Space Elevators

Subject should read Space Tethers, but this keeps it in-thread.

I note that the entire discussion of the topic has been about the Beanstalk variety of "Space
Elevator" (the synchronous skyhook), as is the entirety of discussion in the media about
the concepts variously described as "space elevators".
What about the rotavator or slingshot? Deployable from the top of an expendable booster
(for small, unmanned loads) with polyethylene, kevlar, or even fiberglass, and even at this
small scale, a boon to a bootstrapping space effort.

Beanstalk enthusiasts say that once we get industrial production of Buckytubes we'll have
it made. I answer that anything that brings the Beanstalk closer to reality just makes these
other versions of space tethers that much more important.
Space tethers, in the many varieties short of the Beanstalk, are indeed near term, feasible,
and useful to something less than a fully space-faring civilization (and I think there's
reason to argue that nothing short of this will be able to build the Beanstalk).

Bootstrapping space Communities with Micro Rovers and High Tensile Boot Laces
(Tethers). How to Start Building Cities and Factories Throughout the Solar System, for What
We Are Now Spending on Space, authored by Bruce A. MacKenzie, Space Studies Institute -
Senior Associate, and National Space Society - Director
http://www.ari.net/moon/forum/mp/mp-4/bootstrap.html

Tethers Unlimited, Inc. (TUI) is a research and development company specializing in
advanced space technologies and scientific computing solutions. TUI was founded in 1994
by Dr. Robert P. Hoyt and Dr. Robert L. Forward to develop products based upon space
tether technologies.
http://www.tethers.com/

See especially their Cis-Lunar tether transport system, and the Mars/Earth Interplanetary
Tether Transport System (MERITTS -90 days transfer trajectories Earth-Mars, using
Martian aerobraking and a tether at the destination). They have several patents of near-
term useful system ideas and very much R&D of the many questions regarding tethers.

The following is otherwise known as the Hypersonic Skyhook, and possibly deserves more
attention than any of the others (except possibly for Mackenzie's small Lunar system).
Certainly it's unfortunate that the hooplah over buckytubes and the Beanstalk takes
serious attention away from this.
Unfortunately I can't find anything else on the 'net which talks about Hypersonic Skyhooks,
sp you have to wade through the other (worthy) ideas on this site.

http://www.affordablespaceflight.com/step3.html

In particular, it's important to think in terms of which combinations of systems might work
well.
Some sort of ground-based rail/sled (short of an evacuated tube catapult) would be good
for spaceplanes. Boost it to mach .8 or so while on level tracks, and you increase the
payload of a hypothetical SSTO plane by 40% (or make a SSTO possible, with this "zero
stage").
Next, use air-breathing laser thermal boost for the ascent while in the lower atmosphere
and close to the launch site. Possibly, for later times, inject monopropellant into the
chamber. In any case, use the hypersonic skyhook or rotavator for the final lift up into
space.

Any of these systems, from the rocket we know, to the tether or lasers, if used alone or
with only one other method, needs to be too far out, too advanced, too specialized and
expensive to develop (especially for a manned payload). Instead, use each in the part of
the flight where it's strengths are maximized and it's shortcomings minimized or
eliminated.