The main purpose of the qualification flight was to test the Fregat's ability to restart several times in space. This capability is essential in order to place the Cluster II spacecraft into the correct operational orbits.

During today's mission, the Fregat performed two 'burns' within 1 � hours of the Soyuz launch from Baikonur Cosmodrome in Kazakhstan. The first of these occurred within minutes of lift-off, and placed the Fregat and its payloads into an elliptical (oval) orbit of approximately 200 x 600 km. A second burn followed when the upper stage was at its apogee (furthest from the Earth) in order to circularise the orbit at 600 km.

"This is a major step forward for both the Cluster II programme and the Starsem consortium which provides the Soyuz launcher," said Cluster II project manager John Ellwood. "If the detailed analyses confirm the early flight data, the way should be clear for the second qualification flight and the start of the Cluster II launch campaign."

Once its main objective was achieved, the remainder of the Fregat mission was devoted to an innovative experiment involving a new Inflatable Re-entry and Descent Technology (IRDT) heat shield, which has been developed with funding from ESA, the European Union, the German Daimler Chrysler (DASA) aerospace company and the Russian Khrunichev company. This was the first time that such a lightweight, inflatable system had been tested in space.

A small ESA experiment, known as 'Stone 2', was also carried out during re-entry. Three samples of different rocks (basalt, dolomite and an artificial compound of cement and carbonate) were embedded in the heat shield on the IRDT demonstrator. By exposing them to the extreme heat of re-entry, scientists hoped to learn more about the processes that affect meteorites which have travelled all the way from Mars to the Earth.

After completing five orbits and two more engine firings, the Fregat and its IRDT dummy payload separated and began to re-enter the upper atmosphere. Both the small heat shield on the demonstrator and the large shield on the Fregat inflated at an altitude of 50 km and then functioned as parachutes to deliver their cargo safely back to Earth. About 17 minutes after the final Fregat burn, the upper stage and the demonstrator hit the flat Russian steppes at a velocity of 13 metres/sec. The overall mission had lasted about eight hours.

The inflatable heat shield has a number of advantages over existing designs. Not only can it be folded into a very small package, but it can save weight and transportation cost. In the future, it may be used to transport samples and cargoes from the International Space Station back to Earth, or for re-usable rocket upper stages.

The Fregat upper stage has a single-chamber main engine built by Lavotchkin, which can be restarted up to 20 times, and four groups of three 50-N hydrazine thrusters to provide attitude control. Although a similar system has been used to power the Phobos probes to Mars, and the main engine has been fitted on nearly 30 interplanetary spacecraft, this was the first time that it has flown in this configuration.

Cluster II is scheduled for launch from Baikonur Cosmodrome in Kazakhstan in the summer of 2000. The four satellites will be put into orbit in pairs by two Russian-made Soyuz rockets.

When the Cluster II mission was approved by ESA's Science Programme Committee in April 1997, it was decided that a launch on a European Ariane rocket would be too expensive. It was, therefore, decided to launch the spacecraft using a Soyuz launch vehicle equipped with a newly designed Fregat upper stage.

These rockets are procured through Starsem, a French-Russian company which is marketing Soyuz launchers outside Russia. Starsem has four shareholders - Aerospatiale, Arianespace, the Russian Space Agency and TsSKB Samara, the manufacturer of the Soyuz vehicle. The contract for launch of the Cluster II satellites was signed by ESA and Starsem on 24 July 1998 at ESA Headquarters in Paris.

The first pair of Cluster II satellites (FM6 and FM7) are currently set for launch in mid June, 2000, to be followed by the second pair (FM5 and FM8) in mid July, 2000. The two launches are separated by 2 - 6 weeks so that fewer people are required for mission control in the European Space Operations Centre (ESOC), Darmstadt, (Germany) - especially in the flight dynamics and flight control teams.

The Soyuz launcher will place the upper stage and its Cluster II payload in an orbit inclined at 64.8� to the equator. The fairing is jettisoned during operation of the Soyuz third stage. Once the booster reaches the correct altitude, 8 minutes 48 seconds after lift off, the Fregat payload assist module and two Cluster spacecraft will be released. The Fregat main engine will fire almost immediately to achieve a circular orbit of approximately 200 km altitude. About one hour later, the Fregat engine will fire again to inject the spacecraft into the desired elliptical separation orbit of 200 by 18,000 km.

The two satellites will then be released, one after the other. They will use their own on-board propulsion systems to reach the final operational orbit of 125,000 km by 25,500 km. Each Cluster spacecraft main engine will perform a series of six manoeuvres to raise the orbital perigee (low point) and apogee (high point) and change the orbital inclination from 64.8� to 90�. These major manoeuvres are possible since fuel makes up approximately half of each spacecraft's launch mass.