High-resolution Topomapping of Candidate Mer Landing Sites with Moc: New Results and Error Analyses

Introduction: This abstract describes the continuation of work initially reported last year [1] on topographic mapping and roughness analysis of candidate Mars Exploration Rover (MER) landing sites using high-resolution images from the Mars Global Surveyor Mars Orbiter Camera Narrow-Angle subsystem (MGS MOC-NA; [2]). The main goal of this work at present is to contribute to assessments of whether the MER spacecraft could land safely at each site. To this end our data suggest that the sites now being considered are much more likely to be safe than several sites reported on previously [1] and since eliminated. Topographic data for the sites that are ultimately selected will also be useful in planning mission operations and analyzing the scientific return from the rovers, however, and it is likely that the topographic models we report on here will be augmented by more extensive coverage in the coming year. Since our earlier report there have been several changes and advances in the process of mapping the candidate landing sites and assessing their safety. First, the approach to quantifying landing safety has become much more elaborate. Topography affects the landing process in a number of ways on different lengthscales, necessitating the use of different input datasets. Our high-resolution (typically 3–10 m) mapping with MOC provides information that is needed to evaluate safety as the spacecraft bounces to a stop on the surface. Initially, slopes ≥ 15° on a 5-m baseline (approximately the diameter of the MER airbag cluster) were determined to be "unsafe" and sites with ≥ 1% probability (later, ≥ 2%) of such slopes were to be excluded. This simple criterion has been replaced by the requirement that Monte Carlo simulations of the trajectory carried out by mission engineers at JPL result in an acceptably low failure rate as determined by various criteria (e.g., excessive vertical or horizontal velocity). For sites with a significant range of surface roughnesses, these simulations must be carried out for each "hazard unit" and the results combined in a weighted average that represents the overall failure rate for the site. Our digital elevation models (DEMs) of hazard units, rather than the roughness statistics derived from them, are thus the input to the safety assessment process. Summary roughness statistics are nevertheless useful for comparing sites and for making a rough, unofficial assessment of site safety, based on the prevalence of 15° slopes. We therefore report slope statistical measures for the …