OPTICAL SIGNATURES OF PARTICLES IN-SPACE

Particles leaving spacecraft surfaces will interfere with the remote o bservation of emissions from objects in space, the earth, and its uppe r atmosphere. The goal of our analysis is to create a methodology that will permit the particle environment surrounding spacecraft to be qua ntitatively assessed, the particle composition to be determined from i ts spectral distribution, and the orbital particle source to be estima ted from the particle composition and trajectory analysis. We report o n 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-of-focus particles for staring and scanning sensor systems, and (3) automated image processing tools for particle trajectory anal yses and image enhancement. We present a review of the sources, sizes, and composition of particles observed in local spacecraft environment s. Predictions of the optical radiance signatures generated by likely contaminant species are made for several compositions and sizes as mod eled and observed on previous space observations. Predictions of the s pectrally 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 observation s from the sensitive CIRRIS1A IR radiometer/interferometer. The range and size of discrete particles were extracted from the temporally vary ing spectral radiances on detector arrays. The difficulty of locating particle events within large databases motivated the development of au tomated particle identification algorithms. Previous space missions ha ve observed particles in selected wavelength regions. The Midcourse Sp ace Experiment (MSX) (successfully launched in Spring 1996) will provi de simultaneous spectral coverage from 0.1 to 26 mu m that will permit particle composition to be extracted through analysis. We also presen t illustrations of how the automated extraction and enhancement algori thms will facilitate the analysis of the large MSX optical data bases. Particle detection thresholds and effects on sensitive UV-IR instrume nts are presented. The goal of this effort is to assess the effectiven ess of the practices and procedures instituted by the MSX satellite, t o enable contamination source identification and to guide remedies for future space missions. These predicted radiances and effects will ena ble future system designers to assess the potential impact of particle s on their mission's performance. (C) 1997 Society of Photo-Optical In strumentation Engineers.