The Great Ear of ESOC is Under Construction

The promising science program of ESA will continue into the next years and will include interplanetary missions, such as the comet probe Rosetta. A high-power antenna is necessary on the Earth to establish a link with the satellite.The European Space Agency is building a Deep Space Ground Station in Australia, with a 35-metre wide antenna for transmission and reception to this purpose.

High Precision Required

Interplanetary spacecraft travel several hundred million kilometres from the Earth as they follow their often very complicated flight paths. At the same time, the size of such high-tech device is quite limited, due to technical and financial reasons, meaning that the transmission and reception equipment on board can only send low-power signals through space to Earth. This is why a lot of effort is devoted to the receiving side here on Earth. Giant antennae are specific to the ground stations supporting these missions. They must be able to pick out the almost imperceptible signals from the general cosmic background noise. But that isn’t everything. Particularly sensitive receivers amplify the signal and put it on another carrier frequency for further processing. In order to suppress local noise, the systems must be cooled.

The data can be sent and received for longer periods and the movement of the antenna must be very precise. Imprecision in the movement, known in expert circles as “Tracking Error”, is only allowed to be a few thousandths to a hundredth of a degree (depending on the frequency); thus, during the construction of the antenna precision down to the millimetre is necessary, in spite of the huge dimensions

SMART, Rosetta and the Mars Express — The First Customers
It is planned that at the end of 2002 ESA will begin with the launch of a series of interplanetary probes for the exploration of the Moon (SMART), comets, asteroids (Rosetta) and Mars. They will be the first “customers” who will use the Deep Space Ground Station, now under construction in Australia. The greatest challenge is presented by the comet probe Rosetta, because it will be sent to a distance of 900 million kilometers, reaching its destination in 2011, the comet Wirtanen. A lander will then be set on the surface. The valuable data which the instruments on board the lander collect must then be received by the ground station in Australia. The Deep Space Antenna (DSA) serves as the data transfer from the probe, as well as the link for sending commands in the S and X bands. The evaluation of the signals will also be used to decide the orbital parameters of the space probes.

The construction site in New Norcia
The system is not yet ready. At present the ES engineers and contractors of several companies have a lot to do in order to set up the Australian ground station, which should be finally ready for hand over in April, 2002. New Norcia lies about one and a half hour North of Perth, on the western coast of Australia. ESA is already running a ground station near Perth, which is used for the XMM mission among other things.

When all the work is finished, the enormous parabolic reflector will reach 40 metres into the sky (higher than a fourteen-storey building), with a diameter of 35 metres and a weight of 120 tonnes. The entire antenna actually weighs 630 tonnes, 580 of which must be turned along with the reflector with a precision in the order of the millemetre. Visitors can already get an impression of the appearance of the parabolic reflector. The mighty base rotor has been completed and mounted, and the parabolic reflector is also lying completely assembled next to the base. In the next days it will be raised onto the base structure by two cranes. The panels of the reflector must also be installed and adjusted mechanically to the highest precision. After assembling the high frequency components there will be a final test of the whole system.

When ready for action, the antenna site will be given over to the European Space Operations Centre (ESOC) in Darmstadt. ESOC is responsible for the operation of all scientific and applications missions of ESA. It uses a network of ground stations throughout the world. The Deep Space Ground Station in New Norcia will expand the network and be the showpiece of the ESOC ground stations.