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[Madman198237]

Right now most satellites are designed to just deorbit themselves when their service life is up. It's usually easier. Well, deorbit or move to a "graveyard orbit" where they're not in anybody's way.

Recycling them sounds cool and all, but the materials in a satellite aren't worth all that much compared to the cost of deorbiting them safely, as opposed to deorbiting them such that they burn up in the atmosphere.

[LordBaal]

They already ARE-- the dumptruck is "earth's atmosphere"

But doesn't itself brings another whole set of dangers too? The dump truck would be soft retrieval.

[MrRoboto75]

They already ARE-- the dumptruck is "earth's atmosphere"

But doesn't itself brings another whole set of dangers too? The dump truck would be soft retrieval.

It works for most space rocks.

[Starver]

Back to seriousness (if you hadn't twigged), ideally at the moment every sat would have an end-of-life action (deorbit from low-enough orbits, shift to a graveyard one for the high up ones[1]). Though anything that arrives dead-in-(wrong?)-orbit or fails-in-mission might well be subject to staying up for as long as the vagaries of space allow (I wonder how many are drifting in one or other of the frozen orbits indefinitely?) without the benefit of station-keeping.


The tech to (safely) grapple and deorbit dead stuff is ongoing in development, as already posted, but you still need
 to send that stuff up (hopefully not go wrong itself) and down again (it might be able to do several visits before it does - if that's to attach a solar/atmospheric-sail as a drag-anchor to hasten the degrading, it won't mean dragging awkwardly-tethered loads between each vendezvous).

Dumprecoverytrucks to fully soft-retrieve hardware back to ground add complexity not usually used beyond the returning man-cans (or the subunits of spy-film, sample-returners, etc). In the future, some handy space-station/workshop could be set up as an orbital destination for the recovery, for in-situ handling, but that's not gonna be soon. (Nearest equivalent is sending the Shuttle up to manhandle, refurb, refurb and perhaps boost the Hubble in-situ, but that wasn't a cheap or rapid option.)




[1] Includes GEO, which it's expensive to get to and proportionally so to de-orbit. (Similar fuel needs to return, less the difference of the Rocket Equation premium outwards, but you also wouldn't need to maintain accuracy/reserve adjustment propellant once you're destined to deorbit (ideally firmly onto the SPOUA?) So they generally go for 'up and further out', which doesn't get as crowded as quickly with dead hardware (even in the supra-Geostationary annular ring, and I expect the merely Geosynchronous oblique and eccentric ones (like those in a Tundra orbit) to have a suitably compatible disposal option.

[TomJo]

However, reusable space tugs are already in development. Perhaps engineers will come up with something much simpler and more efficient solution. By the way, I really liked your idea about the station. I think this is a pretty elegant solution to the problem. It would be possible to deliver the necessary equipment once to a station like the ISS and maintain it from there. Still, I agree that not everything that is in orbit requires additional intervention.

[Bumber]

What if satelites start being designed with recuperation in mind? Like, the last year of its service life it manouver to be recaptured to an orbiting space dump truck?

They maneuver to a satellite retirement home.

[LordBaal]

I was told they went to the satellite farm up in the galactic north to play with other satellites.

[bloop_bleep]

What if you have a bunch of magnetic junk-collecting satellites orbiting outside of normal operating radius near where dead satellites would maneuver and be sucked radially into a closer-to-atmosphere orbit where they would deorbit. Theoretically they'd be traveling at a slower tangential speed than the junk-collectors so they would deorbit and the junk-collectors wouldn't. There wouldn't necessarily be physical contact between them.

In fact you could have two magnets in the satellite with opposite orientations. Then you can rotate one of them and boom, you have a magnetic satellite that can be better attracted to any junk-collector magnetic satellite. In fact they would naturally want to align so maybe you just release some latch holding them in opposite orientations. The point being you use less resources per satellite launch than using rocket fuel to deorbit. Is that the problem with deorbiting by thrusters, the extra launch cost?

I guess a problem could be the sheer size these magnets would be. Plus maybe interference with operating satellites' sensors.

Now it kinda just seems like a dumb idea, but I'm just theorycrafting here.

[Starver]

Magnetism is a pathetic force vs. gravity for your purposes[1]. Once you prise a fridge magnet off the fridge, throw it a long way away from anything ferric. Even on a frictionless surface, it's in no hurry to return. Go to it and try to throw it the same distance from the planet (i.e. up). It'll return to it as much as physically possible. (And directly hitting and sticking to a fridge you'd hoisted up there in advance is cheating!)

Also I don't fully understand your orbital mechanics, so I'm not sure where conservation of momentum, or potential+kinetic energy, is happening and thus what's happening to the magnet-equipped 'collector'.

I suspect you're trying to use some sort of exchange of orbital momentum (to the disadvantage of the non-magnet item(s) flying by) but I can't see it being more than a micronudge unless you're practically docked with it already.


What you might want to look into is electrodynamic tethers. Doesn't (overly) act as a magnet itself, but with its interactions with the planet's magnetic field (with 'free' solar electrical power going to delta-V, or being recovered from its loss) and a clever system to not only navigate through orbital layers to 'catch' handy co-orbitting stuff at either end but also to induce spin (slowly, to prevent wrapping itself up) could turn it into a 'thing-flinger' by releasing the grabbed stuff into less pro-grade (and decaying) orbits... Or higher ones. I suppose you could make the ends electromagnets instead of/as well as any other netter/grabber/harpooner solution, but that'd mostly only be useful at near-contact ranges and near-matching velocities of ends for enough cumulative time to perturb the target into proper contact.



[1] Yes, the usual analogy is the reverse. The magnetic force is 10^30-odd times stronger than gravity, all else being equal, that's why a tiny magnet can hold up a suitable object against the force exerted by the whole mass of the Earth. But in orbit you're still being influenced so, so much by the Earth at a distance of R_e plus the orbital altitude, and you somehow need to get a magnet effectively bigger (at inter-orbital ranges) than even that great big Earthly magnetic field or all you're doing is adding smaller magnetic purturbations to a satellite than it's already likely experiencing.

[Cthulhu]

I mean you're not gonna be able to just sit a bunch of magnetized satellites in space and have them scoop up debris, no, but there are movements in similar directions.  A big limitation is fuel.  You gotta synchronize with your debris, grab it, then either maneuver it into graveyard orbit or re-entry course, which is multiple burns for each removal mission.  Even if you have enough fuel, you also need helium to pressurize the fuel, and that system needs its own tanks and plumbing, and it all gets very expensive very quickly if you're going for longevity.

ULA's IVF system was designed to increase upper stage longevity by replacing all the plumbing with an integrated system based on an old straight-six car engine modified to work in space, and one of the proposed applications was debris cleanup.  Launch your rocket, drop off your satellite, and the upper stage can go around doing other things like servicing old satellites or cleaning up junk.  I have no idea what's going on with that now, I haven't heard anything in a long time, but they are doing stuff with debris cleanup, just not with magnets.

[bloop_bleep]

Hold on, S, I think you’ve contradicted yourself there. You said a tiny magnet is able to pull an object against gravity, but you also said that magnets in space wouldn’t do that. I guess the big difference is distance there. But what if the magnets were really close, orbiting a few meters below? And the satellite you’re trying to deorbit is highly magnetic as well? Also you should consider magnetic potential energy in this situation as well. The idea is that the magnetic satellite would orbit closer to the earth than the main satellite, and would pull it radially inwards. Yes, the main satellite would accelerate and gain momentum, but it would be designed so that it’s mostly radial acceleration and not tangential acceleration. Once the satellite is in that closer orbit where orbiting bodies have higher tangential speeds it finds it has a relatively small tangential speed to sustain that orbit, having nearly the same tangential speed as in its original farther orbit, so it deorbits from there.

What if the magnetic satellites had long vertically extending arms that could bring magnets closer to any orbiting satellites they want to deorbit? It’s essentially grabbing them out of orbit but without clunky grips you might do it mechanically with, and additionally could deorbit multiple objects, including tiny objects, at the same time. Plus if you put activatable magnets on satellites, they could tend to coalesce together once they use their fuel and shed their orbital momentum on their own.

[Starver]

Hold on, S, I think you’ve contradicted yourself there. You said a tiny magnet is able to pull an object against gravity, but you also said that magnets in space wouldn’t do that.

I was qualifying 'for your purposes'.

A mere child's toy magnet[1] will hold a steel can up from falling to Earth. If in contact. It will also lift that can up from the Earth it might have been in contact with, but needs to be (practically) touching before it does so. It doesn't do much if it's held away from the can (either time) by a few centimetres. Either with an actual gap or a (non-magnetisable) buffer material. That's because it's a gradient down from the little (but effective) force vs a similar gradient down from a huge (but subtle, by direct comparison) one.

Orbitting 10m above/below each other? You're finely tuning your magnasat to travel in near-matching orbit (inclination, eccentricity and the appropriate set of major/minor/semi-major axes too). The difference in velocity is ~0.5cm/s, or making up/lagging about ¹/_50th of a second, per orbit, over an orbit of maybe 1.5-2 hours (depending upon the orbit, but assumed low-ish, for our purposes), so you'd also be orbitally-inserting at an extremely accurate time in order not to be a significant angle of the orbit away for hundreds of thousands of their slightly different orbital periods, which could mean you'd wait up to 50 years between being actually just 10m away (if I've not misplaced a magnitude or two, somewhere in that rough calculation.

If you've got that much control (or accuracy of launch such that you no longer need to adjust anything once orbital insertion is complete) you might as well unfurl a physical (yes, perhaps magnetic, but could as easily be grabbing) arm while you're effectively stationary next to your target. I doubt you've got a string of 'dead' satellites all doing exactly the same orbit as each other that you can afford to skim your '10m lower' magnasat past over 50 years to save sending more than one magnasat up.

Also think what happens when magnasat passes magnatarget. As the force becomes significant between the two, on approach, magnasat slows already slightly slower magnatarget (perhaps before the vector even includes significant 'up/down' components). Magnasat is bent towards a higher orbital profile, rushes (slightly!) past no longer 'parallel', radially-speaking then is retarded (as it drags magnatarget faster again) as it starts to slowly move away. It messes up your expensively-obtained fine-tuning somewhat[2], unless you somehow create a resonant co-orbit (taking into account periodic lunar and solar influences, and the complicatedly oblative and heterogenously dense nature of the Earth's mass, including the pull of the tide-pulled oceans themselves lumped up by Sun and Moon periods and land-mass/ocean-floor undulations). Fifty years later, if that's what you're content with (and nothing like solar particles or even other, unrelated, debris has further made your passive and patient rendezvous even more chaotic[3]) it perturbs both (all of..?) the magnacraft yet again and you've perhaps got to wait until the century anniversary before you know how.

Nor could you expect subtly imperfectly-aligned orbits to gently coalesce their group together. Perhaps enough stuff up there going all Kessler-like would eventual form rings (afted generally bashing together, sending far more random bits back to Earth or even entirely ejecting them outwards in the process) but by then you've already failed to clean up the orbits to some quite spectacular degree... Gently sticking together would be the exception, not the rule. The relative scale of things just isn't on your side, sorry.



[1] N.B.: these days you're clearly asked to keep magnets away from small children. Maybe because they've got too much iron in their diets already. /s

[2] As anybody with KSP, or similar, experience knows, thrust applied in orbit doesn't always dump straight into perigee/apogee (or perikerb/apokerb?) adjustment, or straight-forward orbital interception even of a craft in easy visual range.

[3] Assuming that 50 years already isn't enough for the orbit to decay completely or intersect something far less gentle in its relative approach velocity.

[wierd]

This is a convoluted way of pointing out that magnetism obeys the inverse cube rule, while gravity obeys the inverse square rule.

[Starver]

That needs the explanation that, in the absence of magnetic monopoles, the combined force felt from the simplest dipole magnet falls off because the inverse-squared effect of the idealised point of the near pole combines with the inverse-square from the (increasingly marginally/less significantly different) more distant far pole, such that they become proportionately less distinct and therefore as a sum-total you effectively feel the dominent one less at a quicker rate than you'd feel when retreating from a gravitational/optical/electrical monopole single point magnitude where the flux is just a single 2d surface 'dilution' out into 3d space as radius increases. (Give or take the tiny hidden dimensions that may be progressively leaching a significant additional bit of gravity away at galactic-halo distances, etc.)

But there were other far more interesting, and demonstable, problems (IMO) to dwell on, so I skipped on to them. 

[Cthulhu]

There's lots of things, but I think you don't really need anything more than the distances and velocities involved meaning you're going to need lots of disposable vehicles or vehicles that can maneuver through multiple orbits, or both (hence something like centaur/ACES with IVF, which is literally just an upper stage that can keep operating after it deploys its payload), and if you're doing that then there's no reason not to use regular robot grabby arms which we already have.