orbital debris cleanup - gells

[madd0c0t0r2]

Hello,

For a sci-fi story* I'm playing with, the earth orbital space has been completely choked with crap and debris, and humanity is trying to clean it up again from earth side. The technology I'm playing with is a launch loop https://en.wikipedia.org/wiki/Launch_loop and using it to bulk send up canisters of sticky gel that in space, balloon out. When a fragment of paint debris penetrates the gel, it tears straight through, slowing down slightly and picking up a few micrograms of gel on it - these two things mean it drops to a lower orbit, starts picking up drag from the edge of the atmosphere, and gets pulled down and burnt up. The launch loop is used to keep as much launch equipment (aka heavy potential debris) below the messed up orbit plane, and because space is big and thousands of launches would be needed to provide assurance the zone is safe for humans within a decent time period.

I'm saying 'gel' as water is dead cheap to send up, but it is very cold in space, but I'm not convinced filling the orbits with high speed ice fragments is really any better. We're talking something that would be probably gaseous at room temperature, and a sticky liquid at orbital temp. Black body temp in earth orbit IS above freezing (https://space.stackexchange.com/questio ... -the-earth) but I'd assume the gel is not a black body.

Thoughts?

[Formless]

I think the problem with this is that the Earth's atmosphere already extends into orbit as high as the ISS currently orbits as well as many other satellites. It is already necessary for most spacecraft like the ISS to have thrusters to cancel out the deceleration caused by friction against the Earth's atmosphere, which will eventually clear all orbital paths of debris anyway. It just won't work fast enough to keep Kessler syndrome from being a problem for human spaceflight (and this is already an issue, not a mere speculation or science fiction). Nor will it clear the higher orbits.

A much more likely technology to work is laser brooms. The idea here is to burn the surface of the debris off with a high powered laser, which in turn creates thrust in the opposite direction of the debris orbital velocity. This works to slow it down much faster than the Earth's atmosphere, and lets gravity take over even at those higher orbits. Its the same idea as a laser-thermal rocket. You can swap out the laser for some kind of particle beam, which could theoretically impart greater momentum. What you do not want to do is smash the object, which is a major danger of your gel idea (but in reverse). Just push it into Earth's atmosphere and let nature do its thing.

[madd0c0t0r2]

I know the ISS has a laser on it already, but I'm not sure if the laser boom concept scales. I'm talking about a chockful orbit here, with billions* of mostly sub 10cm stuff on all sorts of trajectories, bouncing off each other. Not the relatively orderly position we have today with it as a problem, but ground based telescopes can track most of it to the point we move the ISS if we need to.

I'm talking the sort of sand storm scenario where time before an impact in LEO is measured in minutes, and anything that disintegrates under that assault adds to the problem. The laser broom needs good luck or great mapping to hit tumbling objects at the right time to reduce their energy and not speed them up or just redirect them, but also it needs to survive in this environment.

*wikipedia has "As of January 2021, the US Space Surveillance Network reported 21,901 artificial objects in orbit above the Earth,[8] including 4,450 operational satellites.[9] However, these are just the objects large enough to be tracked. As of January 2019, more than 128 million pieces of debris smaller than 1 cm (0.4 in), about 900,000 pieces of debris 1–10 cm, and around 34,000 of pieces larger than 10 cm (3.9 in) were estimated to be in orbit around the Earth"

The 'natural' falling back to earth time goes up super exponentially with height of orbit. We're talking 2000 years on the upper edge of LEO, and basically never in the geosynchronous orbits, which would be some of the most key to clear for GPS and comms satellites to be put back. https://www.esa.int/ESA_Multimedia/Imag ... _long_time

What you do not want to do is smash the object, which is a major danger of your gel idea (but in reverse).

Could you explain this one? I'm getting stuck on the idea of a major danger in reverse being a good thing. Are you saying the major danger is the stuff hitting it causing the gel to be scattered? Making the gel part of the problem?

[Jub]

The gel idea probably isn't that feasible simple due to the volume you'd need and the properties the gel would need to stay liquid in space. There's also the issue that anything used to send the gel up into orbit risks becoming more debris and making the issue worse.

As for the laser scaling, the laser array doesn't need to be small points. It could fan the laser out into a similar shape used to clean rust. Then it could sweep an orbital corridor clear so space based solutions could be launched.

[Solauren]

What about a simple, straight forward net? Dredge orbit like you would a river.
Yeah, it would be one hell of a net, both in size and needed material strength, (and fuel to keep it moving) but it's workable.

[Gandalf]

What about a simple, straight forward net? Dredge orbit like you would a river.
Yeah, it would be one hell of a net, both in size and needed material strength, (and fuel to keep it moving) but it's workable.

When I saw the thread title, I pictured just a massive blob of sticky goo which floated about, catching small bits of debris.

[madd0c0t0r2]

The gel idea probably isn't that feasible simple due to the volume you'd need and the properties the gel would need to stay liquid in space. There's also the issue that anything used to send the gel up into orbit risks becoming more debris and making the issue worse.

As for the laser scaling, the laser array doesn't need to be small points. It could fan the laser out into a similar shape used to clean rust. Then it could sweep an orbital corridor clear so space based solutions could be launched.

Most of the papers I've seen are talking about aerogel catcher's mitt, or basically builders foam. It's not strictly liquid, more like a froth or cloud (or rigid foam in the case of aerogel). It needs to be soft enough when hit at high velocity.

[Formless]

The gel idea probably isn't that feasible simple due to the volume you'd need and the properties the gel would need to stay liquid in space. There's also the issue that anything used to send the gel up into orbit risks becoming more debris and making the issue worse.

As for the laser scaling, the laser array doesn't need to be small points. It could fan the laser out into a similar shape used to clean rust. Then it could sweep an orbital corridor clear so space based solutions could be launched.

Most of the papers I've seen are talking about aerogel catcher's mitt, or basically builders foam. It's not strictly liquid, more like a froth or cloud (or rigid foam in the case of aerogel). It needs to be soft enough when hit at high velocity.

I've heard of those as well, but I'm not certain they scale up well enough for solving an extreme Kessler syndrome situation. What you're talking about equates to either a specialty spacecraft that is sent up to remove a known cloud of debris (which might as well have multiple debris-mitigation technologies aboard like brooms and I believe there are electrostatic and electromagnetic technologies that can be used) or another kind of armor that spacecraft carry alongside conventional whipple shielding in order to protect their most vulnerable equipment.

But it does not equate to a big mass of foam that just floats in space collecting debris. Its a more complex setup that has already been used as a scientific device for collecting cometary samples which had relatively low kinetic energy. It also isn't mere builders foam as that just won't cut it; iirc it needs to be high molecular weight polyethylene laminated into hundreds of tiny layers that delaminate on impact. Such material is already used as bulletproof armor when you need something relatively light weight but able to stop rifle rounds. You have to understand that micrometeorites, natural or manmade, have huge kinetic energy, and energy matters much more than momentum in these kinds of impacts. A lightweight aerogel lacks the structural integrity to survive this kind of impact, it will simply shatter into more micrometeorites that will need to be caught by something else behind it. Just look at tests of whipple shields and realize how big of a hole a piece of styrofoam can make when its traveling at hypervelocity.

The problem with the idea as an outright replacement to a laser broom is that of volume. The debris clouds you could be facing might easily be hundreds of kilometers in diameter, but your ship might have a face of only a few dozen feet. Payload mass is everything. Frankly, you get to a point where to really build big spacecraft they need to be built in space from materials found in space, not on Earth. At that point, Kessler syndrome starts to work itself out because you are no longer launching so many large vehicles from the ground to begin with. However you are also likely to start using higher and higher orbits, possibly even cislunar space. Intercept flights like you see in the anime Planetes to remove orbital debris isn't justified in real life to remove every screw that ever came off a spacecraft, only for larger satellites that should be dismantled before they can shatter into a debris cloud. Warfare in Earth orbit is also inadvisable if you want to avert extreme Kessler syndrome, and if you are already at the point where seriously large clouds of debris are threatening manned spaceflight entirely, it may even be declared a war crime to shoot down satellites using kinetic impactors. Again, we already see Kessler syndrome happening in real life, and need to start managing it sooner not later.

Could you explain this one? I'm getting stuck on the idea of a major danger in reverse being a good thing. Are you saying the major danger is the stuff hitting it causing the gel to be scattered? Making the gel part of the problem?

What I mean is that you do not want the spacecraft with the catchers mit to be struck in a vulnerable area and be rendered debris itself. If the mit is not sufficient to stop the momentum and energy of the impactor due to miscalculations, then not only will the micrometeorite go straight through the mit, it will create new debris in the form of spalling coming off the now destroyed mit. Alternatively, sending up an intercept flight risks the intercept flight getting struck somewhere unprotected and thus disable it, turning the whole mission into a new large piece of debris. Any intercept flight in a Kessler event has to be considered risky by the very nature of the phenomenon. Tracking of launches and debris, careful planning of flights with end of life plans to de-orbit them properly, legal sanctions on testing or even launching anti-satellite weapons like we've seen in the past are all much more important to solving the problem than any one technology. Because even a laser broom has to be carried by a spacecraft, and that spacecraft can't stay up forever.

[madd0c0t0r2]

The problem with the idea as an outright replacement to a laser broom is that of volume. The debris clouds you could be facing might easily be hundreds of kilometers in diameter, but your ship might have a face of only a few dozen feet. Payload mass is everything.

To further expand on the gell idea - In this setting cheap launch capacity is available (its how enough stuff was in space to cause the problem in the first place). The available technology is a launch loop, which is pretty good at throwing things into 'an' orbit, but sucks if you need to go off at 90 degrees into a polar orbit, or if you want a retrograde orbit. It also needs constant energy input to stay up, so there's a very strong incentive to 'get back to space' asap, as otherwise you basically have to bring it down in a controlled way and it's very very expensive to put back up again in the future. Payloads are five tonnes, and basically sized to shipping containers (this is not a coincidence).

My very rough idea is basically equivalent to throwing giant squirty cream canisters up (image at bottom), with small rockets boosters intended to push it into the right direction, and the gas emptying through the liquid to 'squirt' the colloid gel heading upwards, and a retro sending the canister back down below the danger zone with a parachute landing and recovery. The spray stream is not a single blob/cloud, but more like a ribbon due to the velocity involved. 4 tonnes is still not a huge ribbon, but the loop is capable of launching millions of tonnes a year. If we assume a Specific gravity of about 0.1, a four tonnes active payload gets us a a 10cm thick, 20m wide and 2 km long ribbon. It could possibly be thinner and longer. It only needs to be thick enough to smear onto penetrating objects, being thicker than that has no beneficial effect. In terms of comparison of specific gravities, without actually designing it I think 0.1 is doable - squirty cream is about 0.5, rigid aerogel is 0.0015, and the earth atmosphere at 180km up is 1x10-9. https://www.spaceacademy.net.au/watch/d ... mosmod.htm

I don't want this to seem like me moving the goal posts. In a Doylian sense, the setting 'has' to have launch loops, and the near earth space was heavily populated with multiple shipyards. I can see a point where the area has been cleaned enough, or traffic has returned, and the laser brooms to be sent up and finish the job with their superior reach and employability. I guess the analogy would be indiscriminate water planes vs fire beaters.

I say 'push it in the right direction', not orbit, because I think the aim would be for this stuff to be on steep parabolic orbits intended to pierce the maximum volume that needed cleaning, before returning back and burning up itself. It wants to be travelling as slowly as possible to maximize intercept chances and impart as much drag as possible. The spray stream is like a wide dispersed ribbon that's moving through the space at an angle. We're not talking a single huge wad slowly orbiting and collecting dust, more like a succession of squeege swipes across a dirty window.

The risk of bits being sliced off or redirected by sharp rigid debris is high, but the gel itself should be a less dangerous thing to be hit by, and there's a possible strategy that the sliced bits will continue the 'dragging and slowing' mission of debris, while also being easier for future foam to collect than metal shards. Some sort of high reflectivity additive to it would be an idea to make it easier to track.

Spoiler to hide the big image of squirty cream (American might be whipped cream, although that's really a different superior product?) Either way, squirty cream as a Briticism is NOT safe to google. Spoiler

[Formless]

Dude, spoiler tags on SDN are broken. If you include both quotes and spoiler tags, the spoilers can't be opened at all.

[Formless]

Anyway, launch loops don't prevent you from doing proper end of life planning. If anything it makes the orbits more predictable and controllable, not less. All you need to de-orbit a vehicle is an ion engine and patience. Having another vehicle match velocity and essentially add mass to the target is an extremely inefficient way to take a vehicle out of orbit, and yes the foam is a debris threat the way you are describing it. Again, orbital velocities are unimaginably huge, especially once you realize that what matters is relative velocity. Your spray of foam might seem like a harmless cloud of goo that will cover the threatening target without shattering it, but to another object traveling at a different trajectory to the foam it looks like a concrete barrier! This idea is completely infeasible. Kessler syndrome happens precisely because one object colliding into another creates more impactors. That foam is no different. Again, at orbital velocities even a piece of styrofoam can threaten a spacecraft. NASA learned the hard way how seemingly soft, harmless objects can fatally destroy a spacecraft when Columbia burned up in the atmosphere and the culprit... was a piece of foam!

Edit: plus, launch loops are themselves an orbital installation that are threatened by Kessler syndrome. They would be one of the first things to be destroyed in a Kessler event. Your setting has a fatal contradiction in it, I'm afraid.

[madd0c0t0r2]

Edit: plus, launch loops are themselves an orbital installation that are threatened by Kessler syndrome. They would be one of the first things to be destroyed in a Kessler event. Your setting has a fatal contradiction in it, I'm afraid.

Ah crap. Yeah. 80km tall, I thought that was low enough to be safe , but there will be a lot of stuff only part burnt up at 80knm and it's a relatively large target.

Fuck. Back to the compost launch story

[Solauren]

Question - how much of our orbital space degree is magnetic in some way? Or could be induced to be magnetic?

[madd0c0t0r2]

Question - how much of our orbital space degree is magnetic in some way? Or could be induced to be magnetic?

metals - but not paint, insulation foam, bits of solar panel or lumps of frozen fuel.

One of the methods in the literature is a magnetic tether - a long wire attached to major debris to create magnetic drag, but it needs to be seriously long to work on sub decade schedule, and the tether itself is a major collision hazard until that point.

[Solauren]

Question - how much of our orbital space degree is magnetic in some way? Or could be induced to be magnetic?

metals - but not paint, insulation foam, bits of solar panel or lumps of frozen fuel.

One of the methods in the literature is a magnetic tether - a long wire attached to major debris to create magnetic drag, but it needs to be seriously long to work on sub decade schedule, and the tether itself is a major collision hazard until that point.

I was more thinking something more like a large magnetic 'catchers mitt' set up. Something big enough you see it coming from a distance, and solid enough that collisions won't be a major problem. So really, a space station acting like a garbage scoop.

[Khaat]

I would put a laser on the surface of the moon, and aim it at the Western horizon/skyspace of Earth, with operational cut-outs for operational satellites. Tiny, repeated laser ablation over time, from high orbits to low, countering orbital speed each time they see moonrise.

Biggest drawback: "unlisted satellites" getting hit.
Once you get past "put it on the moon," obviously.
Or accusations of "Star Wars" anti-ICBM functionality. Maybe duck that by capping the laser output?

[bilateralrope]

The beam would spread too far at that kind of distance to be useful.

[fnord]

As OP said, things have already gone full Kessler, creating the need for orbital debris removal on nontrivial scales. IIRC, stuff under 1 cm in size can be cost-and-mass-effectively shielded against, stuff > 10 cm can be tracked (and thus dodged), it's the stuff in that middle size range is the big problem.

Why is everyone seeming to assume a laser broom system has to be on-orbit?

I'm not seeing a much better option than 1 or more ground-based laser broom sites. Nothing to launch, meaning no additional debris would be created by a cleanup craft getting clobbered. I expect the needed international co-operation would (eventually) happen, even if out of national self-interest.

Are any large (>100 kg or so) derelict objects still intact and in orbit, or have they largely been pulverised already?

If any large derelicts are still intact, then they should be deorbited early to reduce the debris sources in orbit. Smaller objects are more frequent, but the bigger ones make the bigger messes when clobbered.

A presumably prototype system outlined on p7 of Removing Orbital Debris with Lasers claims to be able to deorbit 100k small objects (in the problematic range) in 8.7 months at a 50% availability - assuming that proves out, that scales up to 137k problematic-sized objects deorbited per year per site.

P8 of that pdf says, about 1-tonne derelicts:

With the parameters listed in the Table, it takes 3.7 years to re‐enter one object. However,
167 different objects can be addressed in one day.

If any big stuff is still around, it could be tackled along with the little stuff.

Given the size of the problem (taking "billions" of problematic objects as "10 billion") and assuming all the problematic objects start 1200 km up (per that ESA link), a 2-millennium lifetime means on average, 5 million objects would de-orbit each year.

3 such prototype sites, spread roughly evenly in longitude, would be able to deorbit ~410k problematic objects per annum. Yes, that's swamped by the natural decay and so wouldn't significantly alter orbital lifetime (1849 years).
However, they are prototypes and could be expanded and/or more sites built as experience accumulates in their operation, meaning the broom closet would be able to deorbit more stuff per year.

I would expect cleanup to initially focus on lower altitudes (500 km and below - approx ISS altitude), to prove the system out and provide some room to resume orbital operation.

Phipps et al (in the PDF) seem to lean towards the actual orbital debris removal as first and rearmost. A side effect they seem to think at least as important:

building a LODR system necessitates detection and
tracking technology that permits location of targets with 1m precision, far better
than present practice. This capability will allow more accurate collision prediction

That would reduce that upper bound on size of problematic objects. If, for sake of argument, that side effect dropped the upper bound to (say) 4 cm, how many objects would remain problematic (in the 1-4 cm size range)?