Spacecraft Pointing for Science Observations forMESSENGER's Venus Flyby 2 and Mercury Flyby

摘要

The MESSENGER (MErcury Surface, Space ENvironment, GEochemsitry, and Ranging) spacecraft completed its second flyby of Venus in June 2007 and its first flyby of Mercury in January 2008. A comprehensive set of science observations was obtained with the instrument suite during both of these flybys. Complex and tightly coordinated sets of spacecraft attitude and instrument commands were designed to achieve the diverse geometries required for these observations. The flyby pointing sequences exercised nearly all of the available guidance targeting options, often in combination with scan patterns. Durations and start times of each spacecraft turn and instrument observing session had to be carefully chosen based on control system capabilities. Observed areas had to be chosen to keep the sunshade pointing within the allowable zone for spacecraft thermal safety. The successful completion of both flybys has demonstrated the versatility of the MESSENGER pointing options and has provided valuable experience that will now be applied in designing observations for the remaining two Mercury flybys and for the orbital phase of the mission.