The Cluster mission consists of four formation flying satellites investigating the electric field and plasma in Earth’s magnetosphere. The first launch attempt in 1996 failed when the rocket exploded short after liftoff, new satellites where launch successfully in 2000 and are still operating today.
The instrument is built to do electric field measurements using metal spheres at the end of 50 m long wires. By measuring the difference in potential and divide that by the distance one finds the electric field in the unit V/m. The satellite is rotating in order to keep the wires stretched.
The boom mechanism itself was developed in cooperation with Weitzman Corp., Berkeley University and Uleåborgs University. In the bottom of the unit one finds a circuit board developed here at KTH by the Space and Plasma Physics group. This circuit board takes care of the measured signal from the spheres, the signal is then made digital in another instrument before being sent to Earth by radio.
Footage from the Ariane 5 rocket explosion where Cluster 1 was a part of the payload.