A mannequin of Alan B. Shepard, Jr., the first American in space, is part of an exhibit at the National Air and Space Museum in Washington, D.C.

Photograph by Joseph D. Lavenburg and Robert S. Oakes, National Geographic
  • On May 5, 1961, Navy Commander Alan Bartlett Shepard, Jr., was launched into space from Cape Canaveral, Florida, in a capsule called Freedom 7. Shepard was the first American to travel to space. The flight took off at 9:34 a.m., and lasted just 15 minutes. In that short time, Shepard reached an altitude of 187 kilometers (116 miles) above the Earth.
    This launch was part of Project Mercury, an American effort to test humanity's capabilities in a space environment, as well as the conditions during and after a flight there. During his travel into space, Shepard and Freedom 7 passed through each level of the atmosphere: the troposphere, stratosphere, mesosphere, and thermosphere. In each level of the atmosphere, there are drastic shifts in pressure, density, temperature, and chemical composition.
    Freedom 7, as well as almost all spacecraft that came after, were single-use vehicles. Engineers working on the space shuttles, the only spacecraft designed for multiple use, used knowledge from early missions such as Freedom 7 to know more about the atmosphere and its layers in order to make shuttle missions safe.
  • Term Part of Speech Definition Encyclopedic Entry
    altitude Noun

    the distance above sea level.

    Encyclopedic Entry: altitude
    atmosphere Noun

    layers of gases surrounding a planet or other celestial body.

    Encyclopedic Entry: atmosphere
    density Noun

    number of things of one kind in a given area.

    Encyclopedic Entry: density
    mesosphere Noun

    region in Earth's atmosphere between the stratosphere and the thermosphere, about 50-80 kilometers (31-50 miles) above the Earth's surface.

    outer space Noun

    space beyond Earth's atmosphere.

    pressure Noun

    force pressed on an object by another object or condition, such as gravity.

    spacecraft Noun

    vehicle designed for travel outside Earth's atmosphere.

    stratosphere Noun

    level of Earth's atmosphere, extending from 10 kilometers (6 miles) to 50 kilometers (31 miles) above the surface of the Earth.

    temperature Noun

    degree of hotness or coldness measured by a thermometer with a numerical scale.

    Encyclopedic Entry: temperature
    thermosphere Noun

    layer of the Earth's atmosphere located between 80 kilometers (50 miles) and 550 kilometers (341 miles) above the Earth's surface.

    troposphere Noun

    lowest layer of the Earth's atmosphere, extending from the surface to about 16 kilometers (10 miles) above.