Following thermal vacuum/thermal balance testing, a gray haze was discovered on the corners of the Wide Field/Planetary Camera (WF/PC) aperture window. The phenomenon was suggested to be a result of molecular transport from a low outgassing structural adhesive. Detailed analyses, both chemical and analytical, were conducted to assess the formation of the haze. Each material was considered individually, as it was not known if the actual contamination was a result of one, many, or possibly none of the materials considered. Results of the analytical assessment and the comparison with the aforementioned chemical analyses provided incontrovertible evidence as to the cause of the window haze. The resultant cleanup and subsequent elimination of the problem are also addressed. [Editor's Note: This 1990 paper is republished as part of the Journal of the IEST 50th anniversary celebration. It is accompanied by remarks from Patti Hansen, author of "Overview of the HST Contamination Engineering Program at 15 Years: A Cleanliness Metric for Success with Optical Satellites" paper in this issue.]

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The prediction of contaminant deposition on the cold (-100°C) charge coupled device (CCD) sensors of the Wide Field Planetary Camera (WFPC) due to sources internal to the instrument is crucial to the evaluation of expected performance and to the assessment of approaches for improvement. An integral component in such predictions is a model of the transport from the internal sources to the CCD's. In the present work, the model used is based on the Jet Propulsion Laboratory (JPL) Contamination Analysis Program (CAP).A CAP model comprises a geometric multinodal representation of the instrument, internodal shape factors for line of sight transport, nodal contaminant sources and the necessary deposition and re-emission kinetics. In CAP, indirect transport by way of intermediate nodes (of considerable importance to the internal problem) is explicitly calculated as a diffuse reflection for each internodal exchange. This leads to rather long computer run times for each required 30 day prediction for separate sourcesand for various internal modifications to reduce the accumulation on the CCD sensors. A method has been developed to pre-calculate the effective total transport factors from each source node to each receiving node (including the CCD sensors) and from each re-emitting node to each receiving node. The effects of this preprocessing calculation are to sharply reduce the number of nodes, to increase the allowable time step in the transient CAP analysis, and to greatly reduce the run time.Some results of this work to date are presented and the interpretation of the results are discussed. The discussion includes the implications of the results for other space instruments.

The accuracy, lifetime, and mission effectiveness of a spacecraft is affected adversely by any degradation of sensitive spacecraft surfaces. With a trend towards more sophisticated and complex spacecraft systems capable of performing multimissions over longer time periods, there is increasing concern about the effects of plume contamination. Analytical tools in concert with a good data base are necessary to predict the transport of plume contaminants and their effects on spacecraft surfaces. This paper describes an assessment of bipropellant thrusters, the production and transport of plume contaminants from these thrusters and the use of the JPL Contamination Analysis Program to assess the effects of plume contamination on the Galileo spacecraft.