A.2 Mitigate solar glare/glint, and control the thermal and contamination environments
Reflection of direct sunlight into the sensor will not damage LIS, but sufficient glint signal has the potential to momentarily “blind” LIS by filling its first-in/first-out (FIFO) buffer. Pre-launch, Manipulator Analysis Graphics and Interactive Kinematics (MAGIK) analysis was performed by NASA Johnson Space Center (JSC) to assess potential glare/glint and its impact. No glare spots or rapidly changing illumination were detected from either the solar panels or radiator. Images obtained from nadir-viewing cameras in STP-H4 (another STP mission located close to ISS LIS) qualitatively corroborate this result. Analysis of numerous other ISS images and videos also supported this inference (not shown).
During mission development, STP-H5 and LIS engineers examined both survival (during transfer) and temperature exceedance during operation. It was found that on-orbit temperatures remained within acceptable limits. Realtime housekeeping data from ISS LIS, including relevant temperatures, are gathered and posted to an internal website. These data are regularly monitored to ensure nominal instrument performance.
Modeling analysis was conducted for the molecular contamination effects on the LIS window transmission at 777.4 nm. The modeling was based on previous flight data from materials exposed in the ISS environment and estimations of outgassing rates in that environment for the mission duration of 3 years. Values were taken from baseline external contamination assessments collected during pre-launch testing. Worst case scenario showed only a 5% decrease in absolute transmission over 3 years due to typical contaminates. However, no significant loss has been observed to date with ISS LIS, and the nearly identical TRMM LIS instrument showed very limited performance degradation over its 17-year life span [Buechler et al. , 2014].