Spacecraft & Instuments

The ELECTRIC FIELD/LANGMUIR PROBE SENSORS measure the electric fields in the space around the Earth. These sensors look like spherical balls located on long wires. FAST spins like a ferris wheel as it orbits the Earth. This spinning forces the spheres at the end of the wires to be pulled inertially outward. There are two spheres on each wire separated by a 5 m distance with the furthest being 28 m from the spacecraft. Each sphere houses a special amplifier circuit that measures electric fields without disturbing the plasma. In Langmuir probe mode, the spheres measure the density of electrons in the plasma in which they are surrounded.