Working outside a spacecraft in a spacesuit—or walking on the Moon in one—is among the most dangerous activities that an astronaut can take part in. Officially referred to as "EVA" in NASA acronym shorthand—that's short for "extravehicular activity"—and commonly called "spacewalking" by the public, leaving the pressurized metal protection of your ship or station and floating in the void means committing yourself to a dynamic environment where conditions can change very rapidly. EVAs typically last a few hours but require months of training in the agency's giant swimming pool to ensure everything goes well.

The capstone activities of Apollo were the surface EVAs, where astronauts planted flags, placed experiments, drove space cars, and otherwise tried to cram as much activity as possible into very short windows of time. It's difficult to come up with a meaningful estimate for the per-minute cost of each lunar EVA, but estimates in the millions of dollars per minute aren't far off; with that kind of cost pressure, Apollo astronauts on the lunar surface had to do everything they could to maximize the impact of each trip outside the lunar module.

We sat down with EVA flight controller Grier Wilt, who gave us some interesting information on how EVAs work now and how the Apollo and Gemini programs formed the basis for the way EVAs are planned and conducted today. She also gave us excellent historical perspective on NASA today versus NASA in the 1960s—even if we don't have Moon bases in 2017, space continues to inspire.