Communications station dish. Photo: ESA

The European Space Agency's Rosetta mission to Comet Wirtanen is one of the most ambitious scientific missions to be launched during the next decade. A particular challenge posed by Rosetta is the problem of receiving a stream of data from a spacecraft which is flying alongside a small, fast-moving comet almost 900 million km from Earth.

In order to maintain the vital link with its comet-chasing Rosetta spacecraft in the depths of the outer Solar System, ESA has recently signed an agreement with the Australian government to build a second Deep Space ground station down under.

ESA's latest 35-metre diameter Telemetry, Tracking and Command antenna will be located at New Norcia, about 140 km north of Perth, Western Australia. The prime contract to build the antenna has been awarded to SED Systems Incorporated from Saskatoon, Saskatchewan, Canada. Other members of the project team include Vertex Antennentechnik of Duisburg, Germany and Vertex Antenna Systems Division of Santa Clara, California, USA.

The 630 tonne antenna should be operational in late 2001, more than one year before the launch of Rosetta. After launch in January 2003, the dish will be used to send commands to the roaming spacecraft and receive the avalanche of data sent back from Rosetta as it flies past the Earth and Mars, traverses the asteroid belt and swings into orbit around Comet Wirtanen.

In order to do all of this, the 120 tonne New Norcia dish will have a pointing accuracy of 0.01 degrees, equivalent to one fiftieth the diameter of a full Moon. It will be able to receive faint signals from Rosetta in the 2 GHz (S-band) and 8 GHz (X-band) wavelengths simultaneously, while its 20 kW transmitters will also operate in both wavebands. Later upgrades will enable additional high frequency Ka-band reception.

Most of the time, the station will be unmanned. Operations will be remotely monitored and controlled from the station in Gnangara / Perth, though it might be occupied by staff during critical stages, such as Rosetta's orbital insertion around the tiny cometary nucleus.

An artist's concept of the Rosetta comet probe. Photo: DSS

Throughout Rosetta's decade-long adventure, the new Australian antenna will be the main communications link between the spacecraft and Mission Control at the European Space Operations Centre (ESOC) in Darmstadt, Germany. However, a 15-metre dish at Kourou in French Guiana will also be available for near-Earth mission phases in support of satellite check-out, and NASA's Deep Space Network will be used as a back-up during critical mission phases.

Although its first Deep Space operations will be for the Rosetta mission, the antenna will be used to support other deep space and high elliptical orbit missions, including ESA's Mars Express orbiter-lander, which is also scheduled for launch in 2003.

When completed, New Norcia will be the jewel in the worldwide network of ground stations operated by ESOC. Other ESA ground stations are located in Kiruna (Sweden), Redu (Belgium), Villafranca (Spain), Maspalomas, Canary Islands (Spain), Perth (Australia) and Kiruna (French Guiana).