Preparations for Lunar Reconnaissance Orbiter gravity and altimetry missions

Details Preparations for Lunar Reconnaissance Orbiter gravity and altimetry missions Preparations for Lunar Reconnaissance Orbiter gravity and altimetry missions

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p31b1401m&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #P31B-1401

Physics

1221 Lunar And Planetary Geodesy And Gravity (5417, 5450, 5714, 5744, 6019, 6250), 5417 Gravitational Fields (1221), 6250 Moon (1221)

Scientific paper

The launch of the Lunar Reconnaissance Orbiter is expected in early 2009. We present results of the preparations undertaken at the NASA Goddard Space Flight Center for the Lunar Orbiter Laser Altimeter (LOLA) instrument and the Radio Science experiment. A new lunar reference frame, vital to current exploration efforts for a return to the Moon, will be developed from the combined data sets collected by both experiments. In addition to collecting topographic data, LOLA will assist the Precision Orbit Determination of the LRO spacecraft. The 50-m total positioning requirement is very challenging due to the low altitude (50km on average) and the lack of radio tracking over most of the lunar far side. While commercial S-band tracking data will be the principal measurements used for orbit reconstruction, the unique five-beam altimeter enables the use of the altimetric cross-over technique with unprecedented accuracy. Previous simulations showed that the more numerous (by a factor of 25) crossings could greatly help in reducing the uncertainties in the recovered orbit. We show here that cross-track information contained in the acquired topographic swaths (compared to multiple two-dimensional profiles) can constrain orbits to a few meters horizontally and better than 50cm vertically. Swath cross-overs will be most valuable in mid-latitudes, where cross-overs are sparse and tracks intersect at shallow angles. A spacecraft physical model, for use in the GEODYN II orbit determination program, includes inter-plate self- shadowing in the calculation of the spacecraft cross-sectional area for solar radiation pressure. Simulations indicate that solar radiation effects on the orbit can be on the order of 10-20m. Because the thermal radiation forces are larger and more variable than on Mars, the current model of the thermal flux map was updated, with effects on the order of 1-5m. The benefit of using the self-shadowing model for the albedo and thermal forces is currently being assessed. Historical radio tracking data has also been reprocessed using the latest ephemerides (DE421) and improved force models (albedo and thermal radiation for all spacecraft; attitude model and estimated panel reflectivities for Lunar Prospector). The resulting normal equations will be important for the early LRO gravity solutions.

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