Molecular contamination degrades sensitive spacecraft surfaces and can adversely affect the useful life of a spacecraft.
In order to accurately predict spacecraft performance and end of life, an understanding of the primary mechanisms and
processes involved in the deposition and "fixing" of molecular contaminants is necessary. The objective for this research
effort has been to investigate how solar vacuum ultraviolet (VUV) radiation and surface temperature influence
photochemical reactions of molecular contaminants. This report presents the effects of VUV intensity and surface
temperature on photo-deposition and "photo-fixing" of dioctyl phthalate (DOP) films.
Particle-induced light scatter reduces sensitivity and degrades performance of optical systems. Though particles are generally considered to be the primary source responsible for stray radiation, there is evidence that molecular contaminants also induce light scatter. The primary objective for this research effort has been to increase our understanding of molecular contaminant film growth and its implications for light scatter. Herein, our new molecular film deposition and imaging facility is described. In-situ imaging data, acquired from non-uniform films of contaminant analogues, has revealed that even small quantities (less than 100 angstrom mass equivalent) of molecular contamination can produce scattered light. These data suggest that small amounts of molecular contamination have the potential to significantly impact the performance of scatter sensitive optical systems.
This paper describes progress in the development of a new contamination prediction code, The Aerospace Satellite Contamination Model Evaluator (ASCME). This paper provides fitted parameters for Langmuire evaporation models of contaminants from 15 materials based upon kinetic testing according to the ASTM E1559-93 procedure. It is shown that the evaporation rate parameters, p1 and p2, derived from the E1559 TGA testing do not always agree with corresponding parameters calculated from published vapor pressure data. The uncertainty in extracting p1 and p2 parameters due to experimental scatter is estimated to be about ±5.6% and ±4%, respectively. It is demonstrated that m desorption profiles can vary significantly, depending upon the originating source material. It is shown that evaporation rate parameters depend strongly on the test method, static vs. kinetic.
Conference Committee Involvement (2)
Optical System Contamination: Effects, Measurements and Control IX
15 August 2006 | San Diego, California, United States
Optical System Contamination: Effects, Measurements, and Control VIII