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While I know Scientific American is a fairly mainstream targeted and softer science publication, this >And the problem is now poised to get much worse because

by xoa 6y ago

While I know Scientific American is a fairly mainstream targeted and softer science publication, this >And the problem is now poised to get much worse because of the rise of satellite “mega constellations” requiring thousands of spacecraft, such as SpaceX’s Starlink, a broadband Internet network. really could have used a LOT more qualification particularly since it's become a major recent talking point. There is one ultimate sure-fire way to reduce space junk: launch stuff to very low orbits. There is still some atmosphere (varying with heating and other factors) up a long ways in "space", and it's only above 600km or so that orbital drag becomes negligible enough that lifetimes really stretch out. The ISS for example requires regular reboosts or it would decay back into the atmosphere. SpaceX focusing on economics has made it feasible to start planning constellations of comm sats that are low and very low earth orbit, with the understanding that inherently their lifetimes will be measured in single digit years. But that's ok since they can be replaced so cheaply. This is much better, not worse. Even if they go offline or got hit, the debris would have a very restricted lifetime. The media should do a better job of conveying how cheaper $/kg to LEO opens up a lot of new possibilities in what regulations are feasible and how we think about the basics of satellite design. A simple "Mega constellation bad!" is all wrong, and that's not necessarily going to be intuitive to everyone.

phreeza 6y ago
Wait, how does launching stuff to low orbits reduce space junk? Edit: I think I now understand your comment. I mean sure it maybe adds less space junk than launching things into higher orbits, but it doesn't really reduce it, right?
- aftbit 6y ago
  There's atmosphere up there, so it creates drag which slows the stuff down and causes it to re-enter and burn up or crash onto the planet in only a few years. Compare that to higher orbit, where there's much less drag and space junk could last centuries or more before it deorbits.
- ericbarrett 6y ago
  Low Earth orbit satellites drag in the fringes of the upper atmosphere a lot more, so their lifetime in space, unboosted, is typically only a few years. If your satellite dies, it's "self-cleaning." That said, an impact at this level can still spew debris into higher orbits, as the chaos of the collision can impart enough energy to some collision ejecta to change their orbit significantly. So you still don't want things bumping into each other.
  - deleted 6y ago
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- gumby 6y ago
  It’s subject to drag from the whispy atmosphere and relatively quickly de orbits and burns up (thus no junk is left behind)
- jkilpatr 6y ago
  It's not a matter of 'more' or 'less' rather than 'easier to deal with'. LEO sats will probably produce more space junk by mass but junk in LEO will be gone in a few years, no matter how much or little of it their is. On the other hand Geostationary satellites produce much less junk in terms of mass, but once it's up there it's not coming down for centuries.
- ortusdux 6y ago
  Atmospheric drag causes a relatively speedy deorbit if not actively resisted. The starlink satellites use Hall effect thrusters to maintain their orbit. If a unit fails, it should deorbit in under 5 years. If the thrusters work, they could also force it to deorbit much faster. The risk comes from debris from a possible collision being ejected into a higher orbit. https://en.wikipedia.org/wiki/Orbital_decay#Atmospheric_drag https://en.wikipedia.org/wiki/Orbital_decay#Atmospheric_drag https://en.wikipedia.org/wiki/Starlink#Space_debris https://en.wikipedia.org/wiki/Starlink#Space_debris
  - gregmac 6y ago
    > The risk comes from debris from a possible collision being ejected into a higher orbit. Is that a thing that can happen? My intuition is it would be possible if a rocket currently boosting to a higher orbit were to collide with something on its way there, but two objects in the same orbit colliding couldn't get enough delta-v to actually get to a higher orbit. They could maybe get "higher", but not at orbital speeds and so would rapidly decay. I know next to nothing about orbital mechanics, so maybe someone who does can provide some better insight here.
    - pilom 6y ago
      Set a baseball on top of a basket ball and drop them both from waist high, the baseball will shoot really high into the air by stealing energy from the basketball. The same principle can occur when you start breaking pieces off of spacecraft with collisions. Also the two colliding objects might not be in "the same orbit" one could be in a polar orbit and one could be in a more equitorial orbit. One could be circular and the other highly eliptical, etc. This could boost parts of one of them into a higher orbit (though honestly it would be just as likely to slow things down).
    - SideburnsOfDoom 6y ago
      > Ejected into a higher orbit. Is that a thing that can happen? Apparently not as such. See sibling comment here:https://news.ycombinator.com/item?id=26809297 https://news.ycombinator.com/item?id=26809297
    - 6y ago
- myself248 6y ago
  It's like building a structure in the middle of the plains where it'll sit untouched for decades, versus building a structure on the beach where the incessant waves will grind it to bits in short order. Objects in low orbit don't stay there. They're slowed down by the atmosphere, and re-enter in a few months or a few years. Only if they're healthy enough to orient themselves, and have the fuel to do it, can they perform the re-boost maneuvers necessary to overcome atmospheric drag and stay up for longer. So, a satellite which loses control, or gets smashed into bits which can't individually control themselves, just becomes fodder for the drag. It gets swept out of orbit by the wisps of atmosphere out there. Low orbit is very "clean" in terms of junk, because junk simply can't linger there. Just like there aren't a lot of ancient ruins on the beach. The exact degree of drag is unpredictable because the exosphere is subject to a lot of variables, hence the "months to years" ambiguity. But they don't stay out there for decades or millennia, like junk in higher orbits.
  - cptskippy 6y ago
    > It's like building a structure in the middle of the plains where it'll sit untouched for decades, versus building a structure on the beach where the incessant waves will grind it to bits in short order. That is a fantastic analogy.
  - aledalgrande 6y ago
    Does that mean the material can still fully burn when falling down from under 2000km altitude? Or would we see pollution for example from battery materials?
    - KiwiJohnno 6y ago
      The original altitude is not relevant to how the item burns up. Its not the vertical velocity when it hits the atmosphere, its the horizontal velocity. Anything re-entering the atmosphere is subjected to temperatures around 8000 deg. Most things are just totally incinerated, unless they are well-enough insulated to withstand that temperature until they slow down from orbital velocity.
- dahfizz 6y ago
  > I mean sure it maybe adds less space junk than launching things into higher orbits, but it doesn't really reduce it, right? Sure, but that's not really the point. Using biodegradable plastic is much better than traditional plastic that stays in landfills forever. "Just don't generate trash" isn't an option.
  - ouid 6y ago
    There is literally no problem with plastics that stay in landfills forever. Landfills are underground, like the oil that the plastic is derived from.
    - simonh 6y ago
      Landfills are generally very close to the surface, filling holes created by activities like strip mining, so they do occupy surface area. Unless you're wiling to dig down under existing landfill to dig out voids to pack with more landfill.
      - ouid 6y ago
        Landfills are covered when they are full, effectively isolating them from surface ecosystems.
        simonh 6y ago
        The point is you can't use that area for getting rid of landfill anymore. From that perspective that area is 'used up'.
        deleted 6y ago
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- bombcar 6y ago
  If the cost to LEO is a fraction of the cost to HEO or geostationary, it becomes economical to send cheap satellites to LEO and let them burn up in a few years than to send expensive satellites to HEO or geostationary and let them become multi-decade space junk. Eg if it is $10m to LEO and $15m to HEO you will pay the extra to get to HEO and put a satellite designed for long life - but if it is $1m to LEO you can build a cheaper satellite and launch it 5 times over the following decades.
  - jakear 6y ago
    But they aren’t building 1 satellite and launching it 5 times over the next decade. They’re maintaining a constant fleet of 42000 satellites, which means putting up new junk to replace the old junk while its still flying junk and not de-orbited junk. I like the idea of having internet on my sailboat as much as the next guy, but it takes some serious cognitive dissonance to convince oneself that 42,000 pieces of nearby junk is better than a handful of pieces of far away junk.
    - xoa 6y ago
      >They’re maintaining a constant fleet of 42000 satellites, which means putting up new junk to replace the old junk while its still flying junk and not de-orbited junk. No. First, The whole reason they need to maintain a fleet, rather then just having it sit there for decades, is that they're so low. The vast majority of planned Starlink satellites from that number are from Phase 2, and are V-band VLEO sats with orbits around 340 km, which is really low. At that altitude, natural decay time is measured in weeks at best. To work they'll need both active thrusters providing regular boost and aerodynamic low drag design (and maintaining orientation for that will itself require fuel). Should they actually lose all control through malfunction or a collision, they and resulting debris will deorbit very rapidly (they'll both have no boost and be less aerodynamic). And second, "through malfunction or collision", because it's not as if SpaceX (and other LEO satellite operators) doesn't have, and indeed are required to have, plans for controlled deorbit at EOL. Most of the satellites can be expected to get deorbited in a controlled way as planned. Making sure everything burns up has been one of the things slowing Starlink development, it took some work to ensure the optical links would properly go for example. SpaceX is not interested in leaving them up there. I mean, FFS people, who would be hurt more than SpaceX by Kessler Syndrome!? >I like the idea of having internet on my sailboat as much as the next guy, but it takes some serious cognitive dissonance to convince oneself that 42,000 pieces of nearby junk is better than a handful of pieces of far away junk. Your dismissiveness towards hundreds of millions of underserved people and challenging use cases and ignorance of orbital dynamics does you no favors here.
- ravi-delia 6y ago
  It's not less so much as zero. Space junk isn't really a problem to worry about below a certain point.
deleted 6y ago
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WhompingWindows 6y ago
Can you give a rough estimate of what fraction of space waste is due to differing orbits of satelites? Like very low vs low vs geostationary? I don't know the gradations between those either.
- Ottolay 6y ago
  Wikipedia to the rescue (note the log-log scale) https://en.wikipedia.org/wiki/File:Spacedebris_small.png https://en.wikipedia.org/wiki/File:Spacedebris_small.png The biggest issue is by far the 600km to 2000km altitude band. It is popular for both LEO and SunSync sats and is high enough above the atmosphere that minimal propellant is needed for orbit boosting.
- orbital-decay 6y ago
  The actual amount/distribution of stuff can be misleading. What really matters is the risk of collision, which is the highest for Sun-synchronous orbits. The fact that lower SSOs are also the most convenient for remote sensing work doesn't help. GEO is more or less safe because it's unstable (dead stuff drifts outwards), well kept (slots are limited by the resolution of customers' terminals) and typically doesn't have high relative velocities.
yread 6y ago
SpaceX is planning to launch up to 42 000 satellites (there are about 3000 now). Cheaper $/kg leads to more space junk and higher risk of Kessler syndrome, that doesn't need any qualifications, I think. If something goes wrong the fact that the cloud of debris will be there for 10 years and not 100 years is not a huge consolation
- LeifCarrotson 6y ago
  Timing is absolutely a huge qualification to Kessler syndrome. If the cloud of debris is gone in 5 years, that's a hurdle to some careers and a (hopefully) temporary shutdown for some businesses. Covid has taught us that the modern economy has traded a lot of robustness for profit and efficiency, and those would certainly be significant losses of billions or trillions of dollars, but it would be a small fraction of GDP, we would hopefully learn from the mistake, and we would still be a spacefaring species. If Kessler syndrome occurred among geostationary satellites, that could potentially be a problem for millions of years. That's six orders of magnitude different and definitely needs qualification.
  - yread 6y ago
    But there is a lot more space in geostationary orbits and lot less stuff so the risk of chain of collisions is lower
    - duskwuff 6y ago
      There is far less space in geostationary orbit, because the locus of GEO is a one-dimensional ring above the equator.
      - fogof 6y ago
        It's true that there is less GEO real estate in this sense. But to kick off Kessler syndrome, you need two objects in different orbital planes so that they collide at very high speed. It wouldn't be possible for two defunct GEO satellites to collide, because two nearby GEO satellites are moving in the same direction at the same speed.
SideburnsOfDoom 6y ago
> There is one ultimate sure-fire way to reduce space junk: launch stuff to very low orbits Really? If there's a collision in LEO, doesn't debris spray in all directions, including some in the direction of higher, more stable orbits?
- enchiridion 6y ago
  Not a physicist, but I doubt the debris would have the energy to reach geostationary orbits.
  - SideburnsOfDoom 6y ago
    Not relevant? There are many orbits that are below geostationary and are also high enough to avoid atmospheric drag for a long time.
- wizzwizz4 6y ago
  In the direction, yes, but it would still cross the original orbit. You need a second collision to actually get stuff into higher orbits.
- ravedave5 6y ago
  With my limited knowledge of orbital mechanics I believe this wouldn't be a problem. It takes a lot of energy to move to a higher orbit. I would think the probability of enough energy to fling something to a higher orbit where it would be stable for a noticeably longer time would be very low. Think of exploding something 2 miles up the side of a mountain, what are the chances a piece goes another mile up the mountain. Like that but even harder.
- mediaman 6y ago
  This would just create an oblong orbit, which would still cause re-entry into thicker atmosphere for a portion of the orbit.
- hinkley 6y ago
  I thought the debris that gets lifted upward tends to go into elliptical orbits. Apogee would still create a significant amount of drag, wouldn't it?
nabla9 6y ago
Altitude Lifetime 200 km 1 day 300 km 1 month 400 km 1 year 500 km 10 years 700 km 100 years 900 km 1000 years
- tim333 6y ago
  Ha - and the altitude of the space station is 408 km so most of the junk should clear out in a year? That sounds too easy.
  - pilom 6y ago
    The space station has to add energy almost weekly to overcome drag. If it didn't it would likely come down within a couple years. When they want to throw trash away, they literally just drop it off the side and it burns up eventually: https://gizmodo.com/iss-ditches-2-9-ton-pallet-of-batteries-creating-its-m-1846476992 https://gizmodo.com/iss-ditches-2-9-ton-pallet-of-batteries-...
    - spookthesunset 6y ago
      Would that stuff cause a huge fireball in the night sky? 2.9 tons is a hell of a lot of mass... amazing to think it will just burn up in the atmosphere.
      - aledalgrande 6y ago
        I don't think it is to worry about, 1 cubic meter of iron weighs 7.8 tons for example... it is not a huge mass in the end.
      - KiwiJohnno 6y ago
        I'd say it would burn up pretty nicely. Its not gonna be one homogenous lump of stuff that holds together on re-entry, its a bunch of smaller "things" (battery cells) bundled up and held together with an external shell. As soon as that shell burns through its going to break apart and each individual part will start burning up.
boringg 6y ago
Also, take out SpaceX from the name and add all the competitors (potentially lower quality) that are starting or about to get into the space and you can understand the concern. edit: my concern is the long chain of the curve of low-orbit satellite companies as price continues to have downward pressure.
- samstave 6y ago
  Why not incentivize these companies with grant such that they will get the grant if their TO orbit launches _include_ the retrieval of space junk as well on the RETURN back to earth. In order to go up, you have to bring something back.
  - simonh 6y ago
    Rendezvousing with, capturing and then manoeuvring with a captured object is an extremely hard and as yet unsolved problem, although there are some experiment. Also it is only feasible to rendezvous with a target on an almost identical orbit, otherwise the fuel and thrust requirements to reach it very quickly balloon to hugely prohibitive proportions.
    - ChickeNES 6y ago
      > Rendezvoing with, capturing and then manoeuvring with another object is an extremely hard and as yet unsolved problem, although there are some experiment Umm...this is utterly wrong, and has been since Gemini 10 in 1966, not to mention Skylab, Mir, ISS
      - nordsieck 6y ago
        > Umm...this is utterly wrong, and has been since Gemini 10 in 1966, not to mention Skylab, Mir, ISS There's a big difference between docking with a spacecraft that is designed to be docked with and capturing a satellite that was not designed to be captured. People are making good progress on this - Northrup Grumman just had a successful life extension satellite mission very recently. But it's far from a mature technology.
IlliOnato 6y ago
This is important correction. But a high-speed collision at a very low orbit can trow debris to not-so-low orbit. How big of a problem this can be is something to model and calculate, it's not something one figures out just from the general principles.
- cogman10 6y ago
  I don't see how that's a major issue, It'd take a pretty odd angle for a high speed collision to push something into a higher orbit. That seems like a pretty rare event.
  - bodhiandphysics 6y ago
    Not really. High speed collisions are high entropy events, so debris fills state space, and you get SOME debris at high altitudes (usually in highly eccentric orbits). That being said, low altitude is much safer since you don’t get as many long lived dead satellites
    - jerf 6y ago
      From super-low Earth orbits, more of the orbits that go really high also impact Earth or its atmosphere on the other side, so they only are up there once, rather than over and over and over.
      - bodhiandphysics 6y ago
        Yep!
- fooker 6y ago
  > But a high-speed collision at a very low orbit can trow debris to not-so-low orbit. This seems wrong, from what I understand of orbital mechanics.
  - bdamm 6y ago
SavantIdiot 6y ago
> inherently their lifetimes will be measured in single digit years. But that's ok since they can be replaced so cheaply Oh cool, let's shoot even more soon-to-obsolete pollution into the atmosphere. That's working so well on Earth. /s
- javagram 6y ago
  1000s of satellites are irrelevant to atmospheric pollution. The numbers are so small compared to the vast size of the atmosphere it isn’t really a concern to worry about. Atmospheric pollution from earth based sources is different because it’s something that is being done in the scale of billions of people, not 1000s, and CO2 doesn’t naturally disappear from the atmosphere over time and is growing decade after decade.
  - SavantIdiot 6y ago
    You're so confident. How adorably naive.
    - valuearb 6y ago
      Do you math? Over one hundred metric tons of space dust falls on the earth daily. Do you really think SpaceX de-orbiting a 200 Kg satellite once a day or so is going to change that significantly?
    - concordDance 6y ago
      Comments like this aren't constructive.
- mminer237 6y ago
  Aren't their lifetimes so short because they will fall out of orbit? That's not really polluting orbit.
vict7 6y ago
You seem to know a lot about this subject! Years ago, an acquaintance of mine told me of their idea to use railguns to remove space junk. Is this a remotely feasible solution?
- TeMPOraL 6y ago
  From space, maybe. A railgun on the surface of Earth that was trying to slow down a piece of space junk would, by necessity, be aimed at a low angle. Getting a projectile a couple hundred kilometers up while launching at such angle would make this railgun be something between a window-shattering nuisance and a weapon of mass destruction, depending on muzzle velocity and the size of the projectile. The problem is, of course, the atmosphere. That thick soup of gas that's at its densest near the surface, and has the annoying tendency of engulfing hypersonic projectiles in a thick ball of screaming-hot plasma.
azinman2 6y ago
When these satellites burn up in the atmosphere, what happens to all the particles? Do we have lots of likely toxic material just constantly being burned and circulating around?
- simonh 6y ago
  We estimate that the amount of dust and meteorites entering earth's atmosphere is about 100 metric tons per day. Combine that with emissions from volcanoes, many of which are highly toxic, and vaporised satellites are really insignificant.
  - kitsunesoba 6y ago
    The proportions remind me of another somewhat common space-related misconception, which is that rocket launches are big polluters. With each launch emitting roughly as much as a single commercial flight and typically around 100 launches happening globally per year, even a tiny change in the tens of millions of commercial flights per year has a far larger impact on emissions than launches will for the foreseeable future.
    - TeMPOraL 6y ago
      > With each launch emitting roughly as much as a single commercial flight It's one of those "connective" facts that puts so many distinct things into perspective. When I first learned it a few years ago, I became simultaneously very relieved that a rocket launch doesn't really have that big of a carbon footprint, and horrified by how much emissions a single passenger plane can make. It's a lesson about how visuals can be misleading: a plane looks tiny and doesn't really seem to be doing anything, while a rocket is big and rises to heavens on a pillar of flame, propelled by the anger of hell itself - and yet it turns out they're roughly the same, emissions-wise.
    - gus_massa 6y ago
      An easy way to compare the amount of CO2 they release is looking at the size. They only can burn the fuel they carry, and the density of the fuel is similar. The best images I got are https://twitter.com/rocketrundown/status/956079854511972352 https://twitter.com/rocketrundown/status/956079854511972352 https://twitter.com/erdayastronaut/status/1239595527114838018 https://twitter.com/erdayastronaut/status/123959552711483801... To make the calculation more difficult, like the 80% of the volume of a Boeing 747 is room for humans, and like 50% of the volume of a Falcon 9 is room for Oxygen and thrusters.
Gwypaas 6y ago
Here's an awesome diagram of all tracked space debris from 1959 to 2021 showing the constant cleaning by drag happening at lower orbits. It's the higher ones we really need to care about. https://www.reddit.com/r/space/comments/ld4vlq/gabbard_diagram_animation_of_space_debris_since/ https://www.reddit.com/r/space/comments/ld4vlq/gabbard_diagr...
- lend000 6y ago
  That's an amazing visual. Really helps to inform the debate. (Watch on full screen).
- hn_throwaway_99 6y ago
  Was waiting for that time in the '00s when China conducted an anti-satellite missile test. Did not disappoint. Let's not do that again.
- jacquesm 6y ago
  Can someone explain the reason for the mirror across the diagonal? Is there some altitude/velocity ratio that causes debris to spiral outward vs inward?
  - mutagen 6y ago
    The mirror line would be a circular orbit, this plots each tracked orbiting debris with two dots, the blue dot being the lowest altitude of the orbit and red the highest.
  - mjevans 6y ago
    I'm not an expert BUT... I suspect the diagonal line between the colors represents the duration of a stable orbit at that altitude. Anything with a more elliptical orbit will drag when it's in the closer phase and decay. Anything with a lower orbit is already slowing to a tighter orbit (and more drag on the denser atmosphere).
- misterkrabs 6y ago
  Thank you for showing me the coolest graph I have ever seen.
sandworm101 6y ago
>> launch stuff to very low orbits. >>Even if they go offline or got hit, the debris would have a very restricted lifetime. That approach can help, but the problem persists. Lower orbits are much smaller than higher orbits. Focusing megaconstellations into a narrow 100-110km band is asking for trouble. The kessler syndrome could occur in a very narrow band, quickly rendering even short-lived satellites uneconomical. The narrower the band of orbits, the more likely and more aggressive kessler becomes. It is one thing to loose a few sats every year, very much another to have your entire constellation wiped out every year.
- Tuna-Fish 6y ago
  If you are low enough, Kessler is simply not possible because square-cube scaling means that the fragments deorbit in less than a single orbit.
- tuatoru 6y ago
  > Lower orbits are much smaller than higher orbits. Not "much". A 1200 km circular orbit is ~10% longer than a 550 km one, so a max of ~20% more "room" in the larger orbital shell. The quicker de-orbiting of debris from the lower shell more than makes up for this IMHO.
  - sandworm101 6y ago
    Not longer, three dimensions. Low orbits range from about 110 to 200km. The next range, from 200 to a few thousand km is vastly larger in three dimensions.
    - deleted 6y ago
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- MPSimmons 6y ago
  You can't have a stable orbit at 110km. The atmosphere is much too thick. You'll need at least twice that, and likely more to maintain vehicle attitude unless you have a very smooth drag profile, which is uncommon in orbital craft.
Hypocritelefty 6y ago
It is weird how these clowns turn up to defend space karen
euroderf 6y ago
I really wonder tho what this does to isolated tribes. To look up at an unchanging night sky, and on a regular basis new movement, new pinpoints of light. What does this do to the conception of The World ?
- dTal 6y ago
  They will likely view it - correctly - as an ominous omen of change and upheaval.
xyzzy21 6y ago
Sigh. Strictly the low orbits of StarLink actually make it a sort of non-issue: there's PLENTY of atmospheric friction at the orbits used so re-entry is only a matter of time. The bigger issue is higher orbits where orbital decay has far small perturbations to rely on. Those can be 10,000 year orbits which makes for a real problem.

by xoa 6y ago

phreeza 6y ago

Wait, how does launching stuff to low orbits reduce space junk? Edit: I think I now understand your comment. I mean sure it maybe adds less space junk than launching things into higher orbits, but it doesn't really reduce it, right?

aftbit 6y ago
There's atmosphere up there, so it creates drag which slows the stuff down and causes it to re-enter and burn up or crash onto the planet in only a few years. Compare that to higher orbit, where there's much less drag and space junk could last centuries or more before it deorbits.
ericbarrett 6y ago
Low Earth orbit satellites drag in the fringes of the upper atmosphere a lot more, so their lifetime in space, unboosted, is typically only a few years. If your satellite dies, it's "self-cleaning." That said, an impact at this level can still spew debris into higher orbits, as the chaos of the collision can impart enough energy to some collision ejecta to change their orbit significantly. So you still don't want things bumping into each other.
- deleted 6y ago
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gumby 6y ago
It’s subject to drag from the whispy atmosphere and relatively quickly de orbits and burns up (thus no junk is left behind)
jkilpatr 6y ago
It's not a matter of 'more' or 'less' rather than 'easier to deal with'. LEO sats will probably produce more space junk by mass but junk in LEO will be gone in a few years, no matter how much or little of it their is. On the other hand Geostationary satellites produce much less junk in terms of mass, but once it's up there it's not coming down for centuries.
ortusdux 6y ago
Atmospheric drag causes a relatively speedy deorbit if not actively resisted. The starlink satellites use Hall effect thrusters to maintain their orbit. If a unit fails, it should deorbit in under 5 years. If the thrusters work, they could also force it to deorbit much faster. The risk comes from debris from a possible collision being ejected into a higher orbit. https://en.wikipedia.org/wiki/Orbital_decay#Atmospheric_drag https://en.wikipedia.org/wiki/Orbital_decay#Atmospheric_drag https://en.wikipedia.org/wiki/Starlink#Space_debris https://en.wikipedia.org/wiki/Starlink#Space_debris
- gregmac 6y ago
  > The risk comes from debris from a possible collision being ejected into a higher orbit. Is that a thing that can happen? My intuition is it would be possible if a rocket currently boosting to a higher orbit were to collide with something on its way there, but two objects in the same orbit colliding couldn't get enough delta-v to actually get to a higher orbit. They could maybe get "higher", but not at orbital speeds and so would rapidly decay. I know next to nothing about orbital mechanics, so maybe someone who does can provide some better insight here.
  - pilom 6y ago
    Set a baseball on top of a basket ball and drop them both from waist high, the baseball will shoot really high into the air by stealing energy from the basketball. The same principle can occur when you start breaking pieces off of spacecraft with collisions. Also the two colliding objects might not be in "the same orbit" one could be in a polar orbit and one could be in a more equitorial orbit. One could be circular and the other highly eliptical, etc. This could boost parts of one of them into a higher orbit (though honestly it would be just as likely to slow things down).
  - SideburnsOfDoom 6y ago
    > Ejected into a higher orbit. Is that a thing that can happen? Apparently not as such. See sibling comment here:https://news.ycombinator.com/item?id=26809297 https://news.ycombinator.com/item?id=26809297
  - 6y ago
myself248 6y ago
It's like building a structure in the middle of the plains where it'll sit untouched for decades, versus building a structure on the beach where the incessant waves will grind it to bits in short order. Objects in low orbit don't stay there. They're slowed down by the atmosphere, and re-enter in a few months or a few years. Only if they're healthy enough to orient themselves, and have the fuel to do it, can they perform the re-boost maneuvers necessary to overcome atmospheric drag and stay up for longer. So, a satellite which loses control, or gets smashed into bits which can't individually control themselves, just becomes fodder for the drag. It gets swept out of orbit by the wisps of atmosphere out there. Low orbit is very "clean" in terms of junk, because junk simply can't linger there. Just like there aren't a lot of ancient ruins on the beach. The exact degree of drag is unpredictable because the exosphere is subject to a lot of variables, hence the "months to years" ambiguity. But they don't stay out there for decades or millennia, like junk in higher orbits.
- cptskippy 6y ago
  > It's like building a structure in the middle of the plains where it'll sit untouched for decades, versus building a structure on the beach where the incessant waves will grind it to bits in short order. That is a fantastic analogy.
- aledalgrande 6y ago
  Does that mean the material can still fully burn when falling down from under 2000km altitude? Or would we see pollution for example from battery materials?
  - KiwiJohnno 6y ago
    The original altitude is not relevant to how the item burns up. Its not the vertical velocity when it hits the atmosphere, its the horizontal velocity. Anything re-entering the atmosphere is subjected to temperatures around 8000 deg. Most things are just totally incinerated, unless they are well-enough insulated to withstand that temperature until they slow down from orbital velocity.
dahfizz 6y ago
> I mean sure it maybe adds less space junk than launching things into higher orbits, but it doesn't really reduce it, right? Sure, but that's not really the point. Using biodegradable plastic is much better than traditional plastic that stays in landfills forever. "Just don't generate trash" isn't an option.
- ouid 6y ago
  There is literally no problem with plastics that stay in landfills forever. Landfills are underground, like the oil that the plastic is derived from.
  - simonh 6y ago
    Landfills are generally very close to the surface, filling holes created by activities like strip mining, so they do occupy surface area. Unless you're wiling to dig down under existing landfill to dig out voids to pack with more landfill.
    - ouid 6y ago
      Landfills are covered when they are full, effectively isolating them from surface ecosystems.
      - simonh 6y ago
        The point is you can't use that area for getting rid of landfill anymore. From that perspective that area is 'used up'.
        deleted 6y ago
        [deleted]
bombcar 6y ago
If the cost to LEO is a fraction of the cost to HEO or geostationary, it becomes economical to send cheap satellites to LEO and let them burn up in a few years than to send expensive satellites to HEO or geostationary and let them become multi-decade space junk. Eg if it is $10m to LEO and $15m to HEO you will pay the extra to get to HEO and put a satellite designed for long life - but if it is $1m to LEO you can build a cheaper satellite and launch it 5 times over the following decades.
- jakear 6y ago
  But they aren’t building 1 satellite and launching it 5 times over the next decade. They’re maintaining a constant fleet of 42000 satellites, which means putting up new junk to replace the old junk while its still flying junk and not de-orbited junk. I like the idea of having internet on my sailboat as much as the next guy, but it takes some serious cognitive dissonance to convince oneself that 42,000 pieces of nearby junk is better than a handful of pieces of far away junk.
  - xoa 6y ago
    >They’re maintaining a constant fleet of 42000 satellites, which means putting up new junk to replace the old junk while its still flying junk and not de-orbited junk. No. First, The whole reason they need to maintain a fleet, rather then just having it sit there for decades, is that they're so low. The vast majority of planned Starlink satellites from that number are from Phase 2, and are V-band VLEO sats with orbits around 340 km, which is really low. At that altitude, natural decay time is measured in weeks at best. To work they'll need both active thrusters providing regular boost and aerodynamic low drag design (and maintaining orientation for that will itself require fuel). Should they actually lose all control through malfunction or a collision, they and resulting debris will deorbit very rapidly (they'll both have no boost and be less aerodynamic). And second, "through malfunction or collision", because it's not as if SpaceX (and other LEO satellite operators) doesn't have, and indeed are required to have, plans for controlled deorbit at EOL. Most of the satellites can be expected to get deorbited in a controlled way as planned. Making sure everything burns up has been one of the things slowing Starlink development, it took some work to ensure the optical links would properly go for example. SpaceX is not interested in leaving them up there. I mean, FFS people, who would be hurt more than SpaceX by Kessler Syndrome!? >I like the idea of having internet on my sailboat as much as the next guy, but it takes some serious cognitive dissonance to convince oneself that 42,000 pieces of nearby junk is better than a handful of pieces of far away junk. Your dismissiveness towards hundreds of millions of underserved people and challenging use cases and ignorance of orbital dynamics does you no favors here.
ravi-delia 6y ago
It's not less so much as zero. Space junk isn't really a problem to worry about below a certain point.

deleted 6y ago

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WhompingWindows 6y ago

Can you give a rough estimate of what fraction of space waste is due to differing orbits of satelites? Like very low vs low vs geostationary? I don't know the gradations between those either.

Ottolay 6y ago
Wikipedia to the rescue (note the log-log scale) https://en.wikipedia.org/wiki/File:Spacedebris_small.png https://en.wikipedia.org/wiki/File:Spacedebris_small.png The biggest issue is by far the 600km to 2000km altitude band. It is popular for both LEO and SunSync sats and is high enough above the atmosphere that minimal propellant is needed for orbit boosting.
orbital-decay 6y ago
The actual amount/distribution of stuff can be misleading. What really matters is the risk of collision, which is the highest for Sun-synchronous orbits. The fact that lower SSOs are also the most convenient for remote sensing work doesn't help. GEO is more or less safe because it's unstable (dead stuff drifts outwards), well kept (slots are limited by the resolution of customers' terminals) and typically doesn't have high relative velocities.

yread 6y ago

SpaceX is planning to launch up to 42 000 satellites (there are about 3000 now). Cheaper $/kg leads to more space junk and higher risk of Kessler syndrome, that doesn't need any qualifications, I think. If something goes wrong the fact that the cloud of debris will be there for 10 years and not 100 years is not a huge consolation

LeifCarrotson 6y ago
Timing is absolutely a huge qualification to Kessler syndrome. If the cloud of debris is gone in 5 years, that's a hurdle to some careers and a (hopefully) temporary shutdown for some businesses. Covid has taught us that the modern economy has traded a lot of robustness for profit and efficiency, and those would certainly be significant losses of billions or trillions of dollars, but it would be a small fraction of GDP, we would hopefully learn from the mistake, and we would still be a spacefaring species. If Kessler syndrome occurred among geostationary satellites, that could potentially be a problem for millions of years. That's six orders of magnitude different and definitely needs qualification.
- yread 6y ago
  But there is a lot more space in geostationary orbits and lot less stuff so the risk of chain of collisions is lower
  - duskwuff 6y ago
    There is far less space in geostationary orbit, because the locus of GEO is a one-dimensional ring above the equator.
    - fogof 6y ago
      It's true that there is less GEO real estate in this sense. But to kick off Kessler syndrome, you need two objects in different orbital planes so that they collide at very high speed. It wouldn't be possible for two defunct GEO satellites to collide, because two nearby GEO satellites are moving in the same direction at the same speed.

SideburnsOfDoom 6y ago

> There is one ultimate sure-fire way to reduce space junk: launch stuff to very low orbits Really? If there's a collision in LEO, doesn't debris spray in all directions, including some in the direction of higher, more stable orbits?

enchiridion 6y ago
Not a physicist, but I doubt the debris would have the energy to reach geostationary orbits.
- SideburnsOfDoom 6y ago
  Not relevant? There are many orbits that are below geostationary and are also high enough to avoid atmospheric drag for a long time.
wizzwizz4 6y ago
In the direction, yes, but it would still cross the original orbit. You need a second collision to actually get stuff into higher orbits.
ravedave5 6y ago
With my limited knowledge of orbital mechanics I believe this wouldn't be a problem. It takes a lot of energy to move to a higher orbit. I would think the probability of enough energy to fling something to a higher orbit where it would be stable for a noticeably longer time would be very low. Think of exploding something 2 miles up the side of a mountain, what are the chances a piece goes another mile up the mountain. Like that but even harder.
mediaman 6y ago
This would just create an oblong orbit, which would still cause re-entry into thicker atmosphere for a portion of the orbit.
hinkley 6y ago
I thought the debris that gets lifted upward tends to go into elliptical orbits. Apogee would still create a significant amount of drag, wouldn't it?

nabla9 6y ago

Altitude Lifetime 200 km 1 day 300 km 1 month 400 km 1 year 500 km 10 years 700 km 100 years 900 km 1000 years

tim333 6y ago
Ha - and the altitude of the space station is 408 km so most of the junk should clear out in a year? That sounds too easy.
- pilom 6y ago
  The space station has to add energy almost weekly to overcome drag. If it didn't it would likely come down within a couple years. When they want to throw trash away, they literally just drop it off the side and it burns up eventually: https://gizmodo.com/iss-ditches-2-9-ton-pallet-of-batteries-creating-its-m-1846476992 https://gizmodo.com/iss-ditches-2-9-ton-pallet-of-batteries-...
  - spookthesunset 6y ago
    Would that stuff cause a huge fireball in the night sky? 2.9 tons is a hell of a lot of mass... amazing to think it will just burn up in the atmosphere.
    - aledalgrande 6y ago
      I don't think it is to worry about, 1 cubic meter of iron weighs 7.8 tons for example... it is not a huge mass in the end.
    - KiwiJohnno 6y ago
      I'd say it would burn up pretty nicely. Its not gonna be one homogenous lump of stuff that holds together on re-entry, its a bunch of smaller "things" (battery cells) bundled up and held together with an external shell. As soon as that shell burns through its going to break apart and each individual part will start burning up.

boringg 6y ago

Also, take out SpaceX from the name and add all the competitors (potentially lower quality) that are starting or about to get into the space and you can understand the concern. edit: my concern is the long chain of the curve of low-orbit satellite companies as price continues to have downward pressure.

samstave 6y ago
Why not incentivize these companies with grant such that they will get the grant if their TO orbit launches _include_ the retrieval of space junk as well on the RETURN back to earth. In order to go up, you have to bring something back.
- simonh 6y ago
  Rendezvousing with, capturing and then manoeuvring with a captured object is an extremely hard and as yet unsolved problem, although there are some experiment. Also it is only feasible to rendezvous with a target on an almost identical orbit, otherwise the fuel and thrust requirements to reach it very quickly balloon to hugely prohibitive proportions.
  - ChickeNES 6y ago
    > Rendezvoing with, capturing and then manoeuvring with another object is an extremely hard and as yet unsolved problem, although there are some experiment Umm...this is utterly wrong, and has been since Gemini 10 in 1966, not to mention Skylab, Mir, ISS
    - nordsieck 6y ago
      > Umm...this is utterly wrong, and has been since Gemini 10 in 1966, not to mention Skylab, Mir, ISS There's a big difference between docking with a spacecraft that is designed to be docked with and capturing a satellite that was not designed to be captured. People are making good progress on this - Northrup Grumman just had a successful life extension satellite mission very recently. But it's far from a mature technology.

IlliOnato 6y ago

This is important correction. But a high-speed collision at a very low orbit can trow debris to not-so-low orbit. How big of a problem this can be is something to model and calculate, it's not something one figures out just from the general principles.

cogman10 6y ago
I don't see how that's a major issue, It'd take a pretty odd angle for a high speed collision to push something into a higher orbit. That seems like a pretty rare event.
- bodhiandphysics 6y ago
  Not really. High speed collisions are high entropy events, so debris fills state space, and you get SOME debris at high altitudes (usually in highly eccentric orbits). That being said, low altitude is much safer since you don’t get as many long lived dead satellites
  - jerf 6y ago
    From super-low Earth orbits, more of the orbits that go really high also impact Earth or its atmosphere on the other side, so they only are up there once, rather than over and over and over.
    - bodhiandphysics 6y ago
      Yep!
fooker 6y ago
> But a high-speed collision at a very low orbit can trow debris to not-so-low orbit. This seems wrong, from what I understand of orbital mechanics.
- bdamm 6y ago

SavantIdiot 6y ago

> inherently their lifetimes will be measured in single digit years. But that's ok since they can be replaced so cheaply Oh cool, let's shoot even more soon-to-obsolete pollution into the atmosphere. That's working so well on Earth. /s

javagram 6y ago
1000s of satellites are irrelevant to atmospheric pollution. The numbers are so small compared to the vast size of the atmosphere it isn’t really a concern to worry about. Atmospheric pollution from earth based sources is different because it’s something that is being done in the scale of billions of people, not 1000s, and CO2 doesn’t naturally disappear from the atmosphere over time and is growing decade after decade.
- SavantIdiot 6y ago
  You're so confident. How adorably naive.
  - valuearb 6y ago
    Do you math? Over one hundred metric tons of space dust falls on the earth daily. Do you really think SpaceX de-orbiting a 200 Kg satellite once a day or so is going to change that significantly?
  - concordDance 6y ago
    Comments like this aren't constructive.
mminer237 6y ago
Aren't their lifetimes so short because they will fall out of orbit? That's not really polluting orbit.

vict7 6y ago

You seem to know a lot about this subject! Years ago, an acquaintance of mine told me of their idea to use railguns to remove space junk. Is this a remotely feasible solution?

TeMPOraL 6y ago
From space, maybe. A railgun on the surface of Earth that was trying to slow down a piece of space junk would, by necessity, be aimed at a low angle. Getting a projectile a couple hundred kilometers up while launching at such angle would make this railgun be something between a window-shattering nuisance and a weapon of mass destruction, depending on muzzle velocity and the size of the projectile. The problem is, of course, the atmosphere. That thick soup of gas that's at its densest near the surface, and has the annoying tendency of engulfing hypersonic projectiles in a thick ball of screaming-hot plasma.

azinman2 6y ago

When these satellites burn up in the atmosphere, what happens to all the particles? Do we have lots of likely toxic material just constantly being burned and circulating around?

simonh 6y ago
We estimate that the amount of dust and meteorites entering earth's atmosphere is about 100 metric tons per day. Combine that with emissions from volcanoes, many of which are highly toxic, and vaporised satellites are really insignificant.
- kitsunesoba 6y ago
  The proportions remind me of another somewhat common space-related misconception, which is that rocket launches are big polluters. With each launch emitting roughly as much as a single commercial flight and typically around 100 launches happening globally per year, even a tiny change in the tens of millions of commercial flights per year has a far larger impact on emissions than launches will for the foreseeable future.
  - TeMPOraL 6y ago
    > With each launch emitting roughly as much as a single commercial flight It's one of those "connective" facts that puts so many distinct things into perspective. When I first learned it a few years ago, I became simultaneously very relieved that a rocket launch doesn't really have that big of a carbon footprint, and horrified by how much emissions a single passenger plane can make. It's a lesson about how visuals can be misleading: a plane looks tiny and doesn't really seem to be doing anything, while a rocket is big and rises to heavens on a pillar of flame, propelled by the anger of hell itself - and yet it turns out they're roughly the same, emissions-wise.
  - gus_massa 6y ago
    An easy way to compare the amount of CO2 they release is looking at the size. They only can burn the fuel they carry, and the density of the fuel is similar. The best images I got are https://twitter.com/rocketrundown/status/956079854511972352 https://twitter.com/rocketrundown/status/956079854511972352 https://twitter.com/erdayastronaut/status/1239595527114838018 https://twitter.com/erdayastronaut/status/123959552711483801... To make the calculation more difficult, like the 80% of the volume of a Boeing 747 is room for humans, and like 50% of the volume of a Falcon 9 is room for Oxygen and thrusters.

Gwypaas 6y ago

Here's an awesome diagram of all tracked space debris from 1959 to 2021 showing the constant cleaning by drag happening at lower orbits. It's the higher ones we really need to care about. https://www.reddit.com/r/space/comments/ld4vlq/gabbard_diagram_animation_of_space_debris_since/ https://www.reddit.com/r/space/comments/ld4vlq/gabbard_diagr...

lend000 6y ago
That's an amazing visual. Really helps to inform the debate. (Watch on full screen).
hn_throwaway_99 6y ago
Was waiting for that time in the '00s when China conducted an anti-satellite missile test. Did not disappoint. Let's not do that again.
jacquesm 6y ago
Can someone explain the reason for the mirror across the diagonal? Is there some altitude/velocity ratio that causes debris to spiral outward vs inward?
- mutagen 6y ago
  The mirror line would be a circular orbit, this plots each tracked orbiting debris with two dots, the blue dot being the lowest altitude of the orbit and red the highest.
- mjevans 6y ago
  I'm not an expert BUT... I suspect the diagonal line between the colors represents the duration of a stable orbit at that altitude. Anything with a more elliptical orbit will drag when it's in the closer phase and decay. Anything with a lower orbit is already slowing to a tighter orbit (and more drag on the denser atmosphere).
misterkrabs 6y ago
Thank you for showing me the coolest graph I have ever seen.

sandworm101 6y ago

>> launch stuff to very low orbits. >>Even if they go offline or got hit, the debris would have a very restricted lifetime. That approach can help, but the problem persists. Lower orbits are much smaller than higher orbits. Focusing megaconstellations into a narrow 100-110km band is asking for trouble. The kessler syndrome could occur in a very narrow band, quickly rendering even short-lived satellites uneconomical. The narrower the band of orbits, the more likely and more aggressive kessler becomes. It is one thing to loose a few sats every year, very much another to have your entire constellation wiped out every year.

Tuna-Fish 6y ago
If you are low enough, Kessler is simply not possible because square-cube scaling means that the fragments deorbit in less than a single orbit.
tuatoru 6y ago
> Lower orbits are much smaller than higher orbits. Not "much". A 1200 km circular orbit is ~10% longer than a 550 km one, so a max of ~20% more "room" in the larger orbital shell. The quicker de-orbiting of debris from the lower shell more than makes up for this IMHO.
- sandworm101 6y ago
  Not longer, three dimensions. Low orbits range from about 110 to 200km. The next range, from 200 to a few thousand km is vastly larger in three dimensions.
  - deleted 6y ago
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MPSimmons 6y ago
You can't have a stable orbit at 110km. The atmosphere is much too thick. You'll need at least twice that, and likely more to maintain vehicle attitude unless you have a very smooth drag profile, which is uncommon in orbital craft.

Hypocritelefty 6y ago

It is weird how these clowns turn up to defend space karen

euroderf 6y ago

I really wonder tho what this does to isolated tribes. To look up at an unchanging night sky, and on a regular basis new movement, new pinpoints of light. What does this do to the conception of The World ?

dTal 6y ago
They will likely view it - correctly - as an ominous omen of change and upheaval.

xyzzy21 6y ago

Sigh. Strictly the low orbits of StarLink actually make it a sort of non-issue: there's PLENTY of atmospheric friction at the orbits used so re-entry is only a matter of time. The bigger issue is higher orbits where orbital decay has far small perturbations to rely on. Those can be 10,000 year orbits which makes for a real problem.