Apollo 16, the penultimate mission of the program, lifted off on April 16, 1972, headed for the Descartes highlands in search of volcanic rocks. Although the astronauts didn't come back with those, their skill in picking out geologic targets and their ability to cope with changing fortunes made this mission a highlight of scientific discovery on the moon.
The Apollo 16 commander, John Young, was among NASA's most seasoned astronauts. The former Navy aviator flew twice in the Gemini program, taking the right-hand seat in the first mission (Gemini 3) and commanding Gemini 10, which did rendezvous with two separate target vehicles in space. In Apollo, Young was the command module pilot on Apollo 10 and performed the first docking above the surface of the moon.
Apollo 16 command module pilot Ken Mattingly was getting a second chance to go to the moon after he was pulled from the Apollo 13 mission due to a medical concern. Before joining NASA, he was a Navy aviator.
Charles Duke, the lunar module pilot, is perhaps best known as being the CapCom during the Apollo 11 landing, saying "You've got a bunch of guys about to turn blue down here" after the crew's landing on little fuel. Duke was an Air Force pilot instructor when NASA selected him as an astronaut.
Balky engine and snagged cable
Apollo 16's destination, the Descartes highlands, was believed to contain volcanic rocks. Geologists were hoping to get samples of these rocks to find out how the moon's interior was formed.
The spacecraft reached lunar orbit on April 20. Shortly after lunar module Orion separated from command module Casper, Mattingly noticed the command module engine vibrating strangely when he touched one of the controls in the backup system.
Uneasily, the crew circled the moon for six hours in their two spacecraft as Mission Control decided whether it was safe to proceed. After analyzing the data, Houston gave the thumbs-up and Orion descended successfully to the moon's surface.
The next day, Young stood on the moon for the first time with his fists raised in happiness. "There you are, our mysterious and unknown Descartes highland plains. Apollo 16 is going to change your image," he said.
Duke and Young's first job was to deploy an experiment package on the surface. All Apollo astronauts knew how hard it was to see your feet and feel what they were touching through the bulky spacesuit. Young thus accidentally pulled a vital cable free from a heat flow experiment when his boot snagged on the cable, ruining the experiment.
Apologizing profusely, the astronauts finished setting up the package and moved on to their next tasks. They drove the lunar rover to two geologic locations, finding only sedimentary breccia rocks, and not the volcanic ones geologists had hoped to find.
Breccias and a big rock
Duke and Young were never able to find any volcanic rocks while roaming around the surface. On their second day in the rover, they drove to a set of five craters on Stone Mountain, picking up rocks showing how meteor impacts had formed the hills around them.
Observers of their mission later commented on how self-assured the crew appeared with their equipment and their ability to walk around on the surface. The astronauts weren't afraid to kneel, jump high, or to pick up their rover and move it if it wasn't sitting in quite the right spot. Eight men had walked on the moon before Apollo 16, and Young and Duke had learned from watching their extra-vehicular activities.
That's not to say everything went smoothly. For example, Young accidentally snagged his hammer against part of the dust guard of the rover and broke it off, meaning the astronauts were showered with regolith as they drove around the surface. But they adapted as best as they could.
On their third day on the moon, the crew had to cut operations short because they had landed so late, but they squeezed in time to visit North Ray Crater. While they were working, they spotted a very large rock somewhat in the distance. The crew sprinted toward the rock.
Bemused mission controllers watched as the astronauts got smaller and smaller on the TV screen. Astronaut and geologist Jack Schmitt commented, "And as our crew sinks slowly in the west," drawing laughter from others in the control room.
The rock, later dubbed House Rock, was a gigantic breccia, showing the odds of any volcanic activity in the region were slim indeed.
On the final day on the lunar surface, Duke placed a photo of his family on the ground, took some pictures of it. The photo shows Duke, his wife, Dorothy, and their sons Charles and Thomas. Then he left it there.
Casper landed safely in the Pacific on April 27, carrying a load of rocks that turned out to be mostly breccias. Although the crew found something different from what experts had expected, the trove of rocks would provide scientists many hours of study in the decades to come.
— Elizabeth Howell, SPACE.com Contributor