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Wikipedia states that Vanguard I is the oldest artificial satellite still in orbit. What is the oldest that's still in use?

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    $\begingroup$ The problem is the correct answer is going to change over time. $\endgroup$ – Deer Hunter Aug 25 '13 at 13:12
  • $\begingroup$ @DeerHunter, true enough. $\endgroup$ – Don Branson Aug 25 '13 at 13:15
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    $\begingroup$ You didn't say in orbit about what. If you permit orbiting the center of our galaxy, then probably Voyager 2, launched August 20, 1977. (Yes, it launched before Voyager 1.) $\endgroup$ – Mark Adler Aug 25 '13 at 18:31
  • $\begingroup$ @DeerHunter, If you look over the questions on this site, many of the questions require answers that will change over time. Still, that will make them irrelevant as they age. $\endgroup$ – Don Branson Aug 25 '13 at 19:22
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    $\begingroup$ Depending on how you define "in use", the answer could be "Vanguard I". It's still being optically tracked as part of upper-atmosphere drag experiments. $\endgroup$ – Mark Mar 14 '14 at 4:55
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GOES 3 is most likely the oldest satellite in operation as of early 2014. Launched in 16 June 1978 as a weather forecasting satellite, it was repurposed as a communications satellite when it became unusable for meteorological studies in 1989.

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The first satellites listed by SATCAT with a status of + (operational) are CALSPHERE 1 & 2, passive spherical surveillance calibration targets built by the Naval Research Laboratory, first one launched in December of 1962, but apparently no longer in use. LCS 1, a hollow metal sphere with a precisely defined radar cross-section launched on the 6th of May 1965, is still used (along with LCS 4, 7th Aug 1971) to calibrate ground-based radars.

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  • $\begingroup$ @DavidHammen same thing, though. Drilling down thru SATCAT shows quite a few reflectors still up there. Still no conflict with my other question. $\endgroup$ – Jerard Puckett Mar 17 '14 at 20:39
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    $\begingroup$ I consider listing as active a satellite that only has passive systems cheating ;) $\endgroup$ – SF. Feb 4 '16 at 13:16
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The oldest still operational communication satellite in use is the low budget amateur radio satellite AMSAT-OSCAR 7 made by radio amateurs.

It was launched on 15th of November 1974 from Vandenberg Air Force Base with a Delta 2000 rocket. OSCAR 7 has operational HF/VHF/UHF transponders, which allows communication over distances of up to 9,000 km with a relatively simple ground station equipment.

The satellite is in a 1,500 km retrograde polar orbit. The batteries are dead, although the satellite's solar cells works fine. The satellite is used daily during times when the solar cells are sunlit.

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    $\begingroup$ But it should be mentioned that AMSAT-OSCAR 7 was silent between 1981 and 2002 for 21 years. It was estimated that the cause of the outage was a short circuit in the battery. That short turned into an open circuit after 21 years. The satellite was used even in January 2017. $\endgroup$ – Uwe Jan 11 '17 at 12:40
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What is the oldest that's still in use?

Depending on what "still in use" means, I would venture that it is LAGEOS-1, launched on 4 May 1976. That's two years before GOES-3, and over a year before the Voyager spacecraft. The LAGEOS satellites are simple to the extreme. They are balls of solid brass covered with retroreflectors, and that's it. No sensors, no effectors, no attitude control, no comm, no avionics.

Researchers ping those retroreflectors with ground-based lasers. That was and remains the intended use of these satellites. The returns from those pings tells researchers range, range rate, and bearing. From that, the orbits of the LAGEOS satellites can be determined with very high precision. From those very precise orbit determinations, LAGEOS provides insight on diverse topics such as the validity of general relativity, the shape of the Earth and the distribution of mass within the Earth, and plate tectonics.

The LAGEOS satellites will cease to serve their initial function when they deorbit (that's million of years from now), when their retroreflectors degrade to such an extent that they can't be seen (that's also a long time), or when they are smashed by another satellite or by orbital debris.

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