Other Free Encyclopedias » Science Encyclopedia » Science & Philosophy: Adam Smith Biography to Spectroscopic binary » Manned Spacecraft - Ongoing Debate: Crewed Vs. Uncrewed Flight, Overview, One-person Crewed Spacecraft, Two- And Three-person Spacecraft - Technical requirements of crewed spacecraft

Manned Spacecraft - Reentry Problems And Solutions

earth human vehicle moon

Ensuring that astronauts and cosmonauts are able to survive in space is only one of the problems facing space scientists. A spacecraft must also be able to return its human passengers safely to the earth's surface. In the earliest crewed spacecraft, this problem was solved simply by allowing the vehicle to travel along a ballistic path back to the earth's atmosphere and then to settle on land or sea by means of one or more large parachutes. Later spacecraft were modified to allow pilots some control over their reentry path. The space shuttles, for example, can be piloted back to Earth in the last stages of reentry in much the same way that a normal airplane is flown.

Perhaps the most serious single problem encountered during reentry is the heat that develops as the spacecraft returns to the earth's atmosphere. Friction between vehicle and air produces temperatures that exceed 3,000°F (1,700°C). Most metals and alloys would melt or fail at these temperatures. To deal with this problem, spacecraft designers have developed a class of materials known as ablators that absorb and then radiate large amounts of heat in brief periods of time. Ablators have been made out of a variety of materials, including phenolic resins, epoxy compounds, and silicone rubbers.

Some are beginning to look beyond space shuttle flights and the International Space Station. While NASA's main emphasis for some time will be unmanned probes and robots—in terms of spacecraft variety, not funding (most of which goes to the manned spaceflight program)—the most tempting target for a manned spacecraft will surely be Mars. Besides issues of long-term life support, any such mission will have to deal with long-term exposure to space radiation. Without sufficient protection, galactic cosmic rays would penetrate spacecraft and astronaut's bodies, damaging their DNA and perhaps disrupting nerve cells in their brains over the long-term. (Manned flights to the Moon were protected from cosmic rays by the earth's magnetosphere.) Shielding would be necessary, but it is always a trade-off between human protection and spacecraft weight. Moreover, estimates show it could add billions of dollars to the cost of any such flight.

See also Space probe.


Resources

Books

Compton, W. David, and Charles D. Benson. Living and Working in Space. Washington, DC: NASA, 1983.

Dotto, Lydia, Stephen Hart, Gina Maranto, and Peter Pocock. How Things Work in Space. Alexandria, VA: Time-Life Books, 1991.

Newton, David E. U.S. and Soviet Space Programs. New York: Franklin Watts, 1988.

Periodicals

Kahn, Joseph. "Chinese Space Effort Challenges Russia and U.S." New York Times (January 3, 2003).

Purdum, Tom S. "After Moon, No Giant Leaps in Space Allure." New York Times (February 9, 2003).

Wald, Matthew L. and John M. Broder. "Tapes of Shuttle's Descent Show Dawning of Disaster." New York Times (February 12, 2003).

David E. Newton
Larry Gilman
Alexander Ioffe
K. Lee Lerner

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Crewed spacecraft

—A vehicle designed to travel outside the earth's atmosphere carrying one or more humans.

Docking

—The process by which two spacecraft join to each other while traveling in orbit.

EVA

—Extravehicular activity, a term describing the movement of a human being outside an orbiting spacecraft.

LRV

—Lunar roving vehicle, a car-like form of transportation used by astronauts in moving about on the moon's surface.

Module

—A cabin-like space in a spacecraft, usually part of a larger system.

Orbital flight

—The movement of a spacecraft around some astronomical body such as the earth or moon.

Redundancy

—The process by which two or more identical items are included in a spacecraft to increase the safety of its human passengers.

Space shuttle

—A crewed spacecraft used to carry humans and materials from the earth's surface into space.

Space station

—A manned artificial satellite in orbit about the earth, intended as a base for space observation and exploration.

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