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Lander radio science experiment with a direct link between Mars and the Earth

机译：着陆器无线电科学实验与火星和地球之间的直接联系

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Mars' Orientation and rotation Parameters (called here MOP): precession, nutation, polar motion and length of day (LOD) variations, are related to the interior of the planet as well as to the dynamics of its atmosphere. The MOP can be determined using the Doppler shift on radio signal data due to the motion of a probe landed on Mars relative to tracking stations on Earth. In this paper we perform numerical simulations for assessing the precision on the determination of the MOP using Direct-To-Earth (DTE) X-band Doppler measurements for a nearly equatorial lander. We then discuss how a better knowledge of the MOP could improve our understanding on the interior structure. The sensitivity of such a DTE radio link to these rotation parameters is first investigated. This shows that the latitude of the landing; site must be higher than 20° to detect the Chandler Wobble component of the polar motion in DTE Doppler data and must be at least 40° to get tight constraints on it. It is found that the precision in the determination of the seasonal LOD variations will be significantly improved after about 350 days of operation, reaching the 5% level after 550 days, thereby better constraining the CO_2 mass budget in the Martian atmosphere and ice caps. The current precision in the precession rate (25 milliarcsecond (mas) per year) will be matched after 150 days of mission. An uncertainty of less than 5 mas/year will be reached after 700 days, improving the precision on the polar moment of inertia by a factor of five. The precision on the determination of the amplitudes of nutation is estimated at a few mas after one Martian year of mission (about 12 mas on the prograde/retrograde semi and terannual amplitudes) allowing for the detection of the contribution expected from the liquid core. Considering Mars with a liquid core in accordance with recent geodesic measurements, the Free-Core-Nutation (FCN) period is estimated with a precision of less than 10 days after 550 days of mission in case of an actual FCN period equal to -240 days and with a precision of 1 day after 300 days of observation for an FCN period at -230 days, which is close to the forcing terannual period of 228.9 days (resonance). It is shown that only 100 days of mission duration are needed to detect the liquid core contribution to the nutation near the resonance from the estimates of the amplitudes of nutation. Finally, the precisions on core physical parameters are inferred from the FCN period estimate. We show that a precision of 30% for the core moment of inertia and 5% for the dynamical flattening can be obtained after one Martian year of mission duration.
机译：火星的方向和自转参数（在此称为MOP）：进动，章动，极地运动和一天的长度（LOD）的变化与行星的内部以及大气的动力学有关。可以使用无线电信号数据的多普勒频移来确定MOP，这是由于着陆在火星上的探测器相对于地球上的跟踪站的运动所致。在本文中，我们进行了数值模拟，以评估使用赤道着陆器的直接对地（DTE）X波段多普勒测量MOP的精度。然后，我们讨论对MOP的更好了解如何增进我们对内部结构的理解。首先研究这种DTE无线电链路对这些旋转参数的敏感性。这表明着陆的纬度；站点必须高于20°才能检测DTE多普勒数据中极运动的Chandler摆动分量，并且必须至少40°以获得严格的约束。已发现，在确定运行约350天后，确定季节性LOD变化的精度将显着提高，在550天后达到5％的水平，从而更好地限制了火星大气层和冰盖中的CO_2质量预算。任务执行150天后，当前的进动速度精度（每年25毫秒）将得以匹配。 700天后将达到小于5 mas / year的不确定性，从而将极惯性矩的精度提高了五倍。估计在火星飞行一年后几个mas上确定章动幅度的精度（在前进/后退的半年和三年级幅度上大约为12 mas），从而可以检测到液芯的预期贡献。考虑到火星具有根据最近的大地测量获得的液态核，如果实际FCN周期等于-240天，则估计空核（FCN）周期的精确度在执行任务550天后不到10天观测到的FCN周期为-230天，经过300天的观测后，精度为1天，接近强制性的每半年228.9天（共鸣）。结果表明，仅需要100天的任务持续时间即可根据章动幅度的估计值来检测共振附近液核对章动的贡献。最后，从FCN周期估算值可以推断出核心物理参数的精度。我们表明，在经过一年的火星飞行年后，可以获得30％的核心惯性矩和5％的动态展平精度。

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