A magnetic ion-mass spectrometer was flown to measure in situ the concentrations of
the ambient positive ion species in the mass range from 1 to 90 atomic mass units (u). Mounted on
the satellite equator normal to the spin axis, the entrance aperture faced forward when the
spacecraft was in the despun mode. The electric and magnetic fields were arranged to produce
a mass spectrum along the focal plane following the magnetic analyzer. Three slits were placed
along this plane in appropriate places to simultaneously collect ions in the mass ratio 1-4-16.
Ionospheric ions were accelerated into the analyzer system by a negative voltage that varied
from -1060 to -225 V. The three mass ranges measured simultaneously were 1 to 4, 4 to 16,
and 14 to 72 u. Following each slit was an electron multiplier and logarithmic
electrometer-amplifier detector. The detector output was either measured directly for an analog
output, or was supplied to a "peak" circuit that determined the amplitude of each peak in the
spectrum. Only the amplitude of each peak was telemetered in the "peak" mode, and in this mode
the time required to simultaneously sweep all three mass ranges was 1 s. Other modes of
operation were possible. In the analog short mode, the three mass ranges were swept in 2 s,
alternating with 1-s "peak" mode scans. An 8-s sweep time was required in the analog long mode,
again alternating with 1-s "peak" mode scans. An option existed in the locked mode to
continuously measure any set of mass numbers in the ratio 1-4-16 to give high spatial resolution.
More experiment detail can be found in J. H. Hoffman et al., Radio Sci., v. 8, n. 4, p. 315,

1973. NSSDC has all the useful data that exist from this investigation.