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starship-design: Re: Required microwave-antenna size. 100-light-year trip.

Kelly replied to me:

>> To overcome difficulties, building it on a moon would 
>> not be a bad idea
>No moon is large enough, nore would any point on them have a clear view of
>the ship at all times, and/or a clear view of the sun (assuming you want
>solar powered.

I cannot agree with both:

Moons can have a clear view all the time, you are probably thinking in 2
dimensions. Think of the polar star, it never goes under the horizon (that
is on most places of the Northern half of the World). So while some
locations on a moon indeed won't have a clear view all the time, lots of
other places on that moon will.

About the size, not being large enough, that depends on what interstellar
distances we want, and what wavelength we are going to use. (See today's
reply to Rex.)
For a clear view, in the best case we can use an entire half of a moon to
build on. (In the worst case we have nothing to build on, if our destination
is within the solar plane).
I've even been thinking of finding an asteroid and bringing it in the
optimal orbit. I know this sounds as if I'm creating a bigger problem than
the initial one, but all this depends on the mass of the asteroid. Getting
not too heavy asteroids in the right orbit may take far less energy than to
get our starship accelerated, since its final velocities are 4 orders of
magnitude lower. (8 orders less energy needed)
Of course one can also build a frame of lasers, instead of a lot of loose
ones (as Zenon proposed), the problem I see there is that their weight may
be too little, so that gets blow away too easely by its own "photon-recoil".
(I have some ideas how to get rid of this, but some are a bit complicated.)