Motion, Heat, and Energy
The spacecraft system provides the support structure and environment necessary for the telescope and the science instruments to work as an observatory.
In order to provide motion to the observatory, Chandra has two different sets of thrusters: one for propulsion and the other for momentum unloading. The propulsion thrusters were used immediately after launch to help propel Chandra into its final orbit, which is elliptical and very high in altitude. The momentum unloading thrusters are periodically used to apply torques to Chandra and, thereby, lower the accumulated momentum in its reaction wheels, which are used to control Chandra's altitude.
To control the temperatures of critical components, Chandra's thermal control system consists of a cooling radiator, insulators, heaters and thermostats. It is particularly important that the temperature near the X-ray mirrors be well controlled to keep the mirror in focus. The temperature in many parts of the spacecraft is continually monitored and reported back to mission control.
There is no single operating temperature of Chandra, as there is a lot of variation. One of the coldest parts of the spacecraft is the Advanced CCD Imaging Spectrometer (ACIS) focal plane which is regulated at -120 C. It gets passively cooled by the ACIS radiator which faces straight out into cold space and is even colder than -120 C. The High Resolution Mirror Assembly (HRMA) is held at a very stable temperature and is a balmy 71 F to within about a 1 degree F. Other parts of the spacecraft have wild temperature swings, for instance the Fine Sun Sensor (which is mounted on the sun-facing exterior of the spacecraft) goes from around 30 F to almost 200 F, sometimes in the space of a few hours!
Chandra's electrical power comes from its solar arrays. This energy is then stored in three banks of batteries and distributed in a carefully regulated manner to the Observatory by the electrical power system. The solar arrays generate approximately two kilowatts of power for the heaters, science instruments, computers, transmitters, etc.