JAXA is developing a contamination analysis tool “J-SPICE” (Japanese Spacecraft Induced Contamination analysis software). Generally speaking, contamination analysis tools predict based on various input data and mathematical models of contaminant behavior, which means prediction accuracy depends on the validity of mathematical models as well as of input data. We investigated the validity of a diffuse reflection model applied in J-SPICE by comparing the reflection flux of contaminant molecules measured by the ground experiment and the analytical result of the J-SPICE. The result showed that the diffuse reflection model of J-SPICE reasonably explains molecule distribution reflected by a flat surface.
Molecular contamination by outgassing can degrade the performance of optical components. In orbit, spacecraft are exposed to various environments. UV is one of the most critical. It may also have the potential to cut the chains of organic molecules in contaminants due to its high energy, degrading optical properties and even re-emission behavior. In the present study, using two kinds of UV sources with different wavelength ranges, we compare the effect of UV lights irradiated on an optical surface with silicone contaminants. The irradiated samples were evaluated in terms of their optical properties and re-emission behavior, i.e. transmittance, and thermal desorption.
Outgassing rate measurements are basically performed for fresh materials, e.g. just cured adhesives, paints, etc. and reveal a lot about how the material can behave as a contamination source. It is also important to determine the bakeout process sufficiently. In the present study, a typical silicone adhesive for use in space, RTV S-691, Wacker Chemie, was selected for the measurement. Two cured specimens, 40 × 40 mm in size, were applied for several isothermal tests under identical conditions: a specimen at 125 degrees C for 144 hours with CQCM at -193 degrees C to measure TML. Consequently, it was determined that the TML and TML rate could be reduced by bakeout as expected. It also emerged that a longer bakeout, i.e. a longer cumulative bakeout time, for the material would reduce the TML and TML rate more effectively. The results suggest that bakeout mainly affects the behavior in the “low-rate” phase, whereby the TML rate curve can be divided into two phases. The elapsed time for a specimen can also be considered the cumulative test time. Based on the cumulative elapsed time, the TML rate curve is replotted and a correlation emerges between the cumulative bakeout time and TML rate. The first measurement data of TML and the TML rate could be affected by the stored time from cure, which might result from the change in unreacted substances declining as the stored time elapsed.