(Richard Alexander) writes:

I like the plan to have a perpetually cycling ferry running between
Earth and Mars. It could be a simple craft.

I like the idea of a cycler, too.

http://www.spacer.com/news/tourism-02b.html

http://clowder.net/hop/railroad/railroad.html

Maybe we could beam power
to it, perhaps by laser to solar panels? Then, we would could have
simpler, lighter and safer power for the astronauts (the only
realistic alternative would be nuclear reactor, which is fine for
unmanned craft, but not so great for manned).

Beaming wouldn't be practical: once an orbit or so it would be behind
the Sun. There would also have to be multiple beaming stations on the
Moon since the Moon revolves. In addition, I don't think you could
focus a beam at interplanetary distances (without a REALLY big lens).

I'm in favor of one or more nuclear reactors, perhaps with solar
panels as alternates.

It seems to me that we need something with a lot of volume for long
distances. It doesn't need a lot of mass, maybe something like a big
bubble.

ASSUMING the human body needs some "gravity" to stay healthy in the
long run, we need some rotation. I favor a central core, with
storage, landers, main engines, etc., and two habitat modules on long
cables or "towers" (masts for rigidity).

At 2 rpm and .5 g, the cables or towers would be 450 m each. In
comparison, the Eiffel Tower is 300 m, the Petronas Towers are 452 m,
and the CN Tower is 553 m.

To accelerate, the cycler could reel in the habitats, if they were on
cables, or have strong enough masts or towers (or have independent and
coordinated rockets on each section).

-paul-
--
Paul E. Black