From: Michael Lorrey (mlorrey@datamann.com)
Date: Mon Mar 19 2001 - 13:34:27 MST
"Robert J. Bradbury" wrote:
>
> On Mon, 19 Mar 2001, Michael Lorrey wrote:
>
> > Well sealed cannon plugs are not difficult to make or use. The rationale
> > for putting stuff outside is that it maximizes the space inside to use
> > for people and real equipment. Wires don't need air to live (and are
> > less likely to make a high O2 atmosphere go fizzle...boom). This also
> > minimizes pressure vessel mass for a given amount of workspace.
>
> Mike, think about this for a minute -- the quotes I keep seeing
> are that the inside volume is going to be ~ that of the cabin
> of a 747. The maximum head count that I've seen for "occupation" of
> the ISS is 7 people. Thats 7 people inside the volume of a 747 cabin.
> Don't you think its unlikely they will be tripping over each other?
> Cables can't take up *that* much space.
You'd think so, if you had never worked on an aircraft or spacecraft
before. While I've not worked on spacecraft, I have worked on many
different aircraft. On large planes like transports/airliners, the wire
bundles running through the wings can easily exceed the diameter of your
leg, with hundreds or thousands of wires, and a minimum of several dozen
up to several hundred 'Cannon' plug connectors. And this is just the
wiring. You also have environmental ducting, as well as suplly and drain
lines for water, sewage, any gasses required, plus signalling/avionics
cables (co-ax, bi-ax, tri-axial cabling, fiber-optics, etc.)
As someone else commented, on Mir, you can see from photos of much
tubing, ducting, and cabline going through the compartment interface
tunnels of the difficulty of running it all straight through from
compartment to compartment via the access hatches, not so much in
setting up the station this way (its probably very cheap to do it this
way), but in the problems with shutting the hatches if one compartment
has a catastrophic leak. This was done in Mir because the USSR's space
suit technology was primitive compared to the US, requiring several
hours of suit-up time with limited run-time, and so EVAs were kept to a
minimum. Working in US suits is far more pleasant, and easier to prepare
for than the older technology.
Each lab has its own circuitry, and over the period of the construction
of the full station (at least the next 10 years), modules will be
unplugged and shuffled around at least a couple times, so each interface
hatch cannot simultaneously carry interface plugs in the hatch to work
with all possible modules it might come in contact with. Better to have
the cable interfaces separate and do the wiring on the outside, leaving
the hatchways free for shutting in emergency situations.
>
> Its fascinating if you go over this design. You have the U.S.
> Destiny lab, then the ESA lab, then the Japanese lab, then a
> couple of Russian labs. What precisely are all these labs going
> to do? What can the labs do that hasn't already been done on
> the the Mir or Spacelab? Have you looked at the prices that NASA
> anticipates charging for the hourly allocation of an astronaut
> as a "lab operator"? Makes hourly rates for lawyers and doctors
> look positively "minimum wage".
>
> The whole thing has a bad smell. In contrast if you positioned
> it as an orbiting observatory platform or an "assembly" operation
> then you would be getting something from it.
>
> Answer this -- why can't one attach a couple of dozen Baby Hubble's
> to the space station? Is there some orbital difference between
> the Hubble and the ISS that makes it unusable as an observatory?
> Is it simply not stable enough? What gives here?
>
> Robert
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