The magnetic ion-mass spectrometer is designed to measure the abundances of the ambient positive ions in the ionosphere. It will be calibrated in flight against the retarding-potential analyzer and the cylindrical electrostatic probe to give absolute concentration data for the ion species detected. These parameters can be measured to approximately ±10% in well-behaved regions where concentrations are above 103 cm−3. However, in highly structured polar regions, some degradation in accuracy may be expected.
Three mass ranges, covered simultaneously by the scan of the instrument, 1 to 4, 4 to 16, and 16 to 64 amu, permit measurement of the entire mass range, 1 to 64 amu, in 1 sec in the main (peaks) mode. An alternate mode, analog-long, will extend the mass range to 90 amu with a 9-sec period. Capability is provided to lock onto any set of mass numbers in the ratio 1:4:16 to give very high spatial resolution, e.g., 500, 250, and 125 m in the low-, mid-, and high-mass ranges, respectively. This mode will be most useful in the despun satellite orientation to provide fine-structure data on ion concentrations. In the spinning mode the phase shifts between roll modulation maxima of heavy and light ions determine the vertical component of the individual ion-drift velocities. Values from a few km sec−1 to over 20 km sec−1 can be determined. Such data are applicable to the study of polar wind phenomena.