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Publisher: Elsevier   (Total: 3162 journals)

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Showing 1 - 200 of 3162 Journals sorted alphabetically
A Practical Logic of Cognitive Systems     Full-text available via subscription   (Followers: 9)
AASRI Procedia     Open Access   (Followers: 15)
Academic Pediatrics     Hybrid Journal   (Followers: 31, SJR: 1.655, CiteScore: 2)
Academic Radiology     Hybrid Journal   (Followers: 22, SJR: 1.015, CiteScore: 2)
Accident Analysis & Prevention     Partially Free   (Followers: 90, SJR: 1.462, CiteScore: 3)
Accounting Forum     Hybrid Journal   (Followers: 25, SJR: 0.932, CiteScore: 2)
Accounting, Organizations and Society     Hybrid Journal   (Followers: 34, SJR: 1.771, CiteScore: 3)
Achievements in the Life Sciences     Open Access   (Followers: 5)
Acta Anaesthesiologica Taiwanica     Open Access   (Followers: 7)
Acta Astronautica     Hybrid Journal   (Followers: 403, SJR: 0.758, CiteScore: 2)
Acta Automatica Sinica     Full-text available via subscription   (Followers: 2)
Acta Biomaterialia     Hybrid Journal   (Followers: 27, SJR: 1.967, CiteScore: 7)
Acta Colombiana de Cuidado Intensivo     Full-text available via subscription   (Followers: 2)
Acta de Investigación Psicológica     Open Access   (Followers: 3)
Acta Ecologica Sinica     Open Access   (Followers: 8, SJR: 0.18, CiteScore: 1)
Acta Haematologica Polonica     Free   (Followers: 1, SJR: 0.128, CiteScore: 0)
Acta Histochemica     Hybrid Journal   (Followers: 3, SJR: 0.661, CiteScore: 2)
Acta Materialia     Hybrid Journal   (Followers: 242, SJR: 3.263, CiteScore: 6)
Acta Mathematica Scientia     Full-text available via subscription   (Followers: 5, SJR: 0.504, CiteScore: 1)
Acta Mechanica Solida Sinica     Full-text available via subscription   (Followers: 9, SJR: 0.542, CiteScore: 1)
Acta Oecologica     Hybrid Journal   (Followers: 10, SJR: 0.834, CiteScore: 2)
Acta Otorrinolaringologica (English Edition)     Full-text available via subscription  
Acta Otorrinolaringológica Española     Full-text available via subscription   (Followers: 2, SJR: 0.307, CiteScore: 0)
Acta Pharmaceutica Sinica B     Open Access   (Followers: 1, SJR: 1.793, CiteScore: 6)
Acta Poética     Open Access   (Followers: 4, SJR: 0.101, CiteScore: 0)
Acta Psychologica     Hybrid Journal   (Followers: 27, SJR: 1.331, CiteScore: 2)
Acta Sociológica     Open Access  
Acta Tropica     Hybrid Journal   (Followers: 6, SJR: 1.052, CiteScore: 2)
Acta Urológica Portuguesa     Open Access  
Actas Dermo-Sifiliograficas     Full-text available via subscription   (Followers: 3, SJR: 0.374, CiteScore: 1)
Actas Dermo-Sifiliográficas (English Edition)     Full-text available via subscription   (Followers: 2)
Actas Urológicas Españolas     Full-text available via subscription   (Followers: 3, SJR: 0.344, CiteScore: 1)
Actas Urológicas Españolas (English Edition)     Full-text available via subscription   (Followers: 1)
Actualites Pharmaceutiques     Full-text available via subscription   (Followers: 6, SJR: 0.19, CiteScore: 0)
Actualites Pharmaceutiques Hospitalieres     Full-text available via subscription   (Followers: 3)
Acupuncture and Related Therapies     Hybrid Journal   (Followers: 6)
Acute Pain     Full-text available via subscription   (Followers: 15, SJR: 2.671, CiteScore: 5)
Ad Hoc Networks     Hybrid Journal   (Followers: 11, SJR: 0.53, CiteScore: 4)
Addictive Behaviors     Hybrid Journal   (Followers: 16, SJR: 1.29, CiteScore: 3)
Addictive Behaviors Reports     Open Access   (Followers: 8, SJR: 0.755, CiteScore: 2)
Additive Manufacturing     Hybrid Journal   (Followers: 9, SJR: 2.611, CiteScore: 8)
Additives for Polymers     Full-text available via subscription   (Followers: 22)
Advanced Cement Based Materials     Full-text available via subscription   (Followers: 3, SJR: 0.732, CiteScore: 3)
Advanced Drug Delivery Reviews     Hybrid Journal   (Followers: 138, SJR: 4.09, CiteScore: 13)
Advanced Engineering Informatics     Hybrid Journal   (Followers: 11, SJR: 1.167, CiteScore: 4)
Advanced Powder Technology     Hybrid Journal   (Followers: 16, SJR: 0.694, CiteScore: 3)
Advances in Accounting     Hybrid Journal   (Followers: 8, SJR: 0.277, CiteScore: 1)
Advances in Agronomy     Full-text available via subscription   (Followers: 12, SJR: 2.384, CiteScore: 5)
Advances in Anesthesia     Full-text available via subscription   (Followers: 28, SJR: 0.126, CiteScore: 0)
Advances in Antiviral Drug Design     Full-text available via subscription   (Followers: 2)
Advances in Applied Mathematics     Full-text available via subscription   (Followers: 10, SJR: 0.992, CiteScore: 1)
Advances in Applied Mechanics     Full-text available via subscription   (Followers: 10, SJR: 1.551, CiteScore: 4)
Advances in Applied Microbiology     Full-text available via subscription   (Followers: 22, SJR: 2.089, CiteScore: 5)
Advances In Atomic, Molecular, and Optical Physics     Full-text available via subscription   (Followers: 14, SJR: 0.572, CiteScore: 2)
Advances in Biological Regulation     Hybrid Journal   (Followers: 4, SJR: 2.61, CiteScore: 7)
Advances in Botanical Research     Full-text available via subscription   (Followers: 2, SJR: 0.686, CiteScore: 2)
Advances in Cancer Research     Full-text available via subscription   (Followers: 30, SJR: 3.043, CiteScore: 6)
Advances in Carbohydrate Chemistry and Biochemistry     Full-text available via subscription   (Followers: 7, SJR: 1.453, CiteScore: 2)
Advances in Catalysis     Full-text available via subscription   (Followers: 5, SJR: 1.992, CiteScore: 5)
Advances in Cell Aging and Gerontology     Full-text available via subscription   (Followers: 3)
Advances in Cellular and Molecular Biology of Membranes and Organelles     Full-text available via subscription   (Followers: 12)
Advances in Chemical Engineering     Full-text available via subscription   (Followers: 27, SJR: 0.156, CiteScore: 1)
Advances in Child Development and Behavior     Full-text available via subscription   (Followers: 10, SJR: 0.713, CiteScore: 1)
Advances in Chronic Kidney Disease     Full-text available via subscription   (Followers: 10, SJR: 1.316, CiteScore: 2)
Advances in Clinical Chemistry     Full-text available via subscription   (Followers: 28, SJR: 1.562, CiteScore: 3)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 19, SJR: 1.977, CiteScore: 8)
Advances in Computers     Full-text available via subscription   (Followers: 14, SJR: 0.205, CiteScore: 1)
Advances in Dermatology     Full-text available via subscription   (Followers: 15)
Advances in Developmental Biology     Full-text available via subscription   (Followers: 11)
Advances in Digestive Medicine     Open Access   (Followers: 8)
Advances in DNA Sequence-Specific Agents     Full-text available via subscription   (Followers: 5)
Advances in Drug Research     Full-text available via subscription   (Followers: 24)
Advances in Ecological Research     Full-text available via subscription   (Followers: 43, SJR: 2.524, CiteScore: 4)
Advances in Engineering Software     Hybrid Journal   (Followers: 27, SJR: 1.159, CiteScore: 4)
Advances in Experimental Biology     Full-text available via subscription   (Followers: 7)
Advances in Experimental Social Psychology     Full-text available via subscription   (Followers: 44, SJR: 5.39, CiteScore: 8)
Advances in Exploration Geophysics     Full-text available via subscription   (Followers: 1)
Advances in Fluorine Science     Full-text available via subscription   (Followers: 9)
Advances in Food and Nutrition Research     Full-text available via subscription   (Followers: 54, SJR: 0.591, CiteScore: 2)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 16)
Advances in Genetics     Full-text available via subscription   (Followers: 15, SJR: 1.354, CiteScore: 4)
Advances in Genome Biology     Full-text available via subscription   (Followers: 8, SJR: 12.74, CiteScore: 13)
Advances in Geophysics     Full-text available via subscription   (Followers: 6, SJR: 1.193, CiteScore: 3)
Advances in Heat Transfer     Full-text available via subscription   (Followers: 21, SJR: 0.368, CiteScore: 1)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 11, SJR: 0.749, CiteScore: 3)
Advances in Human Factors/Ergonomics     Full-text available via subscription   (Followers: 21)
Advances in Imaging and Electron Physics     Full-text available via subscription   (Followers: 2, SJR: 0.193, CiteScore: 0)
Advances in Immunology     Full-text available via subscription   (Followers: 36, SJR: 4.433, CiteScore: 6)
Advances in Inorganic Chemistry     Full-text available via subscription   (Followers: 8, SJR: 1.163, CiteScore: 2)
Advances in Insect Physiology     Full-text available via subscription   (Followers: 2, SJR: 1.938, CiteScore: 3)
Advances in Integrative Medicine     Hybrid Journal   (Followers: 6, SJR: 0.176, CiteScore: 0)
Advances in Intl. Accounting     Full-text available via subscription   (Followers: 3)
Advances in Life Course Research     Hybrid Journal   (Followers: 8, SJR: 0.682, CiteScore: 2)
Advances in Lipobiology     Full-text available via subscription   (Followers: 1)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 9)
Advances in Marine Biology     Full-text available via subscription   (Followers: 14, SJR: 0.88, CiteScore: 2)
Advances in Mathematics     Full-text available via subscription   (Followers: 11, SJR: 3.027, CiteScore: 2)
Advances in Medical Sciences     Hybrid Journal   (Followers: 6, SJR: 0.694, CiteScore: 2)
Advances in Medicinal Chemistry     Full-text available via subscription   (Followers: 5)
Advances in Microbial Physiology     Full-text available via subscription   (Followers: 4, SJR: 1.158, CiteScore: 3)
Advances in Molecular and Cell Biology     Full-text available via subscription   (Followers: 21)
Advances in Molecular and Cellular Endocrinology     Full-text available via subscription   (Followers: 8)
Advances in Molecular Toxicology     Full-text available via subscription   (Followers: 7, SJR: 0.182, CiteScore: 0)
Advances in Nanoporous Materials     Full-text available via subscription   (Followers: 3)
Advances in Oncobiology     Full-text available via subscription   (Followers: 1)
Advances in Organ Biology     Full-text available via subscription   (Followers: 1)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 16, SJR: 1.875, CiteScore: 4)
Advances in Parallel Computing     Full-text available via subscription   (Followers: 7, SJR: 0.174, CiteScore: 0)
Advances in Parasitology     Full-text available via subscription   (Followers: 5, SJR: 1.579, CiteScore: 4)
Advances in Pediatrics     Full-text available via subscription   (Followers: 24, SJR: 0.461, CiteScore: 1)
Advances in Pharmaceutical Sciences     Full-text available via subscription   (Followers: 10)
Advances in Pharmacology     Full-text available via subscription   (Followers: 16, SJR: 1.536, CiteScore: 3)
Advances in Physical Organic Chemistry     Full-text available via subscription   (Followers: 8, SJR: 0.574, CiteScore: 1)
Advances in Phytomedicine     Full-text available via subscription  
Advances in Planar Lipid Bilayers and Liposomes     Full-text available via subscription   (Followers: 3, SJR: 0.109, CiteScore: 1)
Advances in Plant Biochemistry and Molecular Biology     Full-text available via subscription   (Followers: 8)
Advances in Plant Pathology     Full-text available via subscription   (Followers: 6)
Advances in Porous Media     Full-text available via subscription   (Followers: 5)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 18)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 20, SJR: 0.791, CiteScore: 2)
Advances in Psychology     Full-text available via subscription   (Followers: 62)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 6, SJR: 0.371, CiteScore: 1)
Advances in Radiation Oncology     Open Access   (SJR: 0.263, CiteScore: 1)
Advances in Small Animal Medicine and Surgery     Hybrid Journal   (Followers: 3, SJR: 0.101, CiteScore: 0)
Advances in Space Biology and Medicine     Full-text available via subscription   (Followers: 5)
Advances in Space Research     Full-text available via subscription   (Followers: 392, SJR: 0.569, CiteScore: 2)
Advances in Structural Biology     Full-text available via subscription   (Followers: 5)
Advances in Surgery     Full-text available via subscription   (Followers: 10, SJR: 0.555, CiteScore: 2)
Advances in the Study of Behavior     Full-text available via subscription   (Followers: 31, SJR: 2.208, CiteScore: 4)
Advances in Veterinary Medicine     Full-text available via subscription   (Followers: 17)
Advances in Veterinary Science and Comparative Medicine     Full-text available via subscription   (Followers: 13)
Advances in Virus Research     Full-text available via subscription   (Followers: 5, SJR: 2.262, CiteScore: 5)
Advances in Water Resources     Hybrid Journal   (Followers: 46, SJR: 1.551, CiteScore: 3)
Aeolian Research     Hybrid Journal   (Followers: 6, SJR: 1.117, CiteScore: 3)
Aerospace Science and Technology     Hybrid Journal   (Followers: 335, SJR: 0.796, CiteScore: 3)
AEU - Intl. J. of Electronics and Communications     Hybrid Journal   (Followers: 8, SJR: 0.42, CiteScore: 2)
African J. of Emergency Medicine     Open Access   (Followers: 6, SJR: 0.296, CiteScore: 0)
Ageing Research Reviews     Hybrid Journal   (Followers: 11, SJR: 3.671, CiteScore: 9)
Aggression and Violent Behavior     Hybrid Journal   (Followers: 438, SJR: 1.238, CiteScore: 3)
Agri Gene     Hybrid Journal   (SJR: 0.13, CiteScore: 0)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 16, SJR: 1.818, CiteScore: 5)
Agricultural Systems     Hybrid Journal   (Followers: 32, SJR: 1.156, CiteScore: 4)
Agricultural Water Management     Hybrid Journal   (Followers: 44, SJR: 1.272, CiteScore: 3)
Agriculture and Agricultural Science Procedia     Open Access   (Followers: 1)
Agriculture and Natural Resources     Open Access   (Followers: 2)
Agriculture, Ecosystems & Environment     Hybrid Journal   (Followers: 57, SJR: 1.747, CiteScore: 4)
Ain Shams Engineering J.     Open Access   (Followers: 5, SJR: 0.589, CiteScore: 3)
Air Medical J.     Hybrid Journal   (Followers: 6, SJR: 0.26, CiteScore: 0)
AKCE Intl. J. of Graphs and Combinatorics     Open Access   (SJR: 0.19, CiteScore: 0)
Alcohol     Hybrid Journal   (Followers: 11, SJR: 1.153, CiteScore: 3)
Alcoholism and Drug Addiction     Open Access   (Followers: 9)
Alergologia Polska : Polish J. of Allergology     Full-text available via subscription   (Followers: 1)
Alexandria Engineering J.     Open Access   (Followers: 1, SJR: 0.604, CiteScore: 3)
Alexandria J. of Medicine     Open Access   (Followers: 1, SJR: 0.191, CiteScore: 1)
Algal Research     Partially Free   (Followers: 10, SJR: 1.142, CiteScore: 4)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 2)
Allergologia et Immunopathologia     Full-text available via subscription   (Followers: 1, SJR: 0.504, CiteScore: 1)
Allergology Intl.     Open Access   (Followers: 5, SJR: 1.148, CiteScore: 2)
Alpha Omegan     Full-text available via subscription   (SJR: 3.521, CiteScore: 6)
ALTER - European J. of Disability Research / Revue Européenne de Recherche sur le Handicap     Full-text available via subscription   (Followers: 9, SJR: 0.201, CiteScore: 1)
Alzheimer's & Dementia     Hybrid Journal   (Followers: 50, SJR: 4.66, CiteScore: 10)
Alzheimer's & Dementia: Diagnosis, Assessment & Disease Monitoring     Open Access   (Followers: 4, SJR: 1.796, CiteScore: 4)
Alzheimer's & Dementia: Translational Research & Clinical Interventions     Open Access   (Followers: 4, SJR: 1.108, CiteScore: 3)
Ambulatory Pediatrics     Hybrid Journal   (Followers: 6)
American Heart J.     Hybrid Journal   (Followers: 50, SJR: 3.267, CiteScore: 4)
American J. of Cardiology     Hybrid Journal   (Followers: 54, SJR: 1.93, CiteScore: 3)
American J. of Emergency Medicine     Hybrid Journal   (Followers: 44, SJR: 0.604, CiteScore: 1)
American J. of Geriatric Pharmacotherapy     Full-text available via subscription   (Followers: 10)
American J. of Geriatric Psychiatry     Hybrid Journal   (Followers: 14, SJR: 1.524, CiteScore: 3)
American J. of Human Genetics     Hybrid Journal   (Followers: 32, SJR: 7.45, CiteScore: 8)
American J. of Infection Control     Hybrid Journal   (Followers: 26, SJR: 1.062, CiteScore: 2)
American J. of Kidney Diseases     Hybrid Journal   (Followers: 34, SJR: 2.973, CiteScore: 4)
American J. of Medicine     Hybrid Journal   (Followers: 43)
American J. of Medicine Supplements     Full-text available via subscription   (Followers: 3, SJR: 1.967, CiteScore: 2)
American J. of Obstetrics and Gynecology     Hybrid Journal   (Followers: 200, SJR: 2.7, CiteScore: 4)
American J. of Ophthalmology     Hybrid Journal   (Followers: 61, SJR: 3.184, CiteScore: 4)
American J. of Ophthalmology Case Reports     Open Access   (Followers: 5, SJR: 0.265, CiteScore: 0)
American J. of Orthodontics and Dentofacial Orthopedics     Full-text available via subscription   (Followers: 6, SJR: 1.289, CiteScore: 1)
American J. of Otolaryngology     Hybrid Journal   (Followers: 25, SJR: 0.59, CiteScore: 1)
American J. of Pathology     Hybrid Journal   (Followers: 27, SJR: 2.139, CiteScore: 4)
American J. of Preventive Medicine     Hybrid Journal   (Followers: 28, SJR: 2.164, CiteScore: 4)
American J. of Surgery     Hybrid Journal   (Followers: 37, SJR: 1.141, CiteScore: 2)
American J. of the Medical Sciences     Hybrid Journal   (Followers: 12, SJR: 0.767, CiteScore: 1)
Ampersand : An Intl. J. of General and Applied Linguistics     Open Access   (Followers: 6)
Anaerobe     Hybrid Journal   (Followers: 4, SJR: 1.144, CiteScore: 3)
Anaesthesia & Intensive Care Medicine     Full-text available via subscription   (Followers: 62, SJR: 0.138, CiteScore: 0)
Anaesthesia Critical Care & Pain Medicine     Full-text available via subscription   (Followers: 16, SJR: 0.411, CiteScore: 1)
Anales de Cirugia Vascular     Full-text available via subscription  
Anales de Pediatría     Full-text available via subscription   (Followers: 3, SJR: 0.277, CiteScore: 0)
Anales de Pediatría (English Edition)     Full-text available via subscription  
Anales de Pediatría Continuada     Full-text available via subscription  
Analytic Methods in Accident Research     Hybrid Journal   (Followers: 5, SJR: 4.849, CiteScore: 10)
Analytica Chimica Acta     Hybrid Journal   (Followers: 40, SJR: 1.512, CiteScore: 5)
Analytical Biochemistry     Hybrid Journal   (Followers: 169, SJR: 0.633, CiteScore: 2)
Analytical Chemistry Research     Open Access   (Followers: 10, SJR: 0.411, CiteScore: 2)
Analytical Spectroscopy Library     Full-text available via subscription   (Followers: 11)
Anesthésie & Réanimation     Full-text available via subscription   (Followers: 2)
Anesthesiology Clinics     Full-text available via subscription   (Followers: 23, SJR: 0.683, CiteScore: 2)
Angiología     Full-text available via subscription   (SJR: 0.121, CiteScore: 0)
Angiologia e Cirurgia Vascular     Open Access   (Followers: 1, SJR: 0.111, CiteScore: 0)

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Journal Cover
Advances in Space Research
Journal Prestige (SJR): 0.569
Citation Impact (citeScore): 2
Number of Followers: 392  
 
  Full-text available via subscription Subscription journal
ISSN (Print) 0273-1177
Published by Elsevier Homepage  [3162 journals]
  • List of Referees
    • Abstract: Publication date: 15 August 2018Source: Advances in Space Research, Volume 62, Issue 4Author(s):
       
  • Modeling approaches for precise relativistic orbits: Analytical,
           Lie-series, and pN approximation
    • Abstract: Publication date: 15 August 2018Source: Advances in Space Research, Volume 62, Issue 4Author(s): Dennis Philipp, Florian Woeske, Liliane Biskupek, Eva Hackmann, Enrico Mai, Meike List, Claus Lämmerzahl, Benny Rievers Accurate orbit modeling plays a key role in contemporary and future space missions such as GRACE and its successor GRACE-FO, GNSS, and altimetry missions. To fully exploit the technological capabilities and correctly interpret measurements, relativistic orbital effects need to be taken into account.Within the theory of General Relativity, equations of motion for freely falling test objects, such as satellites orbiting the Earth, are given by the geodesic equation. We analyze and compare different solution methods in a spherically symmetric background, i.e. for the Schwarzschild spacetime, as a test bed. We investigate satellite orbits and use direct numerical orbit integration as well as the semi-analytical Lie-series approach. The results are compared to the exact analytical reference solution in terms of elliptic functions. For a set of exemplary orbits, we determine the respective accuracy of the different methods.Within the post-Newtonian approximation of General Relativity, modified orbital equations are obtained by adding relativistic corrections to the Newtonian equations of motion. We analyze the accuracy of this approximation with respect to the general relativistic setting. Therefore, we solve the post-Newtonian equation of motion using the eXtended High Performance Satellite dynamics Simulator. For corresponding initial conditions, we compare orbits in the Schwarzschild spacetime to those in its post-Newtonian approximation. Moreover, we compare the magnitude of relativistic contributions to several typical perturbations of satellite orbits due to, e.g., solar radiation pressure, Earth’s albedo, and atmospheric drag. This comparison is done for our test scenarios and for a real GRACE orbit to highlight the importance of relativistic effects in geodetic space missions. For the considered orbits, first-order relativistic contributions give accelerations of about 20 nm/s2 and are dominant in the radial direction.
       
  • Exploring Titan's cryogenic hydrocarbon seas with boat-deployed expendable
           dropsondes
    • Abstract: Publication date: 15 August 2018Source: Advances in Space Research, Volume 62, Issue 4Author(s): Ralph D. Lorenz, Steven R. Oleson, Anthony J. Colozza, Robert Jones, Thomas Packard, Jason Hartwig, J. Michael Newman, John Z. Gyekenyesi, Paul Schmitz, Justin Walsh We present a preliminary design for a 3 kg expendable measurement system to descend to a depth of up to 1 km in the cryogenic hydrocarbon seas (Kraken and Ligeia Mare) of Saturn’s moon Titan. These could profile the temperature and gross composition (methane/ethane) and providing information on the constitution of the seabed. Particular features of the Titan environment distinct from Earth are (1) the interior of this small vehicle must be thermally isolated from the 94 K liquid (2) 1 km depth on Titan entails overpressures of only 10 bar, and (3) that the low dielectric loss of the liquid allows data transmission by radio link. A surface vessel equipped with such expendable dropsondes could accomplish much of the science previously considered for submersible vehicles, while avoiding the challenges of buoyancy control.
       
  • Determination of impact position on an impact ionization detector by
           electrostatic induction
    • Abstract: Publication date: 15 August 2018Source: Advances in Space Research, Volume 62, Issue 4Author(s): Yanwei Li, Sebastian Bugiel, Heiko Strack, Jonas Simolka, Zoltan Sternovsky, Sascha Kempf, Mihály Horányi, Eberhard Grün, Xingji Li, Ralf Srama The application of impact ionization for the measurement of micrometeoroids in space is a sensitive and established method for particles in the size range between a few nanometers and a few micrometers. For the measurement of micrometeoroid trajectories, the knowledge of the velocity vector and the related impact position is required. A typical impact ionization detector employs a hemispherically shaped conductive metal target, and a hemispherical grid electrode. The impact charge is dependent on the particle mass, particle speed and incident angle. For a collimated particle flux which is parallel to the symmetry axis, the impact direction and its related impact angle relative to the target normal varies with the radial distance from the symmetry axis. It is therefore essential to consider the impact position during calibration of impact ionization detectors. Furthermore, the induced charge signal shape varies with impact position. We perform simulations with the Coulomb software package and we do compare the results with experimental data. An empirical formula is derived to determine the impact location of the particle from the target and grid induction signals.
       
  • The shallow subsurface structures of Chang’E-3 landing site based on the
           wavefield characteristics of LPR Channel-2B data
    • Abstract: Publication date: 15 August 2018Source: Advances in Space Research, Volume 62, Issue 4Author(s): Na Zhao, Peimin Zhu, Yuefeng Yuan, Bingzheng Zhang, Jian Deng The Lunar Penetrating Radar (LPR) carried by the Yutu rover has imaged the shallow subsurface of the Chang’E-3 (CE-3) landing site at the northern Mare Imbrium. In this paper, by processing LPR Channel-2B data we obtained radar waveform profile. According to the radar wavefield characteristics in the profile, three evident strata can be discovered in the lunar shallow subsurface below the CE-3 site. Most notably, many arc-shaped reflection and/or diffraction events are observed in the profile, especially more in the second layer. In order to find out what caused those arc-shaped events, we conducted radar wavefield numerical simulation. The numerical simulation results reveal that those arc-shaped events are most possibly resulted in by the rocks of different sizes and shapes from the craters surrounding the landing site, especially the C1 crater.
       
  • Improved retrieval of aerosol optical depth from POLDER/PARASOL
           polarization data based on a self-defined aerosol model
    • Abstract: Publication date: 15 August 2018Source: Advances in Space Research, Volume 62, Issue 4Author(s): Yue Li, Long Li, Yong Zha The characterization of surface reflection and the selection of an appropriate aerosol model are key problems in aerosol retrieval over land. Due to the amount of polarized light reflected by ground targets is small, the selection of an aerosol model is the main problem in aerosol retrieval based on polarization data. In this study, a self-defined aerosol model is proposed to retrieve aerosol optical depth (AOD) from 2008 to 2009 in the Yangtze River Delta from Polarization and Directionality of the Earth’s Reflectance (POLDER) and Polarization and Anisotropy of Reflectance for Atmospheric Sciences coupled with Observation from a Lidar (PARASOL) data. The model was established using the volume percentages of aerosol components retrieved by Aerosol Robotic Network (AERONET) ground-based measurements. The results show that the volume percentages of aerosol components in the study area are 0.31, 0.55, 0.01 and 0.13 for dust, water-soluble, oceanic and soot particles, respectively, which are quite different from those of the continental model defined in the standard radiation atmosphere (SRA) aerosol models. The accuracy of AOD retrieved by the self-defined aerosol model (r = 0.75, RMSE = 0.20) is higher than that by the continental model (r = 0.41, RMSE = 0.39). Therefore, selecting a more suitable aerosol model can significantly improve the retrieval precision of AOD.
       
  • Coastal currents in the Eastern Gulf of Tehuantepec from coastal altimetry
    • Abstract: Publication date: 15 August 2018Source: Advances in Space Research, Volume 62, Issue 4Author(s): J. Salazar-Ceciliano, A. Trasviña-Castro, E. González-Rodríguez We study the seasonal and interannual variability of the coastal currents along the eastern shelf of the Gulf of Tehuantepec. We use sea level from coastal altimetry distributed by the Centre de Topographie des Océans et de l’Hydrosphère (Toulouse, France). Local validation using tide gauge and hydrographic data indicates that this coastal product measures well the seasonal and interannual scales along this tropical coastline. Long (12 years) time series of altimetry-derived currents, 39–57 km from the coast, reveal new details of the seasonal cycle: currents flow poleward from October to February and equatorward from April to August. Spectral analysis reveals that mesoscale processes are at least as energetic as the seasonal mean. The combination of both determines to a large extent the seasonal and interannual variability of the coastal currents.
       
  • A dynamic single epoch ambiguity resolution algorithm with straight
           trajectory constraints
    • Abstract: Publication date: 15 August 2018Source: Advances in Space Research, Volume 62, Issue 4Author(s): Ning Liu, Qin Zhang, Yangyang Yang The key problem of dynamic single epoch GPS positioning is the rapid decomposition of ambiguity. In some special dynamic positioning, the coordinates of the GPS receiver placed on the rover station often have the constraint condition, if this useful information is taken into account, it will help to determine the ambiguity accurately. For this reason, the straight motion trajectory of GPS receiver is used as the constraint condition for single epoch ambiguity resolution, in this algorithm, the wide lane ambiguities are calculated by using the MW combination, and the corresponding alternative combinations of wide lane ambiguity are established, which are determined according to the minimum residual sum of squares criterion firstly, it is used to lay the foundation for the subsequent L1 and L2 frequency ambiguity solution. And then the straight trajectory constraint condition and the phase observation equation are used to solve the integer ambiguity N1. When the constraint information of the trajectory is unknown, the space linear equation is established as the constraint condition according to the coordinate solution by wide lane relative positioning to solve the unknown problem. By designing the corresponding experiments, the results of this algorithm are proved to be feasible by using different experimental schemes, such as without constraint condition, the constraint condition with known prior information, introducing dynamic constraint condition and so on, to solve the ambiguity, and to compare and analyze the effect of linear constraint condition on single epoch ambiguity resolution.
       
  • Modeling of the GPS satellite clock error and its performance evaluation
           in precise point positioning
    • Abstract: Publication date: 15 August 2018Source: Advances in Space Research, Volume 62, Issue 4Author(s): Haojun Li, Xilin Liao, Bofeng Li, Ling Yang The different functions, which include the polynomial and the harmonics based functions, are used to model and extrapolate the GPS satellite clock for simplifying the service mode and real-time application. The modeling accuracy decreases with the increasing modeled time, when the polynomial functions are used. The 4th order harmonics based function is used to model the one-year single day satellite clocks. The results indicate that the accuracies of the modeled Rb clocks are better than 0.30 ns, while that of the Cs clocks just are better than 0.79 ns. Meanwhile, we noticed that the daily fitted amplitudes for 16 Block IIF and Block IIR-M Rb clocks vary regularly with a 6 months periodicity. This is mostly visible for the harmonics of 6 and 12 h periods. However the initial phases of these 12 and 6 h harmonics have obvious linear variation for the 16 Block IIF and Block IIR-M Rb clocks. Additional periods of 8 h, 4.8 h, 3.43 h and 2.67 h are noticed by analyzing the modeling residuals of 4th order harmonics based function. The modeling of 8th order harmonics based function is implemented and the modeled accuracy is improved. The extrapolated results of the 4th and 8th order harmonics based functions are better than that of the broadcast ephemerides and the predicted parts of International GNSS Service (IGS) Ultra-Rapid (IGU) products. The performances of the modeled clocks in precise point positioning (PPP) show that the results of 4th and 8th order harmonics based functions reach centimeter level although their convergence times are slower than that of the IGS clock series product.
       
  • The effect of geomagnetic activity changes on the ionospheric critical
           frequencies (foF2) at magnetic conjugate points
    • Abstract: Publication date: 15 August 2018Source: Advances in Space Research, Volume 62, Issue 4Author(s): Erdinç Timoçin, İbrahim Ünal, Yurdanur Tulunay, Ümit Deniz Göker In this work, we investigate the possible effects of geomagnetic activity on the ionospheric critical frequencies (foF2) in geomagnetic conjugate points. For this purpose, hourly foF2 data measured for the year 1976 from the ionosonde stations Akita, St. John's and Resolute Bay in the Northern hemisphere and their corresponding magnetic conjugate ionosonde stations Brisbane, Halley Bay and Scott Base in the Southern hemisphere are examined. Planetary geomagnetic activity “3h-Kp” indices are used as a geomagnetic activity indicator. foF2 data in the magnetic conjugate points (MCP) are investigated by using a superposed epoch analysis method. This analysis is done depending on the response of foF2 to geomagnetic activity variations in MCP based on geomagnetic stormy days around equinoxes (March 21, September 23) and solstices (June 21, December 21), and the results obtained from these MCP are compared. From these results, it is found that foF2 values in magnetic conjugate pairs give similar reactions to geomagnetic activity variations simultaneously, although this relationship differs according to the seasons and magnetic latitudes of the stations.
       
  • 3-D ionospheric tomography from dense GNSS observations based on an
           improved two-step iterative algorithm
    • Abstract: Publication date: 15 August 2018Source: Advances in Space Research, Volume 62, Issue 4Author(s): Shuanggen Jin, Du Li Computerized ionospheric tomography (CIT) can image 3-D ionospheric variations from ground Global Navigation Satellite System (GNSS) observations. However, due to the sparse and inhomogeneous ground GNSS observations, the prior information from the empirical models (e.g., IRI-2012 and NeQuick 2) have to be used, which affect the reconstructed results in the CIT, particularly the peak parameters of the F2 layer, namely foF2 and M(3000)F2. In this paper, an improved two-step CIT algorithm is developed to image the ionospheric electron density (IED) distribution up to 2000 km over Japan using dense GNSS Earth Observation Network (GEONET) observations operated by the Geospatial Information Authority (GSI) of Japan. Firstly, we update the IRI-2012 using the ground-based GNSS observations. The NeQuick-2 is used to provide the vertical ionospheric profile, and foF2 and M(3000)F2 derived from CCIR model in NeQuick 2 are improved by the B-spline modeling methods. Secondly, the updated IRI-2012 is input as a prior value and the multiplicative algebraic reconstruction technique (MART) is implemented to reconstruct the IED distribution. The reconstructed results are validated by the simulation and observation results from ground-based GNSS, GNSS Radio Occultation (GNSS-RO) observations and ionosonde measurements. The results demonstrate the feasibility and superiority of our new method. The standard deviations of TEC residual errors from the updated NeQuick 2 are at least 20% less than those from the original NeQuick 2 model, and the updated NeQuick 2 has better performance for the ionospheric correction.
       
  • Nonlinear dependence of ionospheric F2 layer critical frequency on solar
           activity in southern latitudes during solar cycle 23
    • Abstract: Publication date: 15 August 2018Source: Advances in Space Research, Volume 62, Issue 4Author(s): C.S. Seema, P.R. Prince Latitudinal, seasonal, and diurnal variations in the nonlinear response of F2 layer critical frequency (foF2) with respect to 10.7 cm solar flux data (F10.7) in southern stations during the 23rd solar cycle (1996–2008) are investigated. A two-segmented linear fit method is used in both ascending and descending phases of the cycle, thus revealing the nonlinear response of foF2 with F10.7. The rate of change in foF2 with respect to F10.7 may decrease (saturation) or increase (amplification) at high solar activity epochs. Furthermore, the foF2 values for the same F10.7 value differ between the ascending and descending phases of the cycle (hysteresis). The linear temporal increment of foF2 with F10.7 at low solar activity epochs is more evident in low-latitude stations. A low-latitude station, Vanimo, shows clear evidence of saturation in all seasons. In high-latitude stations, the effect is weak in the midnight to morning hours, particularly during the descending phase of the cycle. The amplification effect is dominant only at high latitudes mainly during early morning hours of March Equinox. Negative hysteresis effect is observed to be stronger at lower latitudes, but positive effects are seen to be stronger at higher latitudes.
       
  • Relative geoeffectiveness of high-speed solar wind streams from different
           solar sources
    • Abstract: Publication date: 15 August 2018Source: Advances in Space Research, Volume 62, Issue 4Author(s): Badruddin, F. Mustajab, M. Derouich We study relative geoeffectiveness of the high-speed streams (HSS) coming from different sources on the Sun, identified from 16 years (1996–2011) of continuous plasma and field data. These HSS could be associated to a single coronal hole, multiple coronal holes, single coronal mass ejection, multiple coronal mass ejections, or both the coronal holes and the coronal mass ejections. We analyze the solar wind plasma and field data during the passage of the HSS, and study the relative importance of different parameters in influencing the geomagnetic activity. We apply the method of superposed epoch analysis on the geomagnetic as well as solar plasma and field data. Based on our analysis, we found that the average (Dst)min is lowest (∼20 nT) due to streams from single coronal hole and multiple coronal holes, and it is comparatively higher (∼25 nT) due to compound streams. However, as compared to single coronal hole, the (Dst)min is nearly twice (∼40 nT) and thrice (∼65 nT) due to single coronal mass ejection and multiple coronal mass ejections, respectively. We found differences in not only the magnitudes but also the time profiles and recovery characteristics of geomagnetic disturbances due to the HSS from different solar sources. We performed correlation analysis between (Dst)min and the amplitudes of various plasma/field parameters, separately, due to the HSS associated with different solar sources. We found that, during the passage of all five group of streams, the (−Bz) and/or Ey is best correlated with the Dst amplitude. However, comparatively, the relationship between the amplitudes of (−Bz) and (−Dst) is weakest (cc = 0.71) during the passage of multiple coronal holes associated stream, and the relation is strongest (cc = 0.89) during the passage of single CMEs. As regards the relationship between (Ey) and (−Dst) amplitudes, it is weakest (cc = −0.71) during multiple coronal associated streams and strongest (cc = −0.91) during streams due to multiple coronal mass ejections.
       
  • The 2D features of tropical cyclone Usagi’s effects on the
           ionospheric total electron content
    • Abstract: Publication date: 15 August 2018Source: Advances in Space Research, Volume 62, Issue 4Author(s): Yuxin Zhao, Tian Mao, Jing-Song Wang, Zhou Chen The effects of the tropical cyclone Usagi on ionospheric total electron content (TEC) during September 16–24, 2013 are investigated based on the high spatial and temporal resolution TEC data. The Spectral Whitening Method (SWM), a new method to identify aperiodic disturbances, is applied to process the TEC map to ionospheric disturbances map. It is found that the ionosphere is most disturbed along the track of tropical cyclones (TC), and could change its behavior while the typhoon approaching the continent (as well as big island). It is the first result about the 2D features of the ionospheric responses to a tropical cyclone using SWM derived index Js.
       
  • Ray-tracing solar radiation pressure modeling for QZS-1
    • Abstract: Publication date: 15 August 2018Source: Advances in Space Research, Volume 62, Issue 4Author(s): Francesco Darugna, Peter Steigenberger, Oliver Montenbruck, Stefano Casotto Precise orbit determination requires accurate models for the orbital perturbations. Next to the well-known gravitational forces, the solar radiation pressure (SRP) is the main perturbation for navigation satellites. SRP results from the interaction between the photons of the Sun and the surfaces of the satellite. Hence, its modeling depends on proper knowledge of the geometry and optical properties of the satellite. Previous work showed that the use of an a priori box-wing model for the SRP significantly improves the estimated orbit products as well as orbit predictions compared to purely empirical models. However, the presently available box-wing models for the first satellite of the Japanese Quasi-Zenith Satellite System, QZS-1, do not consider an accurate geometry. Based on a computer-aided design model of the QZS-1 satellite, a ray-tracing simulation is performed to compute SRP accelerations in a more realistic manner. The resulting SRP model is validated through QZS-1 precise orbit determination over a two year data arc covering yaw-steering and orbit-normal attitude regimes. In yaw-steering mode, the ray-tracing model shows a better overall performance than a box-wing model and improves the standard deviation of QZS-1 satellite laser ranging residuals by a factor of three compared to orbits without a priori model. On the other hand, the ray-tracing SRP model does not account for thermal accelerations and thus performs worse than an adjusted box-wing model in orbit-normal mode.
       
  • List of Referees
    • Abstract: Publication date: 1 August 2018Source: Advances in Space Research, Volume 62, Issue 3Author(s):
       
  • New manoeuvre detection method based on historical orbital data for low
           Earth orbit satellites
    • Abstract: Publication date: 1 August 2018Source: Advances in Space Research, Volume 62, Issue 3Author(s): Tao Li, Kebo Li, Lei Chen A new method of deriving satellite manoeuvring information from historical two-line element (TLE) data is proposed. The historical manoeuvres of a satellite are detected by identifying abnormal data segments in the TLE derived time series of selected orbital parameters (semi-major axis and inclination). Firstly, moving window approach is used to divide the time series into a series of equal-length data segments. Secondly, two anomaly indexes are introduced to measure the anomaly degree of the semi-major axis segment and the inclination segment with respect to the propagated states. Finally, the corresponding detection thresholds are separately derived by analysing the anomaly indexes of the two types of data segments indicative of orbit manoeuvre. When the anomaly index of a semi-major axis segment or inclination segment exceeds the corresponding threshold, a specific type of orbit manoeuvre with specific magnitude is declared. The manoeuvre detection results of two low Earth orbiting satellites indicate that the proposed method can efficiently eliminate data noise interference and accurately detect historical manoeuvres. Furthermore, manoeuvres with designated magnitudes can be exclusively detected by adjusting the user-specified arguments in the threshold expression levels.
       
  • Study on command attitude law for refracted starlight observation in
           SINS/RCNS integrated navigation
    • Abstract: Publication date: 1 August 2018Source: Advances in Space Research, Volume 62, Issue 3Author(s): Haiyong Wang, Ziqian Gao, Tengfei Wang, Guoyuan Tian To ensure the validity of refracted starlight observation, a command attitude law for maneuver is built for strapdown star sensor. The constraint relations between the relative attitude angles and the constant boresight apparent height are first established, by which attitude control command is generated, and the following attitude maneuver enables the star sensor FOV (Field of View) to keep covering the stratosphere during the midcourse. The simulating environment is set up, which involves the schema trajectory designing, the simulating algorithm of refracted star map and the modeling of the complete autonomous SINS/RCNS (Strapdown Inertial Navigation System/Refraction Celestial Navigation System) integrated navigation system. In the SINS/RCNS integrated navigation, the star sensor boresight is directed to the stratosphere in a suitable height with the command attitude law. The test simulation results show that the SINS/RCNS system prominently increases the precision of position and velocity at reentry point by 87.8% and 39.5% respectively than the sole SINS, and using of wide FOV helps to increase the positioning accuracy.Graphical abstractGraphical abstract for this article
       
  • Modified kernel regression method for the denoising of X-ray pulsar
           profiles
    • Abstract: Publication date: 1 August 2018Source: Advances in Space Research, Volume 62, Issue 3Author(s): Jianing Song, Jiawei Qu, Guodong Xu In this paper, a modified kernel regression algorithm is proposed to reduce the noise of pulsar profiles autonomously. Taking advantage of the classical autonomous kernel regression the presented algorithm based on the second-order derivative compensation is developed to improve the performance of the Nadaraya-Watson kernel estimator. The periodic extension technique is introduced to eliminate the boundary issue inherent in kernel regression means. Four indexes are utilized to explore the performance of the proposed method via both emulated and real data. Additionally, other widely accepted denoising methods based on wavelet transformation and empirical model decomposition are simulated to make a comparison. The experimental results have shown that the proposed algorithm achieves a higher quality profile than the compared methods, which will help to discover the emission mechanism of pulsars. According to our experiments, we would like to point out that a smooth profile cannot guarantee an accurate measurement (time of arrival, TOA), which indicates that it is not necessary to denoise the epoch folding profile for estimating the TOA information in X-ray pulsar-based navigation systems.
       
  • Two-phase shaping approach to low-thrust trajectories design between
           coplanar orbits
    • Abstract: Publication date: 1 August 2018Source: Advances in Space Research, Volume 62, Issue 3Author(s): Kui Zeng, Baolin Wu, Yunhai Geng To rapidly design low-thrust trajectories between coplanar orbits for the orbit transfer and rendezvous problems, an analytic shape-based approach is proposed. Unlike all of the existing analytic shape-based approaches, the trajectory is divided into two phases. The finite Fourier series functions are employed to shape each phase of the trajectories. As a result, the fitting performance for the transfer and rendezvous trajectories by using the proposed method is improved. Consequently, the proposed approach can provide solutions with less fuel consumption and smaller maximum thrust acceleration. In addition, the trajectory safety is also ensured by the proposed method. The effectiveness of the proposed approach is validated by extensive numerical simulations.
       
  • A New Compound Control for Mars Entry Guidance
    • Abstract: Publication date: 1 August 2018Source: Advances in Space Research, Volume 62, Issue 3Author(s): Ganghui Shen, Yuanqing Xia, Lijun Zhang, Jinhui Zhang, Bing Cui In this paper, a novel compound control method consisting of adaptive finite-time sliding mode control (AFTSMC) law and final position guidance (FPG) is proposed to achieve high-precision guidance for Mars entry. In the first stage of entry, by employing adaptive law and extended state observer (ESO), an AFTSMC law is designed to avoid the overestimating control gains and then eliminate the chattering effectively. Furthermore, the proposed AFTSMC law not only provides strong robustness against uncertainties but also achieves finite-time convergence of tracking error. In the second stage, a new FPG is used to accurately deliver the vehicle to the required target in three-dimensional space. Therefore, the compound controller combines the advantages of AFTSMC law and FPG method, and numerical simulation results show that the proposed compound controller can not only provide favorable control performance but also improve the entry guidance precision under large uncertainties.
       
  • Phase-matching homotopic method for indirect optimization of long-duration
           low-thrust trajectories
    • Abstract: Publication date: 1 August 2018Source: Advances in Space Research, Volume 62, Issue 3Author(s): Chuanmin Guo, Jin Zhang, Yazhong Luo, Luyi Yang For low-thrust trajectory designs, indirect optimization methods remain attractive, as they can guarantee optimality. Previous studies presented many effective ways to overcome the problems in the indirect optimization process, but they still suffer from the initialization difficulty and numerical instability for the long-duration many-revolution problems. A method with three major steps is proposed to conquer those difficulties. First, the original trajectory with the energy objective function is divided into multiple phases with relatively short time of flight by several trials of indirect optimization. Second, the number of phases is reduced by a smoothing procedure, and the whole trajectory with multiple phases is now improved to be close to the undivided and energy-optimal one. Third, the near-optimal trajectory with the fuel objective function is solved by homotopic iterations. In addition, two specific treatments for the search of the initial co-state variables are designed to improve the convergence ability. The proposed method is applied to solving several kinds of low-thrust transfer problems, including an Earth-Venus transfer, a large orbital rendezvous transferring to the hyperbolic orbit and a very-low-thrust orbital rendezvous transfer. Moreover, a comparison between the proposed method and the multiple-shooting method is made by solving an LEO-GEO (low Earth orbit to geostationary Earth orbit) transfer problem. The results show that the proposed method can successfully obtain the near-optimal solutions with high convergence rate.
       
  • A geometrical approach to association of space-based very short-arc LEO
           tracks
    • Abstract: Publication date: 1 August 2018Source: Advances in Space Research, Volume 62, Issue 3Author(s): Xiangxu Lei, Kunpeng Wang, Pin Zhang, Teng Pan, Huaifeng Li, Jizhang Sang, Donglei He Conventional methods of association between uncorrelated tracks (UCTs) require knowledge of UCT covariance and their accurate propagations, which are difficult to achieve in some cases. For space-based angles-only very short-arc (SBVSA) LEO tracks, errors of initial tracks determined through the initial orbit determination (IOD) could be very large, for example, the semi-major axes (SMA) could have errors exceeding 100 km. Therefore, the conventional methods may fail if two tracks are apart by tens of orbital periods because of the need to correctly propagate the errors over the time span. In this paper, a geometrical approach to associating the SBVSA LEO tracks is proposed. This approach uses an analytical orbital propagator to propagate two UCTs to the middle of the time interval, and then adjust the SMA of one UCT to minimise position difference between the two UCTs at the middle point. After several iterations, an acceptable along track bias is obtained and a judgement on whether the two UCTs are associated is made. Preliminary simulations show that, the true positive rate is about 90% for LEO near-circular UCT associations. Furthermore, the geometrical method is tested on the non-circular LEO track association problem, the true positive rate is about 80%. A comparison with the Covariance Based Track Association (CBTA) method is also presented in the paper.
       
  • An environmental estimation model for in-situ measurements of small space
           debris
    • Abstract: Publication date: 1 August 2018Source: Advances in Space Research, Volume 62, Issue 3Author(s): Masahiro Furumoto, Toshiya Hanada Space debris smaller than 2 mm that cannot be detected by ground-based observations may lead to a spacecraft's missions end. Therefore, IDEA, the project for In-situ Debris Environmental Awareness, which aims to detect sub-millimeter-size debris using a group of micro satellites, has been initiated at Kyushu University. To estimate the debris environment based on in-situ measurements from the project, this paper proposes an environmental estimation model with a Sequential Monte Carlo (SMC) filter. First, this paper reviews the previous research that investigated the nature of an orbit on which a piece of debris can be detected through in-situ measurements, and applies this phenomenon to the algorithm of the SMC filter. Second, the proposed model is evaluated by a simulation using MASTER-2009, which is the environmental model developed at European Space Agency. Comparison between the debris distributions predicted by MASTER-2009 and the simulated estimation verifies that the proposed model can estimate the debris environment sufficiently. Finally, this paper also investigates the effect of the measurement duration on the estimation. It is concluded, therefore, that the estimation model proposed and evaluated in this paper can provide a better definition of the sub-millimeter-size debris environment with in-situ measurements.
       
  • Physics of meteor generated shock waves in the Earth’s atmosphere
           – A review
    • Abstract: Publication date: 1 August 2018Source: Advances in Space Research, Volume 62, Issue 3Author(s): Elizabeth A. Silber, Mark Boslough, Wayne K. Hocking, Maria Gritsevich, Rodney W. Whitaker Shock waves and the associated phenomena generated by strongly ablating meteoroids with sizes greater than a few millimeters in the lower transitional flow regime of the Earth’s atmosphere are the least explored aspect of meteor science. In this paper, we present a comprehensive review of literature covering meteor generated shock wave phenomena, from the aspect of both meteor science and hypersonic gas dynamics. The primary emphasis of this review is placed on the mechanisms and dynamics of the meteor shock waves. We discuss key aspects of both shock generation and propagation, including the great importance of the hydrodynamic shielding that develops around the meteoroid. In addition to this in-depth review, the discussion is extended to an overview of meteoroid fragmentation, followed by airburst type events associated with large, deep penetrating meteoroids. This class of objects has a significant potential to cause extensive material damage and even human casualties on the ground, and as such is of great interest to the planetary defense community. To date, no comprehensive model exists that accurately describes the flow field and shock wave formation of a strongly ablating meteoroid in the non-continuum flow regime. Thus, we briefly present the current state of numerical models that describe the comparatively slower flow of air over non-ablating bodies in the rarefied regime. In respect to the elusive nature of meteor generated shock wave detection, we also discuss relevant aspects and applications of meteor radar and infrasound studies as tools that can be utilized to study meteor shock waves and related phenomena. In particular, infrasound data can provide energy release estimates of meteoroids entering the Earth’s atmosphere. We conclude with a summary of unresolved questions in the domain of meteor generated shock waves; topics which should be a focus of future investigations in the field.
       
  • Formation of multiple landers for asteroid detumbling
    • Abstract: Publication date: 1 August 2018Source: Advances in Space Research, Volume 62, Issue 3Author(s): Michael C.F. Bazzocchi, M. Reza Emami This work develops a method for ascertaining the landing locations and thruster orientations of a formation of multiple spacecraft on an irregular asteroid for discrete time optimal detumbling control, as a prerequisite to asteroid redirection. Asteroid geometries are known to be extremely irregular, especially for small asteroids, which are the typical targets for redirection missions. The method entails the modelling of asteroids as convex polyhedra with triangular facets, and computing the mass and inertial properties through the divergence theorem and Green’s theorem. Given the asteroid geometry, mass, and inertial properties, the feasible lander locations and thruster orientations are determined. The model ensures full attitude control of the asteroid, using multiple spacecraft with fixed-orientation, low-thrust modules, through measures imposed on the location and orientation of each thruster. A linear control scheme is employed to assess the time and fuel requirements of the asteroid detumbling maneuver, given feasible spacecraft formation configurations and thruster orientations. The method then assesses the detumbling time performance of each formation configuration to determine the discrete optimal landed formation configuration for a given asteroid. Simulations are performed to demonstrate the method using an irregular asteroid with characteristics derived from available asteroid data. Extensions of the method are further discussed in light of the results.
       
  • Grid fins shape design of a launch vehicle based on sequential
           approximation optimization
    • Abstract: Publication date: Available online 12 July 2018Source: Advances in Space ResearchAuthor(s): Ke Peng, Fan Hu, Donghui Wang, Patrick N Okolo, Min Xiang, Gareth J. Bennett, Weihua Zhang This paper performed the optimization of grid fins shape of a launch vehicle based on Sequential Approximation Optimization (SAO) and Computational Fluid Dynamics (CFD) simulation coupling. An efficient and reliable method is proposed for determining the width of Gaussian functions based on a logical relationship between the width and local density. The performance of the proposed method is evaluated using five classical test functions. The proposed method for width determination generates almost no excessive calculation costs, and improves the accuracy, reliability, and stability of the Radial Basis Function (RBF) surrogate model notably. Based on the improved RBF surrogate model, a framework and detailed procedure for the SAO algorithm is presented, and the performance of the proposed SAO algorithm is tested, with obtained results showing that the proposed SAO algorithm reduces the calling times of the original model and improves the optimization efficiency remarkably. The objective function is strictly deduced and reflects the momentum loss caused by aerodynamic drag directly. Three constraints are imposed to ensure the static stability and controllability of the launch vehicle. Finally, grid fins shape optimization problem of the launch vehicle is solved, with the objective function and constraints calculation tasks accomplished automatically by batch mode CFD simulations. The global optimal solution is obtained after 54 calling times of the original model, and 92 hours (3.84 days) of computation on a 96-core cluster. Once the baseline shape is replaced with the optimized shape, it is detected that (1) taking the minimum fuel as an objective function, the take-off mass is 2.07% lighter than the take-off mass of the baseline shape, (2) taking the maximum payload mass as an objective function, the payload mass is 14.3% heavier than the payload mass of the baseline shape.
       
  • Vertical Coupling between the Mesopause region and Sporadic-E layer during
           Equatorial Counter Electrojet events - A case study
    • Abstract: Publication date: Available online 11 July 2018Source: Advances in Space ResearchAuthor(s): A.Ajesh., T.K. Pant, C. Vineeth, N. Mridula, K.K. Kumar This paper presents a case study exploring the variability of daytime ionospheric sporadic E (Es) during Counter Equatorial Electrojet (CEJ) events over Trivandrum (8.5o N, 77o E, 0.5o N dip lat.), a dip equatorial station in India. It makes use of collocated measurements of (a) daytime mesopause temperature estimated using a Multiwavelength Dayglow Photometer, (b) base height of sporadic E-layer i.e. Esq obtained from a Digital Ionosonde, (c) Equatorial Electrojet (EEJ) induced magnetic field at the surface measured using a Proton Precession Magnetometer and (d) neutral meridional and zonal winds measured using meteor wind radar. The study addresses why, only on certain CEJ days, the Es layer turns into a blanketing Es layer, also referred to as Esb layer, appearing for a brief period and almost simultaneously as the CEJ induced magnetic field on the surface is either zero or very small, and not on all the CEJ days despite the reversal of the zonal winds in the dynamo region (∼98 km). Further, a simulation using the simultaneously measured zonal wind and temperature shows that during CEJ, especially when the zonal wind reverses and the mesopause temperature lowers, the conditions are in fact less favourable for the ionization to converge resulting in Esb. On the other hand, on such occasions, the meridional wind exhibits a tendency to turn equatorward with time with the changeover gradually happening as the altitude decreases. These observations have been discussed to allude to the possible role of the overall wind system and its spatio-temporal changes in the ionospheric altitudes which could influence the gradual transition of Esq to Esb over the dip equator.
       
  • PL612 LOFAR station sensitivity measurements in the context of its
           application for pulsar observations
    • Abstract: Publication date: Available online 11 July 2018Source: Advances in Space ResearchAuthor(s): L.P. Błaszkiewicz, W. Lewandowski, A. Krankowski, J. Kijak, A. Froń, T. Sidorowicz, B. Dąbrowski, K. Kotulak, M. Hajduk The Low Frequency Array (LOFAR) is relatively new interferometric radio telescope. LOFAR operates in poorly explored part of the spectrum (10-240 MHz. In this frequency range pulsars are bright, and LOFAR observations of pulsars are import for probing fundamental physics and the interstellar medium. In this work we present the description of the international LOFAR station frontend and backend parameters related to pulsar observations with a single LOFAR station, based on observations with the Polish station, located in Bałdy near Olsztyn. We present new results from observations aimed at better characterizing the telescope sensitivity. These measurements are important for efficient planning of pulsar observating campaigns. Observations show good sensitivity for pulsar measurements above 25 degrees elevation and show the noise level rises significantly for elevations below 25 degrees.
       
  • Torque model verification for the GOCE satellite
    • Abstract: Publication date: Available online 5 July 2018Source: Advances in Space ResearchAuthor(s): Tim Visser, Eelco N. Doornbos, Coen C. de Visser, Pieter N.A.M. Visser, Bent Fritsche The modeling of torques acting on satellites is essential for the design of satellite attitude control systems. The GOCE satellite, equipped with accurate accelerometers, star trackers and GPS receivers, presents an opportunity to validate these models. Although the forces on GOCE and other accelerometer-carrying missions have been extensively analyzed in the past, a similar analysis has so far not yet been made for the torques.In this paper, we present a set of torque models for the GOCE satellite. It consists of six main parts: (1) magnetic torquer actuators, (2) aerodynamic torque, (3) gravity gradient torque, (4) solar radiation pressure torque, (5) thruster torque, and (6) passive magnetic torque. The magnetic properties of the payload are approximated using a parametrization, of which the parameters are estimated from the observation data.Based on data recorded during selected spacecraft events, the model for the control torques can be validated and error sources are identified in the other models. The models perform best in roll and pitch, where the standard deviation is reduced to 15.2% and 2.1% of the standard deviation of the control torque around those axes respectively. In yaw the standard deviation is significantly larger at 30.5%. The remaining differences between models and observations show magnetic signatures due to electric currents and signatures of aerodynamic model errors. The latter correspond well with an increase in thermosphere density and wind speed with increased geomagnetic activity. The pitch torque is found to be a potential source of vertical wind data.
       
  • Lithological discrimination using ASTER and Sentinel-2A in the Shibanjing
           ophiolite complex of Beishan orogenic in Inner Mongolia, China
    • Abstract: Publication date: Available online 4 July 2018Source: Advances in Space ResearchAuthor(s): Wenyan Ge, Qiuming Cheng, Linhai Jing, Costas Armenakis, Haifeng Ding The Shibanjing ophiolite complex, located in the Mingshui-Shibanjing-Xiaohuangshan ophiolite belt of Beishan collage, is one of the most important components in the Beishan orogenic belt, Inner Mongolia, China. It comprises tectonic slices of ophiolite rocks including mylonitic gabbros, meta-ultramafic rocks, metabasalts, and clastic rock in a matrix of turbidites, and the mélange contains blocks of schists, gneiss, and marble. In this study, multispectral data Sentinel-2A and ASTER were employed to discriminate lithological units in the unvegetated arid region. Several image enhancement algorithms, including Band Ratio (BR), Principal Components Analysis (PCA), Minimum Noise Fraction (MNF), and Support Vector Machine (SVM), were applied to the data for lithological mapping. A specialized band ratio, (Sentinel-2A band 3+ASTER band 9)/(Sentinel-2A band 12+ASTER band 8), combining ASTER and Sentinel-2A data was designed to distinguish serpentine minerals in the ophiolite complex. Color composites of principal components (PCs) of ASTER and Sentinel-2A data were utilized to differentiate rock units within the ophiolite complex. It was found that the color composites of PCs of Sentinel-2A have higher color contrast and saturation than ASTER, enabling to better visually interpret the ophiolite rock units and provide a more detailed geological map of the study area. The SVM classification results of the original and MNF versions of the ASTER data indicate that the image processing methods such as MNF could highlight specific rock units and improve classification accuracy. In addition, with the comparison between MNF images for lithological classification of Sentinel-2A and ASTER data, it was demonstrated that Sentinel-2A data outperformed ASTER in lithological mapping in the Shibanjing ophiolite complex.
       
  • Space tether deployment with explicit maximum libration angle constraint
           and tension disturbance
    • Abstract: Publication date: Available online 4 July 2018Source: Advances in Space ResearchAuthor(s): Ming Liu, Zheng H. Zhu, Xingqun Zhan This paper investigates the deployment control problem of tethered space systems subject to an explicit constraint of maximum libration angle and disturbance of tether tension. A two-stage control procedure is developed to design a simple and effective tension control law that is capable of limiting the magnitude of libration angle and suppressing the tension disturbance in the tether deployment process. First, the deployment reference trajectory is designed by a modified barrier Lyapunov function with an explicit constraint on the maximum libration angle. Then, a disturbance observer-based tension control law is developed to track the reference trajectory with the consideration of tension disturbance. Stability analysis of the controller shows that the estimate and tracking errors are bounded to desired ranges. Simulation results demonstrate the proposed simple tension control law is effective and robust in restricting the maximum amplitude of libration angle and suppressing tension disturbance, while guaranteeing a stable deployment without tether slack.
       
  • Real-time cycle slip correction for a single triple-frequency BDS receiver
           based on ionosphere-reduced virtual signals
    • Abstract: Publication date: Available online 4 July 2018Source: Advances in Space ResearchAuthor(s): Xiao Gao, Zhiqiang Yang, Ying Liu, Bing Yang Being an essential part of GNSS processing, cycle slip detection and repair has been intensively investigated. This paper develops an improved real-time cycle slip correction method based on three types of independent linear combinations of time-difference triple-frequency BDS observables. At first, one geometry-free pseudorange minus phase linear combination is selected as extra-wide lane (EWL) virtual signal and its cycle slips can be easily detected and repaired due to the long wavelength. Then, one geometry-free phase combination, treated as wide lane (WL) signal, is used to detect and repair cycle slips on WL combination based on fixed EWL ambiguity. Similarly, another one geometry-free phase combination is adopted to correct cycle slips on narrow lane (NL) signal. As a result of the short wavelength of NL combination, the residual ionospheric delay cannot be ignored and should be accurately estimated by the original observables. When the time-difference ambiguities of EWL, WL and NL signals are determined, the cycle slips on the original observables can be uniquely corrected by matrix operation. As the ionospheric delay plays a vital role in estimating ambiguities of combination signals, the second-order time-difference of ionospheric delay is used to detect the epoch with cycle slips and participate in estimating the time-difference ambiguity of NL signal. Considering that satellite elevation can be treated as quality factor of observables, we build a model to calculate the standard deviations of the selected combinations and 20 degree can be used as threshold value to correct cycle slips or not. The method has been tested on real 30s triple-frequency BDS data with artificial cycle slips. Results show that the three-step method can detect and repair cycle slips correctly and effectively when the elevation is higher than 20 degree. While the elevation is lower than the threshold, the cycle slips should just be detected without repair to avoid miscalculation.
       
  • The relationship between equatorial ionization anomaly and nighttime
           equatorial spread F in East Africa
    • Abstract: Publication date: Available online 4 July 2018Source: Advances in Space ResearchAuthor(s): Ephrem Beshir, Melessew Nigussie, Mark B. Moldwin We study the relationship of equatorial ionization anomaly (EIA) to the occurrence of nighttime spread F using data from ground-based GPS stations and a horizontal meridional neutral wind model for the East African sector. Anomaly strength and symmetry and magnitude of rate of TEC index (ROTI), which are obtained from TEC observations, are compared. We find the appearance of strong EIA with mean crest to trough ratio (CTR) ≥ 1.4 and symmetrical EIA with mean north crest to south crest ratio (CCR) between 1 ± 0.1 TEC at conjugate stations (≈ ± 11.5 magnetic latitudes) and other north-south stations between 16:00 UT (19:00 LT) and 18:00 UT (21:00 LT) are good conditions for the occurrence of night time spread F with the conjugate stations being better. The rate of TEC index (ROTI) is found to be relatively large when CCR of EIA are symmetrical (CCR between 1± 0.1) and CTR is ≥ 1.4, but decreases as the CCR of EIA shows asymmetry and/or CTR of EIA is < 1.4. EIA magnitude strength and symmetry between 18:00 UT to 20:45 UT are not well related with spread F occurrences. Post-sunset spread F occurrence close to anomaly crest locations are found to be greater than spread F occurrence at magnetic equatorial station. Shifting of EIA crest locations on either side of the magnetic equator is found to depend on season and meridional wind magnitude and direction. The relative difference in spread F occurrence among the four seasons is also discussed.
       
  • Horizontal spatial correlation of the ionospheric TEC derived from GPS
           global ionospheric maps
    • Abstract: Publication date: Available online 3 July 2018Source: Advances in Space ResearchAuthor(s): Shuo Liu, Jinsong Yang, Tao Yu, Zhiqiang Zhang The spatial correlations of ionospheric day-to-day variability are investigated by statistical analysis on TEC production that provided by the Jet Propulsion Laboratory (JPL). First, we use the monthly-averaged TEC over the world to calculate the deviation of the TEC and then the spatial correlation coefficient matrix of the deviation is also derived. According to the definition of correlation distance in statistics, the spatial characteristic scale is retrieved in the Zonal and meridian directions, and their variation of solar activity levels, geomagnetic field configuration conditions and seasonal conditions are investigated in details. Our study indicates strong correlations between geomagnetic conjugate points, which are large at low-latitudes than at mid-latitudes. Furthermore, in the equatorial anomaly region, due to the process of forming double crest structure, the electron distribution at low-latitudes will be affected by the upwelling of the plasma, thus the anomaly of correlation scale is notable. The correlation scale, which usually increases in LT 6:00, peaks at LT 12:00 and LT 14:00 and then decreases. It is overall larger in the daytime and smaller in the nighttime. These spatial correlations are important for understanding the physical mechanisms that cause ionospheric weather variability. For the potential application in development of ionospheric data assimilation model, the spatial correlations are fitted by elliptic Gaussian formula scale. In general, the correlation scale is regressed better in the Zonal direction than in the Meridional direction, better in low-latitude than in middle-latitude, and better in spring and autumn than in winter and summer. These results can help us to accurately construct the background field error covariance matrix in ionospheric data assimilation.
       
  • A Transfer Network Linking Earth, Moon, and the Triangular Libration Point
           Regions in the Earth-Moon System
    • Abstract: Publication date: Available online 3 July 2018Source: Advances in Space ResearchAuthor(s): Lucia R. Capdevila, Kathleen C. Howell In the near future, several space applications in the Earth-Moon system may require a spacecraft to hold a stable motion, but the transfer trajectory infrastructure to access such stable motions has not been fully investigated yet. The triangular libration points, L4 and L5, in the Earth-Moon system have long been thought of as potential locations for a communications satellite. Recently, Distant Retrograde Orbits (DROs) and Near-Rectilinear Halo Orbits (NRHOs) in the vicinity of the Moon have been identified as orbits of interest for manned and unmanned missions with a focus on operations in cislunar space. The triangular libration points, as well as lunar DROs and NRHOs describe special types of possible motion for a spacecraft/satellite that is influenced solely by the gravitational fields of the Earth and the Moon. What is common to the three types of solutions is that they are practically stable, that is, a spacecraft/satellite can naturally follow the solution for extended periods of time without requiring significant course adjustment maneuvers. This investigation proposes the lunar region as the central link to a transfer network that enables travel throughout the Earth-Moon system, connecting the lunar region to the vicinity of the Earth and the neighborhood of the triangular libration points. The work presented here also contributes to the infrastructure supporting such a network by expanding the transfer options available between these regions. Several new transfer options between regions of stability are presented and discussed, including transfer options between Low Earth Orbit (LEO) and lunar DRO, lunar DRO and periodic orbits near L4 and L5, as well as lunar DRO and L2 NRHOs. Underlying dynamical mechanisms enabling transfers between selected orbits are analyzed, and sample itineraries are provided.
       
  • Atmospheric test environments for planetary in-situ missions: Never quite
           “Test as you fly”
    • Abstract: Publication date: Available online 3 July 2018Source: Advances in Space ResearchAuthor(s): Ralph D. Lorenz The planetary atmospheric and surface environments that planetary probes, landers and rovers may encounter cannot be perfectly replicated in tests on Earth. The temperature, pressure and composition of atmospheric test environments for previous missions are reviewed, and the differences between the conditions used in tests and the actual conditions at the target body are discussed. Generally, it has been the practice to replicate only those few key parameters that determine the phenomena of interest, and the effects of gravity and of minor atmospheric constituents are rarely simulated explicitly. Typically tests have been performed in nitrogen atmospheres (rather than carbon dioxide for Mars and Venus) or Helium (instead of hydrogen for Jupiter): exceptions are a handful of specific tests where the composition was considered critical. In-flight thermal anomalies are generally attributable to differences between the static conditions in a test chamber and the dynamic environment of flight, rather than to the composition of test atmospheres.
       
  • Construction of a BDSPHERE solar radiation pressure model for BeiDou GEOs
           at vernal and autumn equinox periods
    • Abstract: Publication date: Available online 3 July 2018Source: Advances in Space ResearchAuthor(s): Xiaojie Li, Rui Guo, Xiaogong Hu, Chengpan Tang, Shan Wu, Zhiqiao Chang, Shuai Liu Geostationary Earth Orbit (GEO) satellites are important components of the BeiDou System (BDS). Long-term orbit ephemeris accuracy monitoring in the Operational Control System (OCS) of BDS indicates that the orbit accuracy for the BDS GEOs is unstable and degraded by several meters during the vernal and autumn equinox periods of each year. The SPHERE solar radiation pressure (SRP) model does not do a good job of reflecting the characteristics of the SRP during equinox periods. In view of this problem, this study proposes to replace SPHERE with BDSPHERE for the BDS GEOs during both equinox and non-equinox periods. We smooth the orbits of the BDS GEOs provided in SP3 precise orbit file format of Wuhan University (WHU, Wuhan, China) in the Multi-GNSS Pilot Project (MGEX), re-estimate the SRP parameter over a 2-year period and construct a 2-year continuous time series of the SRP model parameter. By analyzing the time series, a BDSPHERE model is constructed. The polynomial coefficients during the equinox periods are determined based on historical data and new data. Experiments with Beidou data show that during the equinox periods the orbit-only contribution to the signal-in-space range error (SISRE(ORB)) using the BDSPHERE model for GEOs in orbit determination arc and the 8-h and 24-h orbit predictions arc are 0.77, 0.80 and 1.62 m, respectively, which are smaller than those of the conventional SPHERE model by 53%, 60% and 61%, respectively. An evaluation based on global satellite laser ranging (SLR) data shows that during the equinox periods the BDSPHERE model can provide a radial orbit accuracy of 0.61 m, which is 70% better than that of the SPHERE model, and reach the SPHERE model's orbit accuracy in non-eclipsing periods. The BDSPHERE model during equinox periods considerably improves the orbit accuracy and stability of the BDS GEOs. This paper can provide technical support for constructing SRP models for the BDS.
       
  • Atmospheric Chaoticity and Complexity from Radio Refractivity Derived from
           Akure Station
    • Abstract: Publication date: Available online 1 July 2018Source: Advances in Space ResearchAuthor(s): B.O. Ogunsua, J.S. Ojo, A.T. Adediji Understanding the hidden dynamics of the atmosphere and its effect on radio wave propagation is paramount. Therefore proper characterization of atmospheric dynamics especially for its annual and seasonal variation is necessary. In this paper, atmospheric weather parameters (pressure, relative humidity and temperature), were used to obtain the radio refractivity at the surface Ns level, at 100 m height, N100 and the differential radio refractivity dN/dH. The extracted radio refractivity parameters were characterized based on chaoticity and dynamical complexity, for Akure meteorological station (7° 15' 9.22“ N, 5° 11' 35.23” E). The data analysis has been based on the Combined application of Largest Lyapunov Exponent and Tsallis Entropy (CLLETE). The data sets for the year 2011 and 2012 have been used for the computation. It was observed that the CLLETE parameters follow similar trend in most cases, and the Lyapunov exponent is generally positive indicating the presence of chaos for all radio refractivity data sets. It was further revealed that the pattern of the dynamical complexity variations in 2012 follow a similar trend from July to December for N100 and dN/dH with the values of the dynamical complexity parameters computed for NS having a huge departure from the other two heights with lower complexity values. However, the dynamical complexity parameters computed for NS and N100 a have similar a trend from the beginning of the year to June. The values of the Chaos and complexity parameters also show a similar variation in 2011 with NS following the same trend between July and December. This indicates the dynamical response of radio refractivity to varying weather conditions.
       
  • Physics and Human-Based Information Fusion for Improved Resident Space
           Object Tracking
    • Abstract: Publication date: Available online 1 July 2018Source: Advances in Space ResearchAuthor(s): Emmanuel Delande, Jérémie Houssineau, Moriba Jah Maintaining a catalog of Resident Space Objects (RSOs) can be cast in a typical Bayesian multi-object estimation problem, where the various sources of uncertainty in the problem – the orbital mechanics, the kinematic states of the identified objects, the data sources, etc. – are modeled as random variables with associated probability distributions. In the context of Space Situational Awareness, however, the information available to a space analyst on many uncertain components is scarce, preventing their appropriate modeling with a random variable and thus their exploitation in a RSO tracking algorithm. A typical example are human-based data sources such as Two-Line Elements (TLEs), which are publicly available but lack any statistical description of their accuracy. In this paper, we propose the first exploitation of uncertain variables in a RSO tracking problem, allowing for a representation of the uncertain components reflecting the information available to the space analyst, however scarce, and nothing more. In particular, we show that a human-based data source and a physics-based data source can be embedded in a unified and rigorous Bayesian estimator in order to track a RSO. We illustrate this concept on a scenario where real TLEs queried from the U.S. Strategic Command are fused with realistically simulated radar observations in order to track a Low-Earth Orbit satellite.
       
  • Rain fade duration prediction models for A high elevation angle based on
           measured data in tropical climate
    • Abstract: Publication date: Available online 1 July 2018Source: Advances in Space ResearchAuthor(s): Hassan Dao, Megat Farez Azril Zuhairi, MD Rafiqul Islam Rain fade duration is one of the essential components for engineers to design and plan satellite communication systems at high frequency bands. In this paper, rain fade duration was obtained for twelve consecutive months at Ku-band with 77.4° elevation angle from MEASAT3 in Kuala Lumpur, Malaysia. Empirically, the fade duration was found discrepant to the results predicted by models. Therefore, a modification of fade duration model is proposed based on measured data for this tropical climate and high elevation angle.
       
  • Fractional order PDD control of spacecraft rendezvous
    • Abstract: Publication date: Available online 30 June 2018Source: Advances in Space ResearchAuthor(s): Niloofar Sarafnia, Maryam Malekzadeh, Javad Askari In this study, a rendezvous mission between two spacecraft is programmed. The system is modelled as a 6-DOF formation flying. It is expected that this system be robust against various uncertainties and disturbances while minimizing the energy consumption, considering thrusters and control torques limitations. For this purpose, three robust fractional-order PDD (FOPDD) controllers are designed. The first one is designed based on robust constraint on transfer function. In the second method, the controller gains are tuned by using Particle Swarm Optimization (PSO) algorithm. The third designed controller is implemented according to Model Reference Adaptive Controller with Fractional Order Adjustment Rules (FOAR-MRAC) which is a combination of FOPDD controller tuned by PSO algorithm and an adaptive time variable gain. The performance of these controllers are compared in—various uncertain conditions (disturbances, mass and inertia uncertainty and sensor noises) considering actuators limitations.
       
  • Recent advancements in the EST project
    • Abstract: Publication date: Available online 30 June 2018Source: Advances in Space ResearchAuthor(s): Jan Jurčák, Manuel Collados, Jorrit Leenaarts, Michiel van Noort, Rolf Schlichenmaier The European Solar Telescope (EST) is a project of a new-generation solar telescope. It has a large aperture of 4 m, which is necessary for achieving high spatial and temporal resolution. The high polarimetric sensitivity of the EST will allow to measure the magnetic field in the solar atmosphere with unprecedented precision. Here, we summarise the recent advancements in the realisation of the EST project regarding the hardware development and the refinement of the science requirements.
       
  • Graphene synthesized as by-product of gas purification in long-term space
           missions and its lithium-ion battery application
    • Abstract: Publication date: Available online 30 June 2018Source: Advances in Space ResearchAuthor(s): Yao Nie, Clayton Kacica, Marit E. Meyer, Robert D. Green, Pratim Biswas To support long-term missions in space, it is important to recycle valuable consumables, such as oxygen (O2) and water. In a Sabatier reactor, hydrogen is employed to reduce carbon dioxide (CO2) to methane (CH4) and O2, then an integrated system is designed to recycle hydrogen from CH4, which includes a methane purification assembly (MePA), a plasma pyrolysis assembly (PPA), an acetylene separation assembly (ASepA). In the PPA reactor, carbon particulates were observed to form as a by-product. In this study, this carbon material was characterized and a significant fraction is graphene with a low oxygen content. HRTEM images clearly showed a partially crystalline hexagonal structure, which is a characteristic graphene signature. The specific surface area of the graphene was measured to be 258.5 m2/g, one tenth of the theoretical value of single layer graphene, which can be attributed to stacking of the few layers and partial crumpling of this material. To explore potential uses of this material, the crumpled graphene was used to synthesize anodes of lithium-ion batteries (LIBs), which were then tested for their electrochemical performance. In long-term cycle tests, LIBs made with crumpled graphene demonstrated a high retention rate after the first cycle, indicating very little additional degradation of the electrode. The high stability of the cells can be attributed to the greater variety and higher number of lithium ion storage sites in the crumpled graphene, compared with bulk graphite. Considering the crumpled graphene as a by-product and the high electrochemical performance of the crumpled graphene LIBs, crumpled graphene synthesized in the NASA plasma reactor has great promise in better supporting the long-duration space missions.
       
  • Passive microwave response associated with two main earthquakes in Tibetan
           Plateau, China
    • Abstract: Publication date: Available online 27 June 2018Source: Advances in Space ResearchAuthor(s): Feng Jing, Ramesh P. Singh, Ke Sun, Xuhui Shen The thermal anomalies associated with earthquakes using satellite infrared data are being studied in different parts of the world for more than three decades. The thermal anomalies have emerged as one of the potential earthquake precursor. However, often cloud cover obstructs detection of the thermal anomalies. Compared to infrared, passive microwave sensors provide information about the thermal radiations under any weather conditions. In the present study, we have carried out detailed analysis of brightness temperature data derived from the Defense Meteorological Space Program (DMSP) Special Sensor Microwave/Imager (SSM/I) to determine thermal anomalies associated with the 1997 Manyi and 2001 Kokoxili earthquakes. Brightness temperature data for 13 years period from 1996 to 2008 observed from F13 satellite were considered to avoid difference in the sensor sensitivity. Based on 9 years background data that ignoring data for the years in which strong earthquake occurred, we computed Index of Microwave Radiation Anomaly (IMRA) over the Manyi-Yushu Fault (MYF) and Kun Lun Fault (KLF) zones, Tibetan Plateau. Our results indicate that the microwave brightness temperature at 19.35 GHz has higher sensitivity to the seismic anomalies in comparison to the other higher frequency channels. The IMRA with multi-region, multi-frequency, and multi-parameter variation were analyzed to validate our results. In addition, variation of different parameters (microwave brightness temperature, near surface air temperature and carbon monoxide-CO) observed for Kokoxili earthquake shows the transfer process of thermal anomalies from the focal region to the atmosphere during the preparation and occurrence of earthquake. Passive microwave satellite data combined with other surface and atmospheric parameters provide better understanding of physical mechanism of thermal anomalies associated with earthquakes.
       
  • An efficient surrogate-based framework for aerodynamic database
           development of manned reentry vehicles
    • Abstract: Publication date: Available online 27 June 2018Source: Advances in Space ResearchAuthor(s): Meysam Mohammadi-Amin, Moein M. Entezari, Alireza Alikhani In this study, an efficient framework is developed via surrogate modeling for aerodynamic database generation and management of reentry vehicles. For reentry vehicles with the wide range of flight envelope, a large number of coefficients are required to fulfill the aerodynamic multi-dimensional tables. To reduce the number of high-fidelity analyses without considerable accuracy loss, a proper combination of sampling, interpolation, and data fusion methods are required. The proposed framework includes a multi-dimensional nonlinear interpolation (Kriging), a data fusion (co-Kriging) and a sampling method (Latin Hypercube Sampling) in an integrated structure coupled with aerodynamic solvers. The main idea is applying Kriging interpolation method on cheap data points to estimate the aerodynamic coefficients' trends over the entire space of variables, and refining the trends with accurate sample points and data fusion. Latin hypercube sampling method is used for optimal distribution of cheap samples and initial accurate sample points. After a few high-fidelity analyses, co-Kriging data fusion method is applied for the improving aerodynamic database fidelity via augmentation of trends with the accurate data. The process iterates using new accurate sample points (located on maximum mean squared error) until the mean squared error criteria is met. Cheap data are produced by a variety of low-fidelity solvers e.g. potential and Euler solvers and high-fidelity data are calculated by full Navier-Stokes solvers (CFD). For each regime of the flight envelope, i.e. subsonic, transonic, supersonic and hypersonic and each type of reentry configurations, e.g. Apollo-type, grid studies are done separately and the optimum grid and solver settings are implemented into the framework to facilitate the automatic aerodynamic database generation and management. All parts of the presented framework are validated independently in compare to some reference test cases. To show the capabilities of the developed framework, Orion reentry capsule with complete flight envelope is assumed as a sample. Orion aerodynamic database is generated efficiently and the obtained results are in good agreement in comparison with experimental data. In conclusion, the framework accuracy, flexibility, and efficiency are demonstrated.
       
  • On the growth rate instability of nonextensively opposite polarity dusty
           plasmas
    • Abstract: Publication date: Available online 26 June 2018Source: Advances in Space ResearchAuthor(s): S.K. Zaghbeer, E.K. El-Shewy, A.M. El-Hanbaly, H.H. Salah, N.H. Sheta, A. Elgarayh Nonlinear obliquely and wave instability features in a magnetized collisionless dusty plasma containing negative- positive dusty grains are theoretically explored. The equation of Zakharov Kuznetsov is derived by reductive perturbation calculations and three dimensional wave instability is examined using small k expansion procedure. The system parameters namely, cyclotron frequency, the polarity grain charges ratio, nonextensive effects on DA wave properties and instability growth rate are discussed. Present dissection can be important in phenomena of nonlinear perception in astrophysical plasma of space.
       
  • Direct Thrust and Plume Divergence Measurements of the IFM Nano Thruster
    • Abstract: Publication date: Available online 23 June 2018Source: Advances in Space ResearchAuthor(s): David Jelem, Alexander Reissner, Bernhard Seifert, Nembo Buldrini, Lissa Wilding, David Krejci The IFM Nano Thruster, which consists of a porous tungsten crown ion-emitter to provide thrust in the range of 10µN to 1mN at 2000 to 5000s ISP, has been tested on a µN thrust balance that has previously been verified at the ESA Propulsion Laboratories. A comprehensive assessment of the thrust performance has been complemented by measurements of the plume divergence using a novel segmented collector setup that allows to assess the ion current distribution within a 2D-section of the plume in a high time resolution. From the plasma probe measurements, an upper bound of 0.93 for the thrust coefficient has been derived, while direct thrust measurements have shown a thrust coefficient between 0.8 and 0.9 over the entire thrust range. From the test results, a complete thruster performance map could be established linking emitter current and voltage with thrust and Isp.
       
  • A refined regional empirical pressure and temperature model over China
    • Abstract: Publication date: Available online 22 June 2018Source: Advances in Space ResearchAuthor(s): Weixing Zhang, Yidong Lou, Jinfang Huang, Wenxuan Liu Accurate pressure and temperature are indispensable in the GNSS water vapor retrievals. A refined regional empirical model, WHU_CPT, for estimating pressure, temperature and water vapor weighted mean temperature (Tm) with a horizontal resolution of 0.75° over China was developed. We found that the surface level reanalysis products are more reliable in reproducing surface temperature than pressure level products in the model construction. The model form was then determined individually for each meteorological variable by comparing performances of different models and by analyzing the Power Spectra Density of time series. Average RMS of pressure and temperature errors over China in WHU_CPT is about 4.07 hPa and 3.76 K, compared to 5.95 hPa and 5.92 K for GPT, 4.25 hPa and 5.14 K for GPT2, and 4.14 hPa and 5.14 K for GPT2w. Two Tm models were also developed in WHU_CPT. One is an empirical model, WHU_CPT (Tm1), which takes user location and time as inputs and the other one, WHU_CPT (Tm2), which additionally makes use of the measured temperature, is more suitable for users with surface temperature available. The mean RMS of Tm errors over China are about 4.45, 4.19, 3.81 and 2.97 K for the Bevis equation, GPT2w, WHU_CPT (Tm1) and WHU_CPT (Tm2).
       
  • DustCube, a nanosatellite mission to binary asteroid 65803 Didymos as part
           of the ESA AIM mission
    • Abstract: Publication date: Available online 21 June 2018Source: Advances in Space ResearchAuthor(s): Franco Perez, Dario Modenini, Antonio Vázquez, Fernando Aguado, Ricardo Tubío, Gergely Dolgos, Paolo Tortora, Alberto Gonzalez, Riccardo Lasagni Manghi, Marco Zannoni, Adeeb Nazeeruddin, Mauro Melozzi, Ian Carnelli Nanosatellites are a promising option for the exploration of the solar system and near-Earth objects, providing an agile, reduced cost and mass solution for interplanetary missions. This paper summarises the efforts done during the Phase A study aimed at assessing the feasibility of a nanosatellite-based mission concept for a 3U CubeSat to the vicinity of the binary asteroid 65803 Didymos. The nanosatellite is meant to be part of the Asteroid Impact Mission (AIM) which is the European element of the NASA-ESA jointly developed Asteroid Impact & Deflection Assessment (AIDA) mission. The inclusion of a scientific optical payload based on a Nephelometer, the selected orbital and navigation strategy, together with the differences found between the Beyond-Earth space environments (radiation, micrometeoroids, ejected material, illumination conditions, communications access) and a typical LEO polar environment, unveils new technical challenges to be faced along interplanetary missions. These challenges have been identified and analysed to be included within the DustCube concept of operations, are described in this manuscript.
       
  • Integrated simulations of Mars flights on the ISS
    • Abstract: Publication date: Available online 21 June 2018Source: Advances in Space ResearchAuthor(s): L. Narici, G. Reitz, C. Lobascio The human quest towards the exploration of the solar system and beyond will likely continue to grow in the next few decades. Many scientific and technological challenges still need to be approached and solved to enable long deep space human exploration. Once answers to these challenges are available, they will be integrated in the flight plans as ad hoc operational strategies.For the solution of specific scientific and technological problems, experiments using ground analogues may provide optimal responses; however, only the International Space Station (ISS) can play the role of integrated analogue, where the impact of micro-gravity, radiation, living and psychological conditions that astronauts will face during a deep space cruise, can be mimicked at the same time, in part or in whole.Today the ISS is a unique technological and scientific platform that enables researchers from all over the world to work on innovative experiments that could not be performed anywhere else. However, it is conceivable to use the deep space analogue features of the ISS to perform integrated tests of those operational strategies needed to allow for deep space voyages, towards a potential final integrated in-space test of the entire voyage to Mars, with a fidelity as high as achievable. This utilization strategy for the ISS would help focusing research and technology on open questions for deep space exploration, also enabling further tests of the journey to Mars using other advanced platforms that will be available on Moon orbit or surface in the near future. It will also provide the ISS with the rank of “springboard” towards deep space for the general public, increasing the awareness for human space exploration. In this paper we present the ISS4Mars idea, underlining its major goals and challenges.
       
  • DISCUS – The Deep Interior Scanning CubeSat mission to a rubble pile
           near-Earth asteroid
    • Abstract: Publication date: Available online 19 June 2018Source: Advances in Space ResearchAuthor(s): Patrick Bambach, Jakob Deller, Esa Vilenius, Sampsa Pursiainen, Mika Takala, Hans Martin Braun, Harald Lentz, Manfred Wittig We have performed an initial stage conceptual design study for the Deep Interior Scanning CubeSat (DISCUS), a tandem 6U CubeSat carrying a bistatic radar as the main payload. DISCUS will be operated either as an independent mission or accompanying a larger one. It is designed to determine the internal macroporosity of a 260–600 m diameter Near Earth Asteroid (NEA) from a few kilometers distance. The main goal will be to achieve a global penetration with a low-frequency signal as well as to analyze the scattering strength for various different penetration depths and measurement positions. Moreover, the measurements will be inverted through a computed radar tomography (CRT) approach. The scientific data provided by DISCUS would bring more knowledge of the internal configuration of rubble pile asteroids and their collisional evolution in the Solar System. It would also advance the design of future asteroid deflection concepts. We aim at a single-unit (1U) radar design equipped with a half-wavelength dipole antenna. The radar will utilize a stepped-frequency modulation technique the baseline of which was developed for ESA’s technology projects GINGER and PIRA. The radar measurements will be used for CRT and shape reconstruction. The CubeSat will also be equipped with an optical camera system and laser altimeter to support navigation and shape reconstruction. We provide the details of the measurement methods to be applied along with the requirements derived from the known characteristics of rubble pile asteroids. Additionally, an initial design study of the platform and targets accessible within 20 lunar distances are presented.
       
  • Study of aerosol types and seasonal sources using wavelength dependent
           Ångström exponent over North-East India: Ground-based measurement and
           satellite remote sensing
    • Abstract: Publication date: Available online 19 June 2018Source: Advances in Space ResearchAuthor(s): Pranab Dhar, Trisanu Banik, Barin Kumar De, Mukunda M. Gogoi, S. Suresh Babu, Anirban Guha The spectral estimates of Aerosol Optical Depth (AOD, τ) were made by operating a Microtops-II sun photometer in the spectral range 0.380–0.870 μm over Tripura in north-eastern India and analyzed to infer the aerosol types and source characteristics in different seasons. The Ångström exponent (α) derived from spectral AOD in different wavelength (λ) range and subsequent second order derivative of Ångström exponent (i.e., α′) and their curvature analysis in the ln τ versus ln λ relationship has revealed the crucial information related to the dominance of different aerosol types and their characteristics in different seasons. The average AOD (mean ± standard deviation) at 0.5 μm in winter, pre-monsoon, monsoon and post-monsoon seasons are observed to be 0.70 ± 0.28, 0.74 ± 0.18, 0.55 ± 0.20, 0.44 ± 0.19 respectively; while the corresponding seasonal mean values of α (over 0.380–0.870 μm spectral range) are found to be 1.09 ± 0.17, 0.92 ± 0.24, 0.51 ± 0.27, 0.89 ± 0.38 respectively. Examination of the Ångström exponents derived from satellite retrieved AOD by Moderate Resolution Imaging Spectroradiometer (MODIS) instrument operating onboard Terra satellite, along with MODIS fine mode aerosol fraction and aerosol types indicates broad seasonal features of aerosol size spectrum over the study region similar to those observed from ground-based measurements. The estimation of the values of α at different spectral ranges indicate that winter season is mainly influenced by the fine-mode aerosols having fine-mode fraction (FMF) ∼ 0.7; whereas coarse-mode aerosols dominate in the monsoon season having FMF ∼ 0.3. The pre-monsoon and post-monsoon seasons exhibit the presence of mixed type of aerosols, with slightly greater fraction of fine-mode aerosol in pre-monsoon. Curvature analyses of Ångström exponent put insight into the consistency of observed features of seasonal aerosol types.
       
  • 3D radar wavefield migration of comet interiors
    • Abstract: Publication date: Available online 19 June 2018Source: Advances in Space ResearchAuthor(s): Paul Sava, Erik Asphaug Imaging the interior structure of small planetary bodies facilitates a deep understanding of their origin and evolution, thus addressing fundamental questions about the formation of the Solar System. We show that high resolution 3D imaging of their interior structure is possible using radar waves that reflect from internal discontinuities of dielectric properties. A radar imaging mission at a comet nucleus would have the benefit of orbiting all around a finite and transparent body, collecting echoes that derive only from the target, and processing them collectively in phase.As is the case in the medical field, imaging a comet nucleus requires its illumination from multiple directions, which can be accomplished with a spacecraft in slow polar orbit around the studied object. Long acquisition time leads to a dense acquisition array resembling that of conventional synthetic aperture radar systems, but completely surrounding the nucleus (4π steradians). Acquisition with an orbiter at large distance from the comet nucleus (5× the mean diameter) results in relatively coarse data sampling relative to the radar wavelength, thus enabling 3D imaging with a short (
       
  • Rapid initialization method in real-time deformation monitoring of bridges
           with triple-frequency BDS and GPS measurements
    • Abstract: Publication date: Available online 19 June 2018Source: Advances in Space ResearchAuthor(s): Ruijie Xi, Weiping Jiang, Xiaolin Meng, Xiaohui Zhou, Qiyi He Rapid initialization with ambiguity fixed resolution plays a key role in real-time Global Navigation Satellite Systems (GNSS) displacement monitoring of bridges. In this study, we propose a rapid initialization method with triple-frequency (TF) BeiDou Navigation Satellite System (BDS) and Global Positioning System (GPS) observations. The key step of this method is to form extra-wide-lane (EWL) ambiguity with TF BDS and GPS carrier-phase to reduce the ambiguity search space. In order to improve the speed of ambiguity resolution (AR) further, the strategies of fixing ambiguities in groups sequentially from long wavelength to the short and partial AR (PAR) with elevation and signal-to-noise ratio (SNR) criterions were proposed. Based on the real monitoring data on the Baishazhou Yangtze River Bridge, the AR efficiency was tested. The results illustrate that over 90% EWL ambiguities can be fixed by only single-epoch with TF BDS + GPS. After EWL ambiguity is fixed, the wide-lane (WL) ambiguity success rate could improve from 20% with dual-frequency (DF) BDS + GPS data to 70% with TF BDS + GPS data, 50–80% and 80–90% for the three stations respectively. Since the area of ambiguity search space is reduced by TF observations, the ambiguity search time decrased significantly compared with the DF BDS + GPS. In the Time-to-first-fix (TTFF) test, over 85% of epochs can complete the initialization process by only one epoch with one hour of 10 Hz TF BDS + GPS data. However, DF BDS + GPS has only 25%. As for the initialization time longer than two epochs, the counts of TTFFs of TF BDS + GPS are significantly less than that of DF BDS + GPS. Meanwhile, the integrated BDS and GPS can further enhance the geometry of satellites, which will be better for the precision improvement than the increase of signal frequencies.
       
  • DEM thermal simulation of bit and object in drilling of lunar soil
           simulant
    • Abstract: Publication date: Available online 18 June 2018Source: Advances in Space ResearchAuthor(s): Jinsheng Cui, Xuyan Hou, Guilin Wen, Zhongwei Liang The bit and object thermal problem was investigated in this study with particular regard to the drilling of lunar soil simulant. The discrete element method (DEM) was used to establish a thermal model of the simulant that considered convection, radiation, and geometry. Parameter calibration of the DEM heat transfer model was undertaken, and drilling experiments were performed under normal pressure to verify the model. Thermal simulations of the drilling of the lunar soil simulant under normal pressure and in a vacuum were also conducted, and very good agreement was observed between the simulation and experimental results. The temperature rise of the lunar soil simulant was found to be much less during drilling in a vacuum compared to drilling under normal pressure for comparable temperatures of the drill bit. And in a vacuum, lunar soil simulant had little effect on heat dissipation from the drilling tool.
       
  • Direct and indirect charged aerodynamic mechanisms in the ionosphere
    • Abstract: Publication date: Available online 18 June 2018Source: Advances in Space ResearchAuthor(s): C.J. Capon, M. Brown, R.R. Boyce Objects in a flowing plasma may exchange momentum both directly, through gas-surface interactions, and indirectly, through field effects. Applying a control surface approach developed in the study of dusty (complex) plasmas, this work outlines a framework for investigating the relative contribution of direct and indirect charged aerodynamic forces that may arise from the aerodynamic interaction of LEO objects with the ionosphere i.e. ionospheric aerodynamics. In particular, this work focuses on plasma interaction phenomena described by the scaling parameters αk and χ, which describe the ratio of body potential energy to ion kinetic energy and the ratio of body size to sheath thickness respectively. Ion kinetic dominated flows (αk≪1) were found to be well approximated by neutral aerodynamic treatments, the charged drag coefficient (CD,C) of a long (2D) cylinder with a diffusely reflecting surface with complete thermal accommodation to a 500 K wall calculated as 2.232. Body potential dominated systems (αk≫1), however, were dominated by indirect charged aerodynamic mechanisms, an example being the indirect thrust required to balance the sheath driven acceleration of ions through the fore-body sheath, which caused an 82% reduction in net charged drag for the αk=16.9 case. This drag reduction was partially offset by indirect drag forces caused by the deflection of non-colliding ions, the net CD,C being 7.741 for the αk=16.9. A similar study of the relative sheath thickness, described by χ, saw asymptotic behaviours given a constant αk of 1.072; direct charged drag forces becoming either Orbital Motion Limit (OML) for thick-sheath systems (χ→0) or sheath-limited (χ≫1). These results demonstrate the importance of accounting for both direct and indirect charged aerodynamic forces when studying ionospheric aerodynamics, while also providing new physical insights into physical mechanisms momentum exchange processes between a flowing plasma and immersed object.
       
  • Validation of enhanced orbit determination for GPS satellites with LEO GPS
           data considering multi ground station networks
    • Abstract: Publication date: Available online 18 June 2018Source: Advances in Space ResearchAuthor(s): Tian Zeng, Lifen Sui, Xiaolin Jia, Zhipeng Lv, Guofeng Ji, Qin Dai, Qinghua Zhang Deriving the precise satellites orbits is a prerequisite condition for global navigation satellite system (GNSS) to provide the high precision positioning service. With GPS observations from low earth orbiters (LEOs) and terrestrial tracking stations, the orbit and clock parameters of GPS and LEO satellites can be estimated by a simultaneous least squares adjustment, called the combined precise orbit determination (CPOD) method. We select GPS data from three LEOs (GRACE, HY2A and Jason-2) and 150 terrestrial stations over half-month period to investigate the improved performance for GPS orbits when LEO GPS data are included in the process of POD. With the inclusion of LEO GPS data, the improved levels of GPS orbits are analyzed for different types of LEOs and different station networks. First the effect of LEO satellite with different orbital altitude and inclination on GPS orbits is analyzed under three ground station networks. Results show that the improved differences among different LEOs can achieve at millimeter and centimeter level for global and regional station networks, respectively. Then comparative experiments of POD with/without three LEOs are designed for global well-distributed (GW), global regional (GR), Asian-overseas regional (AOR) and Asian regional (AR) station networks, including fourteen station networks. The orbit accuracy of both GPS and LEO satellites and the improved level for GPS orbits are summarized. With the inclusion of three LEOs, contributions from LEO GPS data are comparative in GW and GR cases (more than 30 stations), 3D RMS for GPS orbits improving at mm level w.r.t. corresponding ground-only POD. With 20 stations, the improved levels are 4, 11 and 31 mm in the case of GW, AOR and AR, respectively; with 10 stations, the corresponding improved levels are 16, 24 and 87 mm. The improvements in GW and AOR cases are insignificant, within 3 cm level. In the AR case, the improved level can achieve at decimeter level, while the orbit accuracy with the inclusion of three LEOs is comparative to the inclusion of 5 ground stations evenly distributed in a non-regional area (i.e. AOR case). This study is helpful for deriving the final post-products or broadcast ephemerids for GNSS satellites when considering joining LEO data into the process of orbit determination.
       
  • The exploration of PHOBOS: Design of a Sample Return mission
    • Abstract: Publication date: Available online 18 June 2018Source: Advances in Space ResearchAuthor(s): Antonella Ferri, Stewart Pelle, Maurizio Belluco, Thomas Voirin, Rolando Gelmi The long-term goal of enabling human exploration of the Moon and Mars drives International space exploration plans. Robotic space missions must therefore develop and demonstrate the feasibility and robustness of the enabling technologies and capabilities.The Phobos Sample Return mission is a candidate mission of the Mars Robotic Exploration Preparation programme. Its objective is to acquire and return a sample from the Mars moon Phobos. The main science goal of this mission will be to understand the formation of the Martian moons Phobos and Deimos and acquire further data on the evolution of the solar system. From a technology standpoint, it would be a big step forward in the development of many technologies, ranging from low-gravity body landing capabilities to Earth re-entry of samples from deep space, from semi-autonomous robotic acquisition of surface samples to sample preservation and further analysis in dedicated ground laboratories.Thales Alenia Space represents one of two industrial contractors studying the mission to Phase A level. This phase involves investigation of all aspects of the mission and spacecraft design to ensure its feasibility and robustness. The planned launch date for the mission is between 2025 and 2027. The Ariane 5 ECA launch vehicle will be launched from Kourou. A chemical propulsion module will transfer the spacecraft composite to the Martian system, and will then be separated at Phobos. A full characterization campaign of Phobos at different altitudes from orbit will follow. This will include quasi-satellite orbits and flybys, using a payload suite of cameras and spectrometers. When the preferred landing site is identified, a controlled descent and touchdown onto the surface of Phobos will be performed, with a touchdown accuracy of 50 m. A robotic arm and sampling mechanism will obtain and verify a sample of surface regolith, and insert it into the Earth re-entry capsule. Part of the Spacecraft will return to the Earth from Phobos and deliver the re-entry capsule to the Earth’s atmosphere. The capsule will perform a fully passive Earth entry, descent and landing in Woomera, Australia. It will then be recovered and transferred to a sample curation facility for sample extraction and analysis. This paper summarises the results of the Thales Alenia Space Phobos Sample Return mission and spacecraft design, with a focus on the key elements and mass drivers.
       
  • NON-CALIBRATION RADIOMETRIC METHOD APPLIED TO EFFECTIVE EMISSIVITY
           MEASUREMENT OF ROUGHENED OCEAN SURFACE
    • Abstract: Publication date: Available online 18 June 2018Source: Advances in Space ResearchAuthor(s): V.V. Sterlyadkin The paper considers the new ground-based non-calibration radiometric method for measuring the effective emissivity Eeff of roughened ocean surface. The method makes it possible in microwave range 6-50 GHz on any polarization to study the emissivity dependence both on the parameters of the underlying surface itself and on the parameters of the atmosphere, which are recorded at the place of measurements. The effective emissivity Eeff harmonically corresponds to the radiation transfer model and to the equations that can be used to determine the atmospheric and underlying surface parameters when sensing from the spacecraft board. The data of field measurements, carried out from the marine platform, are presented. The experimentally obtained dependences of Eeff on incidence angles, surface wind speed and wind direction are given. If the sounding geometry and the ground radiometer parameters will be identical to the satellite hardware, then the Eeff dependences, obtained by the proposed method, will automatically take into account both the antenna pattern and the multifactor effect of the surface roughness, and, therefore, they will be harmoniously consistent with the tasks of radiometric sensing from space.
       
  • Multi-objective trajectory optimization for a hybrid propulsion system
    • Abstract: Publication date: Available online 18 June 2018Source: Advances in Space ResearchAuthor(s): Taibo Li, Zhaokui Wang, Yulin Zhang It is attractive to use a hybrid propulsion system (HPS) consisting of solar electric propulsion (SEP) and solar radiation pressure (SRP) in interplanetary and near-Earth missions. Compared with the equivalent pure sail and pure SEP trajectories, HPS can reduce fuel consumption and transfer time. A multi-objective optimization model for the three-dimensional rendezvous mission of hybrid propulsion system is established in this paper. The optimization index is defined as a weighted sum of transfer time and the fuel consumption. Solutions with the bang-bang thrust profile are obtained under the specific mission constraints of time and fuel consumption. The influence of weights on the optimization results is discussed, and a reasonable weight range is given based on the magnitude analysis. By combining the homotopy approach with time-optimal solar sail trajectory, the initial value of the covariates are well estimated. Numerical simulations are performed both on Earth–2000SG344 and Earth–Apophis rendezvous. The results indicate that the proposed method is advantageous to obtain solutions with different mission time and fuel consumption flexibility.
       
  • Uniaxial mechanical properties of multi-layer thin films in use for
           scientific balloons
    • Abstract: Publication date: Available online 15 June 2018Source: Advances in Space ResearchAuthor(s): Jianhui Hu, Yipo Li, Wujun Chen, Tengfei Zhang, Chengjun Gao, Taibai Shi, Deqing Yang Essential and accurate mechanical parameters of multi-layer thin films for scientific balloons are indispensable for performing structural analysis. This study focuses on the determination of uniaxial mechanical properties of a new multi-layer thin film and the understanding of the effects of mechanical properties on structural behavior and altitude with three-dimensional numerical models. For uniaxial monotonic mechanical properties, a method to determine yield stress is proposed in combination of geometrical and energetic principles. It is found that average yield stresses are 20.5 MPa and 15.0 MPa for machine and transverse directions. The cyclic mechanical properties in terms of elastic modulus and ratcheting strain tend to be stable after certain cycles. Moreover, the Poisson’s ratios of 0.31 and 0.15 in machine and transverse directions are determined with digital image correlation (DIC) technique. Furthermore, these mechanical properties are utilized to analyze a 12 m diameter spherical superpressure balloons floating at the altitude of 20 km. A corresponding three-dimensional numerical model is developed to understand the effects of mechanical properties on structural behavior and altitude. The numerical results in terms of elastic moduli show that the effects of mechanical properties on structural behavior and altitude are relatively apparent and slight, respectively.
       
  • Thermal performance of liquid hydrogen tank in reduced gravity
    • Abstract: Publication date: Available online 14 June 2018Source: Advances in Space ResearchAuthor(s): Zhan Liu, Guoqing Zhou, Yanzhong Li, Penghui Gao Fluid temperature stratification is significant to the safe operation of space storage tanks. A calculation model, accounting for the liquid–vapor phase change, is developed to investigate the thermal physical process in a liquid hydrogen (LH2) tank in reduced gravity. Viscous flow is considered in calculation model with Ra ranging from 0.1 to 105 to ensure the continuity of natural convection. The stratified layer parameters, the tank pressure rise, and the interface phase change are studied respectively. Influences of the initial liquid height, the initial ullage temperature and the tank wall heat flux on the development of thermal stratification are estimated. The results show that the stratified layer thickness rises with the initial liquid height. While the initial liquid height is large, it costs more time for the wholly development of fluid thermal stratification. Largely influenced by the temperature of the stratified layer, both tank pressure and phase change capacity increase with the initial liquid height. It seems that the initial ullage temperature has a weak effect on the development of fluid thermal stratification. Both the tank pressure and the phase change quality increase with the initial ullage temperature. The external tank wall heat flux promotes the development of thermal stratification. The stratified layer has a larger thickness and develops faster for the larger heat flux. Both tank pressure and phase change capacity increase with the external heat flux. Meanwhile, the intersection point exists between any two profiles.
       
  • Investigation of gravity effect on penetration resistance in Tongji-1
           lunar regolith simulant by centrifuge tests
    • Abstract: Publication date: Available online 12 June 2018Source: Advances in Space ResearchAuthor(s): Mingjing Jiang, Banglu Xi, Huayang Lei Cone Penetration Tests (CPTs) are usually performed on the lunar regolith simulant on the Earth to study the geotechnical characteristics of lunar soil, which will be then used for the possible human activities on the Moon in the future. However, the gravity effect should be fully investigated before applying these experimental results to the Moon exploration, because the gravity level on the Moon is much lower than that on the Earth. For this aim, a series of CPTs was carried out in a centrifuge with a carefully designed testbed made of Tongji-1 lunar regolith simulant (TJ-1 simulant). The measured results were employed to examine the applicability of two traditional solutions and linear equation in describing the gravity effect along with some other existing experimental data. In addition, the linear equation fitted by the experimental data was used to predict the values of normalized tip resistances of lunar soil on the Moon. The results show that the two traditional solutions cannot describe the gravity effect well while the linear relationship between the peak (stable) normalized cone tip resistance and the reciprocal of gravity level can quantitatively describe the gravity effect on the penetration resistance. The predicted normalized peak (stable) tip resistances are larger than those of lunar soil on the Moon, which may be probably due to the unique in-situ conditions on the Moon.
       
  • Impact of long ocean waves on wave height retrieval from SAR altimetry
           data
    • Abstract: Publication date: Available online 12 June 2018Source: Advances in Space ResearchAuthor(s): T. Moreau, N. Tran, J. Aublanc, C. Tison, S. Le Gac, F. Boy SAR altimetry is a new high-resolution operation mode exploited in new-generation altimeter missions, such as Sentinel-3. It takes advantage of its enhanced along-track resolution to make measurements of sea surface height variations in much greater detail than what can be achieved with conventional low resolution instruments (e.g. the Jason-3 altimeter). However, contrary to what is observed for conventional altimetry, long-wavelength ocean waves of a few hundred meters (swell and extreme wind waves) are no longer fully imaged in the instrument ground cells, and SAR waveforms have distorted shapes in such wave conditions. This affects the final retrieval of significant wave height (SWH). This paper analyzes the impact of long ocean waves on SAR-mode data by using both Cryosat-2 measurements and simulated data. Results from these two approaches are in good agreement and show that the estimated parameters from SAR-altimetry waveforms are particularly noisy under long-wave conditions and also biased when compared with conventional altimetry data. Additionally, we found evidence that these impacts are different between the two directions (along and cross-track directions) due to the asymmetry of the SAR-altimetry footprint. Simulations indicate that statistics of sea surface elevations within the SAR-altimetry footprint deviate from Gaussian behavior. The assumption commonly used for ocean retracking algorithms is therefore inaccurate. The sensitivity of SAR-mode altimetry data to long waves is a key issue for the ocean altimetry community, which is concerned to ensure the continuity of high-quality time series of the global sea-surface topography in future years. This is not only an issue for these new-generation radar altimeters (Sentinel-3 and Sentinel-6) but also for all innovative techniques or processing methodologies capable of providing higher spatial resolution of the ocean surface.
       
  • Accelerating real-time PPP ambiguity resolution by incorporating
           multi-GNSS observations
    • Abstract: Publication date: Available online 22 May 2018Source: Advances in Space ResearchAuthor(s): Zhao Li, Hua Chen, Peng Yuan The performance of Real-Time (RT) Precise Point Positioning (PPP) ambiguity resolution can be further improved by incorporating multiple Global Navigation Satellite System (GNSS) observations. RT PPP with ambiguity resolution based on raw GNSS observations, aided by the satellite clock offsets and GPS un-calibrated phase delays (UPDs), is realized to evaluate the effect of GNSS observations. Compared with previous studies, Galileo observations are integrated in this analysis and the effect of new BeiDou/Galileo systems in RT PPP ambiguity resolution is analyzed for global users. Comparing with the GPS-only and GPS/GLONASS solution, the time to first fix (TTFF) is 18.8% and 7.9% improved for those users in the Asia-Pacific regions, while it is 9.6% and 3.8% improved for other users by adding the BeiDou/Galileo observations. The improvement of the fixing rate and positioning accuracy is similar for users in different regions. The fixing rate is 2.1% and 0.5% improved when adding BeiDou/Galileo observations on top of GPS and GPS/GLONASS respectively. The accuracy of the north, east and up components are 0.4, 0.0 and 0.5 mm improved when adding on top of GPS, while 0.2, 0.1 and 0.4 mm when adding on top of GPS/GLONASS. By utilizing observations of four systems, an accuracy of 9.0, 9.1 and 28.3 mm is achieved for the fixed kinematic PPP solution after a mean initialization time of 797.9 s.
       
  • Comparative analysis of positioning accuracy of GNSS receivers of Samsung
           Galaxy smartphones in marine dynamic measurements
    • Abstract: Publication date: Available online 22 May 2018Source: Advances in Space ResearchAuthor(s): C. Specht, P.S. Dabrowski, J. Pawelski, M. Specht, T. Szot One of the most popular functions of modern mobile phones is determining the coordinates of the device using built-in GNSS receivers. By using map images extensively available on the Internet, today's smartphones have become basic navigation devices of the average user.Mobile devices with built-in GNSS receivers are primarily used in land navigation. However, marine sailing, tourism and recreation are fields where the use of mobile phones as navigation devices is also very common. The average position errors of GNSS receivers mounted on smartphones decisively influence the ability and accuracy of navigation based on those devices.This publication analyses the accuracy of the dynamic positioning of six Samsung Galaxy smartphones during vessel manoeuvring. As part of the parallel tracking studies, the telephone positions were compared to those of precise GNSS receivers, using corrections from an active geodetic network with an accuracy of 2–3 cm (p = 0.95). As a result of the 4-h measurement, the accuracy statistics for each of the phone models were defined based on approximately 10,000 positions. Studies indicate that there are significant differences in the accuracy of positioning as performed by the models in question.
       
  • Small launch platforms for micro-satellites
    • Abstract: Publication date: Available online 19 May 2018Source: Advances in Space ResearchAuthor(s): Chantal Cappelletti, Simone Battistini, Filippo Graziani The number of small satellites launched into orbit has enormously increased in the last twenty years. The introduction of new standards of micro-satellites has multiplied the launch demand around the world. Nevertheless, not all the missions can easily have access to space: not all kinds of micro-satellites have granted a deployer system and, furthermore, once a micro-satellite is able to reach it, it cannot usually choose its final orbit. Recently two new platforms have been introduced for the release of micro-satellites as piggy-backs. These platforms are totally operative spacecrafts that act like motherships, and allow to select some parameters of the final orbit of the piggy-backs. They provide a solution for three different nano-satellites standard, and at the same time they are being developed in order to reach more powerful orbital release capabilities in the future. The design and the mission of these platforms are described in this paper.
       
  • DME pulse interference mitigation for airborne BDS and flight test results
    • Abstract: Publication date: Available online 17 May 2018Source: Advances in Space ResearchAuthor(s): Jiu-yuan Guo, Xiao-lin Zhang BeiDou Navigation Satellite System (BDS) B2 signal works in the aeronautical radio navigation services (ARNS) band. It suffers high-power pulse interference, particularly from distance measuring equipment (DME), which will affect signal acquisition, signal tracking, as well as positioning of airborne BDS receiver. Regarding the problem, a DME pulse interference mitigation algorithm based on FLOC-TDE (Fractional Lower Order Covariance-Time Delay Estimation) is proposed in this paper, which can effectively mitigate DME pulse and retain useful BDS satellite signals. We firstly analyzed the live data collected from COMAC (Commercial Aircraft Corporation of China Ltd) Airborne BDS First Flight Project. And then, experiments on COMAC airborne BDS experiment platform were performed. The proposed algorithm, time domain pulse blanking algorithm and non-mitigation algorithm were compared in the experiments. The values of correlation peak to secondary peak ratio (CPSP) and the correlation peak to mean peak ratio (CPMP), and carrier-to-noise ratio (C/N0) using the proposed algorithm were the biggest. The results verify that the proposed algorithm can mitigate DME pulse interference, improve acquisition and tracking performance of airborne BDS receiver, which can ensure the system integrity.
       
  • Exploring small bodies: Nano- and microlander options derived from the
           Mobile Asteroid Surface Scout
    • Abstract: Publication date: Available online 17 May 2018Source: Advances in Space ResearchAuthor(s): Caroline Lange, Tra-Mi Ho, Christian D. Grimm, Jan T. Grundmann, Christian Ziach, Roy Lichtenheldt The MASCOT lander currently flying on-board of the Japanese Hayabusa2 spacecraft, both set to explore the C-type Near-Earth Asteroid (162173) Ryugu, is not the first, but certainly one of the more complex nanolander systems having been designed for being carried along a bigger interplanetary spacecraft. Other concepts and current missions have shown the attractiveness of the class of nanosystems now increasing its application range from Earth orbiting cubesats to interplanetary scientific exploration endeavors, from orbiting to landing missions. This paper is intended to investigate nanolander options derived based on the MASCOT lander concept. For this purpose we gather interesting target bodies and analyze their respective environmental properties as well as their influence on the nanolander design, for example the landing system, the surface mobility, the power subsystem and the communication architecture. Further, an expansion of the scientific objectives of the current MASCOT lander from geological surface scout to other scientific objectives opens a range of new possibilities. For deeper analysis on this, we provide an overview over possible alternative payloads to the ones already flying on MASCOT and analyze their influence on the system design as it is. Obviously, the experience that has been gained with MASCOT provides us with a head start for future missions, if it is properly exploited. With this paper we intend to recommend MASCOT type of nanolanders for a range of possible future applications.
       
  • Preface: Origins of cosmic rays
    • Abstract: Publication date: Available online 30 April 2018Source: Advances in Space ResearchAuthor(s): Igor V. Moskalenko, Eun-Suk Seo
       
  • The SSDC contribution to the improvement of knowledge by means of 3D data
           projections of minor bodies
    • Abstract: Publication date: Available online 28 April 2018Source: Advances in Space ResearchAuthor(s): Angelo Zinzi, Mauro Ciarniello, Vincenzo Della Corte, Stavro Ivanovski, Andrea Longobardo, Alessandra Migliorini, Maria Teresa Capria, Ernesto Palomba, Alessandra Rotundi The latest developments of planetary exploration missions devoted to minor bodies required new solutions to correctly visualize and analyze data acquired over irregularly shaped bodies.ASI Space Science Data Center (SSDC – ASI, formerly ASDC – ASI Science Data Center) worked on this task since early 2013, when started developing the web tool MATISSE (Multi-purpose Advanced Tool for the Instruments of the Solar System Exploration) mainly focused on the Rosetta/ESA space mission data.In order to visualize very high-resolution shape models, MATISSE uses a Python module (vtpMaker), which can also be launched as a stand-alone command-line software.MATISSE and vtpMaker are part of the SSDC contribution to the new challenges imposed by the “orbital exploration” of minor bodies: (1) MATISSE allows to search for specific observations inside datasets and then analyze them in parallel, providing high-level outputs; (2) the 3D capabilities of both tools are critical in inferring information otherwise difficult to retrieve for non-spherical targets and, as in the case for the GIADA instrument onboard Rosetta, to visualize data related to the coma.New tasks and features adding valuable capabilities to the minor bodies SSDC tools are planned for the near future thanks to new collaborations.
       
  • Functional/thermal verification and validation of an S-band radio for the
           nanosatellites
    • Abstract: Publication date: Available online 26 April 2018Source: Advances in Space ResearchAuthor(s): Yaseen Zaidi, Norman G. Fitz-Coy, Robert van Zyl An S-band radio designed with commercial-grade components for the nanosatellites is functionally and thermally characterized for quiet transmission. The QPSK modulation impairments are minor over −20 °C to +50 °C at 24, 26, 28 and 30 dBm RF levels. The channel response is linear in error vector magnitude, frequency, phase, amplitude and IQ errors. On the average, the stability of amplifier bias and nonlinearity gives −22 dBc maximum upper/lower adjacent channel power and 1.27 MHz occupied channel bandwidth. The acceptable level test results provide good confidence toward robust space-to-earth transmission in variable solar weather at low earth orbital altitudes.
       
  • Robust finite time control of heliostationary flight over asteroids
    • Abstract: Publication date: Available online 26 April 2018Source: Advances in Space ResearchAuthor(s): Fengdi Zhang, Jisheng Zhang, Yonglong Zhang, Zhanggang Lv Maintaining a heliostationary flight over an asteroid is challenging because of the complex dynamical environment. During exploration, external disturbances and uncertainties make it difficult for a spacecraft to stably hover at the libration point to complete its mission. In this paper, a globally robust finite time control law is proposed to solve this problem. First, we design a time variant sliding mode control law for the convergence of the tracking error to zero. Based on this, a nonsingular terminal sliding mode control law is designed to maintain the underlying track error at zero. The performance of the proposed control law is demonstrated through numerical simulations.
       
  • CryoSat: ESA’s ice mission – Eight years in space
    • Abstract: Publication date: Available online 25 April 2018Source: Advances in Space ResearchAuthor(s): T. Parrinello, A. Shepherd, J. Bouffard, S. Badessi, T. Casal, M. Davidson, M. Fornari, E. Maestroni, M. Scagliola CryoSat-2 is a satellite of the European Space Agency that was launched in April 2010. It is intended to monitor changes in the thickness of the marine ice, floating in the polar oceans, and to measure variations in the thickness of the vast ice sheets that overlie Greenland and Antarctica.The CryoSat-2 satellite has replaced the original CryoSat, which became lost due to a launch failure in October 2005.CryoSat-2 carries an innovative radar altimeter called SIRAL (Synthetic Aperture Interferometric Altimeter). It has two radar antennas, which met the measurement requirements for ice-sheet elevation and sea-ice freeboard with unprecedented accuracy. The satellite orbits the planet at an altitude of around 720 km with a retrograde drifting orbit inclination of 92° and a “quasi” repeat cycle of 369 days (30 days sub-cycle). CryoSat-2 is therefore able to reach latitudes up to 88° covering more than 4.6 million km2 of unexplored areas over the poles when compared with previous polar missions carrying an altimetry.The mission has achieved its prime objectives and is delivering high quality data, providing unique contributions to several Earth Science and applications domains, including ice, ocean, geodesy and hydrology, both at global and regional scales.The purpose of this paper is to provide a general overview of the mission and of its main scientific achievements after eight years in space.
       
  • A new strategy of stochastic modeling aiming at BDS hybrid constellation
           in precise relative positioning
    • Abstract: Publication date: Available online 17 April 2018Source: Advances in Space ResearchAuthor(s): Shaoshi Wu, Xiubin Zhao, Chunlei Pang, Liang Zhang, Yong Wang A realistic stochastic model is the prerequisite in global navigation satellite system (GNSS) positioning applications. Considering that Beidou satellite navigation system (BDS) consists of geostationary earth orbit (GEO), inclined geosynchronous satellite orbit (IGSO) and medium earth orbit (MEO) satellites operating in different orbits with different heights, only one model being used in stochastic modeling is probably inadequate, which is the usual case for Global Positioning System (GPS). In this contribution, a new strategy of stochastic modeling for hybrid constellation BDS precise relative positioning is proposed, namely multiple elevation-dependent models (MEDM). In MEDM, parameters of three elevation-dependent models for GEO, IGSO, MEO satellites are estimated independently. After that, variances of phase and code observations for different orbits satellites can be estimated, then the stochastic model specific for BDS can be constructed in real time. The experimental results reveal that, when MEDM is compared with the sole elevation-dependent model and the carrier-to-noise power density ratios (C/N0)-dependent model, the maximum improvements in ambiguity resolution success rates (SR) in 5, 6, 7, 8 available satellites cases are about 0.2%, 13%, 3%, 1% for B1 frequency, and 1%, 6%, 2.5%, 0.2% for B2 frequency, respectively. The overall improvements in baseline solutions by using MEDM are in millimeter or submillimeter level. Hence, MEDM is more suitable for hybrid constellation of BDS in precise relative positioning applications.
       
 
 
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