RE: starship-design: Massively Distributed Computing for SETI

["L. Parker" <lparker@cacaphony.net>]

> I can't see how this wouldn't be a trivial problem?  Your not
> talking a high
> lateral movement, or any delta-V of the two stars.   On the
> scale of the
> galaxy the two stars are right on top of one another.  (A
> couple light years
> out of a 30-40 THOUSAND light year orbital radius.)

It all depends upon which star you choose, some do display quite a bit of
proper motion relative to us. However, you are correct, that most do not, IF
you average for the effects of our own planetary orbit.

> >
> >Then you must add for the motion of the beam array in its
> orbit about Sol.
>
> Already covered the other problem.  Tacking, or otherwise
> manuvering into the
> path of the beam is nessisary.  If you fly out of the beam
> you'll need
> secoundary motors to manuver back into the beam.  You'll need
> manuvering
> engines anyway for in systems work.

Tacking is quite possible, it also puts unnecessary stress upon a rather
delicate craft. If it can be done at the emitter, it should be done there.
Repair from Earth is easy for the emitter. If you break a halyard between
the stars, no amount of paddling is going to get you home.

> Note, I've always assumed beam dispersal would make beamed
> power useless out
> more then a few light months from the transmitters (hence my
> fuel-sail idea).

Actually, this is probably the best point of all in FAVOR of beamed
propulsion. Remember that aperture size controls beam width and with an
array of emitters in orbit, we could have an aperture as large as we wanted,
just pick the proper orbit. There are some trivial corollary problems such
as maintaining the emitters' orbits, but I can think of several solutions.

> I'm wondering how bad the dopler shift would disrupt the
> acceleration of a
> sail driven craft?

As I said, it depends upon how fast we get the sail going, what the
acceleration rate is, and what type of beamed power we use. A solar pumped
optical laser, or for that matter, just a whole bunch of solar collimators
(fancy mirrors) would due the trick without having to worry quite so much
about Doppler effects.

> It is completly impossible that we would be able to precisely
> know the
> possition and sppeed of a ship months or years after the last
> view of it.
> Any system that has to depend on that would be to dangerous
> and unrelyable.
> So the system must be designed to not need to rely on that degree of
> precision to function.

Depends upon what you mean by "precisely". Yes there would be an ever
growing feedback problem. But barring some catastrophic course change event,
we should be able to build a good enough profile while the sail is still
within reasonable communication range that we can compensate for the lag.

Lee