asteroid habitats

--- In spacesettlers@yahoogroups.com, "Dave Logsdon" wrote:

> are supported by columns left in place during excavation, without
> any additional bracing.

What's the span between the columns? I'd venture a guess that it's
far, far off from the miles envisioned in a Habitat. The rock in the
ceiling can only support so much force before it needs to be
redirected into the columns. Bracing is like an exoskeleton and helps
distribute the forces.

> Decades after
> these mines were played out, they're still being used as underground
> offices, warehouses, industrial parks... even a few restaurants.

I've been in some. Pretty cool, heh?

> the stony, stony-iron, and metallic classes of asteroids may well
> have enough structural integrity to be turned into habitats with
> minimal bracing.

Here are my assumptions:
The asteroid will have to be spun to induce coriolis forces.
It will have to be pressurized to contain an atmosphere.
There are substandard parts which don't meet specifications for
today's machinary.

To melt out a hollow core and rely on the remainder to be structurally
sound, and to make this decisions at the outset of the process, is
IMO, looking for unexpected trouble. Regions of ore problems can doom
the habitat. Unless you scope the whole asteroid and note the
composition to be uniform throughout and to a certain depth then
you're counting on something you shouldn't be. I'd rather count on
quality control in a steel mill, with the right mixes and
temperatures, and cooling sequences to come out with a uniform
engineered product than count on the thermodynamics involved in
melting iron ore out of a mtallic class asteroid and the uncontrolled
crystallization that results from cooling across spans of, I don't
know, hundreds of meters, maybe.

> "When you pressurize that asteroid you're going to have a lot of
> tensile force exerted on bare rock walls, and this is harder to
> compensate for than the bracing used for the compressive forces in a
> mina. "

> Different, yes. But "harder"? In what way?

There are optimum materials for different tasks. A concrete dam is
more efficient than a steel dam. A steel pressure vessel is more
efficient than a concrete pressure vessel. Different technique would
be used to construct each of these facilities, but I would venture the
opinion that a concrete pressure vessel is going to be, in an
objective sense, a much harder task to engineer and construct than a
steel vessel.

I'm not assuming that the asteroid is a solid chunk or one
undifferentiated element. I assumed rock. My understanding of the
engineering principles is that rock is better suited to compressive
forces than tensile forces. You can engineer it for tensile of course,
but now the challenge is greater, or IOW, harder.

> But with some of the other classes, such as the ones I mentioned
> earlier, this may be an issue that can be addressed in much the same
> way that geologists and mining engineers determine the subterranean
> structure of a given piece of real estate here on Earth.

My assumptions:

We're talking about a Habitat, one with wide open spaces.
We're not talking about a station, with load bearing walls.

If you're referring to a Metallic class asteroid, I'd hate to be
tasked with the job of digging it out. Blowing up whole chunks of
metal in a controlled fashion is not going to be an easy job.

If we're melting the thing, which I think is the premise of the
question, then again, a controlled melting of whole regions, where the
metal is, I assume vaporized rather than liquified, I'm not sure how
we're going to leave load bearing columns standing in the midst of the
furnace that will be the interior of this asteroid.

Further, I'd be concerned about the crystalline structure of the metal
that remained on the interface between the exterior of the shell and
the interior that has been vaporized away.

> If tunnelling a habitat into an asteroid *isn't* an option, then I'm
> with you: Take it apart, and build the habitat.

> Dave

I'd have to go back and check but I thought the premise to the
question was a melt operation. Though, even with tunneling, I think
that the problems discussed above are still present.

TangoMan