12 ms·
Monitoring a high risk conjunction between two large defunct objects in LEO
- MarkMarine 6y agoThose are two massive objects (2800kg or 6100 lbs) with a high relative velocity (14km/s or 31,000 mph) basically head on, so a crash would be a disaster.
- kortilla 6y agoSorry if stupid, but why? Wouldn’t the head-on nature mean most of the energy goes into destroying each other’s velocity and they just fall into the atmosphere?
- TeMPOraL 6y agoAt these velocities, the objects behave as if being made of glass or water. Upon collision, we can expect a large number of small fragments flying out in pretty much every direction - some still fast enough to retain orbital velocity. And given the altitude of the event, 991 km, even those fragments that fall down may shred something on their way down.
- raverbashing 6y agoBut if they are on LEO the atmospheric drag shouldn't be too negligible no?
- lmm 6y ago991km is pretty high for LEO - ISS is at ~400km, Hubble is at ~500km.
- mikewarot 6y agoFrom up stream in the comments, one was launched 31 years ago... so yeah, this stuff could stick around a while.
- threatripper 6y agoFor every 100-200 km in height the lifetime seems to increase by a factor of 10. At 900 km the lifetime of big objects is 1000 years. Smaller objects can still orbit 10s to 100s of years.
- yetihehe 6y agoThose fragments will scatter in all directions. Some will go down, some will go up or in eccentric orbits, some wil go sideways, some will stay in the same or similar orbits. There will be A LOT of those fragments, all going at orbital speeds in various directions.
- TeMPOraL 6y agoIt isn't negligible on the timescales we care about. Skimming through the graphs in [0], at 900km we're talking 100+ years of orbital lifetime. And even if most fragments were to disappear sooner[1] - giving them a generous 20 years - that's still 20 years of dealing with a swarm of untrackable hypervelocity bullets coming at you from random directions. While space is big, it's not that big in LEO, and any such bullet will, upon impact, spawn more bullets. I don't think we'll have a catastrophic cascade leading to Kessler syndrom even if these two satellites collide today, but few more such events might be enough. EDIT: Also, the collision will be off-center and, eyeballing the orbital diagrams, some 15 degrees shy of being head-on. That means you can expect most of the both satellites not being directly involved in the collision, but instead gaining spin and breaking apart under stress. Those surviving pieces will then keep most of their orbital velocity and heading, but scatter like buckshot, each piece on slightly different orbit, migrating further over time. -- [0] - https://www.spaceacademy.net.au/watch/debris/orblife.htm https://www.spaceacademy.net.au/watch/debris/orblife.htm [1] - Orbital decay due to atmospheric drag is a function of mass to area ratio. I'm not sure whether the debris from a hypervelocity collision tends to be more like irregular, high-drag shatter, or like low-drag spheres of superheated metal that cooled off radiatively.
- dmurray 6y ago> Also, the collision will be off-center and, eyeballing the orbital diagrams, some 15 degrees shy of being head-on. How can we tell it will be off-centre if there's enough uncertainty in the orbital prediction that they are only "1% to 20%" to collide at all?
- TeMPOraL 6y agoBecause if there's 1% to 20% chance they'll collide at all, then the chance they'll collide centrally is even smaller.
- nabla9 6y agoIt depends on LEO altitude (exponentially) and aerodynamic properties of the object. ~ 150 km making single orbit becomes impossible. ~ 300 km orbital decay is ~km/month, so it already takes years to fall down to earth. ISS is at 400 km and decays 2 km/month. It has unfavourable mass to area ratio due to all those solar panels. ~ 500 km it takes few decades to fall down. (Hubble space telescope is here) 990 km is the altitude where these two satellites might collide. Debris can stay up thousands of years .
- xvector 6y agoKessler syndrome - hundreds of thousands of tiny shards would explode at the point of impact ripping into other satellites and rendering them defunct (causing more collisions). An exponential growth would occur which would result in Earth orbit being unusable. This might effectively lock use of Earth orbit away for centuries. See the video by Kurzgesagt - “End of Space: Creating a Prison for Humanity.” [1] [1]: https://youtube.com/watch?v=yS1ibDImAYU https://youtube.com/watch?v=yS1ibDImAYU
- staticassertion 6y agoCan't wait to be boiled alive on this stupid planet because we filled space with garbage.
- ladberg 6y agoIf it makes you feel any better it's pretty much impossible to make Earth less habitable than anywhere else in a few light years, so I wouldn't worry about missing out on a space-paradise!
- jyriand 6y agoSo, will it be something similar to the collision scene in "Gravity", movie?
- MarkMarine 6y agoYup. Not good for anything in LEO
- jfoster 6y agoFor anyone who hasn't seen the movie: https://www.youtube.com/watch?v=vKW-Gd_S_xc https://www.youtube.com/watch?v=vKW-Gd_S_xc What's the likelihood of any given collision like this initiating a space debris chain reaction? I'm guessing it's fairly low for any given collision, but quite high if we continue to allow collisions to happen. Would love to hear from someone who knows better than I do, though.
- slazaro 6y agoThere's lots of info around that here: https://en.wikipedia.org/wiki/Kessler_syndrome https://en.wikipedia.org/wiki/Kessler_syndrome
- panarky 6y agoProbability of collision between 1% and 20%. These are extraordinarily high numbers. https://en.wikipedia.org/wiki/Kessler_syndrome https://en.wikipedia.org/wiki/Kessler_syndrome
- ignoramous 6y agoGiven SpaceX's (and Amazon's) plans to deploy upwards of 12000 LEO satellites, how do they factor for avoiding these debris (given Kessler Syndrome's premise that this avoidance is only going to get exponentially harder as time goes on and not easier, especially what seems to my untrained eye one satellite too many)? Also, how do Rockets and other launch vehicles avoid these (I am guessing the debris are extensively tracked or are the launch vehicles built to withstand hits)? Excuse my naivety but it seems like a future where humanity locks itself out from Space altogether isn't a distant possibility at all but one that could happen in our lifetimes?
- Joeri 6y agoTheir satellites are mostly in low orbits that deorbit naturally after a few years. That doesn’t reduce the risk of collisions, but it does reduce the risk of being locked out of space for a long time. Still, I find it troubling that a single private US company is basically “using up” a particular orbital elevation without other countries getting a say in it.
- TeMPOraL 6y ago> Still, I find it troubling that a single private US company is basically “using up” a particular orbital elevation without other countries getting a say in it. Space is big enough. They aren't using it up. They create some minor burden for space objects tracking and mission planning, but you could still fit the same orbital band with many more constellations, and other nations/companies will be able to do so if they so choose.
- bryanrasmussen 6y ago
- coolspot 6y agoThis is the satellite [1] - launched in 1989 [2]. At least it doesn’t have a nuclear reactor as many other soviet military sats do. [1] - https://en.m.wikipedia.org/wiki/Parus_(satellite) https://en.m.wikipedia.org/wiki/Parus_(satellite) [2] - https://www.n2yo.com/satellite/?s=19826 https://www.n2yo.com/satellite/?s=19826
- ilogik 6y agonot really sure if having a nuclear reactor would make much of a difference in this case
- taneq 6y agoEven if there's no radiation risk, they're pretty dense and heavy. We use depleted uranium in armour-piercing rounds for a reason.
- TeMPOraL 6y agoWhich would be a nice thing to have in a collision, as more pieces would keep tighter together and closer to original orbit. Having a nuclear reactor onboard is the opposite of a problem in a case like this.
- dmurray 6y agoWouldn't the other, lighter, satellite experience the opposite though? It would be like a road collision: you'd rather have two small cars collide than a car and a semi-truck, assuming the same speeds. The truck has more kinetic energy to send fragments of the car flying everywhere. Clearly you'd rather a collision between two 1kg satellites than two 1000kg ones - where does this logic break down as we make one or both sats bigger?
- TeMPOraL 6y agoThe reason you prefer cars to be lighter if they're going to get into collision is because cars can absorb only so much kinetic energy before it spills out and affects the squishy humans inside. You're optimizing for safety of the passengers of both cars simultaneously. Satellites don't have this constraint. Of course you'd generally prefer smaller sats to collide (smaller = less fragments), but assuming fixed size, denser (= heavier) pieces will have more inertia, and so deviate less from their original flight path. This keeps the debris trail more concentrated. If only one of the two is heavy, the pieces of the heavier one should end up more concentrated. I'm not sure whether the wreckage of the lighter one gets spread more widely, or - with these velocities - just flash-fuses itself with the heavier one.
- ladberg 6y agoConsidering they have nearly opposite velocities, would any debris have enough velocity to stay in orbit after a collision? I'd assume the majority would fall out of orbit while maybe a few smaller pieces stay up, but if anyone knows of similar past events or simulations for reference then I'd be interested in seeing them!
- p1mrx 6y agoHere's a video of two paintballs colliding in midair. Use your imagination: https://youtu.be/0fP_k6y9ows?t=372 https://youtu.be/0fP_k6y9ows?t=372
- TeMPOraL 6y agoNow for even more accurate picture, imagine the balls colliding off-centre, and their velocities misaligned by ~15 degrees. Enough to break them and induce some spin, not enough for significant cancellation of velocities.
- hinkley 6y agoAbout half the mass keeps going or moves upward, but half moves down. A small amount gains altitude but loses velocity (so it will fall to earth or go eccentric, which might be worse)
- mabbo 6y agoAt these speeds and masses, it's best to think of the objects as if they were water. Imagine two globs of water colliding at high speed. Are they going to just cancel out and drop? Or are they going to splash in all directions? In this case, the splash will be metal pieces, hitting every other satellite in orbit.
- colechristensen 6y agoThe kinetic energy has to go somewhere, some of it will be heat, much of it will stay as kinetic energy. Many pieces in many different orbits. A collision like this could be disastrous to earth orbit.
- sparkling 6y agoELI5 please
- Cthulhu_ 6y agoTwo satellites are on a head-on trajectory to crash into one another, chances of impact are between 1 and 20%.
- csunbird 6y agoAt least that they are not on reverse/opposite orbits, hopefully one of the orbits will shift after this event and the intersection would be a non-issue. If none of the orbits decay, the intersection is extremely likely to happen again, with a similar result. Edit: I am mistaken, they are on reverse/opposite orbits, which is actually a huge problem!
- threatripper 6y ago* Satellites are kept in orbit by gravity. * They fly around earth in circular or elliptical orbits. * These satellites are at 900 km height. That is 100 times higher than the highest mountain on earth. * Up there is still a tiny bit of air which makes slower and slower. But at that height it takes 1000 years until they fall back down to earth. That is more than 10 times the life span of a human. * We have many satellites and leftover parts of rockets up there in space. But space is also big, so there is rarely the danger of a collision. Most big parts move on paths where they don't hit each other. * When these two satellites hit each other they will break apart into thousands of small pieces. The satellites fly very fast and the small pieces will be faster than a bullet. * Some of the small pieces fall back to earth where they will burn in the atmosphere. Other pieces fly away in all directions. Some pieces as tiny as a bullet will hit other satellites and destroy them. Some bigger pieces will rip apart other satellites creating more bullets. * There is the danger that many satellites are destroyed and millions of small pieces fly around in space. * When you launch a rocket you must pass through this area with a high danger of being hit by one of the bullets which would destroy the rocket and create more bullets. * We might have to wait until most of the dangerous debris has fallen back to earth until we can launch rockets again. This could take hundreds of years. * If we don't clean up space and put more and more waste in orbit we will never be able to leave earth and explore deep space. * Good night and sleep tight.
- deleted 6y ago[deleted]
- deleted 6y ago[deleted]
- seg_lol 6y agoNow would be a good time to push one of the satellites out of the way (softly). Maybe one of those big airborne lasers [1] Every piece of junk we put in space should be able to de-orbit on command. [1] I know, I know the ranges are way off, but it _could_ work if something on the outside of the object would gas off and provide a propellant https://en.wikipedia.org/wiki/Boeing_YAL-1 https://en.wikipedia.org/wiki/Boeing_YAL-1
- TeMPOraL 6y agoHere's my rough impression of what we may expect to see if the collision happens. Note that the collision isn't going to be perfectly heads-on, and is statistically unlikely for the centers of mass to collide. BEFORE: ^ / | | | o - CZ-4C R/B | / | | | / |/ | * /| | | / | / o - COSMOS 2004 | | / | v | AFTER: aaa^ / aaaa | aaaa | aa / b aa b b bb b bb b b ccc b b ccccc b b b ccccc b b b b ccc b b b b b b a | aa | aaa | aaa | aaa | Legend: a - Shattered fragments of the parts of satellites that weren't involved in direct hypervelocity collision, but got torn off and spun. Essentially like a shotgun discharge, but in space. These will carry most of their original kinetic energy and follow close to their satellite's original trajectory, slowly spreading over time and becoming untrackable. These will stay around the longest. b - Pieces that were close to or directly involved in the collision, retaining enough orbital velocity to stay in space. May be on highly eccentric orbits. Should decay faster than pieces labeled "a" (I think, I'm not sure). c - Pieces that lost enough velocity to fall either straight down, or fly upwards and then fall straight down. These may cause some damage on their way down to ground, but should disappear quickly. For reference, here are some (much prettier) diagrams of the 2009 collision, that happened at close to 90 degree angle: http://celestrak.com/events/collision/ http://celestrak.com/events/collision/.
- saagarjha 6y agoIt’s interesting to see how much debris remained confined to the original orbit-although it makes sense because any fragments that go sideways would need to happen to pick up a fairly high tangential velocity as a result of the collision. Not impossible, but fairly unlikely for any given part I’d guess.
- TeMPOraL 6y agoIt's not easy to change the inclination. The best way to get a feel for what a tangential component would do is to boot up KSP and start playing with the maneuver node tool in-game. I can't find any equivalent tool on-line, but there are some animated GIFs here: https://t-neumann.github.io/space/OrbitalManeuvers/ https://t-neumann.github.io/space/OrbitalManeuvers/ Scroll down to "Normal and anti-normal maneuvers". Basically, adding sideways velocity will change inclination a little bit, but also make it more eccentric - as you're not cancelling your original velocity, so the speed along the new orbital direction is greater than it was for your current altitude.
- bryanrasmussen 6y agoI am trying to wrap my head around this, assuming collision, what would be the likely secondary effects - many satellites knocked out? Communications grids down? Falling debris doing real damage (seems unlikely to me, but maybe airplanes?) The first two seem likely given Kessler syndrome.
- saagarjha 6y agoThose are probably not likely, but we’ll see a bunch more debris and perhaps a couple other satellites might get a few holes poked in them.
- baq 6y agomost likely nothing but the one after that - or a few more - will be exponentially worse.
- threatripper 6y agoGiven that the orbital lifetime is 100-1000 years and given that we don't have too much stuff in this orbit so far it could take dozens of years until it gets really bad.
- deleted 6y ago[deleted]
- jonplackett 6y agoWhen is the potential impact time? edit: it says in the tweet: Oct 16 00:56 UTC
- yters 6y agoDo we know whose old satellites these are? Why aren't we able to predict this way ahead of time?
- Diederich 6y agoThe exact orbital paths that various orbital objects take varies very slightly but unpredictably because the amount of atmospheric drag at a given altitude varies over time, and the exact geometry of each object makes that atmospheric interaction even more unpredictable. There are other factors as well.
- Rebelgecko 6y agoOne belongs to the USSR and one belongs to China Standard orbital propagation models like SGP4 can have a few km of error over the course of days. There's a lot of variables that change over time. As hard as it is to predict terrestrial weather, space weather is even worse. It looks like the objects' orbits take them above and below the thermopause, and the thermopause itself is mobile which makes things even more complicated
- JshWright 6y agoOne if them isn't what you'd likely call a "satellite" in the first place (though it certainly is, from a technical perspective). CZ-4C is the upper stage of a Chinese Long March rocket that was used to launch a reconnaissance satellite in 2009.
- totetsu 6y agoIf there were a collision, and a chain reaction that led to disruption of other satellites, what is the chances that certain world leaders use it as an excuse to declare state of emergency, and if so does that effect election dates?
- rbanffy 6y agoThe people at the South Pole stations will be able to catch some interesting fireworks. At 900 km it should be above the horizon about 3000 km away, so it'll be pretty high in the sky for them.
- 7373737373 6y agoDoes someone know if anyone will film this event?
- caf 6y agoSOCRATES seemed to see a much smaller probability for this event when it recalculated around the same time: https://celestrak.com/SOCRATES/search-results.php?IDENT=NAME&NAME_TEXT1=COSMOS+2004&NAME_TEXT2=&CATNR_TEXT1=&CATNR_TEXT2=&ORDER=MAXPROB&MAX=25&B1=Submit https://celestrak.com/SOCRATES/search-results.php?IDENT=NAME... I wonder why?
- JshWright 6y agoSOCRATES is using NORAD TLEs, with potentially a pretty wide accuracy margin. LeoLabs is using their own S-Band phased array radar in New Zealand. It's possible LeoLabs just has better data (it's unlikely to be worse).
- SethTro 6y agoI have seen a third conjecture tracker that displayed odds of current(?) collisions as arcs plotted in real time. Do you know what this system is called? I searched for 10+ minutes and can't find it.
- mturmon 6y agoI'd been wondering about the accuracy of the probabilities too. It's one thing if your dynamical model produces two state estimates and covariances, and another entirely when they actually match reality quantitatively! LeoLabs has a recent paper [1] that evaluates the state prediction accuracy. They're finding the right thing (Mahalanobis distance at various temporal separations between their state estimate and an object position). See secs. 4 and 5. But: they are not getting the chi-squared distribution that you'd want. They are getting log-normals, with significant probability mass out to a Mahalanobis distance of 10 and higher (!) -- see the figure in sec. 5. That's a very high deviation. It's not unexpected, because this is a hard problem, but the deviations do not appear to follow the expected law. If their collision-probability takes this into account, that's good. But if not -- if they're assuming a Gaussian prediction cloud -- then their collision-probability will not be well-calibrated. If my cursory examination of their (well-done!) paper is correct, a poorly-calibrated probability would be very wrong indeed. [1] https://amostech.com/TechnicalPapers/2019/Astrodynamics/Park.pdf https://amostech.com/TechnicalPapers/2019/Astrodynamics/Park...
- snewman 6y agoA couple of questions: 1. How likely is it that a collision like this (two large satellites, high enough for the fragments to have a long orbital lifetime) occurs in any given year? 2. This announcement popped up on HN a couple of days before the event. Are we not able to project potential collisions farther ahead? I would think objects of this size are well tracked. I'm wondering how difficult it would be to detect these far enough in advance to send something up to nudge one of the dead satellites out of the way.
- caf 6y agoA couple of hours before the event they still can only give a probability cloud. There's still considerable uncertainty in their projected positions: https://twitter.com/LeoLabs_Space/status/1316822400131104768/photo/1 https://twitter.com/LeoLabs_Space/status/1316822400131104768...
- distortedsignal 6y agoI believe this should be a live-track of these two objects on NORAD: https://www.n2yo.com/?s=36123|19826 https://www.n2yo.com/?s=36123|19826
- dzdt 6y agoLeolabs has updated maximum likely encounter distance to 12 meters, >10% chance of collision. [1] The objects are a Russian Parus navigation satellite (see [2] for image) and a Chinese expended rocket booster, the third stage of a Chang Zheng 4C rocket (see [3] for image). [1] https://twitter.com/LeoLabs_Space/status/1316410780552699909 https://twitter.com/LeoLabs_Space/status/1316410780552699909 [2] https://space.skyrocket.de/doc_sdat/parus.htm https://space.skyrocket.de/doc_sdat/parus.htm [3] https://space.skyrocket.de/doc_lau_det/cz-4c.htm https://space.skyrocket.de/doc_lau_det/cz-4c.htm
- rurounijones 6y agoGiven how much cheaper and frequent it is becoming to get into space with SpaceX launches. how long until we start seeing high-risk-debris deorbit missions? I think these would be good candidates for well used falcon stages that might fail since I doubt the payload would be that expensive in hte form of a small'ish, mass-produced, short-life robot that separates from the stage, grabs on to the debrit and pushes. (Yet I know I am glossing over a lot of technical details, still cheaper than what we normally send up). Robot is disposable and goes down with the debris. Falcon-9 returns to land for the next robot. But in my super-fantastical dream, the robot would detach from the nearby falcon 9 stage, do the pushing on the debris, then return and reattach to the falcon-9 (Opening and closing fairing) and the falcon 9 brings the robot back. Refuel and repeat.
- ColanR 6y agoI imagine that we don't have sufficiently precise data to plan far enough ahead to launch a mission that can deorbit the debris.
- rurounijones 6y agoDoesn't need to be debris hours / days away from impact, just general "Yeah, over the course of 10 years, these ones look the most suspect" levels.
- jnurmine 6y agoIf we disregard the Kessler syndrome/ablation cascade happening, what kind of worst case scenario are we looking at?
- SiempreViernes 6y agoThe same basic thing but slow enough it doesn't quite reach some threshold for just outright being ablation cascade I guess?
- forsakenharmony 6y agohttps://twitter.com/LeoLabs_Space/status/1316919600160903168 https://twitter.com/LeoLabs_Space/status/1316919600160903168 No collision