Re: starship-design: We need to get on the same (pellet) track first

[kuo@bit.csc.lsu.edu (Isaac Kuo)]

Timothy van der Linden wrote:
>Isaac,
>>>>>I should note that anything above 0.3c doesn't apply to pure
>>>>>fusion designs, but only for designs that use a more energy
>>>>>rich fuel.

>>>>Which means antimatter.  (Or something even more bizzare, like a black
>>>>hole.)

>>>Or a partial beamed design...

>>Not exactly.

>I suppose a black hole as stardrive does comply with the rocket equation?

Well, it would be bizarre, but you could theoretically build a
"rocket" around a black hole.  For instance, it could be a large
sphere with a hole.  It absorbs Hawking radiation from the black
hole, except for that hole (which is where thrust comes from).
This black hole is kept from evaporating away by feeding it extra
mass from the fuel storage.

A really bizzare starship, considering how much better it would be
to just use the black hole as a highly effective anti-matter producer
(in a fixed anti-matter factory).

>>If you'd like, I can rehash my calculations on the potential muzzle
>>velocities and other limitations of mass drivers.  The overall
>>conclusions are actually pertinent to this discussion, since EM mass
>>drivers would be used to fire pellets from the fuel packets in my
>>stardrive proposal.

>Any numbers with calculations are welcome. What I'm most interested in, is
>how much mass you will need (and thus how much effort one has to do to put
>it in a pellet track).

I should recalculate things and type them up on my web page.
Anyway, the important factor to keep in mind is that for any
useful muzzle velocity, the acceleration occurs essentially
instantly for purposes of rejecting waste heat.

For a pellet launcher meant to fire frozen DT pellets, this
would seem to be disastrous.  The solution, as I see it, is
to use a "pusher plate" of plasma pushing a frozen DT sabot
which sacrificially melts, leaving a core frozen pellet which
leaves the muzzle.  Beyond the muzzle is a cylinder which
looks a little like a large gun silencer.  It is rotating
quickly and has a series of conical baffles; its only openning
is through the center, which the frozen pellet passes through.
Gas pressure expansion forces most of the waste gas into the
conical baffles, where centrifugal "force" funnels the gas to
reclaimation pumps along the outer surface of the cylinder.
Thus, most of the pusher plate and plasma material can be
recycled.

>>When it comes to exhaust velocity, the harshest fact of rocket design
>>is that the limiting factor is _availability_.

>True, but I wonder, is a ramjet of the size that we need physically
>possible?

This ramjet isn't supposed to scrounge around for interstellar
hydrogen, so its diameter is determined by how accurate the
pellet tracks can be laid and followed.

>It may be so inefficient that the power losses melt it away the
>instant that it starts to produce 1E16 Watt of power.

The coolest thing about ramjets is that using superconducting
coils and an aneutronic fusion reaction _no_ waste heat is
absorbed by the starship.  Superconductors aren't just almost
lossless, they are _entirely_ lossless.

>The same may be true for other designs, I just don't know. For that matter,
>I don't know that exactly what the availability and cost of the several
>designs will be.

No one knows.
-- 
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
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