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Re: starship-design: Still doing stardrives?

Hi Group

----- Original Message -----
From: Johnny Thunderbird <jthunderbird@nternet.com>
To: L. Clayton Parker <lparker@cacaphony.net>
Cc: <KellySt@aol.com>; <starship-design@lists.uoregon.edu>
Sent: Tuesday, February 16, 1999 5:18 PM
Subject: 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
>> 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.
We could be on the inside of a bubble which has swept up near space's matter
into a "high pressure" front, leaving a relative "vacuum" behind it.

>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
Oort comets are a lot less dense, if spread out, than interstellar matter. A
trillion comets may seem huge, but the volume they occupy thins them out.
Comets could be mined for fuel, but they aren't likely prospects for
scooping up as you fly.

>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.
>Johnny Thunderbird
Perhaps a better system would be to beam "propellant" at the ship. Leave all
your power and fuel at home. But Bussard ramjets make continuous
acceleration almost possible, if we can reduce the drag of the scoop fields.
Presently there's no clear way on just how that can be done. Magnetic
braking however is a real possibility and it dramatically improves starship
performance. Other possibilities involve fringe physics - tapping GUT
energy, or the Higgs field, or quantum vacuum energy - and are just a bit
beyond our current reach. When we know just how the 11 or so dimensions of
space-time are folded up then we might be able to figure out how to bend
space to our needs.