Using Concrete to build space ships...

>Val and Frank, I'm still uncertain as to the advantages of this
>concrete spaceship you're envisioning. You guys seem to be ignoring
>the rocket equation, or are under the impression that it only
>applies to launches from Earth. Even if you launch from orbit, you
>need fuel. You need more fuel at the beginning to propel the fuel
>itself. The only thing that is different is that you don't need to
>achieve as high a delta-v.

Part of my proposal was using a solar sail carrier craft to transport
smaller prospectors and their payload.
The prospectors would fly but mainly between carrier and asteroid.

The carrier does not need fuel for propulsion. Although in this case
would it need some fuel but only for steerage.
A carrier of 1 km diameter would produce about 7 Newton of constant
and free thrust.

So for the building phase transportation would be cheap.

As the building material transportation would be cheap we could build
the cycler on the earth-sun libration region were the sun and earth
gravitation outweighs each other.

When we would push the cycler toward earth, earth gravitation would
help to accelerate the craft.

As a feather is accelerated as fast as a piece of steel through
gravitation, the cycler would be accelerated as fast as the feather
also through the gravitational pull of earth - regardless of the
cyclers mass.

So we have gravity assisted slingshot propulsion for free acceleration
of the cycler available which could be additional supported through
the cyclers thrusters. Just doing the first push and the craft will
start accelerating.

The standstill which you see as a disadvantage has the advantage that
you need a lot less energy to point to the exact orbit youll like as
you would need to change the inertia of a fast moving asteroid already
influenced through earth gravitation when we would get to it.

>
>Here is a paper on Earth-Mars Cyclers:

Thank you for the links, I will take a deeper look this weekend.

Frank