SAFE HAVEN FOR AN INFRARED TELESCOPE IN LEO ORBIT (WISE Sun Earth Pointing Prevention)

摘要

The Wide-Field Infrared Survey Explorer (WISE) mission launched in December of 2009 is a true success story. The instrument had to be protected from infrared heat of the Sun and the Earth. To accommodate the requirement of keeping the Sun and Earth significantly away from the instrument boresight, there were large instrument keep-out zones. So large in fact, it is easier to describe them as keep-in zones. The algorithm to keep the Sun and Earth out of these zones and optimize the direction of travel to reduce risk of spending more time in the keep out zones was developed during Phase B. This algorithm was not only tested on the ground during Phase C/D but was intentionally exercised on-orbit in Phase E. The algorithm had to be developed because no previous Ball missions had both Sun and Earth Exclusion zones in quite the same way. Additionally, the Emergency Mode Controller (EMC), which could only do simple math functions, had to be able to implement Sun & Earth Pointing Prevention (SEPP). The mission performed beyond expectations on-orbit and never required the use of the algorithm; however, it was flight proven because in the commissioning phase ground ops intentionally commanded the instrument into the Earth Keep-out zone and the spacecraft responded to keep the instrument from entering it.