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# Re: Orbit B

```Timothy van der Linden

>Kelly
> >But I suppose it isn't critical for our discusion.  Assumeing a beam
> >diameter 40 times the dimeter of earth.  4.76Km/s will still have you
cross
> >the beam in 31 hours.

> Yes, but theoretically you could build the beam-array much farther away
from
> the Sun. I guess the only limit is where the gravitational acceleration of
> the Sun becomes less than that of nearer bodies or less than the
> acceleration caused by the beaming itself.

Which means you lose the beam in the middle of no where?

Anyway for the system to work the beam reflectors would need to hold place
for years.  Which orbital mechanics wouldn't allow.

The problem of the beam push on the other hand is critical, and I'm surprised
I didn't think of this (maybe this cold is worse than I think?).  The
reflectors would be boosting at 10 m/s/s from the beam. FGorget about orbits.
You won't even say in the star system!

> Besides that, you assume the array is moving perpendicular to its beaming
> direction. Since the array is slowly moving in a circle it could start
> beaming at a time where it's own motion is in about the same direction as
as
> the direction of the beam. This way the perpendicular movement is much
less.

That would make for trickier orbital choices, and still.  Could that keep you
in the beam for years?

> >>Don't we already have computers that could be programed to reasonably
figure
> >>this aiming problem out?
> >
> >They could given current accurate info.  But given that the info has to
> >travel at the spped of light, it would be months out of date by the time
> >the mirror systems got it.  Given that the actuall rates will varry back
> >and forth a bit durring the interveaning time (given random flexing of the
> >sail, and random variations of the beam), and we can't predict what these
> >variations will be.  The aiming calculations will be precise calculations
> >bases on very bad information.  I.E. computer generated guesses.  Even
> >assuming not one unexpected thing ever happens on the ship or mirror.  If
> >you guess wrong even once.  You're aiming the beam into empty space and
the
> >ship is racing away from where you think it is.
>
> >Just to complicate things.  The mirror is moring at a high fraction of the
> >speed of light.  So relatavistic distortion will distort the beam, mirror,
> >and apparent space.

> All this is irrelevant, computers could calculate the path far in advance.
> Besides that, the Asimov could follow the beam (up to certain limits).

Ha, you have a lot of misplaced faith.  Calculations only work when you can
rely on acurate data.  In this case the data would be months old, and we'ld
have no way to know exactly what happend in the mean time.  Any slight
deviation or flutter (inevitable with these huge flimsy structure) and the
ship would not be doing exactly the speeds and accelerations we think it
would.

Follwing the beam might be possible if the angular change was minimal.  But
given the high speeds and accelerations involved I'm suspicious.

Kelly

```

• Follow-Ups:
• Re: Orbit B
• From: Kevin C Houston <hous0042@maroon.tc.umn.edu>