Travel-time to GEO (LEO vs GSO; colony-isolation tests)

> > are there reasons -- besides launch or orbit-transfer energy
> > -- for preferring LEO to geostationary, or higher, orbit?
> Yes: there's travel time to/from Earth (which is quite a separate
> issue from the energy requirement)

That sounds like a good point -- and it is one on which I am
ignorant. Please enlighten me. How long does it take to travel
from Earth to LEO vs to GEO?

By the way, I have heard different figures for the energy. This
recent Mike-Snead post seems to claim it is only double (or less):
http://spacefaringamerica.net/2007/12/14/response-to-reader-comments-
on-sa-blog-17.aspx
http://tinyurl.com/6nppzf

"The assumption used during the study was that the satellite mass
would be 20,000 tons. This value is doubled to add mass for
propellants, on-orbit assembly support, payload holding structure,
etc. Assume 40,000 tons for each SSP satellite needs to be
transported to LEO and 20,000 tons to GEO."

> radiation shielding tends to dominate the mass of a space habitat,
> especially if you choose some volume-inefficient geometry like a
> torus.

In my back-of-the-envelope figuring, I am usually trending toward
larger, and therefore more space-efficient relative to shielding,
structures -- in order to be able to accomodate a reasonable mass
of brainpower. For example: a one-mile diameter sphere, possible
with some guyed ladder-towers sticking out from the equator to
help ensure rotational stability. The surface area of such a
structure would be 3.14 square miles. If the shielding were 600 lbs
per square foot (equivalent of about two meters of dirt), the mass
would be pi * 5280 * 5280 * 600 = ~53 billion pounds. Hmmm. That's
pretty massive. Maybe the shielding requirement could be reduced.