Orbit determination of the Lunar Reconnaissance Orbiter: Status after seven years. (1st November 2018)

• Record Type: Journal Article
• Authors: Mazarico, Erwan; Neumann, Gregory A.; Barker, Michael K.; Goossens, Sander; Smith, David E.; Zuber, Maria T.
• Is Part Of: Planetary and space science. Volume 162(2018)
• Page Start: 2
• Page End: 19
• Publication Date: 2018-11-01
• Subjects: Lunar Reconnaissance Orbiter -- Moon -- Orbit determination -- Radio tracking -- Laser altimetry; Space sciences -- Periodicals; Atmosphere, Upper -- Periodicals; Sciences spatiales -- Périodiques; Haute atmosphère -- Périodiques; 523
• DOI: 10.1016/j.pss.2017.10.004
• Languages: English
• ISSNs: 0032-0633

Abstract

Abstract: 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 m) 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 m, 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 m). 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. Highlights: The LRO trajectory was reconstructed from July 2009 to November 2016. GRAIL gravity and radio tracking result in typical overlap performance of 50 cm radially and <10 m in total position. We use altimetric ranges as geodetic tracking data directly against global, high-resolution LOLA basemaps. Altimetry alone supports orbit reconstruction better than 20 m in total position, of interest for future lunar exploration.