NASA satellite that studied the Earth's aurorae. Launched on 21 August 1996 from a Pegasus rocket, FAST was the second mission of NASA's Small Explorer Satellite Program (SMEX). The primary objective of the mission was to study the microphysics of space plasma and the accelerated particles that cause aurore. It measured the electric and magnetic fields, energetic electrons and ions, plasma waves, and thermal plasma density and temperature. Its instruments included 16 electrostatic analysers (ESAs). FAST crossed the doughnut-shaped auroral zones on the poles four times in each orbit, collecting ‘snapshots’ of high-resolution data. The FAST electric field instrument stopped providing meaningful data around 2002; all other instruments and systems continued to function nominally until operations ended on 4 May 2009.