Video shot by Joshua Ballinger, edited and produced by Jing Niu and David Minick. Click here for transcript. (video link)

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 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.