Van Allen Probes - Instruments: EFW
Electric Field and Waves Suite (EFW)
Principal Investigator: John Wygant, University of Minnesota, Minneapolis
The EFW measures electric fields to help understand what processes provide energy to the particles and speed them on their way. Some electric fields last for milliseconds and extend over only half a mile, while others last for hours and extend over 100,000 miles. So one major question is to determine which kinds of fields help accelerate the material in the belts.
These electric fields are measured by metal spheres at the ends of six huge antennae, or booms, that stretch out from the main body of the spacecraft. Four of the booms stick out from the sides of the spacecraft, like the spokes of a bicycle, and are held in place by centrifugal forces. Each of these booms is a cable about as wide as a fishing line. One pair extends 130 feet from the spacecraft, while those in the other pair are 164 feet long. The second pair of booms is rigid, and lines up with the spacecraft's spin axis. Each of these booms is some 40 feet long. At launch time, all the booms tuck into the spacecraft and then deploy once RBSP is in orbit.
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