WF/PC INSTRUMENT SCIENCE REPORT 91-03:
WF/PC-1 Contamination Control
By R. E. Griffiths
March, 1991
Abstract excerpted from the report:
The prediction of contaminant deposition on the cold (-100C) charge coupled device (CCD) sensors of the Wide Field Planetary Camera (WF/PC-1) 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 sources and 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.
For a copy of the report, please contact help@stsci.edu.