A flight evaluation of a system for the measurement of earth magnetic field components, using a vapor magnetometer and orthogonal biasing coils is described. The magnetic field components relative to an earth-fixed frame is inferred from the output of an antenna array installed for the purpose of establishing vehicle orientation relative to a ground based illuminating radar beam. The flight vehicle, ground based instrumentation, and data reduction techniques are described. Two vehicle launches were carried out from the Churchill Research Range. Payload tumbling in both flights prevented full evaluation of the measurement system. (Author).