keithl@vice.UUCP (Keith Lofstrom) (11/29/83)
I wrote the Analog article under discussion; I thought I'd sit back
and watch people argue for a while. It's been fun watching; I think
I'll jump into the coriolis whirlwind ( :-) ).
First, I must have missed the reasons for moving the Launch Loop to the
northern temperate zone; I know it puts you closer to Earthside business,
but it has problems:
1) More plane changes are required to GEO, lunar destinations.
2) Militarily, the Loop is more threatening and an easier target.
3) Off-equator weather is NASTY.
4) Less over-ocean area, more populated areas in launch path.
There are more problems, but you get the idea.
Coriolis "forces" are not a problem, directly. The path followed by ribbon
and track is more-or-less a ballistic one; the ground track is CURVED the
same way the ground track of an inclined satellite orbit is. Sure, lots
of side forces would be required to make a Loop follow a latitude line,
but there is no reason to do so.
Another way to think about it is to imagine an ~8000 m/s (orbital velocity)
gun at West station, and a target at East station. With proper aiming,
and the right velocity, you can hit the target at East station, wherever
that is, with no further forces applied to the projectile.
The ribbon path is "aimed" in a similar manner. Note that the return track
must be lighter than the forward track, the ballistic effects are similar to a
projectile velocity change.
The real problem is that the retrograde "return" ribbon will have a
different curvature than the prograde "forward" ribbon. The two tracks
will form a complex lens shape:
^^^ to pole ^^^
forward .................... - - - - latitude line
..... .....
... reverse ... greatly exaggerated in
.. ---------------- .. horizontal direction
. ------ ------ .
. ---- ---- .
. --- --- .
West Station East Station
The return track is used in the Loop as a stable measurement platform,
to gauge the amount of correction force that must be applied before the
forward ribbon reaches East station. If the tracks are further apart,
the measurements become more difficult. If the Loop is at the North Pole,
the spacing between the tracks is approximately 5 kilometers in the middle;
the measurement interferometers will have to track well.
Forcing the tracks into the same path does require a significant force;
the mechanical coupling implied by that force can lead to gross system
instability (perturbations do not propagate properly to the stations).
All in all, I think I'll stick to the equator.
Further information on the Launch Loop is in the December 1983 Analog,
on sale near you, with a supplemental article available from
Launch Loop, P.O. Box 1538, Portland OR 97207
(by the way, if you send netmail, please include a complete return address
to a few major USENET nodes; the header doesn't often work).
--
Keith Lofstrom
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