That's Kelly playing pingpong. He's been on the space station for 10 months.

He uses hydrophobic paddles. They work "kind of like a raincoat."

The ball is a water droplet in microgravity.

So what else are they doing?

"Our mission here is to understand the effects, mostly the effects on our physiology and psychology, of long-duration spaceflight, so we can eventually go onto Mars," Kelly said.

The one-year mission ends in March. (Video via NASA)