Using Concrete to build space ships...

> Would it be safe to say that the propelling of the
> ship is the more difficult detail? To have both
> radiation shielding and artifical gravity you are
> going to have high mass one way or another.

The 220,000 tons of concrete will have to come from somewhere. I
haven't been following this thread that closely, so I apologize in
advance if I've missed some crucial detail, but my understanding is
that this material would have to be fetched from some NEO. Just
hauling that material back down to L1 or LEO is going to take fuel.
Where will that come from?

By the time that we need cyclers to Mars we should have the ability
to land on NEOs and mine them while they ply their orbit.

Also consider that even if you break the whole asteroid apart, all
of the pieces will still maintain their velocity. They can be
reconstructed into a manmade cycler if you wish to go to that
trouble, and in such a process you won't have to accelerate the
whole mass of the ship and put it into a cycler orbit.

The issue of radiation shielding doesn't necessitate using concrete
for a thick outer shell. Unless it is unmanagably thick the concrete
will produce all sorts of secondaries from the cosmic rays.

The ideal solution is to use shielding that has a high component of
hydrogen, for when hydrogen is struck it doesn't produce secondaries.

Here is a newsgroup thread that discusses shielding:
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-
8&c2coff=1&threadm=joe-110619990843271502%
40chinacat.salk.edu&rnum=1&prev=/groups%3Fq%3Dradiation%2Bshielding%
2Bwater%2Bcosmic%2Brays%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%
26c2coff%3D1%26selm%3Djoe-110619990843271502%2540chinacat.salk.edu%
26rnum%3D1

Read the 2nd response written by Geoffrey Landis.

Here is another take on the same situation:
http://groups.google.com/groups?
q=radiation+shielding+hydrogen+cosmic+rays&hl=en&lr=&ie=UTF-8&oe=UTF-
8&c2coff=1&selm=79cf0a8.0310101942.7dae63d7%
40posting.google.com&rnum=7

Here is a quote from the "Lunar Base Handbook" p.522

"Light elements such as hydrogen, carbon and oxygen and their
compounds, such as water and plastic, are the most effective shields
per unit mass. In charged particle shielding applications, lead and
other heavy elements are poor shields."

p. 523
"Furthermore, if any materials used as a radiation shield can serve
a dual purpose, mission costs can be reduced. Other examples of dual
use materials are food, water and waste water."

The folks over at Moon Miner's Manifesto have already calculated the
shielding difference between regolith and water.
http://www.asi.org/adb/06/09/03/02/104/design-rad-protect.html

"Combined primary and secondary radiation effects are reduced to a
level of about 0.5 REM per year by a radiation shield composed of
regolith type material which is about two meters thick or a water
shield of about five meters thickness."

As I wrote before, on your ship or your cycler, you create a large
tube. The wall thickness on the tube is five meters. The walls are
hollow and filled with water, and waste water. Inside the tube are
the living sections of your ship. Outside the tube are the storage
and equipment functions. Nothing bad will happen to the crew when
they have to make brief excursions outside the living section.

Further, rather than being dead weight like the concrete hull, the
water serves as life support, is still useful as it is being
recycled, and you need less mass than you would for a concrete hull.

Also, if you have electrolytic cells on board and a source of power,
the water can be a very easy way to store emergency oxygen. No need
for cryogenic tanks. If you have a hull leak, just patch it, take
some water and split it and you've replaced the oxygen. Do the same
with some liquid ammonia and you've replaced your nitrogen.

> I have heard somewhere that the Russians can use
> oxygen in their ion systems. If true this would
> eliminate the dependency on terrestrial Xenon.

You're probably referring to Hall Thrusters. They can use oxygen,
but the oxygen is very corrosive. It's not a good idea. You really
should be using a noble gas like Argon, Xenon, etc.

TangoMan