# Re: starship-design: Massively Distributed Computing for SETI

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>[...]
>> >"Moved visibly" is not the same thing as haven't moved. All stars are
>in
>> >motion, they follow their own orbits about the center of the galaxy
>> >as I am sure you know. Our sun is in one such orbit, any target star
>> >is going to be in another orbit traveling at a different velocity.
>> >
>> >We cannot simply aim the beam at the star, the star will not be there
>when
>> >the beam arrives. We must aim the beam at where the star will be when
>the
>> >beam gets there. This is a non-trivial task considering that all distances
>> >to stars are currently _estimated_.
>>
>> 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.)
>>
>For a starship what is important is not the _relative_ change
>of the star position with respect to its distance from the center
>of the Galaxy, but _absolute_ change of its position
>(in light years, say). If the star moves a light year with respect
>to the aim of the starship, the starship must simply travel
>this additional light year (laterally, say) in order to catch it,
>no matter how far (or near) the center of the Galaxy is.

Relative movement is related to the degree of difference of the orbit.  In
this case the fractinal difference would be trivial.  As long as the two
stars don't move relative to one another - effectivly they can be treated as
unmoving for nav purposes.

>[...]
>> 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.
>>
>Notice however, that the lateral movement of the beam due to
>any jitter od the beaming antenna will be rather rapid - in fact,
>it may easily exceed the speed of light!

So don't jitter.

>Also, helical tacking to follow the orbital path (around the Sun, say)
>of the beaming antenna will use lots of additional fuel,
>since it must provide constant acceleration to curve
>the path appropriately.

Or you'ld need to tack the sail.  Eiather way the fuel costs would be trivial
compared to the main boost.

>
>-- Zenon Kulpa
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