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].