Cluster II on track after maiden flight of Fregat upper stage
8 February 2000The first qualification flight of the new Fregat ('Frigate' in English) upper stage on the Russian Soyuz rocket was completed today. This is thefirst time that the Fregat has flown on a Soyuz and represents a major milestone on the road towards the launch of ESA's four Cluster II satellites this summer.
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 1½ 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.
Another qualification flight for the Fregat, with a dummy Cluster II satellite, is scheduled for 20 March 2000. If all goes well in this second trial, the road will be clear for the dual Cluster II launches by Soyuz-Fregat in June and July.
The Soyuz-Fregat has also been selected to launch ESA's Mars Express satellite in 2003.