This experiment was flown to measure, throughout the AE-C orbit, the individual concentrations of
all thermal ion species in the mass range of 1 to 72 atomic mass units (u), and in the ambient
density range from 8.E1 to 5.E6 ions/cc. Any combination of the following three mass ranges,
expressed in u, were selected by ground command: range A, -1 to 4, range B, -2 to 18,
range C, -8 to 72. Each range was normally scanned in 1.7 s (approximately 12 km along orbit).
Normal operation consisted in sequence ABCABC (1 to 72 u in 5.1 s). Laboratory and inflight
determination of spectrometer efficiency and mass discrimination permitted direct conversion
of measured ion currents to ambient concentrations. The experiment's four primary mechanical
components were guard ring and ion-analyzer tube, collector and preamplifier assembly, vent,
and main electronics housing. The guard ring was normally at ground potential, but it could
be placed at -6 V by command if desirable, e.g., if the spacecraft acquired a positive charge.
A three-stage Bennett tube with 7 to 5 cycle drift spaces was flown and was modified to permit
ion concentration measurements to be obtained at low altitudes. The frequency of the 30 V
peak-to-peak RF voltage varied with the mass range measured: range A, -10 MHz, range B, -5
MHz, and range C, -2.5 MHz. Primary analog instrument output was a compressed ion current
spectrum which displayed the full dynamic range of the amplifier system on a single
telemetry channel. Onboard data processing provided a readout of primary experiment
data in the form of two digital words for each peak in the ion spectrum. One 8-bit word
indicated peak amplitude (current) and the other 8-bit word identified sweep position,
i.e., species identification. More complete details can be found in H. C.
Brinton et al., Radio Sci., v. 8, n. 4, p. 323, 1973. NSSDC has all the useful data that
exist from this investigation.