Using Concrete to build space ships...

Hello Val,

>>
>>It would be rather cheap reachable with inexpensive missions using
>>very lightweight space crafts like the ion thruster driven Japanese
>>Space probe Muses C which is out to get asteroid samples now.
>>
>>The possibility to get resources without having to struggle with a
>>steep gravity well shows so much potential that we should do that step
>>first.
>
>Because of the masses involved, I don't think ion thrusters would work. If
>we are looking at bringing in several hundred thousand tons, what would an
>ion engine have to be like to move it in a reasonable amount of time?
>

Several hundred thousand tons are a lot, I have to admit.
However that is earth weight you mentioned.

If we handle that in free space, shouldnt it be a lot easier to get
it moved?

The hardest part to move those earth equivalent tons would be to get
them off of the asteroids.

For instance the asteroid 1998 SF36 were the Japanese space craft
Muses C (which is propelled with 4 ion thrusters) will try to land
next year take asteroid samples and bring them back to earth.
see
http://www.spacedaily.com/news/japan-muses-c-04a.html

This asteroid has an estimated size of 490 by 180 meters and an
estimated gravitation of one 750 thousandth of earth gravitation.

That means asteroid materials which have a weight of one ton on the
asteroid have an earth weight of 750 thousand tons.
The concrete cycler would have (only :-) a mass of about 220-230
thousand (earth equivalent) tons.
So moving about 350 kg asteroid weight material of asteroid 1998 SF 36
would get you the materials for the cycler spacecraft.

Now we would come to the ion thruster driven prospector crafts. The
crafts I have envisioned would have about 120 millie Newton of upward
thrust, thats about 12 grams.

So I figure they would be able to lift about 4 grams of asteroid
weight materials off the asteroid (with a safety margin), that's
equivalent to 3 tons on earth for each fare.

Those prospector probes would not deliver the material to the
destination if that would be far away. The would simply dock into the
carrier which has a lot more of thrust.

Frank