Space plumbing, was Re: SPACE: Why so much EVA on ISS?

From: Michael M. Butler (
Date: Sat Mar 17 2001 - 09:17:49 MST

I suspect the tradeoffs on doing connections inside vs. doing them
outside are nontrivial, and that there's no good answer for where to put
them. I'd expect submarines have somewhat similar problems (modulo the
corrosive sea salt). Consider (this list is off the top of my head):

         Location: Shirtsleeve environment Fixed bulkhead mount
Exposed outside
  Typical Trait: ==================
================ ============
+Ease of assembly High to medium High (initial mate)
Medium to low (EVA)
+Accessibility High to low, depending Very low
(unmate+EVA) High
-Risk of access Low to high, depending High (unmate+EVA+remate)
Medium to high (EVA)
-Risk of fire Significant Potential
(depends) Low
-phys stress Low to high (hatch close) Low to very
high Low?
                                                   (frame flex)
-thermal stress Very low to low Low to medium
Medium to high
-contaminants Very high to medium High to
low Low
  /corrosion expos.
-UV/particle/01 exp. Essentially zero Close to
zero High
-cold soak Low Low to medium
Medium to high
-outgassing Slow to no
Probable Likely
-vacuum welding No
Possible Occurs
-Potential leak? No
Yes Yes
-Gets in the way
  /uses up elbow room Yes
Maybe No
  /valuable "cubic"
+Can dog hatches and No
Probably Yes
  maintain connection?

Also consider that TONS of EVA were scheduled for stuff related to
assembly and maintenance. EVA was deemed the method of choice for lots
of other structure related functions. There could be a chicken and egg
problem here.

Offhand, I'd guess the last two points I listed were significant factors
in the decision to do the plumbing outside. In particular, the prospect
of having to blow a bunch of explosives-driven cable cutters in order to
lock the station down is perhaps unappealing.

Greg, all: I'm looking into what the ISS bus architectures are, and will
report back ASAP.

Chuck Kuecker wrote:
> More than that - what's the rationale behind putting all those cables on
> the outside of the units? Every cable that pierces the hull is a potential
> leak - and any wiring problems now force an EVA, with attendant loss of
> expensive atmosphere. The cabling is now more susceptible to damage from
> space junk, etc.
> What's so difficult about running the cabling and piping inside the
> interconnections?
> Chuck Kuecker
> At 08:38 AM 3/17/01 -0500, you wrote:
> >It seems like designing a standard modular protocol for power and data bus
> >connections would be an important part of developing a robust space
> >infrastructure. I've envisioned a basic system in which design modules are
> >applied to one or two basic structural "envelopes", a la LEGOs(tm). You see
> >hints of this in the video downlinked in the last couple of days from ISS in
> >the way that the Italian Leonardo MPLM "moving van" is just a simplified
> >version of the design for the US lab module in size, shape and basic
> >mechanical structure. Why isn't this approach applied at a finer-grained
> >level to the power and data cabling?
> >
> > Greg Burch <>----<>
> > Attorney ::: Vice President, Extropy Institute ::: Wilderness Guide

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