How does NASA ensure that astronauts going into space for months at a time don’t get sick?

Question

I assume the astronauts are healthy, thoroughly vetted by doctors, trained in basic medical principles, and have basic medical supplies on board.

But what happens if they get appendicitis or kidney stones or some other acute onset problem?

In: 2048

Answer 1

One of the original astronauts scheduled for Apollo 13 was grounded because he’d been exposed to measles.