The second-degree gravity coefficients of Phobos from two Mars Express flybys

Ye, Xuan; Yan, Jianguo; Andert, T. P.; Ye, M; Pätzold, M.; Hahn, M.; Jin, Weitong; Li, F; Barriot, Jean‐Pierre

doi:10.1093/mnras/stz2695

Cited by 20 publications

(27 citation statements)

References 36 publications

(62 reference statements)

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“…From a technical viewpoint, it is a great challenge implementing a sampling method that complies with the above criteria in the absence of detailed information on the state of the regolith on the martian moons. Although gravity on the martian moons is much smaller than that of Mars or Earth's moon, it is several orders of magnitude larger than that of asteroids (Yang et al, 2019). This requires a more-tailored propulsion system directed towards the martian moons during touchdown and lift-off.…”

Section: Sampling Asteroids Versus Phobosmentioning

confidence: 99%

Mars: new insights and unresolved questions

Changela

Chatzitheodoridis

Antunes

et al. 2021

International Journal of Astrobiology

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Mars exploration motivates the search for extraterrestrial life, the development of space technologies, and the design of human missions and habitations. Here, we seek new insights and pose unresolved questions relating to the natural history of Mars, habitability, robotic and human exploration, planetary protection, and the impacts on human society. Key observations and findings include: – high escape rates of early Mars' atmosphere, including loss of water, impact present-day habitability; – putative fossils on Mars will likely be ambiguous biomarkers for life; – microbial contamination resulting from human habitation is unavoidable; and – based on Mars' current planetary protection category, robotic payload(s) should characterize the local martian environment for any life-forms prior to human habitation. Some of the outstanding questions are: – which interpretation of the hemispheric dichotomy of the planet is correct; – to what degree did deep-penetrating faults transport subsurface liquids to Mars' surface; – in what abundance are carbonates formed by atmospheric processes; – what properties of martian meteorites could be used to constrain their source locations; – the origin(s) of organic macromolecules; – was/is Mars inhabited; – how can missions designed to uncover microbial activity in the subsurface eliminate potential false positives caused by microbial contaminants from Earth; – how can we ensure that humans and microbes form a stable and benign biosphere; and – should humans relate to putative extraterrestrial life from a biocentric viewpoint (preservation of all biology), or anthropocentric viewpoint of expanding habitation of space? Studies of Mars' evolution can shed light on the habitability of extrasolar planets. In addition, Mars exploration can drive future policy developments and confirm (or put into question) the feasibility and/or extent of human habitability of space.

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Section: Sampling Asteroids Versus Phobosmentioning

confidence: 99%

Mars: new insights and unresolved questions

Changela

Chatzitheodoridis

Antunes

et al. 2021

International Journal of Astrobiology

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“…MAGREAS uses an iterative weighted batch-least squares (WBLS) estimator to find an initial spacecraft state solution that results in the minimum residual variance for a given set of measurements. The performance of the MAGRREAS software was confirmed by cross-validation against the GEODYN II planetary spacecraft orbit determination and dynamic parameter solution platform, and it also has been employed to process MEX radio tracking data [ 31 , 32 ]. Moreover, a Monte Carlo method was applied to validate the capability of image data for MEX precise orbit determination during the MEX Phobos flyby [ 33 ].…”

Section: Resultsmentioning

confidence: 99%

Precise Orbit Determination of MEX Flyby Phobos Using Simulated Radiometric and Image Data

Zhu

Liu

et al. 2021

Sensors

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A navigation camera or topography camera is a standard payload for deep space missions and the image data are normally used for auto-navigation. In this work, we study the potential contribution of image data in precise orbit determination for deep space spacecraft. The Mars Express (MEX) spacecraft has generated extensive Phobos image data during flybys of Phobos, but these data have not been used in precise orbit determination because of the difficulty in employing these image data. Therefore, we did an experiment using simulated image data as the first step for exploring how to use real image data in precise orbit determination of spacecraft. Our results demonstrate that image data can provide stronger constraints on orbit in the tangential and normal directions than Doppler data. When the image data were used in the MEX orbit determination during the MEX Phobos flyby, the orbit determination accuracies in the tangential and normal directions were significantly improved. This work will provide a reference for real image data processing during MEX Phobos flyby to improve MEX orbit accuracy as well as Phobos ephemeris accuracy.

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“…In addition to the nominal accuracy, the observation scheduling also repeats that of the A48, page 5 of 13 A&A 644, A48 (2020) All the POD simulations were performed using a stable version of Wuhan University Deep space Orbit determination and Gravity recovery System (WUDOGS), an in-house developed software. It has been used in Moon (Yan et al 2020;Liu et al 2020), Mars (Yan et al 2018;Yang et al 2019), Mercury , and asteroid missions (Jin et al 2020).…”

Section: Concept and Significance Of A Pod Simulationmentioning

confidence: 99%

Possible approach to detecting the mysterious Saturnian convective dynamo through gravitational sounding

Liu

Kong

Yan

2020

A&A

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Context. Planetary dynamo research is mathematically and numerically difficult. Forward calculations are numerically expensive and subject to much uncertainty in key magnetohydrodynamics parameters. For a gaseous planet such as Saturn, even the precise location of its dynamo and typical convective strength are unknown, which further complicates studies. Aims. We test the idea of inversely probing Saturnian convective dynamo through gravitational sounding, based on the principle that the convective fluid motion can distort the internal density distribution and hence induce the gravitational anomaly. Methods. The Cassini Grand Finale mission has reported unprecedentedly accurate measurements of the gravitational field of Saturn. An unexplained nonaxisymmetric component of the gravitational field was detected in the data. By performing precise orbit determination (POD) simulations, we studied the possibility that the Cassini spacecraft might sense the dynamo-related nonaxisymmetric gravitational signature in the Grand Finale phase. In addition, further extensively simulated missions of various orbit configurations were carried out in order to explore promising mission strategies that might fulfill the objective of detecting the Saturnian convective dynamo. Results. Our POD simulations show that the gravity science carried out in the Cassini Grand Finale mission is insufficient to determine weak nonaxisymmetric gravitational moments because good subspacecraft-point coverage is lacking. The origin of the unexplained Saturnian gravity remains a puzzle. However, it is positively indicated by our simulations that future gravitational sounding is probably able to detect dynamo-related gravity when the subspacecraft-point coverage of a mission is sufficient. We suggest that the mission orbits be purposely designed into a near-polar orientation with a height of about 6000 km at periapsis and a moderate eccentricity of 0.5. A total POD tracking time of five months would enable the detection of the secular nonaxisymmetric gravitational moments that are caused by the deep convective dynamo of Saturn. The orbit strategy can facilitate engineering implementation by keeping the spacecraft marginally away from the Saturn radiation belt throughout the mission.

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The second-degree gravity coefficients of Phobos from two Mars Express flybys

Cited by 20 publications

References 36 publications

Mars: new insights and unresolved questions

Mars: new insights and unresolved questions

Precise Orbit Determination of MEX Flyby Phobos Using Simulated Radiometric and Image Data

Possible approach to detecting the mysterious Saturnian convective dynamo through gravitational sounding

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