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Showing 1 - 200 of 3031 Journals sorted alphabetically
AASRI Procedia     Open Access   (Followers: 15)
Academic Pediatrics     Hybrid Journal   (Followers: 20, SJR: 1.402, h-index: 51)
Academic Radiology     Hybrid Journal   (Followers: 16, SJR: 1.008, h-index: 75)
Accident Analysis & Prevention     Partially Free   (Followers: 79, SJR: 1.109, h-index: 94)
Accounting Forum     Hybrid Journal   (Followers: 22, SJR: 0.612, h-index: 27)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 27, SJR: 2.515, h-index: 90)
Achievements in the Life Sciences     Open Access   (Followers: 4)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 5, SJR: 0.338, h-index: 19)
Acta Astronautica     Hybrid Journal   (Followers: 302, SJR: 0.726, h-index: 43)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 3)
Acta Biomaterialia     Hybrid Journal   (Followers: 25, SJR: 2.02, h-index: 104)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription  
Acta de Investigación Psicológica     Open Access   (Followers: 2)
Acta Ecologica Sinica     Open Access   (Followers: 8, SJR: 0.172, h-index: 29)
Acta Haematologica Polonica     Free   (SJR: 0.123, h-index: 8)
Acta Histochemica     Hybrid Journal   (Followers: 3, SJR: 0.604, h-index: 38)
Acta Materialia     Hybrid Journal   (Followers: 195, SJR: 3.683, h-index: 202)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5, SJR: 0.615, h-index: 21)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.442, h-index: 21)
Acta Oecologica     Hybrid Journal   (Followers: 9, SJR: 0.915, h-index: 53)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription   (Followers: 1)
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 3, SJR: 0.311, h-index: 16)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 2)
Acta Poética     Open Access   (Followers: 4)
Acta Psychologica     Hybrid Journal   (Followers: 21, SJR: 1.365, h-index: 73)
Acta Sociológica     Open Access  
Acta Tropica     Hybrid Journal   (Followers: 5, SJR: 1.059, h-index: 77)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 4)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 3)
Actas Urológicas Españolas     Full-text available via subscription   (Followers: 3, SJR: 0.383, h-index: 19)
Actas Urológicas Españolas (English Edition)     Full-text available via subscription   (Followers: 2)
Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 5, SJR: 0.141, h-index: 3)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 4, SJR: 0.112, h-index: 2)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 4)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.967, h-index: 57)
Addictive Behaviors     Hybrid Journal   (Followers: 15, SJR: 1.514, h-index: 92)
Addictive Behaviors Reports     Open Access   (Followers: 5)
Additive Manufacturing     Hybrid Journal   (Followers: 7, SJR: 1.039, h-index: 5)
Additives for Polymers     Full-text available via subscription   (Followers: 20)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 119, SJR: 5.2, h-index: 222)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 11, SJR: 1.265, h-index: 53)
Advanced Powder Technology     Hybrid Journal   (Followers: 16, SJR: 0.739, h-index: 33)
Advances in Accounting     Hybrid Journal   (Followers: 8, SJR: 0.299, h-index: 15)
Advances in Agronomy     Full-text available via subscription   (Followers: 15, SJR: 2.071, h-index: 82)
Advances in Anesthesia     Full-text available via subscription   (Followers: 24, SJR: 0.169, h-index: 4)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 3)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 6, SJR: 1.054, h-index: 35)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 10, SJR: 0.801, h-index: 26)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 21, SJR: 1.286, h-index: 49)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 16, SJR: 3.31, h-index: 42)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.277, h-index: 43)
Advances in Botanical Research     Full-text available via subscription   (Followers: 3, SJR: 0.619, h-index: 48)
Advances in Cancer Research     Full-text available via subscription   (Followers: 26, SJR: 2.215, h-index: 78)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 9, SJR: 0.9, h-index: 30)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 2.139, h-index: 42)
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: 24, SJR: 0.183, h-index: 23)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 10, SJR: 0.665, h-index: 29)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 8, SJR: 1.268, h-index: 45)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 28, SJR: 0.938, h-index: 33)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 18, SJR: 2.314, h-index: 130)
Advances in Computers     Full-text available via subscription   (Followers: 16, SJR: 0.223, h-index: 22)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 11)
Advances in Digestive Medicine     Open Access   (Followers: 4)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 5)
Advances in Drug Research     Full-text available via subscription   (Followers: 22)
Advances in Ecological Research     Full-text available via subscription   (Followers: 39, SJR: 3.25, h-index: 43)
Advances in Engineering Software     Hybrid Journal   (Followers: 25, SJR: 0.486, h-index: 10)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 7)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 38, SJR: 5.465, h-index: 64)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 3)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 8)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 41, SJR: 0.674, h-index: 38)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 14)
Advances in Genetics     Full-text available via subscription   (Followers: 15, SJR: 2.558, h-index: 54)
Advances in Genome Biology     Full-text available via subscription   (Followers: 11)
Advances in Geophysics     Full-text available via subscription   (Followers: 6, SJR: 2.325, h-index: 20)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 18, SJR: 0.906, h-index: 24)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 8, SJR: 0.497, h-index: 31)
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: 0.396, h-index: 27)
Advances in Immunology     Full-text available via subscription   (Followers: 33, SJR: 4.152, h-index: 85)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 9, SJR: 1.132, h-index: 42)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 3, SJR: 1.274, h-index: 27)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 4)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 4)
Advances in Life Course Research     Hybrid Journal   (Followers: 7, SJR: 0.764, h-index: 15)
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: 16, SJR: 1.645, h-index: 45)
Advances in Mathematics     Full-text available via subscription   (Followers: 10, SJR: 3.261, h-index: 65)
Advances in Medical Sciences     Hybrid Journal   (Followers: 5, SJR: 0.489, h-index: 25)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 5)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 4, SJR: 1.44, h-index: 51)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 21)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 10)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 6, SJR: 0.324, h-index: 8)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 3)
Advances in Oncobiology     Full-text available via subscription   (Followers: 3)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 15, SJR: 2.885, h-index: 45)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7, SJR: 0.148, h-index: 11)
Advances in Parasitology     Full-text available via subscription   (Followers: 7, SJR: 2.37, h-index: 73)
Advances in Pediatrics     Full-text available via subscription   (Followers: 20, SJR: 0.4, h-index: 28)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 14)
Advances in Pharmacology     Full-text available via subscription   (Followers: 13, SJR: 1.718, h-index: 58)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 7, SJR: 0.384, h-index: 26)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.248, h-index: 11)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 8)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 5)
Advances in Porous Media     Full-text available via subscription   (Followers: 4)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 18)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 17, SJR: 1.5, h-index: 62)
Advances in Psychology     Full-text available via subscription   (Followers: 56)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 5, SJR: 0.478, h-index: 32)
Advances in Radiation Oncology     Open Access  
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 1, SJR: 0.1, h-index: 2)
Advances in Space Research     Full-text available via subscription   (Followers: 332, SJR: 0.606, h-index: 65)
Advances in Structural Biology     Full-text available via subscription   (Followers: 7)
Advances in Surgery     Full-text available via subscription   (Followers: 6, SJR: 0.823, h-index: 27)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 28, SJR: 1.321, h-index: 56)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 14)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 12)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 1.878, h-index: 68)
Advances in Water Resources     Hybrid Journal   (Followers: 42, SJR: 2.408, h-index: 94)
Aeolian Research     Hybrid Journal   (Followers: 5, SJR: 0.973, h-index: 22)
Aerospace Science and Technology     Hybrid Journal   (Followers: 303, SJR: 0.816, h-index: 49)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.318, h-index: 36)
African J. of Emergency Medicine     Open Access   (Followers: 4, SJR: 0.344, h-index: 6)
Ageing Research Reviews     Hybrid Journal   (Followers: 7, SJR: 3.289, h-index: 78)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 389, SJR: 1.385, h-index: 72)
Agri Gene     Hybrid Journal  
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 15, SJR: 2.18, h-index: 116)
Agricultural Systems     Hybrid Journal   (Followers: 29, SJR: 1.275, h-index: 74)
Agricultural Water Management     Hybrid Journal   (Followers: 36, SJR: 1.546, h-index: 79)
Agriculture and Agricultural Science Procedia     Open Access  
Agriculture and Natural Resources     Open Access   (Followers: 1)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 48, SJR: 1.879, h-index: 120)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.434, h-index: 14)
Air Medical J.     Hybrid Journal   (Followers: 3, SJR: 0.234, h-index: 18)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.285, h-index: 3)
Alcohol     Hybrid Journal   (Followers: 9, SJR: 0.922, h-index: 66)
Alcoholism and Drug Addiction     Open Access   (Followers: 5)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 1, SJR: 0.436, h-index: 12)
Alexandria J. of Medicine     Open Access  
Algal Research     Partially Free   (Followers: 7, SJR: 2.05, h-index: 20)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 3)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.46, h-index: 29)
Allergology Intl.     Open Access   (Followers: 5, SJR: 0.776, h-index: 35)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 6, SJR: 0.158, h-index: 9)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 45, SJR: 4.289, h-index: 64)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 5)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 3)
American Heart J.     Hybrid Journal   (Followers: 45, SJR: 3.157, h-index: 153)
American J. of Cardiology     Hybrid Journal   (Followers: 47, SJR: 2.063, h-index: 186)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 34, SJR: 0.574, h-index: 65)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 6, SJR: 1.091, h-index: 45)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 14, SJR: 1.653, h-index: 93)
American J. of Human Genetics     Hybrid Journal   (Followers: 32, SJR: 8.769, h-index: 256)
American J. of Infection Control     Hybrid Journal   (Followers: 25, SJR: 1.259, h-index: 81)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 31, SJR: 2.313, h-index: 172)
American J. of Medicine     Hybrid Journal   (Followers: 48, SJR: 2.023, h-index: 189)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 173, SJR: 2.255, h-index: 171)
American J. of Ophthalmology     Hybrid Journal   (Followers: 51, SJR: 2.803, h-index: 148)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 2)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.249, h-index: 88)
American J. of Otolaryngology     Hybrid Journal   (Followers: 22, SJR: 0.59, h-index: 45)
American J. of Pathology     Hybrid Journal   (Followers: 23, SJR: 2.653, h-index: 228)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 21, SJR: 2.764, h-index: 154)
American J. of Surgery     Hybrid Journal   (Followers: 32, SJR: 1.286, h-index: 125)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 13, SJR: 0.653, h-index: 70)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 5)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.066, h-index: 51)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 52, SJR: 0.124, h-index: 9)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 3)
Anales de Cirugia Vascular     Full-text available via subscription  
Anales de Pediatría     Full-text available via subscription   (Followers: 2, SJR: 0.209, h-index: 27)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription   (SJR: 0.104, h-index: 3)
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 2, SJR: 2.577, h-index: 7)
Analytica Chimica Acta     Hybrid Journal   (Followers: 38, SJR: 1.548, h-index: 152)
Analytical Biochemistry     Hybrid Journal   (Followers: 152, SJR: 0.725, h-index: 154)
Analytical Chemistry Research     Open Access   (Followers: 7, SJR: 0.18, h-index: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 10)
Anesthésie & Réanimation     Full-text available via subscription  
Anesthesiology Clinics     Full-text available via subscription   (Followers: 21, SJR: 0.421, h-index: 40)
Angiología     Full-text available via subscription   (SJR: 0.124, h-index: 9)
Angiologia e Cirurgia Vascular     Open Access  
Animal Behaviour     Hybrid Journal   (Followers: 141, SJR: 1.907, h-index: 126)
Animal Feed Science and Technology     Hybrid Journal   (Followers: 5, SJR: 1.151, h-index: 83)
Animal Reproduction Science     Hybrid Journal   (Followers: 5, SJR: 0.711, h-index: 78)
Annales d'Endocrinologie     Full-text available via subscription   (SJR: 0.394, h-index: 30)
Annales d'Urologie     Full-text available via subscription  
Annales de Cardiologie et d'Angéiologie     Full-text available via subscription   (SJR: 0.177, h-index: 13)
Annales de Chirurgie de la Main et du Membre Supérieur     Full-text available via subscription  
Annales de Chirurgie Plastique Esthétique     Full-text available via subscription   (Followers: 2, SJR: 0.354, h-index: 22)
Annales de Chirurgie Vasculaire     Full-text available via subscription   (Followers: 1)

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Journal Cover Acta Astronautica
  [SJR: 0.726]   [H-I: 43]   [302 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0094-5765
   Published by Elsevier Homepage  [3031 journals]
  • Green hypergolic combination: Diethylenetriamine-based fuel and hydrogen
    • Authors: Hongjae Kang; Sejin Kwon
      Abstract: Publication date: August 2017
      Source:Acta Astronautica, Volume 137
      Author(s): Hongjae Kang, Sejin Kwon
      The present research dealt with the concept of green hypergolic combination to replace the toxic hypergolic combinations. Hydrogen peroxide was selected as a green oxidizer. A novel recipe for the non-toxic hypergolic fuel (Stock 3) was suggested. Sodium borohydride was blended into the mixture of energetic hydrocarbon solvents as an ignition source for hypergolic ignition. The main ingredient of the mixture was diethylenetriamine. By mixing some amount of tetrahydrofuran with diethylenetriamine, the mixture became more flammable and volatile. The mixture of Stock 3 fuel remained stable for four months in the lab scale storability test. Through a simple drop test, the hypergolicity of the green hypergolic combination was verified. Comparing to the toxic hypergolic combination MMH/NTO as the reference, the theoretical performance of the green hypergolic combination would be achieved about 96.7% of the equilibrium specific impulse and about 105.7% of the density specific impulse. The applicability of the green hypergolic combination was successfully confirmed through the static hot-fire tests using 500N scale hypergolic thruster.

      PubDate: 2017-04-16T07:58:03Z
      DOI: 10.1016/j.actaastro.2017.04.009
      Issue No: Vol. 137 (2017)
  • Space-based pseudo-fixed latitude observation mode based on the
           characteristics of geosynchronous orbit belt
    • Authors: Yun-peng Hu; Lei Chen; Jian-yu Huang
      Abstract: Publication date: August 2017
      Source:Acta Astronautica, Volume 137
      Author(s): Yun-peng Hu, Lei Chen, Jian-yu Huang
      The US Lincoln Laboratory proved that space-based visible (SBV) observation is efficient to observe space objects, especially Geosynchronous Orbit (GEO) objects. After that, SBV observation plays an important role in the space surveillance. In this paper, a novel space-based observation mode is designed to observe all the GEO objects in a relatively short time. A low earth orbit (LEO) satellite, especially a dawn-dusk sun-synchronous orbit satellite, is useful for space-based observation. Thus, the observation mode for GEO objects is based on a dawn-dusk sun-synchronous orbit satellite. It is found that the Pinch Point (PP) regions proposed by the US Lincoln Laboratory are spreading based on the analysis of the evolution principles of GEO objects. As the PP regions becoming more and more widely in the future, many strategies based on it may not be efficient any more. Hence, the key point of the space-based observation strategy design for GEO objects should be emphasized on the whole GEO belt as far as possible. The pseudo-fixed latitude observation mode is proposed in this paper based on the characteristics of GEO belt. Unlike classical space-based observation modes, pseudo-fixed latitude observation mode makes use of the one-dimensional attitude adjustment of the observation satellite. The pseudo-fixed latitude observation mode is more reliable and simple in engineering, compared with the gazing observation mode which needs to adjust the attitude from the two dimensions. It includes two types of attitude adjustment, i.e. daily and continuous attitude adjustment. Therefore, the pseudo-fixed latitude observation mode has two characteristics. In a day, the latitude of the observation region is fixed and the scanning region is about a rectangle, while the latitude of the observation region centre changes each day in a long term based on a daily strategy. The capabilities of a pseudo-fixed latitude observation instrument with a 98° dawn-dusk sun-synchronous orbit are discussed. It is found that most of GEO objects can be visited every day and almost all the GEO objects can be visited in two days in the whole year using a sensor with 20°×2° field of view (FOV). The seasonal drops, which are caused by the characteristics of GEO belt and the influence of earth shadow at the two equinoxes, have been overcome under the pseudo-fixed observation mode.

      PubDate: 2017-04-16T07:58:03Z
      DOI: 10.1016/j.actaastro.2017.03.031
      Issue No: Vol. 137 (2017)
  • Investigation of transient ignition process in a cavity based scramjet
           combustor using combined ethylene injectors
    • Authors: Xiao Liu; Zun Cai; Yiheng Tong; Hongtao Zheng
      Pages: 1 - 7
      Abstract: Publication date: August 2017
      Source:Acta Astronautica, Volume 137
      Author(s): Xiao Liu, Zun Cai, Yiheng Tong, Hongtao Zheng
      Large Eddy Simulation (LES) and experiment were employed to investigate the transient ignition and flame propagation process in a rearwall-expansion cavity scramjet combustor using combined fuel injection schemes. The compressible supersonic solver and three ethylene combustion mechanisms were first validated against experimental data and results show in reasonably good agreement. Fuel injection scheme combining transverse and direct injectors in the cavity provides a benefit mixture distribution and could achieve a successful ignition. Four stages are illustrated in detail from both experiment and LES. After forced ignition in the cavity, initial flame kernel propagates upstream towards the cavity front edge and ignites the mixture, which acts as a continuous pilot flame, and then propagates downstream along the cavity shear layer rapidly to the combustor exit. Cavity shear layer flame stabilization mode can be concluded from the heat release rate and local high temperature distribution during the combustion process.

      PubDate: 2017-04-16T07:58:03Z
      DOI: 10.1016/j.actaastro.2017.04.007
      Issue No: Vol. 137 (2017)
  • Discharge reliability in ablative pulsed plasma thrusters
    • Authors: Zhiwen Wu; Guorui Sun; Shiyue Yuan; Tiankun Huang; Xiangyang Liu; Kan Xie; Ningfei Wang
      Pages: 8 - 14
      Abstract: Publication date: August 2017
      Source:Acta Astronautica, Volume 137
      Author(s): Zhiwen Wu, Guorui Sun, Shiyue Yuan, Tiankun Huang, Xiangyang Liu, Kan Xie, Ningfei Wang
      Discharge reliability is typically neglected in low-ignition-cycle ablative pulsed plasma thrusters (APPTs). In this study, the discharge reliability of an APPT is assessed analytically and experimentally. The goals of this study are to better understand the ignition characteristics and to assess the accuracy of the analytical method. For each of six sets of operating conditions, 500 tests of a parallel-plate APPT with a coaxial semiconductor spark plug are conducted. The discharge voltage and current are measured with a high-voltage probe and a Rogowski coil, respectively, to determine whether the discharge is successful. Generally, the discharge success rate increases as the discharge voltage increases, and it decreases as the electrode gap and the number of ignitions increases. The theoretical analysis and the experimental results are reasonably consistent. This approach provides a reference for designing APPTs and improving their stability.

      PubDate: 2017-04-16T07:58:03Z
      DOI: 10.1016/j.actaastro.2017.04.006
      Issue No: Vol. 137 (2017)
  • Robustness analysis method for orbit control
    • Authors: Jingrui Zhang; Keying Yang; Rui Qi; Shuge Zhao; Yanyan Li
      Pages: 15 - 24
      Abstract: Publication date: August 2017
      Source:Acta Astronautica, Volume 137
      Author(s): Jingrui Zhang, Keying Yang, Rui Qi, Shuge Zhao, Yanyan Li
      Satellite orbits require periodical maintenance due to the presence of perturbations. However, random errors caused by inaccurate orbit determination and thrust implementation may lead to failure of the orbit control strategy. Therefore, it is necessary to analyze the robustness of the orbit control methods. Feasible strategies which are tolerant to errors of a certain magnitude can be developed to perform reliable orbit control for the satellite. In this paper, first, the orbital dynamic model is formulated by Gauss’ form of the planetary equation using the mean orbit elements; the atmospheric drag and the Earth's non-spherical perturbations are taken into consideration in this model. Second, an impulsive control strategy employing the differential correction algorithm is developed to maintain the satellite trajectory parameters in given ranges. Finally, the robustness of the impulsive control method is analyzed through Monte Carlo simulations while taking orbit determination error and thrust error into account.

      PubDate: 2017-04-16T07:58:03Z
      DOI: 10.1016/j.actaastro.2017.03.034
      Issue No: Vol. 137 (2017)
  • Rosetta Lander - Philae: Operations on comet 67P/Churyumov-Gerasimenko,
           analysis of wake-up activities and final state
    • Authors: Stephan Ulamec; Laurence O'Rourke; Jens Biele; Björn Grieger; Rafael Andrés; Sylvain Lodiot; Pablo Muñoz; Antoine Charpentier; Stefano Mottola; Jörg Knollenberg; Martin Knapmeyer; Ekkehard Kührt; Frank Scholten; Koen Geurts; Michael Maibaum; Cinzia Fantinati; Oliver Küchemann; Valentina Lommatsch; Cedric Delmas; Eric Jurado; Romain Garmier; Thierry Martin
      Pages: 38 - 43
      Abstract: Publication date: August 2017
      Source:Acta Astronautica, Volume 137
      Author(s): Stephan Ulamec, Laurence O'Rourke, Jens Biele, Björn Grieger, Rafael Andrés, Sylvain Lodiot, Pablo Muñoz, Antoine Charpentier, Stefano Mottola, Jörg Knollenberg, Martin Knapmeyer, Ekkehard Kührt, Frank Scholten, Koen Geurts, Michael Maibaum, Cinzia Fantinati, Oliver Küchemann, Valentina Lommatsch, Cedric Delmas, Eric Jurado, Romain Garmier, Thierry Martin
      The Lander Philae, part of the ESA Rosetta mission successfully landed on comet 67P/Churyumov- Gerasimenko on November 12th, 2014. After several (unplanned) bounces it performed a First Scientific Sequence (FSS), based on the energy stored in its on board batteries. All ten instruments of the payload aboard Philae have been operated at least once. Due to the fact that the final landing site was poorly illuminated, Philae went into hibernation on November 15th. Signals from the Lander were received again in June and July 2015, which indicated multiple awakening episodes of the lander. However, various attempts to re-establish reliable and stable communications links failed. Based on the analysis of the data gained during FSS, and during the contacts in June and July 2015 we draw conclusions on the state of Philae. In addition, images from the OSIRIS camera aboard the Rosetta Orbiter have allowed the identification of the exact position of Philae and its attitude, relative to the local surface terrain. This paper also gives an overview of the implications of Philae results for future engineering comet models, required particularly for the design of in-situ (landing) or sample return missions. Rosetta is an ESA mission with contributions from its member states and NASA. Rosetta's Philae Lander is provided by a consortium led by DLR, MPS, CNES and ASI with additional contributions from Hungary, UK, Finland, Ireland and Austria.

      PubDate: 2017-04-23T08:02:41Z
      DOI: 10.1016/j.actaastro.2017.04.005
      Issue No: Vol. 137 (2017)
  • Flow field characteristics analysis and combustion modes classification
           for a strut/cavity dual-mode combustor
    • Authors: Chenlin Zhang; Juntao Chang; Yuanshi Zhang; Youyin Wang; Wen Bao
      Pages: 44 - 51
      Abstract: Publication date: August 2017
      Source:Acta Astronautica, Volume 137
      Author(s): Chenlin Zhang, Juntao Chang, Yuanshi Zhang, Youyin Wang, Wen Bao
      Experimental and numerical study of a strut/cavity dual-mode combustor has been conducted in this paper. Under different fuel equivalence ratio and allocation proportion conditions, the pressure distribution and flow field structure of combustor show distinct characteristics. For strut fuel injecting at a low equivalence ratio, the luminosity images show that combustion zone distributes in the shear layer behind the strut. The wall fuel injecting before strut would change the starting point of pressure rising. Based on the flow field structure, the dual-mode combustor operation process is classified into three combustion modes, including scramjet mode, weak ramjet mode and strong ramjet mode. Because of a strong interaction of the shock wave with the boundary layer, weak ramjet mode has a stronger isolator compression effect and higher combustion efficiency than scramjet mode. With heat release increasing, the thermal throat formation is an indication of the strong ramjet mode, which has a subsonic gap in the isolator. Further, by judging the pressure from dominant pressure sensor before the strut, the three different combustion modes could be classified. Comparing the specific impulse of combustor, it has an obvious distinction in the different combustion modes.

      PubDate: 2017-04-23T08:02:41Z
      DOI: 10.1016/j.actaastro.2017.03.023
      Issue No: Vol. 137 (2017)
  • The influence of cavity parameters on the combustion oscillation in a
           single-side expansion scramjet combustor
    • Authors: Hao Ouyang; Weidong Liu; Mingbo Sun
      Pages: 52 - 59
      Abstract: Publication date: August 2017
      Source:Acta Astronautica, Volume 137
      Author(s): Hao Ouyang, Weidong Liu, Mingbo Sun
      Cavity has been validated to be efficient flameholders for scramjet combustors, but the influence of its parameters on the combustion oscillation in scramjet combustor has barely been studied. In the present work, a series of experiments focusing on this issue have been carried out. The influence of flameholding cavity position, its length to depth ratio L/D and aft wall angle θ and number on ethylene combustion oscillation characteristics in scramjet combustor has been researched. The obtained experimental results show that, as the premixing distance between ethylene injector and flameholding cavity varies, the ethylene combustion flame will take on two distinct forms, small-amplitude high frequency fluctuation, and large-amplitude low frequency oscillation. The dominant frequency of the large-amplitude combustion oscillation is in inverse proportion to the pre-mixing distance. Moreover, the influence of cavity length to depth ratio and the aft wall angleθexists diversity when the flameholding cavity position is different and can be recognized as unnoticeable compared to the impact of the premixing distance. In addition, we also find that, when the premixing distance is identical and sufficient, increasing the number of tandem flameholding cavities can change the dominant frequency of combustion oscillation hardly, let alone avoid the combustion oscillation. It is believed that the present investigation will provide a useful reference for the design of the scramjet combustor.

      PubDate: 2017-04-23T08:02:41Z
      DOI: 10.1016/j.actaastro.2017.03.018
      Issue No: Vol. 137 (2017)
  • Reentry trajectory optimization with waypoint and no-fly zone constraints
           using multiphase convex programming
    • Authors: Dang-Jun Zhao; Zheng-Yu Song
      Pages: 60 - 69
      Abstract: Publication date: August 2017
      Source:Acta Astronautica, Volume 137
      Author(s): Dang-Jun Zhao, Zheng-Yu Song
      This study proposes a multiphase convex programming approach for rapid reentry trajectory generation that satisfies path, waypoint and no-fly zone (NFZ) constraints on Common Aerial Vehicles (CAVs). Because the time when the vehicle reaches the waypoint is unknown, the trajectory of the vehicle is divided into several phases according to the prescribed waypoints, rendering a multiphase optimization problem with free final time. Due to the requirement of rapidity, the minimum flight time of each phase index is preferred over other indices in this research. The sequential linearization is used to approximate the nonlinear dynamics of the vehicle as well as the nonlinear concave path constraints on the heat rate, dynamic pressure, and normal load; meanwhile, the convexification techniques are proposed to relax the concave constraints on control variables. Next, the original multiphase optimization problem is reformulated as a standard second-order convex programming problem. Theoretical analysis is conducted to show that the original problem and the converted problem have the same solution. Numerical results are presented to demonstrate that the proposed approach is efficient and effective.

      PubDate: 2017-04-23T08:02:41Z
      DOI: 10.1016/j.actaastro.2017.04.013
      Issue No: Vol. 137 (2017)
  • Crack cause analysis of a graphite nozzle throat insert
    • Authors: Lin Sun; Futing Bao; Yu Zhao; Lian Hou; Weihua Hui; Ning Zhang; Wei Shi
      Pages: 70 - 77
      Abstract: Publication date: August 2017
      Source:Acta Astronautica, Volume 137
      Author(s): Lin Sun, Futing Bao, Yu Zhao, Lian Hou, Weihua Hui, Ning Zhang, Wei Shi
      With an objective to determine the failure cause of a throughout crack at an angle of 45° and a breach during a firing test, a simplified analysis procedure with consideration of the structure gap was established to simulate the thermo-structural response of a nozzle. By neglecting erosion and pyrolysis of the insulating materials and establishing temperature-dependent or anisotropic material models, ANSYS Parameter Design Language codes were written to perform the fully coupled thermal-structural simulation. A Quasi-1D flow was calculated for supplying boundary conditions. Study on mesh independence and time step independence was also conducted to evaluate simulated results. It was found that shortly after ignition, compressive stress in the x direction and tensile stress in the y direction contributed to anomalies. And through contact status analysis, inappropriate gap design was regarded as the origin of the too large stress, which was the primary cause of these anomalies during firing test. Simulation results were in good agreement with firing test results. In addition, the simplified analysis procedure was proven effective. Gap size should be seriously dealt with in the future design.

      PubDate: 2017-04-23T08:02:41Z
      DOI: 10.1016/j.actaastro.2017.04.016
      Issue No: Vol. 137 (2017)
  • Teófilo Tabanera, Father of the Argentine Space Program
    • Authors: Pablo de León; Marcela Tabanera; Marisol Tabanera
      Pages: 91 - 97
      Abstract: Publication date: August 2017
      Source:Acta Astronautica, Volume 137
      Author(s): Pablo de León, Marcela Tabanera, Marisol Tabanera
      No other figure was able to organize and catalyze the seminal interest of space exploration in Argentina more than Teófilo Tabanera. Born in 1909, Tabanera showed an early interest in the possibilities of space travel and dedicated most of his life to popularize it in his country. He created the Sociedad Argentina Interplanetaria (1949), which was the first space enthusiast's organization in Latin America. Present in the first meeting of representatives of various space societies, which led to the creation of the International Astronautical Federation, Tabanera was able to bring his enthusiasm to this new organization. A prolific writer, Tabanera wrote the first books about space exploration in Spanish, and organized many courses and conferences on the subject. When the Comisión Nacional de Investigaciones Espaciales (the Argentine Space Agency) was created in 1960 by a decree of President Arturo Frondizi, Tabanera was appointed as its first administrator. There, with meager funds, he organized launch campaigns and international projects on sounding rockets. Thanks to his knowledge of the international space sector, Tabanera invited many experts to Argentina, among them Wernher von Braun and even the Apollo XI crew, just a few months after their return from the Moon. He continued his activities in the IAF (International Astronautical Federation) serving as vice president for seven terms, and was a cofounder of the International Academy of Astronautics (I.A.A.). His many contributions, both to the Argentine and international space sector, are a testimony to his undying enthusiasm and interest in space as a way of advancing humankind.

      PubDate: 2017-04-23T08:02:41Z
      DOI: 10.1016/j.actaastro.2017.04.003
      Issue No: Vol. 137 (2017)
  • Solving fuel-optimal low-thrust orbital transfers with bang-bang control
           using a novel continuation technique
    • Authors: Zhengfan Zhu; Qingbo Gan; Xin Yang; Yang Gao
      Pages: 98 - 113
      Abstract: Publication date: August 2017
      Source:Acta Astronautica, Volume 137
      Author(s): Zhengfan Zhu, Qingbo Gan, Xin Yang, Yang Gao
      We have developed a novel continuation technique to solve optimal bang-bang control for low-thrust orbital transfers considering the first-order necessary optimality conditions derived from Lawden's primer vector theory. Continuation on the thrust amplitude is mainly described in this paper. Firstly, a finite-thrust transfer with an “On-Off-On” thrusting sequence is modeled using a two-impulse transfer as initial solution, and then the thrust amplitude is decreased gradually to find an optimal solution with minimum thrust. Secondly, the thrust amplitude is continued from its minimum value to positive infinity to find the optimal bang-bang control, and a thrust switching principle is employed to determine the control structure by monitoring the variation of the switching function. In the continuation process, a bifurcation of bang-bang control is revealed and the concept of critical thrust is proposed to illustrate this phenomenon. The same thrust switching principle is also applicable to the continuation on other parameters, such as transfer time, orbital phase angle, etc. By this continuation technique, fuel-optimal orbital transfers with variable mission parameters can be found via an automated algorithm, and there is no need to provide an initial guess for the costate variables. Moreover, continuation is implemented in the solution space of bang-bang control that is either optimal or non-optimal, which shows that a desired solution of bang-bang control is obtained via continuation on a single parameter starting from an existing solution of bang-bang control. Finally, numerical examples are presented to demonstrate the effectiveness of the proposed continuation technique. Specifically, this continuation technique provides an approach to find multiple solutions satisfying the first-order necessary optimality conditions to the same orbital transfer problem, and a continuation strategy is presented as a preliminary approach for solving the bang-bang control of many-revolution orbital transfers.

      PubDate: 2017-04-23T08:02:41Z
      DOI: 10.1016/j.actaastro.2017.03.032
      Issue No: Vol. 137 (2017)
  • Reconfigurable phased antenna array for extending cubesat operations to
           Ka-band: Design and feasibility
    • Authors: G. Buttazzoni; M. Comisso; A. Cuttin; M. Fragiacomo; R. Vescovo; R. Vincenti Gatti
      Pages: 114 - 121
      Abstract: Publication date: August 2017
      Source:Acta Astronautica, Volume 137
      Author(s): G. Buttazzoni, M. Comisso, A. Cuttin, M. Fragiacomo, R. Vescovo, R. Vincenti Gatti
      Started as educational tools, CubeSats have immediately encountered the favor of the scientific community, subsequently becoming viable platforms for research and commercial applications. To ensure competitive data rates, some pioneers have started to explore the usage of the Ka-band beside the conventional amateur radio frequencies. In this context, this study proposes a phased antenna array design for Ka-band downlink operations consisting of 8×8 circularly polarized subarrays of microstrip patches filling one face of a single CubeSat unit. The conceived structure is developed to support 1.5GHz bandwidth and dual-task missions, whose feasibility is verified by proper link budgets. The dual-task operations are enabled by a low-complexity phase-only control algorithm that provides pattern reconfigurability in order to satisfy both orbiting and intersatellite missions, while remaining adherent to the cost-effective CubeSat paradigm.

      PubDate: 2017-04-23T08:02:41Z
      DOI: 10.1016/j.actaastro.2017.04.012
      Issue No: Vol. 137 (2017)
  • Effect of 21-day head down bed rest on urine proteins related to
           endothelium: Correlations with changes in carbohydrate metabolism
    • Authors: D. Kashirina; L. Pastushkova; M.A. Custaud; I. Dobrokhotov; A. Brzhozovsky; N. Navasiolava; A. Nosovsky; A. Kononikhin; E. Nikolaev; I. Larina
      Pages: 122 - 127
      Abstract: Publication date: August 2017
      Source:Acta Astronautica, Volume 137
      Author(s): D. Kashirina, L. Pastushkova, M.A. Custaud, I. Dobrokhotov, A. Brzhozovsky, N. Navasiolava, A. Nosovsky, A. Kononikhin, E. Nikolaev, I. Larina
      We performed liquid chromatography-mass spectrometric study of the urine proteome in 8 healthy volunteers aged between 20 and 44 y.o. who have completed 21-day head-down bed rest. ANDSystem software which builds associative networks was used to identify the urinary proteins functionally related to the endothelium. We identified 7 endothelium-related biological processes, directly linked to 13 urine proteins. We performed manual annotation of the proteins which were the most important in terms of endothelial functions. Analysis of the correlations with biochemical variables revealed a positive correlation between fasting blood glucose and the following urine proteins: albumin, CD44 antigen, endothelial protein C receptor, mucin-1, osteopontin, receptor tyrosine kinase. As well, we found a positive correlation between HOMA-insulin resistance index and the following urine proteins: endothelial protein C receptor and syndecan-4. These results might suggest the involvement of above-mentioned proteins in glucose metabolism and their participation in the response to changes in blood glucose level.

      PubDate: 2017-04-23T08:02:41Z
      DOI: 10.1016/j.actaastro.2017.04.020
      Issue No: Vol. 137 (2017)
  • Time-optimal spacecraft attitude maneuver path planning under boundary and
           pointing constraints
    • Authors: Changqing Wu; Rui Xu; Shengying Zhu; Pingyuan Cui
      Pages: 128 - 137
      Abstract: Publication date: August 2017
      Source:Acta Astronautica, Volume 137
      Author(s): Changqing Wu, Rui Xu, Shengying Zhu, Pingyuan Cui
      The rapid large angle attitude maneuver capability of spacecraft is required during many space missions. This paper addresses the challenge of time-optimal spacecraft attitude maneuver under boundary and pointing constraints. From the perspective of the optimal time, the constrained attitude maneuver problem is summarized as an optimum path-planning problem. To address this problem, a metaheuristic maneuver path planning method is proposed, Angular velocity-Time Coding Differential Evolution (ATDE). In the ATDE method, the angular velocity and time are coded for attitude maneuver modeling, which increases the number of variables and results in a high-dimensional problem. In order to deal with this problem, differential evolution is employed to perform variation and evolution. The boundary and pointing constraints are constructed into the fitness function for path evaluation. Finally, numerical simulations for the different cases were performed to validate the feasibility and effectiveness of the proposed method.

      PubDate: 2017-04-23T08:02:41Z
      DOI: 10.1016/j.actaastro.2017.04.004
      Issue No: Vol. 137 (2017)
  • Examining personal values in extreme environment contexts: Revisiting the
           question of generalizability
    • Authors: N. Smith; G.M. Sandal; G.R. Leon; A. Kjærgaard
      Pages: 138 - 144
      Abstract: Publication date: August 2017
      Source:Acta Astronautica, Volume 137
      Author(s): N. Smith, G.M. Sandal, G.R. Leon, A. Kjærgaard
      Land-based extreme environments (e.g. polar expeditions, Antarctic research stations, confinement chambers) have often been used as analog settings for spaceflight. These settings share similarities with the conditions experienced during space missions, including confinement, isolation and limited possibilities for evacuation. To determine the utility of analog settings for understanding human spaceflight, researchers have examined the extent to which the individual characteristics (e.g., personality) of people operating in extreme environments can be generalized across contexts (Sandal, 2000) [1]. Building on previous work, and utilising new and pre-existing data, the present study examined the extent to which personal value motives could be generalized across extreme environments. Four populations were assessed; mountaineers (N =59), military personnel (N = 25), Antarctic over-winterers (N = 21) and Mars simulation participants (N = 12). All participants completed the Portrait Values Questionnaire (PVQ; Schwartz; 2) capturing information on 10 personal values. Rank scores suggest that all groups identified Self-direction, Stimulation, Universalism and Benevolence as important values and acknowledged Power and Tradition as being low priorities. Results from difference testing suggest the extreme environment groups were most comparable on Self-direction, Stimulation, Benevolence, Tradition and Security. There were significant between-group differences on five of the ten values. Overall, findings pinpointed specific values that may be important for functioning in challenging environments. However, the differences that emerged on certain values highlight the importance of considering the specific population when comparing results across extreme settings. We recommend that further research examine the impact of personal value motives on indicators of adjustment, group working, and performance. Information from such studies could then be used to aid selection and training processes for personnel operating in extreme settings, and in space.

      PubDate: 2017-04-23T08:02:41Z
      DOI: 10.1016/j.actaastro.2017.04.008
      Issue No: Vol. 137 (2017)
  • Numerical study on dynamic characteristics for sharp opening procedure of
           boundary-layer suction slot
    • Authors: Yubao He; Hang Yin; Hongyan Huang; Daren Yu
      Pages: 145 - 156
      Abstract: Publication date: August 2017
      Source:Acta Astronautica, Volume 137
      Author(s): Yubao He, Hang Yin, Hongyan Huang, Daren Yu
      Based on the sharp forward of shock train and taking the forthcoming unstart for a background, the dynamic characteristics for sharp opening procedure of boundary-layer suction slot are investigated numerically using the dynamic mesh technique. Results indicate that the climbing path of shock train with the complex background waves exhibits a sharp and slow forward state at different time. The compression waves in the primary shock sweep the trailing edge of the separation bubble, and the recirculation within the shock train is communicated with the separation bubble, which reveals that the flow is in a critical state and is about to be unstart at the subsequent time. Furthermore, the dynamic pattern for sharp opening procedure of boundary-layer suction slot can be classified into four distinct stages, namely, the formation of the jet plume without suction mass loss, the formation of the barrier shock with suction mass loss characterized by gradient increase and subsequent two oscillations, the evolution of the barrier shock and jet plume with suction mass loss that ramps up via a series of discrete step increases, and the formation of the stable structure accompanied by the linear suction mass loss.

      PubDate: 2017-04-23T08:02:41Z
      DOI: 10.1016/j.actaastro.2017.04.019
      Issue No: Vol. 137 (2017)
  • Finite time attitude takeover control for combination via tethered space
    • Authors: Yingbo Lu; Panfeng Huang; Zhongjie Meng; Yongxin Hu; Fan Zhang; Yizhai Zhang
      Pages: 9 - 21
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Yingbo Lu, Panfeng Huang, Zhongjie Meng, Yongxin Hu, Fan Zhang, Yizhai Zhang
      Up to April 6, 2016, there are 17,385 large debris in orbit around the Earth, which poses a serious hazard to near-Earth space activities. As a promising on-orbit debris capture strategy, tethered space robots (TSRs) have wide applications in future on-orbit service owing to its flexibility and great workspace. However, lots of problems may arise in the Tethered Space Robots (TSRs) system from the approaching, capturing, postcapturing and towing phases. The postcapture combination attitude takeover control by the TSR is studied in this paper. Taking control constraints, tether oscillations and external disturbances into consideration, a fast terminal sliding mode control (FTSMC) methodology with dual closed loops for the flexible combination attitude takeover control is designed. The unknown upper bounds of the uncertainties, external disturbances are estimated through adaptive techniques. Stability of the dual closed loop control system and finite time convergence of system states are proved via Lyapunov stability theory. Besides, null space intersection control allocation was adopted to distribute the required control moment over TSR's redundant thrusters. Simulation studies have been conducted to demonstrate the effectiveness of the proposed controller with the conventional sliding mode control(SMC).

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.02.022
      Issue No: Vol. 136 (2017)
  • Strategies to utilize advanced heat shield technology for high-payload
           mars atmospheric entry missions
    • Authors: Max Braun; Paul Bruce; Errikos Levis
      Pages: 22 - 33
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Max Braun, Paul Bruce, Errikos Levis
      Present Entry, Descent and Landing (EDL) technology for interplanetary missions does not have the capabilities to meet the demanding requirements that come with future missions. A popular target for such missions is Mars and today efforts are made to send manned as well as sophisticated robotic probes to the Martian surface. Because present EDL technology has reached its limits, fundamentally new approaches are needed to significantly extend capabilities. Systematic evaluation of novel EDL technologies and optimization of EDL strategies are crucial needs for conceptual design. A computational framework will be presented tailored to enable systematic EDL analysis with special regards to novel EDL technology and event strategies. The benefits of flexible heat shield concepts that come with liberties in the choice of the ballistic coefficient will be shown in comparison with solid shield alternatives for payload classes of 2, 25 and 40 tonnes to show potential for manned and robotic missions. Furthermore, benefits of the new methodology for novel EDL event strategies are presented and discussed. The introduced methodology will help designers exploit new directions for conceptual design regarding EDL systems in terms of entry mass optimization and mission capabilities.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.003
      Issue No: Vol. 136 (2017)
  • Kinematic accuracy and dynamic performance of a simple planar space
           deployable mechanism with joint clearance considering parameter
    • Authors: Junlan Li; Hongzhou Huang; Shaoze Yan; Yunqiang Yang
      Pages: 34 - 45
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Junlan Li, Hongzhou Huang, Shaoze Yan, Yunqiang Yang
      Joint clearance and the uncertainty of geometric and physical parameters significantly influence the kinematic accuracy and dynamic response of space deployable mechanisms. Such mechanisms have been widely employed in astronautic missions to improve the capabilities of launchers. This paper proposes a methodology to investigate the kinematic accuracy and dynamic performance of space deployable mechanism with joint clearance while considering parameter uncertainty. The model of space deployable mechanism with a planar revolute joint is provided. With consideration of several uncertain parameters, the solving procedure of the dynamic equations is presented based on the Monte Carlo method. A case study is conducted to reveal the effect of parameter uncertainty on its kinematic accuracy and dynamic performance. The results indicate that parameter uncertainty should be considered to accurately evaluate the performance of long-term operating space deployable mechanisms, especially for such systems with clearance joints. According to the results, brief suggestions for design and evaluation of the mechanisms are provided.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.02.027
      Issue No: Vol. 136 (2017)
  • Ablation spot area and impulse characteristics of polymers induced by
           burst irradiation of 1µm laser pulses
    • Authors: Hisashi Tsuruta; Oskar Dondelewski; Yusuke Katagiri; Bin Wang; Akihiro Sasoh
      Pages: 46 - 54
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Hisashi Tsuruta, Oskar Dondelewski, Yusuke Katagiri, Bin Wang, Akihiro Sasoh
      The ablation spot area and impulse characteristics of various polymers were experimentally investigated against burst irradiation of Nd: YLF laser pulses with a pulse repetition frequency of 1kHz, wavelength of 1047nm, temporal pulse width of 10ns, and single-pulse fluence of 6.1J/cm2 to 17.1J/cm2. The dependences of ablation area on the pulse energy from 0.72 to 7.48mJ and the number of pulses from 10 pulses to 1000 pulses were investigated. In order to characterize their impulse performance as a function of fluence, which should not depend on ablation material, an effective ablation spot area was defined as that obtained against aluminum, 1050A, as the reference material. An impulse that resulted from a single burst of 200 pulses was measured with a torsion-type impulse stand. Various impulse dependences on the fluence, which were not readily predicted from the optical properties of the material without ablation, were obtained. By fitting the experimentally measured impulse performance to Phipps and Sinko's model in the vapor regime, the effective absorption coefficient with laser ablation was evaluated, thereby resulting in three to six orders of magnitude larger than that without ablation. Among the polymers examined using polytetrafluoroethylene (PTFE) as the best volume absorbers, the highest momentum coupling coefficient of 66 μNs/J was obtained with an effective absorption coefficient more than six times smaller than that of the other polymers.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.006
      Issue No: Vol. 136 (2017)
  • Asteroid deflection using a spacecraft in restricted keplerian motion
    • Authors: Yohannes Ketema
      Pages: 64 - 79
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Yohannes Ketema
      A method for asteroid deflection that makes use of a spacecraft moving back and forth on a segment of a Keplerian orbit about the asteroid is described and studied. It is shown that on average the spacecraft can exert a significantly larger force on the asteroid than e.g. a stationary gravity tractor, thereby reducing the time needed to effect the desired deflection of the asteroid. Furthermore, the current method does not require canted thrusters on the spacecraft (unlike a stationary gravity tractor) markedly reducing the amount of fuel needed for a given deflection to be realized. The method also allows for the simultaneous use of several spacecraft, further strengthening the overall tugging effect on the asteroid, and distributing the thrust requirement among the spacecraft.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.004
      Issue No: Vol. 136 (2017)
  • Ablation characteristics and reaction mechanism of insulation materials
           under slag deposition condition
    • Authors: Yiwen Guan; Jiang Li; Yang Liu
      Pages: 80 - 89
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Yiwen Guan, Jiang Li, Yang Liu
      Current understanding of the physical and chemical processes involved in the ablation of insulation materials by highly aluminized solid propellants is limited. The study on the heat transfer and ablation principle of ethylene propylene diene monomer (EPDM) materials under slag deposition condition is essential for future design or modification of large solid rocket motors (SRMs) for launch application. In this paper, the alumina liquid flow pattern and the deposition principle in full-scale SRM engines are discussed. The interaction mechanism between the alumina droplets and the wall are analyzed. Then, an experimental method was developed to simulate the insulation material ablation under slag deposition condition. Experimental study was conducted based on a laboratory-scale device. Meanwhile, from the analysis of the cross-sectional morphology and chemical composition of the charring layer after ablation, the reaction mechanism of the charring layer under deposition condition was discussed, and the main reaction equation was derived. The numerical simulation and experimental results show the following. (i) The alumina droplet flow in the deposition section of the laboratory-scale device is similar to that of a full-scale SRM. (ii) The charring layer of the EPDM insulator displays a porous tight/loose structure under high-temperature slag deposition condition. (iii) A seven-step carbothermal reduction in the alumina is derived and established under high-pressure and high-temperature environment in the SRM combustion chamber. (iv) The analysis using thermodynamic software indicates that the reaction of the alumina and charring layer initially forms Al4C3 during the operation. Then, Al element and Al2OC compound are subsequently produced with the reduction in the release of gas CO as well with continuous environmental heating.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.02.001
      Issue No: Vol. 136 (2017)
  • Dynamics and mixing mechanism of transverse jet injection into a
           supersonic combustor with cavity flameholder
    • Authors: Chaoyang Liu; Yanhui Zhao; Zhenguo Wang; Hongbo Wang; Mingbo Sun
      Pages: 90 - 100
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Chaoyang Liu, Yanhui Zhao, Zhenguo Wang, Hongbo Wang, Mingbo Sun
      The interaction between sonic transverse jet and supersonic crossflow coupled with a cavity flameholder is investigated using large eddy simulation (LES), where the compressible flow dynamics and fuel mixing mechanism are analyzed emphatically. An adaptive central-upwind 6th-order weighted essentially non-oscillatory (WENO-CU6) scheme along with multi-threaded and multi-process MPI/OpenMP parallel is adopted to improve the accuracy and parallel efficiency of the solver. This simulation aims to reproduce the flow conditions in the experiment, and the results show fairly good agreement with the experimental data for distributions of streamwise and normal velocity components. Instantaneous structures such as the shock, large scale vortices and recirculation zone are identified, and their spatial deformation and temporal evolution are presented to reveal the effect on the subsequent mixing. Then some time-averaged and statistical results are obtained to explain the interesting phenomenon observed in the experiment, that there are two pairs of counter-rotating streamwise vortices existing in and above the cavity with the same rotation direction. The above pair is induced by the transverse momentum of jet in supersonic crossflow, which is so-called counter-rotating vortices (CRVs) in the flat-plate injection. On account of the entrainment, the reflux in the cavity transports to the core of jet wakes, and then another pair of counter-rotating streamwise vortices is formed below with the effect of cavity. A pair of trailing CRVs is generated at the trailing edge of cavity, and the turbulent kinetic energy (TKE) here is obviously higher than that in other regions. To some extent, the cavity can enhance the mixing, but will not bring excess total pressure loss.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.010
      Issue No: Vol. 136 (2017)
  • Robust, fast and accurate vision-based localization of a cooperative
           target used for space robotic arm
    • Authors: Zhuoman Wen; Yanjie Wang; Jun Luo; Arjan Kuijper; Nan Di; Minghe Jin
      Pages: 101 - 114
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Zhuoman Wen, Yanjie Wang, Jun Luo, Arjan Kuijper, Nan Di, Minghe Jin
      When a space robotic arm deploys a payload, usually the pose between the cooperative target fixed on the payload and the hand-eye camera installed on the arm is calculated in real-time. A high-precision robust visual cooperative target localization method is proposed. Combing a circle, a line and dots as markers, a target that guarantees high detection rates is designed. Given an image, single-pixel-width smooth edges are drawn by a novel linking method. Circles are then quickly extracted using isophotes curvature. Around each circle, a square boundary in a pre-calculated proportion to the circle radius is set. In the boundary, the target is identified if certain numbers of lines exist. Based on the circle, the lines, and the target foreground and background intensities, markers are localized. Finally, the target pose is calculated by the Point-3-Perspective algorithm. The algorithm processes 8 frames per second with the target distance ranging from 0.3m to 1.5m. It generated high-precision poses of above 97.5% on over 100,000 images regardless of camera background, target pose, illumination and motion blur. At 0.3m, the rotation and translation errors were less than 0.015° and 0.2mm. The proposed algorithm is very suitable for real-time visual measurement that requires high precision in aerospace.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.008
      Issue No: Vol. 136 (2017)
  • Numerical simulations on unsteady operation processes of N2O/HTPB hybrid
           rocket motor with/without diaphragm
    • Authors: Shuai Zhang; Fan Hu; Donghui Wang; Patrick Okolo.N; Weihua Zhang
      Pages: 115 - 124
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Shuai Zhang, Fan Hu, Donghui Wang, Patrick Okolo.N, Weihua Zhang
      Numerical simulations on processes within a hybrid rocket motor were conducted in the past, where most of these simulations carried out majorly focused on steady state analysis. Solid fuel regression rate strongly depends on complicated physicochemical processes and internal fluid dynamic behavior within the rocket motor, which changes with both space and time during its operation, and are therefore more unsteady in characteristics. Numerical simulations on the unsteady operational processes of N2O/HTPB hybrid rocket motor with and without diaphragm are conducted within this research paper. A numerical model is established based on two dimensional axisymmetric unsteady Navier–Stokes equations having turbulence, combustion and coupled gas/solid phase formulations. Discrete phase model is used to simulate injection and vaporization of the liquid oxidizer. A dynamic mesh technique is applied to the non-uniform regression of fuel grain, while results of unsteady flow field, variation of regression rate distribution with time, regression process of burning surface and internal ballistics are all obtained. Due to presence of eddy flow, the diaphragm increases regression rate further downstream. Peak regression rates are observed close to flow reattachment regions, while these peak values decrease gradually, and peak position shift further downstream with time advancement. Motor performance is analyzed accordingly, and it is noticed that the case with diaphragm included results in combustion efficiency and specific impulse efficiency increase of roughly 10%, and ground thrust increase of 17.8%.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.005
      Issue No: Vol. 136 (2017)
  • Finite time coordinated formation control for spacecraft formation flying
           under directed communication topology
    • Authors: Dechao Ran; Xiaoqian Chen; Arun K. Misra
      Pages: 125 - 136
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Dechao Ran, Xiaoqian Chen, Arun K. Misra
      This paper investigates the finite time coordinated formation control problem for spacecraft formation flying (SFF) under the assumption of directed communication topology. By using the neighborhood state measurements, a robust finite time coordinated formation controller is firstly designed based on the nonsingular terminal sliding mode surface. To address the special case that the desired trajectory of the formation is only accessible to a subset of spacecraft in the formation, an adaptive finite time coordinated formation controller is also proposed by designing a novel sliding mode surface. In both cases, the external disturbances are explicitly taken into account. Rigorous theoretical analysis proves that the proposed control schemes ensure that the closed-loop system can track the desired time-varying trajectory in finite time. Numerical simulations are presented that not only highlights the closed-loop performance benefits from the proposed control algorithms, but also illustrates the effectiveness in the presence of external disturbances when compared with the existing coordinated formation control schemes.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.01.010
      Issue No: Vol. 136 (2017)
  • A wall grid scale criterion for hypersonic aerodynamic heating calculation
    • Authors: Jianlong Yang; Meng Liu
      Pages: 137 - 143
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Jianlong Yang, Meng Liu
      The theory of molecular motion was used to study the wall cell Reynolds number method, and it found that the height of the first grid point off wall is related to the molecular mean free path near wall. A wall grid scale criterion based on the molecular mean free path at the stagnation point was proposed by considering both the flow parameters and the wall temperature boundaries. The criterion was verified through numerical calculations and comparative analyses of the wall heat flux in different hypersonic flow fields. Research results draw the following conclusions: The optimal height of the first grid point off wall is a molecular mean free path. The influence of height of the first grid point off wall on aerodynamic heat is much greater than that of aerodynamic force. The criterion is not only effective for the wall heat flux predictions in air conditions, but also useful to that of non air environments. With the weakening of aerodynamic heating along the flow direction, the effect of wall grid scale on the wall heat flux gradually decreases.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2016.11.043
      Issue No: Vol. 136 (2017)
  • The ultimate limits of the relativistic rocket equation. The Planck photon
    • Authors: Espen Gaarder Haug
      Pages: 144 - 147
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Espen Gaarder Haug
      In this paper we look at the ultimate limits of a photon propulsion rocket. The maximum velocity for a photon propulsion rocket is just below the speed of light and is a function of the reduced Compton wavelength of the heaviest subatomic particles in the rocket. We are basically combining the relativistic rocket equation with Haug's new insight on the maximum velocity for anything with rest mass. An interesting new finding is that in order to accelerate any subatomic “fundamental” particle to its maximum velocity, the particle rocket basically needs two Planck masses of initial load. This might sound illogical until one understands that subatomic particles with different masses have different maximum velocities. This can be generalized to large rockets and gives us the maximum theoretical velocity of a fully-efficient and ideal rocket. Further, no additional fuel is needed to accelerate a Planck mass particle to its maximum velocity; this also might sound absurd, but it has a very simple and logical solution that is explained in this paper.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.011
      Issue No: Vol. 136 (2017)
  • Long-range AIS message analysis based on the TianTuo-3 micro satellite
    • Authors: Shiyou Li; Lihu Chen; Xiaoqian Chen; Yong Zhao; Yuzhu Bai
      Pages: 159 - 165
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Shiyou Li, Lihu Chen, Xiaoqian Chen, Yong Zhao, Yuzhu Bai
      The "Type-27 AIS message" is the long-range AIS broadcast message, which is primarily intended for the long-range detection of AIS typically by satellite. The TT3-AIS uses a four-frequency receiver scheme which includes two frequency channels conventionally applied by the AIS system and two new frequency channels allocated to the long-range AIS broadcast message. To the end of April 2016, the TT3-AIS has already received more than 11,400 packets of Type-27 AIS messages. In this paper, a detailed analysis of the Type-27 AIS messages is performed. Firstly, an eavesdropper diagram of the space-borne AIS received from the worldwide vessels is obtained. Secondly, the analysis to the trend of the number and the ratio of the new-type vessels is performed based on the Type-27 AIS message. The detection probability of the new-type vessels is also discussed. The result would be helpful on the usage of the long-range AIS message both for data application and for the improvement in designing the next space-based AIS receiver.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.02.014
      Issue No: Vol. 136 (2017)
  • Robust high-precision attitude control for flexible spacecraft with
    • Authors: Chuang Liu; Dong Ye; Keke Shi; Zhaowei Sun
      Pages: 166 - 175
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Chuang Liu, Dong Ye, Keke Shi, Zhaowei Sun
      A novel improved mixed H 2/H ∞ control technique combined with poles assignment theory is presented to achieve attitude stabilization and vibration suppression simultaneously for flexible spacecraft in this paper. The flexible spacecraft dynamics system is described and transformed into corresponding state space form. Based on linear matrix inequalities (LMIs) scheme and poles assignment theory, the improved mixed H 2/H ∞ controller does not restrict the equivalence of the two Lyapunov variables involved in H 2 and H ∞ performance, which can reduce conservatives compared with traditional mixed H 2/H ∞ controller. Moreover, it can eliminate the coupling of Lyapunov matrix variables and system matrices by introducing slack variable that provides additional degree of freedom. Several simulations are performed to demonstrate the effectiveness and feasibility of the proposed method in this paper.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.009
      Issue No: Vol. 136 (2017)
  • Cruise status of Hayabusa2: Round trip mission to asteroid 162173 Ryugu
    • Authors: Yuichi Tsuda; Sei-ichiro Watanabe; Takanao Saiki; Makoto Yoshikawa; Satoru Nakazawa
      Pages: 176 - 181
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Yuichi Tsuda, Sei-ichiro Watanabe, Takanao Saiki, Makoto Yoshikawa, Satoru Nakazawa
      The Japan Aerospace Exploration Agency launched an asteroid sample return spacecraft "Hayabusa2" on December 3, 2014 by the Japanese H2A launch vehicle. Hayabusa2 aims at the round trip mission to the asteroid 162173 Ryugu. Hayabusa2 successfully conducted the Earth gravity assist on December 3, 2015, and now the spacecraft is flying toward Ryugu with the microwave discharge ion engine as the means of propulsion. As of September 2016, 1346h of the ion engine operation has been achieved as planned. Three touch downs/sample collections, one kinetic impact/crater generation, four surface rovers deployment and many other in-situ observations are planned in the asteroid proximity phase. The operation team will perform extensive operation practice/rehearsal using a hardware-in-the-loop simulator in the year 2017 to be ready for the asteroid arrival in the summer 2018.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.015
      Issue No: Vol. 136 (2017)
  • A new concept of space solar power satellite
    • Authors: Xun Li; Baoyan Duan; Liwei Song; Yang Yang; Yiqun Zhang; Dongxu Wang
      Pages: 182 - 189
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Xun Li, Baoyan Duan, Liwei Song, Yang Yang, Yiqun Zhang, Dongxu Wang
      Space solar power satellite (SSPS) is a tremendous energy system that collects and converts solar power to electric power in space, and then transmits the electric power to earth wirelessly. In this paper, a novel SSPS concept based on ε-near-zero (ENZ) metamaterial is proposed. A spherical condenser made of ENZ metamaterial is developed, by using the refractive property of the ENZ metamaterial sunlight can be captured and redirected to its center. To make the geometric concentration ratio of the PV array reasonable, a hemispherical one located at the center is used to collect and convert the normal-incidence sunlight to DC power, then through a phased array transmitting antenna the DC power is beamed down to the rectenna on the ground. Detailed design of the proposed concept is presented.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.017
      Issue No: Vol. 136 (2017)
  • Diamagnetic antimatter storage
    • Authors: Oleg G. Semyonov
      Pages: 190 - 203
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Oleg G. Semyonov
      The prime candidate for fueling relativistic starships is antimatter and reaching the stars will require antimatter storage on board of a spacecraft in a compact form, most likely liquid or solid antihydrogen. The problem is how to store antimatter in a container made of conventional matter. The solution is an energy barrier on the inner surface of the tank wall preventing antimatter from contacting the wall. Diamagnetic antihydrogen can be kept apart of conventional matter, if a gradient magnetic barrier is created near the inner surface of a tank. In this article, various magnetic barriers induced by arrays of current-carrying superconductive loops are studied by numerical simulations such as mosaics of rectangular loops, arrays of concentric circular loops (top and bottom of a cylindrical container), arrays of identical circular loops that form the cylinder element of the container, and arrays of loops distributed over sphere. The force acting on liquid and solid antihydrogen and the maximum height of antihydrogen ‘fuel’ in a tank are calculated. The problems and challenges caused by antihydrogen vapors are discussed.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.012
      Issue No: Vol. 136 (2017)
  • Design for CubeSat-based dust and radiation studies at Europa
    • Authors: Ashish Goel; Siddharth Krishnamoorthy; Travis Swenson; Stephen West; Alan Li; Alexander Crew; Derek James Phillips; Antoine Screve; Sigrid Close
      Pages: 204 - 218
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Ashish Goel, Siddharth Krishnamoorthy, Travis Swenson, Stephen West, Alan Li, Alexander Crew, Derek James Phillips, Antoine Screve, Sigrid Close
      Europa is one of the icy moons of Jupiter and the possibility of an ocean of liquid water beneath its icy crust makes it one of the most fascinating destinations for exploration in the solar system. NASA's Europa Multiple Flyby Mission (EMFM, formerly Europa Clipper) is slated to visit the icy moon in a timeframe near the year 2022 to study the habitability of Europa. CubeSats carried along by the primary mission can supplement the measurements made, at a relatively low cost, and with the added benefits of involving students at universities in this challenging endeavor. Further, such a mission holds the key to extending the applicability of CubeSats to interplanetary missions. In this paper, we present the design of the Europa Radiation and Dust Observation Satellite (ERDOS), a 3U CubeSat designed to be deployed by the Europa Multiple Flyby Mission to carry out measurements of the radiation and dust environment, before impacting Europa's surface. We present a detailed design for a CubeSat-based secondary mission, and discuss the science goals that may be accomplished by such a mission. Further, we discuss results from a comprehensive analysis of various engineering challenges associated with an interplanetary CubeSat mission, such as radiation shielding and thermal environment control. Our results show that a short duration CubeSat-based flyby mission is feasible when the CubeSat is carried on board the primary mission until the Jovian system is reached. Such a flyby mission can provide important supplementary information to the primary mission about Europa's environment at a closer range and lead to a substantial increase in scientific knowledge about surface processes on Europa.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.016
      Issue No: Vol. 136 (2017)
  • Aluminum agglomeration involving the second mergence of agglomerates on
           the solid propellants burning surface: Experiments and modeling
    • Authors: Wen Ao; Xin Liu; Hichem Rezaiguia; Huan Liu; Zhixin Wang; Peijin Liu
      Pages: 219 - 229
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Wen Ao, Xin Liu, Hichem Rezaiguia, Huan Liu, Zhixin Wang, Peijin Liu
      The agglomeration of aluminum particles usually occurs on the burning surface of aluminized composite propellants. It leads to low propellant combustion efficiency and high two-phase flow losses. To reach a thorough understanding of aluminum agglomeration behaviors, agglomeration processes, and particles size distribution of Al/AP/RDX/GAP propellants were studied by using a cinephotomicrography experimental technique, under 5MPa. Accumulation, aggregation, and agglomeration phenomena of aluminum particles have been inspected, as well as the flame asymmetry of burning agglomerates. Results reveals that the dependency of the mean and the maximum agglomeration diameter to the burning rate and the virgin aluminum size have the same trend. A second-time mergence of multiple agglomerates on the burning surface is unveiled. Two typical modes of second mergence are concluded, based upon vertical and level movement of agglomerates, respectively. The latter mode is found to be dominant and sometimes a combination of the two modes may occur. A new model of aluminum agglomeration on the burning surface of composite propellants is derived to predict the particulates size distribution with a low computational amount. The basic idea is inspired from the well-known pocket models. The pocket size of the region formed by adjacent AP particles is obtained through scanning electron microscopy of the propellant cross-section coupled to an image processing method. The second mergence mechanism, as well as the effect of the burning rate on the agglomeration processes, are included in the present model. The mergence of two agglomerates is prescribed to occur only if their separation distance is less than a critical value. The agglomerates size distribution resulting from this original model match reasonably with the experimental data. Moreover, the present model gives superior results for mean agglomeration diameter compared to common empirical and pocket models. The average prediction error is lower than 5% for the four propellants tested. Results of this study are expected to provide better insight and enrich in the theoretical frame of aluminum agglomeration.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.013
      Issue No: Vol. 136 (2017)
  • In-situ grown MgO-ZnO ceramic coating with high thermal emittance on Mg
           alloy by plasma electrolytic oxidation
    • Authors: Hang Li; Songtao Lu; Wei Qin; Xiaohong Wu
      Pages: 230 - 235
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Hang Li, Songtao Lu, Wei Qin, Xiaohong Wu
      Intense solar radiation and internal heat generation determine the equilibrium temperature of an in-orbit spacecraft. Thermal control coatings with low solar absorptance and high thermal emittance effectively maintain the thermal equilibrium within safe operating limits for exposed, miniaturized and highly integrated components. A novel ceramic coating with high thermal emittance and good adhesion was directly prepared on the Mg substrate using an economical process of controlled plasma electrolytic oxidation (PEO) in the electrolyte containing ZnSO4. XRD and XPS results showed that this coating was mainly composed of the MgO phase as well as an unusual ZnO crystalline phase. The adhesive strength between the coating and substrate determined by a pull-off test revealed an excellent adhesion. Thermal and optical properties test revealed that the coating exhibited a high infrared emittance of 0.88 (2–16µm) and low solar absorptance of 0.35 (200–2500nm). The result indicated that the formation of ZnO during the PEO process played an important role in the improvement of the coating emittance. The process developed provides a simple surface method for improving the thermal emittance of Mg alloy, which presents a promising application prospect in the thermal management of the spacecraft.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.021
      Issue No: Vol. 136 (2017)
  • On the advantages of exploiting the hierarchical structure of
           astrodynamical models
    • Authors: Diogene Alessandro Dei Tos; Francesco Topputo
      Pages: 236 - 247
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Diogene Alessandro Dei Tos, Francesco Topputo
      In this paper an algorithm is developed that combines the capabilities and advantages of several different astrodynamical models of increasing complexity. Splitting these models in a strict hierarchical order yields a clearer grasp on what is available. With the effort of developing a comprehensive model overhead, the equations for the spacecraft motion in simpler models can be readily obtained as particular cases. The proposed algorithm embeds the circular and elliptic restricted three-body problems, the four-body bicircular and concentric models, an averaged n-body model, and, at the top hierarchic ladder, the full ephemeris SPICE-based restricted n-body problem. The equations of motion are reduced to the assignment of 13 time-varying coefficients, which multiply the states and the gravitational potential to reproduce the proper vector field. This approach yields an efficient and quick way to check solutions for different dynamics and parameters. We show that in bottom-up applications, a gradual increase of model complexity benefits accuracy, the chances of success and the convergence rate of a continuation algorithm. Case studies are simple periodic orbits and low-energy transfers.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.02.025
      Issue No: Vol. 136 (2017)
  • Thermal protection performance of magnetohydrodynamic heat shield system
           based on multipolar magnetic field
    • Authors: Li Kai; Liu Jun; Liu Weiqiang
      Pages: 248 - 258
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Li Kai, Liu Jun, Liu Weiqiang
      In order to cover the shortage of dipole magnetic field in the magnetohydrodynamic(MHD) heat shield system, physical model of a multipolar magnetic field with central and peripheral solenoids is constructed. By employing the governing equations of three dimensional thermochemical nonequilibrium flow with electromagnetic source terms based on the low magneto-Reynolds assumption, the flow control performance of the dipole and multipolar magnetic fields are numerically simulated. To make the results comparable, two groups of cases are designed by first assuming equal stagnation magnetic induction strength and secondly assuming equal ampere-turns. Results show that, the five-magnet system, whose central polar orientation is the same with the peripheral ones, have stronger work capability and better shock control and thermal protection performance. Moreover, the five-solenoid systems are the best when the ampere-turns of the central solenoid are twice and fourth of the peripheral ones under those two circumstances respectively. Compared with the dipole magnetic field, the stagnation non-catalytic heat fluxes are decreased by a factor of 47.5% and 34.0% respectively.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.02.011
      Issue No: Vol. 136 (2017)
  • Study of the unsteady mode transition process for an over-under TBCC
           exhaust system
    • Authors: Zheng Lv; Jinglei Xu; Jianwei Mo
      Pages: 259 - 272
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Zheng Lv, Jinglei Xu, Jianwei Mo
      The present study focuses on the unsteady mode transition process of an over-under TBCC exhaust system. The method of characteristics is applied to design the over-under TBCC exhaust system according to the entrance parameters of the turbine nozzle and ramjet nozzle at the design point. The dynamic mesh is adopted to adjust to the update of the computational domain, and the unsteady numerical method is employed to simulate the dynamic flowfield of the exhaust system during the mode transition process. The results show that the flowfield structure and the performance vary greatly during the mode transition. Owing to the interaction between the turbine exhaust jet and ramjet plume, the flowfiled in the turbine nozzle is affected by the ramjet exhaust jet considerably. The axial thrust of the turbine nozzle decreases, while that of the ramjet nozzle increases gradually during the mode transition, but the total axial thrust of the entire exhaust system varies smoothly. Both the axial thrust coefficient and pitching moment of the exhaust system increase along with the open of the ramjet nozzle, while the result for the lift is contrary. However, the axial thrust coefficient, lift and pitching moment all decrease rapidly with the shutdown of the turbine nozzle, and the decreases in axial thrust coefficient, lift and pitching moment are 1.04%, 67.15% and 80.92%, respectively. Besides, two sudden change of the axial thrust coefficient exist at the beginning and end of the motion of the splitter plate.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.020
      Issue No: Vol. 136 (2017)
  • Multi-objective trajectory optimization of Space Manoeuvre Vehicle using
           adaptive differential evolution and modified game theory
    • Authors: Runqi Chai; Al Savvaris; Antonios Tsourdos; Senchun Chai
      Pages: 273 - 280
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Runqi Chai, Al Savvaris, Antonios Tsourdos, Senchun Chai
      Highly constrained trajectory optimization for Space Manoeuvre Vehicles (SMV) is a challenging problem. In practice, this problem becomes more difficult when multiple mission requirements are taken into account. Because of the nonlinearity in the dynamic model and even the objectives, it is usually hard for designers to generate a compromised trajectory without violating strict path and box constraints. In this paper, a new multi-objective SMV optimal control model is formulated and parameterized using combined shooting-collocation technique. A modified game theory approach, coupled with an adaptive differential evolution algorithm, is designed in order to generate the pareto front of the multi-objective trajectory optimization problem. In addition, to improve the quality of obtained solutions, a control logic is embedded in the framework of the proposed approach. Several existing multi-objective evolutionary algorithms are studied and compared with the proposed method. Simulation results indicate that without driving the solution out of the feasible region, the proposed method can perform better in terms of convergence ability and convergence speed than its counterparts. Moreover, the quality of the pareto set generated using the proposed method is higher than other multi-objective evolutionary algorithms, which means the newly proposed algorithm is more attractive for solving multi-criteria SMV trajectory planning problem.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.02.023
      Issue No: Vol. 136 (2017)
  • Robust distributed control of spacecraft formation flying with adaptive
           network topology
    • Authors: Behrouz Shasti; Aria Alasty; Nima Assadian
      Pages: 281 - 296
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Behrouz Shasti, Aria Alasty, Nima Assadian
      In this study, the distributed six degree-of-freedom (6-DOF) coordinated control of spacecraft formation flying in low earth orbit (LEO) has been investigated. For this purpose, an accurate coupled translational and attitude relative dynamics model of the spacecraft with respect to the reference orbit (virtual leader) is presented by considering the most effective perturbation acceleration forces on LEO satellites, i.e. the second zonal harmonic and the atmospheric drag. Subsequently, the 6-DOF coordinated control of spacecraft in formation is studied. During the mission, the spacecraft communicate with each other through a switching network topology in which the weights of its graph Laplacian matrix change adaptively based on a distance-based connectivity function between neighboring agents. Because some of the dynamical system parameters such as spacecraft masses and moments of inertia may vary with time, an adaptive law is developed to estimate the parameter values during the mission. Furthermore, for the case that there is no knowledge of the unknown and time-varying parameters of the system, a robust controller has been developed. It is proved that the stability of the closed-loop system coupled with adaptation in network topology structure and optimality and robustness in control is guaranteed by the robust contraction analysis as an incremental stability method for multiple synchronized systems. The simulation results show the effectiveness of each control method in the presence of uncertainties and parameter variations. The adaptive and robust controllers show their superiority in reducing the state error integral as well as decreasing the control effort and settling time.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.001
      Issue No: Vol. 136 (2017)
  • Method of interplanetary trajectory optimization for the spacecraft with
           low thrust and swing-bys
    • Authors: M.S. Konstantinov; M. Thein
      Pages: 297 - 311
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): M.S. Konstantinov, M. Thein
      The method developed to avoid the complexity of solving the multipoint boundary value problem while optimizing interplanetary trajectories of the spacecraft with electric propulsion and a sequence of swing-bys is presented in the paper. This method is based on the use of the preliminary problem solutions for the impulsive trajectories. The preliminary problem analyzed at the first stage of the study is formulated so that the analysis and optimization of a particular flight path is considered as the unconstrained minimum in the space of the selectable parameters. The existing methods can effectively solve this problem and make it possible to identify rational flight paths (the sequence of swing-bys) to receive the initial approximation for the main characteristics of the flight path (dates, values of the hyperbolic excess velocity, etc.). These characteristics can be used to optimize the trajectory of the spacecraft with electric propulsion. The special feature of the work is the introduction of the second (intermediate) stage of the research. At this stage some characteristics of the analyzed flight path (e.g. dates of swing-bys) are fixed and the problem is formulated so that the trajectory of the spacecraft with electric propulsion is optimized on selected sites of the flight path. The end-to-end optimization is carried out at the third (final) stage of the research. The distinctive feature of this stage is the analysis of the full set of optimal conditions for the considered flight path. The analysis of the characteristics of the optimal flight trajectories to Jupiter with Earth, Venus and Mars swing-bys for the spacecraft with electric propulsion are presented. The paper shows that the spacecraft weighing more than 7150kg can be delivered into the vicinity of Jupiter along the trajectory with two Earth swing-bys by use of the space transportation system based on the "Angara A5" rocket launcher, the chemical upper stage "KVTK" and the electric propulsion system with input electrical power of 100kW.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.02.018
      Issue No: Vol. 136 (2017)
  • Modeling of aerodynamic heat flux and thermoelastic behavior of nose caps
           of hypersonic vehicles
    • Authors: Marina G. Persova; Yury G. Soloveichik; Vasiliy K. Belov; Dmitry S. Kiselev; Denis V. Vagin; Petr A. Domnikov; Ilya I. Patrushev; Denis N. Kurskiy
      Pages: 312 - 331
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Marina G. Persova, Yury G. Soloveichik, Vasiliy K. Belov, Dmitry S. Kiselev, Denis V. Vagin, Petr A. Domnikov, Ilya I. Patrushev, Denis N. Kurskiy
      In this paper, the problem of numerical modeling of thermoelastic behavior of nose caps of hypersonic vehicles at different angles of attack is considered. 3D finite element modeling is performed by solving the coupled heat and elastic problems taking into account thermal and mechanical properties variations with temperature. A special method for calculating the aerodynamic heat flux entering the nose cap from its surface is proposed. This method is characterized by very low computational costs and allows calculating the aerodynamic heat flux at different values of the Mach number and angles of attack which may vary during the aerodynamic heating. The numerical results obtained by the proposed approach are compared with the numerical results and experimental data obtained by other authors. The developed approach has been used for studying the impact of the angle of attack on the thermoelastic behavior of nose caps main components.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.02.021
      Issue No: Vol. 136 (2017)
  • High accuracy GNSS based navigation in GEO
    • Authors: Vincenzo Capuano; Endrit Shehaj; Paul Blunt; Cyril Botteron; Pierre-André Farine
      Pages: 332 - 341
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Vincenzo Capuano, Endrit Shehaj, Paul Blunt, Cyril Botteron, Pierre-André Farine
      Although significant improvements in efficiency and performance of communication satellites have been achieved in the past decades, it is expected that the demand for new platforms in Geostationary Orbit (GEO) and for the On-Orbit Servicing (OOS) on the existing ones will continue to rise. Indeed, the GEO orbit is used for many applications including direct broadcast as well as communications. At the same time, Global Navigation Satellites System (GNSS), originally designed for land, maritime and air applications, has been successfully used as navigation system in Low Earth Orbit (LEO) and its further utilization for navigation of geosynchronous satellites becomes a viable alternative offering many advantages over present ground based methods. Following our previous studies of GNSS signal characteristics in Medium Earth Orbit (MEO), GEO and beyond, in this research we specifically investigate the processing of different GNSS signals, with the goal to determine the best navigation performance they can provide in a GEO mission. Firstly, a detailed selection among different GNSS signals and different combinations of them is discussed, taking into consideration the L1 and L5 frequency bands, and the GPS and Galileo constellations. Then, the implementation of an Orbital Filter is summarized, which adaptively fuses the GN1SS observations with an accurate orbital forces model. Finally, simulation tests of the navigation performance achievable by processing the selected combination of GNSS signals are carried out. The results obtained show an achievable positioning accuracy of less than one meter. In addition, hardware-in-the-loop tests are presented using a COTS receiver connected to our GNSS Spirent simulator, in order to collect real-time hardware-in-the-loop observations and process them by the proposed navigation module.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.014
      Issue No: Vol. 136 (2017)
  • Numerical investigation of switching mechanism for the supersonic jet
    • Authors: Y. Xu; G.Q. Zhang
      Pages: 342 - 353
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Y. Xu, G.Q. Zhang
      Based on the unsteady viscous flow simulation, the flow characteristics inside the supersonic jet element have been investigated numerically. The corresponding initial switching process has been overall divided into two major stages. The results have shown that the switching process for the supersonic jet flow is an extremely complex process, which can include the complex shock system evolution, the free shear layers together with the boundary layers evolution and multiple vortex region unsteady evolution etc. The presence of the switching oblique shock near the control port is not the necessary condition to make the jet deflect, but its formation is good for the early transverse extension of the stripping vortex zone. A new concept named minimum control mass flow rate has also been proposed and emphasized. The Viscosity and adverse pressure gradient have been found to be the key factors for the occurrence of flow separation to shorten the switching time. The vortex structures at different switching time together with the variations (thrust, static pressure as well as oblique shock waves etc.) inside the supersonic jet element have been obtained computationally and analyzed in details.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.022
      Issue No: Vol. 136 (2017)
  • The final year of the Rosetta mission
    • Authors: Andrea Accomazzo; Paolo Ferri; Sylvain Lodiot; Jose-Luis Pellon-Bailon; Armelle Hubault; Jakub Urbanek; Ritchie Kay; Matthias Eiblmaier; Tiago Francisco
      Pages: 354 - 359
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Andrea Accomazzo, Paolo Ferri, Sylvain Lodiot, Jose-Luis Pellon-Bailon, Armelle Hubault, Jakub Urbanek, Ritchie Kay, Matthias Eiblmaier, Tiago Francisco
      The International Rosetta Mission was launched on 2nd March 2004 on its 10 year journey to rendezvous with comet 67P Churyumov-Gerasimenko. Rosetta performed comet orbit insertion on the 6th of August 2014, after which it characterised the nucleus and orbited it at altitudes as low as a few kilometres. In November 2014 Rosetta delivered the lander Philae to perform the first soft landing ever on the surface of a comet. After this critical operation, Rosetta began the escort phase of the comet in its journey in the Solar System heading to the perihelion, reached in August 2015. Originally foreseen till the end of 2015, the mission was extended for another nine months to follow the comet on its outbound arc of the orbit. In view of the acquired experience and of the approaching end of mission the spacecraft was flown at much closer distances from the nucleus so that the scientific instruments had the chance to perform unique measurements. Following this phase of very close orbits, on the 30th of September 2016 Rosetta was set on a collision course trajectory with the comet to terminate the mission with a controlled impact. This paper describes the details of the extended mission phase and the issues encountered during these months. It also includes the changes implemented on the spacecraft and in the operations concept to optimise the remaining mission time. The paper also includes the lessons learned from this unique and complex mission phase.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.027
      Issue No: Vol. 136 (2017)
  • Self-calibration rank filter for unknown dynamic inputs mitigation during
           the Mars powered descent phase
    • Authors: Qiang Xiao; Huimin Fu; Zhibao Deng; Huanxu Bai; Sheng Wang; Mingyi Sun
      Pages: 360 - 368
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Qiang Xiao, Huimin Fu, Zhibao Deng, Huanxu Bai, Sheng Wang, Mingyi Sun
      Advanced navigation systems for pinpoint landing are required in the entry, descent and landing phase of future missions to Mars. To overcome the horizontal position estimation problem in the Mars powered descent phase, the inertial measurement unit, Doppler radar and surface beacon integrated navigation scheme is proposed, and a conventional filter such as an extended or unscented Kalman filter is adopted. However, in engineering practice, these conventional filters for nonlinear systems with unknown dynamic inputs may degrade or even diverge. The lack of navigation accuracy may result in a large growth of spurious navigations. To solve this problem, based on the rank filter, a self-calibration rank filter is proposed for state estimation of a nonlinear system to mitigate the effects of unknown dynamic inputs. Monte Carlo simulation results are presented to demonstrate the good performance of the self-calibration rank filter for the Mars powered descent navigation. The self-calibration rank filter not only prevents the divergence of the filtering but also significantly improves the state estimation accuracy.

      PubDate: 2017-04-09T10:12:35Z
      DOI: 10.1016/j.actaastro.2017.03.024
      Issue No: Vol. 136 (2017)
  • Transfer orbits to L4 with a solar sail in the Earth-Sun system
    • Authors: Ariadna
      Abstract: Publication date: August 2017
      Source:Acta Astronautica, Volume 137
      Author(s): Ariadna Farrés
      Solar sails are enablers for long interplanetary transfers, but also offer many advantages in Libration Point Orbits missions. The extra effect of the Solar Radiation Pressure allows a space vehicle, by changing the sail orientation, to be artificially displaced from the classical Lagrangian equilibrium points, L 1 , … , L 5 , as well perturbed from the Lyapunov, Halo and Lissajous orbits that appear around them. Most of these equilibrium points are linearly unstable and have stable and unstable invariant manifolds associated with them. In this paper we explore the possibilities that these invariant manifolds offer to navigate in a natural way around a circular, restricted, three-body system. We take the Earth-Sun Restricted Three Body Problem as a model and, for different fixed sail orientations, we compute the stable and unstable manifolds associated with the equilibrium points of the system. We find natural trajectories that allow the vehicle to move around the family of equilibria in a controlled way and to go from a region close to L 1 or L 2 to a region close to L 4.

      PubDate: 2017-04-23T08:02:41Z
  • Optimal thrust level for orbit insertion
    • Authors: Max Cerf
      Abstract: Publication date: July 2017
      Source:Acta Astronautica, Volume 136
      Author(s): Max Cerf
      The minimum-fuel orbital transfer is analyzed in the case of a launcher upper stage using a constantly thrusting engine. The thrust level is assumed to be constant and its value is optimized together with the thrust direction. A closed-loop solution for the thrust direction is derived from the extremal analysis for a planar orbital transfer. The optimal control problem reduces to two unknowns, namely the thrust level and the final time. Guessing and propagating the costates is no longer necessary and the optimal trajectory is easily found from a rough initialization. On the other hand the initial costates are assessed analytically from the initial conditions and they can be used as initial guess for transfers at different thrust levels. The method is exemplified on a launcher upper stage targeting a geostationary transfer orbit.

      PubDate: 2017-04-09T10:12:35Z
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