hello,
For instance the walls for a Bernal Sphere.
As I see it, we would have to get a temperature above frost limit for
the concrete to bind.
That would make a near sun location my first choice were it is
possible, to use direct sun irradiation to heat up the concrete. For
instance using black painted forms for the parts of a bernal sphere
and than place it in a appropriate distance to sun to get the positive
overall temperature .
But what about mixing sand and beton? How to hold sufficient pressure
in the form-parts in an no gravity/ micro gravity environment?
Would artificial gravity through rotation be enough to get this job
done since the concrete wouldnt have enough contact to the
rotating form or mixing drum when pouring the material into them.
I am assuming that material is used from Near Earth Asteroids and
cheap extraction of ore/regolit and transporting problems are solved
through the use of solar sails.
Regards
Frank
> hello,
>
> I am wondering how to concrete in space.
>
> For instance the walls for a Bernal Sphere.
>
> As I see it, we would have to get a temperature above frost limit
for
> the concrete to bind.
>
> That would make a near sun location my first choice were it is
> possible, to use direct sun irradiation to heat up the concrete.
For
> instance using black painted forms for the parts of a bernal sphere
> and than place it in a appropriate distance to sun to get the
positive
> overall temperature .
>
> But what about mixing sand and beton? How to hold sufficient
pressure
> in the form-parts in an no gravity/ micro gravity environment?
>
> Would artificial gravity through rotation be enough to get this job
> done since the concrete wouldnt have enough contact to the
> rotating form or mixing drum when pouring the material into them.
>
> I am assuming that material is used from Near Earth Asteroids and
> cheap extraction of ore/regolit and transporting problems are
solved
> through the use of solar sails.
>
addresses the use of concrete for Lunar Base Construction.
It should answer most of your questions and quite probably, help you
form more questions :)
http://f3.grp.yahoofs.com/v1/MDEyPznQiavhxAe84l29-
ktJx9aIgADQcKSNBtTgWahbzuvu9rxGuqIzyRgRdAgom9naFWoGIhLRftZYgvsh8PbzkD
5k5aLmcdi5Xw/Concrete%20for%20Lunar%20Base%20Construction.pdf
TangoMan
>I've uploaded a file to the FILES section of the website that
>addresses the use of concrete for Lunar Base Construction.
>
>It should answer most of your questions and quite probably, help you
>form more questions :)
>
>http://f3.grp.yahoofs.com/v1/MDEyPznQiavhxAe84l29-
>ktJx9aIgADQcKSNBtTgWahbzuvu9rxGuqIzyRgRdAgom9naFWoGIhLRftZYgvsh8PbzkD
>5k5aLmcdi5Xw/Concrete%20for%20Lunar%20Base%20Construction.pdf
I am getting a "Document not found" when using this link.
Frank
>
> >I've uploaded a file to the FILES section of the website that
> >addresses the use of concrete for Lunar Base Construction.
> >
> >It should answer most of your questions and quite probably, help
you
> >form more questions :)
> >
> >http://f3.grp.yahoofs.com/v1/MDEyPznQiavhxAe84l29-
>
>ktJx9aIgADQcKSNBtTgWahbzuvu9rxGuqIzyRgRdAgom9naFWoGIhLRftZYgvsh8Pbzk
D
> >5k5aLmcdi5Xw/Concrete%20for%20Lunar%20Base%20Construction.pdf
>
> Hello TangoMan
> I am getting a "Document not found" when using this link.
>
> Frank
the top line, into your web browser.
Alternatively, go to the website, and in the menu on the left side
of the page, click on FILES, and youy'll see the file amongst others
there.
TangoMan
Message The way to look at it is this: the only thing which makes lunar material "ores" (which is only defined as material from which it is economical to extract a substance) is the high cost of lifting materials off the Earth. If not discussing in the context of major construction programs in cislunar space, we would call these ores "dirt", which is in fact what it is. It's like TangoMan said, who's your competition? Launch costs make dirt off the Earth economically competitive with the most highly prized ores found on theEarth.
Mike Combs
I don't
want to go too far into Mining metallurgy, but there are some very
basic misconceptions that I hear with respect to lunar materials.
The first one is that the various percentages of mettles reported by
the Apollo analysis are readily available..
>The way to look at it is this: the only thing which makes lunar material
>"ores" (which is only defined as material from which it is economical to
>extract a substance) is the high cost of lifting materials off the Earth.
>If not discussing in the context of major construction programs in cislunar
>space, we would call these ores "dirt", which is in fact what it is.
>
I do not think of lunar material. I am thinking of material derived
from asteroids as near to sun as possible.
Were low gravitation makes it possible for solar sails to land on and
starting of with the additional help of ion thrusters
(for the solar sails I am thinking of see at
www.solar-thruster-sailor.info look under "STS")
The robotic construction process being in place near the asteroid.
So the asteroidal dirt would be ore in this case.
>It's like TangoMan said, who's your competition? Launch costs make dirt off
>the Earth economically competitive with the most highly prized ores found on
>the Earth.
But launch costs from the moon would be also more than launch costs
from an asteroid since the asteroid has only micro gravitation.
Frank
But launch costs from the moon would be also more than launch costs
from an asteroid since the asteroid has only micro gravitation. But the moon is much closer to the markets in near-Earth space. Travel times are days rather than months. But don't get me wrong, I'm not arguing that lunar resources are superior to asteroidal. I would only argue that each scenario have advantages and disadvantages. I wouldn't even place bets on which will happen first, but I think one way or another, both will happen.
Mike Combs
--- In ssi_list@... "Combs, Mike"
> OK, here's the cite. I was wrong about the article being in the
JBIS
> (probably was just remembering that the author was British), it was
> "Spaceflight". The author's name is D. J. Sheppard, and here's
the cite:
>
> "Concrete Space Colonies"
> Spaceflight, Jan 1979
Henry Spencer did a synopsis of the article back in 1998.
I'm copying below Henry Spencer's post to the sci.space.policy group.
Would you say that Henry's treatment hits all of the points that
Sheppard made in his article, or did Sheppard go into a lot more
detail?
TangoMan
BEGIN QUOTE
Let's see here, I finally got around to digging up the Jan 1979 issue
of Spaceflight... "Concrete Space Colonies", Dr. D.J. Sheppard,
Spaceflight v21n1, Jan 1979, pp 3-8. Summarizing quickly...
Normal civil-engineering practice accepts working stresses in steel
cables of 1100-1600 N/mm^2, about six times what is acceptable in
plate or rolled sections. The mass of steel in a Stanford Torus is
reduced by about a factor of 4 by using prestressed concrete rather
than a steel shell, using the same design rules (ASME Boiler and
Pressure Vessel Code, Section III, 1977) for both. (Other design
rules give somewhat different numbers for one or both -- there is a
table in the paper -- but the advantage of reinforced concrete
remains large.) Given that you need a lot of rock for shielding
anyway, it makes sense to use it structurally to reduce your need
for steel.
A quick sketch of a design concept for a Stanford Torus shows 1kt
slabs of fused lunar rock, 17x13x1.6m, as the basic materials. The
compressive stress is limited to 40 N/mm^2, about 10% of available
compressive strength, at full prestress before imposition of spin
and pressure loads. Window sections could either concentrate the
cables in narrow concrete ribs serving as window frames, or perhaps
(if glass manufacturing is easy and techniques for casting thick
slabs of high-transparency glass can be developed) simply replace
some rock slabs with glass slabs (compressive strength of glass is
quite high). Prestress would be applied gradually as construction
proceeded, eliminating most need for scaffolding etc. There is no
separate shield, the pressure hull is the radiation shield.
Prestressed concrete is safer than a metal shell for several reasons:
1. Cracks are harmless, whereas in a metal shell they are of great
concern.
2. There is extensive structural redundancy, almost impossible in
metal.
3. It is difficult to arrange a metal shell to leak before it fails -
- a highly desirable property -- while this is trivial in
prestressed concrete (the rock goes into tension, cracks, and leaks,
at a point where the steel cables are still in their elastic region
and hence have considerable reserve strength left).
4. All portions can be strength-tested during construction. The
rock is at maximum stress -- 2-3 times operating load -- before
pressurization and spin-up, and since this stress is all from the
prestressing, it can be applied as necessary for testing during
construction. The cable can be 100% proof-tested, in the same load
environment it will see in operation (single-axis tension), as part
of its production (this being one reason why the permissible working
stresses of cables are so high). Comparably realistic tests are not
possible for metal shell sections.
5. Rock is known to be stable and inert in both the internal
environment and the external one, whereas steel structures suffer in
the former (unless they are continuously repainted) and are unknown
in the latter. The cables are in a protected environment of their
own within the rock.
6. Cables can be removed for inspection, testing, and replacement
while the structure is in service. Depending on design, this might
even be done from inside. There is not much that can go wrong with
the rock, and repairs to it (using ordinary concrete) are simple.
We have multi-thousand-year structural-life experience with rock,
and not with steel. "With a metal hull one could only hope for a
hundred-year life... [with concrete] we can think in terms of a
thousand-year colony."
The main need for Earthly materials for construction will be alloying
elements to turn lunar iron into steel. Not only does the concrete
design use less steel, but steel cable needs smaller percentages of
alloying elements than high-grade (crack-stopping) steel plate.
Cable is easier to make than large flawless steel plates, and
eliminates the need for large-scale welding and X-ray inspection.
The thickness and non-critical nature of the rock part of the
construction simplifies anchoring of structures to its inside,
something that would have to be done rather carefully with a thin
steel shell.
END QUOTE
http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-
8&selm=EsrKpB.Jq3%25spenford%40zoo.toronto.edu&rnum
Would you say that Henry's treatment hits all of the points that
Sheppard made in his article, or did Sheppard go into a lot more
detail? I've not actually seenthe "Spaceflight" article, but I would say Henry provided some details which weren't in the encyclopedia article I've read. But it was pretty much the same listing of advantages, so I'd say Henry hit all of the major points.
Mike Combs
But launch costs from the moon would be also more than launch costs
from an asteroid since the asteroid has only micro gravitation. But the moon is much closer to the markets in near-Earth space. Travel times are days rather than months. But don't get me wrong, I'm not arguing that lunar resources are superior to asteroidal. I would only argue that each scenario have advantages and disadvantages. I wouldn't even place bets on which will happen first, but I think one way or another, both will happen.
Mike Combs
Rig an engine on and take them closer to hearth orbit, you can start mine them on the way anyway, Yeah, one thing that I always liked about the mass driver as a reaction engine for asteroid retrieval is that if you're mining and refining on the way in, you can use the less-valuable parts of what you're separating out as reaction mass. I hate to see people propose things like nuclear steam rockets, because there you're throwing away one of the most valuable parts of the material you're bringing back.
Mike Combs