Mazarico Erwan, Neumann Gregory A, Barker Michael K, Goossens Sander, Smith David E, Zuber Maria T
NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, Maryland, USA.
Sigma Space Corporation, 4600 Forbes Boulevard, Lanham, Maryland, USA.
Planet Space Sci. 2018 Nov 1;162:2-19. doi: 10.1016/j.pss.2017.10.004. Epub 2017 Oct 12.
The Lunar Reconnaissance Orbiter (LRO) has been orbiting the Moon since 2009, obtaining unique and foundational datasets important to understanding the evolution of the Moon and the Solar System. The high-resolution data acquired by LRO benefit from precise orbit determination (OD), limiting the need for geolocation and co-registration tasks. The initial position knowledge requirement (50 meters) was met with radio tracking from ground stations, after combination with LOLA altimetric crossovers. LRO-specific gravity field solutions were determined and allowed radio-only OD to perform at the level of 20 meters, although secular inclination changes required frequent updates. The high-accuracy gravity fields from GRAIL, with 10 km spatial resolution, further improved the radio-only orbit reconstruction quality (10 meters). However, orbit reconstruction is in part limited by the 0.3-0.5 mm/s measurement noise level in S-band tracking. One-way tracking through Laser Ranging can supplement the tracking available for OD with 28-Hz ranges with 20-cm single-shot precision, but is available only on the nearside (the lunar hemisphere facing the Earth due to tidal locking). Here, we report on the status of the OD effort since the beginning of the mission, a period spanning more than seven years. We describe modeling improvements and the use of new measurements. In particular, the LOLA altimetric data give accurate, uniform, and independent information about LRO's orbit, with a different sensitivity and geometry which includes coverage over the lunar farside and is not tied to ground-based assets. With SLDEM2015 (a combination of the LOLA topographic profiles and the Kaguya Terrain Camera stereo images), another use of altimetry is possible for OD. We extend the 'direct altimetry' technique developed for the ICESat mission to perform OD and adjust spacecraft position to minimize discrepancies between LOLA tracks and SLDEM2015. Comparisons with the radio-only orbits are used to evaluate this new tracking type, of interest for the OD of future lunar orbiters carrying a laser altimeter. LROC NAC images also provide independent accuracy estimation, through the repeated views taken of anthropogenic features for instance.
月球勘测轨道飞行器（LRO）自2009年以来一直在绕月运行，获取了对于理解月球和太阳系演化至关重要的独特且基础的数据集。LRO获取的高分辨率数据得益于精确的轨道确定（OD），减少了对地理定位和配准任务的需求。通过地面站的无线电跟踪，并结合LOLA测高交叉点，满足了初始位置知识要求（50米）。确定了LRO特定的重力场解，使得仅通过无线电的轨道确定能够在20米的精度水平上运行，尽管长期的倾角变化需要频繁更新。来自GRAIL的具有10千米空间分辨率的高精度重力场，进一步提高了仅通过无线电的轨道重建质量（10米）。然而，轨道重建部分受到S波段跟踪中0.3 - 0.5毫米/秒测量噪声水平的限制。通过激光测距进行的单向跟踪可以用20厘米单次精度的28赫兹距离补充用于轨道确定的跟踪数据，但仅在近月面（由于潮汐锁定而朝向地球的月球半球）可用。在此，我们报告自任务开始以来超过七年时间里轨道确定工作的进展情况。我们描述了模型改进和新测量方法的使用。特别是，LOLA测高数据提供了关于LRO轨道的准确、均匀且独立的信息，其具有不同的灵敏度和几何形状，包括覆盖月球背面且不依赖于地面资产。利用SLDEM2015（LOLA地形剖面和辉夜姬地形相机立体图像的组合），测高法可用于轨道确定的另一种用途。我们扩展了为ICESat任务开发的“直接测高法”技术，以执行轨道确定并调整航天器位置，以最小化LOLA轨道与SLDEM2015之间的差异。与仅通过无线电的轨道进行比较，以评估这种新的跟踪类型，这对于未来搭载激光高度计的月球轨道器的轨道确定具有重要意义。LROC NAC图像还通过例如对人为特征的重复观测提供独立的精度估计。
