Explorer 39
{{Short description|NASA satellite of the Explorer program}}
{{Use American English|date=November 2021}}
{{Use dmy dates|date=November 2021}}
{{Infobox spaceflight
| name = Explorer 39
| names_list = AD-C
Air Density experiment-C
| image = EXPLORER_39.jpg
| image_caption = Explorer 39 satellite
| image_size = 300px
| mission_type = Air density
| operator = NASA
| COSPAR_ID = 1968-066A
| SATCAT = 03337
| mission_duration =
| spacecraft = Explorer XXXIX
| spacecraft_type = Explorer
| spacecraft_bus = AD
| manufacturer = Langley Research Center
| launch_mass = {{cvt|9.4|kg}}
| dimensions = {{cvt|3.6|m}} diameter
| power = Solar cells and
rechargeable batteries
| launch_date = 8 August 1968, 20:12:00 GMT{{cite web |url=http://www.planet4589.org/space/log/launchlog.txt |publisher=Jonathan's Space Report |title=Launch Log |date=21 July 2021 |access-date=13 November 2021}}
| launch_rocket = Scout B (S-165C)
| launch_site = Vandenberg, SLC-5
| launch_contractor = Vought
| entered_service = 8 August 1968
| last_contact = June 1971
| deactivated =
| decay_date = 22 June 1981
| orbit_reference = Geocentric orbit
| orbit_regime = Low Earth orbit
| orbit_periapsis = {{cvt|670|km}}
| orbit_apoapsis = {{cvt|2538|km}}
| orbit_inclination = 80.60°
| orbit_period = 118.20 minutes
| apsis = gee
| instruments = Nonsystematic Changes of Air Density
Systematic Changes of Air Density
| programme = Explorer program
| previous_mission = Explorer 38
| next_mission = Explorer 40
}}
Explorer 39, also known as AD-C (Air Density experiment-C), was a NASA scientific satellite belonging to series Air Density. It was launched on 8 August 1968, join with Explorer 40, from Launch Complex 5 of the Vandenberg Air Force Base, through a Scout launch vehicle.{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1968-066A |title=Display: Explorer 39 (AD-C) 1968-066A |publisher=NASA |date=28 October 2021 |access-date=13 November 2021}} {{PD-notice}}
Spacecraft
Explorer 39 was an inflatable sphere, {{cvt|3.6|m}} in diameter. It was orbited to make atmospheric density determinations. The satellite 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.
Launch
Explorer 39 orbited the Earth once every 118.20 minutes, at an inclination of 80.60°. Its perigee was {{cvt|670|km}} and apogee was {{cvt|2538|km}}.{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/displayTrajectory.action?id=1968-066A |title=Trajectory: Explorer 39 (AD-C) 1968-066A |publisher=NASA |date=28 October 2021 |access-date=13 November 2021}} {{PD-notice}}
Mission
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 Smithsonian Astrophysical Observatory (SAO) Baker-Nunn camera network for tracking.
Experiments
= Nonsystematic Changes of Air Density =
This experiment was designed to determine nonsystematic upper atmospheric density changes. The data are derived from studies of the drag on a {{cvt|3.6|m}} in diameter low-density sphere caused by short-term differences in solar activity. Density values near perigee were deduced from sequential observations of the spacecraft position using optical (Baker-Nunn camera network) and radio and/or radar tracking techniques. This experiment has determined reasonable density values, and it is capable of yielding long-term atmospheric density values, as Explorer 39 has an expected orbital lifetime of 50 years.{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1968-066A=01 |title=Experiment: Nonsystematic Changes of Air Density |publisher=NASA |date=28 October 2021 |access-date=13 November 2021}} {{PD-notice}}
= Systematic Changes of Air Density =
This experiment was designed to determine systematic changes of air density as a function of altitude, latitude, and time of day, by measuring the drag on a {{cvt|3.6|m}} in diameter low-density sphere with ground tracking.{{cite web |url=https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1968-066A=02 |title=Experiment: Systematic Changes of Air Density |publisher=NASA |date=28 October 2021 |access-date=13 November 2021}} {{PD-notice}}
Decay
Explorer 39 reentered the atmosphere on 22 June 1981.
See also
{{Portal|Spaceflight}}
References
{{Reflist|30em}}
External links
- [http://rammb.cira.colostate.edu/dev/hillger/explorer.htm Explorer Series Satellites] Colorado State University
- [http://www.nasm.si.edu/collections/artifact.cfm?id=A19772726002 Explorer 39] {{Webarchive |url=https://web.archive.org/web/20110403032430/http://www.nasm.si.edu/collections/artifact.cfm?id=A19772726002 |date=3 April 2011}} Smithsonian Institution
{{Explorer program}}
{{Orbital launches in 1968}}