The first U.S. astronauts were selected in 1959. Since then, only a select number of applicants out of thousands have been accepted into NASA's Astronaut Candidate training program. With the closing of NASA's Space Shuttle program in 2011, American astronauts currently serve aboard the International Space Station. The ISS was launched in 1998 and represents an ambitious international effort undertaken by the U.S., Russia, Canada, Japan and other participating countries form the European Space Agency. Every day, the station's multicultural astronauts perform scientific research and experiments 240 miles above Earth.
Astronauts aboard the ISS spend much of their time conducting scientific experiments in zero gravity conditions. In many cases, this theoretical research is intended to lead to practical applications on Earth. For example, by studying how a candle burns in zero gravity, astronauts have observed that the candle's flame is rounded and smaller than on Earth. Other experiments have involved mixing liquids and metal under weightless conditions. Armed with this knowledge, scientists back on Earth work to improve human life. Some examples include designing more efficient car and aircraft engines.
Astronauts are typically stationed aboard the ISS for six months and must exercise regularly to prevent bone and muscle issues. On average, astronauts exercise two hours per day, including lifting heavier equipment to compensate for the zero gravity conditions. Treadmills and exercise bicycles are also used to keep astronauts healthy. To supplement their exercise regimen, astronauts wear special trousers that pull blood to their legs and make the heart work harder.
Eating meals in space is no ordinary activity. Like on Earth, astronauts eat three meals per day. Some foods are available in their natural form, such as brownies and fruit, while others require adding water, such as macaroni and cheese. Salt and paper are only available in liquid form for safety reasons and because it would be difficult to sprinkle them onto food. Since there aren't any refrigerators, all food is packaged to avoid spoilage. Nutritionists back on Earth look after each astronaut's diet to ensure that they consume optimal levels of calories, vitamins and minerals for their body type.
As on Earth, astronauts sleep eight hours and wake up according to mission schedules. Unlike on Earth, however, astronauts are able to sleep in any position due to zero gravity. In order to prevent injury, astronauts must tether themselves to avoid floating about the station in their sleep. Usually astronauts elect to snooze in sleeping bags in cabins accommodated to house an individual astronaut. Astronauts sometimes sleep with greater difficulty in space due to motion sickness or even the excitement of being among the stars.
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