ESA's new antenna is quite a dish!
20 September 2001Sending a spacecraft such as Rosetta millions of kilometres into space to explore other worlds is one of the most exciting endeavours undertaken by modern science. However, the fiery launch and prolonged trek to rendezvous with a comet is not the only part of the story. Without a means of gathering the data from deep space, analysing and storing it, the spacecraft's mission is worthless.
In preparation for a new era in Solar System exploration, ESA has decided to construct a 35-metre deep space antenna in Australia. (ESA is already running a 15-metre antenna at a ground station near Perth, which is used for missions such as the powerful XMM-Newton X-ray observatory.)
The New Norcia ground station, which should be finally ready for handover to the Agency in July 2002, lies on the western coast of Australia, about one and a half hours' drive north of Perth.
Visitors to the site can see evidence of rapid development, with all of the roads and basic infrastructure already completed. One of the most notable advances came on 18 August, when the skeletal framework of the 35-metre-diameter parabolic reflector dish was raised into position on the rotating base with the aid of two powerful cranes.
In the coming weeks, the panels of the reflector will be installed and adjusted so that variations in the surface smoothness of the main reflector are no greater than 0.3 mm.
"We are very pleased with the progress being made," said Manfred Warhaut, who is the Rosetta ground segment manager at the European Space Operations Centre (ESOC) in Darmstadt, Germany, and the project manager for the Deep Space Ground Station.
"In October, we expect the first equipment to arrive. This will include the telemetry and telecommunications equipment and the active radio frequency components," he added.
When all the work is finished, the 120 tonne antenna will reach 40 metres into the sky (higher than a 14-storey building). The entire antenna structure will eventually weigh approximately 630 tonnes, of which some 550 tonnes will be movable. Imprecision in the movement, known to experts as 'tracking error', is only allowed to be a few thousandths to a hundredth of a degree (depending on the radio frequency) - less than one fiftieth the diameter of a full Moon.
After completion of assembly and performance verification, the antenna site will be handed over to ESOC. Although its first Deep Space 'customer' will be the Rosetta comet mission, the new ground station will also be used to support ESA's SMART-1 Moon orbiter, which is scheduled for launch in November 2002, and the Mars Express orbiter and Beagle 2 lander, which will follow Rosetta in the summer of 2003.
The greatest challenge will be presented by Rosetta. After launch in January 2003, the New Norcia dish will be used to send commands to the roaming spacecraft and to 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 - a space odyssey of some 900 million kilometres.
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.
Once Rosetta reaches its destination in 2011, the spacecraft signals will be analysed to determine the characteristics of Rosetta's orbit around Wirtanen's solid nucleus. A lander will then be released onto the surface of the comet.
The valuable data collected by the instruments on the lander will be transmitted at low power - little more than the power of a typical light bulb - to the highly sensitive 'ears' of the New Norcia ground station. These receivers will amplify the signal and put it on another carrier frequency for further processing. The antenna systems will be cooled in order to suppress local background noise.
Most of the time, the station will be unmanned. Operations will be remotely monitored and controlled from the ESA station in Perth, though it might be occupied by staff during critical stages, such as Rosetta's orbital insertion around the tiny cometary nucleus.
Throughout Rosetta's decade-long adventure, the new Australian antenna will be the main communications link between the spacecraft and the ESOC Mission Control 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 an add-on / back-up during critical mission phases.
When completed, New Norcia will be the jewel in the worldwide network of ground stations operated by ESA/ESOC. Other ESA ground stations are located in Kiruna (Sweden), Redu (Belgium), Villafranca (Spain), Maspalomas, Canary Islands (Spain), Perth (Australia) and Kourou (French Guiana).
For further information please contact:
Project manager for the New Norcia ground station
ESOC, Darmstadt, Germany
Tel: +49 6151 90 2791