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All astronauts look forward to living in the lonely and unpredictable environment of space. In low earth orbit, for instance, you get to see 16 sunrises and 16 sunsets! For the day fades into night every 45 minutes as the spacecraft rotates slowly to keep its solar panels facing the sun. Viewers in Delhi shared a bit of this excitement with Sunita Williams aboard the international Space Station, when she telechatted with them earlier this month. 

Astronauts spend long periods in weightlessness of 'zero gravity'. It may be fun for us sitting in our gravity cocooned rooms and watching them on TV, as they float around. But inside their bodies things are happening that aren't any fun at all. Scientists study the effects of outer space on the human body to see how it behaves in zero gravity and then re-adapts to earth`s gravity at the end of the spaceflight. In space the number of red blood cells, bone and muscle tissues are all altered and the metabolic process upset. 

On Earth, gravity pulls blood to lower body, away from the head. Nerves called the baroreceptors detect this and redirect blood flow, ensuring that the brain gets enough oxygen and sugar. In space baroreceptors don't sense any pressure difference and the astronaut flies with an atypical redistribution of blood. On earth we build bones by running or jumping. But without gravity, the bones begin to lose calcium, which is absorbed in the body. (Bedridden and paraplegics suffer the same problem, losing 30% of their lower body bone mass within months). The minerals lost from the leg and hipbones aren't excreted and they migrate to the head, making the skull dense. This is the body's way of making better use of its resources: legs are useless in space, so the body moves to protect the brain!. 

Unlike on earth there is no muscle tension in space. Muscles are relaxed, stretched and actually grow by five to seven inches in a space flight. Surprisingly one gets taller while one sleeps, too, because of relaxed muscles - sometimes enough to readjust one's car's rear-view mirror in the morning. To offset this, the astronauts aboard the ISS exercise on a treadmill every day. So every space payload has a large component of medical experiments to help scientists figure out what we gain-or lose-up there.

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