Extra Vehicular Activity (EVA)


The harsh environment of space challenges human survival. A lack of oxygen and atmospheric pressure, intense radiation, and the lack of gravity confront humans in space. The metals and machines of our space vehicles ensure some safety, but a human outside the protection of a spacecraft bears the brunt of the danger.


Astronauts on EVA face danger, but they do not merely pull on a spacesuit and stroll outside. Most EVA's are planned and well practiced beforehand. Once assigned to a mission, astronauts go to school. Attending classes on technical and theoretical aspects of the mission, the astronauts also perform simulations of procedures to be used during the mission. The simulations are conducted in an environment as similar to space as possible -- a swimming pool. A very special swimming pool, the Weightless Environmental Training Facility, or WETF, contains a life size mockup of the space shuttle cargo bay. Here astronauts put their classroom training to the test.


The classes also teach astronauts about the necessary tools for EVA's. In addition to a spacesuit, an astronaut also carries a manned maneuvering unit, or MMU. Basically a backpack, this device is propelled by gaseous nitrogen. It and the astronaut's spacesuit are considered the smallest manned spacecraft ever made. EMU lights are mounted on the helmet to provide light in shade. A TV camera, also mounted on the helmet, allows ground support and shuttle crew to give better instructions during problem situations. Tethers at the waist prevent tools from floating off, and thermal mittens protect against extreme temperatures. A checklist on a wrist provides procedures for performing EVA tasks and correcting EMU problems.


Extra vehicular activity, or EVA, is needed for many of our tasks in space. The historic landing on the moon by Neil Armstrong, Michael Collins, and Buzz Aldrin began a series of lunar landings, the Apollo missions. These missions brought new knowledge due to lunar surface explorations -- all EVA's. In addition, many of the satellites that now ring our planet are launched, repaired, and serviced during EVA's, providing increased communications. More than easing the passing of voices and information around the globe, more than increasing mankind's knowledge banks, EVA's demonstrate the awesome immensity that surrounds our world, and mankind's ability to exist in it.

Class Discussion

  1. The WETF mimics the microgravity of space as close as possible, yet the human body is buoyant. How do the astronauts keep from rising to the surface while performing underwater experiments?

  2. In space it is much more difficult to work because the lack of gravity leaves nothing to provide leverage. Every movement will not only displace the object being worked on but also the astronaut as well. How do astronauts maintain leverage? Can you name any device that helps in such situations?

  3. Name some examples of extra-vehicular activity that you have heard about, or what you think astronauts do on EVA's.

  4. The EMU light provides illumination in shady work areas. Where could you find shade in space?

Class Activities and Research

  1. Find out if there are other ways to simulate microgravity on Earth. What does the United States use in its space program? What did the Soviet Union use to train their astronauts?

  2. What was the most recent EVA about?

  3. Discuss what you think an astronaut feels like on an EVA. Write a letter to an astronaut who has been on a space walk. Ask what did he or she did on EVA, what he or she thought or felt.

  4. How many astronauts from other countries have been involved in EVA's?

Man-Vehicle Laboratory
MIT Department of Aeronautics and Astronautics
17 March 1997