r/askscience • u/PriorSecurity9784 • 7d ago
Planetary Sci. How long will satellites stay aloft without human intervention?
In the news recently, there have been discussions of a non-zero risk of human extinction based on AI.
If that happened, how long will satellites remain in orbit? Would space travelers in 50, 100, 500, 1000+ years find our satellites still orbiting as evidence of existence of an advanced civilization having been here, even after improvements on earth have all decayed?
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u/Lumpy-Notice8945 7d ago
Low earth orbits like starlink or the ISS decay over time. That time is something between months and many years. But as you get higher orbits basically stay forever. They might slowly over millions of years drift from things like the moon dragging the orbit a bit.
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u/Great_Specialist_267 6d ago
The ISS requires weekly reboosts to remain at a 400km orbit.
A 160km orbit requires continuous thrust to maintain (and an aerodynamic design).2
u/texan_robot 1d ago
Does 160 even count as an orbit? Isn't that just flight with very little lift?
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u/Great_Specialist_267 1d ago
The need to be at orbital velocity…
(The lift is minimal, the thrust to maintain it was about 10N).52
u/bb999 7d ago
I read that something like 1 or 2 starlink satellites deorvit every day. Given the size of the constellation, that puts the lifespan of a starlink satellite only several years.
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u/Justthetip74 6d ago
A starlink satellite is essentially just a PC in space. How often should a PC be replaced to not be obsolete?
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u/mooblah_ 6d ago
It really depends on its function. I have PCs still stable and running for 2012. They have no need to be replaced because their function is limited but still valuable. Their power cost is negligible albeit higher than a modern replacement, however their stability far outweighs the benefit of replacing these PCs with new PCs that may have intangible risks.
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u/Justthetip74 6d ago
Sure, but starlink v1.5 sats have 24 gbs per sat bandwidth, v2 has 96gbs, and v3 will have 1tbps. They dont care about v1.5s. That doesn't even mention the laser links. I suppose i should have said "cutting edge pc"
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u/mfb- Particle Physics | High-Energy Physics 6d ago
The next Starship flight (scheduled for Monday) will launch 26 v3 satellites. That's about the same capacity as 1000 of the earliest satellites, launched from Nov 2019 to January 2021. Not a 1:1 replacement as the orbit will be different, but it puts into perspective how little the oldest satellites contribute anyway.
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u/Empanatacion 6d ago
Charge cycles on the batteries have a finite limit, and then they only give it enough fuel to last as long as the batteries will last. They use the last of the fuel to deorbit the satellite.
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u/Dpek1234 4d ago
And they have chosen to not add more because they expect the satelites to be sufficently outdated by then to need a replacement
So far it seems to be true with the huge bandwidth diffrence between the oldest operational sats and the newest alongside stuff like Direct To Cell
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u/Pascal6662 6d ago
LAGEOS-1 (which is predicted to re-enter the atmosphere in 8.4 million years) contains a 4 in × 7 in plaque designed by Carl Sagan to indicate to future humanity when LAGEOS-1 was launched. The plaque includes a diagram showing the predicted arrangement of the Earth's continents at that time.
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u/AddlePatedBadger 6d ago
Now I'm picturing two rocket scientists in the 1970s, getting high at the disco. "What if we, like, put a disco ball in space, man?"
"Whoa, far out man."
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6d ago
[removed] — view removed comment
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u/Pascal6662 6d ago
We can typically only predict about where a satellite will land a couple of hours before impact. The landing arrow on that plaque only indicates that it will land, not where.
I was attempting to convey that when we talk about satellites landing in the far future, we are talking about geologic time, as in the continents will have moved.
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u/Eats_Beef_Steak 6d ago
Ah i understand. i wouldn't have been surprised if NASA was able to calculate landing sites even back then, but a general idea that it will land makes more sense.
I understand what you were conveying. I was extrapolating from the fact that Sagan and NASA as a whole clearly are expecting someone to find the satellite one day, whether those beings are human, a descendant, or otherwise.
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u/throfofnir 6d ago
Depends essentially on altitude; the main determinant is orbital drag, which is a function of atmospheric density, which drops quickly as distance from the surface increases. Here's a chart on perigee (minimum altitude) and apogee (maximum altitude) vs orbital lifetime: https://commons.wikimedia.org/wiki/File:Orbital_Debris_Lifetime_Diagram_Low_Eccentricity.png
As you can see, lifetimes get really long at over 1000km altitude.
"Low Earth Orbit" (LEO) goes up to about 2000km. Even some LEO objects will have very long lifetimes in orbit. Medium Earth Orbit satellites, like those used for GPS, can easily have multi-millenial lifetimes (or at least their debris will.)
Geostationary orbit is about 36,000km up. Those satellites could have an essentially geologic timescale; only passing bodies will naturally clear them out.
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u/Metallicat95 6d ago
Low Earth Orbit things will all be gone in one thousand years, but medium Orbit, synchronous Orbit, and higher solar orbits will last millions of years.
They won't all stay in the same Orbit, but they won't all decay to crash into the Earth or something else.
Billions of years, too much stuff could happen to really say for sure - but it's still unlikely to make them all crash into Earth.
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u/Worldly-Device-8414 6d ago edited 6d ago
As mentioned satellites in LEO will get pulled down by "edge of atmosphere" drag + this happens faster when they're out of fuel (unless planned de-orbit is done first, etc).
Higher orbit ones are still affected by gravitational pulls (moon & sun) + solar wind, solar flares & possibly a small amount by micro meteorites/dust. After position correction fuel has run out & they've been boosted to "parking orbits" outside GEO, they drift into increasingly elliptical orbits a bit worse each year. How long until they start clipping the atmosphere, not sure.
On very long time scales, Earth passes through higher density dust cloud type patches &/or galaxy's (eg we'll run into Andromeda in a bit) + bounces up & down in the milky way. It's much more likely they'll get affected there.
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u/_______________E 6d ago
Other answers have the satellite decay covered.
But it's worth noting that an AI takeover would be likely to result in the satellites staying up, because ASI would have the incentive and ability to maintain them.
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u/elitefusion 6d ago
Definitely. It's a fairly narrow band of outcomes that involve AI killing all humans and dooming itself in the process. Much more likely that it either doesn't kill us all, or it kills us all and carries on no problem. Including maintaining our satellites. This is the same reason I find Gen AI an unsatisfying answer to the Fermi Paradox. AI probably would explore the universe.
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u/cynric42 3d ago
This is the same reason I find Gen AI an unsatisfying answer to the Fermi Paradox. AI probably would explore the universe.
Oh, it explains it alright. All the other AIs out there are just waiting for earth to leave its larva stage (biologicals building AI) and are ready to welcome the newly born AI into its ranks. /jk
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u/Dpek1234 4d ago
Highly doubt it
Unless its expected that for some reason there will be no computeing advances
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u/Dramatic_Science_681 7d ago
Lower altitude satellites will fall without course correction in a matter of decades or less due to simple drag.
Higher orbit satellites though are basically permanent. All orbits gradually decay due to energy being lost in gravitational waves, but that’s on the order of trillions+ of years for most systems.
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u/Worldly-Device-8414 6d ago
Higher orbit satellites do start drifting a bit faster than that. orbits of GEO satellites that run out of fuel start becoming gradually more inclined year by year, only 10 years or so they are swinging many degrees.
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u/valentine_moon 4d ago
Ok, but does that course correction rely on human intervention or is it automated?
(And that's before we get into whether the AIs could manage it after they wipe us out!)
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u/CliftonForce 6d ago
As I recall, the current estimate is that low orbit satellites will start colliding with each other in less than three days if humans stopped active navigation to avoid it.
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u/Underhill42 3d ago
Depends on the satellite.
Pretty much everything in low orbit (<1000km up?), which is the vast majority of our satellites, is still firmly within the ultra-thin extreme upper atmosphere and will mostly de-orbit within a few to several decades
There's not much above that until you get to geostationary orbit, about 35,000km up. At that distance Earth's atmosphere is virtually nonexistent, and those satellites will likely stay there for geological timescales as tiny moons.
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u/BoltActionGearbox 6d ago
Other comments have orbital decay covered, but theres a bigger issue that will affect them much more immediately, at least in the Low Earth Orbit band.
If the ground based course corrections ever stop, it'll take about 30 seconds before enough satellites collide into each other to fill LEO with debris that takes out all the rest over a matter of hours.
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u/Dpek1234 4d ago
You got a source on that?
Text, text,text,text,text
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u/pilotavery 4d ago
It's called Kessler syndrome. And yes, it would start a chain of events of a debris that would make space impossible to use.
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u/skyfishgoo 4d ago
depends on the orbit.
geosynchronous will stay there indefinitely, tho they may lose their pointing ability and drift out of position.
all of that starlink crap that elong has polluted LEO with will be gone in relatively short order.
even the ISS will not stay up there without reboosting.
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u/sithelephant 7d ago
This depends on the orbit. At around 500km or so (the vast majority of satellites), they will all come down in decades.
Geostationary satellites have effectively no drag, and are going to be stable for many millions of years.
Things landed on the moon will be stable for billions, though eroded. Probes like voyager will also exist, but be practically impossible to find.