The ground station established in 1968 at Weilheim by the German Aerospace Center (DLR) is the communications link between Earth and satellites in orbit. With its help, it is possible to create a communications link with a satellite when it flies over that allows data to pass either way.
Information received from satellites falls into one of two categories:
- "House-keeping" data, reporting the position and condition of the satellite.
- Payload data from scientific instruments.
This data is received by the ground station and relayed to ground control. Traffic in the opposite direction includes commands to control the satellite’s path. For example, a particular scientific instrument on board the satellite might be turned on or off, or the satellite’s orbit might be corrected to compensate for drift. Another function of the ground station is to track the satellite’s path. It does not take much to deflect a satellite from its course: atmospheric disturbances, micrometeoroids or solar radiation pressure.
Hence the course of the satellite, its distance from Earth and its speed are all measured when it flies overhead. The values recorded are used by ground control to plot its flight path for the following days. A ground station’s most important component parts are the radio telescopes, which have a significant influence on the quality of the transferred data.
In order to meet the demands of satellites and space probes, the radio telescopes need to have a range of properties:
- To track space probes, which may attain great distances from Earth, radio telescopes need to be very sensitive and manoeuvrable.
- Radio telescopes tracking satellites in orbit around Earth must be able to reposition themselves quickly in order to follow the satellite's path.
- Satellites in geostationary orbit need little or no correction from radio telescopes.
The positioning of all radio telescopes is computer-controlled. Radio telescopes tracking satellites in orbit around Earth have automatic tracking systems (Autotrack). All radio telescopes must be attuned to the relevant signal frequencies of the satellites.
The radio telescopes and systems at the station are controlled and monitored from a joint control room in Oberpfaffenhofen. It co-ordinates the operations of the radio telescopes and relays the commands generated in the control room to the ground station in Weilheim. In the other direction, signals received from space craft are converted into digital format, so that they can be relayed to the control room.
The Weilheim ground station is staffed in shifts 24 hours a day, seven days a week. 44 people work here in total.