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Re: starship-design: Massively Distributed Computing for SETI

In a message dated 3/18/01 3:53:39 PM, lparker@cacaphony.net writes:

>> 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
>proper motion relative to us. However, you are correct, that most do not,
>you average for the effects of our own planetary orbit.

Agreed.  Actually, how many if any do show serious "drift"?

>> >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.

True, but if you have a problem with the ship that will let it follow the 
beam, but not stay on the correct acceleratio schedule.  An untracked beam 
will still work as well.  One optimized for a ship at a precise position, 
might be useless.

>> 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 don't follow how that relates to my comments about beam dispersal or 

>> 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.

I would assume this was only possible within a couple light weeks or perhaps 
months.  That would seriously restrict speed.