Why do astronauts hop on the moon? After carefully watching hapless volunteers use a treadmill under variable gravity, researchers think it had more to do with the stiffness of spacesuits than anything else.

Harrison Schmitt run-hopping on the moon during Apollo 17. Image credit: NASA

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The experiments took place during flights in an unusual trajectory. As the plane climbs and dives while tracing out each parabola, the gravity increases and decreases, with way-too-brief moments of zero gravity at the peak.

Trajectory of a flight with a zero-gravity segment. Image credit: NASA

These particular took place under lunar gravity (one-sixth Earth gravity), each experiment period lasting just six to twenty seconds. At the end, they concluded that astronauts on the moon were hopping not because it was the most comfortable and efficient form of movement under lunar gravity, but because their spacesuits were too stiff to bend their knees and walk in a more familiar manner.

Why were early space suits so stiff? They prioritized life support systems over mobility. (And, it could've been a lot worse...) It'll be interesting to see where the next generational of space suits draw the line, if they shift closer to skin-tight ultra-mobile designs, and how that changes for tourist space suits. If the knee joins are flexible enough, the next time astronauts visit the moon, those small steps may look a lot more like walking than giant metaphorical leaps of greatness.

I admit it: while I can't fault designers for aiming for a more flexible, functional spacesuit, I would be a bit forlorn over the loss of gleeful bounding as a primary method of transportation.

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Humans aren't the only ones who have undergone biomechanical studies on the vomit comet: some of the very earliest experiments involved dropping cats, setting pigeons in-flight, and terrifying snakes.

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Read more about the experiment on Scientific American, or the research article here.

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