In order to be able to communicate with spacecraft, antenna systems are needed. The DLR ground station in Weilheim, 60 kilometres south-west of Munich, was established in 1969 (start of construction November 1967) and is one of the links between Earth and its orbiting satellites. It helps establish communication links with a satellite during its trajectory, thereby allowing simultaneous two-way data transmission. The data exchange with the spacecraft takes place via a variety of different antennas (ranging from 4.5 to 30 metres in diameter). The satellite ground station in Weilheim is operated by the DLR German Space Operations Center (GSOC).
Data from the satellite is called telemetry and can be divided into two categories: ‘housekeeping’ data that gives information on the satellite's condition and attitude (its position and orientation in space) and science data originating from scientific instruments.
This telemetry data is received and processed by the ground station and forwarded in digital form to the GSOC control centre in Oberpfaffenhofen. Data in the opposite direction – i.e. from the ground to the satellite – is known as telecommands. These contain control commands to the satellite – examples are switching scientific devices on/off or correcting the satellite's attitude. These are generated in the GSOC control room and transmitted directly to Weilheim.
A further function of the ground station is the on-going determination of the satellite's orbit. Satellite orbits are subject to disturbances, by the residual atmosphere, micro-meteorites and solar radiation pressure, for example. The satellite's direction, range (i.e. distance from the Earth) and speed – its so-called tracking data – are therefore measured during its trajectory. Using these readings, orbit predictions for the coming days are calculated in the control centre.
Multi-mission operation, around the clock
According to the Consultative Committee for Space Data Systems (CCSDS), Weilheim is classified both as a Deep Space Network and a Non-Deep Space Network (Near Earth Network) and can support space missions in the L, S, X, Ku and Ka frequency bands.
The individual antenna stations at Weilheim can be operated independently – which means that the Weilheim ground station can support several missions simultaneously (multi-mission operation). All antennas and station facilities are monitored and controlled from one common control room. New software developed at GSOC allows the necessary sequences to be standardised, regardless of the particular mission, frequency range and orbit type, which considerably simplifies the operation.
The Weilheim ground station is operated 24 hours a day, seven days a week. A total of 44 people work here.
To ensure maximum availability, the antenna stations are equipped with redundant devices. All systems vital to satellite operation at Weilheim's ground station are fed by an uninterruptible power supply (UPS) that draws its power from a battery during short-term failures of the energy grid and from a 1250 kVA Diesel generator during long-term failures.
Weilheim and Oberpfaffenhofen in the global network
Weilheim ground station is connected with the GSOC in Oberpfaffenhofen via a redundant communication link. GSOC coordinates the antenna operations, generates the control commands for the satellites and receives and processes the satellite data from Weilheim (telemetry and tracking data).
In addition, other space agencies or external customers regularly lease 'antenna time' for their missions. Weilheim is therefore embedded in a worldwide communication network via GSOC. GSOC thereby ensures that all the necessary operational data connections between Weilheim and other integrated ground stations and the respective satellite control room are available and correctly configured. Various interfaces and protocols must be implemented and antennas, facilities and systems must be planned, configured and serviced, along with the network infrastructure.