Tim Little wrote:
 > You can get a bit of both worlds if instead of truly
 > reactionless drives, you have a reaction drive with tachyonic exhaust.
 > That would satisfy all the usual conservation laws.

How about other non-FTL particles? Photons? Neutrinos?

I wrote:
 > In special relativity, the relationship:
 >
 > (kinetic energy)^2 = (momentum x c)^2 + (rest mass x c^2)^2
 >
 > is true in all frames of reference.

The energy-momentum relationship is actually:

(energy)^2 = (momentum x c)^2 + (rest mass x c^2)^2

energy = gamma x mc^2
momentum = gamma x mv
where gamma is the Lorentz factor 1/sqrt(1-(v^2/c^2))

Conservation of momentum is the tricky bit to deal with.

If we say gravitics sometimes allows you to convert mass-energy to
momentum, a la the existing diameter rules, and satisfy the
energy-momentum relationship...

Richard Aiken wrote:
 > Now all I need to figure out is how much volume 5% of mass represents
 > as water (because I use a variant of the LBB ship construction system)
 >  . . .

Free trader in Megatraveller is about 2270 tonnes in 200 displacement
tons, without power plant/M-drive fuel.

So density is 2270 tonnes in 200*13.5 cubic metres, or 0.84 tonnes/cubic
metre. This seems like a good ballpark for a ship with standard armor.

System defense boat is 9720 tonnes in 400*13.5 cubic metres, or 1.8
tonnes/cubic metre. This seems like a good ballpark for a heavily
armored ship.

For the first case, for every 10 cubic metres of ship (8.4 tonnes) I
need 5% of this in water: 0.42 cubic metres of water.

For the second case, for every 10 cubic metres of ship (18 tonnes) I
need 18/20 or 0.9 cubic metres of water.

Rob O'Connor