National Aeronautics and Space
Administration
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Suited for Spacewalking

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Excerpt: Suited for Spacewalking
SSR: Editing

Earth and Space

If we loosely define an astronaut as someone who travels through space, then everyone is an astronaut. Even though we may be standing still on the surface of the Earth, we are actually traveling through space. Indeed, our planet may be thought of as a spaceship on a never-ending voyage. As "astronauts" traveling through space on the surface of the Earth, we take for granted the complex environment that sustains life. Earth's gravitational attraction holds a dense atmosphere of nitrogen, oxygen, carbon dioxide, and water vapor in a thick envelope surrounding Earth's entire surface. The weight of this atmosphere exerts pressure, and its movements distribute heat from the Sun to balance global temperatures. Its density filters out harmful radiations and disintegrates all but the largest meteoroids. Earth's atmosphere is a shell that protects and sustains the life forms that have evolved on its surface. Without the atmosphere's protection, life as presently known would not be possible.

When Earth astronauts leave the surface of their planet and travel into space, they must carry some of their environment with them. It must be contained in a physical shell because their body masses are too small to hold it in place by gravitational attraction alone. The shell that is used is called a spacecraft—a rigid collection of metal, glass, and plastic.