Using Concrete to build space ships...

--- In ssi_list@... "Valens Agnitio"

> I am not so sure that we need hydrogen for the nuke idea. It seems
> that pretty much anything can be heated to plasma and accelerated
> out the back. Why not use materials organic to the cycler itself?

Hydrogen gives you the most kick for the buck. Its low mass gives a
higher ISp which in turn lowers the fuel mass fraction of the rocket
equation.

You can though use other gases in the chamber. You could also go
solar electric, and get the same advantage of nuclear, but in that
case you'd need solar infrastructure.

I'm not sure if this idea of yours is applicable to the crew vehicle
that transports everything to the asteroid or to the asteroid
itself. The former I can see, the latter I can't.

> If not, the only real obstacle is
> the hysterical Greenies. If they can be byppassed, then we just
> launch from Earth.

While I'm happy to also poke fun at hysterical Greenies, let's be
fair and acknowledge that there are many people who aren't keen on
having nuclear material sitting ontop of rockets that are known to
blow up in flight. No amount of engineers talking on TV will
reassure these folks. Especially if they are NASA engineers. Look
how well they handled the shuttle.

Nuclear is a big, political *Hot Potato.* Good luck.

> Here's an idea for you: Start the fully constructed skeleton
> on the way to mars, and then launch buckets of regolith after it
via .......

Where will the regolith come from? Where will the launch equipment
be stationed? How will you catch the regolith that is arriving at
4.3 km/sec?

> A good concept. The crew can build their own shielding from the
> asteroid when they get there, and leave it for follow on crews.

Yes. Good idea.

> So, it will take a long time before it's a danger...

They won't be any more a danger than an orbiting satellite. Orbital
mechanics is a very predictable subject.

> They will need corrections. I doubt that we can place them
> accurately enough to obviate the need. In addition, there will be
> loads on and off, which you yourself pointed out would change the
> orbits to a small degree.

Considering that the bulk of the mass is the ship, and the cargo and
passengers will be a small fraction of the total mass, the energy
lost and gained by mass shifting will be small and easily
correctable, and would only result in a small velocity change.
Nothing severe here after the cycler is in operation.

> Interesting ideas, and sound as well. However, suppose most of
> these things are just rubble piles, and there aren't any that are
> suitably close to what we need. Then building the cycler may be a
> necessity.

Hard to tell at this point. That's where probes would be helpful. If
it is a rubble pile, then you can move on to another asteroid, or
mine it for material to fabricate a man-made cycler rather than
burrowing into the asteroid.

TangoMan