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A Safe Crew T ere are many dangers in space. One danger is radiation. Large doses of radiation can cause cancer or even kill people. Spacecraſt and spacesuits block some

radiation, but not all of it. People going to Mars would be in space for a long time. T eir spacecraſt and spacesuits would need to protect them from most radiation. Engineers are trying to invent materials that could better shield astronauts.

A Healthy Crew T ere are other problems to solve, too. Long missions in space weaken human bones. On Earth, bones stay healthy when muscles pull on them. T e muscles fight against gravity. Yet there is no gravity in space. So bones begin to break down. T ey become brittle and weak. Scientists have studied how the body

changes in space. T e record for the longest stay in space belongs to a Russian man. He spent nearly 438 days in space. When he returned to Earth, he wanted others to see that he was fit. He leſt his ship without help. He walked

around in front of reporters. He wanted to prove that his bones were strong. When tested, his bones were found to be weaker, though. T is is a serious problem for most space travelers. If astronauts have weak bones and muscles, they could fall and hurt themselves. Scientists are working on the problem. One

solution may be exercise. Astronauts on the International Space Station are testing a new exercise machine now. It makes astronauts feel like they are pushing against gravity. It may help bones stay strong. Scientists are also studying a medicine that could slow bone loss.

GRAVITY is a force that causes two objects to pull toward each other. The gravity on Mars is a little over a third what it is on Earth. So a person would weigh a third as much.

The surface of Mars, as seen by the rover, Spirit.

Picking the Right Crew T ere will be other challenges for the crew, too. T ey will have to handle being cooped up in a spaceship for a long time. Crew members might become bored or restless. T ey might miss Earth and their families. T ey might become depressed. T ey might argue. Yet no matter how they’re feeling, these

astronauts must work together. If something goes wrong, it will be hard to call for help. A message from Mars could take 20 minutes to reach Earth. An answer from Earth could also take 20 minutes. It’s easy to see that it will take a special group of astronauts to work and live together so far from home.


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