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Guided Tour Of The Workings Of a Space Suit
By Guided Tour Of The Workings Of a Space Suit
3/18/04

SHUTTLE SPACE SUIT

N A S A
EDUCATIONAL BRIEFS For The Classroom

Outer space is a hostile environment. In order for astronauts to
survive there, part of the Earth's environment must be carried with
them. Air, pressure, and moderate temperatures have to be contained in
a shell surrounding the space traveler. One method of doing this is to
encase the astronaut in a protective flexible capsule called the space
suit.

Up to now, space suits on space missions from the Mercury Program
through the Apollo/Soyuz Test Project have been effective protection
but have been handicapped by certain design problems. They were
custom-fitted garments and in some suit models, more than 70 different
measurements had to be taken of the astronaut in order to manufacture
the suit to the proper fit. As a result, a space suit could be worn by
only one astronaut on only one mission. Space suits were stiff, and
simple motions such as grasping objects sapped the strength of an
astronaut. Even donning the suit was an exhausting process lasting, at
times, more than an hour and requiring the help of an assistant.

For the Space Shuttle astronauts, a new suit has been developed that
offers many improvements in comfort, convenience, and mobility over
the previous models. The suit, which is worn only outside the Shuttle,
is modular and features many interchangeable parts. Torso, pants,
arms, and gloves comes in several different sizes and can be assembled
for each mission in the proper combinations to suit individual
astronauts. This modular feature makes the Shuttle suit wearable on
more than one mission and results in significant cost savings. Space
Shuttle astronauts wear the suit when leaving the Orbiter cabin to
deploy payloads, repair and service satellites in orbit, and assemble
large structures from parts carried in the Orbiter cargo bay.

MAJOR COMPONENTS

The Shuttle suit, known as an EMU for Extravehicular Mobility Unit,
consists of three main parts: liner, pressure vessel, and primary life
support system. These components are supplemented by a drink bag,
communications set, helmet, and visor assembly.

The suit liner is technically called the liquid cooling and vent
garment. It is quite similar in appearance to long underwear with one
important difference. The stretchy, form-fitting nylon Spandex fabric
is laced with small Tygon plastic tubes. The outside layers of the
Shuttle suit are exceptionally well insulated making body heat
dissipation a critical concern. Water cooled in the life support
system circulates around the body it encloses through the plastic
tubes for temperature control. Openings in the fabric weave also
permit ventilation of the body.

The liquid cooling and vent garment is the first major suit component
donned by the astronaut. It is followed by the pressure vessel, a
multilayered garment. Actually, only one of the layers contains the
pressure. The remainder are comprised of alternating layers of
aluminized mylar plastic and unwoven Dacron that insulate the suit
from the Sun-to-shade temperature extremes of 148 degrees to minus 129
degrees in outer space. On top of those layers is a single outside
layer of though Ortho fabric, a combination of Teflon, Kevlar, and
Nomex with a neoprene liner, that serves as an abrasion and tear
resistant cover as well as the primary micrometeoroid shield.

The principal function of the pressure vessel is the containment of
oxygen under pressure to make a livable atmosphere for the astronaut.
One layer of Kevlar, lined with a polyurethane plastic bladder and
Dacron shell, contains the oxygen at a pressure of 281.24 grams per
square centimeter (4 psi). With a normal atmospheric mixture of
gasses, this pressure would be hardly livable. However, pure oxygen of
the suit atmosphere makes the pressure acceptable.

One of the major challenges in designing space suits has been to make
the pressure vessel flexible. With inside pressure, the vessel
inflates balloon-like and becomes stiff. On previous models, joint
areas such as the shoulders were made of molded neoprene rubber and
reinforced with cables. These joints required constant muscle exertion
to hold them in a flexed position. The pressure vessel fabric however,
permits tucks to be stitched in the shoulder, elbow, wrist, knee, and
ankle area. The tucks allow the joints to retain a flexed shape
without constant muscle exertion.

The final major component of the Shuttle suit is the PLSS or Primary
Life Support System. It is a two-part system consisting of a backpack
unit and a control and display unit on the suit's chest. The PLSS is
relatively heavy and the attachments of similar systems on Apollo
suits was an arduous process. To simplify the Shuttle suit, a
fiberglass shell, called the Hard Upper Torso or HUT, is built inside
the upper torso of the pressure vessel. The HUT is similar in
appearance to the breastplate of a suit of armor. The PLSS is
permanently mounted to the HUT and all necessary connections are made
through the suit's upper layers.

The backpack portion of the PLSS supplies oxygen for breathing, suit
pressurization, and ventilation. It also cools and circulates the
water used in the liquid cooling and vent garment and controls the
oxygen temperature. Still another function of the PLSS is the cleaning
of carbon dioxide and odors as well as other contaminants from the
suit's atmosphere. Depending upon the exertion of the astronaut
wearing the suit, there is a seven-hour oxygen supply in the backpack
with an extra half-hour emergency supply.

The front of the PLSS is a control and display unit. A microprocessor
automatically provides startup instructions, checks out the suit's
major functions, and warns the wearer of malfunctions. The
microprocessor is literally a computer on a tiny circuit chip.

WASTE CONTAINMENT SYSTEM

Containment of body wastes is a significant problem in space suit
design. As previously discussed, the PLSS will handle odors, carbon
dioxide, and contaminant gasses in the suit's atmosphere. A separate
system is required for urine relief. Because the Space Shuttle carries
both male and female crewmembers, two different systems have been
designed. Both systems are capable of containing approximately 900
milliliters of urine. Due to the short time durations of anticipated
space suit activity, fecal containment is considered unnecessary.

MINOR COMPONENTS

The final items in assembling the Shuttle suit for use are the helmet
and visor assembly. The helmet is a rigid, one-piece hemisphere of
ultraviolet polycarbonate plastic. Donning the helmet automatically
aligns the upper torso and helmet portions of the suit ventilation
system. On top of the helmet is placed a visor assembly that consists
of a visor with thermal/optical coatings, and center and side shades.
This assembly provides impact, visible light, and thermal protection
to the head region.

Prior to fixing the helmet in place, a "Snoopy-type" skull cap with
microphone and earphones for communications is placed on the head. A
radio in the PLSS relays crew voice transmissions as well as telemetry
from sensors that monitor the physiological condition of the
astronaut.

One other item is fixed in place prior to attaching the helmet. A
small in-suit drink bag is filled with 950 ml of water from the
Orbiter's portable water supply and placed inside the neck area of the
upper torso's HUT. A drink tube with a suction-actuated valve permits
occasional refreshment during EVA.

DONNING THE SPACE SUIT

To make ready for work outside the Space Shuttle, the astronaut enters
an airlock that exists into the Orbiter cargo bay. Here the crewmember
puts on the appropriate urine collection system and the liquid cooling
and vent garment. To simplify putting on the outer layers, the upper
torso of the pressure vessel and PLSS are mounted to one of the
airlock walls. The crew member pulls on the pants and then "dives" up
into the upper torso. The pants and upper torso are easily joined by a
metal ring connector at the waist. After the life support system is
actuated and all connections are made, the communications cap, helmet,
visor assembly, and gloves are attached. The entire process can be
completed without assistance and the crew member can be ready for work
in just minutes.

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QUESTIONS AND ACTIVITIES FOR THE CLASSROOM

1. What are the advantages of the Shuttle suit over previous
space suit models?

2. What makes it possible for the crewmember to survive in low
pressure atmosphere of the Shuttle suit?

3. What is one of the most challenging aspects in designing a space
suit? Why?

4. What are the main components of the Shuttle suit? What are their
functions?

5. Compare the environmental functions of space suits, space
capsules, and the Earth.

6. Research the history of space suit design from the early high-
altitude pressure suits to the new Shuttle suit.

7. Illustrate the need for tucked joints in the Shuttle suit
pressure vessel by inflating a long toy balloon. Bend the balloon
in the middle and note the need to constantly exert force to
retain the new shape.

8. Investigate the insulative properties of a variety of materials
such as aluminum foil, mylar plastic, and cloth. Form small
pouches from these materials and insert the bulb end of a
thermometer. Use a strong light bulb to radiate the pouch and
note the temperature changes over a unit of time. Also evaluate
the materials for tear and puncture resistance and flexibility.

9. Research the minimum environmental parameters required for human
survival in outer space.

10. Challenge the students to design an experiment that measures the
oxygen requirements of a "typical" astronaut during rest, and
light and strenuous exertion.

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NASA EDUCATIONAL BRIEFS For The Classroom, Shuttle Space Suit, EB-81-2

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