Those 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.
Sorry 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?
At 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.
For 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.
Those 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.
It 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.
[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.
It 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 .
Kessler 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]
If 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!
DO you have a source for this? I cant't find something for 2400, but from https://en.wikipedia.org/wiki/Representative_Concentration_P... the prediction of the IPCC for 2300 is an increase of 3.0 to 12.6 °C that is really bad but by far not enough to start boiling the oceans.
The article shows that 2.3% is an extreme upper bonnet because humanity has already lost its need of ability to generate 2.3% more growth per year. It's another case of people looking at a logistic graph and pretending it's exponential
that's the underlying theme of the series - it shows that exponential growth of economy is tied to exponential growth of energy consumption and it's something economists can't quite wrap their heads around.
From my understanding of Kessler syndrome after reading more about it - only LEO would be locked out for a couple of centuries, even in a worst-case scenario. We should still be able to go beyond that with minimal repercussions.
This is in conflict with the Kurzgesagt video. I wonder what their source was for the Kessler effect preventing excursions into space altogether.
You go through LEO, you just don't park there. Think direct insertion into higher-altitude orbits, in the style beginners in Kerbal Space Program do it - i.e. going straight up through LEO and only then turning sideways to gain orbital velocity.
The risk will be much lower (you'll be spending very little time in the band filled with hypervelocity bullets), but it'll also be much more expensive. You'll need a much bigger rocket.
Not an AE, but from my understanding of orbital mechanics, I think we usually use a LEO orbit to insert payloads into higher orbits or onto escape trajectories. Even Starship, which could be considered a next gen orbital vehicle, relies on LEO for reloading fuel before leaving Earth.
LEO is pretty important, first we have people there right now, and with the notable exceptions of weather and GPS, everything I take for granted in life that works because of satellites is in LEO. Not having it for 150 years would make space exponentially more expensive in every way.
I really enjoyed the first third of the book, the second third was decent too. I had to drop it when I got to the last third, it just became too boring.
Same here. I felt like the book could actually end after the remaining women decided on genetic manipulations. What followed thereafter was quite boring, and I stopped reading it as well. Actually sad, because the backstory is likely just preparation for what follows. But it was just too boring to go on.
Prompted by a comment from someone yesterday, I actually replayed the Snow Crash audiobook in the evening. Comparing SC and SE I notice that SC feels quite juvenile. I didnt notice that as much when I first read it in my 20s. But these days, it feels a bit too much over the top. Contrary to that, SE somehow feels too grown up.
Completely agree. He overwrote himself into a blind corner - wasted so much time describing the orbital mechanics of chains that my eyes rolled all the way up into the back of my head, completely spoiled any remote semblance of hard sci-fi he had going with the surprise Ur-Middle Earth origin story, and finally never justified all the self-indulgence with even a single word about the agent.
I haven’t read Seveneves, but that describes many Neal Stephenson novels. The Diamond Age is the clearest example for me -- brilliant beginning, with a really compelling setting; confused middle; terrible ending.
I don't get why people dislike the end of The Diamond Age in particular.
Spoilers. Like, I mean, this isn't a plot summary, but this is in some sense what happens so look away now if you wish you didn't know:
The Primer has been calling her Princess Nell for a long time. Once you realise what's going on with the vast number of "specially adapted" Primers for the orphan girls, that Princess has got a ready made tribe with shared values in the form of the Mouse Army, waiting for her say so.
The whole book has been telling you that in this era what matters isn't control over a land mass, which is what the Fists are fighting for in the Leased Territories on behalf of Han, but a Tribe with shared values.
The Mouse Army shows up, rescues Nell and takes her to her mother. The Victorian Queen recognises Nell as the leader of a novel but important tribe.
The novel is flawed in many usual Stephenson ways (e.g. use of rape in place of actual character development) but I don't know what people expected from these endings, they seemed perfectly satisfactory to me on multiple re-readings.
Space is extremely large and mostly empty.
People tend to misunderstand Kessler syndrome a lot because they build their idea on faulty representations. For example, if you go to the wikipedia article on Kessler syndrome, you will see an image where centimeters long debris are symbolised by kilometers wide dots.
> This might effectively lock use of Earth orbit away for centuries.
It would make exiting earth orbit and placing an object there significantly more complicated because you would need to take into account debris, probably detect them from the object and manoeuvre a lot more but it wouldn't entirely lock up use of Earth orbit. It would also be a solvable situation. Cleaning debris is doable.
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.
Given 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?
Their 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.
> 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.
They create a minor burden currently, thus distributing that burden without paying for it themselves, at what point does that burden get to be bad enough we can say they are using it up.
AIUI there are already regulations requiring that satellites be able to de-orbit themselves at EOL, and have some maneuvering capability in order to actively avoid collisions. This is directly paid for by the owners of these satellites as part of the development cost. Most of the objects at high risk of collision are either very old satellites, or debris from collisions of old satellites, from before these requirements existed.
Tracking space debris and other objects in orbit of the earth is something we'd probably want to do anyway, and it makes no sense to duplicate that effort, so of course that burden will be distributed. If that burden becomes too high I'm sure some tax or licensing fee will be introduced to pay for it (assuming such a thing doesn't already exist) but in the grand scheme of things those costs are irrelevant compared to the cost of launching something into space to begin with... Especially when the satellite is still functioning, and generally aware of its own position anyway.
The SpaceX satellites are in such a low orbit that anything that is not actively being pushed back up (well given more speed in reality but whatever) by engines will come down in a couple years due to drag from the atmosphere. Most of the Starlink satellites from the first patch have already come down on their own as planned (as have the 2 tintin proto ones)
This applies for ISS even more (it is huge and thus a lot of drag) and thus it has one of the Progress spacecraft docked or the Russian service module use its engines to boost it back into proper orbit so that it wont crash down on earth.
> This applies for ISS even more (it is huge and thus a lot of drag)
Wouldn't drag be proportional to the surface area, hence the square of the length scale, whereas orbital energy is proportional to the mass, which is cubic in the length scale. I would expect the orbital lifetime to be roughly proportional to their quotient and thus for larger objects to stay up longer.
On the other hand, ISS has a lot more empty (well, air-filled) space inside of it, so it might be a lot less dense than a SpaceX satellite.
Drag is enough of an issue for the ISS that they actually rotate the solar panels to reduce drag when they're not in sunlight, which saves them ~1000kg of propellant per year.
> Wouldn't drag be proportional to the surface area, hence the square of the length scale, whereas orbital energy is proportional to the mass, which is cubic in the length scale.
Are you assuming the ISS has a similar surface-to-volume ratio as other orbiting objects?
It does have a lot of empty space. But I would presume it also has a lot of heavy metal structure to keep that space pressurized to a human-breathable pressure and allow entry and exit. Satellites don't need to keep much under pressure except maybe their maneuvering fuel in a small perfectly-shaped container with a single small hole.
The ISS has a lot of doohickeys hanging off it, so the cross section is going to be much larger than if the ISS was condensed into a sphere or cube. The ISS is also a lot less dense than most satellites, so even if the drag were the same it would have more of an impact
Wouldn'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?
The 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.
Is it? More mass means more kinetic energy. If the core of the satellite is extremely heavy, it only has to lose a tiny percentage of velocity to send a lightweight piece off at 90 degrees at extremely high velocities.
Taken to the extreme I'd rather hit a feather than a bowling ball at 14 km/s.
> Taken to the extreme I'd rather hit a feather than a bowling ball at 14 km/s.
But what matters here isn't what you would rather do, it's what both you and the feather/bowling ball would rather do, in context of minimizing the size of the resulting fragmentation.
Intuition tells me that a hypervelocity bowling ball will barely notice you, much less have time to deposit lots of energy into you.
Sure not a great example, but fire two bowling balls at eachother and fire two feathers at eachother at equal speeds, how big do you expect the debris fields to be in either case?
The bowling ball collision has a lot more energy involved, it can eject more debris at high velocities in various directions.
Depends what else shares that orbit, or crosses its path at close orbital distances, doesn't it? If it does break up into pieces then you have a slowly dispersing shotgun blast of heavy metals polluting a wide range of orbits. If it doesn't, you have one tiny hard-to-track but very massive cannonball lurking out there waiting to strike.
The heavier the fragments and the less eccentric the orbit of untracked space junk, the more dangerous it is, because the longer it'll be hanging around before it gets close enough to Earth to de-orbit itself.
Considering 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!
Now 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.
About 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)
At 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.
The 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.
When metal tears, there’s a shockwave that sends most of the energy of the initial tear across the material. Like a martial artist breaking board, most of the effort goes into the initial break, and the rest is a much smaller input.
It’s why structural members on planes and the feet of the Starship prototypes have holes. It arrests the fracture.
Satellites won’t have as much material that behaves this way, so I wouldn’t count in too much KE being converted.
At 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!
* 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.
How does a five year old know what a "satellite", "gravity", "orbit", or half a dozen of other words used here is?
The "ELI5" meme needs to die, it does not make any sense in most of the situations it is used, and also it's a self-disgrace to anyone using it to compare their own intelligence and knowledge to that of a five year old.
"A meme is an idea, behavior, or style that becomes a fad and spreads by means of imitation from person to person within a culture and often carries symbolic meaning representing a particular phenomenon or theme."
Contrary to what Internet would like us to believe, a "
meme" is not a picture of a cat with some written words around it.
What, pedantic about correct terms describing correct things? If we cease to care about that, any communication using words simply stops working, because orange breathe knit, attend evasive colour and lonely arrogant arithmetic chemical wonder twig.
The operative word is 'like'. That is, explain to a similar degree of domain understanding as you'd expect from a 5 year old, rather than explain using a 5 year old's vocabulary.
But all that aside, what nerd kid wasn't drawing space shuttles and rockets by age 5?!? That was my jam!
That's just it - a five year old might be into rockets and astronauts and all that fancy stuff (I was too), but his or her "degree of domain understanding" is nowhere near enough to grasp how those things really work, nor does he or she have the education underpinnings needed to do so.
"ELI10" or "ELI15" would be a much less ridiculous request. It's still rather grating how people willingly denigrate themselves by comparing their own intelligence to that of a child's.
What's wrong with good old "explain it to a layperson"? The fact that it does not make a cool acronym? We're not on twitter (or in high school, for that matter), learn to express yourself like an adult.
I think that most kids already know what a satellite looks like. Those trash cans that often have solar cell wings and some satellite dishes. They fly way up in the sky.
Gravity pulls you down to earth. It gives you weight. Without gravity everything on earth would start hovering and flying around like on the space station. Things in space near earth also get pulled towards earth.
Orbit is if you throw something so very fast that it doesn't fall back to earth but instead moves on a circle around earth like if you have a stone on a string and spin it.
On the moon you can throw a stone very far. On the moon there is no atmosphere that slows it down. If you throw the stone harder and harder it will fly very far until it gets dragged down by the moons gravity. Maybe use a cannon to throw it very fast it will fly past the horizon. If you have just the right velocity it will fly all the way around the moon and hit you in the back of your head.
---
I think this topic is something that can be explained very well to kids. Also many kids are fascinated by rockets and space. The explanations and visualizations may not always be 100% accurate but I think they do the job.
Yes, with enough explanation, you can maaaaybe, possibly, eventually come up with enough lies (simplifications) understandable by a five year old to make some kind of explanation. (The grandparent post would certainly not be enough.)
But you've been caught into a hole you (and grandparent poster) have dug for yourself, by trying to explain it fully. A better explanation for a five year old would be something like: satellites all fly high above us, and we are putting more and more satellites up there, and eventually they will crash into each other, and then into other satellites, and so on, until there is nothing but broken satellites flying up there.
If the kid is interested and has more questions about "how" and "why" (the favourite world exploration tools for every kid), only then it's time to introduce him or her to gravity , the fact that Earth is round, and the basics of orbital mechanics.
I just asked my four year old and they had no trouble with "satellite" and "gravity". I did have to give them a little bit of an explanation for "orbit" (but again, they're 4, not yet 5)
Now 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
Here'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.
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/.
It’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.
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:
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.
Small fragments are just smaller satellites, and the rules are the same. Inclination changes are hard (since you still have all of your original velocity, which is quite high at this altitude).
But it does! Your orbit is defined by where your velocity vector is pointing at the moment. If you add a sideways component, you're a) increasing the magnitude, and b) rotating the vector.
Nope, but I see now why we're disagreeing. It's because the animation you linked to is misleading.
Work is the dot product of force and velocity. If the thrust is always orthogonal to the velocity, then the burn does no work on the rocket, and so it can't increase the magnitude of the velocity.
In the animation you linked, it's plotting out what would happen if you continue to burn due north for some period of time as your velocity vector changes. But you wouldn't do that--if you're trying to change your inclination, you burn perpendicular to your velocity, and as the direction of velocity changes, the direction of the burn changes too, such that it's always orthogonal.
It's easy to watch this happen in the game if you don't use the maneuver node, but just use SAS to burn in the normal direction. The direction of "normal" changes during the course of the burn, and (except for small errors), your apoapsis and periapsis stay constant.
I see your point, but we're talking about two different things.
Yes, you can rotate your orbit if you continuously burn in the direction orthogonal to your momentary velocity vector. In essence, this is the same thing the body below is doing to you already, with continuous acceleration in the radial direction. But we're talking about impact debris here, which do not accelerate under their own power. What happens is they get an impulse - a one-shot, near-instant change in velocity. If you just apply an impulse sideways, the eccentricity will increase, because your speed is now greater. The shape of your orbit around a spherical body is fully defined by your momentary position in 3D space and your speed. If your speed increases, the shape changes.
KSP maneuver node planner shows what would happen to your orbit if you applied an impulse to it, of a configured magnitude and direction. It's not accounting for the burn time. Which makes it perfect for the purpose of talking about debris propelled by a collision.
i think but better ability to using sharing and ability to stabilize, you can recectified the characterization of the approximation of the differential geometry where more identicable smater to sweeep betweeen some limited bands hz and then also with generalizable ability to beam [software ecnoded:particles] to the necessary [newer conventions] so the complicated uncertainty propagation problem.
just like your eyes have are not beaming k-vector spaces but feeling in the spectum of sesning so just like we have gained a lot of freqs you can think of it this way, lets say
hypo just like two: let's just say instead of not sharing, we built the international telcommunication of unicode which has given us a more univeral crosstalk, it's usually events and viral id that is sometimes the unproblematic way to fix, for example: https://www.reuters.com/article/us-cyber-disinformation-face...
so the can just erase the linear case i could only describe as a event as a f-surface homology dag in some deformation theoric space but at least usually in academic theory of computing where the most semantic influnce is felt in usually kripian terms philosophically but you can see in the ppublic source code but privately data db but usually as you can se instead of focus history has shown our species has shown great research on the very historical 1d greek:pythagorean problem but now clearly see arxiv is a decent place to look.
I think the argument is: It’s normal to the direction of travel, so it does increase velocity, and eccentricity is what you get when you add velocity at one point in an orbit. Same as other burns. If you were to burn retrograde of normal (but still tangent to the orbit’s radius), there’s an orientation where the retrograde component of your thrust matches the component in the component that’s...prograde in a new orbit. Which now sounds to me like it would just be 45° from retrograde, tangent to the radius
Question: This was posted half a day ago and was estimated to happen (or not) in less than 1.5 days from now. Now, or later today, when there is less time to the collision, can't they calculate with far more accuracy, whether the objects will collide?
prob they can measure speed at a higher accuracy than one mm/s, also orbit have a relatively low inclination difference and objects have a size, so that the impact area is not a point but a larger ellipses of varying overlap between bodies.
Don't disparage ASCII art. The very internet you used to make this comment has most of its protocol's defined in ASCII art (See RFCs). Its the back-of-the-napkin of the engineers who created the internet age. ;-)
It's based on what happened in 2009 (pictures linked in the comment), some familiarity with orbital mechanics, as well as the rest of discussion in this thread.
There are a bunch of subthreads here that show people have a hard time imagining how a head-on collision in space would play out; this is an attempt to put it in a more visual form.
I 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?)
Given 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.
The 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.
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
If 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?
The 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.
SOCRATES 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).
I 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.
I'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. 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.
Leolabs 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).
Given 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.
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[ 3.6 ms ] story [ 208 ms ] threadI 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.
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[0] - 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.
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?
~ 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 .
See the video by Kurzgesagt - “End of Space: Creating a Prison for Humanity.” [1]
[1]: https://youtube.com/watch?v=yS1ibDImAYU
i heartily recommend the whole series. i made a mistake in the post before - the post assumes 2.3% yoy.
This is in conflict with the Kurzgesagt video. I wonder what their source was for the Kessler effect preventing excursions into space altogether.
The risk will be much lower (you'll be spending very little time in the band filled with hypervelocity bullets), but it'll also be much more expensive. You'll need a much bigger rocket.
We don't worry about hitting an asteroid if going through the belt, because the density of objects is so low.
If you wanted to stay in the asteroid belt you would have many more opportunities for a collision, so avoiding asteroids becomes a lot more important.
Prompted by a comment from someone yesterday, I actually replayed the Snow Crash audiobook in the evening. Comparing SC and SE I notice that SC feels quite juvenile. I didnt notice that as much when I first read it in my 20s. But these days, it feels a bit too much over the top. Contrary to that, SE somehow feels too grown up.
Spoilers. Like, I mean, this isn't a plot summary, but this is in some sense what happens so look away now if you wish you didn't know:
The Primer has been calling her Princess Nell for a long time. Once you realise what's going on with the vast number of "specially adapted" Primers for the orphan girls, that Princess has got a ready made tribe with shared values in the form of the Mouse Army, waiting for her say so.
The whole book has been telling you that in this era what matters isn't control over a land mass, which is what the Fists are fighting for in the Leased Territories on behalf of Han, but a Tribe with shared values.
The Mouse Army shows up, rescues Nell and takes her to her mother. The Victorian Queen recognises Nell as the leader of a novel but important tribe.
The novel is flawed in many usual Stephenson ways (e.g. use of rape in place of actual character development) but I don't know what people expected from these endings, they seemed perfectly satisfactory to me on multiple re-readings.
> This might effectively lock use of Earth orbit away for centuries.
It would make exiting earth orbit and placing an object there significantly more complicated because you would need to take into account debris, probably detect them from the object and manoeuvre a lot more but it wouldn't entirely lock up use of Earth orbit. It would also be a solvable situation. Cleaning debris is doable.
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.
These are extraordinarily high numbers.
https://en.wikipedia.org/wiki/Kessler_syndrome
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?
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.
Tracking space debris and other objects in orbit of the earth is something we'd probably want to do anyway, and it makes no sense to duplicate that effort, so of course that burden will be distributed. If that burden becomes too high I'm sure some tax or licensing fee will be introduced to pay for it (assuming such a thing doesn't already exist) but in the grand scheme of things those costs are irrelevant compared to the cost of launching something into space to begin with... Especially when the satellite is still functioning, and generally aware of its own position anyway.
This applies for ISS even more (it is huge and thus a lot of drag) and thus it has one of the Progress spacecraft docked or the Russian service module use its engines to boost it back into proper orbit so that it wont crash down on earth.
Wouldn't drag be proportional to the surface area, hence the square of the length scale, whereas orbital energy is proportional to the mass, which is cubic in the length scale. I would expect the orbital lifetime to be roughly proportional to their quotient and thus for larger objects to stay up longer.
On the other hand, ISS has a lot more empty (well, air-filled) space inside of it, so it might be a lot less dense than a SpaceX satellite.
https://en.wikipedia.org/wiki/Night_Glider_mode
Are you assuming the ISS has a similar surface-to-volume ratio as other orbiting objects?
> ISS has a lot more empty (well, air-filled) space
and this dominates.
[1] - https://en.m.wikipedia.org/wiki/Parus_(satellite)
[2] - https://www.n2yo.com/satellite/?s=19826
Having a nuclear reactor onboard is the opposite of a problem in a case like this.
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?
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.
Taken to the extreme I'd rather hit a feather than a bowling ball at 14 km/s.
But what matters here isn't what you would rather do, it's what both you and the feather/bowling ball would rather do, in context of minimizing the size of the resulting fragmentation.
Intuition tells me that a hypervelocity bowling ball will barely notice you, much less have time to deposit lots of energy into you.
The bowling ball collision has a lot more energy involved, it can eject more debris at high velocities in various directions.
The heavier the fragments and the less eccentric the orbit of untracked space junk, the more dangerous it is, because the longer it'll be hanging around before it gets close enough to Earth to de-orbit itself.
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!
https://youtu.be/0fP_k6y9ows?t=372
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.
It’s why structural members on planes and the feet of the Starship prototypes have holes. It arrests the fracture.
Satellites won’t have as much material that behaves this way, so I wouldn’t count in too much KE being converted.
However debris ejected sideways will have significant velocity, orbital or sometimes even higher and that's the real risk here.
Edit: I am mistaken, they are on reverse/opposite orbits, which is actually a huge problem!
* 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.
The "ELI5" meme needs to die, it does not make any sense in most of the situations it is used, and also it's a self-disgrace to anyone using it to compare their own intelligence and knowledge to that of a five year old.
No need to overthink it.
"A meme is an idea, behavior, or style that becomes a fad and spreads by means of imitation from person to person within a culture and often carries symbolic meaning representing a particular phenomenon or theme."
Contrary to what Internet would like us to believe, a " meme" is not a picture of a cat with some written words around it.
But all that aside, what nerd kid wasn't drawing space shuttles and rockets by age 5?!? That was my jam!
"ELI10" or "ELI15" would be a much less ridiculous request. It's still rather grating how people willingly denigrate themselves by comparing their own intelligence to that of a child's.
What's wrong with good old "explain it to a layperson"? The fact that it does not make a cool acronym? We're not on twitter (or in high school, for that matter), learn to express yourself like an adult.
And yes, I am fun at parties. :)
Gravity pulls you down to earth. It gives you weight. Without gravity everything on earth would start hovering and flying around like on the space station. Things in space near earth also get pulled towards earth.
Orbit is if you throw something so very fast that it doesn't fall back to earth but instead moves on a circle around earth like if you have a stone on a string and spin it.
On the moon you can throw a stone very far. On the moon there is no atmosphere that slows it down. If you throw the stone harder and harder it will fly very far until it gets dragged down by the moons gravity. Maybe use a cannon to throw it very fast it will fly past the horizon. If you have just the right velocity it will fly all the way around the moon and hit you in the back of your head.
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I think this topic is something that can be explained very well to kids. Also many kids are fascinated by rockets and space. The explanations and visualizations may not always be 100% accurate but I think they do the job.
But you've been caught into a hole you (and grandparent poster) have dug for yourself, by trying to explain it fully. A better explanation for a five year old would be something like: satellites all fly high above us, and we are putting more and more satellites up there, and eventually they will crash into each other, and then into other satellites, and so on, until there is nothing but broken satellites flying up there.
If the kid is interested and has more questions about "how" and "why" (the favourite world exploration tools for every kid), only then it's time to introduce him or her to gravity , the fact that Earth is round, and the basics of orbital mechanics.
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
BEFORE:
AFTER: 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/.
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/
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.
Work is the dot product of force and velocity. If the thrust is always orthogonal to the velocity, then the burn does no work on the rocket, and so it can't increase the magnitude of the velocity.
In the animation you linked, it's plotting out what would happen if you continue to burn due north for some period of time as your velocity vector changes. But you wouldn't do that--if you're trying to change your inclination, you burn perpendicular to your velocity, and as the direction of velocity changes, the direction of the burn changes too, such that it's always orthogonal.
It's easy to watch this happen in the game if you don't use the maneuver node, but just use SAS to burn in the normal direction. The direction of "normal" changes during the course of the burn, and (except for small errors), your apoapsis and periapsis stay constant.
Yes, you can rotate your orbit if you continuously burn in the direction orthogonal to your momentary velocity vector. In essence, this is the same thing the body below is doing to you already, with continuous acceleration in the radial direction. But we're talking about impact debris here, which do not accelerate under their own power. What happens is they get an impulse - a one-shot, near-instant change in velocity. If you just apply an impulse sideways, the eccentricity will increase, because your speed is now greater. The shape of your orbit around a spherical body is fully defined by your momentary position in 3D space and your speed. If your speed increases, the shape changes.
KSP maneuver node planner shows what would happen to your orbit if you applied an impulse to it, of a configured magnitude and direction. It's not accounting for the burn time. Which makes it perfect for the purpose of talking about debris propelled by a collision.
just like your eyes have are not beaming k-vector spaces but feeling in the spectum of sesning so just like we have gained a lot of freqs you can think of it this way, lets say hypo just like two: let's just say instead of not sharing, we built the international telcommunication of unicode which has given us a more univeral crosstalk, it's usually events and viral id that is sometimes the unproblematic way to fix, for example: https://www.reuters.com/article/us-cyber-disinformation-face...
so the can just erase the linear case i could only describe as a event as a f-surface homology dag in some deformation theoric space but at least usually in academic theory of computing where the most semantic influnce is felt in usually kripian terms philosophically but you can see in the ppublic source code but privately data db but usually as you can se instead of focus history has shown our species has shown great research on the very historical 1d greek:pythagorean problem but now clearly see arxiv is a decent place to look.
, so oyin applied , but i'm
There are a bunch of subthreads here that show people have a hard time imagining how a head-on collision in space would play out; this is an attempt to put it in a more visual form.
https://www.youtube.com/watch?v=BiHY5dR5Jsg
The first two seem likely given Kessler syndrome.
edit: it says in the tweet: Oct 16 00:56 UTC
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
CZ-4C is the upper stage of a Chinese Long March rocket that was used to launch a reconnaissance satellite in 2009.
https://celestrak.com/SOCRATES/search-results.php?IDENT=NAME...
I wonder why?
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...
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.
https://twitter.com/LeoLabs_Space/status/1316822400131104768...
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 [2] https://space.skyrocket.de/doc_sdat/parus.htm [3] https://space.skyrocket.de/doc_lau_det/cz-4c.htm
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.
Is it known which satellites might be at risk?
No collision