From all the spacecraft that orbit or orbited the Moon, which one lasted the longest in lunar orbit? By defunct spacecraft includes.
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Interesting question! Lunar Reconnaissance Orbiter was launched June 18, 2009 and spotted in a pretty amazing way on July 03, 2017. Why was the 100m Green Bank dish needed together with DSN's 70m Goldstone dish to detect Chandrayaan-1 in lunar orbit?, so that's roughly 8 years. Looking at older orbit projections before that it was expected to be stable at around 95 km for years to come due to its polar orbit. – uhoh Dec 06 '20 at 07:00
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And this answer to Are low, polar lunar orbits in general relatively stable? suggests it could stay there a long time. So that means that it could be 11 years so far but there may not be any verification after 8 years – uhoh Dec 06 '20 at 07:08
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1Why 8 years? It is still active that makes 11 years – Joe Jobs Dec 06 '20 at 10:48
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The comments are slightly out of date. The Lunar Reconnaisance Orbiter, launched in 2009, is still going strong and is expected to last at least until 2026:
As of 2019, LRO has enough fuel to continue operations for at least seven more years, and NASA expects to continue utilizing LRO's reconnaissance capabilities to identify sites for lunar landers well into the 2020s.[1]
Although lunar orbits are inherently unstable because of the Moon's mass inhomogeneities and tidal effects from the Earth and the Sun, spacecraft can be kept in such orbits as long as fuel is available and used for station-keeping.
Cited Reference
- Clark, Stephen (June 18, 2019). "10 years since its launch, NASA lunar orbiter remains crucial for moon landings". Spaceflight Now. Retrieved June 20, 2019.
Oscar Lanzi
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LRO (Lunar Reconnaisance Orbiter) might be a good candidate from which we have data to know it's exact state.
But since you included "defunct spacecraft" as well there might be something in orbit since more than 50 years. Something quite unexpected, to be honest. Namely the Ascent Stage of Apollo 11 might still be orbiting the moon.
We don't have definite proof but the sumulations that were run from the last data available do not lead to a crash into the lunar surface in most cases.
Discussion about this news here: Could the ascent stage of Apollo 11's Eagle still orbit the Moon?
TrySCE2AUX
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