Do you have any references for the physiological effects of human space travel?

Numerous biological impacts of space environments have been catalogued and studied. I would try visiting the NASA Johnson Space Flight Center which specializesin human factor studies. The worst of these is the loss of calcium in bone tissue and radiation effects. These still remain the biggest challenges of interplanetary space travel. We simply don't know how to prevent astronauts from returning to earth with brittle bones and radiation damage which can have long-term risks for cancer.

You can also vist the Ask a Life Scientist which covers the biological issues rather well in a series of FAQs.

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