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From: throopw@dg_rtp.UUCP (Wayne Throop)
Newsgroups: net.space
Subject: Asynchronous orbital skyhooks (those two masses...)
Message-ID: <70@dg_rtp.UUCP>
Date: Thu, 2-Jan-86 15:30:52 EST
Article-I.D.: dg_rtp.70
Posted: Thu Jan  2 15:30:52 1986
Date-Received: Sat, 4-Jan-86 04:46:20 EST
References: <8512312026.AA15784@s1-b.arpa>
Lines: 63

> At the intersection point the masses are moving
> with a relative velocity of ~6000 mph (~2.7 kps).  A deceleration
> of 5g for 1 minute will bring them to relative rest - which doesn't
> seem too hairy.

I was assuming that the join must happen in a few dozens of meters
distance, or at most a few hundred meters.  To happen over many tens of
kilometers as proposed above is much more reasonable.  But about the
only reasonable thing I can think of that would provide that kind of
interaction between two masses over that kind of distance is a skyhook
variant of some sort.  Can a currently-designable skyhook provide ~2.7
KPS of delta-v?  I suspect so.

I'm not sure how to position and maintain the skyhook (or any other
"joiner" device) in the two masses scenario, but this is much more
reasonable than what I read into the proposal at first. (I was led to
imagine an inelastic colision of two relativly small, dense, balls of
silly-putty.  Splat!  :-)

But what is wrong with the more "traditional" scenario of an
asynchronous skyhook in medium-high orbit?  Once constructed, it could
provide the couple-of-KPS-delta-v needed to modify a long eliptical
orbit (or suborbital arc) into a more nearly circular orbit, and could
be kept on station by performing the reverse delta-v on ballast masses.

(Note that these ballast masses could be provided from a ground
catapult, or from high orbit.  Providing the ballast from the ground is
quite similar to the two-masses scenario, but the "join" strictly
speaking never happens, and the interaction between the cargo mass and
the ballast mass (which in this scheme might also be a cargo mass!) can
be time-delayed.)



Question: Is a (ground-catapult / orbital injection skyhook) system more
economical than a (ground-catapult / traditional injection via a
reaction motor) system?  Even with the orbital skyhook, the injection
would probably have to be modified by a "trim" reaction burn to get
really good and precise orbits, and the station-keeping activities for
the skyhook are probably not trivial.

Answer: I don't know.  I expect there is some volume of traffic at which
        a skyhook would be more economical, but not at the low volumes
        we now have.

Question:  since synchronous orbital skyhooks are considered feasible
for Mars and the Moon, why isn't more attention given to asynchronous
orbital skyhooks for providing various delta-vs in orbital injection
scenarios near Earth?  Is the idea intrinsically non-feasible, or what?

Answer: I don't know, but I suspect they are most useful if the ground
        catapult problem is solved, and ground catapults aren't too
        terribly feasible yet.

Question: Why wouldn't an asynchronous skyhook allow a high-flying
air-breather (or detachable part thereof) to be injected into LEO?

Answer: I don't know that either, but it may have something to do with
        "drag".  Also, feeding such a skyhook ballast wouldn't be
        cheap.  Sigh.
-- 
Wayne Throop at Data General, RTP, NC
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