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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:
  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


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.

Spacesuit Design  contents

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.

 Shuttle EMU Components  contents

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.

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.
 drawing of space suit

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.

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.

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.

 Terms  contents
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.

Classroom Activities

The following hands-on activities demonstrate some of the concepts presented in this videotape.

Potato and Straw


Large potato
Plastic straws (not flexible type)
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.

potato and straw illustration

Vacuum Pump Demonstrations


School vacuum pump,
plate, and bell jar
Balloon filled with water
Windup alarm clock

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.
vacuum pump illustration

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.

Bending Under Pressure


Two long balloons
Plastic or metal rings or heavy rubber bands

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.

balloons bending

References  contents

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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