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@BillGray's excellent answer in September 2018 mentions that the Soviet magnetospheric research satellite 1977-093A (NORAD 10370) was expected to reenter the atmosphere in 2019 due to effects including the Kozai mechanism.

Is this currently the artificial Earth satellite that survived the longest before then reentering the Earth's atmosphere (40+ years) or has one stayed in orbit longer, then reentered?

I'm asking primarily about payloads (satellites) but discarded rocket bodies (R/B) or other objects of note will receive honorable mentions.

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    $\begingroup$ Are you asking which object stayed in orbit the longest (which would include still orbiting satellites), or is re-entry necessary? $\endgroup$
    – Polygnome
    Commented Dec 28, 2019 at 0:35
  • $\begingroup$ @Polygnome Yes, it's the not-as-easily answered question of the object "that survived the longest before then reentering the Earth's atmosphere". Reentry is required. If you can think of a way to improve the wording please feel free to edit, thanks! $\endgroup$
    – uhoh
    Commented Dec 28, 2019 at 0:37

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My bet would be on needles of the Project West Ford experiment, launched 9 May 1963.

a ring of 480,000,000 copper dipole antennas (needles which were 1.78 centimetres long [...] was placed in orbit to facilitate global radio communication.

Fifty years later, in 2013, some of the dipoles which had not deployed correctly still remained in clumps, contributing a small amount of the orbital debris tracked by NASA’s Orbital Debris Program Office. Their numbers have been diminishing over time as they occasionally re-enter. As of May 2019, 40 clumps of needles were still known to be in orbit

In other words, they keep reentering. The larger clumps are observable. The smaller ones - not. We may be seeing a reentry every couple of days or weeks. That would be around 56 years by now and the number will grow as more of the needles reenter.

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    $\begingroup$ Those turned out to be the answer to What is the largest number of identical satellites launched together? as well as Highest number of satellites launched on a single rocket (similar but not identical questions) so they might as well be the answer this one as well! If only there was a reentry that has a timestamp on it, we could be sure. If I understand correctly the individual needles have long since reentered, right? $\endgroup$
    – uhoh
    Commented Dec 28, 2019 at 13:49
  • $\begingroup$ If it's just the clumps with the high mass/area (low BSTAR) that remain, then perhaps there's a notable clump reentry with a date associated $\endgroup$
    – uhoh
    Commented Dec 28, 2019 at 13:53
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    $\begingroup$ "Needles" is a little misleading: their diameter is just 17 microns, at the lower bound for human hairs (says Wikipedia). The total mass of 480 million copper "needles" seemed implausible, but at just 40 micrograms each that's just 20kg of sparkly dust. $\endgroup$
    – Tom Goodfellow
    Commented Dec 28, 2019 at 20:18
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    $\begingroup$ I'd seriously doubt the clumps are firmly bound in any way - I'd bet even minor perturbations make them lose needles now and then, and then these needles will reenter soon after. $\endgroup$
    – SF.
    Commented Dec 28, 2019 at 21:06
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If you want intact payloads, Explorer 26 is the satellite that has reentered with the longest on-orbit lifetime with almost 57 years (SCC Number 963, INTLDES 1964-086A; launched 1964-12-21, reentered 2021-08-21).

For intact rocket bodies, the SL-3 R/B that launched Cosmos 389 had the longest on-orbit lifetime, almost 54 years (SCC Number 4814, INTLDES 1970-113B; launched 1970-12-18, reentered 2024-04-06).

The tracked object that has reentered with the longest on-orbit lifetime is a piece of debris associated with the breakup of a Thor Ablestar upper stage (the first known on-orbit breakup, occurring shortly after launch on 1961-06-29 after delivering Transit 4A to orbit). This reentered recently (2024-03-28), after nearly 63 years in space.

Note

There are things in orbit now that were launched before any of these three objects that will reenter in the future, becoming the new longest-lived reentry objects, so this list is only accurate as of the date of writing (2024-05-10).

All data obtained from Space-Track.

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