Re: Spacecraft drives

So you want a ship that is 30% fuel to be able to reach 4% of c?

ok, the mass-ratio of the ship is:

Mr = 1/.7 = 1.428...

the final velocity (.04 c) is:
Vb = Ve * ln(Mr)
.04 c = Ve * ln(1.428..)
.04c = Ve * .03566...
1.2e7 = Ve * .03566..
3.36e7 = Ve

So we need an exhaust velocity of bwtter than 11% of c!

Isp = Ve * g
Isp = 3.36e7 / 9.8
Isp = 3.4e6

Now the good news. Wer have engines *now* that can do this. The bad
news is that they are ion drives with a thrust measured in *hundredths*
of a g... <sigh>.

I suspect that you won't get a *fusion* drive to do this well, as the
"standard" 6e5 figure is likely figured by assuming *all* the energy
released in the fusion reaction is deposited in the exhaust of helium.
You *can't* improve that. Not without changing it into something other
than a fusion drive.

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