# Re: starship-design: Howdy Christoph :-)

```Hi Group,

Hi to you Christoph. I'm realtively new myself, though I've been designing
back of the envelope starships for years.

>I am particularly impressed by your Explorer class design concept. It
>looks like a well-thought and consistent idea. I'm a bit sad not to be on
>board...
>
You and me both.

>For the beginning I have a simple question. In your design overview for a
>fusion powered ship you give the fuel to mass ratios for different speeds
>and specific impulses. Certainly the mass of the fuel and the still
>relatively "low" speed imposes a heavy burden on the project.

Fuel mass and specific impulse. We need a power source better than fusion,
but none of us has anything that is more thought out than fusion at present.
I think we're waiting for inspiration. Tho no warp-drives please, that's
just depressing since we have no idea how that can be done yet.

>Just for curiosity: If you suppose a speed of 0.5 c and a specific impulse
>of 2,500,000 sec (25,000,000 m/s), what would be the fuel to mass ratio
>required?

Something obscene... about 500,000 to one, if you carry fuel to stop. About
700 to 1 if you stop via a magnetic-sail or some other non-fuelled braking
system.

> Or from the other way, for a speed of 0.5 c, what specific
>impulse would be required to keep the fuel to mass ratio below 50:1?

0.28 c if you carry braking fuel, or 0.14 c if you don't.

>I don't have the formula at hand, but maybe one of you could give a quick
>
The formula is easy ;-)

Mi/Mf = [ (1+ v/c)/(1-v/c)]^c/Ve, if you brake with rockets, and the
square-root if you don't.

Mi= initial mass, Mf=final mass; v, is obvious as is c; Ve is the exhaust
velocity [Isp x g, of course]

to reverse of the equation is a bit tricky...

to find Ve/c it's (log[(1+v/c)/(1-v/c)]) / log(Mi/Mf), and you've guessed
it's half that if you don't carry gas to stop.

to find v it gets trickier...

especially in ASCII !!!

I'm kind of hoping that we'll figure out a way of powering up to a Ve of
+0.4 c, which would make starflight that much easier. If you check out one
of my posts on the EQ Pegasi thing I discuss recent work that suggests the
GUT unification energy might be lower than the "orthodox" 10^16 GeV. Perhaps
as low as a mere 1000 GeV. With GUT unification we should be able to
"dissolve matter", perhaps converting it to energy without mucking around
with anti-matter. Or we might be able to liberate "phase-transition energy"
which according to some theorists created matter and energy in this
Universe - that'd open up the possibility of continuous acceleration flight
to anywhere in the Universe. That's about the best I can imagine until we
crack how to make wormholes.