Explorer 55, also called as AE-E (Atmospheric Explorer-E), was a NASA scientific satellite belonging to series Atmosphere Explorer, being launched on 20 November 1975 from Cape Canaveral Air Force Station (CCAFS) board a Thor-Delta 2910 launch vehicle.
Mission
The purpose of the Explorer 55 (AE-E) mission was to investigate the chemical processes and energy transfer mechanisms that control the structure and behavior of the atmosphere of Earth and ionosphere in the region of high absorption of solar energy at low and equatorial latitudes. The simultaneous sampling at higher latitudes was carried out by the Explorer 54 (AE-D) spacecraft until its failure on 29 January 1976, and then by Explorer 51 (AE-C), until it reentered on 12 December 1978. The same type of spacecraft as Explorer 51 was used, and the payload consisted of the same types of instruments except that the low-energy electron and ultraviolet (UV) nitric oxide experiments were deleted and a backscatter UV spectrometer was added to monitor the ozone content of the atmosphere.
The 2 experiments that were deleted were more appropriate for the high-latitude regions. The perigee swept through more than 6 full latitude cycles and two local time cycles during the first year after launch when the orbit was elliptical and the perigee height was varied between and . The circularization of the orbit around was made on 20 November 1976 and the spacecraft was raised to this height whenever it would decay to about .
Experiments
Miniature Electrostatic Accelerometer (MESA) The Miniature Electrostatic Analyzer (MESA) obtained data on the neutral density of the atmosphere in the altitude range of to , 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 instrument determined the applied acceleration from the electrostatic force required to recenter a proof mass. The output of the device was a digital pulse rate proportional to the applied acceleration. The sample time of each instrument was 0.25 seconds. The measurements allowed determination of the density of the neutral atmosphere, monitored the thrust of the "Orbit-Adjust Propulsion System" (OAPS), determined the satellite minimum altitude, measured spacecraft roll, and provided some attitude-sensing information. Spacecraft nutations of less than 0.01° were monitored. The instrument had three sensitivity ranges: 8.E-3 Earth's gravity (G) in OAPS monitor mode; 4.E-4 G between (± 2%) and (± 10%); and 2.E-5 G between (± 2%) and (± 10%). Numbers in parentheses represent errors. There may be a systematic error of up to ± 5% due to drag coefficient uncertainty. The highest measurement altitude was determined assuming the instrument could sense to 0.2% of full scale.
Backscatter UV Spectrometer (BUV) The Backscatter Ultraviolet instrument (BUV) monitored the spatial distribution of atmospheric ozone by measuring the intensity of the UV radiation backscattered from the Earth's atmosphere. To obtain this ozone distribution, the BUV subsystem measured direct solar radiation and backscattered UV radiation from the daytime Sun-illuminated atmosphere. The instrument consisted of a spectrometer (monochromator) and a photometer. The monochromator measured the intensity of UV radiation backscatter and reflected radiation from the Earth's atmosphere in 12 wavelengths (2555 to 3398 A) in which ozone attenuation occurs. The photometer measured the reflected UV radiation in a single wavelength span in which attenuation by ozone does not occur. The BUV had four operating modes.