The contamination control for the next-generation space infrared observatory SPICA is presented. The optical performance of instruments on space observatories are often degraded by particulate and/or molecular contamination. Therefore, the contamination control has a potential to produce a significant risk, and it should be investigated in the risk mitigation phase of the SPICA development. The requirements from contamination- sensitive components onborad SPICA, the telescope assembly and focal plane instruments, are summarized. Possible contamination sources inside and outside the SPICA spacecraft were investigated. Based on impact on the SPICA system design, the following contamination sources were extensively studied through simulation and measurement; (1) outgassing from the payload module surrounding the telescope mirror and focal plane instruments, (2) contamination due to the thruster plume, and (3) environmental contamination during the integration, storage and verification phases. Although the outgas from the payload module and the thruster plume were estimated to produce only a negligible influence, the environmental contamination was suggested to affect significantly the telescope and focal plane instruments. Reasonable countermeasures to reduce the environmental contamination were proposed, some of which were confirmed to be actually effective.
Based upon our previous study, the outgassing and deposition phenomena under thermal vacuum conditions can be expressed by empirically based mathematical models for each material. Herein, we compared several time-dependent outgassing models and temperature-dependent sticking models with the data obtained from ASTM E1559 tests. This study suggests that the Volatile Condensable Materials (VCMs) on a receiver at wide-range temperature can be simulated in consideration of re-evaporation effect of deposited species. On the other hand, we found that temperature-dependent outgassing models were necessary to predict actual molecular contamination environments considering the on-orbit thermal cycles. This paper describes evaluation results of temperature-dependent outgassing models and deposition models where deposited species are taken into consideration by using the test data of Outgassing Rate Measurement Apparatus in accordance with ASTM E1559. In these isothermal tests, operating temperatures of four QCMs were set <90 K, 213 K, 263 K and 298 K. The effusion cell temperature was 323 K, 373 K and 423 K for each test. Furthermore, we discussed validity and issues of the mathematical models in order to predict on-orbit molecular contamination deposition.