Description

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The Electric Field Instrument (EFI) on the Polar spacecraft is designed to measure the vector electric field and thermal electron density at the spacecraft location. The EFI consists of three orthogonal pairs of spherical probes which can be used for either inter-sphere potential difference measurements or Langmuir probe-type operation. The frequency range of the EFI is DC to 20 kHz, and its sensitivity spans the range .02 to 1000 mV/m. Thermal electron densities between 0.1 and 100 cm-3 can be determined in the Langmuir probe mode.

Two pairs of spheres are deployed in the spacecraft spin plane on long wire booms, producing opposing sphere separations of 100 m and 130 m. A third pair is deployed on rigid booms along the spin axis, producing a 14 m sphere separation. The latter are realeased by pyro devices, while the wire booms are gradually fed out by motors during and after spacecraft spin-up. A picture of the spacecraft with the booms deployed can be seen by clicking here.

The EFI Characteristics are summarized below:

Characteristic	Mass	Power
Spin plane wire booms and spheres	15.4 kg	3.5 W
Axial booms and spheres	9.2 kg	2.3 W
Axial boom stabilizer	3.4 kg	0 W
Electronics package on spacecraft	7.7.kg	6.6.W

For more information, reference the paper the following paper:

Harvey, P., F. S. Mozer, D. Pankow, J. Wygant, N. C. Maynard, H. Singer,
    W. Sullivan, P. B. Anderson, R. Pfaff, T. Aggson, A. Pedersen,
    C. G. Falthammar, and P. Tanskannen,
    THE ELECTRIC FIELD INSTRUMENT ON THE POLAR SATELLITE, Space Science Reviews
    71: 583-596, 1995.

Last updated: March 25, 1997