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Re: starship-design: Still doing stardrives?
L. Clayton Parker wrote:
> > > I used a Broussard ramscoop to supplement onboard
> > > fuel, so your discouraging asessment of the prospects
> > > of this technology will need further checking.
> The last paper I saw published on the ISM gives a density of 0.05 for the
> local area out to about 150 ly and 0.001 after that. The average for the
> galaxy however, is closer to 10.0. The reason for the low local density was
> given as old supernova events in the local area.
That's pretty thin. An atom for 1 cc is sparse, but an atom for 20 cc's is
discouraging. My guesswork is based on the assumption that a starship
will have plenty of energy available. What runs short is reaction mass.
Mass gets expensive in a fractional-C framework, but you have to have
something to throw out the back. Before going to more elaborate schemes
to procure reaction mass, let me check a couple of notions.
I spotted a paper a couple years ago, to the effect our system had just
entered the fringe of an interstellar gas cloud. Was this (a) just bunk, or
(b) included in the accounting? I could easily accept that both concepts,
that we're in a low-density region, and that we're also in a gas cloud, can
be true together, just a matter of relative scale.
Then again, another factor: our system is englobed in the Oort Cloud of
widely scattered solid debris, out to maybe 1 ly. This is made of chunks
of ices. It's really chilly so far from the Sun, but there has to be some
kind of residual vapor pressure, sublimed off these pieces of ice. So it's
just a light year out; well, that's enough room to get up a fair head start.
But what if it doesn't sublime? What if there's no appreciable vapor
pressure out there? Well, as humans, we have a general answer for
undesirable situations, we shoot. We have ways of making things
vaporize. A few months of burning a powerful laser should create a
channel of enhanced vapor through the Oort cloud. Accelerating
through this channel, our ship should build up enough speed to cope
with the rarefied environment of deep space.
I'm perhaps too optimistic, but I don't think the Broussard ramjet
scheme should be written off prematurely. It's such an elegant notion,
it's hard to let go.