wrote:
wrote:

Have you looked into NASA's Transhab?

Yes, It seemed too much trouble for too little additional volume.

I was recommending looking into Transhab not because it gave you the
space structure you wanted, but because it answered your material
questions and would give you working mass estimates. I've used
Transhab's shell mass to scale up to assorted hypothetical inflated
stations.

Not interested in developing new launchers. I want it
up there NOW.

Well, alrighty then. I can work with that estimate. But there are some
problems with insisting on

First problem: Shell strength and mass.

You want an environment with enough pressure that construction workers
can promptly ditch their space suits, or at least reduce them. That's
going to require ~3psi of air pressure (pure oxygen). If you cut the
first shell down to a bare minimum with little margin of safety for
restraining just 3psi, it's still going to need to be 0.5mm thick and
made out of an ultra-strong fiber like Zylon. At a minimum, the shell
will be 24 tons (assuming a fully dense Zylon shell; more likely it'd
be about 36-40 tons). That shell will be inadequate for a 14.7psi
atmosphere.

Aluminized Kapton does not have anywhere near the yield strength to
handle 3psi at 0.5mm thickness. With a 30000psi yield strength (at room
temperature), a Kapton sphere would need to be 3.5-4mm thick, which
would result in a 160-ton shell (just to handle 3psi).

Second problem: air mass.

The 3psi oxygen atmosphere will be about 250 tons. That's a lot of
tonnage to lift with current launchers. Which brings up problem
three...

Third problem: existing rocket payload capacity.

If you want existing, in-production launchers to get the job done,
you're going to need 11-12 uprated Delta IV heavy launches (22 metric
tons to LEO) or 11 shuttle launches just to get to the stage where you
have a bare minimum, air-filled sphere. However, you'll probably want a
couple more launchers to deliver some climate control equipment (to
keep all that air from overheating), power systems, etc. So you're up
to about 13 launches before the workers get to climb out of their space
suits during construction. Note that the Delta IV heavy, as currently
flown, is not really up to snuff for launching the initial, bare
minimum shell.

Alternately, if you don't want to wait on internal construction
activities for 11 big launches to fill the sphere with air, then you
can deliver the sphere shell (1 launch) and support equipment, probably
including that bunkhouse you mentioned (2 more launches) and get to
work after 3 launches.

But then the astronauts will be spending all their construction time in
suits, at least until 11 more launches have delivered enough oxygen to
give the sphere minimal pressure.

Fourth problem: existing launch capacity

This goal... "There will need to be weekly shipments of all sorts of
materials and equipment. In inexpensive 5, ten and twenty ton
launches." ...requires greater commerical rocket production than is (I
think) currently available.

Boeing would LOVE to expand its factories to help you launch 20-ton
payloads every week. The idea of firing off 12-13 Delta IV Heavies (33
total common core boosters! wee! profits!) just to get the station
started would make Boeing very happy. And you'll eventually need 30
such launches just to bring the sphere up to 14.7psi, not to mention
another 30 launches to get the shell up to full strength, plus an
unknown number of launches to fill the station with that water,
machinery, etc...

Yes, you could be looking at 100 launches of some rocket in the class
of the Delta IV heavy (or a lot more launches of smaller rockets). If
you want that to happen on a weekly basis, using existing rockets, the
rocket maker(s) you contract will need to expand their factories.

Which leads me back to my prior suggestion of taking the time to modify
the rockets. You're already going to have to pay for changes in the
rocket industry, so why not simplify the construction process with
bigger launchers?

The bare minimum shell you want is probably going to be 36-40 tons even
with super strong materials. Just sticking with the Delta IV example so
I don't have to google up alternatives, you can get about 30-35 tons to
LEO with the Delta IV heavy if you strap some solid boosters to it.
Boeing hasn't flown that yet, but it looks like an easy stretch.

Boeing also claims its Delta IV common core booster can be scaled up to
Saturn V payloads. It'll take modifications to the launch pad and some
engineering work, but its mostly just strapping 7 common core boosters
together. It recently flew 3 of them strapped together. With such an
(almost off-the-shelf) rocket, you could launch a full-strength shell
in one leap. You could give a minimum working atmosphere in the shell
in 2 launches, not 11-12.

Alternately, if you're really insistent on launching weekly, perhaps
you should take the time to develop a reusable launcher like the
VentureStar. It'll probably save you headaches in the long run.

Summary of problems:

Getting the station built in exactly the manner you want is somewhere
on the edge of possible/impossible with existing rockets. You need a
shell launched in one piece that's probably going to be 35-40 tons.
Your bare minimum air pressurization ("Once the shell is up and only
slightly pressurized, the facility is open for business") is going to
need 250 tons of oxygen. You want flight rates that are beyond the
immediate abilities of rocketmakers, but could be achieved with a
little development.

I recommend you relax some of your requirements - particularly for
existing rockets - and pay for the development of a higher capacity
rocket. It'll make everything else much more possible.

Mike Miller, Materials Engineer