The Atmospheric Explorer-D (AE-D) spacecraft (designation: 08353 /
75096A ) was designed as a multi- sided polyhedron shaped frame with a
mean diameter of about 1.4 meters. AE-D was in most respects
... similar
to AE-C. The AE-D was launched on 1975-10-6 and decayed 1976-03-12.
The purpose of the AE-D mission was a direct continuation of the EA-C
mission: to investigate the chemical and physical processes in the
uppermost layer of the earth's atmosphere, the thermosphere, with
emphasis on energy transfer and other controlling processes.
Photochemical processes related to the absorption of solar UV
radiation were studied by making coordinated measurements of reacting
constituents and the solar input in the region of high absorption of
solar energy.
The payload included instrumentation to measure: Solar UV Fluxes, the
Composition of Positive Ions and Neutral Particles, the Density and
Temperature of neutral particles, positive ions and electrons,
Atmospheric airglow emissions, Photoelectron Energy Spectra, and
Proton and Electron Fluxes with particle energy up to 25 keV.
This mission was planned to sample the high latitude regions at the
same time that the AE-E mission was sampling the equatorial and low
latitude regions. The same type of spacecraft as AE-C was used, and
the payload consisted of the same types of instruments except for
deletion of the extreme solar UV monitor and the Bennett ion mass
spectrometer both of which were part of the AE-E payload.
AE-D was placed in a high inclination (polar) orbit. The polar orbit
provided sampling of all latitudes, the perigee moved through all
latitudes in 3 months, and all local times in 4 months.
Unfortunately, a failure in the solar power panels resulted in the
termination of AE-D operations on January 29, 1976, after slightly
less than 4 months of useful spacecraft life. However, all the
regions at the perigee altitudes were sampled during this time. The
AE-D spacecraft re-entered the earth's atmosphere about 1 month after
the cessation of telemetry. To continue the correlated observations
with the AE-E mission, the earlier AE-C spacecraft was then
reactivated on February 28, 1976 as replacecment for AE-D. Power to
AE-D was supplied by a solar cell array. The spacecraft used a PCM
telemetry data system that operated in real time or using a tape
recorder. 
