Spaceflight

paceflight means traveling in space. Manned spacecraft of dif­ferent kinds, from the space cap­sules of the 1960s and 1970s to the Space Shuttle, have carried people on spaceflights. Spacecraft called satellites are in flight as they orbit Earth. Space probes have visited planets such as Mars, Venus, and Jupiter, and they have even flown beyond the solar system.

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WHERE DOES SPACE START?

There are several definitions for where space begins. The atmosphere, a blanket of air around Earth, gradu­ally thins as altitude (distance from Earth’s surface) increases. Earth’s atmosphere fades away almost completely at the top of the thermo­sphere, which is about 400 miles (640 kilometers) from Earth’s surface. In terms of spaceflight, however, people define space as beginning much closer to home, either 50 miles (80 kilometers) or 62 miles (100 kilo­meters) above Earth’s surface. Space scientists and engineers refer to "entry interface" as being just over 75 miles (120 kilometers) above Earth’s surface. This is the point at which the air becomes thick enough to begin heating up a spacecraft as it returns from space.