The instrument consisted of three single-axis accelerometers, mounted mutually at right angles, two in the spacecraft X-Y plane and the other in the Z-axis.

The PSB consisted of two spherical, thermally controlled chambers, separated by a thin membrane stretched flat and under radial tension.

[5] The cold cathode-ion gauge flown on AE-D 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 1300 VDC, and a permanent magnetic field of about 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.

Mounted on the satellite equator normal to the spin axis, the entrance aperture faced forward when the spacecraft was in the despun mode.

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.

[9] This experiment measured in situ the spatial distribution and temporal changes of the concentrations of the neutral atmospheric species.

The mass-spectrometer sensor included a gold-plated stainless steel thermalizing chamber and ion source, a hyperbolic-rod quadrupole analyzer, and an off-axis electron multiplier.

When operating in the "normal" format, the analyzer measured all masses in the range 1 to 44 with emphasis on hydrogen, helium, oxygen, nitrogen, and argon.

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 a 14-stage electron multiplier, where they were turned 90° to strike the first dynode.

These output pulses constituted the measurement and the count rate was proportional to the chamber density of the selected species.

Analysis of the measured molecular nitrogen density variation over a spin cycle with knowledge of the satellite's motion and orientation led to a determination of the ambient temperature, independent of scale height.

In addition, values for the zonal wind were obtained, from measurement of the "stream" position relative to the satellite velocity.

An alternate measurement of neutral temperature also was 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.

Those ambient particles that did not strike the ion source retained their incoming energy of several eV after ionization and escaped into the accelerating region of the analyzer.

With the retarding grid at constant zero volt, current changes could be observed for 3-second 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.

[17] This Ultraviolet Nitric-Oxide Experiment (UVNO) consisted of a two-channel fixed-grating Ebert-Fastie spectrometer, which measured the airglow in the (1, 0) gamma band in a 15-A region centered at 2149 A.

The observed intensity was produced by resonance fluorescence of sunlight by the nitric-oxide molecules in the instrument's field of view.

The intensity data obtained yielded altitude profiles of nitric oxide density as a function of time and location.

The remote sensing character of the UVNO experiment permitted measurements of nitric oxide to be made at altitudes both above and below satellite perigee.

As the spacecraft spun, the spectrometer, which looked outward through the rim of the satellite, repeatedly had its field of view carried down through the atmosphere onto the earth's limb, and altitude profiles of the emitted airglow intensity were obtained.

The sensor's spherical fused-quartz telescope mirror had a 125-mm focal length, and focused incident light on the entrance slit of the spectrometer.

One channel had a large field of view (3° half-angle) for high sensitivity, normally pointing toward the local zenith, and the second channel had a small field of view (0.75° half-angle) for high spatial resolution, pointing tangent to the surface of the Earth when the satellite was in the despun mode.

Photons that had been spectrally and spatially selected were sensed by a pulse-counting photomultiplier system capable of counting at a rate of 5.E6 counts/seconds.