The first qualification flight of the new Fregat (‘Frigate’ in
English) upper stage on the Russian Soyuz rocket was completed
today. This is the first 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 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.

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.