Newsgroups: sci.space.policy
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: hangars (was Re: SSTO size (was Re: landings))
Date: Mon, 15 Jan 1996 18:09:06 GMT

In article <960112201152@kernow.demon.co.uk> vulch@kernow.demon.co.uk writes:
>  >> Incidentally, why assume that in-orbit assembly has to be
>  >> done by EVA? A pressurized assembly hangar would be
>  >> immensely valuable and not all that difficult to build. 
>  > ...Safety becomes an issue if a puncture occurs with unsuited
>  > mechanics inside.  What is the minimum protective outfit
>  > required?  Torso skinsuit with sleeves, helmet (visor up if
>  > no emergency), and a 2 minute oxygen  bottle.
> 
>'Beachball' rescue bubble rolled up and fixed to the small of the back?

The key question here is, *how big* a puncture are we talking about?  Even
an inflatable hangar would have to have rip-stops in its fabric, so that a
small puncture would not expand dramatically.  And a big hangar will not 
lose pressure all that quickly from a small puncture.

I would suspect that the minimum protective outfit is a pocket containing
a rigid patch the size of one rip-stop section, and adequate hearing for
the "pressure loss, evacuate the hangar" alarm. 
-- 
The Earth is our mother.                           |       Henry Spencer
Our nine months are up...                          |   henry@zoo.toronto.edu

Newsgroups: sci.space.policy
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: SSTO size (was Re: landings)
Date: Mon, 15 Jan 1996 17:51:33 GMT

In article <4d27hf$53l@nntp5.u.washington.edu> doyle@PROBLEM_WITH_INEWS_GATEWAY_FILE () writes:
>> > Incidentally, why assume that in-orbit assembly has to be done by EVA?
>> > A pressurized assembly hangar would be immensely valuable and not all
>> > that difficult to build.
>> ================================================
>> I have long thought that a large air bag, say with 3 psi O2 and 2-3 psi
>> N2, would make assembly of objects in space far easier than today.  
>> One with a 100 meter diameter would contain about 250 tons of air...
>
>What are you making this out of?
>This is much bigger than any inflatable I have heard of and
>the air presure is not significantly lower.

100 meters is ridiculously large -- you could assemble a Saturn V in that!
Really large objects can be assembled by docking modules together.  It's
the assembly of the modules themselves, and other smaller objects, which
would benefit most from a hangar.

I would think that a cylindrical hangar, say, 7m in diameter and 25m long
would cover the vast majority of tasks.  That would accept an assembly the
size of the entire shuttle cargo bay while leaving maneuvering room around
it.  Now, it so happens that I didn't pick those numbers at random -- that
is roughly the size of the shuttle ET hydrogen tank, after allowing some
extra for its internal hardware...  The only tricky part is that you have
to make one end of it flip open to get hardware in and out.

>> In an airbag, one would have a shirtsleave environment, and I suspect 
>> that, once you got used to it, you would find that the disadvanatges of zero
>> g would be offset by its advantages, making space assembly no more difficult
>> than on earth. 
>
>I don't think constructipn in Zero-g will be quite that simple.

Probably not.  There would still be the usual problems of operating in
free fall.  Things -- including your own body -- don't stay where you put 
them.  In principle you can maneuver heavy objects without cranes etc.;
in practice you need to anchor them somehow once you're done maneuvering
them, and that reduces the benefit.  Processes like welding would pose
tricky problems (hot metal drops drifting down the breeze).  But these
things should be manageable.
-- 
The Earth is our mother.                           |       Henry Spencer
Our nine months are up...                          |   henry@zoo.toronto.edu

Newsgroups: sci.space.policy
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: SSTO size (was Re: landings)
Date: Fri, 19 Jan 1996 19:23:47 GMT

In article <4dik35$dgo@hermes.is.co.za> franks@vironix.co.za ( Frank Scrooby) writes:
>A hundred meter wide air bag would also require a ridiculous amount of air to
>pressurize and a long time to depressurize. And if you left in LEO for any
>amount of time its enormous volume and low mass would cause its orbit to decay.

Unless it was actively maintained, which is the obvious thing to do.  The
amount of thrust needed for orbit maintenance, even for quite large objects
(the mass of the object is irrelevant for this), is quite small provided it's
there continuously, e.g. from ion thrusters.

>> ...Now, it so happens that I didn't pick those numbers at random -- that
>> is roughly the size of the shuttle ET hydrogen tank, after allowing some
>> extra for its internal hardware...  The only tricky part is that you have
>> to make one end of it flip open to get hardware in and out.
>
>Wouldn't a double flap of tough kevlar or some other fabric be sufficient...

I'm not quite sure what you're envisioning -- can you elaborate?  I don't
see any great advantage in making the closure flexible, and it adds the
problem of anchoring the fabric to the ET rim against a thrust of many tons.

>> ...In principle you can maneuver heavy objects without cranes etc.;
>> in practice you need to anchor them somehow once you're done maneuvering
>> them, and that reduces the benefit.  Processes like welding would pose
>> tricky problems (hot metal drops drifting down the breeze).  But these
>> things should be manageable.
>
>Surely a little suction pipe could trap any particles or drops of liquid which
>happened along the way? I'm sure I've seen the principle applied somewhere on
>earth...

Suction for things like soldering is routine for air cleanliness, but it 
gets a little harder when it has to be 100% effective against flying drops
of metal.

> ...And how much of the assembly would be
>welding and stuff. I pictured this 'garage' as being a place where a space
>station crew could assemble pre-fabricated units shipped up from earth. I'd
>think nuts and bolts would be preferred over welds by the system designers...

Depends on what's being done.  Nuts and bolts do make for easier assembly,
but they are *heavy*, as are the flanges needed to attach them, and they
don't produce a gas-tight seal without gaskets, which have their own 
complications.  Welding would be wanted eventually.

>Also in a module the size been described couldn't the astronauts simply hook a
>foot into a sort of bunjee cable running along the length of the garage to
>maintain an upright and fixed position...

It's not that easy, as the early Gemini EVA efforts found out, and as
Skylab experience confirmed.  One foot hooked under something will hold
you in the general neighborhood, but won't maintain an upright and fixed
position unless you've got very strong leg and foot muscles and a good
solid anchor point, and will tire the muscles for that foot pretty quickly. 
About the minimum in practice is to have both feet locked down -- not held
down by muscular effort in foot and toes, mind you, but solidly secured --
and even then it's helpful to have back support if you need to stay
upright.  On Earth, gravity helps us in holding our position much more 
than we realize.

The problem is not unsolvable, but it's harder than it looks, and you need
more help than you'd think. 
-- 
The Earth is our mother.                           |       Henry Spencer
Our nine months are up...                          |   henry@zoo.toronto.edu

Newsgroups: sci.space.policy,sci.space.shuttle
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: Alternative space station
Date: Wed, 23 Apr 1997 23:07:10 GMT

In article <5jh2ko$csj$1@news.northwest.com>,
Charles Radley - CSQE  <ftp@ftp://ftp.apk.net/tranq/review.htm> wrote:
>> I will note, the original skylab design was for a wet workshop
>> with the equipment in a central core and pulled in by
>> the crews, as part of a on-orbit integration.
>
>And history has shown that the original design was dropped in favor of a
>pre-integrated solution.

True; so?  Wernher von Braun's firm opinion was that the "wet workshop"
scheme could have been made to work.  The pre-integrated solution was
merely easier, in a program which had an Apollo-surplus heavylift booster
available free but which couldn't afford many crew launches.

>BTW, I just saw part of a recent interview with General Kovalenok...
>He stated that the $ 300 - $ 400 million  per year paid by NASA only
>covers a small portion of the total costs of running Mir...

Um, either you misheard him or he's made a serious goof here.  That's
$400M *total*, not per year, from NASA.  Moreover, the story one hears
from other sources is that that money -- thinned out a bit though it is by
the time it reaches the contractors -- is what is keeping the program
alive.

>So my optmistically low
>estimate  of $ 100 million / year for Mir could be an order of magnitude
>low...

Not likely.  At realistic (black market) exchange rates, even in its glory
days the Soviet space program didn't *have* an order of magnitude more
than that to spend on Mir.  Their whole annual budget was only a few
hundred million, although they didn't pay full costs for some things.

>In the case of the Skylab design decision. Actions speak louder than
>words.

Ah, but what do they say?  They say "a free heavylift launch plus very
limited in-orbit crew time pushes you toward assembly on the ground",
which is not exactly a big surprise.
--
Committees do harm merely by existing.             |       Henry Spencer
                           -- Freeman Dyson        |   henry@zoo.toronto.edu

Newsgroups: sci.space.policy,sci.space.shuttle
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: Alternative space station
Date: Wed, 23 Apr 1997 18:55:23 GMT

In article <335DBA7D.1BD5@net1.net>, Jim Davidson  <davidson@net1.net> wrote:
>> It doesn't meet all needs I can think of, my standard example being a
>> pressurized hangar for in-orbit assembly and checkout of spacecraft.
>
>Excellent point.  Of course, I find myself asking why we would want to
>launch spacecraft components into orbit only to load them into a
>pressurized hangar for checkout and assembly. It is so much easier to
>assemble spacecraft in such hangars on Earth.

Consider an Earth analogy...  You are building a microwave relay tower in
a remote area.  Everything has to be carried in by truck, and the last
100km is over rough gravel roads, and the drivers are paid by the load
rather than by the hour so they all drive like maniacs.  Which is cheaper:
building the microwave relay assembly so that it can be fully assembled,
chained down to an open truck bed, trucked in, and immediately hoisted up
onto the tower where it has to work the first time... or sending the major
subassemblies in one at a time, in padded shipping containers, with final
assembly under controlled conditions and checkout just before hoisting?
Even if the latter was a bit more expensive, which approach would you bet
your career on?

Even setting aside issues of reliability and insurance costs, assembly
after launch is actually rather cheaper (!), according to Fairchild's
"Leasecraft" study.  The reason is that you spend a lot of engineering
effort, and a lot of care in assembly, just to make sure that it will
all survive launch without (say) a connector coming loose.  Doing final
integration in orbit avoids all that.  Being able to take the hardware
up in shipping cases, and plug it together *after* all the stress and
vibration, looked cheaper even when the plugging was to be done by guys in
spacesuits.  (That study was done back in pre-Challenger days, when there
was still some optimism about shuttle flight costs, so it did assume
*somewhat* lower flight costs than we've actually got today.)

Note a crucial point here:  you don't see any benefit, or not much anyway,
if you assume that only one item (the assembly location) changes.  The
situation really improves only when you consider the implications of that
change for other items.  (The same is true of, e.g., lower launch costs.)

>> outfitting time is much cheaper on Earth than in space, regardless of the
>> exact numbers.  But outfitting on Earth is impossible when the inflated
>> hull won't fit in the shuttle cargo bay.
>
>Ah!  So on-orbit assembly helps justify the continued existence of the
>shuttle...

Don't put words in my mouth, Jim, especially fighting words. :-)  Assembly
in orbit would be a major reason for wanting a *low-cost* launcher to have
a passenger capability, rather than being purely unmanned.  (Whether it
would fly manned or unmanned when carrying only cargo is a different
question; personally, I like McDD's idea of making it optional.)

Doing in-orbit assembly at today's shuttle prices is another story.  Using
the shuttle, it makes sense only if it can be added to an existing flight
at a small incremental cost.  Witness the Intelsat salvage flight --
basically an improvised in-orbit assembly mission -- which made commercial
sense to Intelsat only because it could be piggybacked on Endeavour's
shakedown flight for a relatively small fee.  However, such piggybacking
opportunities are rare.

>Of course, the existence of flight proven heavy lift launch
>vehicles such as Energia makes something akin to mincemeat of this
>argument.

See above concerning relative overall costs, even with the ability to
launch it all in one piece.

Besides, *I* don't see any such vehicles in existence today.  I see the
rotting remains of such a capability at Baikonur, and the same at KSC.
--
Committees do harm merely by existing.             |       Henry Spencer
                           -- Freeman Dyson        |   henry@zoo.toronto.edu