MSX contamination environment during the first orbital year

Abstract

The contamination and natural environment at 900 km altitude has been accurately measured by the suite of calibrated instruments on the Midcourse Space Experiment (MSX) satellite. Concentrations of gases, molecular films, and particles were measured as a function of mission elapsed time and as a function of spacecraft activities. Two years ago we reported on the initial orbital observations and trends during a 2-year period on orbit. Further analyses of that data are providing physical insight into the observed trends. The temporal decay of the gaseous environment is driven by solar exposure time, with replenishment magnitude affected by the material and interior spacecraft temperatures between solar exposures. Laser time particle generating events have been observed. Particle trajectories have been analyzed to extract possible generation sources. Data acquisition continues at a low rate and the continuing *Executive Vice President, Senior Member AIAA Principal Research Scientist *Principal Staff Chemist, Member AIAA Senior Staff Engineer 'Engineering Specialist, Associate Fellow AIAA ^Research Scientist, Senior Member AIAA Copyright © 2001 by Physical Sciences Inc. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. decay in accretion rates on surfaces and pressure surrounding the spacecraft will be presented. At this time (greater than 4 years after launch) measurable pressure transients are still observed periodically on MSX even though there are no pressurized gases (from thrusters or sensors) present on the spacecraft. This paper summarizes the magnitudes and timescales associated with the continuing long-term decay trends and discrete events (such as repetitious night time pressure rises). Lessons learned from design, ground preparations, and orbital operations will be presented. This information will be provided to allow improvements in procedures and design for future space platforms.