Even so, there will be plenty of fuel left for the remainder of the Cluster mission. This leaves plenty to spare for future readjustments of the four spacecraft. The satellites are close together because the magnetic structures we want to observe are smaller and more detailed data is required. This will be the first time that this region has been studied simultaneously by four identical spacecraft. This will be a very exciting time for us.
Team work is vital if the orbit changes are to be successfully carried out.
The commands to fire the thrusters are uploaded to the computers on each spacecraft one day before a particular manoeuvre is scheduled to take place. The modified orbits are later checked as the quartet fly within range of the ESA ground stations of Villafranca 1 and 2 in Spain and Perth in Australia. Engineers are monitoring the situation day and night when the manoeuvres are taking place, ready to intervene if necessary. Only eight of the thruster firings take place when the satellites are not 'visible' from Spain or Perth. During this period of unusual activity, the temporary build-up of gases around the spacecraft means that Cluster payload operations have to be reduced.