The particle environment on-orbit: Observations, calculations, and implications

Abstract

The full potential for making remote observations from space free from atmospheric attenuations and distortions may not be realized due to the residual environment surrounding orbital experiments: particulates could overwhelm or severely complicate remote astronomical or atmospheric sounding observations. Small particles are lifted into space by the observatory and its carrier and take considerable time to evolve from surfaces. Single near-field particles have been observed which produce irradiance levels larger than the brightest stars and brighter than the emission from the entire earth limb airglow layer. The existing data bases are reviewed including: 1) the low light level camera videotape data of STS-3 in which large persistent particles were observed; 2) the data from the stereo cameras which were part of the Induced Environmental Contamination Monitor pallet assembled by NASA Marshall - which is being analyzed to obtain particle number densities, trajectories, and decay times; and 3) data from the Particle Analysis Camera for Shuttle which was part of the HITCHHIKER pallet on a January 1986 Mission is current being analyzed to obtain decay rates and correlations with orbital activities. The implications for several other data bases such as the Infrared Telescope is also described. The analysis of these spectrally broad band observations is further complicated by the nature of the particle's scattering of light. Depending on wavelength and particle size, the scattering of solar radiation or earth radiation, or particle self emission will dominate the optical signature. The scattering and emission from particulates will likely be highly structured as a function of wavelength. We present Mie scattering calculations for particle size distributions observed on-orbit. Finally, we assess the consequences of the observations and calculations on future space-based observations.