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 astronaut Sunita Williams aboard the International Space Station (ISS), when she tele-chatted with them earlier this month.
Astronauts spend long periods in the weightlessness of ‘zero gravity’. It may be fun for us to sit in our gravity-cocooned rooms and watch 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 the lower body, away from the head. Nerves called baroreceptors detect this and redirect blood flow, ensuring 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 into the body. (Bedridden people and paraplegics suffer the same problem, losing 30 per cent of their lower body bone mass within months of losing the use of their legs.) The minerals lost from the leg and hipbones aren’t excreted and they migrate primarily 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 centimetres during a spaceflight. Did you know that you get taller while you sleep, too, because of relaxed muscles — sometimes enough to have to readjust your car’s rear-view mirror in the morning? To offset this, 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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