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CX2SA > TECH 23.06.06 23:25l 195 Lines 11387 Bytes #999 (0) @ WW
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Subj: The spacesuit (1/2)
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THE SPACESUIT
=============
To explore and work in space, human beings must take their environment with
them because there is no atmospheric pressure and no oxygen to sustain life.
Inside the spacecraft, the atmosphere can be controlled so that special
clothing isn't needed, but when outside, humans need the protection of a
spacesuit.
Earth's atmosphere is 20 percent oxygen and 80 percent nitrogen from sea level
to about 75 miles up, where space begins. At 18,000 feet, the atmosphere is
half as dense as it is on the ground, and at altitudes above 40/000 feet, air
is so thin and the amount of oxygen so small that pressure oxygen masks no
longer do the job. Above the 63,000-foot threshold, humans must wear
spacesuits that supply oxygen for breathing and that maintain a pressure
around the body to keep body fluids in the liquid state. At this altitude the
total air pressure is no longer sufficient to keep body fluids from boiling.
Spacesuits for the space shuttle era are pressurized at 4.3 pounds per square
inch (psi), but because the gas in the suit is 100 percent oxygen instead of
20 percent, the person in a spacesuit actually has more oxygen to breathe than
is available at an altitude of 10,000 feet or even at sea level without the
spacesuit. Before leaving the space shuttle to perform tasks in space, an
astronaut has to spend several hours breathing pure oxygen before proceeding
into space. This procedure is necessary to remove nitrogen dissolved in body
fluids and thereby to prevent its release as gas bubbles when pressure is
reduced, a condition commonly called "the bends."
Spacesuits designed for the space station era will be pressurized to 8.3 psi;
therefore, the pre-breathing period will be shortened or diminished.
The spacesuit also shields the astronaut from deadly hazards. Besides
providing protection from bombardment by micrometeoroids, the spacesuit
insulates the wearer from the temperature extremes of space. Without the
Earth's atmosphere to filter the sunlight, the side of the suit facing the Sun
may be heated to a temperature as high as 250 degrees Fahrenheit; the other
side, exposed to darkness of deep space, may get as cold as -250 degrees
Fahrenheit.
SPACESUITS FOR THE SPACE SHUTTLE ERA
====================================
Astronauts of the space shuttle era have more than one wardrobe for space
flight and what they wear depends on the job they are doing.
During ascent and entry, each crewmember wears special equipment consisting of
a partial pressure suit, a parachute harness assembly, and a parachute pack.
The suit, consisting of helmet, communication assembly, torso, gloves and
boots, provides counter pressure and anti-exposure functions in an emergency
situation in which the crew must parachute from the orbiter. The suit has
inflatable bladders that fill it with oxygen from the orbiter. These bladders
inflate automatically at reduced cabin pressure. They also can be manually
inflated during entry to prevent the crew member from blacking out. Without
the suit pressing on the abdomen and the legs, the blood would pool in the
lower part of the body and cause a person to black out as the spacecraft
returns from microgravity to Earth's gravity. The partial-pressure suit and
equipment will support a crew member for a 24-hour period in a life raft in
case of an egress over water.
Working Inside the Space Shuttle
--------------------------------
During orbit, astronauts work inside the space shuttle in shirt-sleeve
comfort. Prior to a mission, crew members are outfitted from a selection of
clothing including flight suits, trousers, lined zipper jackets, knit shirts,
sleep shorts, soft slippers, and underwear. The materials of every component
of the clothing are flame retardant. Covering the exterior of the garments are
close-able pockets for storing such items as pens, pencils, data books,
sunglasses, a multipurpose Swiss army pocketknife, and scissors.
Working Outside the Space Shuttle
---------------------------------
To work in the open cargo bay of the space shuttle or in space, astronauts
wear the shuttle extravehicular mobility unit (EMU) spacesuit, which was
developed to be more durable and more flexible than previous spacesuits were.
The suit is modular in design, with many interchangeable parts. The upper
torso, lower torso, arms, and gloves are manufactured in different sizes and
can be assembled for each mission in combinations needed to fit men and women
astronauts. This design is cost-effective because the suits are reusable and
not custom fitted as were spacesuits used in previous NASA manned space flight
programs.
Suiting up
----------
The EMU comprises the spacesuit assembly, the primary life support system
(PLSS), the display and control module, and several other crew items designed
for spacewalks and emergency life support. The EMU accommodates a variety of
interchangeable systems that interconnect easily and securely in single-handed
operation for either normal or emergency use. When preparing to work in space,
the astronaut goes into the airlock of the space shuttle orbiter and puts on
the following parts of the EMU:
* A urine-collection device that receives and stores urine for transfer later
to the orbiter waste management system.
* A liquid cooling and ventilation garment, a one-piece mesh suit made of
spandex, zippered for front entry, and weighing 6.5 pounds dry. The garment
has water-cooling tubes running through it to keep the wearer comfortable
during active work periods.
* An in-suit drink bag containing 21 ounces of potable water, the "Snoopy
Cap," or communications carrier assembly, with headphones and microphones for
two-way communications and caution-and-warning tones, and a biomedical
instrumentation subsystem.
To put on the spacesuit, the astronaut first dons the lower torso assembly and
then rises into the top section of the two-piece EMU spacesuit hanging on the
wall of the airlock. The upper torso of the spacesuit is a hard-shell
fiberglass structure that contains the primary life support system and the
display control module. Connections between the two parts must be aligned to
enable circulation of water and gas into the liquid cooling ventilation
garment and return. Then, the gloves are added and last to be donned is the
extravehicular visor and helmet assembly, which provides protection from
micrometeoroids and from solar ultraviolet and infrared radiation. Bearings in
the shoulder, arm, wrist, and waist joints allow the crewmember freedom of
movement. Bending, leaning, and twisting motions of the torso can all be done
with relative ease.
All fabric-to-hardware connections are made with either mechanical joints or
adhesive bonding. Materials used in the construction of the suit are selected
to prevent fungus or bacteria growth; however, the suit must be cleaned and
dried after flight use.
The entire suit assembly is rated with a minimum 8-year life expectancy. The
nominal operating atmospheric pressure in the suit is 4.3 psid. The suit
comprises several layers including a polyurethane-coated nylon pressure
bladder, a polyester structural restraint layer with folded and pleated joints
(for mobility), and a woven Kevlar, Teflon, and Dacron anti-abrasion outer
layer.
The maximum total weight of the largest size spacesuit assembly, including the
liquid cooling and ventilation garment, urine collection device, helmet and
visor assembly, communications carrier assembly, insuit drink bag, and
biomedical instrumentation subsystem, is 107 pounds.
The astronaut is ready to go to work in space and secures the necessary tools
to the mini-workstation of the suit. The EMU lights are mounted on the helmet
and are a necessity because during orbital operations approximately every
other 45 minutes are spent in darkness.
Communications
--------------
An electrical harness inside the suit connects the communications carrier
assembly and the biomedical instrumentation equipment to the hard upper torso
where internal connections are routed to the extravehicular communicator by
means of a pass-through.
The extravehicular communicator attaches to the upper portion of the life
support system at the back of the hard upper torso. The controls are located
on the display and control module mounted on the chest at the front of the
upper torso. The extravehicular communicator provides radio communication
between the suited crew member and the orbiter. In addition,
electrocardiographic (EKG) information is telemetered through the
extravehicular communicator to the orbiter and to flight surgeons in the
Mission Control Center at Houston, Texas.
The radios for spacewalk communications have two single UHF channel
transmitters, three single-channel receivers, and a switching mechanism. These
backpack radios have a "low profile" antenna--a foot long rectangular block
fitted to the top of the PLSS. The radios weigh 8.7 pounds and are 12 inches
long, 4.3 inches high, and 3.5 inches wide.
Primary life support system
---------------------------
The PLSS consists of a backpack unit permanently mounted to the hard upper
torso of the suit and a control-and-display unit mounted on the suit chest.
The backpack unit supplies oxygen for breathing, suit pressurization and
ventilation. The unit also cools and circulates water used in the liquid
cooling ventilation garment controls ventilation gas temperature, absorbs
carbon dioxide, and removes odors from the suit atmosphere. The secondary
oxygen pack attaches to the bottom of the PLSS and supplies oxygen if the
primary oxygen fails. The control-and-display unit allows the crew member to
control and monitor the PLSS, the secondary oxygen pack, and, when attached,
the manned maneuvering unit.
Maneuvering in space
--------------------
The manned maneuvering unit (MMU) is a one-man, nitrogen-propelled backpack
that latches to the EMU spacesuit's PLSS. Using rotational and translational
hand controllers, the crew member can fly with precision in or around the
orbiter cargo bay or to nearby free-flying payloads or structures, and can
reach many otherwise inaccessible areas outside the orbiter. Astronauts
wearing MMU's have deployed, serviced, repaired, and retrieved satellite
payloads.
The MMU propellant-non-contaminating gaseous nitrogen stored under high
pressure--can be recharged from the orbiter. The reliability of the unit is
guaranteed with a dual parallel system rather than a backup redundant system.
In the event of a failure in one parallel system, the system would be shut
down and the remaining system would be used to return the MMU to the orbiter
cargo bay The MMU, which weighs 310 pounds, includes a 35-mm still photo
camera that is operated by the astronaut while working in space.
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