THE ELECTRIC-FIELD INSTRUMENT ON THE POLAR SATELLITE

The Polar satellite carries a system of four wire booms in the spacecr aft spin plane and two rigid booms along the spin axis. Each of the bo oms has a spherical sensor at its tip along with nearby guard and stub surfaces whose potentials relative to that of their sphere are contro lled by associated electronics. The potential differences between oppo site sphere pairs are measured to yield the three components of the DC to >1 MHz electric field. Spheres can also be operated in a mode in w hich their collected current is measured to give information on the pl asma density and its fluctuations. The scientific studies to be perfor med by this experiment as well as the mechanical and electrical proper ties of the detector system are described.