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Liftoff to Learning: Go For EVA!
Video Title: Go For EVA!
Video Length: 13:48
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Description: Go for EVA! discusses the reasons for wearing
spacesuits during spacewalking missions, how spacesuits work, and
what kinds of jobs astronauts perform while spacewalking.
Science Process Skills:
Observing
Measuring
Inferring
Investigating |
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Subjects: Spacewalking and the environment
of outer space.
Science Standards:
Science as Inquiry
Physical Science
- Position and motion of objects
- Properties of objects and materials
Unifying Concepts and Processes
-Change, constancy, and measurement
- Evidence, models, and exploration
Science and Technology
- Abilities of technological design
History and Nature of Science
-Science as a human endeavor |
Table of Contents
Background
When astronauts travel into space, they must carry part of Earth's environment
with them. Air for breathing and for exerting pressure, food and water,
and moderate temperatures are contained in a physical shell called a spacecraft.
This shell also provides protection against high speed micrometeoroid
particles. On some space missions the shell is deliberately opened and
astronauts pass through an airlock to venture outside. When doing so,
they must still be protected, but by a smaller and specialized version
of their spacecraft called the Extravehicular Mobility Unit (EMU). This
smaller spacecraft is composed of a spacesuit with a life-support system.
It is different from the larger spacecraft by being anthropomorphic (human)
in shape and flexible. Flexibility permits movement of arms and legs and
operation of many types of scientific apparatus, taking pictures, assembling
equipment and structures, piloting the Manned Maneuvering Unit (MMU),
and repairing and servicing defective and worn-out satellites and other
space hardware. All these tasks are called Extravehicular Activities,
or EVAs.
The Outer Space Environment
Outer space is just what its name implies. It is the space, or vacuum,
that surrounds the uppermost reaches of the atmosphere of Earth and all
other objects in the universe. Although it is a void, outer space may
be thought of as an environment. Radiation and objects pass through it
freely. An unprotected human or any other unprotected living being placed
in the outer space environment would perish in a few brief, agonizing
moments.
The principle environmental factor of outer space is the vacuum, or nearly
total absence of gas molecules. The gravitational attraction of large
bodies in space, such as planets and stars, pulls gas molecules close
to their surfaces, leaving the space between them virtually empty. Some
stray gas molecules are found between these bodies, but their density
is so low that they can be thought of as practically nonexistent. Air
inside unprotected lungs would immediately rush out.
On Earth, the atmosphere exerts pressure in all directions. At sea level
on Earth, that pressure is 101 kilopascals. In space, the pressure is
nearly zero. Under virtually no pressure from the outside, dissolved gases
in body fluids expand, pushing solids and liquids apart. The skin expands
much like an inflating balloon. Bubbles that form in the bloodstream render
blood ineffective to transport oxygen and nutrients to the body's cells.
Furthermore, the sudden absence of external pressure, which balances the
internal pressure of body fluids and gases, can rupture fragile tissues
such as eardrums and capillaries. The net effect on the body is swelling,
tissue damage, and a deprivation of oxygen to the brain that results in
unconsciousness in less than 15 seconds.
The temperature range found in outer space provides a second major hazard
for humans. At Earth's distance from the Sun, the sunlit side of objects
in space may climb to over 120 degrees Celsius, and the shaded side may
plummet to lower than minus 100 degrees Celsius. Maintaining a comfortable
temperature range becomes significant.
Other-environmental problems encountered in outer space include weightlessness,
electrically charged particle radiation from the Sun, ultraviolet radiation,
and micrometeoroids. Micrometeoroids are usually very small bits of rock
and metal left over from the formation of the solar system and from the
collisions of comets and asteroids. Though small in mass, these particles
travel at very high velocities and can easily penetrate human skin and
thin metal. Equally dangerous is debris from previous space missions.
A tiny paint chip, traveling at thousands of kilometers per hour, can
do substantial damage.
Spacesuits were first used by the U.S. manned space flight program for EVAs
during the Gemini missions. The suits were custom built to each astronaut's
body size. In the Apollo program, for example, an astronaut had three custom
suits: one for flight, one for training, and one for flight backup. Space
Shuttle spacesuits, however, are tailored from a stock of standard size
parts to fit astronauts over a wide range of individual variations.
In constructing the Shuttle spacesuit, developers were able to concentrate
all their designs toward a single function, going EVA. Spacesuits in earlier
manned spaceflight programs had to serve multiple functions. They had to
provide backup pressure in case the cabin lost pressure, protection if ejection
became necessary during launch, EVA in weightlessness, and EVA while walking
on the Moon in one-sixth Earth's gravity. Suits were worn during lift-off
and re-entry and had to be comfortable under the high-G forces experienced
during acceleration and deceleration.
Now, Shuttle suits are worn only when it is time to venture outside the
orbiter cabin. At other times, crew members wear comfortable shirts and
slacks or shorts. The Shuttle's EMU provides pressure, thermal and micrometeoroid
protection, oxygen, cooling water, drinking water, food, waste collection
(including carbon dioxide and perspiration removal), electrical power, light,
vision, and communications. Maneuvering for traveling beyond the Shuttle
can be added by fitting a gasjet-propelled Manned Maneuvering Unit over
the EMU's primary life support system.
Many Layers
Protection of Shuttle astronauts on EVAs is accomplished with the 12
layers of the EMU. The first two layers, starting from the inside,
make up the liquid cooling and ventilation garment. It is made of Spandex
fabric and plastic tubing. Next comes a pressure bladder layer of urethane
coated nylon and a fabric layer of pressure restraining Dacron. This is
followed by a seven layer thermal micrometeoroid garment of aluminized Mylar,
laminated with Dacron scrim, and topped with a single layer of fabric combining
Gortex, Kevlar, and Nomex.
The Shuttle EMU consists of 19 major components. Fully assembled, it becomes
a short-term spacecraft for one person. On Earth, the suit and all its parts
weigh about 113 kilograms. Orbiting above the Earth, they have no weight
at all. They do, however, retain their mass in space, which is felt as resistance
to a change in motion.
1. Primary Life Support System (PLSS) A backpack unit containing
the oxygen supply, carbon dioxide removal equipment, caution and warning
system, electrical power, water cooling equipment, ventilating fan, and
radio.
2. Display and Control Module (DCM) Chest-mounted control
module containing all controls, a digital display, and the external liquid,
gas, and electrical connections. The DCM also has the primary purge valve
for use with the Secondary Oxygen Pack.
3. Electrical Harness (EH) (not shown) A harness worn inside
the suit to provide bioinstrumentation and communications connections to
the PLSS.
4. Secondary Oxygen Pack
(SOP) (not shown) Two oxygen tanks with a 30-minute emergency
supply, valve, and regulators. The SOP is attached to the base of
the PLSS but it can be removed from the PLSS for ease of maintenance.
5. Service and Cooling Umbilical (SCU) (not shown) Connects
the orbiter airlock support system to the EMU to support the astronaut
before EVA and to provide in-orbit recharge capability for the PLSS.
The SCU contains lines for power, communications, oxygen and water
recharge, and water drainage. The SCU conserves PLSS consumables during
EVA preparation.
6. Battery (not shown) Supplies electrical power for the EMU
during EVA. The battery is rechargeable in orbit.
7. Contaminant Control Cartridge (CCC) (not shown) Cleanses
suit atmosphere of contaminants with an integrated system of lithium
hydroxide, activated charcoal, and a filter contained in one unit.
The CCC is replaceable in orbit.
8. Hard Upper Torso (HUT) Upper torso of the suit, composed
of a hard fiberglass shell. It provides structural support for mounting
the PLSS, DCM, arms, helmet, IDB, EH, and the upper half of the waist
closure. The HUT also has attachments for mounting a miniworkstation
tool carrier.
9. Lower Torso Spacesuit pants, boots, and the lower
half of the closure at the waist. The lower torso also has a waist-bearing
for body rotation and mobility and brackets for attaching a safety
tether.
10. Arm Shoulder joint and armscye (armhole) bearing, upper
arm bearings, elbow joint, and glove-attaching closure. |
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11. Glove Wrist bearing and disconnect, wrist joint, and fingers.
One glove has a wristwatch sewn onto the outer layer. The gloves have tethers
for restraining small tools and equipment. Generally, crew members wear
thin fabric comfort gloves with knitted wristlets inside.
12. Helmet Plastic pressure bubble with neck disconnect ring
and ventilation distribution pad. The helmet has a backup purge valve for
use with the secondary oxygen pack to remove expired Carbon Dioxide.
13. Liquid Cooling and Ventilation Garment (LCVG) (not shown)
Long, underwear-like garment worn inside the pressure layer. It has liquid-cooling
tubes, gas ventilation ducting, and multiple water and gas connectors for
attachment to the PLSS via the HUT.
14. Urine Collection Device (UCD) (not shown) Urine collection
device consisting of a roll-on cuff adapter and storage bag (for male crew
members). The UCD is disposable after use.
15. Disposable Absorption Containment Trunk (DACT) (not shown)
Urine-collection garment consisting of a pair of shorts constructed from
five layers of chemically treated absorbent, non-woven, fibrous materials
(for female crew members).
16. Extravehicular Visor Assembly Assembly containing a metallic
gold-covered sun filtering visor, a clear thermal-impact protective visor,
and adjustable blinders that attach over the helmet. In addition, four small
"head lamps" are mounted on the assembly, and a TV camera transmitter
may also be added.
17. In-suit Drink Bag (IDB) (not shown) Plastic water-filled pouch
mounted inside HUT. A tube projecting into helmet permits crew member to
drink as if with a straw.
18. Communications Carrier Assembly Fabric cap with built-in earphones
and a microphone for use with the EMU's radio.
19. Airlock Adapter Plate (not shown) Fixture for mounting and storing
the EMU inside the airlock and for donning the suit.
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Extravehicular activity (EVA) - All tasks performed by astronauts
outside their spacecraft.
Extravehicular Mobility Unit (EMU) - Spacesuit.
Manned Maneuvering Unit (MMU) - Backpack propulsion unit
worn by astronauts for maneuvering in space.
Micrometeoroids - Tiny bits of naturally occurring rock and
metal traveling through space at high velocities.
Vacuum - A space with nothing in it.
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Classroom Activities
The following hands-on activities demonstrate some of the concepts presented
in this videotape.
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Potato and Straw
Materials
Large potato
Plastic straws (not flexible type)
Instructions
To illustrate why it is important to protect astronauts from high-velocity
micrometeoroids in space, show how easy it is to penetrate a potato
with a straw. First, slowly press the end of a straw to the potato.
The straw will bend or break Take a second straw and sharply strike
the potato with the end of it. It will penetrate completely through
the potato. Even though micrometeoroids have very low mass, they
can cause severe injury to an astronaut because of their high velocities.
Caution: Be careful not to hit your hand.
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Vacuum Pump
Demonstrations
Materials
School vacuum pump,
plate, and bell jar
Balloon filled with water
Windup alarm clock
Instructions
Demonstrate why it is important to provide pressure for an astronaut
in space by placing a balloon filled with water inside the bell jar
and pumping out the air from the jar. |
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As the pressure is lowered, water in the balloon begins to boil and the
balloon expands. The same thing could happen to human tissues exposed to
the vacuum in space. A vacuum pump can also be used to demonstrate why radios
are needed for communication between space-walking astronauts. Start the
clock's alarm ringing, and begin pumping out the air under the bell jar.
Listen to the sound of the alarm diminish as the air is evacuated.
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Bending Under Pressure
Materials
Two long balloons
Plastic or metal rings or heavy rubber bands
Instructions
To provide adequate pressure for astronauts on spacewalks, a flexible,
but nonexpendable layer of the spacesuit contains oxygen. Oxygen
is fed into this layer under pressure, and the pressure is exerted
on the astronaut. Unfortunately, the pressure makes the suit stiff.
To illustrate this problem and what can be done about it, inflate
a long balloon and let students try to bend it. Inflate a second
balloon, but when doing so, use rings or rubber bands to pinch off
the balloon like sausage links. The rings or bands provide joints
that make bending easier.
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STS-37 Crew Biographies
Commander: Steven R.Nagel (Col.,USAF)
Pilot: Kenneth D.Cameron (Lt.Col.,USMC)
Mission Specialist: Linda Godwin (Ph.D.)
Mission Specialist: Jerry L.Ross (Lt.Col,USAF)
Mission Specialist: Jay Apt (Ph.D.)
To obtain biographic information, click on highlighted names
The following books will provide additional information:
Compton,W. & Bensen, C., Living and Working In Space,A History
of Skylab, NASA SP-4208, Scientific and Technical Information Branch,
NASA, 1983.
Cortwright, E.M., ed., Apollo Expeditions to the Moon, NASA SP-350,
Scientific and Technical Information Office, National Aeronautics and
Space Administration, 1975.
Mohler, S.R., Johnson, B.H., Wiley Post. His Winnie Mae. and the World's
First Pressure Suit, Smithsonian Institution Press, 1971.
Vogt, G., Suited For Spacewalking' Teacher's Guide With Activities
For Physical And Life Science, EG-101, National Aeronautics and Space
Administration, 1994.
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