Monitoring a high risk conjunction between two large defunct objects in LEO
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BEFORE:
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/ o - COSMOS 2004
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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.
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.
These are extraordinarily high numbers.
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?
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.
> ISS has a lot more empty (well, air-filled) space
and this dominates.
Are you assuming the ISS has a similar surface-to-volume ratio as other orbiting objects?
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.
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
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...
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
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.
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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]
> 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.
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.
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.
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.
edit: it says in the tweet: Oct 16 00:56 UTC
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!
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.
Having a nuclear reactor onboard is the opposite of a problem in a case like this.
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.
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.
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.
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 first two seem likely given Kessler syndrome.
* 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.
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.
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. :)
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.
Edit: I am mistaken, they are on reverse/opposite orbits, which is actually a huge problem!
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.