Re: starship-design: HIGHLY OPTIMIZED TOLERANCE

[Steve VanDevender <stevev@efn.org>]

Curtis Manges writes:
 > > Typical velocities of nearby stars relative to the sun are in tens of
 > > km/s.  The expansion of the universe is only significant on an
 > > intergalactic scale; orbital motion around the galactic center dominates
 > > the motions of stars in our neighborhood.
 > >
 > > While you'd have to take the relative motion of your destination star
 > > into account, its relative velocity is going to be pretty small compared
 > > to your spacecraft's velocity if you're planning on getting there in
 > > anything less than thousands of years.
 > 
 > Thanks for straightening me out on that. Would I be right in guessing that
 > the time scale is about similar to the precession of Earth's polar axis? I
 > know Polaris wasn't always the pole star . . .

The Earth's precession is caused by tidal interaction with the Moon, and
it takes about 22,000 years for the poles to precess through a complete
circle.  The rotation period of the Galaxy is something like 250 million
years.  The two phenomena aren't really related.