The Planck spacecraft is made up of two major components, the payload module and the service module.
The payload module comprises:
- The telescope, equipped with primary and secondary mirrors that collect microwave radiation and direct it onto the instrument focal plane units and a baffling system to restrict the entry of stray radiation into the telescope optics
- The cryogenic focal plane units of the two instruments
- The instrument cooling chains (excluding the compressors and control electronics)
The service module is an octagonally shaped bus and contains the systems needed to operate the spacecraft:
- Power: generation, storage, conditioning and distribution of electric power
- Attitude and Orbit Control: measurement of the spacecraft's attitude using star trackers and sun sensors, and changing the spacecraft's attitude or orbit by means of hydrazine thrusters
- Control and Data Management: receipt, storage and execution of ground commands, autonomous operation of the spacecraft in the absence of a ground station link, storage and management of observation and housekeeping data
- RF Communications: linking the spacecraft with the ground station to send back data and receive commands
The service module also houses those parts of the instruments that do not require cooling, and the compressors and control electronics for the instrument cooling chains.