Use of two magnetometers for magnetic field measurements on a spacecraft

The accurate in situ measurement; of the weak magnetic fields in interplanetary space and near the m , .)on and planets by satellites, has often been limited more by the spacecraft generated magnetic field than by the zero level stability of the magnetometer or the quantization uncertainty of the telemetry data readout system.A new method is proposed for obtaining accurate results even in the presenec of a large and variable spacecraft field.The method uses simultaneous data from two magnetometers whose sensors are placed at di.:ferent positions along a moderately long boom.The analysis of the data yields a continuous measure of the spacecraft field and the unknown field in space.The accuracy is determined by the validity of assumptions concerning the spacecraft field and the ;zero level drifts of the sensors.It is assumed that the external field to be measured is spatially uniform on the distance scale of the sensors' separation distance.This method can be used on both spin stabilized and fixed attitude spacecraft.Specific application to the future NASA-JPL Mariner Venus Mercury mission in 1973 is presented with an estimated accuracy of +0.5 to +1.0 gamma using a 6 meter boom.