Vacuum Vapor Deposition

>
> Several replies in a single message here. Please accept my
apologies in advance, I was not able to attribute all the quotes
which come from various different people.
>
> > Message: 4
> > Date: Tue, 22 Oct 2002 17:58:10 -0000
> >
> > My concerns center on expansion issues and bonding. Would there
be
> > a problem with the weld joints on the original structure by
having a
> > monolithic layer of metal sprayed on top of them? Do the welds
allow
> > some expansion stresses to be absorbed? How would the VVD
material
>
> The welds can be safely ignored, why are you concerned about
them ?

Because I'm not up on welding theory so it's an unknown to me. Good
to know that they can be ignored.

>Welds are verified using X-ray and N-ray inspection to ensure no
>cracks or voids.

Is this type of equipment portable and can it be designed for use in
orbit?

>After that, for analysis purposes, they do not exist, they can be
>treated as part of the native metal structure.
>
> > adhere to the original structure? Would there be engineering
issues
> > with the cooling of the VVD material between each successive
> > application? This last question is similar to issues that
concrete
>
> Well you would want to depressurize the vessel before applying the
>coating, and then wait for the coating to cool down and "set"
>before repressurizing. I do not see any other issues really.

Good. Switching gears at about this point in my post, I'm now
writing of a scenario where it is a new Habitat being constructed,
so the pressurization wouldn't be an issue. Just the bonding of new
material to the old, and the strength of the bond compared to the
material properties of a piece of metal that has cooled as a unique
piece. Crystalline structure of the cooled metal, atomic bonding,
etc. Matters that I don't deal with much.

>
> > applicators face. If they allow a portion of their pour to cure
and
> > then apply another pour next to it, there is a joint. Because the
> > VVD will be applying layer ontop of layer, will we still have a
> > monolithic shell, or will it be one of many layers?
> >
> Many layers I expect.

What prevents the metallic vapor from bonding in such a fashion as
to eliminate layers?

>
> > If it is a monolithic shell, is that ideal? How would stresses be
> > relieved?
> >
> You do not relieve stresses in a pressure vessel. I am not sure
what you mean.

I mean stresses not associated with the pressure containment design,
but stresses due to rotation, movement of mass within the Habitat,
different soil thickness and construction loads being applied to
different points of the Habitat shell (unlike the uniform pressure
that a contained gas applies) and perhaps, one side of the Habitat
receiving more sun energy than another side and this thermal
disequilibrium acting on the structure of the Habitat.

>
> > If it is one of many layers, then is it less structurally sound?
> >
> > Analysing the load sharing between layers could be complicated,
>perhaps impossible. Probably better to use the extra layer as a
>safety backup structure, rather than a primary structure.

Just to be sure that we're on the same page. By using VVD to deposit
metal over the surface area of the Habitat, I'm using the term
layers as reference to a pass by the VVD equipment whereby metal is
deposited. In my understanding these layers would be microns thick.

To expand further, I envision the form of the non-revolving Habitat
surrounded by numerous VVD machines. Into these machines we would
place bricks of solid metal. These machines would follow a precise
path about the Habitat depositing metal vapor in a continous
fashion. They would revisit the same spot on the Habitat structure
repeatedly. Thus the Habitat will at all times have a uniform
thickness over it's entire surface. It may take years to deposit
enough vaporized metal to certify the Habitat pressure vessel
completed.

With this understanding of the background to my question, does your
definition of "layers" match my own? My question is premised on the
vision of using VVD to build the primary structure, not as a safety
backup feature.

> > Hope that somebody can help with answers to these questions.
> >
> Analysizing layered pressure vessels is a common spacecraft
problem. Many spacecraft tanks have a metal liner with a composite
cladding. Getting them certified is a little complicated.
>
> > Meanwhile, we keep adding more thickness to the shell, thus
allowing
> > more gas pressure to be held.
> >
> No. You need to depressurize between adding layers to the
pressure vessel. The atmosphere will have to be pumped off into a
storage tank.

Why? That kind of deep-sixes my proposal :) I envisioned a Habitat
having vaporized metal sprayed onto its form for a period of a few
years and as its pressure handling ability increased more gases
could be stored within.

What are the technical limitations to adding more thickness to a
pressurized pressure vessel? I infer from your comments that this is
not the "ideal" state, one certified by the National Engineering
Standards Bodies, but is it impossible? Could new standards be
devised that reflect new technologies and techniques? If so, this
would surely save a lot of work in orbit.
>
> > Now for some Habitat designs the windows issue will not allow
this
>
> The window issues is irrelevant here so far as I can see.

For me as well.

Thanks for your reply, TangoMan