Why Astronauts Fall: Low Gravity Troubles [VIDEOS]

The few scenes you've likely seen of Apollo moon walks make near weightless hopping look easy and fun, but according to a new study, it's no walk in the park. In fact, compared to heightened gravity, it's actually a lot harder to keep your balance in gravity less than Earth's, despite how much easier it is on the legs.

That's because our brains have been hardwired to tell up from down at Earth gravity levels. Anywhere else, regardless of what our eyes are telling our brains, our sense of balance can't tell heads from tails.

That's according to a study recently published in the journal PLOS One that details how humans need to feel at least 15 percent of the gravitational force on Earth to figure out which way is up. The Moon's gravity is right on that fence at about 17 percent, meaning that astronauts have to trust their eyes more than their brain when bouncing around on the Moon. (Scroll to read on...)

[Credit: NASA via PlasmaBen]

A team of researchers determined this after questioning volunteers they had placed in a giant centrifuge.

Like one of those vomit-inducing carnival rides that slap you against a padded wall at intense speeds, the researchers spun volunteers on a giant rotating arm to simulate different strength gravitational fields. As they spun, the participants were shown images of a landscape or the letter "p." They then had to answer (while spinning) whether the landscape was right side up, or whether the letter was a "p" or "d."

According to the study authors, that 15 percent barrier is pretty important. Being right on it can cause direction confusion without a sense of disorientation - explaining why astronaut Jack Schmitt, called "twinkletoes" by Mission Control in the video above, has such difficulty finding his footing despite having extensively trained for his Apollo mission.

Still, to give Schmitt some credit, he certainly got the hang of it as his mission went on, and even learned to enjoy himself, as can be seen in the video below.