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Apollo 16 Exploration

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Project Apollo: The Beginnings | Mission Planning | Landing Site Selection | Earthbound Support Systems
Astronaut Selection and Training | The Saturn V | The Saturn 1B | The Apollo Spacecraft
Guidance and Navigation | Command and Service Modules | The Lunar Module
Assembling and Launching | Pathfinders | The Early Missions | Apollo 11, The First Landing
The Intermediate Missions | Apollo 15 Exploration | Apollo 16 Exploration | Apollo 17 Exploration
Skylab and Apollo-Soyuz | Conclusion

Apollo 16 lifted off from pad 39a on the 16 April, 1972, with Mission Commander John Young, Lunar Module Pilot Charles Duke, and Command Module Pilot Ken Mattingly, after a nominal countdown. Their destination: the Descartes-Cayley Formation in the Eastern Central Highlands, a region of highland plain thought to have been formed by volcanic activity. The landing site, targeted on the Cayley formation, (an upland plain between the 30 mile diameter Descartes Crater and the slightly smaller Cayley Crater) was the highest topographical feature on the near side face of the moon. Some of its characteristics, which resembled formations on earth, were formed from volcanic lava flows and were thought to be a relatively young feature due to their light colour. Samples taken in this area would provide an indication of how long ago the moon was volcanically active and show differences in lava composition from young, mountainous terra sites, as opposed to that in the old lowland mare.

The survey of the site had been based on the photographs taken by Stuart Roosa from orbit in Apollo 14. Roosa's Hycon high resolution camera had failed just at a critical moment, as he prepared to photograph the Descartes-Cayley formation. He had been able to substitute a Hassleblad with a long range lens and return some pictures of the site. The resolution of the Hassleblad photographs was not as good as may have been obtained with the Hycon, as the smallest discernible objects were no less than 60 feet in size. All the indications to the mission planners however, were that the site was volcanic in origin and was likely to provide an insight into earliest evolution of the lunar highlands.

Apollo 16's arrival in lunar orbit went without a hitch; but on entering Orion for its pre landing checkout Young and Duke encountered their first problem. A fault in Orion's attitude control thrusters fuel system was causing a dangerous build up of pressure in the fuel tanks which had to be overcome by a series of fuel transfers to the ascent stage tanks. With that problem solved on the lander, Young and Duke separated Orion from Mattingly in the command module, Casper, and stood by while Mattingly checked out the command module's systems prior to taking it into its higher, circular parking orbit. Mattingly soon found that the back up yaw control for the service module's engine was causing the engine to vibrate on its gimbals and the shake could be felt throughout the craft as they were operated. Mission rules required the mission to be aborted unless all the SM's primary and back up engine controls were operating correctly.

Orion was forced to delay its descent and stand by in case its engine was needed for the return journey. The delay lasted six hours, while mission control and the engine's manufacturers analysed downloaded data to find that, although the vibration was still present, they did have directional control of the engine. The 'Go' command was given to continue the landing. The delay, which had involved three extra orbits, brought further problems. Orion would have to begin its descent from 16,000 feet higher than planned due to the drift of the moon under the spacecraft's flight path during the extra orbits. Although the computer could cope with this, they had used an extra six hours of the LM's consumables; and the descent from a greater altitude would mean a longer descent burn, using more fuel.

They would also have to reduce their electrical power usage while on the surface and curtail one of the EVA's, in order to keep their reserve safety margins and still meet the planned take off deadline.

On the previous Apollo 15 mission, both Scott and Irwin had shown signs of heart irregularities, which the medical staff had subsequently attributed to a loss of potassium. This was thought to have been brought about by overheating in their suits causing excess sweating and consequent loss of potassium, which had been insufficiently replaced from their diet. As a consequence, the crew of Apollo 16 were supplied with orange juice drinks laced with potassium. The drink was also available during their EVA's for refreshment from a bag in their suits through a spigot in their helmets . During the descent, Duke found that his head movements were causing his helmet microphone to trigger the release of juice into his helmet through the spigot. Under weightless conditions he was soon faced with a large floating globule of the sticky liquid inside his helmet, which eventually attached itself to the microphone boom, leaching under his cap and into his hair. It wasn't until the landing was completed that he was able to remove his helmet and clean up the mess.

Young brought Orion down over a featureless landing site, which was devoid of defining shadow due to a Sun angle now higher than had been previously planned for. Taking full control at 300 feet, he overflew a crater 50 feet in diameter and (on getting the contact light) paused before hitting the engine stop button in an attempt to soften the landing of the fully loaded LM. Orion still dropped with a heavy thump onto a flat patch just three yards from the craters sloping rim.

Duke: Wowww! Whoa, man! ... Look at that!
Young: Well, we don't have to walk far to pick up rocks Houston. We're down among 'em.
Duke: Ol' Orion has finally hit it, Houston.. Fantastic!

First EVA: Flag Crater

With the schedule's timing now in tatters due to their late arrival, a rest period was brought forward to delay the first EVA by six hours and give the crew a break from what would otherwise have been a 29 hour day. Young and Duke's descent of Orion's ladder to the surface was the first not to be televised from the MESA camera. Young, on stepping off the LM's ladder, said to Capcom Tony England:

There you are, our mysterious and unknown Descartes highland plains, Apollo 16 is going to change your image.

Deployment of the Lunar Rover was straightforward, although its hinged arm once again had come adrift and had to be refitted in the same manner as Apollo 15's. The Rover was set up and the first television pictures were beamed back to earth from its camera. Duke removed the two palettes containing the ALSEP experiment package and carried them on a supporting bar, dumb-bell fashion, out to a site a hundred yards from the LM for deployment. In doing so he dropped one palette off the bar and just saved the other from following it to the ground. Young meanwhile, became the first non terrestrial astronomer when he set up an ultra-violet telescopic camera in the shadow of the LM to take pictures of deep space objects. With the flag planted beside the LM, Duke called to his commander, 'Come out here and give me a salute... big Navy salute'; to which Young responded with a two foot high jump above the surface while executing his salute.

Back at mission control Mark Langseth watched as the two astronauts deployed the ALSEP. He was the principle scientist for the Heat Flow Experiment (HFE) and had worked on that aspect of lunar physics for the previous six years. The first HFE had been aboard the ill fated Apollo 13 and met its end in the Pacific ocean with Aquarius, without coming anywhere near the lunar surface. It had been omitted from its successor, Apollo 14, but had made it to the moon with Apollo 15. The readings it returned on that mission were regarded as inconclusive, as Dave Scott had not been able to drill the holes for its sensors deep enough into the surface to get a reliable result. Duke's modified drill went easily down to the required depth, and it looked as if the experiment would at last be successfully deployed. It was with mounting horror that Langseth watched as Young's foot caught one of the cables and wrenched it out of the central power unit.

Young: Something's happened here.
Duke: What happened?
Young: I don't know, here's a line that pulled loose.
Duke: That's the heat flow...., you've pulled it off.
Young: I don't know how it happened....., God almighty.

The loops in the wiring could easily snag a passing foot, and all previous astronauts had found that they needed to tread carefully around the ALSEP. In gravity only one sixth that of Earth, the cables, which had been stored in coils during transit, would not lay flat on the surface. The connector at the power unit had cut through the multi-cored cable and was irreparable with the time and tools available to the crew. The Heat Flow Experiment was out for Apollo 16.

The ALSEP deployment was completed with Young firing a hand held 'Thumper' to calibrate the Active Seismometer (ASE) and setting out a mortar that would lob four calibrated explosive charges varying distances into the surrounding moonscape when Apollo 16 had departed. The shocks from these explosions were to be picked up by the network of seismometers laid by Apollo 16 and the previous missions, which were still active. They also had been sampling the site; but none of the samples taken showed volcanic origins: all were impact breccias.

The first run out on the Rover was curtailed to the nearby 1,000 foot diameter Flag Crater and a smaller, Plum Crater embedded in Flag's rim, which it was thought would be deep enough to have punched through to the underlying Cayley bedrock. Once more all the rocks found at that site were breccias, but the largest rock taken, a single 26 pound sample named 'Big Muley', after the Apollo programs chief geologist, Bill Muehlberger, proved to be the largest rock returned to earth during the Apollo program.

Spook and Buster, another pair of craters, proved to be the same story; none of the rocks sampled were showing any sign of volcanic origin. The return traverse was enlivened with a repeat of the Rover's test drive. This time the Rover was put through its paces and successfully captured on film. The same event during Apollo 15's EVA had failed to be recorded when the film transport drive on Irwin's movie camera had ceased to operate.

Later that day the orbiting Mattingly, discussed the days events with mission control and was told of the lack of volcanic evidence in the samples. He commented: 'Is that right... Well, it's back to the drawing board, or wherever geologists go.'

Second EVA: Stone Mountain

The second EVA was south to the 1,500 feet high Stone Mountain and to sample a group of five craters, the Cincos, which had drilled into the mountain's side. The route back would take them off the mountain and across the abutment of the Cayley plain, with the Descartes formation, and onto a blanket of brilliant white ejecta from a large crater, South Ray. This crater, thought to be relatively young (only two million years old), lay a further five miles away and out of range of the Rover and the missions walk back constraint. It was hoped that by sampling the ejecta they would in fact be sampling the depths of South Ray. The approach to Stone Mountain meant crossing the Cayley plain, and gaining the high ground of a rough, heavily cratered patch of ejecta named Survey Ridge, to approach the lower flank of the mountain.

The approach along Survey Ridge was slowed, as the Rover had to be steered around a litter of large boulders. Once clear of the ridge however, the Rover took the slope of the mountain in its stride; and the crew stopped to take their first samples on the mountain where Mattingly, overflying at that moment in the CSM, noticed a glint of light from the mountainside through his monocular. 'That's us', Duke responded, on being told by mission control that they had been observed.

Moving up towards the Cincos crater group, they were now at the highest elevation reached by any astronaut on an Apollo mission; but they were unable to positively identify the crater group. In fact, they missed the largest of the Cincos by only 40 yards, hidden behind a ridge on the slope.

>From their vantage point they could now see that the ejecta from South Ray crater had mantled the Cayley plain and Stone Mountain with a blanket that alternated in light and dark rays. Lines of dark rock, which had been excavated from depths of 200 feet in South Ray's basement, could be traced across the plain to the slopes of the mountain. The blanket of ejecta from South Ray meant that, even though they were on the side of a mountain, they were, in fact, still sampling the Cayley plain from 500 feet below.

Returning back along the lower slopes of the mountain they found one last 50 foot crater, which seemed to be free of South Ray's contamination. Working in the lee slope from South Ray they sampled rocks that had the appearance of the volcanic rock, plagioclase; but again they could not be positively identified as volcanic.

Crossing back onto the Cayley plain and towards South Ray, two miles from the LM, the crew negotiated an inclined ridge and found that they had lost the Rovers rear wheel drive, as their speed slowed noticeably. At the next stop, after taking a core sample, Young tried to reconfigure the Rovers drive and found it to be working. One of the switches had been knocked out of position at the previous stop, switching the drive off.

Reconfiguring the Rovers drive had inadvertently reset its navigation system, losing their navigational reference; but, with Smoky Mountain (the following day's target) on the horizon beyond the landing site, they were able to get a line of sight bearing back to the LM. On remounting the Rover, Young's rock hammer caught one of the rear wheel guards and pulled it off. The dust from the unguarded wheel sprayed the crew with dust throughout the remainder of the return journey.

Third EVA: North Ray Crater

The third EVA had been curtailed to five hours due to the late landing and would have to omit the planned visit to Smoky Mountain. The plan now called only for a direct run out to North Ray, a crater in the lower slopes of Smoky Mountain three miles to the north of the landing site. North Ray crater, formed between 30 to 50 million years ago, and 650 feet deep, was large enough to have punched through to the underlying Descartes rock.

Cresting a series of ridges Young and Duke came up to the edge of the crater, which dropped away below them in a 35 degree slope. Walking up to the edge Young said:

Does this thing have steep walls..., Now I tell you, I can't see to the bottom of it, and I'm as close to the edge as I'm going to get. That's the truth.

Once again all the mainly white ejecta samples taken on the edge of the rim were breccias of varying types.

While they sampled the rim, the TV camera panned the rim and came to rest on a large black rock on the escarpment. It was large enough to show up on the mapping photographs, and stood out from the mainly white surrounding ejecta. Being the same colour as the crater's floor, and perched near the crater's rim, it would almost certainly provide a sample from the deepest part of the crater. All previous astronauts had found difficulty judging distance without the reference points that are familiar on earth; and, due to the foreshortening effect of the TV camera, the geology team were also unable to appreciate how far away the boulder was.

As Young and Duke set off at a run from the Rover bounding downhill towards the boulder, the camera followed them, zooming out to full extension as the two figures gradually became smaller and smaller on the screen. When the lower halves of their bodies disappeared, as they ran over a partly obscured incline, it dawned on the observing back room geologists that the rock was much larger and further away than they had anticipated. Astronaut Jack Schmitt, working with the geology team, observed, 'And as our crew sinks slowly in the west... and disappears into the sunset', to howls of laughter as the crew almost disappeared from sight.

Once Young and Duke were beside the rock, which towered almost 40 feet over them, they were able to appreciate its true size. 'Well, Tony. That's your House Rock, right there', observed Duke. Once more the rock proved to be an impact breccia, which finally nailed the volcanic origin theory of Descartes.

On the return trip the crew made one more stop at a large rock with an overhang that created a pool of shadow that had never seen sunlight. It was immediately dubbed Shadow Rock. Duke pushed his sampling scoop into the furthest crevice at the base of the rock and observed dryly that, 'You do that in West Texas and you get a rattlesnake. Here, you get permanently shadowed soil.' Pushing against the inflexibility of his suit, he overreached himself, as he tried to chip a sample from low on the overhung rock, and slipped into the 'V'-shaped space, wedging himself fast. Young had to come to Duke's aid to pull him to his feet and release him from the rock's overhang.

Time was now up on the walk back constraint. They could see their original destination, Smoky Mountain, a mile further on. It had been deleted from their itinerary in order to meet the scheduled take off time; but a realistic assessment suggested that a visit there was unlikely to produce any further evidence of volcanism. The return to the LM saw John Young gain the land speed record for the Rover at almost eleven miles per hour. Closing out the EVA, Duke left a family portrait in the dust near the Rover as Young positioned it to view the LM's take off.

The lift off of Orion took place after a surface stay only a few minutes short of three days. As they ascended, Duke exclaimed excitedly, 'What a ride... what a ride.'

Young and Duke rejoined Mattingly in Casper, bringing with them 208 pounds of rock samples. After transfer, Orion was abandoned in lunar orbit; but, this time, the module was not sent crashing into the moon's surface. The crew were due to remain in orbit for another two days, carrying out a photographic survey of previously unmapped areas of the lunar surface. This would have involved further firings of the CM's engine to change its orbital plane. In view of the earlier difficulties with the engine's controls, Mission Control decided that was too risky and brought the crew back a day early. They did however release the sub-satellite from the SIM bay before departure; but, as their orbit was low, the satellite dropped back to the moon after only five weeks. Splashdown occurred on 27 April, 1972, the crew and spacecraft were picked out of the water by the recovery ship USS Ticongerona.

The results from the Descartes-Cayley survey were disappointing, insofar as they showed that volcanism had played no part in the region's formation, as had been predicted from the photographic evidence available to the mission planners. The origins of Descartes-Cayley were never fully resolved; but when the returned rock samples were analysed, they were found to be predominantly impact breccias of varying types, rather than volcanic basalt. The best interpretation of the evidence was that the Descartes Highlands were laid down by the ejecta mass from the impact that formed the Nectaris Basin 3.92 billion years ago. It was later overlaid by further ejecta, possibly from the later Imbrium event, which formed the Cayley Plain between Stone and Smoky Mountains.

The Active Seismic Experiment showed the regolith to be at least 35 feet deep, twice the depth of those found on the previously-visited mare sites. On 23 May, 1972, under remote control from earth, the mortar that had been laid as part of the ALSEP package fired its series of calibrated charges into the local moonscape. Unfortunately, the firing of the third charge upset the mortar's alignment and rendered the information gained through the seismometer suspect. The fourth charge was not fired, therefore; but the results from the first two charges indicated that the layer underlying the regolith was composed of brecciated rock at least 200 feet deep.

By good fortune, on 17 July, 1972, a meteorite of about five tonnes mass, impacted on the far face of the moon. It was the largest meteor impact ever recorded by the network of seismometers laid out by the Apollo missions, the strong signal propagated through the moon's interior and picked up by the network. When the recorded information was analysed it showed a differentiated, layered structure and a possible inner core to the moon; although the core's size was indeterminate. It also showed that the crust below the highland regolith was about 40 miles thick, and at Procellarum and Fra Mauro about 50 miles thick.

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