Newsgroups: sci.space.tech
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: a whimsical idea
Date: Sat, 12 Jul 1997 18:38:18 GMT

In article <5q302r$cn4@excalibur.gooroos.com>,
Graydon <graydon@gooroos.com> wrote:
>>Of course, then you can take this one step further, as LLNL did, and
>>observe that there is actually no requirement for anything but tensile
>>strength in the shell...
>
>As a pressure vessel, yes.
>
>What did LLNL plan to do about conduit and attachement points?

Build them in, including spare attachment points for future requirements.
Plus, it's easy enough to set up internal structure -- metallic, if you
insist -- that is there only to support subsystems, not to carry pressure
loads.  The LLNL scheme has a central core in each module, which provides
utilities and a passageway down the center connecting the compartments
within a module.  (The compartment walls themselves are part of the
inflatable structure, and incidentally can carry the full internal
pressure if one compartment gets a puncture.)

>It seems to me that despite the considerable rigidity, it's not going to
>be easy to attach things to the balloon; one can use glue, but most glues
>that will stick well to synthetic fabrics produce wretched fumes...

If you really need to set up a new attachment point, you can use localized
ventilation to carry any fumes away during the curing period.  However,
the best basic approach here is simply to provide a grid of uncommitted
attachment points from the start, so you don't *need* to add new ones.
The ISS crew won't routinely be drilling holes in things to attach new
hardware; the necessary holes will be there already.

>Now, it may be that someone has already solved how you attach plumbing to
>an inflatable when you develop a need to run a new cable through the hull...

Even in a metal module, you don't routinely drill a hole through the
pressure hull in some arbitrary place.  You use existing, presupplied
cable penetrations if at all possible.  If you've just got to run a new
one through, perhaps because it's some kind of weird new cable, you go
through a cable-penetration plate which is part of the design from the
beginning, with reinforcing around the edges so that the plate itself
does not carry hull structural loads (and hence you don't have to worry
about fatigue cracking at the edges of the new hole).  Such plates can
just as easily be part of an inflatable hull.
--
Committees do harm merely by existing.             |       Henry Spencer
                           -- Freeman Dyson        |   henry@zoo.toronto.edu

Newsgroups: sci.space.policy,sci.space.history,sci.space.shuttle
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Roton/Inflatable Hab
Date: Wed, 14 Apr 1999 05:41:08 GMT

In article <Pine.GSO.4.10.9904131650200.9650-100000@seds.lpl.arizona.edu>,
Mike Dicenso  <mdicenso@seds.lpl.arizona.edu> wrote:
>I have the Air & Space article to which you refer. However the article
>points out that the technology advances to make inflatable structures like
>Transhab debris-proof have largely occured in just the last fews years...

I haven't seen that article yet... but beware here.  There was no great
fundamental difficulty in making inflatables debris-proof five years ago,
or ten, or fifteen.  What we have here is NASA saving face, finding an
excuse to claim that its previous rejection of the idea wasn't *really* a
stupid mistake.  Which it was.
--
The good old days                   |  Henry Spencer   henry@spsystems.net
weren't.                            |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.policy,sci.space.history,sci.space.shuttle
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Roton/Inflatable Hab
Date: Thu, 15 Apr 1999 02:52:20 GMT

In article <Pine.GSO.4.10.9904141558370.21283-100000@seds.lpl.arizona.edu>,
Mike Dicenso  <mdicenso@seds.lpl.arizona.edu> wrote:
>...The micrometeroid/debris protection
>dilemma is specifically refered to as perhaps the single biggest weak
>point in creating an inflatable spacecraft, which was solved of course by
>using the Nextel/foam.

My point is:  take the article's comments on this with a large grain of
salt, because its sources are far from unbiased.  NASA is *not* going to
admit that its earlier rejection of the concept was a blunder, even if it
clearly was.  This doesn't require a great conspiracy, just self-serving
bureaucrats who will automatically stamp FUNDING REQUEST DENIED on any
project proposal which shows promise of establishing that they, or their
superiors, or their mentors, were idiots.

An essential part of proposing activity in such an area is finding some
explanation which justifies the earlier decisions while still making it
legitimate to reconsider them.  "Technology has improved enough to change
things" is a pretty good bet, because almost always there has been *some*
relevant-looking improvement which can be defended as essential.  Such
excuses should be viewed with a very skeptical eye.

Lesson number one in any how-to-do-history course is that you *always*
examine the biases of your sources and how they might affect their account
of the facts.

>The technology for a Transhab inflatable certainly
>has been around for about five years, but the real trick has been in
>getting everything to come together in the right time, and right place.

This is correct, except that the time span has been longer, and the key
missing ingredient has been approval to pursue the idea seriously, not
some particular piece of technology.
--
The good old days                   |  Henry Spencer   henry@spsystems.net
weren't.                            |      (aka henry@zoo.toronto.edu)

Newsgroups: sci.space.policy,sci.space.history,sci.space.shuttle
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Roton/Inflatable Hab
Date: Thu, 15 Apr 1999 18:24:35 GMT

In article <Pine.GSO.4.10.9904150918030.20038-100000@seds.lpl.arizona.edu>,
Mike Dicenso  <mdicenso@seds.lpl.arizona.edu> wrote:
>The other lesson in history is looking at how past attempts at inflatable
>structures worked. The interesting thing the article mentions is the SEI
>protoype built, and tested in 1989 that kept having all sorts of problems
>with the seams coming apart. That is'nt a big conspiracy, that is'nt the
>result of someone in NASA saying "let's build this thing so it fails, so
>we can say the concept does'nt work". This was an attempt 10 years ago,
>and the technology was'nt up to it.

Careful here.  One data point does not a curve make.  By the same line of
argument, you could claim that the technology is not up to building space
tethers, because both TSS-1 and its reflight were failures.  Except that
Joe Carroll's SEDS and TiPS tethers *did* work; the problem with TSS-1
was not inadequate technology, but inept application of it.

By the way, the tunnel that connects Spacelab with the orbiter, first
flown nearly 20 years ago, is essentially an inflatable structure.  So not
all past "attempts at inflatable structures" have been failures.

>The other major problem was the debris
>issue. Sure we might argue 'till our fingers fall off that more effort
>could've been put into overcoming those problems by pusing the envelope...

You're the only one who's talking about "pushing the envelope", as if it
was a terribly difficult unsolved problem.  Non-trivial engineering, yes,
and it has gotten easier of late, but not a baffling and prohibitive
problem even then.

>> This is correct, except that the time span has been longer, and the key
>> missing ingredient has been approval to pursue the idea seriously, not
>> some particular piece of technology.
>
>No here I'd have to partly disagree Henry, the technologies are just as
>important as much as the will. Practicality plays as much of a role in
>making a thing happen.

In general, that's often true.  In this particular case, not especially.
It's gotten easier -- not gone from impractical to practical, just gotten
a bit easier -- but the major importance of that has been political, not
technical.

>Could an SSTO have been built 10-20 years ago? Sure
>if it was to be expendable, and possibly more costly and ineffcient than
>more conventional designs.

You might want to note that one of the Alternative Space Shuttle Concepts
design studies, nearly 30 years ago, seriously proposed building the
shuttle as a (fully reusable) SSTO.  Phil Bono's detailed designs go back
even farther.  This is one area where *will* has very conspicuously been
the problem, not technology.  (And you'll find the same excuses offered
for NASA's neglect of the idea.  "The technology's just not up to it.")
--
The good old days                   |  Henry Spencer   henry@spsystems.net
weren't.                            |      (aka henry@zoo.toronto.edu)