|
Particles leaving spacecraft surfaces will interfere with the remote observation of emissions from objects in space, the earth, and its upper atmosphere. The goal of our analysis is to create a methodology that will permit the particle environment surrounding spacecraft to be quantitatively assessed, the particle composition to be determined from its spectral distribution, and the orbital particle source to be estimated from the particle composition and trajectory analysis. We report on the analytical tools we developed to permit this goal to be achieved: (1) predictions of radiant intensities over the UV-IR as a function of size and composition, (2) predictions of the image produced by near-field out-offocus particles for staring and scanning sensor systems, and (3) automated image processing tools for particle trajectory analyses and image enhancement. We present a review of the sources, sizes, and composition of particles observed in local spacecraft environments. Predictions of the optical radiance signatures generated by likely contaminant species are made for several compositions and sizes as modeled and observed on previous space observations. Predictions of the spectrally structured radiances for silver, aluminum, alumina, carbon, solid carbon dioxide, water ice, silicon dioxide, and titanium dioxide are presented. The predictions were exercised in the analysis of the orbital particle environment surrounding the shuttle using observations from the sensitive CIRRIS1A IR radiometer/interferometer. The range and size of discrete particles were extracted from the temporally varying spectral radiances on detector arrays. The difficulty of locating particle events within large databases motivated the development of automated particle identification algorithms. Previous space missions have observed particles in selected wavelength regions. The Midcourse Space Experiment (MSX) (successfully launched in Spring 1996) will provide simultaneous spectral coverage from 0.1 to 26 ? m that will permit particle composition to be extracted through analysis. We also present illustrations of how the automated extraction and enhancement algorithms will facilitate the analysis of the large MSX optical data bases. Particle detection thresholds and effects on sensitive UV-IR instruments are presented. The goal of this effort is to assess the effectiveness of the practices and procedures instituted by the MSX satellite, to enable contamination source identification and to guide remedies for future space missions. These predicted radiances and effects will enable future system designers to assess the potential impact of particles on their mission’s performance.
|
