Apollo 16

• 1. Introduction

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  Apollo 16 launched from Kennedy Space Center in Florida on the 16th of April, 1972, carrying three men toward a highland plain that scientists were certain had been sculpted by ancient volcanoes. They were wrong. Commander John Young, Lunar Module Pilot Charles Duke, and Command Module Pilot Ken Mattingly would spend nearly three days on the Moon collecting rocks that shattered one of geology's most confident predictions about our nearest neighbor. Before Young and Duke even climbed back into their spacecraft, they already suspected the truth: the expected volcanic material simply was not there. The questions the mission would ultimately answer were not the ones anyone had planned to ask. How does a mission succeed scientifically by disproving its own premise? What happens when a spacecraft malfunction nearly cancels the landing six hours after it was supposed to begin? And what does it mean to be the youngest human ever to walk on the Moon?

• 2. The Crew

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  John Young was 41 years old at the time of Apollo 16, a Navy captain who had already flown in space three times. He first flew in Gemini 3 in 1965 alongside Gus Grissom, becoming the first American outside the original Mercury Seven to reach orbit. He followed that with Gemini 10 in 1966 and Apollo 10 in 1969, and Apollo 16 made him the second American after Jim Lovell to fly four times.

  Charles Duke, at 36, was the youngest of the twelve astronauts to walk on the Moon during the Apollo program. He had served as a capsule communicator for Apollo 11, the support crew of Apollo 10, and was technically responsible for one of the most consequential personnel shuffles in Apollo history: Duke had exposed Ken Mattingly to rubella while the two were training together on the Apollo 13 backup crew. Duke had caught the illness from one of his children. Mattingly never actually contracted rubella, but NASA removed him from the Apollo 13 prime crew three days before launch and replaced him with his backup, Jack Swigert.

  Mattingly, 36 at the time of Apollo 16, was a Navy lieutenant commander who had originally been on course to fly Apollo 13. He had been a member of the support crews for Apollo 8 and Apollo 9, and had even trained in parallel with Apollo 11's backup command module pilot, William Anders, in case Anders left NASA before the mission flew. After the Apollo 13 setback, Mattingly had been assigned to Apollo 16 from the start, announced as prime crew alongside Young and Duke on the 3rd of March, 1971.

  The backup crew for Apollo 16 included Fred Haise as commander, Stuart Roosa as command module pilot, and Edgar Mitchell as lunar module pilot. The original backup plan had called for William Pogue and Gerald Carr to fill two of those slots, with the goal of rotating them onto Apollo 19. After NASA cancelled Apollos 18 and 19 in September 1970, Director of Flight Crew Operations Deke Slayton reassigned Pogue and Carr to the Skylab program, where they flew on Skylab 4.

• 3. Choosing Descartes

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  Geologist Dan Milton was studying photographs taken by Lunar Orbiter spacecraft when he noticed an unusually high albedo in the Descartes region of the Moon. He theorized that the brightness might indicate volcanic rock, and his idea attracted wide support from the scientific community. Several researchers pointed out that the central lunar highlands resembled terrain on Earth created by volcanic processes, and they hoped Apollo 16 would confirm this pattern.

  The Ad Hoc Apollo Site Evaluation Committee, chaired by Noel Hinners of Bellcomm, met in April and May of 1971 to choose the final two Apollo landing sites. Among the candidates for Apollo 16 were the Descartes Highlands region west of Mare Nectaris and the crater Alphonsus. Scientists briefly considered a landing near the large crater Tycho, but its distance from the lunar equator and the rough approach terrain made it impractical for the Lunar Module.

  On the 3rd of June, 1971, the committee chose Descartes. The specific landing spot was positioned between two young impact craters, North Ray and South Ray, with diameters of 1,000 and 680 meters respectively. Planners described these craters as natural drill holes that penetrated the lunar regolith and exposed bedrock the astronauts could sample directly.

  The two main geologic targets were named the Descartes and Cayley formations. Both were widely believed to be products of lunar volcanism. The entire geological training program that followed was shaped by this assumption, including extensive field work at volcanic sites. As Young later noted, the non-volcanic portions of the training ultimately proved far more useful.

• 4. Training in Canada

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  Young, Duke, and backup commander Fred Haise underwent a geological training program that took them across multiple continents and into a federal nuclear testing facility. In July 1971, the trio became the first American astronauts to train in Canada, visiting Sudbury, Ontario, to study a 60-mile-wide crater created roughly 1.8 billion years ago by a large meteorite impact. Geologists selected Sudbury specifically because the Sudbury Basin displays shatter cone geology, giving the crew direct exposure to the physical evidence left by a massive impact rather than volcanic activity.

  The Apollo 14 landing crew had previously trained in West Germany, but unspecified incidents during that trip had led Slayton to prohibit further European training exercises. The Nevada Test Site served as another training ground, where craters left by nuclear explosions simulated the large lunar craters the crew would encounter. All participants at the Nevada site required security clearances and a listed next-of-kin; even an overflight by Mattingly required special permission.

  By the end of the training program, field exercises had grown to involve as many as eight astronauts and dozens of support staff, drawing media attention. Young later estimated that approximately 350 hours of training were conducted with the crew wearing full space suits, a choice Young considered essential for understanding what the equipment could and could not do on the surface. Mattingly separately trained to identify geological features from orbit by flying over field sites in an airplane, preparing him to operate the Scientific Instrument Module from lunar orbit.

• 5. Six Hours Delayed

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  Apollo 16 launched at 12:54 pm EST on the 16th of April, 1972. The first days of the outbound journey were largely routine, punctuated by minor problems: a potential issue with the environmental control system, a brief alignment problem with the guidance system that Mattingly corrected using the Sun and Moon as reference points, and a strange shower of particles Duke estimated at five to ten per second streaming from a torn patch of the Lunar Module's outer skin.

  The serious trouble arrived on flight day five. During pre-undocking tests of the command and service module's steerable main engine, Mattingly detected oscillations in the backup gimbal system. Mission rules required the Lunar Module to re-dock immediately in such circumstances, since if the landing had to be aborted, the LM's engines might be needed for the return journey. For several hours, mission controllers analyzed the malfunction while Young and Duke held Orion close to Casper rather than re-docking.

  NASA managers seriously considered ordering the crew to abandon the lunar landing and return to Earth. After the analysis, controllers determined the malfunction could be worked around, and the descent was authorized. The powered descent to the lunar surface began roughly six hours behind schedule. Because of the delay, Young and Duke began their approach from an altitude of 20.1 km, higher than any previous mission. The Lunar Module Orion touched down 270 meters north and 60 meters west of the planned site at 2:23:35 UTC on the 21st of April.

  The delay carried lasting consequences. NASA shortened the mission's time in lunar orbit after surface exploration and trimmed the third moonwalk from a planned seven hours to five. The Particles and Fields Subsatellite was released into a lower-than-planned orbit because the burn to correct the spacecraft's path had been cancelled; rather than lasting at least a year, it crashed onto the lunar surface on the 29th of May, 1972, after circling the Moon 424 times.

• 6. Three Days on the Surface

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  Young stepped onto the lunar surface and became the ninth human to walk on the Moon. His first words referenced the Descartes Highlands directly: "There you are: Mysterious and unknown Descartes. Highland plains. Apollo 16 is gonna change your image." Duke followed moments later, at age 36 becoming the tenth person to walk there and, as of that mission, the youngest human ever to do so.

  The first moonwalk lasted 7 hours, 6 minutes, and 56 seconds. An early problem appeared when Young found the rear steering on the lunar rover was not functioning; it eventually began working again while they were parking the vehicle to observe ALSEP deployment. At Plum Crater, a 36-meter crater on the rim of the 240-meter Flag Crater, Duke retrieved the largest rock returned by any Apollo mission. The breccia, nicknamed Big Muley after mission geology principal investigator William R. Muehlberger, weighed in as the heaviest Moon rock collected during all the Apollo landings. By this point, scientists monitoring from Mission Control were already beginning to doubt their volcanic hypothesis, though the geologists there initially did not believe Young and Duke when the astronauts reported finding no volcanic material.

  The second moonwalk took the pair 3.8 km from the Lunar Module to Stone Mountain, where they climbed to 152 meters above the valley floor, the highest elevation above the LM reached by any Apollo crew. The seven-and-a-half-minute excursion lasted 7 hours, 23 minutes, and 26 seconds, breaking a record set on Apollo 15. During the traverse, they collected black and white breccias and crystalline rocks rich in plagioclase at various stops along Stone Mountain's slopes.

  The third and final moonwalk focused on North Ray crater, the largest crater visited by any Apollo expedition, measuring 1 km wide and 230 meters deep. At the crater's rim, they found a boulder taller than a four-story building, which they called House Rock. Samples from House Rock delivered the conclusive evidence that the volcanic hypothesis was incorrect. On the drive back from the crater, traveling downhill on the lunar rover, they set a lunar speed record of an estimated 17.1 km/h. Before returning to the LM, Duke placed a plastic-encased family portrait on the surface and an Air Force commemorative medallion, leaving one and donating the duplicate to the National Museum of the United States Air Force at Wright-Patterson Air Force Base in Ohio.

  Over the three moonwalks, totaling 20 hours and 14 minutes, Young and Duke drove the rover 26.7 km and collected 95.8 kg of lunar samples. Mattingly, meanwhile, spent 126 hours and 64 revolutions orbiting the Moon in Casper, operating cameras and scientific instruments, and became the first command module pilot to use binoculars in lunar orbit.

• 7. What the Rocks Revealed

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  Back on Earth, laboratory analysis of the Apollo 16 samples confirmed what Young and Duke had suspected on the surface: the Cayley Formation was not volcanic. The evidence against the Descartes Formation's volcanic origin was less conclusive, as it was unclear which specific rocks had come from that unit. No evidence emerged to indicate that Stone Mountain had ever been volcanic.

  Geologists traced part of the failure to methodological overconfidence. They had been so certain that Cayley was volcanic that they had not seriously entertained dissenting interpretations. They had also relied too heavily on terrestrial analogues, a model that did not translate cleanly to the Moon because the two bodies share little geologic history. Mattingly's binocular observations from orbit contributed a key piece of evidence: from his vantage point, the Descartes Formation looked nothing like a distinctive volcanic structure. It fit within the broader Mare Imbrium geology without standing out.

  The mission also produced a finding that had nothing to do with the Moon itself. Instruments aboard Apollo 16 detected two new auroral belts around Earth. The Far Ultraviolet Camera/Spectrograph, operated from the surface by placing it in the Lunar Module's shadow, produced the first astronomical observations taken from the Moon. Dr. George Carruthers of the Naval Research Laboratory described the Earth observations as the most immediately obvious results, because the mission captured the first photographs of Earth from a distance in ultraviolet light, revealing the full extent of its hydrogen atmosphere, the polar auroras, and what he called the tropical airglow belt.

  Young went on to command the first Space Shuttle mission, STS-1 in 1981, and STS-9 in 1983, on the latter flight becoming the first person to fly in space six times. He served as Chief Astronaut from 1974 to 1987 and did not retire from NASA until 2004. Mattingly commanded two Shuttle missions, STS-4 in 1982 and STS-51-C in 1985. Duke retired from NASA in December 1975. The Apollo 16 command module Casper is on display at the U.S. Space and Rocket Center in Huntsville, Alabama, following a transfer of ownership from NASA to the Smithsonian in November 1973.