Using Concrete to build space ships...

Hi Frank

1) "While those big mass numbers for concrete hulls
seem to be steep, compare that with the material
masses you would need to make them of steel.
How many tons of ore you would have to dig out and to
process?
I guess this would be considerably more for a steel
hull than for a concrete hull."

Yes iron refining involves a lot more energy and mass
than concrete for sure. The trick is that iron is
useful for a lot of items concrete isn't so you would
need iron production facilities regardless. The iron
on the moon is strategically located close to the
astronauts, easy to control from earth, and able to
ship to orbit without much fuss. Aside from water the
asteroids do not offer much else.

In comparison, the really big consumers of energy are
the production of Silicon and Aluminum for solar
panels and electrolizing water for propellant. These
are an order of magnitude more energy intensive than
iron production. It is not going to make that big a
difference if you use 5% vs 10% of your power to make
iron.

2) "Yeah and you probably have to dig it out perhaps
going underground (mining) while I think getting the
materials for concrete is mainly picking them off the
ground of asteroids. So youll need no mining
gear."

If you have a manned mission to an asteroid backed up
with a pre-existing structure and processing
facilities, then I agree - it would be a snap. Short
of this you have long communication delays which make
the reaction time of low gravity environments an
action every couple of hours rather than minutes.
Without some sophisticated robotic intelligence you
would be reduced to a glacial pace. You may not have
mining gear though everything else would be just as
ponderous.

3) "All this done with heavy gear youll need for
gravitation disadvantaged moon operations. 200
thousand tons of material are more
than 30 thousand tons on the moon but you would have
to process way more tons of ore to get a steel hull."

To start a decent moon base my current estimate is you
only need 100-200 tons of equipment. The biggest
thing you need is electricity and for that you
manufacture solar panels and distribute them about for
continuous power generation. It takes a decade to
build up giving you a solid track record and practice
making things on the moon.

Once you have small facilities you build bigger
facilities and so on. Really large manufacturing
facilities are not ponderous if you build them up
slowly. Processing large amounts of mass is
inevitable and gives rise to the sort of materials you
need to build the habitat to get to the asteroids.

4) "Also to get a decent radiation protection for a
steel hull youll need thick plates of steel, not just
thin metal sheets."

I envision thick plates with sharp crenellations so
that an impact is not head on and distributes the
energy laterally. Behind them is probably insulation
of fiberglass then another layer (double hull). After
this you get into radiation shielding without the
structural need so water, moon dust or any bulky
material would do just fine. Plant 6 layers of
gardens each .5 meter in thickness and you get food
from your radiation shield.

5) "Those plates would be heavy and as the mass
drivers payload capacity is limited youll need a lot
of metal plates (along with an ironwork
and a metal sheet rolling mill and a cutting facility
to fabricate the plates which is not trivial either
when located on the moon because you have to transport
it first to and install it than on the moon)."

Imagine a mass driver that looks like a sled that
hurls multi-ton sized objects of irregular shape.
Round mass drivers look to have some limitations that
might be tricky to overcome. With enough electricity
you can fire the thing every minute or so putting
1400+ loads in orbit per day. My big change is to add
an ion drive to each load to make it a guided missile.

All you need is a form and a lathe and 100-ton rollers
for a mill are pretty easy to create. Industrial
lasers do a pretty good job of cutting and there is
always extrusion to create simple linear forms like
bars and rods.

6) "Since you had a whole lot of metal plates welding
them together to a space ship hull will need a lot of
time consuming labor while filling
the castings with concrete to bind looks just simpler
to me and seems to be easier to accomplish with remote
controlled robots."

You might be right about the labor to cast concrete
into pressurized molds around the asteriods. Robots
that do not more than weld strips of metal into
circular hulls are easy to design as well.

Iron hulls solve the impact debris problem pretty well
and you can cut into the structure at any point to
make additions and modification easily. In case you
had to make a serious repair or change, all of that
concrete would work against you unless you have
figured out a way to seal the cracks.

Cheers, Thor