tmosphere Explorer mission consisted of three Earth-orbiting satellites, AE-C with 68 degree inclination, AE-D with 90 degree inclination, and AE-E with 20 degree inclination. All were equipped with a propulsion system so that perigee could be maintained during the elliptical phase despite the low altitude, and the orbit circularized and adjusted after apogee had decayed. They were spin-stabilized and could be operated either spinning in the orbital plane (spin vector parallel or anti-parallel to the orbit normal) with a period of about 15 seconds or 'despun' - rotating once per orbit to maintain the same attitude with respect to the local horizontal. The following table briefly summarizes the history of the three satellites. AE-D failed after four months and so never entered the circular phase. History of the Atmosphere Explorer Satellites Dates AE-C perige AE-D perigee AE-E perigee 12/73 - 11/74 elliptical 150 km 12/74 - 9/75 circular 250 km 10/75 - 11/75 circular 300 km elliptical 150 km 12/75 - 1/76 circular 300 km elliptical 150 km elliptical 150 km 2/76 - 10/76 circular 300 km elliptical 150 km 11/76 - 2/77 circular 270 km circular 250 km 3/77 - 12/77 circular 400 km circular 270 km 1/78 - 11/78 circular 350 km circular 350 km 12/78 - 12/79 circular 450 km 1/80 - 12/80 circular 400 km 1/81 - 5/81 circular 300 km N.b. - altitudes of perigee are approximate; 'elliptical' orbits have eccentricity from .05 to .25 and apogee from 400 km to 2200 km. The satellites carried a battery of instruments for in-situ and remote sensing measurements of the terrestrial upper atmosphere. A special issue of Radio Science (vol. 8, no. 4, 1973) describes these instruments. They are listed in the following Table with a synopsis of the quantities they measured. Instruments Carried by the Atmosphere Explorer Satellites Acronym Instrument Measured BIMS Bennett ion mass spectrometer ion density and composition CEP Cylindrical electrostatic probe electron density, temperature EAST Ion gauge and capacitance manometer atmospheric pressure ESUM Solar extreme UV photometer solar spectrum 40-1220A EUV Extreme UV spectrophotometer solar spectrum 140-1880A LEE Low energy electron experiment electron, proton flux .2-26 keV MESA Triaxial accelerometer system density, spacecraft accel. MIMS Magnetic ion mass spectrometer ion density and composition NACE Neutral atmosphere composition exp. neutral density, composition NATE Neutral atmosphere temperature instr. neutral density, comp., temp. OSS Open source neutral mass spectrometer neutral density, composition PACT Magnetometer experiment magnetic field PES Photoelectron spectrometer electron flux 2-500 eV RPA Retarding potential analyzer ion density, temp., velocity UVNO UV nitric oxide photometer NO density from emission VAE Visible airglow experiment photons at various wavelenghths Data from the instruments were organized into three levels: Telemetry (TM), Geophysical Unit (GU), and Unified Abstract. The TM database contains fully detailed records of all the information received. GU data are high-resolution records which have been converted to physically meaningful units; much of it was represented by microfilm plots. UA data have been averaged onto 15 second centers and are available from the National Space Science Data Center (NSSDC).