Re: Defense for spacecraft against big lasers...

Bryan Derksen wrote:

I'm unfamiliar with the effects of a large X-ray laser like this.
Would it be able to physically vaporize incoming kinetic weapons, or
just irradiate them uselessly (due to the lack of any electronics or
pilots to fry)? If there's anything that's particularly transparent to
X-rays at the frequencies being used, perhaps make your projectiles
out of those.


Soft x-rays are absorbed too quickly to have much in the way of reliable irradiation effects. The laser would pretty much have to be burning holes (or blasting holes, if it is a pulsed laser). Depending on the specs, it might take a long time to fry a large, dumb, solid chunk of matter used for a kinetic impactor (as opposed to thin-skinned, fragile spacecraft or artificial satellites). In this case, you could send a dozen impactors or so at the laser, and then launch your ship. Give them a choice - spend their time frying the impactors while en-route to the moon, or shoot down the escaping spacecraft. Unfortunately for this scenario, the controllers may just decide to spend 1% of the time turning the spacecraft to slag and the remaining 99% of the time eroding the impactors away. There is no matter held together by chemical bonds that is transparent to soft x-rays at any useful thickness. (Working with soft x-rays is a pain - even a slightly impure vacuum in the beamline can really attenuate your beam - or so the experimentalists tell me.)

X-rays don't penetrate Earth's atmosphere well, so how about armor
made of gas? Either big plumes sprayed out into space as a
quick-deploy emergency thing, or a balloon filled with gas where
hopefully the balloon won't be thick enough to stop enough X-rays to
melt. The gas inside could serve as a coolant. If gas would be too
bulky, I wonder if a layer of water would work - if it vaporizes where
the beam is hitting, more would flow in from the sides to take its
place.

Shielding against a radiation beam basically amounts to how much mass per area you can put between yourself and the emitter (I am ignoring the thermal effects of the beam, here, just radiation attenuation). Emitting a cloud of gas would provide as much protection as surrounding your spacecraft with a uniform shell of the same mass of armor plate - except that if you manuever, you wouldn't leave the armor behind, and interactions with sunlight and the solar wind will eventually strip your gas cloud away (I'll leave the speed of this stripping to other experts). Using a balloon, as you suggest, works a bit better as far as keeping the gas until the balloon gets punctured - how long will the balloon stay inflated after getting holes melted (or vaporized, or blasted) through it? That question is not rhetorical, I don't know the answer. It seems to me, however, that the thin material of the balloon will be vulnerable to being quickly cut by the laser, leaving a large gash that ruins the ability of the baloon to hold up under tension, so it collapses and lets the gas escape.

The liquid armor idea might work, but I'd like to use something with a lower vapor pressure than water (so it does not start escaping into space after the hull gets drilled) and include some sort of "clumping" properties like platelets. Perhaps something like cooking oil, with additives that cause it to form a solid mass once it squirts out of the pipes to give you a sort of self healing property - hmmmm maybe something like that expanding foam you can buy at hardware stores - release the pressure and it foams out and solidifies, making a plug that holds the rest of it in. The more the laser drills away at the plug, the more foam expands to fill the hole, but stop the drilling and the hole plugs up and you don't have all your armor squirting out into the vacuum of space.

Or you could just use a lot of solid armor and spin your spacecraft. If the laser is dwelling on one spot, you will be continually exposing new armored sections to the beam. This can be countered by rastering the beam to follow the same location on the hull. I think it was Isaac Kuo who proposed having concentric armor shells that rotated in different directions, which would counter the effectiveness of the rastering technique until the laser managed to cut a swath all the way through each armored section except for the last. This last method also gives you the benefit of spin gravity without nasty gyroscopic effects throwing off your ability to change orientation (although the stresses on the bearings would be large if you turned too quickly).

Just some thoughts.

Luke
.

Relevant Pages

  • Re: Any limits on relativistic impact blast velocity?
    ... and a tank of inert propellant gas. ... whether acceleration or deceleration is desired). ... The x-ray laser in question gradually accelerates ... lightweight zone plate coated with lead. ...
    (sci.physics)
  • Re: A question about cosmic microwave radiation and specialrelativity
    ... >> if a candle is the right analogy, ... >> of the balloon, leaving the center dark while the light heads ... As the balloon expands the gas expands ...
    (sci.physics.relativity)
  • Re: Hydrogen as Lifting Gas for Airship
    ... of a rarified gas inside the envelope, only 1 percent as dense as the ... Now heat the liftgas enouh to make it half as dense. ... You didn't increase your lift by half, you only increased it by a half ... I think the calculation would be different, if the used balloon was allowed to expand, the calculation would be how much the volume changes when heated, and how much the extra displaced air weighs. ...
    (rec.arts.sf.science)
  • Re: Howlers
    ... with a ray consisting of lots of little refridgerators. ... I'm not convinced that the projection is the problem. ... and a laser. ... When the atoms within the gas are travelling ...
    (rec.arts.sf.composition)
  • Re: Howlers
    ... you end up with a ray consisting of lots of little refridgerators. ... and a laser. ... When the atoms within the gas are travelling ... Reducing the momentum of the atoms cools the gas. ...
    (rec.arts.sf.composition)
Loading