Panel showing the components of the Herschel satellite, which is composed of three sections. First is the telescope, which has a 3.5 m-diameter mirror protected by a sunshade. The telescope focuses light onto three scientific instruments housed in a giant thermos flask, known as a cryostat, which contains liquid superfluid helium colder than -171°C to make the instruments as sensitive as possible. The instruments and the cryostat make up the second section – the payload module. The third element of the satellite is the service module below the payload module. It houses the instrument electronics and the components needed to make the satellite function, such as the hardware for communication with Earth. It also houses the data processing and spacecraft control electronics, operating at ambient temperature.