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Pettit | 
NASA
ISS Science Officer Don Pettit, background, and Expedition
Six Commander Ken Bowersox review a checklist as they
wrap up a U.S. spacesuit demonstration inside the Quest
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Expedition
Six
Space Chronicles #14
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By:
ISS Science Officer Don Pettit
Space
Walk Prep
In the sci-fi
movies, astronauts can quickly don their spacesuits and in short
order, be out the door in the vacuum of space. They seem to always
be in a hurry to chase bad guys, alien monsters, or look for holes
in the hull spewing out precious atmosphere. In the reality of our
current technology, it does not happen this way. Perhaps with future
invention it will be more like in the movies, but for the present,
we have less advanced technology.
Nothing happens
fast during the preparations for a space walk. Thelarge amount of
time needed to prepare is partly due to the sheer magnitude of the
technical chores and partly due to human physiology. And you must
pay attention to the techno-details as if your life depended on
them. Making a mistake here is no longer minus ten points on a midterm
exam. It takes several days over about a week to prepare for a space
walk.
First you do
some house cleaning. The airlock tends to be used as a storage place
for other bulky items so it must be cleaned up and organized. You
do not want anything in the airlock that is not related to your
pending activity lest it interferes in some obtuse way.
Your spacesuit
must be assembled from a suitcase full of parts, where you pay special
attention to the rubber ring seals and corresponding mating surfaces.
You do not want a leak.
There are batteries
to tend, where they are first discharged and then recharged to ensure
the best possible performance. And there are three different kinds
of batteries, a large one that operates your spacesuit, smaller
ones for running your helmet lights, and another for the glove heaters
and helmet video camera. You do not want to be outside and have
your batteries die from the same neglect that so often happens when
you unplug a laptop computer.
It is important
to regenerate the carbon dioxide scrubbers. They are like a small
chemical factory built into the spacesuit using reversible chemical
reactions with silver oxide as the absorption substrate. They are
placed in a special oven and baked out over a 14-hour cycle.
You check the
cooling system that includes a pump and many feet of clear thin-walled
plastic tubing sewn into your long underwear. You check the connections
for leaks and observe the flow for excess bubbles. The pump shaft
rotates at 20,000 revolutions per minute. Cavitation at this speed
is not desirable. If bubbles are present, you bleed them out.
You top off
the water tanks. Water sublimating from an icepack in the vacuum
of space transports away your metabolic heat from the latent heat
of sublimation.
Small details
are important. You clean your visor and spread a thin layer of anti-fog
on the inside surface. If there is too much anti-fog it can make
your eyes sting and water; too little and it will fog up. It has
to be just right if you want to see. You install a valsalva device
on the inside of the helmet. Shaped like two small side-by-side
mounds, this block of soft rubber is used to plug your nose without
a helping hand so you can clear your ears during the pressure changes.
It has the habit of snagging your headset cord if it is not installed
at the correct angle.
You should
not forget to check coated membranes in your headset. They keep
onerous water vapors out of the headphones. Condensing water vapor
from sweat shorts out the headset and results in a loss of communications.
That alone could prematurely end a space walk.
You install
your drink bag and place the straw so it will not tangle in the
headset cord. If there is air in your drink bag, it will expand
and burp out a few ounces creating fluid spheres inside of your
helmet. Like irksome bug spots on your windshield, they invariably
find their way onto the visor right where you need to see the most.
Or they ricochet off obstacles as if playing three-dimensional pinball
until they settle into your eye. You score five thousand points
for that one. You make sure to burp all the air out of your drink
bag.
You dress up
in your spacesuit in a dry-run to check the fit, the sizing, and
to check the operations of all the systems. You do a leak check
to verify the pressure integrity. You check out your SAFER, a compressed
nitrogen thruster backpack used to fly back to structure if by some
mistake you were to drift off. When we do a space walk without the
presence of a docked Space Shuttle, drifting away from structure
would be a fatal mistake. You would literally become Earth's newest
satellite. The most anyone on the ground could do is wish upon a
falling star. If it were to happen, the SAFER backpack gives you
one brief chance to correct this situation and you make certain
the equipment is in good form.
You set up
your tools. Some have batteries to recharge. Some have protruding
handles that always seem to get in the way. Like solving a puzzle
cube, you juggle the tools on your workstation until they all fit
in the right place. You load film and change batteries in the space
camera.
All the tools
have strings attached -- retractable strings we call tethers. You
check all the tethers for cuts and frays and smooth retraction.
A tether that won't retract is as responsive as a tangled spool
of fishing line on a spin-cast reel.
You review
your script. Like part actor in a Broadway play and part Olympic
athlete, you think, you plan, you rehearse your part and your actions
until you know them by heart. In your sleep, you dream about your
part. You know where every bolt and pin is located, what direction
it is oriented, and how much torque is required. You know to expect
a forward lurch and a clunk after 10 turns of a stanchion bolt and
then 17 more before the running torque begins to increase. If it
does not happen this way, something is wrong and you must stop and
investigate.
The Universe
is a tough critic, and the reviews will not be good if you have
slacked in your preparations. Preparing oneself to go out the hatch
on space walk day involves a carefully crafted ritual. The bends,
a condition where nitrogen bubbles are squeezed out from solution
in your blood stream causing all sorts of circulation havoc, are
well known in the field of deep sea diving. You would not expect
such problems associated with diving to the bottom of the oceans
to also occur in the orbital environment of space, but it does.
The space station is pressurized to one atmosphere pressure at 20percent
oxygen and 80percent nitrogen, just what is found on Earth at sea
level. A spacesuit operates with a 100percent oxygen atmosphere
at about 1/4th of an atmosphere pressure. If one were to quickly
go from space station into the spacesuit, a case of the bends could
develop, rendering one incapacitated.
On space walk
day, you start off with an exercise period on a stationary bicycle
while breathing 100percent oxygen through a facemask attached to
120 feet of snaking hose. An exercise prescription, carefully crafted
by flight surgeons, is followed where you exercise at known wattage
rates for set periods of time. The increased cardiovascular circulation
while breathing 100percent oxygen rapidly purges your blood stream
of excess nitrogen. A rather short period of this exercise replaces
many hours of the standard oxygen pre-breath. While still breathing
from a now sweat-fogged facemask, you towel off and take care of
any toilet duties. Wrestling 120 feet of stiff snaking hose is a
pain in weightlessness until you find yourself in need of a toilet
which is located it seems, about 122 feet away. You find your way
back to the airlock and isolate the compartment from the rest of
space station where the pressure is lowered to the equivalent of
being on a mountain at 9,200 feet. Only then can you remove the
oxygen masks.
Now the task
of suiting up begins. You rely on the help from an extra crew member,
referred to in space vernacular as the "IV." He tugs on
the sleeves of your synthetic-fiber long underwear to straighten
out wrinkles, locks connectors forged from aluminum alloy located
in places that are hard to reach, buttons down flaps, and installs
your composite helmet with a gold-plated polycarbonate visor.
Spacesuit gloves
make a nice click when they are installed. Eight little doggies
make a sound with the quality of the finest Swiss-made mechanism.
You have a vested interest in listening for this sound.
This help struck
me as the space age equivalent of squires helping knights of the
middle ages suit up for battle. I can imagine their squires smoothing
wrinkles in chain mail, fastening heavy buckles with leather straps,
tugging hearth-forged metal plates into their proper overlap, and
installing the metal helmet with a forged slit visor.
Our IV helps
us dismount from the wall, assists with the SAFER backpack, and
stuffs us in the now much smaller part of the airlock that will
be vented into space. This part of the airlock, which seemed so
roomy without your spacesuit, now seems cramped. A thousand years
earlier, a squire would attach the scabbard that sheaths the broad-blade
sword and mount the knight on his steed. It amuses me to ponder
how far we have advanced, yet how similar the human actions remain.
It takes about
six hours from the time you start in the morning to the time you
are ready to open the hatch. After having gone through all of this
preparation, you will not take lightly to a hatch that does not
want to open. For us the crank would rotate almost to the open position
and then hang up. It was not a hard metallic type of jam but more
like a piece of rubber that was blocking the mechanism. No amount
of torque would make it budge. I thought we were going to break
the handle off. We wanted to go outside, real bad.
The hatch dogs
were partly released and allowed the hatch to crack open perhaps
3/8th of an inch. A shaft of brilliant sunlight came through the
crack as if teasing us to come out and play when it knew we could
not. Fortunately, experience gained by owning an old pickup truck
with cantankerous doors came in handy. With a little jockeying on
the handle and some soft-spoken words, the hatch came open and we
started our day. If we were chasing bad guys, I am afraid they would
be well into hyperspace by now.
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