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Comment by vlovich123

3 days ago

Rather than protection on each rocket, couldn't you just send a bunch of fortified rockets that absorb the debris during a collision but don't emit anything. Do that a few times and then all other rockets just reuse the path that was cut?

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vlovich123

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mapt  3 days ago

Orbit is not a location. Orbit is a group of velocity-location vectors which form a stable loop around a body, without intersecting that body.

Imagine a bullet circling your head at mach 25. Now imagine a second bullet, circling your head at a slightly different angle, at a slightly different distance from your head. There's a chance that they could collide, and the resulting explosion would leave a great deal of dust... on a mixture of velocities, still circling your head. Now add a third bullet, also on a slightly different vector; Make sure that it doesn't collide with any of that dust!

The actual situation is we aren't dealing with 3 bullets or 100 bullets, we have ~170 million objects orbiting the Earth, and only around 50,000 are large enough to track. They are all moving fast enough in relation to each other that a collision would result in a sizable explosion, not an elastic agglomeration. We have no way of removing them.

The good news is that there is a large volume of space for them to exist in. The bad news is that as we continue to fill it up, odds of collisions increase, and every collision spawns many, many more objects.

  • vlovich123  3 days ago

    You’ve explained what Kessler syndrome is but not why my idea doesn’t work.

    I’m saying send reinforced rockets through the orbits that absorb the collision instead of generating more dust. That should let you clear a path through all orbits that intersect your path. It’s hard to do and the 3d aspect of it might make it expensive but conceptually it could be a solution. Or use super powerful lasers (potentially mounted on a satellite) to deorbit the dust

    • ben_w  3 days ago

      > I’m saying send reinforced rockets through the orbits that absorb the collision instead of generating more dust. That should let you clear a path through all orbits that intersect your path.

      No such material exists, nor can it be made from any matter that is based on electrons bound around a nucleus — the force of impact will break any such material.

      > It’s hard to do and the 3d aspect of it might make it expensive but conceptually it could be a solution.

      "expensive but conceptually it could be a solution" is also why we don't have an Orbital Ring instead of rockets: https://en.wikipedia.org/wiki/Orbital_ring

      The cost requirement for getting something to space with enough momentum to do the cleanup, even if it was able to survive the impacts, would be comparable to the entire cost of getting the stuff constituting the mess into orbit in the first place: bad enough to be prohibitive even today with relatively little mess, much worse if there's an actual Kessler cascade.

      > Or use super powerful lasers (potentially mounted on a satellite) to deorbit the dust

      Could work for the bigger bits, but don't put the lasers on a satellite: 1) Power is short up there, as is cooling, much easier to put a bit laser on the ground and waste some energy going up through the atmosphere; 2) if you solve that constraint, you've now got an orbital laser that's an obvious and easy-to-hit target for all foreign powers to get upset about even if you didn't want to weaponise it.

      For the smaller stuff, you can't see the dust to target it in the first place.

    • mapt  3 days ago

      This doesn't work conceptually, but it's hard to explain without attaining a KSP baseline of understanding. https://xkcd.com/1356

      "Clearing a path" is something you can do with a bulldozer through a traffic jam, but imagine clearing a path through a belt road by driving through the flow of moving traffic sideways at speed. Ultimately you can't hit every car in the outer lane with just one bulldozer, and the cars will close in and fill gaps because they're moving at slightly different speeds.

      The easy elastic collisions you're imagining also just can't occur at these relative velocities. When something hits it looks more like an explosion than a "catch". If you shoot a local stone monument with high explosive artillery shells what happens? Does it reduce the number of things flying through the air or increase it?

    • immibis  3 days ago

      It takes about 90 minutes to complete a low earth orbit. A rocket can't hover in place for 90 minutes at the same altitude, then increase its altitude by its height and repeat. It doesn't have enough fuel for that.

      2 replies →

lmm  3 days ago

> couldn't you just send a bunch of fortified rockets that absorb the debris during a collision but don't emit anything.

"Just" how? Orbital collisions happen at an average of 10km/s, you're going to make what, some kind of sponge that can get hit by a chunk of satellite going ~8x faster than a bullet and absorb it and slow it to a halt without fragmenting at all? Good luck.

> Do that a few times and then all other rockets just reuse the path that was cut?

Things in orbit are constantly moving, you can't "clear a path" any more than you can, IDK, make a safe route through a forest by walking through it once and moving any bears you encounter a couple of feet.