In orbit at 18,000 miles an hour, day and night change places every 90 minutes. Darkness and light, sleep and wake: it's tough to focus on precise tasks floating outside the International Space Station. But not if you're a robot. NASA's Robotic Refueling Mission puts that proposition to the test, with a first-of-its-kind demonstration of a simulated fuel transfer in space, no human in sight. But first, there's a pile of prep before the operation can commence.