Hacker News Reader

Comment by el_don_almighty | Hacker News Reader

How much is removing 1kg from Low-Earth Orbit worth?

Launch cost is ~$3,000 to $5,000 per kg

What's the value of pulling it back down and what drives this value?

You can't reasonably measure this by the kg. Pulling down a single 10000 kg satellite is fairly cheap; all you need to do is latch onto it and deorbit. This can be done with a single vehicle. Deorbiting 10k 1 kg fragments would be vastly more expensive. 1 million 10 gram fragments would be more expensive still.

There are techniques with which deorbiting 1 million 10 gram fragments might end up being quite cheap. E.g. the use of a single laser-equipped base that selectively hits the debris to cause localized evaporation and thrust, disrupting their trajectory.

If a tiny bit of undirected evaporation is enough to push the fragment to deorbit, it's already so low that it would have deorbited on its own very soon anyway.

In that case evaporating it completely would be a better option, as a gas it's harmless

You overestimate the ease of evaporating something and umderestimate the effectiveness of a little bit of thrust.

>You can't reasonably measure this by the kg. Pulling down a single 10000 kg satellite is fairly cheap

On the contrary, this seems reasonable. It (correctly) identifies that deorbiting intact satellites before they fragment is overwhelmingly the cost-optimal strategy.

In the long-run, it's really total mass in a given orbit that's the dominant variable which separates runaway Kessler syndrome from stability. Therefore, a per-kilogram "bounty" (with a sliding scale depending on orbit) wouldn't be a bad incentive model.

Don't pick winners, let the market decide™.

I've heard about space drives which leverage a tether and an electrical wire which allows you to trade electricity for momentum by reacting against Earth's magnetic field. I wonder if a space tug could use this effect and maneuver indefinitely. Grab a dead satellite, spin up to speed using magneto drive, let go and simultaneously yeet the junk retrograde and boost its own orbit.

There's two fold for missions like this

1) Debris is dangerous to orbiting objects. So the value of bringing it down is more valuable than the per kilogram value. It is highly dependent upon potential damage it can do. Space debris is already causing damage to satellites and the ISS. As we place more objects in space this danger increase super-linearly.

2) If you can decommission debris you can decommission satellites. This has obvious military applications. In fact to properly do this you actually have to get pretty close to other satellites without colliding. By solving the debris problem you're solving a lot of the same problems you need for these military applications.

So both incentives are valued far greater than the per-mass value of the trash.

> "If you can decommission debris you can decommission satellites. This has obvious military applications. In fact to properly do this you actually have to get pretty close to other satellites without colliding. By solving the debris problem you're solving a lot of the same problems you need for these military applications."

I'm not sure that's entirely true. Having a collector satellite match orbit with the debris and grab is one way to get rid of it, but I suspect in most cases it's good enough to just position a satellite with, say, a big steel plate in a path that intersects the debris' path and deflect it at the right angle so it returns to Earth. (If you're really clever you might use the impacts to deflect the interceptor satellite into roughly the right orbit to intercept the next piece of debris.)

There might also be ways to "catch" debris with moderately high relative velocity with the collector satellite. I imagine there's limits to the size of thing you can capture that way and the maximum relative velocity if you want to be pretty sure you can catch it without creating more debris.

Maybe the least sophisticated way to deorbit debris would be to just have an object with relatively low mass but very high surface area (e.g. an artificial "asteroid" made of aerogel) in an orbit that gives it the greatest probability of hitting any average piece of space junk, and then you wait for things to hit it by chance. The things that hit it lose momentum and hopefully fall back to Earth.

It's the cheap price of a cover story for capabilities with military applications.

The value will be based on the value of the reduced risk of damage/loss from orbital debris and reduced cost from orbital adjustments to avoid debris (which uses fuel or mass which reduces the lifespan of the satellite). Once we end up with 100k or more LEO satellites it'll be very valuable to reduce the amount of debris at those altitudes.

Reply on news.ycombinator.com