A Magnetic Field Instrunent for the OGO-E Spacecraft

A three-axis, fluxgate magnetometer was selected for flight on the fifth Orbiting Geophysical Observatory. This instrument, along with an electron telescope, will provide data for the study of magnetohydrodynamic waves and other magnetic field structures in space. The magnetometer has sufficient dynamic range to measure magnetic field values from the surface of the earth to apogee. In addition to this wide dynamic range, the instrument provides for a resolution at all field values of 1/16 gamma. This resolution and dynamic range are accomplished by employing a tightly fed-back, closedloop magnetometer and a digital offset field generator in each of the three mutually perpendicular axes. The analog output of each axis is filtered by active filters to prevent frequency aliasing of the signals. The cutoff frequency of these filters is automatically switched to the proper frequency as the spacecraft telemetry data sampling rate is changed. In-flight calibration circuitry provides front-to-back calibration of each magnetometer channel during the flight. Packaging and construction techniques used in this instrument are also discussed.