Imagine watching Neil Armstrong descend the Apollo 11 ladder to take the first steps on the moon. He reaches the bottom rung, pushes off the frame, and plants his foot firmly on the cratered surface below. Only this time, before he can speak the most famous phrase ever uttered outside Earth’s atmosphere, an audible snap slices through the crackling fuzz of his radio transmission. It is the sound of Armstrong’s tibia fracturing.
This is, of course, a hypothetical take on NASA’s 1969 moon landing, but it is indicative of one of the greatest obstacles in space exploration. In space, your bones become their own worst enemies.
Given a long enough space mission, bones will self-cannibalize, becoming porous and brittle—so brittle, in fact, that “one small step” could result in a catastrophic fracture. “One giant leap,” metaphorical as it may be, could cause even graver injuries for our celestial explorers.
Fortunately for the crew of Apollo 11, their mission lasted only eight days. A longer trip, and the bones of Armstrong and his fellow astronauts—much like the moon—might have born a striking resemblance to Swiss cheese.