Apollo 16: Mission Operations and Observations

Apollo 16 was one of NASA's J missions, designed for longer lunar stays and comprehensive scientific investigations. Its 1972 objectives included exploration of the Descartes highlands, collection of rocks and soil, deployment of surface experiments, and measurements and photography from lunar orbit. Preflight material treated the region as an important test of highland volcanism; this was a hypothesis to examine, not an established mission result.

John Young commanded the mission, Thomas Mattingly was command module pilot, and Charles Duke was lunar module pilot. The Manned Spacecraft Center in Houston was responsible for the spacecraft, crew training and flight control; Marshall Space Flight Center for the Saturn launch vehicle; and Kennedy Space Center for launch. The crew's fieldwork depended on these engineering and ground-support systems.

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At 17:54 on 16 April 1972, the Saturn V lifted off from Launch Complex 39A at Kennedy Space Center. Dates and times below are all in Universal Time. The spacecraft entered an Earth parking orbit before translunar injection, docking and course corrections, and reached lunar orbit on 19 April. The command module's call sign was Casper and the lunar module's Orion.

Before the lunar descent, oscillation appeared in the backup yaw-control circuit for the service module's main engine. Rather than landing at the scheduled time, Young and Duke remained near the command and service module while ground teams tested and analysed the problem. Only after engineers determined that the redundant system could still be used safely if needed did the mission proceed on a revised schedule. The delay of approximately five hours and forty-five minutes also changed subsequent science plans.

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The lunar module landed at 02:23:35 on 21 April, approximately 276 metres northwest of the planned point. Young and Duke spent about 71 hours on the surface, using the lunar rover to extend sampling to places difficult to reach on foot. Their three excursions were not repetitions of one circuit: the first passed the Flag Crater area, the second headed toward Stone Mountain, and the third focused on North Ray Crater and nearby boulders.

The mission report recorded approximately twenty hours and fourteen minutes of surface extravehicular activity across the three excursions, with the rover travelling 26.7 kilometres. Time constraints led to cancellation of four planned stops on the third traverse. Route choices, photography, recording sample locations and sealing collections had to be coordinated within life-support and return deadlines, rather than simply maximizing the number of rocks gathered.

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The crew deployed the Apollo Lunar Surface Experiments Package for seismic, magnetic-field and other observations, but an accidental cable break during deployment prevented the heat-flow experiment from operating. Delivery of scientific equipment did not mean that every experiment successfully acquired data, and the mission report recorded failures and their consequences individually.

Another experiment had George Carruthers of the US Naval Research Laboratory as principal investigator: a far-ultraviolet camera/spectrograph placed near the lunar module's shadow observed Earth and celestial targets, with film returned for analysis. It operated for approximately 51 hours, and Earth's hydrogen Lyman-alpha images showed the geocorona extending outward. As the Sun's angle changed, the crew had to move the instrument to keep it shaded, illustrating the need to adapt observing plans to the actual lunar environment.

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Young and Duke collected approximately 95 kilograms of rocks, soil and other samples with recorded locations, and obtained a drill core about 2.6 metres deep near the experiment station. Material from Flag Crater, Stone Mountain, North Ray Crater and elsewhere helped connect plains, uplands and impact ejecta. The mission report also noted that the crew had not directly sampled bedrock in place; understanding deeper strata still depended on interpretations of material ejected from craters and geological relationships.

Returned data showed that the Cayley Formation at the landing site consisted mainly of breccias of varying light and dark colour, rather than the lava flows widely envisaged beforehand. Stone Mountain samples also included light-coloured breccias and crystalline fragments whose precise origins required further study. The importance of the result lay in field observations and physical samples forcing researchers to reconsider interpretations of remotely observed landforms, rather than resolving the entire history of the lunar highlands.

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Mattingly remained in lunar orbit operating spectrometers, a mapping camera and a panoramic camera in the scientific instrument module. Isaac Adler and colleagues' X-ray fluorescence experiment used fluorescence excited by solar X-rays at the lunar surface to estimate relative abundances of magnesium, aluminium and silicon. It could measure effectively only sunlit regions; its output was not a chemical map covering the whole Moon and every element.

The experiment team processed data during the flight and passed preliminary findings about the Descartes region to the crew while they were still on the surface. The highlands' higher aluminium-to-silicon ratio agreed with analyses of some returned samples and supported an understanding of plagioclase-rich highland material. The paper also explained that a planned orbital-plane adjustment was not performed, reducing coverage. Comparing remote sensing, surface sampling and laboratory tests constrained interpretations more effectively than any one form of evidence alone.

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On 24 April, the lunar module lifted off and docked with the command module. On 25 April, the spacecraft left lunar orbit for Earth. During the return journey, Mattingly spent approximately one hour and twenty-three minutes outside the spacecraft retrieving film cassettes from the scientific instrument module's cameras. The command module splashed down in the Pacific at 19:45:05 on 27 April. The mission lasted approximately 265 hours and 51 minutes, ending about a day earlier than originally planned.

Some orbital research was consequently reduced. The particles-and-fields subsatellite left near the Moon also failed to reach its intended orbit and lost its signal on 29 May, falling short of its planned one-year lifetime. Apollo 16's results included highland samples and varied observational data, as well as these explicit records of missing measurements and failed equipment. Understanding its value requires examining what was obtained, how it was obtained and which objectives remained incomplete.

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