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- Explorer 39 was an inflatable sphere, 3.6 m in diameter. It was orbited to make atmospheric density determinations. The spacecraft was successfully launched into a nearly polar, highly elliptical orbit. It was folded and carried into orbit, together with ejection and inflation equipment, as part of the payload of Explorer 40. Two density experiments were performed. One involved the study of systematic density variation, and the other was concerned with nonsystematic density changes. The upper atmospheric densities were derived from sequential observations of the sphere by use of an attached 136.620-MHz radio tracking beacon and by optical tracking. The radio beacon ceased transmitting in June 1971. Since that time it has been necessary to rely solely on the SAO Baker-Nunn camera network for tracking. Explorer 39 had an expected orbital lifetime of 50 years. http://nssdc.gsfc.nasa.gov/database/MasterCatalog?sc=1968-066A Group: Platform_Details Entry_ID: AD-C Group: Platform_Identification Platform_Category: Earth Observation Satellites Platform_Series_or_Entity: AD (Atmospheric Dynamics) Short_Name: AD-C Long_Name: Atmosphere Dynamics C (Explorer 39) End_Group Group: Synonymous_Platform_Names Short_Name: EXPLORER 39 Short_Name: 03337 End_Group Group: Platform_Associated_Instruments Short_Name: OPTICAL BEACON End_Group Group: Orbit Orbit_Inclination: 80.6 degrees Period: 118.2 minutes Perigee: 670 km Apogee: 2538 km Orbit_Type: LEO > Low Earth Orbit > Polar Sun-Synchronous End_Group Creation_Date: 2007-08-22 Online_Resource: http://nssdc.gsfc.nasa.gov/database/MasterCatalog?sc=1968-066A Group: Platform_Logistics Launch_Date: 1968-08-08 Launch_Site: Vandenberg Air Force Base, USA Primary_Sponsor: NASA End_Group End_Group
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