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When an astronaut says she?s floating in ?zero gravity,? does she mean she has escaped Earth?s pull? Not at all. ?Zero g? might sound as if gravity has been magically switched off, but what she?s referring to is the effect of weightlessness caused by a constant state of free fall around the Earth.
To visualize this, imagine riding in the world?s tallest elevator. If the elevator is allowed to drop freely, then under the influence of gravity, it and everyone inside will fall at the same rate. Falling in an elevator is the same feeling as falling outside an elevator, except there?s no wind. Of course, the elevator can?t fall forever?at some moment, it will hit the ground unless we put on the brakes. Like the elevator, astronauts are also in free fall, but there are no cables or brakes to slow them down. So how do they stay in orbit so long without falling all the way to the ground? The space station is moving fast enough and high enough to avoid drag from the atmosphere and to remain in orbit. That?s how objects in orbit remain in orbit so long?everything in orbit must travel at high speeds. In the case of the space station?about 17,500 miles per hour!

U.S. Lab
Explorethe module where many experiments will take place.
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Sixteen countries are spending billions of dollars, many years, and risking the dangers of space to build the space station because they believe the benefits of the station will ultimately outweigh the enormous costs. Perhaps the most important benefit is that the space station allows humans to live and study for long periods in microgravity, or a ?weightless? environment. Since gravity influences almost every biological, physical, and chemical process on Earth, the space station gives us the unprecedented opportunity to study a world without gravity?and better understand gravity?s effects on plants, animals, and humans. Experiments taking place in the station?s six laboratories should have extraordinary benefits:
Future Space Travel
Think of the space station as a stepping-stone to the stars. If humans are ever going to travel to other planets, such as Mars, we must understand the effects of such long journeys on the human body. We?ve learned from past space travel that living in microgravity leads to the weakening of bones and muscles. The space station will allow scientists to understand these effects and study solutions for long-term space travel.
Medical Advances
Without gravity, chemical reactions behave differently than they do on Earth. This means that molecules can be blended and substances created that would be impossible on Earth. These experiments may lead to possible treatments for diabetes, AIDS, cancer, and organ transplants. Finally, watching the long-term effects of gravity in space will teach us about biological processes back on Earth, such as aging and osteoporosis.
New Materials
The space station is a unique environment in which to create and study new materials. The microgravity conditions will allow scientists to study physics, combustion science, fluid flow, and crystal growth in a completely new way. Scientists hope that these experiments will lead to new industrial products that can be used back on Earth?from lighter, stronger metals to new materials for contact lenses.
But studying in microgravity is not the only reason for the space station:
Understanding Earth
For the first time, we will be able to observe Earth from different angles over long periods of time. The space station will allow us to watch large-scale changes in the environment to better understand our own planet.
Understanding Space
The space station will also give us an opportunity to study the harsh environment of space. Kibo, the Japanese module, will include an exposed ?back porch? for such external experiments.
Advances in Technology
Scientist have developed new technologies for the space station that they believe will someday help humans back on Earth. One example is ?Robonaut??a robot that will perform tasks on the station?s exterior. Robonaut has a robotic hand operated by virtual reality, an innovation with great potential for amputees on Earth. But this is only the beginning. Technology with potential for the future also will include computer software, lower-cost and energy efficient heating and cooling systems, air and water purification systems, and advances in communications.

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