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RE: starship-design: Still doing stardrives?

> 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
> 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

Well, the ramscoop idea may return if we learn how to control EM fields tens
of thousands of kilometers in diameter. Given the current local densities it
would be impossible to build such a scoop out of material substances. To put
a little perspective on this try this:

Most of the listers here have heard of beanstalks. Using the top of the line
in current technology we could just barely envision building a beanstalk out
of buckytubes or diamond fiber or some such. In these schemes the loading
(force vector) is parallel to the axis of the beanstalk. This axial load is
the beanstalks strongest dimension. Now to build a scoop 10,000 kilometers
in diameter, we must do the same thing, but each radial spoke can now only
be few millimeters thick, must be much longer than a beanstalk, and the
force vector is now a shear load and has increased in magnitude several
times. Now add to this the additional load imposed by the impact and
channeling of tons of interstellar hydrogen impacting the scoop at 1/3 c.
See the problem?

A properly designed EM field on the other hand weighs only as much as the
generator. It is deep as well as wide so that deflection occurs gradually
rather than abruptly. It "attracts" the particles ahead of it, this
attraction actually increases the acceleration of the ship. In fact
theoretically, if the field could be made strong enough, you wouldn't need
engines...just grab the interstellar medium and fling it backwards. Of
course, this is well beyond anything we currently know how to do

Lee Parker