Effects of the space environment on infrared filters and materials
With a continuously increasing demand for improvements to spaceflight optical instrumentation, for both high optical system performance and lengthening operational lifetimes, an investigation into the effects of the space environment on the durability and spectral stability of infrared filters and materials on the NASA Long Duration Exposure Facility (LDEF) was opportune. Prior to this experiment, assurance of the survivability of filters had been provided by ground-based testing, in an attempt to simulate those aspects of the space environment considered the most serious. Such testing, however, cannot prevent occasional anomalous behaviour or unexplained failures, particularly when filters may have been fabricated at a time considerably earlier than the proposed operating lifetimes, or delays may have extended the operational lifetime of the mission.
To obtain the data necessary for an assessment of the ability of filters to withstand the environmental rigours of space therefore required that in-situ testing was necessary. The experiment to expose infrared interference filters and coatings which had been constructed using traditional design and deposition methods was therefore a necessary requirement for assessing the filter materials suitability and stability when subjected to radiation from the space environment. The optical and physical behaviour of these filters and materials in the space environment being unconfirmed previously, but is critical to their performance.
The principal objectives of the experiment were to investigate the effects of the space environment on the spectral and mechanical stability of the multilayers and materials flown. Assess if a lifetime could be determined for filters and materials operating in the orbital environment, and determine any degradation mechanisms affecting the optical system performance.
Figure 1, Deployment of the LDEF from Challenger Space Shuttle mission 41C