Another out of sequence snippet

I would be surprised if it used random space junk. Even a fairly dumb AI can be pretty selective in the junk it collects

With decent mass-drivers, you don't need a lot of material. You hit 1kT/kg at 3,000 kps impact velocity, and by that point even long slant routes through the atmosphere won't degrade the velocity much, although they will degrade accuracy even with well-designed projectiles. [i have a feeling that the numbers i gave up-thread are off by a factor of 4.2, but i can't be bothered to edit]. So having a range of impactors from 1-100kg available would cover just about any situation, and you can make a lot of them from 10,000T of raw material.

Weird Harold wrote:

DMcCunney wrote:I don't see any reason it can't, but where does it get the ammo?

Grabbing random space junk with tractor beams is one thing. The sort of specially produced projectiles you suggest are a different matter.

OWL can take raw materials and build a PICA. All the OBS needs is raw material to build KEWs. All it really needs is a small heat shield of stronger materials and a lot of aerodynamically shaped mass. Even random space junk should provide enough of the stronger materials needed for the heat shield plus enough "rock" or other material to cast into the aerodynamic shaped mass behind the heat shield.

Louis R wrote:I would be surprised if it used random space junk. Even a fairly dumb AI can be pretty selective in the junk it collects

With decent mass-drivers, you don't need a lot of material. You hit 1kT/kg at 3,000 kps impact velocity, and by that point even long slant routes through the atmosphere won't degrade the velocity much, although they will degrade accuracy even with well-designed projectiles. [i have a feeling that the numbers i gave up-thread are off by a factor of 4.2, but i can't be bothered to edit]. So having a range of impactors from 1-100kg available would cover just about any situation, and you can make a lot of them from 10,000T of raw material.

I think it was said that the optimal size and material for a orbital kinetic system with present day tech is a ~10 ton tungsten rod traveling at Mach 10.

The TF probable has access to better materials but if you want to have a system that can easily reload it self just use rocks (preferable with a high content of metals) that are a bit bigger and traveling much faster.

If you use smaller impactors they run the risk of burning up in the atmosphere and they need to traveling at magnitudes higher speed. The other drawback is that they will probably be less accurate.

Which is a major reason why KEW systems have never been pursued: it's easier and cheaper just to drop the 12T of explosive on people.

Small HV impactors don't really have time to burn up: they are exposed to significant heating for < .1s even on steep slant trajectories [depending on what 'HV' means, of course]. That doesn't make you wrong about accuracy, though. It doesn't take much deviation to throw them off target, and lighter impactors are certainly easier to throw off line.

Joat42 wrote:I think it was said that the optimal size and material for a orbital kinetic system with present day tech is a ~10 ton tungsten rod traveling at Mach 10.

The TF probable has access to better materials but if you want to have a system that can easily reload it self just use rocks (preferable with a high content of metals) that are a bit bigger and traveling much faster.

If you use smaller impactors they run the risk of burning up in the atmosphere and they need to traveling at magnitudes higher speed. The other drawback is that they will probably be less accurate.