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Proceedings Paper

Molecular transport modeling for spaceborne instrument contamination prediction
Author(s): Chung M. Wong; Robert M. Moision; Jesse D. Fowler; De-Ling Liu
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Paper Abstract

We present a finite element model for the prediction of molecular contamination through narrow pathways in a hypothetical spaceborne instrument using the commercially available COMSOL Multiphysics software. The free molecular flow module of COMSOL uses the angular coefficient method as an alternative to particle based methods. In the angular coefficient method, the microscopic dynamical aspect of the material transport problem is reduced to a macroscopic problem by calculating emission and incident fluxes at each surface rather than the trajectories of individual molecules. The model was validated by comparing the simulated and experimentally measured pressure differential between two chambers separated by a mechanical test structure. The mechanical test structure was designed to exhibit narrow pathways with characteristic size that can be found on spaceborne optomechanical structures. It is shown that materials can slowly migrate through these pathways in a spaceborne instrument to cause noticeable performance degradation within a time scale of a few months. The model for material transport through the test structure was also verified using a stochastic method. To simulate water infiltration through narrow pathways of a hypothetical spaceborne instrument, nominal payload temperature profile was used in addition to setting empirical input parameters such as the desorption energy of water and the outgassing rate of water from multilayer insulator thermal blankets to the appropriate surfaces in the modeling domain. The rate of growth of ice films on low temperature optical components and how optical performance can be degraded over time are discussed in this paper.

Paper Details

Date Published: 9 September 2014
PDF: 12 pages
Proc. SPIE 9196, Systems Contamination: Prediction, Measurement, and Control 2014, 919608 (9 September 2014); doi: 10.1117/12.2062288
Show Author Affiliations
Chung M. Wong, The Aerospace Corp. (United States)
Robert M. Moision, The Aerospace Corp. (United States)
Jesse D. Fowler, The Aerospace Corp. (United States)
De-Ling Liu, The Aerospace Corp. (United States)

Published in SPIE Proceedings Vol. 9196:
Systems Contamination: Prediction, Measurement, and Control 2014
Nancy Carosso; Joanne Egges, Editor(s)

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