N° 32–2000: ESA unveils Spanish antenna for unique space mission

The newly refurbished antenna, which is located at the Villafranca del Castillo Satellite Tracking Station site (VILSPA) near Madrid, has been selected as the prime communication link with the Cluster II spacecraft.

The VIL-1 antenna will play a vital role in ESA's Cluster mission by monitoring and controlling the four spacecraft and by receiving the vast amounts of data that will be returned to Earth during two years of operations.

Scheduled for launch in summer 2000, the Cluster quartet will complete the most detailed investigation ever made into the interaction between our pl0anet's magnetosphere - the region of space dominated by Earth's magnetic field - and the continuous stream of charged particles emitted by the Sun - the solar wind.

This exciting venture is now well under way, following completion of the satellite assembly and test programme and two successful verification flights by the newly developed Soyuz-Fregat launch vehicle. The ESA Flight Acceptance Review Board has accordingly given the go-ahead for final launch preparations at the Baikonur Cosmodrome in Kazakhstan.

VILSPA, ESA and Cluster II

Built in 1975, after an international agreement between the European Space Agency and the Spanish government, VILSPA is part of the European Space Operations Centre (ESOC) Tracking Station Network (ESTRACK).

In the last 25 years, VILSPA has supported many ESA and international satellite programmes, including the International Ultraviolet Explorer (IUE), EXOSAT and the Infrared Space Observatory (ISO). In addition to supporting the Cluster II mission, it has been designated as the Science Operations Centre for ESA's XMM Newton mission and for the Far-Infrared Space Telescope (FIRST), which is due to launch in 2007.

There are now more than half a dozen large dish antennae installed at VILSPA. One of these is the VIL-1 antenna, a 15 metre diameter dish which operates in the S-band radio frequency (1.8 - 2.7 GHz). This antenna has been modernised recently in order to support the forthcoming Cluster II mission. As a result, VILSPA now has two fully upgraded 15 metre S-band antennae, which should enable the facility to enter the new millennium confident in its ability to support future space programmes.

Modernisation of VIL-1 included the replacement of the 60 dish panels, the subreflector, the antenna equipment room and other parts of the main structure. One of the most significant modifications has been the replacement of the Servo and tracking systems, since the Cluster II satellites will move in a highly elliptical orbit and require high speed tracking.

Into Orbit

The Cluster II mission will be launched by two Soyuz rockets provided by the French-Russian Starsem consortium. After two engine burns by the Fregat upper stage, the spacecraft will separate and use their own propulsion systems to reach their final orbits. Travelling in close formation, the four Cluster spacecraft will swoop to within 19,000 km of the Earth's surface and then retreat to 119,000 km - almost one third of the way to the Moon.

The four satellites will be visible for an average of about 10 hours per day from the VILSPA ground station. However, only one satellite at a time can be in communication with the ground, which reduces the available time each day to around two and a half hours per satellite.

Further challenges arise from the need to send new instructions to the 11 scientific instruments on each spacecraft, and from the vast amount of data to be returned each day from the 44 experiments. Over two years of operations, this adds up to 580 Gigabytes (580,000,000,000 bytes!) of data - equivalent to 290 million pages of printed text.

VILSPA will be just one link in the overall Cluster II communications network. The day-to-day operation of the four spacecraft will be handled by the Operations Control Centre at ESOC (Darmstadt, Germany). All of the Cluster II data exchange between VILSPA and ESOC will be handled by dedicated communication lines.

European Teamwork.

Industrial enterprises in almost all of the 14 ESA member states and the United States have provided hardware for Cluster II, and several Spanish companies have made important contributions to the project. SENER in Bilbao has designed and built the communication and experiment booms for the spacecraft, while Alcatel Espacio in Tres Cantos (Madrid) has provided on-board transponders and high power amplifiers for the spacecraft.

Construction of the eight Cluster / Cluster II spacecraft has been a major undertaking for European industry. Built into each 550 kg satellite are six propellant tanks, two pressure tanks, eight thrusters, 80 metres of pipework, about 5 km of wiring, 380 connectors and more than 14,000 electrical contacts. All of the spacecraft have been assembled at the Friedrichshafen (Germany) plant of prime contractor Dornier Satellitensysteme, and then sent to IABG in Ottobrunn, near Munich, for intensive vibration, thermal, vacuum and magnetic testing.

Various companies have also participated in the relocation and upgrading of the VIL-1 antenna hardware. MAN (Germany) was responsible for the dismantling of the Odenwald antenna and installation of the dish at VILSPA, while VITROCISET (Italy) handled the transfer of the antenna 'back-end' equipment, which included the computers to process the satellite telemetry and telecommunications signals. These companies were supported by Spanish contractors and local industry.

For more information, please contact:

ESA, Communication Department

Media Relations Office

Tel: +33 (0)1.53.69.71.55

Fax: +33 (0)1.53.69.76.90

Alberto Gianolio, Cluster II Project

Tel: +31 71 565 3394

Email: agianoli@estec.esa.nl

Further information on Cluster II and the ESA Science Programme can be found on the Worldwide Web at: http://sci.esa.int/

For further information on ESA in general : http://www.esa.int