Ice as rocket fuel

Ian Woollard wrote:
> Check out http://www.neofuel.com/
>
> He talks about using ice/steam as a propellent. He uses two
possible energy sources, solar and .... another.
>
> It's got lots of really cool designs. The only problem with steam
is that it has a fairly poor ISP (about 190-200)

> George Perkins wrote:
>> I'm interested in a small space-only craft that can run on
blocks of ice that you can easily shove into it.

Another option is something like laser-thermal. It requires a lot
of infrastructure, for power & laser emplacements, but eventually,
it may be only slightly less competitive than mass drivers (which
can use waste rock, instead of H2O).
It would be ideal for Earth surface to LEO travel, if you need the
extra reaction mass above the atmosphere.
For lifting from the Lunar poles, it would work, but as with
rockets, it would still use more ice than you'd deliver to LLO.

If ice is available in Cis-Lunar space (when somebody brings
back an NEA), then SPS/laser stations could push things around
pretty handily.
This is philosophically similar to using microwave stations
(SPS) to beam power to mass-driver instead of mounting solar
cells to the ship itself -then there's beamed power lightsails.