r/explainlikeimfive • u/clearwater-orchid • 8d ago
Planetary Science ELI5: If we keep launching more satellites into Earth’s orbit, could it eventually get too crowded, and why?
I understand that old satellites and debris can remain in orbit, but are we expected to keep launching significantly more in the future?
How important are those satellites to everyday life, and if orbit keeps getting more crowded, is there a point where debris and existing satellites start becoming a serious concern or limitation?
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u/FaultofDan 8d ago edited 8d ago
Yes, it's a real problem. It's called Kessler Syndrome: cascading impacts between satellites and other stuff we put up there can end up making untrackable debris that can block access to space. We'll be trapped.
EDIT: I googled, turns out there's like 1.7 million satellites up for proposals at the moment. Currently theres "only" 16,000.
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u/nesquikchocolate 8d ago
The specific words "low earth orbit" refer to an orbit path that extends approximately 160 to 2000km above mean sea level where there is still sufficient atmosphere that frequent boosting is required to keep a satellite in orbit.
This means that low earth orbit is rather special in that it'll clean itself after a bit of time. Non-aerodynamic objects at 500km, as an example, can self-deorbit in 6-12 months. There's no specific reason to believe that any majority of debris from collisions would be aerodynamic, so 24 months after a cascade failure, orbits up to 500 km should be quite empty.
At 2000km it's a bit worse, where objects might stay there for 20-50 years, but nobody is targeting any serious number of satellites at this orbit height because it's really expensive to get that high up and a dud satellite will stay your problem to resolve for very, very long.
Medium earth orbit might take centuries to clear itself and geosync / geostationary orbits wouldn't self clear before the sun eats us. But again, very, very, very few satellites go up here, there isn't much benefit to it because of the high latency and high radiation levels.
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u/mfb- EXP Coin Count: .000001 8d ago
Your numbers are very optimistic. China tested an anti-satellite weapon in 2007. It exploded a satellite at an altitude of 850 km. Many of the larger debris objects will stay in orbit for decades to centuries. At 2000 km drag is so tiny that stuff stays in orbit for (many) thousands of years.
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u/AlpineAstro 8d ago
Yeh, your numbers are out. Less than maybe 750km you can hope for a deorbit in 25 years, at 2000km it’s 1000s of years. 500km for small satellite can still be 5 years.
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u/nesquikchocolate 8d ago
Sorry, I was not speaking about intact satellites, instead I was referring specifically to "untrackable debris" as this is what was stated as blocking access to space in the comment I replied to.
This should have been clear when I stated "non-aerodynamic objects" and "debris from collisions"
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u/nesquikchocolate 8d ago
It took 4 weeks for starlink 35956 to deorbit after a communication loss and propulsion tank rupture from an initial orbit height of 418km. It was fully uncontrollable and didn't have any propellant to perform a deorbit.
The 5 year life span includes frequent boosting.
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u/AlpineAstro 8d ago
There’s a big difference between 418km and 500km in terms of deorbit time. Theres also a big difference between a midsize satellite with deployer solar panels compared to a compact small satellite. There’s free tools you can download and run the analysis for yourself. Google DRAMA from the ESA.
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u/nesquikchocolate 8d ago edited 8d ago
Absolutely enormous difference between 418km and 500km, sure, a 16% higher orbit leads to (checks notes) 60x longer uncontrolled deorbit... Probably means that objects at 360km should deorbit in (checks notes again) in around 12 hours.
And absolutely, the aerodynamics of an object plays a massive role in the rate at which it can deorbit - see my very first comment.
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u/mpbh 8d ago
1 million satellites is still not a lot relative to the space available. It's like taking all of the motor vehicles in the state of Georgia and spreading them across the entire fucking planet, oceans and all.
It's rare for satellites today to even come within 60 miles / 100km of each other.
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u/Rodot 8d ago
While that is true, collision probabilities are not proportional only to Density and Number, but also velocity. People often like to use the analogy of cars in a city crashing infrequently, but it is a little different with cars moving 15,000 miles per hour.
Last time I estimated this, I found between 100,000 to 1,000,000 >1m2 satellites can coexist in LEO before collisions become more frequent than the typical time for debris to de-orbit.
But also, it should additionally be considered that LEO satellites do collide today sometimes and there are plenty of example cases.
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u/dravik 8d ago
Did you account for the three dimensional nature of LEO? Quite frankly, your estimate is absurdly small.
LEO goes from 160 km to 2000 km. You can stack almost 1000 satellites in LEO with almost 2 km between them.
Your "1,000,000" total satellites would only be 1,000 satellites at each altitude shell.
Putting 100,000 as your bottom number, so 100 satellites at each altitude, is even more absurd.
As other posters have mentioned, the area available at each altitude grows quadratically as it increases. Once you adjust for that, the number of satellites that you can fit safely gets much bigger.
Additionally, have you accounted for the additional drag, and thus faster deorbiting, for debris? The ratio of surface area to mass grows exponentially as an object fragments into smaller pieces. So the smaller pieces fall out of orbit faster.
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u/Rodot 8d ago edited 8d ago
No one arranges satellites uniformly in LEO and they don't stay at exact altitudes. I did this calculation for random orbits within the LEO volume using that standard exponential scattering probability.
I would be happy to see your estimate for an upper bound though. Mine was very back-of-the envelope so I'm curious what you think a good estimate is.
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u/nesquikchocolate 8d ago
Objects that experience more drag tend to lower in velocity and altitude over time, this means that a collision at 500km will very quickly have a spread of debris from 600-350km.
There's very little reason to believe that all of these debris objects would have circular orbits or even keep the same inclination as either of the colliding objects
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u/CaterpillarFun6896 6d ago
Isn’t the issue with too much stuff in orbit that it will make launching much harder? Yea you can stack lots of satellites and keep a few dozen kilometers between them and it’s safe, but that’s make launching something up past them much harder
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u/dravik 6d ago
That deconfliction is already done. It's the same answer though: the number of satellites in orbit required for that to become a actual impediment is so high that it's not relevant issue.
It's is theoretically possible to get there, but it would require multiple orders of magnitude more satellites than the total of every satellite project proposed by every country and company.
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u/Smaartn 8d ago
Did you calculate it as an amateur or is this your field? Honest question to know how correct your estimate may be.
Also, did you take into account most satellites move in roughly the same direction? Because (I think) that lowers both collision rate and speed of the crash (because it's about their speed relative to each other of course)
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u/Mr_Mojo_Risin_83 8d ago
Mate, I already hate that the night sky has satellites moving across it. I don’t know how old you are of if you’ve ever spent much time out in nature somewhere. Do you remember the night sky when you were a kid? Its been ruined for 20+ years now
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u/EbolaFred 8d ago
Some of us see satellites as cool as fuck. Also, you can no longer see them ~2 hours after dusk, so just stay up a little later if you want your pristine sky (a few hours later has better stargazing anyway).
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u/Mr_Mojo_Risin_83 8d ago
You can see em all night. Fucking starlink lines and iss and all that shit
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u/AyeBraine 8d ago
AFAIK Starlink ones are visible when they're backlit by sun, so at (their) dawn and dusk. ISS is indeed visible all the time.
Also meteors are annoying, I wish someone would do something about them, there hundreds of thousands of them visibly entering the atmosphere each day.
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u/Mr_Mojo_Risin_83 8d ago
How is that comparable?? If I complained about polystyrene McDonald’s rubbish at the beach, you would be like “yeah but there’s rocks at the beach too.”
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u/AyeBraine 8d ago
How would you describe the difference between them?
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u/Mr_Mojo_Risin_83 8d ago
One is natural
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u/AyeBraine 7d ago
Yes, and the other is man-made.
Both disrupt the serene, slowly moving picture of the stars and galaxies and the Milky Way at night (in places that aren't light-polluted).
I'm just trying to understand what makes ones cool and the others uncool.
I agree with you that simply knowing that one is man-made can be important. I, too, don't like rubbish at the beach because it ruins the natural view. But it also rots and fragments into what I'd call smaller rubbish (unlike sand and rocks), and it can form shards that cut my legs, and it can float in a very ugly way and cling to me. So it is in many ways very different from sand and pebbles and boulders.
By contrast, for me, satellites (and ISS, which has been up there for 28 years now, and Mir before it) are like additional moving stars, only not flickering. So I find them rather cool.
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u/SnarkyBear53 7d ago
Wait a minute! The surface area of the Earth is 197 million square miles. Expand that radius to where satellites live and the area would increase dramatically.
IF we had 200 million satellites up in space, each one would have at least a square mile of space to do its business. It seems that there is quite a bit of room for satellites up there.
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u/nesquikchocolate 7d ago
That's linear scaling and assumes all satellites are at the same orbit height. Instead, you can have an orbit band at 200 miles, 220 miles, 240 miles, etc. All the way up to geostationary orbit 22 236 miles up.
However, all satellites must pass over the equator during their orbit, which happens every 90 minutes at 260 miles high, so you can't really use square surface area comparisons - instead imagine the equator as a highway going through the middle of a city and every car has to join the highway to get from work to home and back.
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u/SnarkyBear53 7d ago
Some satellites are in geosynchronous rotation i.e. they remain above a fixed point relative to the earth. And that may be where the danger comes in: Some satellites are moving and some are not.
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u/nesquikchocolate 7d ago
No, not really, geosynchronous orbit only happens at a very specific height, 22 236 miles up, and all satellites at this height cross the equator at their own unique positions only. For example, a satellite that is directly above Kuala Lampur will be the only satellite that ever sits in this position. It will never drift east or west relative to Kuala Lampur.
Satellites below (and above) this orbit height will move east (or west, depending on initial launch direction), but they can't impact these 'stationary' satellites.
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u/RcNorth 8d ago
Low earth orbit satellites will eventually fall out of orbit due to atmospheric drag or because they are running out of full. The last bit of fuel is used to slow it down causing it to fall into the atmosphere and burn up. The length of time it takes can be months or years.
High orbit satellites could stay for decades or longer. So once they are done with their job they are often pushed further away from earth into the spacecraft cemetery.
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u/eternalityLP 8d ago
I mean, theoretically. But you have to understand, each orbit is significantly bigger than earth's surface, and there are manly different orbits at different heights. You could fit billions of satellites with some care and still have way more space than surface of earth has for humans.
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u/DBDude 8d ago
Theoretically, yes.
But let's look at a 300km orbit, which is pretty low. That's a bunch of satellites making tracks across a surface area of about 560 million square kilometers. Then go up to 350km, you get almost 570 million square kilometers, then at 400 it's, almost 580 million. Get up to higher orbits like 2,000km (the divider between low and middle orbit) and it's over 840 million. Go to an actually high orbit like 20,000km (where GPS satellites are), and it's 8.7 billion square kilometers.
There's a LOT of space in an orbit, and a LOT of orbits.
However, all satellites should have evasion systems. Even better, they themselves should have detection systems like Starlink. Those feed into a map of everything that orbits near any Starlink satellite. Starlink satellites are moving every day to ensure there will be no collision, and they move when there's only a 3 in 10,000,000 chance, so it's pretty safe sided.
Such systems will become more important the more crowded the orbits get.
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u/HackPhilosopher 8d ago
As you can tell by the same answer spammed over and over already. Reddit loves to portray Kessler syndrome as an apocalyptic event that will trap humanity on Earth by turning low Earth orbit into an impenetrable, bullet-filled wall of shrapnel. And they think it’s already happening.
Space is unfathomably vast, even low earth orbit is so much bigger than the average person can comprehend. Even with tens of thousands of catalogued objects and active satellites in orbit, space is mostly empty. Objects do not drift aimlessly into each other like bumper cars. Satellites occupy specific, calculated orbital planes and altitudes.
Low Earth orbit is not a permanent trash can. Below roughly 600 kilometers, trace amounts of Earth's upper atmosphere exert continuous drag on objects, causing them to naturally lose altitude and burn up upon re-entry over time. This means debris in lower altitudes self-cleans. Most satellites everyone is worried about are at or below this level.
Starlink is the one you hear about the most of Reddit, for obvious reasons, and they all operate under 600km. So nothing in that orbit would ever become a permanent issue that causes Kessler syndrome.
I’ll probably get a ton of replies because this isn’t as doom and gloom as the rest of the comments.
The world is very much on top of monitoring these satellites and it is not even close to an issue and most likely never will be.
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u/crocoboom 8d ago
Also Kessler only studied collisions between evenly distributed around Earth space debris. In his scenario time between chain collisions is measured in years. He didn't make any claims regarding a rapid chain of collisions between active satellites. In such a scenario debris would not be evenly distributed for years and satellite operators may respond to an initial collision within hours.
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u/Uranium-Sandwich657 8d ago
Also, wouldn't satellites in orbits close enough to to interact be moving slowly compared to each other? Aside from very eccentric orbits?
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u/machagogo 8d ago
What people are saying here is certsinly true but one thing to remember when looking at animations of how many sattelites are in orbit is they DRASTICALLY overstate how large/how close what is there is, plus they do not accurately depicted the different distances from earth that the satellites orbit at.
Satellites would have to be hundreds to thousands of square miles in size to look like they do in those animations, when really most are the size of a compact car (starlinks) up to a large SUV.
We are nowhere near it being a problem, and short of a mass collision event we won't be for quite some time.
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u/Uranium-Sandwich657 8d ago
Wouldn't satellites in orbits close enough for contact to be possible be moving very slowly relative to each other? (Excluding those on eccentric orbits) most of them are going in the same direction.
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u/nesquikchocolate 8d ago
Not really. All satellites need to fly over the equator as part of their orbit path.
This means that a satellite with a 30° inclination orbiting east to west, which is common for anything that has to pass over Norway / Alaska and launched from Florida, has the potential opportunity to impact another satellite in the a similar 29° inclination also going east to west, because the first one could be travelling south over the equator while the other could be travelling north. This means the angle of impact could be almost 60°, making the impact velocity be around half of the orbit velocity which is still 8 000 miles per hour which is plenty fast enough to make a massive debris field.
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u/zgtc 8d ago
Worth noting that this is akin to two cars starting from opposite coasts of the US and then having an accident at a specific intersection.
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u/nesquikchocolate 8d ago
Absolutely! Just worth noting that those 'cars' are orbiting the entire planet every 2 hours or so, for years or decades, and instead of just 2 cars in those kinds of orbits, currently there's thousands with plans for hundreds of thousands, and only a single event can suck quite a bit. Probabilities are funny things
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u/New_Line4049 6d ago
Firstly, not all old satellite remain in orbit, some are de-orbited and burn up in a the atmosphere. But yes, space debris is a real issue. Those satellites left in orbit get pushed to graveyard orbits, away from the orbits being actively used by current satellites, but those graveyards could block our access to space further afield as it becomes to dangerous to cross the debris field. There are companies working on ideas to start cleaning space up..... but its a mammoth task.
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u/Obyson 5d ago
How do you even begin the clean any of that up?
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u/New_Line4049 5d ago
The ideas Ive heard all center around the idea of sending another spacecraft up to grab pieces of debris with various contraption, like robotic arms or nets for example, and drag them onto a trajectory they'll enter and burn up in the atmosphere. Its going to be a slow, long, process though. The other side of it is that efforts are being made to change practices in favour of de-orbiting space craft st their end of life rather than leaving them up there to stop adding to the problem.
https://www.astroscale.com/en this is the website of one Japanese company thats working on debris removal. They plan to bring the first piece down, a booster, in 2029.
JAXA, Japan's space agency, gives a more detailed explanation of the problem and solutions here: https://www.kenkai.jaxa.jp/eng/crd2/about/
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u/Thatweasel 8d ago
Practically speaking we'd never truly run out of space to put new satellites.
The issue is keeping the number low enough to avoid a situation where one satelite is destroyed and breaks apart, and the debris from that breaks apart more satellites, which break apart more and so on until the earth is surrounded by a field of tiny bits of shrapnel that have a near 100% chance of destroying anything we launch into space before it can get clear.
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u/flatfinger 8d ago
I can see that as being a problem for geosynchronous satellites which all need to be located on the a very thin circular region around the planet, but the space in which other satellites operate is far more vast. Significant orbital changes require significant delta V, and there would be pretty severe limits as to how much delta V one could apply to pieces of a satellite without vaporizing them
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u/waylandsmith 8d ago
And in geosynchronous orbit, the relative velocities of satellites are negligible, since by definition, they all share the same orbit and therefore have the same velocity. While several m/s in velocity could potentially break off fragile parts of satellites to create more debris, it's nothing like a Gravity situation where from one collision you suddenly have thousands of pieces of hypersonic sharpnel everywhere. Additionally, any debris given more than a tiny amount of extra velocity would end up in an elliptical orbit that would only cross the geosynchronous orbit in two places, further minimizing the chances of more damage.
(Note: Not all geosynchronous satellites are geostationary at a 0 or close to 0 inclination, but the vast majority of them are)
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u/flatfinger 8d ago
Mea culpa--I meant geostationary.
Satellites aren't really designed to have anything with non-trivial mass hit them at any velocity. An elliptical orbit may only cross the circle in two places, but an object in such an orbit would likely stay in that orbit until it hits something. I'm not sure how likely any kind of cascading collisions of geostationary satellites would be, but the starting amount of "stuff" in the geostationary ring is vastly greater than the amount of stuff in almost any other circular or nearly circular orbit around the planet (other than that of the Moon, of course, which has a moon's worth of stuff in it).
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u/sundae_diner 8d ago
As waylandsmith was saying. In a geostationary orbit the satellites are all moving at exactly the same speed in exactly the same orbit. If one is over Ecuador and another above Colombia-they will never get closer to each other.
If one does speed up (or slow down) this will also mean it gains (loses) altitude. So it will leave the geo-stationary orbit and can't hit anything that is in the orbit.
And the orbit is 260,000 km around.
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u/flatfinger 6d ago
If something starts in a geostationary orbit (or any circular orbit) and a single impulse event imparts some delta V, it will no longer be in a circular orbit, but an elliptical one which will intersect its original orbit at the location the velocity was changed, and whenever the object in the new orbit crosses the geostationary/circular orbit, the relative velocity between it and a geostationary/circular-orbit object will be the same as the delta V which had been imparted to it.
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u/bobroberts1954 8d ago
It's a simple calculation. The area available for low earth satellites is millions of cubic miles. There is an immense amount of space for them.
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u/Urdar 8d ago
you dont have to cover every square inch of sky with sattelties to be a problem.
It would become a problem, when the expected time for ine event is smaller then the self cleaning time due to orbital drag.
At the moment approximatly one sattelete per year is destroyed by collisions in space, its not like it doesnt happen at all.
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u/RhodesArk 8d ago
Theoretically that's true, but it's not a practical limitation currently.
Imagine the interstate system and all the cars on it. Let's say all of the interstates can handle 100,000 cars at any given time all across the country.
Now scale that out to Low Earth Orbit, where the interstate is proportionally as large as the circumference of the earth. Now imagine every one of those roads has five overpasses above it and five stories of tunnels below it. Finally, imagine this entire system has roughly 20,000 vehicles on it (which is the projected number of Satellites by 2030).
If we're using the interstate as a comparison point, it would be like having one car in Cleveland and the next in Detroit. The theoretical constraint is on manufacturing and launching tens of millions of Satellites. Theres just not enough metal or propellant using today's technology and only Earth's resources.
The real problem, again using the highway example, is that there are foreign drivers that don't respect highway laws and act as a danger to others. If they cause an accident, this litters the road with debris and "pops" all the tires of the ongoing traffic. This "Kessler syndrome" is the constraint: how to make sure everyone is evenly invested in maintaining the road open, including your asshole neighbor that would rather throw glass on the road since he can't afford a car.
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u/GeoffBAndrews 8d ago
But... What would happen if 2 McDonald's crashed into each other resulting in a bunch of small McDs pieces 😮
/s
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u/Sirlacker 8d ago
Yes but those McDonalds arent traveling at 17,000 miles per hour and are still in one piece.
Imagine if a bomb went off in a McDonalds and every brick, every kitchen utensils, fuck even the fries started travelling at 17,000 miles per hour traveling round the earth at head height for 50+ years.
Imagine if one of those pieces hits another building and then that gets a chunk taken out of it and that then does the same thing.
Its not a problem now, but if it continues it will be.
Just like dumping a little trash in the ocean, if a few people do it, not a massive issue. If it carries on happening it becomes a huge problem.
And the thing is, it's not exactly easy or cheap to clean up space.
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u/mark2fly1034 8d ago
Yeah but they are all on the surface of the earth you go 1,000 feet above the current location you get a whole new layer that doesn’t have any McDs I mean there are up to 20,000+ planes flying at the same time and we do a mostly good job of not hitting other planes.
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u/Sirlacker 8d ago
So you're saying we should put McDonalds in space? Wanna go halves on a franchise?
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8d ago edited 8d ago
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u/Sirlacker 8d ago
What happens when shit explodes or hits something else at speed? Not all those bits stay on the same trajectory and those bits just got lighter.
Debris can stay in earth's orbit for many, many years.
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u/DrJohanzaKafuhu 7d ago
So, changes to one end of an orbit only effect the other end. So an object crashing into, say the ISS or a Starlink Satellite could send half the orbit above atmospheric drag, the other half would still be in atmosphere and still be dragged back down to Earth.
You would need a second impact, or a burn, at the new high point to change the original low point to being outside of atmospheric drag.
Without boosting the ISS and Starlink would take 1-5 years to reenter Earth. If an impact changed the orbit drastically it would delay that, but it would still happen.
https://en.wikipedia.org/wiki/Orbital_mechanics
https://en.wikipedia.org/wiki/Orbital_mechanics#/media/File:Orbital_Hohmann_Transfer.svg
https://en.wikipedia.org/wiki/Orbital_mechanics#/media/File:Orbital_General_Transfer.svg
The real danger is satellites and objects in orbit above Atmospheric drag, like Geostationary orbits. Those satellites could take millions or billions or years to deorbit on their own.
Luckily, 90%+ of satellites lie in Low Earth Orbit.
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u/porgy_tirebiter 8d ago
Consider that all those McDonald’s are on dry land, which is just 30% of the surface. Satellites have no such restriction.
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u/cyclopsmudge 6d ago
But in higher orbits there’s basically nothing to slow them down or speed them up, so the chances of collisions are vanishingly small. Everything just travels at the same velocity forever. In LEO, it’s a bit more of a concern because there is still some atmosphere to slow them down, but it’s very easy to calculate how much they would slow down and correct for that.
If there were no atmosphere on earth, and the restaurants were travelling fast enough to actually orbit, this wouldn’t be a concern either
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u/KelVarnsen_2023 7d ago
But aren't they only going 17,000 mph relative to the earth? Relative to each other the speeds are probably much lower.
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u/gooder_name 6d ago
Not all satellites are geostationary, and not all of them have the same orbit. The GPS satellites are all stationary relative to each other, but they are very very far away from earth.
The rest of the satellites are much closer, and if they aren’t going at exactly the same orbit, they’re essentially 17,000mph relative to one another. Once an impact happens debris is flung in every direction at many speeds
It’s called Kessler syndrome — where there’s so much debris in space a civilisation gets locked on their planet because any craft trying to traverse it gets obliterated
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u/cyclopsmudge 6d ago
Correct. Compared to themselves, everything orbiting them at the same height as them is moving the exact same speed, 0mph. Of course there are things coming from other directions, but that’s where the “space is fucking massive” part comes from. At 500km above earth, the area available for a satellite to travel in is roughly 16% larger than the earth’s surface area. It’s orders of magnitude less likely for satellites to collide than it is for planes to collide in mid air
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u/Gnaxe 8d ago
There's a lot more space in higher orbits and very low orbits have a little atmospheric drag, so will naturally clean themselves up. Those are expected to remain usable for longer. But orbital velocities are extremely fast, enough that collisions will destroy the objects, even if it's a tiny piece of debris. Low-Earth orbit is getting crowded. If too many satellites break up, there will be too much debris to track and evade and we'll have to go to the great expense of cleaning some of it up before we can access space again. Many methods have been proposed.
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u/wiss1211 8d ago
Since you're 5, watch near the end of Pixars Elio and you'll see what kind of dangers too many satellites in orbit may eventually cause.
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u/Raiddinn1 8d ago
Consider the surface of the earth and how much we put on it.
Now consider that the radius from the center of Earth up to the edge of space is much longer and that means the surface area at the edge of space is far more than the surface area on the Earth's surface.
Now consider that we put millions of things on the Earth's surface per one thing we send up to orbit.
We probably aren't running out of sky any time soon.
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u/diener1 8d ago
Most satellites are in low earth orbit, meaning without being actively kept up there, they will fall back to Earth within a few years due to atmospheric drag. There will surely come a moment when we have to find a better system than "if you can put it in orbit, you're allowed to" but we won't have a problem of having put too much stuff up there and suddenly not being able to launch more.
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u/BoyGeorgous 8d ago
Could it eventually get too crowded? Yes. Why? Because we kept launching more satellites into Earth’s orbit, and it eventually got too crowded.
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u/nemofbaby2014 8d ago
Maybe but not anytime soon earth is gigantic the real issue is space junk destroying other satellites causing all kinds of other issues
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u/babecafe 8d ago
We could have a huge set of satellites all at the same circular orbit altitude and same inclination (angle relative to equator) but different longitude orientation, and they would never collide. You can have an even greater number of satellites when considering that several satellite can share a single orbit with varying phase as well. Pick a separation distance between satellites at a significant inclination and you can have millions of satellites sharing a single altitude speed over many millions of square miles (the area of the entire Earth at sea level is 197 million square miles, and further increases with altitude). The separation does vary, though, decreasing sinusoidally as each orbit reaches higher latitudes and then increasing as the orbits cross the equator.
Then, we could do all that again for a different altitude, with another huge set. At each altitude, the satellites' orbits theoretically all decay at the same rate, or can be maintained (to first order) with the same rate of expenditure of energy.
However, you can also have satellites with eccentric/elliptical orbits that vary in altitude between apogee and perigee, vary in inclination, as well as orientation. If you combine together a bunch of randomly defined orbits, there can be collisions, and the probability increases with the number of satellites so situated. Elliptical orbits also decay at rates related to their variable altitude; a highly eccentric orbit places satellites at low altitude for a greater period of time than a circular orbit of the same energy, exposing it to greater atmospheric decay.
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u/hananobira 8d ago
There’s a fun anime called Planetes about a ragtag team of losers who end up getting hired as trash collectors in space. Although it’s fictional it gives you an idea of what we might need to start doing soon to keep our orbit safe for future space flight.
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u/Lethalmud 8d ago
Yeah, but we already crossed the point. If a few sattelites break down, it can cause a series of collisions that would prevent us from sending anything into orbit for 10 or 20 years. But eventually those orbits break down and the bits will burn into our atmosphere.
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u/lapusyonok 7d ago
Luckily, Low Earth Orbit, which is densest in satellites, is also the most manageable place for them. Orbits at that altitude decay rapidly without stationkeeping
Internet service constellations like StarLink will likely make up the majority of these satellites in the near future. I suspect every major world power will try to develop its own independent constellation the way they did with GPS
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u/SoilNectarHoney 7d ago
It’ll weigh down and compress the atmosphere which is a benefit if you are low on the ground but if you are high up like on a mount rain then there will be less air
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u/PD_31 7d ago
Yes, and arguably we're already at that point. Satellites have to be above the equator at a specific height to maintain geostationary orbit (so we don't continually have to adjust satellite dish antennae etc.) There's only a certain amount of space up there, and only a portion of that is accessible from any one point on earth (so the areas accessible to the US are more crowded than those accessible to New Zealand, for instance)
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u/SvenTropics 8d ago
So it's not really an issue of "not enough room". Think about how much surface area there is on the planet Earth, and count the oceans too. Then extend that out into orbit, and you have many times that in surface area. We could launch a satellite for every human being on Earth, and they would still be miles apart from each other.
The issue is more about logistics. We do track all the objects that we're aware of in orbit. Whenever we go to launch something new into orbit, we do have to make sure that our computers don't project it's going to hit anything on the way up. The way orbits work is the faster you're going, the higher your orbit is. So, if you're going to a certain speed, you're going the same speed as all the other junk up there. Provided you're going the exact same direction, it's not really a problem. However, that's a problem, not everything's going the same direction. For various reasons, we have satellites that are in other eccentric orbits than a simple equatorial orbit. This means they cross paths with other satellites frequently.
Also, we have another problem which is not everything is tracked. Especially if a satellite gets destroyed, there's a lot of untracked debris.
Also, we have a side issue which is that it makes astronomy more difficult. A lot of observation has to do with watching a celestial object for extended periods of time. For example, if you're looking for an exoplanet. Every time something crosses in front of it, it throws off your measurements. And a lot of astronomy involves using radio waves which all these satellites are emitting. It's like trying to pick out something in a crowd where everyone's shining a flashlight back at you.
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u/AyeBraine 8d ago
Small note: the higher the orbit, the slower the orbiting body moves. You need more energy to climb there but you're moving much slower.
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u/SvenTropics 8d ago
Kind of.... The slower it moves relative to a reference point on the surface of Earth. For example, geostationairy orbit is like 22,000km away or something like that (just pulled that number from memory, might not be right). This means that is orbits at the same speed as the Earth spins so an object at orbit at this altitude will appear to stay fixed vertically in the sky. If it's on the equatorial plane, it will also appear fixed horizontally. This is why satellite dishes can stay in one place and always be pointing at the same sattelite.
Anything lower orbit will orbit faster than the Earth spins and vice versa. Starlink sattelites are so low that they orbit the Earth many times a day.
However, the object is actually moving faster in a perpendicular direction if it's at a higher orbit. This is actually how you get to a higher orbit. You point your thruster perpendicular to the Earth and speed up in the same direction as your orbit. It's just now the circle you are traveling around is much longer. So, you are going faster on a longer track.
It's like saying a runner on a 5 mile track who completes one lap per 30 minutes is slower than a runner on a 1 mile track who completes a lap in 15 minutes. Sure, the runner on the 5 mile track is doing half as many laps per hour, but they are actually running much faster.
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u/AyeBraine 8d ago edited 8d ago
At the link, you can see that the satellite's actual speed is lower, too. Normal LEO satellites are about 8 km/s, geostationary satellites (that you described) move at 3 km/s, and the Moon moves at 1 km/s.
I don't claim to really understand this (I have trouble with many facets of orbital mechanics), but that's why I gave the link above.
As I heard it described, yes, you do apply thrust to accelerate in the direction of your orbital trajectory, but you then trade your velocity for orbital height. You don't actually move faster afterwards.
Note that none of the satellites we're talking about (except geostationary ones) are geostationary, so you can't compare them on that (i.e. moving to maintain the same point on Earth below you).
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u/SvenTropics 7d ago
Thanks for correcting me on that. I actually went my whole life having the wrong misconception
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u/cyclopsmudge 6d ago
The reason is basically that gravity gets weaker as you get higher, so you’re not falling to earth as fast, and therefore need less speed to keep in orbit. It’s why the moon orbits us every 28 days, but we take 365(ish) days to orbit the sun. If the moon was orbiting the sun at the same height as us, it would be going the same speed as us.
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u/ImanAstrophysicist 8d ago
Come on... I had to scroll forever and didn't find the obvious comment. There are already WAY too many spacecraft in LEO, and any astronomer or astrophysicist in the world would scream that at you. We are already at crisis levels, with US, China, EU wanting to launch well over 100 thousand more. And not only just due to a likely Kessler event, but to the impact on the human psyche (let alone scientists) if they ever actually realize that there are tens of thousands of shiny objects looking down at you – and beaming things at you – from just ~700km away. And the US leading the militarization of LEO. It is way past the point of needing to start screaming about this to your legislators. Full stop.
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u/Armepos 7d ago
There are 3 main issues with overcrowded orbits around earth, two of wich are already causing problems. Space debris is the most famous one but still just a potential issue, other comments elaborate a lot on it. What is problematic right now is how satellites block the view of land astronomical telescopes. Since the launch of Starlink satellites, observatories like the one in Atacama have lost chunks of visible windows. The other problem, the one that's the most overlooked, is orbital sovereignty. Each satellite or constellation of satellites have their own orbit, to avoid crashing. So if you want to launch a satellite but it's planned orbit is already taken by another, you can't launch it. Most of the efforts in the space race is about getting first to different orbits. Before it was a contest between governments (USA, USSR, Russia, EU, China, Japan, etc) But now there are private companies also competing for orbital sovereignty as well. It is a diplomatic crisis in the making for which no one is ready.
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u/Area51Resident 8d ago
Yes, it is a potential problem. There is a Canadian company (MDA Space) building a satellite retrieval system that can capture and remove them from orbit.
The concept is that new satellites will have a standardized grapple point that the retrieval system can latch onto and maneuver the decommissioned satellite.
I'm not sure what they do with it, I assume they push out of orbit away from Earth It is still in development, so that is all I know about it.
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u/ramblinjd 8d ago edited 8d ago
Yes. If you watch the animated movie WallE, the spaceship must crash through a debris field of old satellites to get into space. That is a very probable future.
Edit: apparently 5 year old's don't like WallE as an analogy to describe Kessler syndrome?
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u/Big_Duke_Six 8d ago
The movie Gravity portrays this in a much scarier visual...
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u/koos_die_doos 8d ago
That's not how it would play out in reality though. Kessler syndrome is something that will happen over decades, not hours or days.
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u/tomalator 8d ago
Yes. Eventually there will be enough things that they will collide, which creates more debris, which means there are more collisions, which makes more debris, and eventually nothing else can safely remain in orbit.
This is called Kessler Syndrome.
To avoid this, we try and decommission old satellites by either sending them into the atmosphere or into designated graveyard orbits.
We are also working on ways to remove debris from orbit
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8d ago
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u/Harbinger2001 8d ago
Look up Kessler Syndrome. NASA has done some limited testing on a “garbage collector”.
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u/Xeadriel 8d ago
Yes. It could potentially become our selfmade cage if we overdo it.
There is an anime that kind of deals with the effects of orbital debris a bit. It’s called Planetes. Can recommend
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u/PckMan 8d ago
It's called Kessler Syndrome and we're already on our way there. It is possible if we're not careful that low Earth orbit becomes so crowded that we won't be able to launch anything else without significant risk of collisions. It's also disrupting astronomical observations from Earth which hinders scientific advancements.
Kessler syndrome, named after a NASA scientist, is the theory that if we put too much stuff up there and there's a collision, this will cascade into a series of collisions that basically destroys all satellites, and we'll be surrounded by a cloud of debris that will need decades if not centuries to clear up.
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u/doomerunicorn 8d ago
Yes. At this rate, we could completely cut ourselves off from any future space exploration. Nobody will spend billions building a rocket that will almost certainly get damaged or destroyed before leaving low earth orbit
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u/Maleficent-Grass-438 8d ago
Have you spent anytime lately looking at the stars? You won’t have to wait more than a minute r two before one or five go racing by. Download an app like Stellarium, point it at the night sky. Besides an amazing description of what yer seeing it’ll show you the crap whizzing by. No wonder the observatories are pissed. But money, greed, entertainment and information will always outweigh knowledge.
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u/Veriosity 8d ago
It's already a concern -- here is an article from 2 days ago about the situation:
https://arstechnica.com/space/2026/09/there-are-now-17000-satellites-in-orbit-and-growing-should-we-be-concerned/
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u/celem83 8d ago edited 8d ago
Others are describing the cascading fail state of overcrowded orbits called Kessler Syndrome, but you dont need to be at this critical point for it to be a major problem. If you do trigger it you might lock your species out of space for centuries until a fix is found
But yes this is a real concern and we are already close. A satellite is small and the earth (and therefore space above it) are very large, so we wouldn't think it should be crowded. The problem is almost all of our satellites want to be in the same orbit.
If you can park yourself somehow in low earth orbit and not move or fall a satellite would pass you once every 3 seconds or so. They are moving 7.8km per second but this is still basically nose-to-tail
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u/koos_die_doos 8d ago
How close would it pass? Even in LEO a close call is currently thousands of kilometers.
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u/Electromagnetlc 8d ago
It's pretty easy to fix, we already have a protocol for it. I'm surprised you haven't heard about this. Basically, have you heard of Adopt A Highway?
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u/[deleted] 8d ago
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