I need some physics help

[gridlore]

OK, another question for my NaNo project. This one gets very geeky, so hold on.

The main weapons in my universe for ship-to-ship combat are grasers - gamma spectrum lasers focused by artificial gravity - that transfer a lot of energy to the enemy ship in the form of heat, which causes explosions, melting, and all sorts of chaos.

The main sublight drives are fusion torches, which I imagine would create a wake of hot gasses.

My question is, would shooting a graser through that fusion exhaust cone degrade it in any way? Especially close to the drive bells where things are the most chaotic?

I'm trying to determine if in the final third of the book the enemy can do a straight on stern chase, or if they'd need to spread out to get around the engine wake to fire effectively.

Thanks in advance.

Comments

[kengr]

If the drive is a fusion "torch", then the exhaust is plasma. Very hot plasma.

It might be somewhat opaque to gamma rays. Not sure how you'd check for opacity values at gamma wavelength of very, very high temp hydrogen & helium plasma.

Of course, you've also got the other problem of diffraction spreading of the beam. Fortunately the wavelength to aperture ration is *way* high, so you should get a good distance before that happens (focusing can't help with that, BTW)

Also, don't forget that the energy transfer is apt to be *explosive* (as in the gamma rays penetrate a short distance into the hull, dump all their energy, and that layer of hull flashes into plasma explosively).

If they penetrate thru the hull before dumping the energy, they''l dump it in the air/fuel/whatever on the inside. Yet another big boom.

Lasers only cause melting at *low* energy densities (low for weapons grade stuff anyway).

Though defocusing the beam to just heat up the hull and overload the life support or the engineering section's heat removal system gives you a way to cripple a ship without doing much damage.

[isomeme]

I doubt there would be any significant attenuation from firing through the drive exhaust. A fusion drive gets high efficiency (Isp) by virtue of having an absurdly high exhaust velocity -- on the order of 25,000 km/s, or just under 0.1 c. Because of that velocity, the mass rate of the thrust can be quite low (momentum is mass times velocity, so you can get more kick per mass at higher velocities). And the mostly-helium-plasma exhaust would spread relatively quickly behind the ship in any case. Gamma rays aren't going to be bothered by a vanishingly thin mist of helium plasma.