Now I'm a story-telling GM, not a gear-head, but I do have a little background
in physics, and a perhaps overly vivid imagination... :-)

Alex Goodwin - alex.goodwin at multitel.com.au writes:

>     Those messy neutrons, and the energy they carry off...

But but but... Once you have control of gravity, you can likely build a reactor
which can confine the said neutrons, and extract at least some of their energy.
OK, at low TLs you might have to wait until they decay and then soak up the
energy of the resulting protons. This all means that the numbers can be, well,
pretty much anything you want within the limits you mention.

The higher the TL, the more options you likely have.

I also mention that if you have grav, you almost certainly have control of the
strong and weak forces, which opens up all sorts of other possibilities: a
direct hydrogen + deuterium -> helium3 fusion path, you name it.

Now, of course, there are ways around this. "We have X much control of <some
fundamental force>, but not Y much, so we can't do Z" and so on. Go for it.

Richard Aiken - raikenclw at gmail.com (I think) writes:

>     One quick point, rocketry draws a distinction between fuel (which provides
>     energy) and propellant (the stuff you throw out the back to make you move forwards).

Indeed. I like the idea of propellant, at least for close-in manoeuvre drives.
But for me this drives plot. It makes ship refuelling a bit more complex, and
I can use that for plot hooks. Bwahahahaha.

Jonathan