Date: Sat, 15 Jan 2000 13:21:13 -0800
From: Doug Jones <random@qnet.com>
Newsgroups: sci.space.policy
Subject: Fuel contamination in vacuo Was: UPI on GRO De-Orbit

Jens Lerch wrote:
>
> "Jorge R. Frank" <jrfrank@ibm-pc.org> wrote:
> >JamesOberg wrote:
>
> >> some of the spacecraft's fuel lines appear to be leaking toxic chemicals
> >> that could endanger the shuttle or spacewalking astronauts.
> >
> >Good article as usual, Jim.
> >
> >Note to NASA: spacecraft designed for EVA servicing should use non-toxic
> >fuels.  Just a thought.
>
> ISS uses also toxic fuels so I wonder if NASA will also abandon it if
> some fuel lines start leaking.

I really have to wonder about this- both UDMH and N2O4 have vapor pressures
higher than that of water... so basking the spacesuit in the sunlight for
most of an orbit should do a mighty good job of removing any accidental
contamination.  A simple set of reflectors (much like a suntanning
fanatic's silvery cardboard) could wrap sunlight all around the astronaut
to heat all surfaces near 100 C.

IIRC the white outer garment is teflon coated glass fiber fabric, and so
should not absorb spills anyway.

--
Doug Jones
Rocket Plumber, XCOR Aerospace
http://www.xcor-aerospace.com

Date: Sat, 15 Jan 2000 14:16:50 -0800
From: Doug Jones <random@qnet.com>
Newsgroups: sci.space.policy
Subject: Re: Fuel contamination in vacuo Was: UPI on GRO De-Orbit

Doug Jones wrote:
> both UDMH and N2O4 have vapor pressures
> higher than that of water...

I just looked UDMH up on the NIST webbook
http://webbook.nist.gov/chemistry/ and its 1 bar boiling point is 64 C,
significantly lower than water.  It should evaporate quickly at anything
over 20 C in vacuum, so the concept should work well, provided the outer
layers of the suit are properly warmed and interior layers can "breathe" to
vacuum after contamination.

N2O4 boils at 21 C, and should evaporate *very* quickly in vacuum.  Simply
using an infrared imager to view the exterior of a suit should confirm that
it is too warm for the volatile propellants to remain.

For reference, acetone boils at 329 K (56 C) and alcohol at 352 K (79 C),
so that should give an idea of how quickly UDMH should evaporate (I trust
that few people on this newgroup have ever handled hydrazine, while many
have experience with solvents).  It's difficult to see how leaked UDMH
would stick around for long in vacuum and sunlight.

--
Doug Jones
Rocket Plumber, XCOR Aerospace
http://www.xcor-aerospace.com

Date: Sat, 15 Jan 2000 19:25:24 -0800
From: Doug Jones <random@qnet.com>
Newsgroups: sci.space.policy
Subject: Re: Fuel contamination in vacuo Was: UPI on GRO De-Orbit

pat wrote:
>
> my understanding is UDMH will pass right through the suit fabric and
> can poison the spacewalker.
>
> pat

I doubt if it will pass through a teflon-matrix glass fiber composite,
which is what the outer layer of a space suit is.  The gloves (most likely
site of contamination) have multiple layers, at least one of them by
necessity gas tight. With the large absolute pressure ratio from inside to
outside, I doubt if you could get any diffusion inward through the pressure
bladder.

Now, *liquid* N2O4 might eat away rubber & such- but given the high vapor
pressures of UDMH and N2O4, I kinda doubt if you could get the liquid phase
to stick around for more than a few seconds before it all boils away...
you'd need to dump enough to chill down the suit surface all the way to the
freezing point before it could accumulate.

I gotta do a web search to see if this is a real problem.  I still doubt
it.

Splashing liquid UDMH on a suit would cause instant chilling of the surface
to around the freezing point of the UDMH (-57 C), just as water in vacuum
flash-freezes, then sublimes.  If the total amount of UDMH is large, quite
a bit of heat may be neded to evaporate it all away. (Recall the various
ice chunks they made on water dump outlets on the shuttle from time to
time- they lasted quite a while in sunlight.)

A black fabric "tent" and sunlight reflector could maximize heating of the
suit exterior- the astronaut would simply climb into the suit sauna for ten
minutes at the end of the EVA. Even though some UDMH could condense on the
ice in the suit cooling system, there is a large flow of water vapor coming
out of it.  Given the continuous purge of water vapor combined with suit
exterior heating, suit contamination should be easy to eliminate.

Of course, the sublimator water consumption would rise dramatically as the
suit is heated, but this would be just a few minutes at the end of the EVA,
not the full duration.

One technique for dealing with eye contamination with Methyl Ethyl Ketone
(MEK) is to hold a blowoff nozzle at arm's length- the MEK evaporates
faster than you can get to an eyewash station.  (A trick I learned from a
machinist with paintbooth experience- obviously only works if you have an
air nozzle immediately at hand.)  Same idea, when you come right down to
it- evaporate the noxious material instead of washing it away.

Bottom line: UDMH and NTO contamination in vacuum appear to be solvable
problems and should not be mission planning contraints.

--
Doug Jones
Rocket Plumber, XCOR Aerospace
http://www.xcor-aerospace.com