[spartanatreyu]

> Active debris removal (harpoon satellites, magnet arms, whatever) are not a solution to this problem and are a huge waste of money.

This is wrong because it's based on a flawed assumption.

That assumption being: Propellant is required to deorbit debris, and the rocket equation makes launching all that propellant prohibitively expensive.

And while we can't do anything about the rocket equation, we don't actually need to have propellant in space to deorbit things.

Ways to deorbit without propellant in space:

1. The ground based methods. Although these would likely be seen by superpowers as military escalation of the status-quo.

2. Propulsion-less drone satellites. All propulsion-less designs use some form of sail which can be used to change the drone's orbit to match the debris before latching on and towing it to a new orbit. Once the debris is now in a decaying or graveyard orbit, the drone can detach and go after it's next target. All that is needed is time, power (readily accessible via solar power this close to the sun), and reaction wheels (which now we know what caused previous designs to fail like in the Kepler mission, can be built to last).

The most common form of sails would be solar sails, but there's also EDTs and magnetic sails.

[dredmorbius]

What about ablation and/or ablative thrust using lasers?

You'd need to fuel a laser platform, but it could target debris over a huge region. The goal would be to both reduce size and to gently nudge smaller debris to lower (and atmosphere-intersecting) orbits.

(As mentioned in another comment, linking: <https://en.wikipedia.org/wiki/Laser_broom>, here: <https://news.ycombinator.com/item?id=41051533>.)

[XorNot]

You don't need to put a laser in space to do this.

You build a ground based laser, and fire it at objects when they're approximately directly overhead. Pushing upwards on the object basically rotates it's orbit so one side of it will not be lower into the atmosphere.

[dredmorbius]

Which should simplify the problem several ways. Thanks.

[rzimmerman]

I'd argue that even propellent-less deorbit devices are a waste of time. The best answer is what we're doing now: rules about deorbit capability and orbit lifetime, as well as debris production. Even when there are failures, as long as they are a small enough percentage of the pie, debris won't accumulate faster than it clears.

Additionally, all the propellant-less solutions are low-thrust (or ground-based, which is another thing entirely). It's absolutely possible to orbit match, dock, and deorbit an object, but whatever low-thrust device you're using is going to deorbit as well. Maybe it's possible to launch a bunch of small devices like this to do cleanup, but it's not necessary or worthwhile.

This is a great example of a solution that sounds fun and interesting to a problem that's easy to understand at a surface-level. It gets attention and funding, but the real unsexy stuff (tracking, monitoring, collision avoidance) is where the money should go.

[panick21_]

The actual solution is reducing cost to orbit. That reduces propellant cost.

And more importantly, just having laws that require people to deorbit sats and force them to pay for deorbit if they fail to make something deorbit.

> 2. Propulsion-less drone satellites.

Nowhere near enough thrust for this.

[dredmorbius]

Absent regulation, decreasing cost-to-orbit has the more likely consequence of increasing overall launches, satellites, and hence, orbital flotsam.

The Jevons Paradox strikes again.

[panick21_]

There already is some regulation. But I agree that companies that launch should be responsable for deorbit.

[dredmorbius]

Depending on how far costs fall, one potential problem would be an equivalent of "flags of convenience" in sea-based shipping. Small countries with little or "favourable" (e.g., short-term profits) regulatory regimes could sustain at least some launch capability. Unless there's some way of reining in that activity, I see the problem manifesting to at least some degree.

Even now, getting launch-capable countries on board with restrictions is a likely problem. The US, EU, and Japan perhaps not so much, but of Russia, China, India, Pakistan (potentially), and North Korea, rather more plausibly.

[panick21_]

True but the solution for that is to punish those companies in the domestic market of the people who signed up.

There was US company that tried to launch on an Indian vehicle not following all the regulation and they got fucked hard.

Of course countries like Russia are simply not gone follow these rules anyway.

[dredmorbius]

Most of the countries named are already under heavy sanctions, and have proved resilient against them to a large extent.

One problem with the Kessler Syndrome is that it's a runaway phenomenon, though one that evolves more slowly than most people appreciate. A few bad actors could trigger events which slowly start to seriously degrade at least low-to-mid Earth orbital ranges.

Geosynchronous orbits are possibly less susceptible as the entire orbital ring is large, though geostationary orbital space, strictly along Earth's equator, is more constrained. The Starlink approach of putting comms satellites in very low Earth orbit, which clears fairly quickly, possibly mitigates this in two ways (it makes geosync less critically necessary, and de-orbits satellites quickly). But LEO is still where higher orbits eventually decay to, and might itself be affected with time as well.

The lax regulatory problem, which invokes another underappreciated economic principle, Gresham's Law, is one that's appeared elsewhere and has proved hard to counter. I'd suggest not underestimating its possible noxious effects.

[spartanatreyu]

> > 2. Propulsion-less drone satellites.

> Nowhere near enough thrust for this.

Of course there is.

If solar sail probes can change their orbits over time (which they can), then they already have enough thrust. There's no static friction to overcome, so there isn't a minimum thrust that you need to reach.

As long as you can continue to apply thrust over time, then you have a solution. It doesn't matter if it takes 6 hours, 6 weeks or 6 months. Even a single probe moving the right piece of debris prevents tens of thousands of more pieces being generated. Imagine what three of them could do, or twenty...

[etrautmann]

Like a space superfund cleanup?

[naikrovek]

I would think that solar sails in such an environment would be as bad of an idea as walking through a thick hedgerow in a silk dress.

The dress would not survive unscathed, and neither would the solar sail.

[dredmorbius]

A solar sail isn't a pressure vessel, fuel tank, electronics bay, or other sensitive instrument. It can take considerable abuse before being substantially degraded, let alone failing.

Space debris impacting on a solar sail would all but certainly simply punch neat holes through it. Much as accumulating dust slowly degrades the light-gathering capability of a large reflector telescope, a modestly-perforated solar sail would lose a very small fraction of its effectiveness. But you could probably lose a heck of a lot of surface area before those effects became significant. Strength of the sail itself is probably a minimal concern, though a design with periodic reinforcing threads (themselves having a cost of increased mass) might be more than sufficient to address any strength compromise.

[naikrovek]

the solar sail would need to be incredibly large for a craft that can move to arbitrary locations in orbit for the purposes of de-orbiting satellites, which means it must have large sails so that both the de-orbiter and the de-orbitee can both be moved via sunlight alone, and achieve the required thrust vector in a reasonable amount of time (this de-orbiter must de-orbit many satellites, remember?)

the larger the sail is, the more likely it is to be affected by space debris at any given moment.

debris passing through a taught mylar solar shield will tear holes in the mylar which are the shape of the debris passing through. any sharp corners in the debris will leave a sharp corner in the hole, and those corners are going to become tears the next time something passes through nearby. the tiny holes become large holes pretty quickly.

other materials will behave differently of course, but i don't know of any solar sails at all, never mind ones made out of not-mylar.