improved method was proposed by introducing cross-sectional area constraints in the optimization process. What's more, two parameters, including total pressure recovery coefficient of basic flow field at the exit and maximum area deviation of traced area and designed area, are chosen as the optimization target. Finally, the basic flow field was optimized through modified method and the traced three-dimensional flow path was analyzed. The results show that the cross-sectional area can be controlled within a certain deviation range through the improving optimization method. And combining the blending function, the rectangular-to-circular isolator is designed and analyzed in the paper. It shows that the three-dimensional shape-transition curved isolator, which has well total pressure recovery performance, can be obtained through the method in this paper.
  • Development of EVA-SEBS based wax fuel for hybrid rocket applications
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Dinesh Mengu, Rajiv Kumar An attempt has been made in the present study to obtain the suitable wax based fuel that could be used in the practical hybrid rocket applications. It is known that wax has high regression rate compare to other polymeric fuels and is a most suitable hybrid fuel but suffers with poor mechanical properties. Thus, additives such as EVA (Ethylene Vinyl Acetate) and SEBS (Styrene-Ethylene-Butylene-Styrene Copolymer Grafted with 2% Maleic Anhydride) have been utilized to enhance its mechanical properties. Apart from the mechanical properties, regression rate, combustion efficiency and sliver loss studies have also been conducted. Various combinations of wax with EVA and SEBS samples have been prepared. Among these fuels developed, wax mixed with the combination of 10% SEBS and 5% EVA had shown significant improvement in the mechanical properties (maximum tensile strength was 4.26 MPa and percentage elongation was 24.6%). These properties are within the range to be utilized as a solid fuel in practical applications. Regression rate studies on the fuels developed in the present study had shown that the wax with SEBS based fuels obtained higher regression rate than wax with EVA based fuels. The wax fuel with combination of 10% SEBS and 5% EVA had shown the best regression rate characteristics along with mechanical properties that required for practical applications. The increment in combustion efficiency was observed with addition of polymeric additives to wax. With the addition of 20% EVA to wax the combustion efficiency improved from 63% to 72%. The burnt profiles from injector end to the nozzle end were more uniform with wax-SEBS fuel grains than pure wax fuel grains. Hence, the sliver loss is expected to be lower with wax-SEBS fuel.
  • A review on enhanced mixing methods in supersonic mixing layer flows
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Jianguo Tan, Dongdong Zhang, Liang Lv The development of supersonic and hypersonic aeronautical projects has led to a renewal of interest and research in supersonic mixing processes and methods to control them. Due to the compressibility effects, the mixing process in supersonic condition is significantly inhibited. Limited flow residence time (at the order of microseconds) for mixing of supersonic airstream and fuel in a scramjet combustor calls for the development of techniques for mixing enhancement. In the present paper, the applicable techniques for mixing enhancement of supersonic mixing layer flows are reviewed comprehensively. Following the brief introduction of fundamentals of supersonic mixing layer, this paper discusses the mixing enhancement methods in the categories of: passive flow control techniques, active flow control techniques and shock wave induced mixing enhancement strategy. Based on the review of former progress, the gaps in current knowledge and areas where more research is needed are pointed out. Meanwhile, the mechanisms of different enhanced mixing methods are summarized, which can be a reference and guidance for the future techniques design for mixing enhancement of supersonic flows.
  • Active use of solar radiation pressure for angular momentum control of the
           PROCYON micro-spacecraft
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): T. Ito, S. Ikari, R. Funase, S. Sakai, Y. Kawakatsu, A. Tomiki, T. Inamori This study proposes a solar sailing method for angular momentum control of the interplanetary micro-spacecraft PROCYON (PRoximate Object Close flYby with Optical Navigation). The method presents a simple and facile practical application of control during deep space missions. The developed method is designed to prevent angular momentum saturation in that it controls the direction of the angular momentum by using solar radiation pressure (SRP). The SRP distribution of the spacecraft is modeled as a flat and optically homogeneous plate at a shallow sun angle. The method is obtained by only selecting a single inertially fixed attitude with a bias-momentum state. The results of the numerical analysis indicate that PROCYON's angular momentum is effectively controlled in the desired directions, enabling the spacecraft to survive for at least one month without momentum-desaturation operations by the reaction control system and for two years with very limited fuel usage of less than 10 g. The flight data of PROCYON also indicate that the modeling error of PROCYON's SRP distribution is sufficiently small at a small sun angle (
  • Astroengineering, Dysonian SETI, and naturalism: A new Catch-22
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Milan M. Ćirković A methodological problem is inherent in any discussion of extraterrestrial engineering and its detectability: how to distinguish detection signatures of such astroengineering from “natural”, non-intentional, albeit exotic, processes' In practice, searches for traces and manifestations of advanced technological civilizations have been reduced so far to searching for outliers in the allegedly well-known regularities expected from natural astrophysical sources. This procedure, however, is an epistemological minefield, for at least two reasons: (i) prior datasets on which the regularities are based might be contaminated by artefacts, and (ii) the procedure of computation of unobservable quantities usually contains the implicit assumption of the non-intentional nature of sources. In other words, we are facing a Catch-22-type problem: in order to prove the artificial nature of a source, we seemingly need to first assume that it is not artificial. In contrast to most problems in science, this one could possibly be aggravated, rather than reduced, with the progress of our scientific understanding. Some possible recourses, as well as directions for further work toward building a comprehensive methodology of the Dysonian SETI, are discussed.
  • Adaptive higher order super-twisting control algorithm for a flexible
           air-breathing hypersonic vehicle
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Yibo Ding, Xiaogang Wang, Yuliang Bai, Naigang Cui A novel adaptive higher order super-twisting control algorithm (AHOSTC) is proposed for a flexible air-breathing hypersonic vehicle (FAHV). Firstly, the nonlinear control-oriented model (COM) is processed using input/output feedback linearization method. Therefore, significant flexible effects aroused by slender fuselage and strong coupling between propulsion and aerodynamic of FAHV could be considered during the application of model-based control techniques. Secondly, an adaptive control gain L is incorporated into normal higher order super-twisting algorithm (HOSTA) via dilation rescaling to improve speed of response and attenuate chattering, in the meanwhile, the matched disturbances can be compensated and the finite-time convergence can be achieved. In addition, gain L could be adjusted by the presented novel adaptive law automatically, especially when Lipschitz constants of disturbances are unknown and time-varying. Furthermore, the stability of adaptive law is analyzed via Lyapnuov criteria. Ultimately, compared with normal HOSTA, the proposed AHOSTC is able to enhance robustness and respond speed, while minimizing effects of chattering efficiently. Simulations on longitudinal model of FAHV are carried out to compare AHOSTC with normal HOSTA. The results demonstrate the superiority and effectiveness of AHOSTC under different simulation conditions, external disturbances and parametric uncertainties.
  • Investigation on gaseous jet in forebody/inlet for shock-induced
           combustion ramjet (shcramjet) engines
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Zhao-bo Du, Wei Huang, Li Yan As one of the most promising propulsion systems in the future, there are unusual advantages of the shock-induced combustion ramjet (shcramjet) engine. In the current study, the slot is placed on the second ramp of the shcramjet inlet to promote the mixing process between the fuel and the hypersonic crossflow. The influences of the injection angle and the jet-to-crossflow pressure ratio have been investigated numerically based on the grid independency analysis and the code validation. The obtained results predicted by the two-dimensional Reynolds-average Navier-Stokes (RANS) equations coupled with the two equation RNG k-ε turbulence model show that the grid scale makes only a slight difference to the wall pressure profiles for all jet-to-crossflow pressure ratios employed in this article. With the smaller injection angle, higher fuel/air mixing efficiency, less loss of the stagnation pressure and lower fuel penetration depth are shown. Low jet-to-crossflow pressure ratio can increase the mixing efficiency and decrease the loss of the stagnation pressure. High jet-to-crossflow pressure ratio results in higher penetration depth. There is an optimum injection angle for each jet-to-crossflow pressure ratio to achieve the maximization of the fuel/air mixing in hypersonic flows.
  • Passive nonlinear actuators for deploying mesh antennas
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Meng Li, Ruoxi Wang, Zhihua Zhao Deployable mesh antennas have dominated high-resolution earth observations and telecommunications, benefitting from their high package ratios and low areal densities. They are usually folded compactly for launch and unfolded to the working configuration once in orbit. This unfolding process is carried out by driving units, composed of pretensioned springs and/or motors, which transfer the energy stored in passive springs and/or outputted by active motors into the potential energy of the antenna. A previous energetic analysis has revealed that the potential energy remains low during the initial deployment stage and grows sharply in the late stage when the structure members are stressed almost to the fully deployed configuration. Therefore, the force required to deploy a mesh antenna increases over the process of unfolding, exhibiting negative stiffness. However, the output force of a normal linear spring has positive stiffness. To tackle this conflict, we proposed, designed, and developed a new type of passive actuator with nonlinear force-displacement curves to meet the specific demand of unfolding mesh antennas. This was achieved through the combined use of a torsional spring and a convex cam. For the desired force displacement curve, the cam profile was theoretically formulated as an optimization problem, the solution of which was numerically obtained by the sequential quadratic programming algorithm. The experimental result showed that the designed cam could generate the target force. We also compared the unfolding processes of a mesh antenna via simulations, driven by three kinds of springs with nearly the same stored energy; one has positive stiffness, one has zero stiffness and the other one has negative stiffness. Results confirmed that the negative-stiffness spring is more suitable for unfolding the mesh antenna. Moreover, the passive nonlinear actuators developed here might also be used in other applications where nonlinear force is needed.
  • Heliogyro solar sail with self-regulated centrifugal deployment enabled by
           an origami-inspired morphing reflector
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Rui Wu, Peter C.E. Roberts, Constantinos Soutis, Carl Diver Solar sails utilise solar radiation pressure to propel spacecraft without the need for propellant. Existing solar sail concepts also achieve propellantless flight control by actively twisting the sail or altering the sail surface reflectivity. However, this usually consumes energy and leads to structural dynamic issues. In the present study, we propose an innovative method, which uses origami to convert the 2D sail into a 3D optical meta-structure with design-able and manoeuvrable optical properties. Such a device could adjust both the magnitude and the direction of solar radiation pressure without inducing overall distortion in the sail and therefore achieve flight control through a quasi-static process. As an example, a centrifugally deployed heliogyro solar sail with meta-structure morphing reflectors is designed. The reflectors generate stress-dependent solar radiation pressure vector, which propels the spinning of the sail and, according to structural dynamic simulation, achieves a closed-loop controlled centrifugal deployment that is fully passive.
  • Ground-based experiment of capturing space debris based on artificial
           potential field
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Zheng Huang, Yun Lu, Hao Wen, Dongping Jin An enabling debris capturing concept is experimentally demonstrated using an air-bearing testbed. To facilitate on-board implementation, the idea of artificial potential field is employed for the controller design of the debris capturing task. In particular, the artificial potential function is constructed such that all of its stable minima stratify the capturing condition, thereby avoiding the possibility of trapping into unwanted local minima. To experimentally simulate the mission of capturing space debris on ground, two air-bearing simulators are designed and developed, in which the first one is equipped with a single-degree-of-freedom robotic arm and the second one serves as a mock-up of the debris to be captured. The location and attitude of the simulators are measured by binocular cameras for control feedback. Experimental studies are performed to verify the results of the theoretic analysis.
  • Verbal reports of neurovestibular symptoms in astronauts after
           short-duration space flight
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Millard F. Reschke, Gilles Clément Because of operational constraints, no research studies are performed during return to Earth, when astronauts perform critical operational tasks such as piloting and egressing the vehicle. The objective of this study was to interview Space Shuttle crewmembers to collect a description of post-flight perception of self-motion and self-performance from the astronauts during reentry and immediately after landing. Thirty-four Space Shuttle crewmembers were interviewed immediately after they returned from space. Transcripts of the interviews recount the crewmembers' experiences associated with head movements during reentry, during egressing the vehicle, and shortly after landing. Head movements made during reentry and immediately after return to Earth caused an increase sensation of self-motion, which affected their balance and gait. Pitch and roll head movements provoked the largest effects. Crewmembers also reported a lag in motion perception after the movement had stopped. More than one-third of crewmembers thought they would be unable to egress the Space Shuttle cabin unaided during an emergency. A clinical otoneurological examination of the crewmembers immediately after landing is needed to better understand the extent of vestibular deficits and track recovery.
  • Development and testing of a pyro-driven launcher for harpoon-based comet
           sample acquisition
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Stefan Völk, Stephan Ulamec, Jens Biele, Matthias Hecht, Peter Lell, Josef Fleischmann, Sebastian Althapp, Markus Grebenstein, Joseph A. Nuth, Donald C. Wegel, Walter F. Smith, Lloyd R. Purves, Douglas S. Adams, Stuart Hill, James C. Leary, Harold A. Weaver, Scott A. Sandford The CORSAIR (COmet Rendezvous, Sample Acquisition, Investigation, and Return) mission was a proposal for the NASA New Frontiers program. It belongs to the Comet Surface Sample Return mission theme which focuses on acquiring and returning to Earth a macroscopic sample from the surface of a comet nucleus. CORSAIR uses a harpoon-based Sample Acquisition System (SAS) with the spacecraft hovering several meters above the comet surface. This stand-off strategy overcomes disadvantages of other systems such as drills. Since comets are low gravity objects, those techniques would require anchoring before sampling, which is not necessary here. Moreover, the harpoon-based system allows for acquiring several samples from different locations on the comet maximizing the scientific output of the mission.Each SAS assembly consists of a pyro-driven launcher, a Sample Acquisition and Retrieval Projectile (SARP) and a retraction system using a deployable composite boom structure. In order to collect enough cometary material, the launcher has to provide the required kinetic energy to the SARP. Due to high energy densities, pyrotechnically actuated devices ultimately reduce the overall system mass and dimensions. First, the scientific and technological background of the CORSAIR mission is explained. Then, an overview of the development, design and testing of the launcher is given. Finally, the launcher theory is introduced explaining the entire reaction chain: initiation → gas dynamics → SARP motion.
  • Relative equilibria and stability of a dumbbell spacecraft about an
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Yu Shi, Yue Wang, Shijie Xu The gravitational orbit-attitude coupling becomes pronounced in spacecraft dynamics about small asteroids, due to the large ratio of the spacecraft's dimension to the orbital radius. In this study, relative equilibria and their stability of the gravitationally coupled orbit-attitude dynamics (full dynamics) of a dumbbell spacecraft about an irregular-shaped asteroid are investigated. The shape of the asteroid is represented by a homogeneous polyhedron, and its non-spherical gravity is calculated accordingly. By using geometric mechanics, the Hamiltonian structure and equations of motion of the full dynamics are derived. Then, the orbit-attitude equilibria about asteroids 4769 Castalia, 433 Eros, and 6489 Golevka are calculated numerically, respectively, and the drift of orbit-attitude equilibria with respect to the dumbbell's varying length is also discussed. By comparing with the equilibria of a point mass, it has been found that a classical point-mass equilibrium can generate three orbit-attitude equilibria located nearby. With the increase of the dumbbell's length, the effects of orbit-attitude coupling become stronger, and the orbit-attitude equilibria diverge further from the classical point-mass equilibria. The spectral stability of the orbit-attitude equilibria is determined numerically and analyzed. It has been found that the gravitational orbit-attitude coupling is likely to make the equilibria unstable in our simulations. The dumbbell is a good approximation of a spacecraft consisting of two modules that are connected by trusses, and its orbit-attitude equilibria have potential applications in asteroid proximity operations, such as body-fixed hovering.
  • Access to space: A new approach by the united nations office for outer
           space affairs
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Ayami Kojima, Daniel García Yárnoz, Simonetta Di Pippo In the context of UNISPACE+50, which will mark the 50th anniversary of the first UNISPACE conference held in Vienna in 1968, the United Nations Office for Outer Space Affairs (UNOOSA) has defined four pillars to address the future of space activities and their role in development: space economy, space society, space accessibility and space diplomacy. Under the space accessibility pillar, UNOOSA intends to enable all communities, particularly in developing countries, to use and benefit from space technologies and applications. Building on previous activities and new partnerships, UNOOSA facilitates and provides (i) access to space education; (ii) access to space data; (iii) access to space technology and research facilities; and finally, for the first time, (iv) direct access to space. At the core of these activities is microgravity research, from on-ground simulation to orbital opportunities, which is one of the main tools of the Human Space Technology Initiative.This shift from on-ground space education, applications, technology and simulation to on-orbit technology is directly linked to a UNISPACE+50 thematic priority on “Global partnerships in space exploration and innovation”. At this stage, three partnership programmes are incorporated in this strategy, with the Japan Aerospace Exploration Agency, the China Manned Space Agency, and Sierra Nevada Corporation. These programmes provide access to a wide spectrum of Low Earth Orbit opportunities.
  • Non-sphere perturbation on dynamic behaviors of spatial flexible damping
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Weipeng Hu, Zichen Deng As one of the main factors affecting the dynamic behaviors of the ultra-large spatial structure, the non-sphere perturbation effects have been considered in the dynamic analysis of the rigid spatial structures recently. In this paper, employing the structure-preserving method developed in our previous job, the non-sphere perturbation effects on the orbit dynamic behavior, the attitude dynamic behavior as well as the transverse vibration of the spatial flexible damping beam are investigated in detail. The remarkable effects of the non-sphere perturbation on the dynamic behaviors of the beam obtained numerically in this paper include: The non-sphere perturbation effects on the evolution of the orbit radius should not be neglected when the attitude angle is far away from the stable attitude state; The non-sphere perturbation accelerates the dissipation of the transverse vibration of the spatial flexible damping beam; It is more important that, the consideration of the non-sphere perturbation results in a new stable attitude of the beam when the initial attitude angle is close to π/2 and the initial attitude angle velocity is small enough. The above novel findings give some good advice on the attitude adjustment scheme design and the vibrational control strategy design for the ultra-large spatial structures.
  • Capture of small near-Earth asteroids to Earth orbit using aerobraking
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Minghu Tan, Colin McInnes, Matteo Ceriotti This paper investigates the concept of capturing near-Earth asteroids into bound orbits around the Earth by using aerobraking. To guarantee that the candidate asteroids cannot present an impact risk during aerobraking, an initial aerobraking hazard analysis is undertaken and accordingly only asteroids with a diameter less than 30 m are considered as candidates in this paper. Then, two asteroid capture strategies utilizing aerobraking are defined. These are termed single-impulse capture and bi-impulse capture, corresponding to two approaches to raising the perigee height of the captured asteroid's orbit after the aerobraking manoeuvre. A Lambert arc in the Sun-asteroid two-body problem is used as an initial estimate for the transfer trajectory to the Earth and then a global optimisation is undertaken, using the total transfer energy cost and the retrieved asteroid mass ratio (due to ablation) as objective functions. It is shown that the aerobraking can in principle enable candidate asteroids to be captured around the Earth with, in some cases, extremely low energy requirements.
  • MPC-based anti-sway control of tethered space robots
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Zhongjie Meng, Bingheng Wang, Panfeng Huang Tether sway in debris towing removal perturbs the removal orbit due to the thrust-tether misalignment. Therefore, this paper proposes an anti-sway method using model predictive control (MPC). The method uses platform attitude maneuver to suppress the sway and track the orbit by orienting the platform thrust to the desired direction, which makes the system non-affine and underactuated. This necessitates a dual-loop control structure where the outer loop provides the desired attitude for the inner attitude control loop. For the outer loop, the attitude angular velocity is extracted as a virtual control input. A higher-order hierarchical sliding mode control (HSMC) and a super-twisting-algorithm (STA) based observer are used to obtain the equivalent law for sliding phase. The system states in controller are estimated by an extended kalman filter (EKF). For the inner loop, a MPC-based control torque forces the angular velocity to follow the equivalent law and steers the states to the sliding surface in an optimal manner. Simulation results show that the control objective is fulfilled by the bounded torque and the controller is robust to the estimation errors.
  • Electrostatic-magnetic-hybrid thrust generation in central–cathode
           electrostatic thruster (CC–EST)
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Akihiro Sasoh, Hayato Kasuga, Yoshiya Nakagawa, Toshihiro Matsuba, Daisuke Ichihara, Akira Iwakawa The thrust characteristics of electrostatic-magnetic hybrid acceleration have been obtained in the central–cathode electrostatic thruster (CC-EST), which has a diverging magnetic nozzle and injects propellant through an annular slit on the inner surface of a ring anode. The electrostatic and electromagnetic contributions are evaluated by fitting experimentally measured thrust characteristics to formulae derived for steady-state, quasi-neutral plasma flows. The thrust is composed of two terms: one corresponds to the electrostatic acceleration interfaced by the magnetized electrons, the other to electromagnetic acceleration yielding a kinetic energy of swirl motion that is converted to that of axial motion in the diverging magnetic nozzle. The thrust performances of three thrusters having an axisymmetric shape with a hollow cathode on the centre axis and a diverging, applied magnetic field are examined. While only an electromagnetic thrust component is obtained in the conventional applied-field magneto-plasma-dynamics thruster, the other two, CC–ESTs, exhibit comparable, electrostatic and electromagnetic thrust components, and thus improve thrust performance.
  • Evaluation criteria for a flameless combustor based on recirculation and
           mixing - A CFD approach
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Hesham M. Khalil, Yehia A. Eldrainy, Khalid M. Saqr, Walid A. Abdelghaffar In the present work, the effect of combustor geometry and inlet air velocity on flameless critical parameters such as recirculation ratio and mixing is investigated. The main objective is to develop evaluation criteria for flameless combustors design based on these critical parameters. A simple lab scale combustor with central air jet arrangement is employed for the analysis. Three-dimensional computations were performed under non-reacting conditions using ANSYS Fluent. Reducing the air jet diameter to half its original value leads to a 100% increase in the recirculation ratio, which promotes flameless operation. Moreover, it results in a slightly more than 200% increase in turbulence intensity, which encourages hot products entrainment and accelerates mixing with incoming reactants. From another side, scaling down the combustor to half its original size results in 66% reduction of recirculation ratio, which might suppress flameless operation. Besides, it accelerates incoming reactants mixing in the near burner region due to the increased jet spreading and decay rate. These results show the considerable influence of combustor geometry on recirculation ratio and mixing. Furthermore, the critical role of later parameters in the previously reported transition between conventional and flameless combustion modes for the present combustor is demonstrated. A threshold value of recirculation ratio, Kcritical, is found critical for flameless operation and is noticed to increase with increasing excess air ratio. Therefore, the two parameters are linked together through a developed mathematical correlation. Finally, combustor geometry is represented through the dimensionless parameters; air jet to combustor diameter ratio, and combustor scaling factor. Recirculation ratio is linked to these parameters through additional correlations. Through these developed correlations, geometry aspects for flameless combustors can be preliminary identified and/or evaluated.
  • Space elevator maturing into a Galactic Harbour
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Peter Swan, Michael Fitzgerald One of the principle elements of the International Space Elevator Consortium's (ISEC) action plan towards an operational Space Elevator is to understand its customer utilization. To fully understand the potential application for commercial ventures on the Space Elevator, the concept of a Galactic Harbour is introduced. Galactic Harbour represents continuous operations moving customer payloads on multiple Space Elevators from entry ports to exit ports. These locations would most logically be an Earth Port where customers have their payloads loaded onto Space Elevators and their release points at multiple altitudes per the desires of the customers. The Galactic Harbour would then be the volume incorporating multiple Earth Ports [on the ocean, with incoming and outgoing ships/helicopters and airplanes] and then stretch up in a cylindrical shape to include tethers and other aspects out to the Apex Anchors. Products and payloads [satellites, people, resources, etc.] would enter the Galactic Harbour around the Earth Ports and exit at some point along the tether [to LEO, to GEO region, to Mars, Moon, asteroids, intergalactic, towards the sun] dependent upon where it is released.
  • Combustion stabilization modes in a hydrogen-fueled scramjet combustor at
           high stagnation temperature
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Yanan Wang, Zhenguo Wang, Mingbo Sun, Hongbo Wang Combustion stabilization modes were studied experimentally under a Mach 2.52 supersonic inflow at a high stagnation temperature of 1629 K. Optical observations including the high-speed flame luminosity and schlieren images were utilized to capture the combustion stabilization characteristics. Effects of the equivalence ratio and the injection distance on the combustion stabilization mode transition were discussed. Two supersonic combustion stabilization modes are identified clearly in the scramjet combustor, as the cavity stabilized mode and the jet-wake stabilized mode. At a relatively low equivalence ratio, the flame is stabilized in the cavity stabilized mode, and it will transfer to the jet-wake stabilized mode with the increase of the equivalence ratio. The flame stabilization mode is also affected by the injection distance. The critical equivalence ratio for mode transition reduces with the decrease of the injection distance. In the cavity stabilized mode, the shear layer of the cavity stabilizes the flame. In the jet-wake stabilized mode, the intense combustion induces high pressure, and leads to a large boundary-layer separation zone that exists in front of the flame. It contributes to the flame stabilization. In addition, a triple-reaction-zone mechanism is proposed to further explain the transition process from the cavity stabilized mode to the jet-wake stabilized mode, and the large boundary-layer separation zone also contributes to the transition process.
  • Analysis of the gas exchange and water balance in a closed experimental
           model of the artificial ecosystem intended for an estimated portion of a
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Sofya Ushakova, Natalia Tikhomirova, Vladimir Velichko, Sergey Trifonov, Yegor Morozov, Galina Kalacheva, Anastasia Pavlova, Alexander Tikhomirov This study was performed to investigate water and gas exchange in the experimental model of a closed ecological system (CES) intended for an estimated portion of a human in the long-duration (several-month) experiment. The diversity of the vegetable conveyor in the system was increased. Human wastes were involved in mass exchange processes, and human respiratory function was periodically connected to the experimental model of a CES. The experimental model of a CES was used to quantify regeneration of the gaseous atmosphere with oxygen and carbon dioxide loops by linking the photosynthesizing compartment with the heterotrophic compartment (soil-like substrate) and by the periodic connection of the human respiratory function. Under the preset light and temperature conditions, atmospheric CO2 concentration in the CES model intended for a portion of a human was maintained at a level that neither limited photosynthetic processes nor was harmful to humans (800–2000 ppm) during the 154-day experiment. At the same time, O2 concentration did not either drop below 20.8% or rise above 22.6%. The amount of the evapotranspiration water collected in the system could satisfy 50% of the daily water requirement of a human (with all the water used and excreted by the human being processed and used to irrigate plants). The evapotranspiration water did not need to be additionally purified before being used by humans. Thus, in the experimental model of the closed ecological system, human oxygen and food requirements (per 0.05 portion of a human) were matched to the function of the heterotrophic compartment and the photosynthesizing activity of the multispecies uneven-aged higher plant community.
  • Serum microRNA as noninvasive indicator for space radiation
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Wenjun Wei, Jufang Wang, Jinpeng He, Xiaodong Xie Ionizing radiation in space is one of the major barriers to long-term or deep-space exploration for human. Although physical dosimeters and biomarkers have been developed to assess the exposure risk during the space flight, there are some limitations existing in these methods such as lack of individual specificity and time-consuming. Serum microRNAs (miRNAs) are ideal biomarkers because they are stable in responding to changes of environments, conservative in different species and easy for collection and detection. The purpose of this study was to identify a set of serum miRNAs which could serve as convenient and sensitive indicators to evaluate the exposure risk of ionizing radiation in space. Eight-week-old Kunming mice were total-body exposed to different doses of carbon ions and X-rays. Serum samples were collected at 24 h after exposure, and miRNAs associated with immune system and hematopoietic system were detected by miRNA PCR array. The serum miRNA expression profiles showed that the levels of 2 miRNAs (let-7a-5p, miR-200b-5p) in irradiated mice were 2 times higher than that in non-irradiated mice (P 
  • Study of satellite formation flying control using differential lift and
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): D. Ivanov, M. Kushniruk, M. Ovchinnikov An algorithm of satellite formation flying control in the Low-Earth Orbit using the aerodynamic force is considered. A simple model of the aerodynamic force that takes into account the lift component of the force is proposed. It allows us to calculate the satellite attitude relative to the incoming flow that provides the required aerodynamic force. For the given model parameters the acceptable control region is obtained. The relative motion control algorithm based on the Linear-Quadratic Regulator is considered. The technique for the algorithm parameters determination is suggested. Numerical study of the controlled motion is carried out. The simulation takes into account the second harmonic of the Earth gravitational field and the inaccuracy of the atmospheric density model.
  • Flexible heat shields deployed by centrifugal force
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Rui Wu, Peter C.E. Roberts, Constantinos Soutis, Carl Diver Atmospheric entry aerodynamic decelerators which also provide thermal protection do not scale well for smaller payloads (e.g. CubeSat) or where the planets atmosphere is significantly less dense than the Earth's (e.g. Mars entry). Both cases require heat shields larger than can be accommodated either within the launch vehicle fairing, or within acceptable payload volumes, so deployable shields are required. Unlike previous designs proposed to fulfil this requirement like inflatable structures or deployable solid mechanisms, the presented research addresses this by utilising inertial force, or specifically, centrifugal force generated from autorotation to deploy and stiffen a flexible heat shield. Structural dynamic analyses including the trajectory simulation on a CubeSat sized system has shown that the autorotation and deployment form a closed loop which reliably leads to an equilibrium of deployment, while the heat shield is near fully deployed at altitudes higher than 30 km with tolerable spin rate (
  • Surrogate modeling for liquid-gas interface determination under
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Zongyu Wu, Yiyong Huang, Xiaoqian Chen, Xiang Zhang, Wen Yao In recent years the advent of on-orbital refueling technology and the accompanying interest in liquid management in space have rekindled attention to the study of the liquid-gas interface determination. So far, a series of numerical methods, such as the Shooting method, are used to calculate the mathematical model of liquid-gas interface. However, these methods have some drawbacks in common, such as poor convergence, dependence on initial value and instability. As a result, long calculation time and sudden calculation interruption are inevitable. Although satisfactory results can be achieved, it requires human intervention. As an important intermediary of capillary flow and liquid management device design, liquid-gas interface calculations need to be done thousands of times. Therefore, the quickness and robustness of liquid-gas interface calculations are needed. Surrogate modeling method arising with the development of aerospace technology in recent years provides a new way to solve this problem. Combining with the characteristics of liquid-gas interface calculation, a double-layer radial basis function surrogate model is proposed to approximate the mathematical model of liquid-gas interface. This surrogate model is approximately equivalent to the mathematical model of liquid-gas interface but is much easier to solve. Compared with the Shooting method, the efficiency of the surrogate model is improved by 99.46%, and the success rate is increased to 100% from 35%.
  • A model for understanding and managing cost growth on joint programs
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Morgan Dwyer, Zoe Szajnfarber, Bruce Cameron, Edward Crawley Although joint programs are typically established to save the government money, recent studies suggest that instead of reducing program cost, jointness may actually induce cost growth. Motivated by three case studies that explored the cost of acquiring systems jointly, this paper presents a model that explains why joint programs often experience large cost growth and how jointness itself may induce it. Specifically, our proposed Agency Action Model suggests that on joint programs, the collaborating agencies' institutional interest in retaining or regaining their autonomy induces cost growth. After explaining the basic components of the model, we demonstrate its ability to explain the cost growth observed in our case studies. Finally, we use the model and our case study data to generate recommendations for managing joint programs in the future.
  • Dynamic and static controller placement in Software-Defined Satellite
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Shuai Wu, Xiaoqian Chen, Lei Yang, Chengguang Fan, Yong Zhao Software-Defined Satellite Networking (SDSN) [1], similar to Software-Defined Networking (SDN) [2], has emerged as a new paradigm that offers the programmability required to dynamically configure and control a satellite network. As SDSN is large-scale network, recent proposals have advocated deploying multiple controllers that work cooperatively to enhance performance and scalability [3,4]. Nonetheless, this approach introduces a new problem: how many controllers are needed, and where should they be deployed' We call this controller placement problem, which can be divided into dynamic and static types. The former assumes that the network operator has already placed plenty of back-up controllers throughout the network. By changing the on-off status of them, it realizes adapting the number and location of active controllers with changing network conditions. On the contrary, the latter decides the controller deployment only for once before building SDSN. Related work only focuses on ground network and several important factors affecting the controller placement are not taken into account comprehensively. In this paper, we propose the framework and mechanism of SDSN, define the Dynamic Controller Placement Problem (DCPP) as well as Static Controller Placement Problem (SCPP), and introduce a heuristic method to solve them. Simulation results show that our solution improves the performance of SDSN.
  • Performance analysis of fixed wing space drones in different solar system
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): M. Hassanalian, D. Rice, S. Johnstone, A. Abdelkefi The aerodynamic coefficients, forces, sizing parameters, and performance of fixed wing drones in different solar system bodies are investigated. Before carrying out the aerodynamic analysis and study of the performance of fixed wing drones, the physical and atmospheric features of various solar system bodies are first determined. Two drones are considered, namely, a fixed wing micro air vehicle with Inverse Zimmerman planform and a tilt-rotor unmanned air vehicle. The effects of Reynolds number on the performance of these drones from an aerodynamic point of view are determined. Furthermore, a parametric study for sizing of fixed wing drones are also investigated. These analyses ultimately lead to the optimum sizing process of fixed wing drones to be used in solar system bodies with different physical and atmospheric features. The comparison between different atmospheric characteristics on the performance of drones is needed to design efficient fixed wing drones which are capable of flight in other planets.
  • Mixing enhancement mechanism induced by the cascaded fuel injectors in
           supersonic flows: A numerical study
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Wei Huang, Yong Li, Li Yan, R. Moradi The mixing process between the injectant and air in the supersonic flow is a crucial problem for the successful design of the scramjet engine, and it almost takes place simultaneously with the combustion process. In the current study, the flow field properties of the cascaded fuel injectors in the supersonic flow with the freestream Mach number being 3.75 have been investigated by means of the three-dimensional compressible Navier-Stokes equations coupled with the SST k-ω turbulence model, and the cascaded fuel injectors have been combined with the front hydrogen jet and the rear air jet. At the same time, the cascaded fuel injectors with pure hydrogen or nitrogen injection have been studied for comparison, as well as the single injection scheme with the same injector area. The obtained results show that the cascaded fuel injectors combined with the front hydrogen jet and the rear air jet are not only beneficial for the near wall mixing process, but also beneficial for the mixing augmentation in the whole flow field. The smaller injector space is not beneficial for the injectant penetration depth improvement, as well as the mixing augmentation. When the injector space is small, the injectant plume would extend downstream irrespective of whether the rear air jet exists or not, and its combustion flow field characteristics should be explored in the near future before it is used for engineering implementation.
  • Optical changes of molecular contamination thin-film outgassed from
           epoxy-based resin during deposition and desorption process
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Kazunori Shimazaki, Eiji Miyazaki, Yugo Kimoto Molecular contaminants outgassed from organic materials used for the spacecraft degrade the performance of optical surfaces of spacecraft. The influence of contaminants outgassed from epoxy resin on the spectral transmittance of the quartz substrate was investigated with an in-situ measurement system. The system can deposit the contaminants on temperature-controlled quartz substrates and the transmittance spectra were measured immediately after deposition in vacuum ambient. We obtained the optical constants of the contaminant using transmittance spectrum and simple optical models for optical calculations. The optical constants were described with a harmonic oscillator model and an effective medium approximation model. This paper reports the in-situ measurement results of transmittance spectra of the epoxy-resin-induced contaminants in deposition and desorption process. The thin contamination layer decreased the transmittance in the ultraviolet region. However, the contamination was entirely desorbed at −20 °C and transmittance recovered to the initial value. In addition, the results of optical calculations using the obtained optical constants were compared to the measurement results.
  • ExMASS: A viable model for authentic student-scientist research
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s): Andrew Shaner, Sandy Watson, Maya Bakerman, Sanlyn Buxner The Exploration of the Moon and Asteroids by Secondary Students (ExMASS) program provides students the opportunity to conduct authentic, student-led, open-inquiry research with assistance from their teacher and a scientist. One goal of the program is to enhance participants' attitudes toward science. Most students enter the ExMASS program with positive attitudes toward science. However, the attitude survey developed for ExMASS measured small but statistically significant increases in attitudes. This paper discusses the ExMASS program, an attitude towards science survey designed for the program's specific audience, and the results of statistical analyses of the survey. The validity of the attitudes survey was tested with an exploratory factor analysis (EFA). The results of the EFA revealed two salient factors measured by the survey: 1) Personal Importance of Science and 2) Importance of Science to Society. A reliability analysis revealed a Cronbach alpha value of 0.89. Paired t-tests revealed statistically significant differences in students' attitudes before and after the program. For Factor 1, participants' before scores were statistically significantly lower than their post scores, t(88) = 3.16, p
  • IFC - Publication Information
    • Abstract: Publication date: November 2018Source: Acta Astronautica, Volume 152Author(s):
  • Psychological and biological challenges of the Mars mission viewed through
           the construct of the evolution of fundamental human needs
    • Abstract: Publication date: Available online 4 October 2018Source: Acta AstronauticaAuthor(s): Konrad Szocik, Steven Abood, Mark Shelhamer The environment of a deep-space Mars mission represents a genetic, epigenetic, and psychological mismatch to the terrestrial environment in which humans evolved. Potential psychological and biological challenges of this mismatch have been gleaned from simulations in space-analog facilities, polar expeditions, and missions served on the International Space Station. Optimal performance and welfare of crew members will depend on successful adaptation to these challenges, which in turn depends on the satisfaction of fundamental human needs. These fundamental human needs – drawn from Maslow's hierarchy of needs – include physiological, security, relationship, and existential needs. The satisfaction of each need over the course of a protracted space mission will require the crew to overcome novel psychobiological obstacles for which they must be prepared. Of particular concern will be the rigors of an isolated environment out of sight from the travelers' terrestrial home, leading to stress-induced depression of the immune system and potential psychological pathologies. A rationally designed mission environment that utilizes technology and measures such as biophilia to optimize the fulfillment of each human need could bolster the psychobiological resilience necessary for a successful odyssey.
  • Topology optimization of pretensioned reflector antennas with unified
           cable-bar model
    • Abstract: Publication date: Available online 3 October 2018Source: Acta AstronauticaAuthor(s): Shufei Feng, Baoyan Duan, Congsi Wang, Xuechao Duan, Wei Wang, You Ban From innovative high-rise buildings through spacecraft, applications of prestressed cables are not uncommon. But the use of prestressed cables in ground-based reflector antennas is very rare. In this paper, prestressed cables were introduced to the ground-based antennas to achieve the lightweight design requirements. To determine the layout of the prestressed cables, a gradient-based topology optimization model was established. In this optimization model, the continuously varying 'lack of fit' is used to replace the discrete element type variables as the design variables, and smooth sigmoid functions are introduced to unify the discrete allowable stress of cable and bar elements. Eventually, the discrete topological variable optimization problem is transformed into a continuous one. Besides, to avoid the occurrence of grey elements in the optimized results, a parameter control strategy for the sigmoid functions is carried out during the optimization procedure. As an example, the optimizations of an 8 m truss antenna and an 8 m cable-truss antenna are implemented, and the discussions of the results are given.
  • Numerical investigation of effect of hydrogen injection frequency on
           supersonic reactive flow
    • Abstract: Publication date: Available online 3 October 2018Source: Acta AstronauticaAuthor(s): Xin Liu, Yuming Xing, Ma Ma, Liang Zhao The pulsed injection strategy is a promising way to improve the mixing and combustion performance in the Scramjet (supersonic combustion ramjet) combustor. However, few researchers focus on the combustion characteristics in the supersonic freestream with the pulsed jet. In this paper, two-dimensional simulation was performed to investigate the effect of hydrogen injection frequency on the supersonic reactive flow field. A detailed 9 species, 19 chemical reactions chemistry mechanism was used to solve the chemical reaction. The results show there is an optimal injection frequency to achieve the best combustion efficiency. The 16 kHz injection frequency is a promising injection strategy which was obtained a global combustion efficiency of about 0.8. Total pressure recovery coefficient increases significantly when the pulsed jet is injected. The combustion improvement mechanism of the pulsed jet is to supply more air for reaction during the injection period.
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