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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.[3]

Explorer 39

Explorer 39 satellite
Names	AD-C Air Density experiment-C
Mission type	Air density
Operator	NASA
COSPAR ID	1968-066A
SATCAT no.	03337
Spacecraft properties
Spacecraft	Explorer XXXIX
Spacecraft type	Explorer
Bus	AD
Manufacturer	Langley Research Center
Launch mass	9.4 kg (21 lb)
Dimensions	3.6 m (12 ft) diameter
Power	Solar cells and rechargeable batteries
Start of mission
Launch date	8 August 1968, 20:12:00 GMT[1]
Rocket	Scout B (S-165C)
Launch site	Vandenberg, SLC-5
Contractor	Vought
Entered service	8 August 1968
End of mission
Last contact	June 1971
Decay date	22 June 1981
Orbital parameters
Reference system	Geocentric orbit[2]
Regime	Low Earth orbit
Perigee altitude	670 km (420 mi)
Apogee altitude	2,538 km (1,577 mi)
Inclination	80.60°
Period	118.20 minutes
Instruments
Nonsystematic Changes of Air Density Systematic Changes of Air Density
Explorer program ← Explorer 38 Explorer 40 →

Spacecraft

Explorer 39 was an inflatable sphere, 3.6 m (12 ft) 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.[3]

Launch

Explorer 39 orbited the Earth once every 118.20 minutes, at an inclination of 80.60°. Its perigee was 670 km (420 mi) and apogee was 2,538 km (1,577 mi).[2]

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. Explorer 39 has an expected orbital lifetime of 50 years.[3]

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 3.6 m (12 ft) 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.[4]

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 3.6 m (12 ft) in diameter low-density sphere with ground tracking.[5]

Decay

Explorer 39 reentered the atmosphere on 22 June 1981.[2]

See also

• Explorer 19
• Explorer 24
• Explorer program

References

External links

• Explorer Series Satellites Colorado State University
• Explorer 39 Smithsonian Institution

На других языках

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- [en] Explorer 39

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[es] Explorer 39

Explorer 39, conocido también como AD-C, fue un satélite artificial de la NASA lanzado el 8 de agosto de 1968 desde la Base Aérea de Vandenberg mediante un cohete Scout. Reentró en la atmósfera el 22 de junio de 1981. Formó parte de la serie de satélites AD (Air Density) para realizar mediciones en la atmósfera superior.

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