A neutral-atmosphere composition experiment for the Atmosphere Explorer-C, -D, and -E

The neutral-atmosphere composition experiment instrumentation is designed to obtain in-situ measurements of neutral thermosphere composition from Atmosphere Explorer-C, -D, and -E. The system is based on previously flown OGO-6 and San Marco-3 composition instruments. The mass-spectrometer sensor includes a gold-plated thermalizing chamber and ion source, a hyperbolic rod quadrupole analyzer, and an off-axis electron multiplier. Automatic ion-source sensitivity control and pulse-counting techniques provide density measurement capability from approximately 125 to 1000 km altitude. The normal operating mode includes measurement at all masses in the range 1 to 44 amu with emphasis on hydrogen, helium, oxygen, nitrogen, and argon. Additional operational modes are optimized for minor constituent studies of any individual gas in this mass range.