< interesting chats aboard the ISS over dinner.>
Fancy a postprandial peregrination?
NASA has delayed a spacewalk scheduled today from the International Space Station amid concerns about debris. The spacewalk by NASA astronauts Thomas Marshburn and Kayla Barron was due to have started today with a switch to spacesuit battery power at 12:10 UTC followed by an exit from the outpost's Quest airlock. The planned …
Debris in orbit is a real issue because of the energy involved in a collision
When v is in the order of 10's of km/s it hardly matters what m is, contact is going to hurt - be it full on or just a glancing blow. Trying to defend a spacecraft from that impact is hard for anything over paint fleck size, it's easier to get out of the way.
I won't try to give examples as I am proven to be incompetent when using calc, so actual figures are left to the reader as an exercise!
A 1g piece of debris (a really tiny nut for example), at low earth orbital speed of 17,500mph (about 8000m/s) has a kinetic energy of about 30KJ. That's equivalent to about 8grams of TNT. And yes, when things collide at orbital speeds, they explode.
An old fashioned WW2 hand grenade had about 50g of TNT equivalent, so an orbital collision with a 1g object is about 1/6 of a hand grenade going off.
Of course, colliding with a slightly larger object, only 6grams (a bit less than a still small M8 nut) is about the same as a hand grenade going off, that's practically impossible to armour a satellite against. Just out of interest, I've weighed a simple biro I had on my desk: 7grams. So a dropped biro in orbit is like a hand grenade when it hits!
That orbital velocity of about 8000 m/s is the one way speed. If two objects collided head on, that's a doubling of the closing velocity, or 4 times the kinetic energy. So a dropped biro colliding head on is like 4 hand grenades going off!
Kind of, but not quite.
Two objects can have a nearly-parallel but intersecting orbit, both going in almost the same direction at orbital speed. The impact is still "head on", in that there is no other frame of reference, but the collision velocity is only a fraction of the two orbital velocities combined.
As an analogy, imagine driving along the motorway next to another car. You're both going exactly 70mph. Imagine the other car drifts slightly in his rather narrow lane and hits the side of your car. You're both going 70mph each, but only probably contacting each other at something less than 1mph. You'd probably both keep going just fine (until you pulled over to have an argument)
Most collisions while be more side on, where the velocity vectors of both objects cross, ie might be the same speed, but different directions. Lots of orbital paths cross like this. Head on in this context means where the velocity vectors (relative to the earth reference frame) are in opposite directions.
Strictly speaking, the only tail-on collisions (velocity vectors in the same direction) would be where two orbits with different eccentricity happen to combine at the same point in space with the same velocity vector directions ( but different speeds)
You couldn't have a tail-on collision between two objects in the identical orbits, since for them to be in exactly the same orbit, they would require the same velocity vector, ie the same direction at the same speed, so would never collide. A bit like the starlink satellites from the same launch, they all follow each other in the same "string of pearls" orbital path and therefore don't collide with each other, unless something goes wrong.
"That orbital velocity of about 8000 m/s is the one way speed. If two objects collided head on, that's a doubling of the closing velocity, or 4 times the kinetic energy. So a dropped biro colliding head on is like 4 hand grenades going off!"
That all sounds very impressive, but of course is an implausible worst case scenario. It's unlikely something travelling at low earth orbital velocity is going to hit something "at rest". As for "head-on", how many sats are in retrograde orbits? And by that, I mean one where you could get a "head on" collision, not just any old orbit with more than 90 degree inclination.
"And yes, when things collide at orbital speeds, they explode."
No, not really. Micrometeorites and small bits of debris will generally just punch a hole straight through things and keep going. Exploding would require hitting something sufficiently rigid that the majority of kinetic energy is liberated into heat. That will almost never be the case with small objects in orbit, they're much more like a bullet hitting a piece of paper.
"Micrometeorites and small bits of debris will generally just punch a hole straight through things and keep going."
No, that's not what happens at orbital speeds, things explode on impact because the shock wave from the impact can't travel through the colliding materials faster than the materials are coming together. The energy released might be sufficient to rupture the material, but it's more like an explosion within the material, not the incoming object cleanly punching through. Sometimes it's hard to tell which direction the micrometeorite actually came from as there is no simple entry and exit structure. Here's a good picture of just such an impact. https://www.orbitaldebris.jsc.nasa.gov/images/gallerypage/solarmaxhole.jpg
The fact that materials vaporise on impact at these speeds is used to advantage in the so called Whipple shield for spacecraft. Rather than a single sheet of protective material, the shield has several layers each spaced apart, to allow the impact debris to disperse before hitting the next layer. A greater level of protection can be had with several layers of thin material, compared to a single layer of the same total material thickness.
It's tempting to think that the faster the collision the more likely it is that the projectile will just punch through, but at these speeds, materials just don't behave the way we might expect from our every day experience.
Here are some interesting pictures of micrometeorite impacts on optical materials exposed to space for long durations. http://www.reading.ac.uk/ir-spaceenvironment-micrometeoriteimpactcharacteristics.aspx
None: the speed of debris is so high that any armor you could plausibly carry would be useless, and any armor that could plausibly help is far too heavy. So you don't use any, you dodge the bits you can track, and you pray hard that the bits you can't track don't hit anything really important.
Nice, thanks, I didn't know about that! I still think that my point mostly stands, in that I don't think armor will feature prominently in any solution to space junk. But it's interesting that there's at least some class of debris that can be shielded against.
No-one can hear you sc<NO CARRIER>
This is getting more and more like "Gravity" every day.
I really feel for these poor folks, they must feel like they are on a terrible reality TV show.
With Covid, space debris and solar flares plus the risk of the station disintegrating around them because
someone forgot to insert a - in the control algorithm, and the risk of the country they came from effectively
taking pot shots at them because they wanted to prove they have bigger cojones than the other country..
Is it no wonder that stress is *1 on their list of ailments?
I heard that someone on Mir needed extensive rehabilitation when he finally came back to Earth after over
a year in space, compounded by several high profile rocket failures.
This is getting more and more like "Gravity" every day.
yet another call for some kind of solution, like maybe "space dredges" trawling some kind of net, electromagnetic and/or electrostatic means of collecting the debris, and so on. A focused beam of electrons [if you could sustain it] might put enough charge on tiny nearby objects to drive them towards a collection net, for example. But you'd have to have a way to maintain a huge charge difference between the negatively charged electron beam and a positively charged net dragging behind you, and not have the electrons just turn right around and short circuit the whole mess.
So, rather than wasting resources on fanciful Moon and planetary escapades our actual real and present priority is to: "CLEAN YOUR MIDDEN OF A ROOM!!!" i.e. tidy up low Earth orbit, so that we can get on with all the exciting exploration stuff undistracted by our filthy laziness.
Designing cost-effective orbital rubbish collectors would be a very worthwhile exercise for further, and less rubbishy, adventures in spaaaaace!
There are already a lot of studies looking into this, but its not a particularly easy problem to sort out.
Mainly because the things you are trying to catch are travelling at massive velocities, so trying to catch them directly, will likely lead to effectively an explosion and more (but smaller) debris, which doesn't help the situation. People are experimenting with various aerogels and foams to try and mitigate this, but well at the velocities we're talking about, things still have a tendency to go boom.
If you try to sidle up to the debris, getting up to speed, entering it's orbit and then slowly closing the distance to it, before grabbing it, well that will work, but you need a lot of fuel, and you can only really do this with big things. So its not considered particularly effective. The recent Lockheed mission to refuel an existing satellite so it can keep operating, is effectively an example of this in practice, but one that actually might have a business case.
The future, probably has a few missions to sidle up and grab big junk (or refuel it to keep it going), but most of the current focus is on making sure anything we put up now, either comes back down quickly on its own (either through drag mechanisms or thrusters), or for the bigger ones that they go out to a graveyard orbit. But unfortunately none of this particularly helps when a$$hats go and deliberately blow shite up, causing massive amounts of new debris. You almost hope that the debris wipes out something valuable of theirs, but unfortunately Karma is rarely that specific or sensible....
It's being a 'hard problem' that makes it so worthwhile to solve.
Electric-ion motors can run for years, so probably have potential in enabling a 'rubbish-truck' to gradually get on with 'sidling up to' junk, grabbing it and boosting into a rapidly decaying orbit.
There could be a bunch of these things quietly getting on with their job, and if it takes ten years or fifty to clear out the worst of it, well, that's what it takes. Anything is better than the head-in-the-sand, 'it's too hard' attitude, where we just allow it to get worse and worse until we've finally shut ourselves out of space through our own laziness and stupidity.
a bunch of these things quietly getting on with their job
Well, yes, if they happen to come across even a small item going the wrong way while they're sidling up to a target catch, the collision won't be audible.
Still, getting on with their job might have become a tad impaired.
So we do nothing?
Actually, a. odds are it won't take a hit until it's already accomplished something useful, and b. the whole point is to learn how to make these things so cost effective that the occasional, even frequent, loss is sustainable and worth the outcome.
OTOH, why not just sit around weeping and wailing, and waiting for the day it becomes to dangerous to send human beings I to orbit?
You seem to have missed entirely what I was saying which was not that we shouldnt do it, but that there are a lot of projects already working on it. BUT it's something that needs to be studied in detail, and tested very thoroughly before you put it up there because if you get it wrong, you will simply exacerbate the Problem.
It's being worked on, but dont expect solutions for another 10 years on the cleaning up jobs. The making sure anything we put up now, comes back down quickly stuff - that stuff is already up and flying (or at the very minimum is having test flights) - tethers, sails, mini thrusters, are all flying now.
As for your ion-motors solution, sorry, but ion motors dont work well in low orbit - gravity and atmoshperic resistance (even up there) make them ineffective. Further out, you would be probably looking at 10 years to get to one piece of junk, it takes a long time to get up to speed, without a rocket boost first. Dont get me wrong ion motors are awesome because you turn them on and they just run and run and run, and eventually you get very very fast, but it takes a very long time to get fast... That's why they are primarily used in interplanetary missions and the reason why they arent particularly used for anything positonal in orbit...
I hope I've not missed your point, but my point is simply that the fact something is difficult doesn't mean it's not worth doing, nor that it can't be done.
Our problem, ATM, seems to be that no one is yet willing to really get serious. Added to which we have an urgent, and arguably more existential, crisis going on down below. Again, of our own making, and we really can't afford to file 'climate change' in the too hard bin.
Instead of charging space tourists big bucks on a mission to nowhere, charge adolescents small bucks to play Space Debris Invaders -- piloting drone cleanup "ships" via VR. High score gets to go on an actual rocket to play Space Debris Invaders -- in real life. And for a refreshing change, there are no _cheats_ in this game.
Okay, joking aside, on the one hand you knock ion-motors because they would take 10 years to get up to speed, and on the other hand you say solutions are 10 years away. So ion-motors could in fact be part of the solution? Like any environmental degradation issue, it doesn't matter how long it takes to finally (sic) fix things. What matters is how long it takes to stop making things worse and start making things better.
"Instead of charging space tourists big bucks on a mission to nowhere, charge adolescents small bucks to play Space Debris Invaders -- piloting drone cleanup "ships" via VR. High score gets to go on an actual rocket to play Space Debris Invaders -- in real life. "
Wasn't that the plot for The Last Starfighter?
Way back around the time of Sputnik (which is still up there), no one considered that low orbit or really any oribit of earth would become crowded with junk. Instead of actively deorbiting things like boosters, dead satellites, etc. It's now become a real problem. Even the Musk satts are creating problems and not just for astronomers.
Space... a real mess. Maybe the final frontier will soon be blocked.
<blockquote>Way back around the time of Sputnik (which is still up there),</blockquote>
What? Are you suggesting Sputnik 1 is still in orbit?
"It orbited for three weeks before its batteries died and then orbited silently for two months before it fell back into the atmosphere on 4 January 1958."
Aww, nuts. Now I feel like an idiot for feeling so good about the ESA orbiter dodging the debris.
Say, anybody heard anything about when Russia will launch their RSS? After all this space junk and the flippety capsule debacle, I can't wait to get a first sample of Russian astro-awesomeness.
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