Instruments II

Electrical charging of a Cluster spacecraft in orbit could have a severe impact on the performance of the scientific instruments. ASPOC emitted charged particles that cancelled out the electrical charge that the satellite acquired. The number of particles needed to do this was determined by other onboard instruments (EFW and PEACE), which recorded the spacecraft's electrical potential.

Analysed the composition, mass and distribution of particles captured by the spacecraft. CIS consisted of two different instruments – a Hot Ion Analyser (HIA) and a time-of-flight COmposition and DIstribution Function analyser (CODIF), plus a sophisticated instrument control and data processing system, which permitted extensive onboard data processing.

EDI fired two beams of electrons into space around each spacecraft. The electrons travelled in orbits of 10 km or more before returning to receivers on the opposite side of the spacecraft. From the firing directions and the round-trip travel time, scientists could determine the strength of the electric and magnetic fields around each Cluster spacecraft.

FGM was composed of two magnetometers that measured the magnetic fields encountered by Cluster. Located on a 5-m-long boom to avoid interference from the spacecraft, FGM could record measurements up to 67 times per second.

Like CIS, this experiment also sifted incoming particles. PEACE looked at electrons in the plasma that have low to medium energies, counted them and measured their direction of travel and speed.

An advanced particle detector that recorded the highest energy electrons and charged particles entering it from space. The particles passed through pinholes to reach the detector, enabling it to build up a picture of where the particles came from.