Bootstrapping - Step two

> > How do you imagine the VVD equipment? An elongated bulb with a
> > hole in one end, metal dust or fragments deposited inside, the bulb
> > spins to keep the unboiled metal inside as well as to be evenly
> > heated by the parabolic mirror? In order to be able to move it more
> > freely, we use both a primary and a secondary mirror, so that the
> > bulb needs not be in the focal point of the primary mirror?

> Can you eleaborate on your vision? I ned some more detail to
> visualize it more accurately.
I imagine something somewhat similar to a Bessemer bulb. That's the one in which raw iron (which is much too high in carbon to be steel) is molten, and air is bubbled through the molten iron to burn off the carbon, thus making steel in bulk quantities. The Bessemer bulb is a container with an opening in the top and air inlets in the bottom. When the molten iron is low enough in carbon, the bulb is tipped to pour the steel. The burning of the carbon provides the heat to keep the process going once the iron has been molten.
I imagine a VVD bulb somewhat like that. An egg-shaped container of a material with a rather higher melting point than the metal it will vapourize. The hole is in the narrow end. The bulb is caused to rotate around its long axis - the axis of rotation passes through the hole - so that the metal dust or ingots inside do not float out of the hole in microgravity, and so that it is heated evenly. The heat is provided by a parabolic mirror, or more than one, concentrating sunlight.
But having only one mirror, the primary concentrating one, will force the VVD bulb to remain in the focal point of that mirror, which will make the set-up clumsy if you want to illuminate a portion of a large object with the vapour beam. Now think of the various types of reflector telescopes that we have. Newton's first one had one secondary mirror to reflect the image away from the axis of the parabolic mirror, so that the astronomer wouldn't have to stick his head in front of it. Another configuration is, IIRC, the Coud set-up, which has *two* secondary mirrors. The light from the object the astronomer is looking at is reflected from the primary mirror to a secondary, and then on to a third mirror, and *thence* onto the actual instruments such as cameras. This set-up has the advantage that the instruments, which may be heavy, need not move as the telescope tracks the observed target.
A similar set-up may be used with the VVD job. The primary mirror, via the secondary ones, illuminates the VVD bulb until it is hot enough that the metal inside melts; in vacuum, this implies that it also is vapourized. The metal vapour is let out through the opening. The vapour beam is not a very narrow one, so the bulb needs to be fairly close to the object being worked on. The sun is not a point source of light, so the light path from the primary mirror to the bulb must also be fairly short. The vapour beam is caused to illuminate the portion of the hull that is to be thickened.
For a large hull, several of these bulbs and attendant mirrors may be used simultaneously, illuminating several portions of the hull. Just turning up the heat may cause the vapour deposited to be so hot that many of the metal atoms fail to stick to the hull, and escape instead. But of course for a small test job, a single VVD bulb and attendant mirror array must suffice.

> I considered ELV dismemeberment as a source of metal but was unsure
> about the equipment needed to break them down into usuable chunks,
> dust, etc. So I've opted to just bring the metal to orbit via
> shuttle launch and have it in forms of bricks of solid or alloyed
> material.
But breaking up an ELV upper stage will provide us with gratis metal. In terms of launch costs, this would give us a hull for almost free, if it is kept small enough that the metal in the upper stages suffices.

> Can you elaborate on what machinery you envision being used for the
> ELV breakdown? Would you put the launch and assembly of this
> machinery at at earlier stage? How many launches would it take to
> assemble? How long would it take to break down a ELV so that we
> could use it for VVD of the assembly bay?
I cannot elaborate very well. I do know, with experience from my own power tools, that cutting up thin sheets of metal is fairly easy on the ground. Presumably you could saw an ELV hull up in a fairly short time, extracting metal sheets of sizes similar to, say, A4 or A3 sheets of paper. These could be crumpled up and put inside the bulb. If the upper stage burns hypergolic propellant, it needs to be well ventilated through tanks and ducts first, of course, since these propellants tend to be less than savoury for the human organism ---
One thing I imagine is that we may launch something similar to a MIR core module, and then build a four or eight meter diameter sphere in the way that you described in your initial post. Add it to the core module, and you have a space hotel, which may cover at least some of your costs. Add perhaps a narrow drum that spins inside the sphere, so slowly that you may simply float onto it in microgravity, and attach yourself to it. It provides a miniscule gravity, enough to take a shower, eat food that isn't all thick gravy with lumps in it, drink from a glass, use a toilet, put small items on a table and not constantly herd them like wide-awake kittens whose eyes have opened, such things.
One weakness of the VVD method is that it doesn't seem to easily enable well.defined edges, such as if you want to build two dry dock halves that may be clamped together and be airtight. So I suppose a wholly closed module (except for the connection tunnels and windows, protected from the metal vapour beam by screens during construction) is best to begin with. Then we can build the more challenging dry dock, if the first attempt didn't prove too hard. The dry dock may be a cylinder, with one end cap detachable: a large hull with a small door is easier to build than a large hull with a large door.
But probably mr. Radley will tell us that the concept has no chance, since the national space agencies of the west will fight against it nail and tooth. :-)

Jon L. Beck.