A Revisit of the Phobos Events

The magnetic field disturbances detected by the Phobos-2 spacecraft in 1989 have been suggested to be caused by a ring of dust and/or gas emitted from the Martian moon, Phobos. The physical nature of these ``Phobos events' is examined using results from related investigations over the last twenty years. It is concluded that there is no clear evidence at present to support the association of magnetic field disturbances in the solar wind with Phobos. The situation will be further clarified taking advantage of the multi-spacecraft observations of the Yinghuo-1(YH-1), Mars Express and MAVEN missions beginning in 2012. It is expected that many novel features of solar wind interaction with Phobos (and possibly also Deimos) itself will also be revealed.      

Mars Phobos and Deimos Survey (M-PADS) – A martian Moons orbiter and Phobos lander

We describe a Mars ‘Micro Mission’ for detailed study of the martian satellites Phobos and Deimos. The mission involves two ∼330 kg spacecraft equipped with solar electric propulsion to reach Mars orbit. The two spacecraft are stacked for launch: an orbiter for remote investigation of the moons and in situ studies of their environment in Mars orbit, and another carrying a lander for in situ measurements on the surface of Phobos (or alternatively Deimos). Phobos and Deimos remain only partially studied, and Deimos less well than Phobos. Mars has almost always been the primary mission objective, while the more dedicated Phobos project (1988–89) failed to realise its full potential. Many questions remain concerning the moons’ origins, evolution, physical nature and composition. Current missions, such as Mars Express, are extending our knowledge of Phobos in some areas but largely neglect Deimos. The objectives of M-PADS focus on: origins and evolution, interactions with Mars, volatiles and interiors, surface features, and differences. The consequent measurement requirements imply both landed and remote sensing payloads. M-PADS is expected to accommodate a 60 kg orbital payload and a 16 kg lander payload. M-PADS resulted from a BNSC-funded study carried out in 2003 to define candidate Mars Micro Mission concepts for ESA’s Aurora programme.     

基于形状的火卫一重力场研究

介绍基于形状对不规则小天体重力场建模的原理和方法,并通过解析法和数值法对火卫一的重力场进行正演建模。相比之前的重力场模型,基于解析算法获得的17阶次球谐展开形式重力场模型,在分辨率上有显著提高。进一步结合火卫一动力学参数,分析了火卫一表面加速度。结果显示,火卫一因其轨道十分接近火星,导致表面离心力和潮汐力十分显著,在某些区域与自引力相当,造成火卫一的特殊表面重力环境。这些结果可为未来的火卫一探测和科学研究提供基本输入物理场模型,也可为其他小天体探测中的类似问题提供方法参考。     

Integrated method for crater detection from topography and optical images and the new PH9224GT catalogue of Phobos impact craters

In a large majority of lunar and planetary surface images, impact craters are the most abundant geological features. Therefore, it is not surprising that crater detection algorithms (CDAs) are one of the most studied subjects of image processing and analysis in lunar and planetary science. In this work we are proposing an Integrated CDA, consisting of: (1) utilization of DEM (digital elevation map)-based CDA; (2) utilization of an optical-based CDA; (3) re-projection of used datasets and crater coordinates from normal to rotated view and back; (4) correction of the brightness and contrast of a used optical image; and (5) tile generation for the optical-based CDA and an assembling of results with an elimination of multiple detections, in combination with a pyramid approach down to the resolution of the available DEM image; and (6) a final integration of the results of DEM-based and optical-based CDAs, including a removal of duplicates. The proposed CDA is applied to one specific asteroid-like body, the small Martian moon Phobos. The experimental evaluation of the proposed CDA is done by a manual verification of crater-candidates and a search for uncatalogued craters. The evaluation has shown that the proposed CDA was used successfully for cataloging Phobos craters. The major result of this paper is the PH9224GT – currently the most complete global catalogue of the 9224 Phobos craters. The possible applications of the new catalogue are: (1) age estimations for any selected location; and (2) comparison/evaluation of the different chronology and production functions for Phobos. This confirms the practical applicability of the new Integrated CDA – an additional result of this paper, which can be used in order to considerably extend the current crater catalogues.     

Investigation of the Mars Express HRSC color channel calibration

The High Resolution Stereo Camera (HRSC) onboard the Mars Express spacecraft in orbit about Mars has four detector channels dedicated to produce images in four spectral channels. Utilizing these spectrophotometric data requires understanding the instrument radiometric calibration and other photometric properties of the data. We present here some results of our investigation into the HRSC color data characteristics. This covers comparison of HRSC measurements with those of telescopes and the Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité (OMEGA) instrument, also on Mars Express. We also investigate the dependence of HRSC Color measurements on solar phase angle and altitude of the Mars surface. These results confirm and extend our earlier findings [McCord, T.B., Adams, J.B., Bellucci, G., Combe, J.-Ph., Hansen, G., Hoffman, H., Jaumann, R., Lumme, K., Neukum, G., Pinet, P., Poulet, F., the HRSC Co-I Team, The Mars Express high Resolution Stereo Camera spectrophotometric data: characteristics and science analysis. J. Geophys. Res. 112, E6, 2007.]. A basic finding from our study is that there are nearly constant offsets between the I/F value derived from the HRSC data and those determined from OMEGA and groundbased telescope measurements, especially in the HRSC red bandpass. These offsets are nearly independent of solar phase angle and Mars surface altitude but are considerably larger for the one comparison at Phobos we were able to make. Several hypotheses could explain these effects: atmospheric scattering, surface photometric effects, shift of the spatial registration or calibration. All these possibilities were investigated.     

火星自然卫星分析历表的建立

为了解环火星探测器的运动规律,就要构造环火星探测器的轨道分析解,这会涉及2个火星自然卫星的分析历表,因而需要首先构造它们的轨道分析解。由于火星与地球类似,参照建立人造地球卫星轨道摄动解的方法,构造火星自然卫星轨道的摄动分析解,分离出短周期项,即可给出所需要的历表计算公式。将其与JPL网站上提供的历表进行比对,结果表明,所采用的数学模型以及构造轨道摄动解的方法均有效,能够达到期望的精度。     

Phobos regolith simulants PGI-1 and PCA-1

The Martian moon Phobos is the target of the upcoming JAXA Martian Moons eXploration (MMX) mission. There are currently no known samples of Phobos, so spacecraft hardware testing and scientific studies require Phobos regolith simulants. Here, we present two new Phobos regolith simulants: Phobos Captured Asteroid-1 (PCA-1) and Phobos Giant Impact (PGI-1). These two simulants reflect the two hypotheses for Phobos’s formation, and thus the two broad possibilities for composition. This work follows previous efforts to document the development of mineralogically accurate simulants, in an effort to overcome past pitfalls with inappropriate uses of simulants. We report physical and geotechnical properties of PCA-1 and PGI-1, including their reflectance spectra, grain size distributions, abrasivity, cohesion, strength, and hardness. Our intent is for PCA-1 and PGI-1 to be open standards for Phobos simulants, and we present the simulant recipes and production methodology for use and modification by the community.     

Phobos-Grunt: Russian sample return mission

As an important milestone in the exploration of Mars and small bodies, a new generation space vehicle “Phobos-Grunt” is planned to be launched by the Russian Aviation and Space Agency. The project is optimized around a Phobos sample return mission and follow up missions targeted to study some main asteroid belt bodies, NEOs and short period comets. The principal constraint is use of the “Soyuz-Fregat” rather than the “Proton” launcher to accomplish these challenging goals. The vehicle design incorporates innovative SEP technology involving electrojet engines that allowed us to increase significantly the mission's energetic capabilities, as well as highly autonomous on-board systems. Basic criteria underlining the “Phobos-Grunt” mission scenario, scientific objectives and rationale including Mars observations during the vehicle's insertion into Mars orbit and Phobos approach maneuvers, are discussed and an opportunity for international cooperation is suggested.     

“火卫1”轨道预报与动力学分析

使用数值积分的方法对"火卫1"(Phobos)轨道进行预报计算,介绍了计算"火卫1"轨道时考虑的动力模型与数值积分方法,分析了不同动力模型及参量对轨道计算结果的影响,并确定最终选择的模型。最后将计算结果与不同机构发布的最新历表进行比较,计算位置和轨道根数的差异。得到的结果与各星历之间差异的量级相同,进而验证了相关模型和算法的精度和可靠性。该轨道预报算法模型与分析结果将对"火卫1"探测任务提供参考。     

Dynamics in the Phobos environment

The dynamical environment on and about the Martian moon Phobos is explored. This planetary moon provides a unique dynamical environment in the solar system, being subject to extreme tidal forces and having a characteristically non-spherical shape. Further, it is not in a fully circular orbit, meaning that it has librations that arise from its eccentricity, contributing to a periodic forcing environment. Thus, to plan and implement missions in the vicinity of and on Phobos will require these considerations be taken into account. In this paper the latest published models of the Phobos shape and dynamics are used to characterize its dynamical environment in close proximity orbit about the body, for motion across its surface and for controlled hovering motion in its vicinity. It is found that surface motion is subject to a number of “speed limits” that can cause a moving vehicle to leave the surface and to possibly escape the moon and enter orbit about Mars. In terms of orbital stability, the existence of libration orbit families are characterized down to the surface using an exact potential, and the known stable QSO orbits are shown to be associated with families of stable quasi-periodic orbits.