A near-scrubbed landing and a disproven volcano theory

Just before the modules were due to separate, Mattingly detected oscillations in the backup steering of the CSM’s main engine. Under mission rules, Orion had to re-dock with Casper in case flight control decided to scrub the mission — but after several hours of analysis, Mission Control judged the fault workable and cleared the landing. Because of the six-hour delay, Young and Duke began their descent to the surface from a higher altitude than any previous mission.

The Orion module landed on 21 April 1972 in the Descartes highlands — the first landing in a mountainous region of the Moon, chosen in hope that it was volcanic terrain. After stepping onto the surface, Young said: “There you are: mysterious and unknown Descartes, highland plains. Apollo 16 is gonna change your image.” He became the ninth person on the Moon; minutes later he was followed by 36-year-old Duke — still the youngest person ever to stand on its surface.

While trying to connect a thermometer into a drilled hole, Young caught his foot on a cable and accidentally unplugged the instrument — the bulky suit meant he could not see his own feet, and a repair would have taken too long. At a giant boulder nicknamed “House Rock,” the pair collected samples that conclusively disproved the expectation that the Descartes highlands were volcanic — an important, if “negative,” scientific result. The crew drove the rover 26.7 km and gathered 95.8 kg of samples, including the largest rock of the entire Apollo program, nicknamed “Big Muley.”