The multiple re-start Fregat upper stage ensured the success of the launch of the second pair of European Space Agency (ESA) Cluster satellites on a Soyuz-Fregat booster last month following the under-performance of the Soyuz stages.

The launch required an extended burn of the Fregat, says Stanislav Kulikov, director of Russia's Lovochkin Association. He indicates that the third stage may not have had a full load of propellant. Another upper stage without the multiple restart capability of the Fregat would not have been able to make up for the loss of altitude, claims Kulikov.

The Fregat has flown four times successfully on Soyuz launches, the first time operationally on the booster that carried the first pair of Clusters launched on 16 July.

The Cluster Satellites are beginning operations as part of the European Space Agency's Horizons 2000 programme.

Source: Flight International