[3] The Miniature Electrostatic Analyzer (MESA) obtained data on the neutral density of the atmosphere in the altitude range of 120 km (75 mi) to 400 km (250 mi), by the measurements of satellite deceleration due to aerodynamic drag, which is directly proportional to atmospheric density.
The instrument consisted of three single-axis accelerometers, mounted mutually at right angles, two in the spacecraft X-Y plane and the other along the Z-axis.
The photometer measured the reflected UV radiation in a single wavelength span in which attenuation by ozone does not occur.
Laboratory and inflight determination of spectrometer efficiency and mass discrimination permitted direct conversion of measured ion currents to ambient concentrations.
Correlation of these measured data with the results from companion experiments, CEP (1975-107A-01) and RPA (1975-107A-04) permitted individual ion concentrations to be determined with high accuracy.
The experiment's four primary mechanical components were guard ring and ion-analyzer tube, collector and preamplifier assembly, vent, and main electronics housing.
A three-stage Bennett tube with 7- to 5-cycle drift spaces was flown; it was modified to permit ion concentration measurements to be obtained at low altitudes.
[6] The capacitance manometer flown on Explorer 55 (AE-E) was primarily an engineering experiment to provide data on spacecraft operations.
The PSB consisted of two spherical, thermally controlled chambers, separated by a thin membrane stretched flat and under radial tension.
[7] The cold cathode ion gauge was primarily an engineering experiment to provide data on spacecraft operation.
The cylindrically shaped sensor package consisted of a wedge-shaped orifice, a cathode near ground potential, an anode operating at about 130 VDC, and a permanent magnetic field of about 0.16t (1600 gauss).
Each instrument was a retarding-potential Langmuir probe device that produced a current-voltage (I-V) curve for a known voltage pattern placed on the collector.
Most modes involved an automatic or fixed adjustment of collector voltage limits (and/or electrometer output) such that the region of interest on the I-V profile provided high resolution.
[11] This experiment measured in situ the spatial distribution and temporal changes of the concentrations of the neutral atmospheric species.
The mass-spectrometer sensor had a gold-plated stainless steel thermalizing chamber and ion source, a hyperbolic rod quadrupole analyzer, and an off-axis electron multiplier.
In orbit, the pre-sealed spectrometer was opened, and the atmospheric constituents passed through a knife-edged orifice into the thermalization chamber and ion source.
Selected ions left the quadrupole analyzer through a weak focusing lens and were accelerated into an electron multiplier, where they were turned 90° to strike the first dynode.
Analysis of the measured molecular nitrogen density variation over a spin cycle with a knowledge of the satellite's motion and orientation led to a determination of the ambient temperature, independent of scale height.
Approximate values for the meridional wind were obtained from the measurement of the "stream" position relative to the satellite velocity.
An alternate measurement of neutral temperature was also undertaken, using a baffle inserted in front of the orifice to intercept a portion of the gas-particle stream entering the chamber.
When the satellite was in the despun mode, the baffle was made to oscillate in a stepwise fashion in order to interrupt the particle stream seen by the orificed chamber.
From the source, this ionized nitrogen beam was directed into a quadrupole analyzer, tuned to pass those particles with a mass-to-charge ratio of 28.
Those ambient particles that did not strike the ion source retained their incoming energy of several eV after ionization and escaped into the acceleration region of the analyzer.
The instrument consisted of two identical oppositely directed hemispherical electrostatic analyzers and contained 30 operating modes.
With the retarding grid at constant zero volts, current changes could be observed for 3-s periods to obtain gradients of ion concentration.
The instrument consisted of 24 grazing-incidence grating monochromators, using parallel-slit systems for entrance collimation and photoelectric detectors at the exit slits.
The other 12 monochromators operated at fixed wavelengths with fields of view smaller than the full solar disk to aid in the atmospheric absorption analysis.
One channel had a 3° half-angle cone field of view for high sensitivity and pointed normally toward the local zenith.
The second had a field of view of 0.75° half cone for high spatial resolution, pointing tangentially to the surface of the Earth when the satellite was in the oriented mode.
The two separate optical channels were monitored at time intervals consistent with their angular resolution in the spinning mode.