Accuracy of the vector magnetometer as an attitude sensing device for auroral sounding rockets
Robinson, Robert M.
Cloutier, Paul A.
Master of Science
A Terrier-Malemute sounding rocket was launched over a stable auroral arc from Poker Flat, Alaska on March 9, 1978 U. T. Among the instruments carried by the payload were a cesium vapor magnetometer and a solid-state star sensor. The star sensor, designed and built at INIK, Lulea, Sweden, measured the time and magnitude of individual star transits during the flight. These data were used to determine the attitude and rotational dynamics of the payload to very high accuracy. Similar information was not available for previous Rice University payloads so that attitude reconstruction for these flights was done using magnetometer data alone. However, the procedure for extracting spin and coning parameters from magnetometer data requires certain assumptions about the direction of the geomagnetic field. Since independent attitude information was available for the present flight, it was possible to test the accuracy of the magnetometer as an attitude sensing device. The following errors were discovered. First, the direction of the rocket coning center as measured by the magnetometer was in error by about 3 degrees of arc. Second, the payload spin frequency computed from the magnetometer data differed by as much as .1 degrees per second from that measured by the star sensor. With regard to the detection of ionospheric currents for this and the previous flights, these errors suggest that (1) unless the rocket coning center is in the plane of the trajectory the orientation of the inferred current system may be uncertain by as much as 15 degrees, and (2) the effects of large scale field-aligned currents may be misinterpreted as a gradual variation in the spin rate of the payload.