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 far-ultraviolet (FLJV) performance of optical imaging instruments using cooled detectors is extremely sensitive to molecular contamination. Conventionally stringent cleanliness standards for material screening, hardware fabrication, and assembly level test and integration are inadequate for instruments which require a stable FUV performance. A multifaceted contamination control strategy has been developed for the second generation Wide-Field and Planetary Camera (WFPC-2) to improve the FIJV stability by several orders of magnitude, compared to the first camera (WFPC-l). This strategy involves: Improved on-orbit boil-off capability of the detector optics, added internal shielding and instrument venting, in-process subassembly vacuum bakeout at elevated temperatures, material substitution, sample testing in ultra-clean vacuum facility, and internal instrument contamination transport modelling. A science performance goal of 1% photometric accuracy at 1470 Angstrom over an extended time (of at least 30 days) has been established as a contamination control target for WFPC-2. The WFPC-2 is currently planned to be launched by the Shuttle in mid-1993 and replace the WFPC-l which was recently launched with the Hubble Space Telescope (HST).