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Space exploration



Once in orbit, the space vehicle and everything inside it experience a condition called microgravity. The vehicle and its contents fall freely, resulting in an apparently weightless floating aboard the spacecraft. For this reason, microgravity is also referred to as zero gravity. However, both terms are technically incorrect. The gravitation in orbit is only slightly less than the gravitation on Earth. The spacecraft and its contents continuously fall toward Earth. But because of the vehicle's tremendous forward speed, Earth's surface curves away as the vehicle falls toward it. The continuous falling seems to eliminate the weight of everything inside the spacecraft. For this reason, the condition is sometimes referred to as weightlessness.

Microgravity has major effects on both equipment and people. For example, fuel does not drain from tanks in microgravity, so it must be squeezed out by high-pressure gas. Hot air does not rise in microgravity, so air circulation must be driven by fans. Particles of dust and droplets of water float throughout the cabin and only settle in filters on the fans.

The human body reacts to microgravity in a number of ways. In the first several days of a mission, about half of all space travelers suffer from persistent nausea, sometimes accompanied by vomiting. Most experts believe that this "space sickness," called space adaptation syndrome, is the body's natural reaction to microgravity. Drugs to prevent motion sickness can provide some relief for the symptoms of space adaptation syndrome, and the condition generally passes in a few days.

Microgravity also confuses an astronaut's vestibular system-that is, the organs of balance in the inner ear-by preventing it from sensing differences in direction. After a few days in space, the vestibular system disregards all directional signals. Soon after an astronaut returns to Earth, the organs of balance resume normal operation.

Over a period of days or weeks, an astronaut's body experiences deconditioning. In this process, muscles grow weak from lack of use, and the heart and blood vessels "get lazy." Strenuous exercise helps prevent deconditioning. Space travelers ride exercise bikes, use treadmills, and perform other types of physical activity.

After many months in space, a process called demineralization weakens the bones. Most physicians believe that demineralization results from the absence of stress on the bones in a weightless environment. The experiences of Soviet cosmonauts who spent long periods in orbit showed that vigorous exercise and a special diet can minimize demineralization.

Contributor: James Oberg, M.S., Spaceflight Engineer; author, UFOs and Outer Space Mysteries.
Source : World Book 2005

Space exploration
What is space?
Getting into space and back
Living in space
Meeting basic needs in space
Communicating with Earth
The dawn of the space age
Space probes
Probes to Venus
Probes to Jupiter and beyond
Probes to comets
Human beings enter space
Apollo: Mission to the moon
Exploring the moon
Returning to Earth
The International Space Station
Space shuttles
Types of shuttle missions