Earth-orbiting satellites confront rapid changes in temperature, repeatedly passing from behind the earth’s shadow into sunlight and then back into shadow again. Moreover, since the orbit lies outside the earth’s atmosphere, the instruments on board the satellite are not able to cool down by conveying their heat to the atmosphere. Because the thermal behavior while on orbit (in the vacuum of space) is different from the thermal behavior while on the ground, it is important to test to see whether or not the instruments can maintain their temperature within the range required of them. For this reason thermal tests were carried out inside a vacuum chamber (tank) that simulates the vacuum of space.
In the picture, the SXI has been placed into the vacuum tank, where it is being subjected to cycles of heating and cooling. During this time, the behavior of the SXI is monitored to see whether or not it is behaving as expected. The monitoring system being used is the same kind of system that will be used while the satellite is on orbit, and the screen displays data that mimics what an actual observation will be like and thus serves as a rehearsal for actual spacecraft operations.