Cluster pair prepare for higher things
19 July 2000
Things are looking up for the first pair of Cluster spacecraft as theygradually move further and further from the Earth.So far, the spacecraft have successfully completed three of the four mainengine burns required to raise the apogee (highest point) of their orbits.The second of these apogee raising manoeuvres took place yesterday morning - at 10.34 CEST by FM 6 (Salsa) and at 10.38 by FM 7 (Samba). Each lasted for approximately 10 minutes.
"The commands for the manoeuvre were stored on board and the manoeuvre itself took place during a period not covered by ground station visibility," explained Alberto Gianolio, Cluster Deputy Project Manager. "Subsequent acquisition of both satellites at exactly the expected orbital position confirmed the successful execution and high accuracy of the onboard propulsion system."
As a result, the orbits of the FM 6 (Salsa) and FM 7 (Samba) spacecraft were altered to 250 x 35,000 km, while their inclination of 64.9 degrees to the equator remained unchanged.
"The spacecraft were so close together that we were able to track both of them in one radio beam from the ground station at Kiruna (Sweden), " said Sandro Matussi, Cluster Spacecraft Operations Manager at the European Space Operations Centre (ESOC) in Darmstadt, Germany.
The third apogee raising manoeuvre was completed earlier today, with engine ignition beginning at 07.08 CEST for FM 6 (Salsa) and at 07.15 for FM 7 (Samba).
Once again, the engines performed perfectly for around 10 minutes, increasing the maximum distance from the Earth to 56,677 km for FM 6 (Salsa) and to 57,010 km for FM 7 (Samba).
"These orbits have an accuracy of 0.1%, which means they are extremely close to what we predicted," said Manfred Warhaut, Cluster Ground Segment Manager at ESOC.
The fourth burn needed to raise the spacecraft apogee will take place early on Thursday morning.
Once the attitude of each spacecraft is adjusted so that its main engine is pointing in the right direction, the fifth and final adjustment in this series of celestial pirouettes will take place around midnight on Thursday.
This major manoeuvre, which involves igniting the main engine for almost twice as long as on previous burns, will kick the satellites into highly elongated orbits of 19,000 x 119,000 km, inclined at 90 degrees to the equator.
The Cluster pair will then have reached their operational orbits, which will carry them over the Earth's poles and almost one third of the distance to the Moon.
