Space debris

[Kryten]

That satellite was destroyed with a SM3 AAM. It delivered 130mj. The rail guns being developed that I was using as example figures generate 360ish...

That would just make the problem worse.

And all the debris DID deorbit.

It was low enough that it was going to deorbit very soon anyway, and the test greatly delayed this. That it did ultimately decay is just an artifact of it's initial extremely low altitude, and hitting something that low for debris mitigation would be pointless-it would destroy itself without intervention in a matter of weeks.

[peadar1987]

Yes, but the debris will have increased velocity, therefore a different orbit. Therefore a different prograde. How much velocity is the question. I searched around for a while trying to get some idea of how fast the particles would be moving, and I'm getting the impression it would be PDF. (pretty damn fast) No more circular orbit, surely, therefore no problem. But like I said, I'm not trying to be contrarian. If someone demonstrates to me that the new debris field from say a destroyed booster that was in LEO would STAY in LEO, I'll concede that a couple of rail guns firing in tandem with small projectiles is a bad idea.

Okay, I get you. New orbit, new prograde, although the orbit will have to be tangent to the original orbit at the point where the impact occurred, so the prograde direction, but not the vector, will remain the same at that point.

Essentially you'd get a load of debris, some of it would deorbit, some would be boosted into an elliptical orbit, some would have its inclination changed, some would stay in much the same orbit as before. You only really need two of the pieces of your satellite to stay in roughly the same orbit for the problem to be worse than it was when you had just one large, easily trackable object there.

[xcorps]

It was low enough that it was going to deorbit very soon anyway

That's true. They killed it because of the fuel tank, how'd I not click to it?

[Seret]

A 4kg retrograde projectile hitting at 5500m/s (so close to 13,000 m/s closing speed) will have an apparent kinetic energy to the target of about 338 MJ, or about the same as 100kg of TNT.

Couple of quick points:

• At the top of it's arc it's not going to have anywhere near the muzzle velocity, so it's would be bringing a lot less KE to the party.
  
• Spacecraft are built pretty lightweight, and a KE projectile of that type would struggle to transfer a lot of energy into it.
  

Regarding that second point, tanks often find this when using their (extremely high velocity) guns on light armoured vehicles or softskins. High velocity small diameter penetrators are devastating against well-armoured targets, but against less tough opponents they simply overpenetrate. The target offers so little resistance that the projectile goes right through both sides without losing much speed (and therefore without delivering much energy into the target). There are numerous stories of lucky armoured personnel carriers being hit through the (unoccupied) troop compartment by sabots, with no real effect except a bit of additional ventilation. Many APCs are, like spacecraft, made from aluminium and it's telling that KE rounds aren't used against aircraft, which are constructed the same way. Tanks always carry an explosive round for the main gun in addition to their KE rounds, and they use this on light vehicles because it's much more likely to get a kill.

Now, I'm not saying a rail gun hit won't completely mash a spacecraft that it scores a direct hit on, because it will, but the actual amount of energy dumped into the target could be well below what you expect. Hits to peripheral equipment such as solar arrays would do a negligible amount of damage. You'd just get a nice neat hole the same diameter as your railgun round.

[Kryten]

A round from a tank gun is not a good model for this kind of impactor; you're still only looking at about 2km/s relative velocity. At 8+ km/s, vapourisation (of impactor and target) and liquefaction (in metals) can't be ignored.

[Seret]

Possibly not a prefect analogue, but I think the point I was making about the ability of the target to provide enough resistance to force the projectile to transfer a lot of energy stands.

Not that it really matters, because nobody is going to be firing rail guns at orbital debris anyway.

[xcorps]

Not that it really matters, because nobody is going to be firing rail guns at orbital debris anyway.

Only because I can't afford one.

Yet.

[Skyler4856]

The problem should be resolved soon

[Rickenbacker]

I remember reading about an idea to "puff up" the atmosphere somehow (explosives? lasers?). I can't remember where now, but the idea was basically to create a temporary "bump" of atmosphere that would slow down and thus eventually deorbit ALL debris that passed through it before it sank back...

[SelectHalfling0]

Although small flecks of paint and such that are travelling at incredibly high speeds can be dangerous to crewed vessels, larger debris and non-functional satellites are so spread out that there is a very small chance of them actually hitting something. Even though Gravity (the movie) was great, the event is extremely unlikely.

[SargeRho]

The event already happened. Not on that scale, but sattelites have collided in the past.

[Dodgey]

That's right. We are past the point of no return. Without human intervention the situation will get worse.