Re: superhero space navigation

On Apr 15, 2:22=A0am, Leonard Erickson <sha...@[EMAIL PROTECTED]
> wrote:
> On Mon, 14 Apr 2008 12:38:56 -0700 (PDT), IsaacKuo <mech...@[EMAIL PROTECTED]
>
> wrote:

> >On Apr 14, 2:02 pm, Bryan Derksen <bryan.derk...@[EMAIL PROTECTED]
> wrote:
> >> IsaacKuo wrote:
> >> > Oh, I don't know about that. =A0What kind of sealant will
> >> > work on the Moon, and how much do you really trust it
> >> > to hold in 1 atmosphere? =A0And what about the interface
> >> > between this "sealant" stuff and the airlock hatches?

> >> In an earlier post I pointed to a URL that discussed the use of
concret=
e
> >> on the Moon, that'd be good for filling in the chinks around the
airloc=
k
> >> hatches.

> >How much would you personally trust it, youself? =A0At
> >the very least, you'd want to do some engineering tests,
> >right? =A0It's not like you can pretest the habitat by
> >inflating it here on Earth and submersing it underwater.
> >It has to be built in place.

> No, but you can pressurize it and come back in a week and see what the
> pressure is.

Okay.  And to no one's surprise, you find out that the
pressure is lower.  Now what?  You can't just find the
leaks by looking for them around the outside.

> >> Where will you _get_ the inflatable structure? This base is being
built=

> >> by a couple of ordinary civilians without a lot of money, they can
> >> probably steal a lot of off-the-shelf stuff if they need to but
making
> >> custom items will be difficult.

> >I'd probably work with a hot air balloon supplier, or start
> >off with a normal hot air balloon (close off the top and
> >bottom for a fully enclosed structure). =A0Really, there
> >should be two concentric balloons, so the space between
> >can be filled with foam.

> The material used for hot air balloons isn't all that airtight.
> Doesn't have to be as the pressure differential between inside and
> outside isn't that high.

> It's not much more airtight than a parachute or racing sail.

Yeah, that's right.  Well, at least a used balloon is a start.
You'd have to spray on something to make it airtight and
stronger.  Too much trouble...it would be easier to work
with a hot air balloon supplier for something stronger and
airtight to begin with.

> Hmmm. =A0It occurs to my that mylar film isn't that hard to get. =A0And
> it's pretty airtight.

> So we use a multi-layer liner. Rigid backing (cave wall, expanded
> steel grating, the heavy wire mesh they use for backing for "sprayed"
> concrete..) Next layer is screening. Hell, ordinary window screen
> might work if it doesn't degrade too badly in vacuum.

> Then a layer of cloth. Nylon?

> Finally a layer of mylar film.

> You might want to have several cloth/mylar layers just to help protect
> the mylar.

> Stick something against the inside to act as a spacer in case
> something hits the inner wall. Layers of corrugated cardboard,
> styrofoam sheet, whatever.

This sounds like a rather involved construction project.
I think it would be easier and more straightforward to
work with an experienced balloon manufacturer to
come up with a simpler solution.

> >Now, money may or may not be a problem. =A0There's no
> >way to do any sort of habitat really "cheap". =A0If money is
> >really tight, then there's really no other option than to
> >squat somewhere here on Earth and hope no one finds
> >your hideout. =A0Even just the amount of "sealant" required
> >for a lunar dugout would have a nontrivial price. =A0A high
> >mountainside cave could be a possibility.

> Depends a lot on what's actually usable, even if not space rated.

You talk about steel gratings and window screen mesh
and such.  For the large areas involved, the only way I
can imagine that being acquired for cheap would be
landfill diving.  Naturally, most of it would be rusted junk
but you could find some usable stuff in active landfills.

Ah, that just sounds silly.  No, if I wanted a secret
hideout for cheap, I'd just find some secluded place on
Earth.  There are plenty of mountainside caves which
are largely inaccessable.  There are plenty of
random islands which are rarely if ever visited.

> >Thus, I assume you can get decent money. =A0The going
> >rate for taking a satellite up into orbit is enough that
> >you really shouldn't have any money problems.

> Getting the parts and mony for that first "demo" satellite is going to
> be a problem.

> And, as I noted, getting things into orbit, much less a specific one,
> is not easy without some sort of instrumentaion.

No, it is really easy to get into some random orbit.  You
just go up and then accelerate a bit sideways.  Then you
just let yourself coast.  If you don't fall into the atmosphere
after an hour, you're in an orbit.  If you find yourself falling
into the atmosphere, just accelerate sideways a bit more.

The demo satellite can be a simple aluminum cookie
sheet.  Just set it spinning so anyone can see it blink
like a lighthouse.

> And even if you somehow convince somebody to use your "service" and
> they've built it so that once you get it close to the right altitude
> and speed, it can do final insertion on its own,

Typical satellites need to do the final insertion on their
own anyway.

> there's the problem
> of picking up the satellite from the owner because it might be a trap.

> And getting paid...

You don't have to do these things personally.

> >> And I think I'd rather trust my life to
> >> a cave's structural integrity or the sheer physical weight of a mound
o=
f
> >> regolith rather than to something I sewed together myself out of
> >> non-space-rated fabric.

> >The physical weight of a mound of regolith is working
> >against you, not for you! =A0It's trying to collapse in the
> >dugout.
> >I'd rather have something I can comfortably and reliably
> >test. =A0An inflatable shell can be tested and patched up
> >here on Earth, using the bubble test. =A0Even after it's
> >up in space, it's possible to see any leaks by looking
> >around the outside of the habitat. =A0Neither of these are
> >options for a lunar dugout.

> But the seal it and wait bit will give you a test of integrity. And
> leaks can be found via things like smoke.

Easier said than done.  On the "outside" of a leak, there
would be an easily visible "jet" of gas (and/or smoke, if
you use smoke).  On the "inside" of a leak, though, air
just sort of gets gently pulled inward equally from all
directions, decreasing in velocity with the cube of the
distance.  You more or less have to already know
where the leak is, unless it's a really strong leak (in
which case you could probably just hear where the
leak is, if not see it directly).

> And if you are on Farside, you can try marking things to help you find
> your way. Nearside, any useful marks that aren't spottable by a good
> telescope on earth won't be much use until you are fairly close.

If you assume that no one can see the Farside, then
obviously no one can reach the Farside.  That implies
that no one can reach the Nearside either.  So why
do you care if the marks are visible by a good telescope
on Earth?

If someone can reach the Nearside, then they can
also reach the Farside.  At that point, they can see
anything on the Farside also.

Isaac Kuo