During Rosetta’s prolonged interplanetary expedition, reliable communications between the spacecraft and the ground will be essential.
All of the scientific data collected by the instruments on board the spacecraft are sent to Earth via a radio link. The operations centre, in turn, remotely controls the spacecraft and its scientific instruments via the same radio link.
The Mission Operations Centre during Rosetta’s entire 12-year journey is the European Space Operations Centre (ESOC) in Darmstadt, Germany. ESOC is responsible for all mission operations, including:
- mission planning, monitoring and control of the spacecraft and its payload;
- determination and control of the spacecraft trajectory;
- distribution of the scientific data received from the spacecraft to the Rosetta scientific community and the Principal Investigators.
A Science Operations Centre will also be located at ESOC during the active phases of the mission. Its task will be to coordinate the requests for scientific operations received from the scientific teams supporting both the orbiter and the lander instruments.
Lander operations will be coordinated through the German Aerospace Research Centre (DLR) control centre in Cologne, and the scientific control centre of CNES, the French space agency, in Toulouse.
Radio communications between Rosetta and the ground will use a newly developed deep-space antenna which was built by ESA at New Norcia, near Perth in Western Australia. This 35-metre diameter parabolic antenna concentrates the energy of the radio signal in a narrow beam, allowing it to reach distances of more than 1000 million kilometres from Earth.
Signals are transmitted and received in two radio frequency bands: S-band (2 GHz) and X-band (8 GHz). The radio signals, travelling at the speed of light, will take up to 50 minutes to cover the distance between the spacecraft and Earth!
ESA is building another 35-metre parabolic antenna at Cebreros in Spain. It will begin to operate in 2005 providing further coverage for Rosetta.
During the mission, the rate at which data can be sent from Rosetta to Earth will vary from 10 to 22 000 bits per second. However, the rotation of the Earth means that real-time communications will not always be possible.
The spacecraft will be visible from the New Norcia antenna for an average of 12 hours per day. In addition, there will be several periods of communications black-out when the spacecraft passes behind the Sun.
To overcome these breaks in communication, Rosetta’s solid-state memory of 25 Gbits capacity is able to store all scientific data and then transmit them to Earth at the next opportunity.