The Herschel spacecraft is made up of two major components, the payload module and the service module.
The extended payload module comprises:
- The Telescope: equipped with a 3.5 m primary mirror, which collects infrared and sub-millimetre radiation from astronomical sources and directs it, via the secondary mirror, onto the detectors of the three instruments
- The Cryostat: contains the cold components of the three instruments, a liquid helium cooling system and dedicated coolers for components requiring even colder conditions than those offered by the cryostat alone
- The Sunshade: serves to protect the telescope and cryostat from solar radiation, shield the telescope from Earth straylight and also supplies the spacecraft with electric power from the solar cells on the lower part of its outer surface
- Support Structures: mechanically connect the various payload module components together and mount them on the service module while providing thermal isolation where required
The service module 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, gyroscopes and Sun sensors, and changing the spacecraft's attitude or orbit by means of reaction wheels and 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.