Apollo 15 Lunar Surface Journal

Mission Summary


Mountains of the Moon

Copyright © 1995 by Eric M. Jones.
All rights reserved.
Last revised 15 October 2010.


Moon Cars

From a practical point of view, the first three successful landing missions were primarily engineering test flights. Exploration and science were of secondary importance and, indeed, the Lunar Modules which were flown on those missions simply couldn't carry much equipment. The LM had been designed as the sparest vehicle capable of completing a landing mission; and it had always been a struggle to find room in the weight budget for scientific equipment and exploration gear. Confidence in the spacecraft - coupled with incremental improvements in performance - permitted slight increases in the amount of useful cargo that could be landed on the Moon but, from a practical point of view, Apollo 14 was about the most sophisticated mission that could have been accomplished with the original Apollo hardware.

Of course, NASA and the space community as a whole had always wanted a good deal more from a mission than what a pair of walking astronauts could accomplish during a thirty-hour stay. As mentioned previously, in the early 1950s rocketeer Wernher von Braun, astronomer Fred Whipple, and science writer Willy Ley published a series of articles in Collier's Magazine in which they described a hypothetical lunar landing mission on a far grander scale. They expected that a crew of fifty lunar explorers would journey to the Moon in three large landers assembled and fueled in Earth orbit. Two of the landers would be able to make the round trip to the Moon and back and, on the outbound leg, would each carry a crew of twenty. The third lander would be the cargo ship, carrying a crew of ten and, in place of fuel for the trip home, about 300 tons of cargo. Von Braun and the others imagined that the expedition would stay on the Moon for six weeks, arriving just after local dawn, staying through that two-week day and the following night, and departing just before sunset on their second lunar day. Rather than live in ships, the explorers would, after unloading the cargo, disassemble the cargo hold and use the resulting half-cylinder sections as Quonset huts - one for living quarters and the other for labs. Of course, there was a great deal of material to be moved and von Braun and the others provided the expedition with cranes - one on each ship - and with three ten-ton tractor-trailers. Once the base was established, the tractor-trailers could be put to use as exploration vehicles, first for trips in the immediate vicinity of the base and then, just before dawn on the second day, for a 300-kilometer cross-country trek to a large crater where, it was hoped, evidence would be found to prove once-and-for-all whether large lunar craters were formed by impacts or by volcanic action.

(In reality, high-quality photos taken with such instruments as the Palomar telescope on Earth and the Lunar Orbiter spacecraft provided enough data that, for the majority of planetary scientists, the question had been answered - generally in favor of impact origins for the vast majority of features - long before Apollo 11. Readers interested in a more complete discussion would do well to consult Don Wilhelms' To a Rocky Moon. However, as Jack Schmitt remarked during our review of this Apollo 15 summary, even for the majority who were convinced that almost all lunar craters were impact structures, "there were a few features we said might be volcanic caldera craters, primarily because they were even more strikingly polygonal than the impact craters. But even the large impact craters end up with polygonal outlines. It's determined by whatever fracture system you have and, in the case of Meteor Crater (Arizona), the fracture systems are northwest and northeast trending and you just get better excavation along those fractures and you end up with a square crater. On the Moon, it looks like it's a hexagonal fracture pattern that predominates and you end up with hexagons. There are some sharply polygonal craters. But, when you look at their rims in cross section, they're delta-shaped instead of ramp shaped. So I said that there's a good possibility that those are calderas rather than impact craters. We've never been to one so we don't know. I gave a paper on Copernicus once, and I think that abstract has more on that. But those are a minor percentage of the large craters.")

Von Braun's imagined lunar expedition was probably grander than anything that was really possible for a first mission. However, if global politics had not forced the early pace and sequence of space exploration and we had built up capabilities and facilities in Earth orbit before mounting the first lunar expeditions, perhaps we would have gone to the Moon with the intent of establishing a permanent base camp. Indeed, even within the constraints of Apollo, NASA would have liked nothing better than to design and build an unmanned, cargo-version of the LM to support long visits and, eventually, a modest lunar base (see, for example, Donald A. Beattie's Taking Science to the Moon); but, in the late 60s, with budgets shrinking and dreams being put on hold, all that was really possible was to upgrade the LM design so that crews could land in more heavily ladened versions which would let them stay a little longer and range farther afield.

Of course, NASA had no way of knowing until quite late in the game just how quickly the first landing would be achieved. Most of the people of Apollo had all they could handle in just getting the first generation hardware designed, built, and tested. Consequently, the agency didn't give serious thought to upgrades or to advanced missions until the first-generation designs were ready for test. Only in September 1967 was NASA ready to put some thought into an upgraded LM which would carry - as it turned out - nearly a ton of extra equipment and supplies. Because productivity could only be increased if the astronauts stayed longer on the Moon, supplies of food, water, oxygen, and power would take up much of the increased allotment. However, because exploration and geologic survey work were expected to be the main focus of the three-day J missions, there were also discussions about taking along an electric-powered car. However, preliminary estimates suggested that there would only be room in the cargo budget for a Rover weighing about 225 kilograms; and it wasn't clear - at least during the Christmas season of 1967 when the first memos were being written - that a reliable, useful vehicle of so low a weight could be built.

According to a paper by historians Bettye Burkhalter and Mitchell Sharpe, the notion of a wheeled, electric-powered lunar exploration vehicle made its first literary appearance virtually at the dawn of the Automotive Age. In 1901, almost as soon as it became plausible to think about driving on the Moon, a Polish writer by the name of Jerzy Zulawski described an early ancestor of the Lunar Rover. Like all those who would follow in his footsteps, Zulawski realized that combustion engines wouldn't be practical on the airless Moon and, rather, chose to power his vehicle with an electric motor. Like most later concepts of lunar rovers - including von Braun's ten-ton tractor-trailer - Zulawski's was a big vehicle with an enclosed cabin. His, he said, could carry a crew of five and a year's worth of supplies.

For about a half century or so, lunar cars made episodic literary appearances and then, in the years following World War II, they received occasional attention from members of the spaceflight fraternity who were beginning to think seriously about what might be done on the Moon once von Braun's V-2 weapon grew into a real space launcher. Most importantly, people started to think about some of the engineering details - about vehicle weight, power supplies, and traction on various types of surfaces. Naturally, it took real money to move the vehicles out of the conceptual stage and it wasn't until the early, heady days of Apollo - when Congress gave NASA all but a blank check - that the first design contracts were let. There was no immediate need for a rover but, with an eye toward an eventual lunar base, it seemed prudent to make a small investment. The design process might take several years and, in the beginning, progress could be made by teams spending sums as small as a couple of hundred thousand dollars. (For comparison, the whole of Apollo cost about $24,000,000,000 in the dollars of the time.) A number of contractors (Boeing, Grumman, Bendix, and others) even invested some of their own research money in the interest of having a competitive advantage when NASA decided that it really did want to fly a rover. The culmination of these early efforts was a concept called MOLAB (Mobile Laboratory): a two-man, three-ton, closed-cabin vehicle with a range of about 100 kilometers. In 1964, the Marshall Space Flight Center awarded design contracts to both Boeing and Bendix and, in 1966, both companies built one-sixth-weight prototypes which, early the following year, were put through field trials in the desert near Yuma, Arizona and scientific trials near Flagstaff. However, it was becoming obvious that a lunar base was very far in the future and that there would be no need for so large a vehicle. After the trials, the MOLAB concept was mothballed but, not surprisingly, NASA turned first to Boeing and Bendix - with General Motors as an additional partner- when it came time to define a lightweight rover for the J missions.

Before proceeding with a discussion of the development of the Apollo Lunar Rover, Dave Scott - the Apollo 15 Commander - urged me to include a story that Jack Schmitt told me about lunar flyers.

"There was a major academic - as well as industrial - competition between the proponents of flyers and rovers. Elbert King at JSC was the in-house proponent of lunar flyers. Geochemists tended to like lunar flyers because they didn't worry too much about the geology that connects individual sample sites. And, those of us who are used to doing field work tended to like the Rover because you were in closer contact with the ground, even though you couldn't go as far away from the landing site. Also, from an astronaut perspective, although some of the astronauts sort of liked the idea of having a flyer, I was concerned that you would have a very difficult time in training. We were right in the middle of trying to use the LLTV (Lunar Landing Training Vehicle) and having all sorts of trouble with that. (Three of four LLTV's crashed during training and testing before the end of Apollo). And, here was something smaller that you had to design a trainer for before you went to the Moon. It just didn't seem to make a lot of sense to me. And the issue was finally decided at a conference in Santa Barbara. I don't remember why we had the conference, but Max Faget was there, of all people. (Faget was an almost legendary NASA engineer who headed Houston's Engineering and Development Directorate and who played a major role in the design of the Mercury and Gemini capsule and the Apollo Command Module). And Max finally said, 'You know, when you finally start to design this, people are going to come up with all sorts of good ideas about how to make it safer. And they'll be good ideas. And it'll grow (in weight) to the point that you can't use it.' And that statement, from Max Faget, killed the Flyer. You just never heard of it again. As soon as these proponents figured out Max Faget didn't want the flyer, they figured out there wasn't much point in proceeding any further."

The decision to proceed with a lightweight Rover wasn't made until May 23, 1969, the day that the crew of Apollo 10 left lunar orbit for the trip home. With the first landing now imminent, NASA had hopes of flying the first of the J-missions within a couple of years and, clearly, the Rover would have to be designed and built on a tight schedule. Preliminary design requests had been issued the previous November (1968) ; final design specifications were released on July 11; and, on October 28, a contract was awarded to Boeing. It was a cost-plus-fixed-fee contract initially valued at $19 million and NASA wanted the first of the flight-ready Rovers delivered by April 1971. Seventeen months wasn't much time and, as it turned out, meeting the deadline meant a lot of extra people working a lot of overtime. The total cost of the project eventually rose to nearly $40 million. In a time of shrinking NASA budgets and some fairly widespread disillusionment with Apollo, the cost overrun generated far more press coverage than was warranted by the relatively small size of the Rover program. Some members of the public - not to mention a few Congressmen - didn't understand how three golf carts could cost 40 million dollars. The answer, of course, is that the major automobile manufacturers regularly spent far greater sums developing new model passenger cars and, if only three copies of a new car were ever built, they would be very pricey, too. When the time came, the Rovers performed beautifully and proved to be worth every dollar that NASA had spent.

The Apollo Lunar Roving Vehicle (LRV)

The Boeing Lunar Rover was a far cry from the ten-ton, closed-cabin, seven-passenger tractor/trailer of the Collier's articles, but it was a nifty little machine nonetheless. Empty, it weighed in at a spare 209 kilograms (460 pounds) and could be folded up and stored (for the trip out from Earth) like an intricate toy. As Dave Scott points out, "the volume into which it could be folded was one of its most significant features," and that volume can be thought of as a sandwich 1 1/2 meters (5 feet) on a side and 1/2 meter (20 inches) thick. Once it was deployed on the Moon, it was 3 meters long and 1 1/2 wide, with the tops of the twin seatbacks about 1 1/2 meters off the ground. When fully loaded with two astronauts and all their gear, it weighed a hefty 700 kilograms (1500 pounds). It rode on four wire-mesh wheels and, when fully loaded, had a ground clearance of about 35 centimeters (14 inches). It had four-wheel, all-electric drive with a 1/4-horsepower motor turning each of the wheels. Steering could be done with either the front pair of wheels, the back pair, or with both pairs; and, at low speed, the Rover could be turned on a radius equal to its own three-meter length. Between the seats and slightly forward of the astronauts, there was a small instrument panel containing displays of, among other things, the Rover's speed and also a range and bearing to the last place where the crew had initialized the navigation system - always a place within sight of the LM.

For control, there was a simple T-shaped handcontroller located between the seats so that, if necessary, the Rover could be operated by either member of the crew. Naturally, none of the three J-mission Commanders ever relinquished control - nor did any of the LMP's breach etiquette by asking to drive. The Rover was capable of 10 to 12 kilometers per hour (6 to 8 miles per hour) on smooth, hard, level ground. By most terrestrial standards, of course, 12 kph is hardly a breathtaking speed; but, on the rough, heavily-cratered lunar surface, hazards could and did appear with exhilarating frequency. If nothing else, it was a very bouncy ride.

Although the Rover had been designed, primarily, to give the astronauts mobility and range, it also served as a scientific platform. Each of the Rovers carried a color-TV camera which could be operated remotely from Houston. Because of the high information content of the TV signal, broadcasts were only possible when Rover's high-gain antenna was pointed almost directly at Earth and, generally, the camera was only operated when the Rover was parked. Once a crew reached one of their work stations, they only needed a few seconds to point the antenna and then could go about their work while Ed Fendell ("Captain Video"), the camera operator on Earth, used zoom and pan features either to follow the astronauts as they worked or to supplement crew observations by using the TV to scan the countryside. And, finally, there was also plenty of room on the Rover for photographic cameras, film magazines, tools, sample bags, and, on Apollo 17, a small receiving station for one of the scientific experiments.

The honor of driving the first Rover on the Moon was supposed to have been John Young's; and, indeed, it was he and Apollo 16 crewmate Charlie Duke who participated in preliminary design discussions with engineers from Boeing and NASA's Marshall Spaceflight Center in January 1970. At the time, the Apollo 13 accident was still a few months in the future and NASA had, as yet, only formally announced the selection of one other crew: Shepard, Roosa, and Mitchell for Apollo 14. Nonetheless, Young and Duke, along with the Command Module Pilot Jack Swigert, were then serving as the Apollo 13 backup crew and, in the normal scheme of crew rotation, were in line for Apollo 16. At the time, it was expected that their flight would be the first of the J missions.

Young and Duke liked what they heard and saw. Boeing had come up with a safe, simple design and the astronauts had only a few substantive suggestions. First, Boeing had given the Rover a pistol-grip control just like the ones the astronauts used to fly the LM and the Command Module. However, Young and Duke pointed out that, on the Rover, they would be wearing bulky gloves and wanted something that would be easier to hold. The pistol grip was replaced with a T-handle. Second, in the interest of providing navigation information so that the astronauts could figure out just where they were, Boeing was proposing a rather complex device which, like a missile guidance system, would provide the astronauts with map coordinates. Given plenty of time and money for development and testing, Boeing might well have produced such a device, but the astronauts were quick to point out that all they really needed was a readout of the direction and distance back to the LM. As it turned out, development of the navigation system still took a lot of time and was a major contributor to the cost overrun; but, eventually, it proved its worth. Not only could the astronauts get back to the LM "on instruments", but, much more importantly, during the traverses they could use the navigation readouts to help them find particular geology stops.

Through the summer of 1970, Young and Duke and a few other astronauts participated in trials of various Rover prototypes. However, in September, budget cuts forced the cancellation of what was to have been a second handcart mission and the crew that was to have flown it - Dave Scott and Jim Irwin - inherited the first of the Rovers. In November, when Boeing delivered the first training version of the Rover, it was Scott who assumed the controls and, in the rough, volcanic country near Flagstaff, put it through its paces.

Dave Scott was a member of the third group of pilots selected to be astronauts. He was the first member of his group to reach space when he flew with Armstrong on Gemini 8; and was the first of the group to fly a second time when he flew as Command Module Pilot with McDivitt and Schweickart on Apollo 9. He then secured a firm place in line for a landing mission when, in April 1969, he was assigned as Commander of the Backup Crew for Apollo 12. By then, a pattern of crew assignments had clearly emerged. A backup crew could expect to skip two missions and then get the next prime-crew assignment; and there was every expectation that Scott and Irwin and their Command Module Pilot Al Worden would, in due course, be given Apollo 15. When the assignment was finally announced in March of 1970 - Scott says that they knew of the assignment well before it was announced - Scott and Irwin found themselves in the enviable position of having already gone through most flight training procedures for Apollo 12. For their own flight, they still spent plenty of the time in the LM simulators, but they were also able to devote nearly a third of their training efforts to geology and other lunar surface activities and, on launch day, were better prepared to do geology than any crew that yet visited the Moon. And, to top it off, they were headed for a geologist's paradise.

Landing at Hadley

From a geologic point of view, the Apollo 15 site was of enormous interest. It had a variety of features to be investigated - and it was also spectacularly beautiful. Scott and Irwin were scheduled to land on the fringe of Mare Imbrium (the Sea of Rains), in a small "bay" surrounded by tall mountains. If, during the Apollo 12 approach, Conrad and Bean thought they were skimming just over the mountain peaks, then this was the real thing. Indeed, in the seconds just before pitchover, as Scott flew the Lunar Module Falcon down through 9000 feet, the summit of 11,000-foot Mount Hadley Delta began to fill his window forward and left; and, on the other side of the spacecraft, Irwin could see the summit of Mount Hadley itself, a round-topped, 14,000-foot peak that dominates the local sky line. And, to add a final touch of grandeur to the scene, out the left window Scott could see a long, winding stretch of Hadley Rille, a mile-wide, V-shaped canyon, that seemed to snake toward him from the southeast.

At pitchover, a scant three minutes before touchdown, Scott got a bit of a surprise. Like most places on the Moon, the Hadley landing area is littered with craters but, as it turned out, few are large enough or deep enough to have early morning shadows. There is nothing that jumps out at you like the Snowman or Cone Crater. Toward the south edge of the landing area, virtually at the foot of Hadley Delta, Scott could see a grouping called the South Cluster and, of course, the rille was out in front of him. But, out in the middle, a couple of kilometers NNW of where Scott wanted to set down, landmarks are few and far between. There are a few moderate-sized craters which, from the pre-flight analysis, looked as though they would have shadows in them at landing time; and Scott had spent time in the simulators learning to recognize them. However, as with the Apollo 14 site, the map and model makers had missed the subtle undulations that make this a rolling countryside and make the identification of small craters difficult at best. Part of the reason was that the Apollo 15 site is well north of the Moon's equator and the photo coverage didn't have the resolution that had been available for the earlier sites; and, the net effect was that, as Scott looked out the window, he couldn't find the patterns he had hoped to see.

Scott would have liked a clear target but, in truth, Apollo-12-style precision really didn't matter much for this landing site. Houston had been watching the tracking data closely and, just before pitchover when Scott was about 6 kilometers east of the target, Houston warned him that he was probably about a kilometer south of the planned track. A quick look at his position relative to the South Cluster and to the point on the rille where it makes a sharp bend at the foot of Hadley Delta gave Scott enough information to show him that Houston's call was a good one. So, he nudged Falcon's line-of-flight toward the north. Without clear local landmarks, he couldn't be certain of setting down right on target, but he'd be close enough that the difference wouldn't matter. He was about the right distance short of the rille (now trending northwest out in front of him); he was just about due north of South Cluster; and he was well out into the middle of the desired landing area. He was certainly within a few hundred meters of the target and, with the mobility that the Rover would give them, a miss of a few hundred meters would be a matter of only a few minutes' drive. The worst that could happen would be that they would spend a few extra minutes during their initial traverse getting their bearings.

In the hours after landing, prior crews had donned their backpacks and had gone outside to do an EVA. However, the timing of the launch and a desire not to thoroughly disrupt their sleep meant that, by the time they landed, Scott and Irwin had been awake for 11 hours and, if they had tried to get in a full 8-hour EVA, would have put in a 26-hour day before they got into their hammocks. Consequently, they planned to spend the next several hours working inside the LM and then to have an eight-hour rest period before going out for the first time.

The Stand-up EVA (SEVA)

To fill out landing day, Scott and Irwin gave the scientists back in Houston a thorough description of the surrounding countryside. Rather than restrict themselves to the views out the forward-facing windows, they donned their helmets and gloves for what was billed as a "Stand-up EVA". (Scott now wishes that they had called it a "Site Survey".) Two hours after the landing they were ready. They bled all the air out of the cabin; and then Scott opened the overhead hatch. With that done and the docking hardware out of the way (a daunting task in the tight confines of the LM), Scott stood on the ascent engine cover with his head and arms outside the spacecraft, bracing himself in the opening as he took pictures with a 70-mm camera equipped with a long, 500-millimeter lens. By standing up in the hatch, Scott had a clear view all the way around the horizon.

The rolling nature of the terrain was, of course, even more evident than it had been during the approach and, as might be expected from the lack of deep, fresh craters in the area, in the near field Scott could see virtually no rocks bigger than a few inches across. "Trafficability," he said, looked "pretty good". They might be in for a bouncy Rover ride but, otherwise, it didn't look like they would have any trouble. In the far field, Scott had a clear view of the mountains and, as far as he could tell, the slopes were remarkably smooth. (Silver Spur photo) On Silver Spur, a feature that looked like a hogback ridge on the eastern flank of Hadley Delta, Scott saw lineations which he thought might indicate either structure or layering, but neither there nor elsewhere on the slopes could he see any large boulders. With no haze to obscure the view, his ability to pick out detail was limited only by his eyesight and, at the distance of Hadley Delta, he would have seen boulders bigger than a meter or so across. Off to the north at a similar distance, he could clearly see rocks blasted out of the bedrock at 800-meter-diameter Pluton Crater; but, on the mountains, the slopes were smooth. As Jim Irwin said later at the start of the first EVA, the Hadley site was a bit reminiscent of Sun Valley, a spectacular ski resort in the mountains of Idaho; and, everywhere Scott looked, there were the gray, rounded contours of the mountains and craters and - as it did for other crews - the mental leap from lunar dust to snow came easily.

After a half hour of verbal description and photography, Scott climbed down, reinstalled the docking hardware, closed the hatch, and then, along with Irwin, started doffing his suit. For the first time on an Apollo mission, the astronauts would sleep in their underwear, free for a few hours from the damp constriction of the pressure garment. They were the first of the LM crews to have the chance to get really comfortable in the LM hammocks.

Scott and Irwin slept soundly that first night, albeit not for as long as they would have liked. They had finished up the prior evening's tasks about an hour later than planned; and then, in the morning, Houston had to wake them up an hour early to check out a small oxygen leak that was soon traced to an unclosed cap on the urine disposal line. It was a problem that was easily fixed and, as Scott told Houston, "the sleeping up here is really good; and if y'all ever see another little problem like that, why, we'd only be too happy to roll over and take care of it. I think, as a matter of fact, we'd even sleep better if we knew that you wouldn't mind waking us." Despite the late start and the early wake-up, they got about five hours of sleep apiece and that was a lot more than any of the prior crews had been able to get.

Out for a Drive

Preparations for the first real EVA went quickly. Scott and Irwin discovered that they could chin themselves on some overhead guard rails and, while they were hanging, stick both feet into the suit. In one-sixth gravity, it was an almost effortless maneuver and, only four and a half hours after Houston wake-up, they were out on the lunar surface. The first order of business was to deploy the Rover. For this mission, rather than deploy the ALSEP experiments first, Scott and Irwin were going to take immediate advantage of the Rover and make a four-kilometer geology trip to the area where the rille abuts the foot of Hadley Delta. The advantages of the Rover didn't come free of cost, but the price certainly wasn't high in relation to the return. It only took them forty-five minutes to unstow and assemble the Rover and another hour to load it with tools and sample bags.

When he took the Rover out on a brief test drive, Scott was a bit disconcerted to discover that he didn't have front steering but, after a few minutes of fiddling with switches, decided to press on. From his pre-mission training, he knew that he could manage on rear steering alone and two hours after they started cabin depressurization, he and Irwin were rolling. The ride was about as bumpy as one might expect in a rough, roadless land. As Scott described it later in the mission, much of the terrain is so hummocky that, from the low spots, "you can hardly see over your eyebrows". Mostly, they drove along at ten kilometers per hour (10 "clicks"), going in and out of subdued craters, pitching up and down and rolling from side to side. At one point, Irwin joked that Scott's driving was making him seasick.

"What do you expect," said CapCom Joe Allen," traveling on the mare!".

In reality, the rolling and pitching motions produced nothing like the thrills that they got when they occasionally crested a rise and came upon a crater fresh enough and big enough to give them a heart-stopping jolt. Often, Scott had no time at all to react and, when they hit, the Rover turned into a "bucking bronco" with all four wheels bouncing up off of the ground. Even if Scott did have a little warning, when he tried to turn hard at any speed above about five klicks, the rear wheels tended to break out and threatened to send the Rover into a flat spin. They were both very glad to be wearing seat belts.

The only real problem that Scott and Irwin had with the Rover concerned the seat belts. Prior to the mission, no one had fully considered that, in the light lunar gravity, the suits wouldn't compress very much when the astronauts sat down. Unfortunately, the belts couldn't be adjusted and the fit was very snug. Indeed, buckling up proved to be a significant chore, but was absolutely necessary. In order to complete all of their planned activities, they needed to make good time. Scott needed to stay as close to maximum speed as he could. He could minimize the unevenness of the ride by keeping his eyes on the road, by driving straight through the subtle craters, and by braking before he attempted any evasive turns; but there was still the occasional hard bump. Because of the weak lunar gravity, oscillations in the suspension system damped out more slowly than they would have on Earth and it was always a bouncy ride. It wasn't a fast drive, but it certainly was "sporty" and they were both glad to be wearing belts. Fortunately, there weren't many rocks big enough to bother the Rover nor, as Scott commented at one point, was there much chance of running into other traffic.

In principle, the problem of reaching a planned geology station was straightforward. There were plenty of landmarks on the horizon and, for the first EVA, the most useful of these was St. George Crater, a dramatic, two-kilometer wide scar which had been blasted into the flank of Hadley Delta just above and beyond their destination. The crater was visible throughout the drive and all that Scott really needed to do was aim his nose at it. However, he had a natural, pilot's interest in the performance of the navigation system and, on the outward drive, he and Irwin attempted to put it to use.

Because the navigation gave them a range and bearing to the LM, the first order of business in finding a specific spot on the map was to figure out just where they had landed. Any uncertainty in the LM location translated directly into an uncertain Rover location. Scott thought he knew where he'd landed but, as they drove along, Irwin wasn't having any luck matching craters they passed with ones on the photomaps. Of course, even if they had known exactly where they had landed, map reading was difficult because (1) there were few large and/or distinctive craters close at hand, (2) judging crater size was inherently difficult, and (3) the maps had been derived from photos of relatively poor resolution. So it was perhaps not surprising that Irwin was still figuratively scratching his head when, thirteen minutes and about a kilometer and a half into the drive, they came - quite unexpectedly - upon the rille. It was immediately obvious that they were well north of where they thought they had been. Looking down the trend of the rille toward the southeast they could see where it bends sharply to the west; and, on the near rim, they could see their immediate target, the appropriately named Elbow Crater. Scott's first thought was that somehow they had been heading too much to the west; but, for now, the details didn't matter. As soon as they reached Elbow, the folks in the Backroom (as the Science Support Room was called) would be able to use the range and bearing at a known place to sort everything out. In the meantime, Scott and Irwin could see where they wanted to go and, so, turned south and drove along the edge of the rille. They reached Elbow Crater about ten minutes later.

Hadley Geology

During this first EVA, Scott and Irwin planned to spend a bit over an hour doing geology field work: fifteen minutes or so at Elbow and the rest up on the hillside near St. George. Although the scientific community had not yet developed a consistent description of lunar evolution, it was generally believed that the mountains at Hadley had been uplifted roughly four billion years ago as a result of the giant impact that formed the Imbrium Basin. During the first few minutes of that impact, great blocks of rock at what is now the edge of the basin were pushed up and out, forming the mountain cores which were then covered with Imbrium ejecta.

(During our review of this Apollo 15 summary, I asked Jack Schmitt how much of the South Massif is rotated block and how much is ejecta covering. "Nobody knows. But probably not a lot, relative to the height of the mountain. For the big basins, what probably happens is that you get down to depths where lithostatic forces can compete with the force of the explosion and you get a lot of lateral motions and you get multi-ring collapse because of the waves that are set up. If there were a lot of ejecta covering the mountains, you wouldn't see the rings. On Orientale, which is our best example of a fresh, multi-ring basin, you still see...In fact, you see mare formed inside the rings. Certainly the tops of the mountains have a covering of ejecta. And, also, I think we know from (Apollo 17) Station 6, that some of the impact melt will be injected into the fractures that form under the crater.")

Over the first few hundred million years that followed the Imbrium impact, the basin filled with lava, apparently a thin sheet at a time. At any one place, a relatively long time may have passed between successive filling episodes; but, by three to three-and-a-half billion years ago, the lavas stopped welling up from the interior and the mare-forming epoch ended. After that, only the steady rain of impactors produced any change, creating a five-meter cover of regolith on top of the lava flows, and adding, as well, to the regolith that had been forming on the mountain slopes. The Apollo 11 and 12 sites had yielded representative samples of the basaltic lavas underlying the Sea of Tranquility and the Ocean of Storms, respectively; and, at Elbow Crater, Scott and Irwin expected to find samples of Imbrium basalts. And then, up on the hillside at St. George, geologists hoped and expected to find samples of ancient lunar crust which, rather than having been strongly shocked and altered like the Imbrium ejecta that Shepard and Mitchell sampled at Fra Mauro, had merely been displaced upward and outward from the center of Imbrium.

As Scott and Irwin got to work at Elbow, it soon became obvious just how productive the J-missions were going to be. At this, their first stop, they were over three kilometers from the LM and, yet, had plenty of cooling water, oxygen, and time for field work. They had plenty of tools, sample bags, core tubes, and film; and, most importantly, they were starting work feeling well rested. For ten minutes or so, they gathered rocks and soil, describing features that the TV couldn't capture and taking plenty of photographs. And then it was time to move on.

"I wish we could sit down and play with these rocks for a while," Scott said as they loped back to the Rover. "Look at those things!" Then, like Bean before him, he stopped to admire the glistening face of a particularly handsome rock. "They're shiny. Sparkly! Look at all these babies in here. Man!"

"Come on, Dave," said Irwin, playing Conrad's role of time manager. "There'll be lots of them. Let's get back (to the Rover)."

But Scott wasn't to be denied. "Can't resist it," he said, and it was only after he'd collected the rock that he was ready to "go find something neat in St. George". During training, Scott had become fascinated with geology and his enthusiasm was not to be denied.

A short distance beyond Elbow Crater, they began to climb up the flank of Hadley Delta. They weren't going to go all the way up to the rim of St. George. That would have required a significant cross-slope drive and, for the moment, all they needed was a point high enough that they could be sure of being up off the young, mare materials. As the Rover began to climb, their speed began to drop. Seven minutes from Elbow they found what they wanted: a meter-sized boulder sitting on the hillside about fifty meters above the valley floor.

What Scott and Irwin were looking for were coarse-grained crystalline rocks called anorthosites which had cooled slowly at depth not long after the Moon had formed. What they discovered was that the boulder was a close cousin to the rocks Shepard and Mitchell had brought back from Fra Mauro. It was a composite, heterogeneous rock called a breccia which had formed when a jumble of rock and soil fragments was fused together, probably by the Imbrium impact or by an even earlier, large impact. Because the first sizable rock they found on the mountain was a breccia, there was a good chance that breccias would be common and anorthosites, perhaps, would be rare. But only a complete set of samples would tell the tale of the mountain and, so, Scott and Irwin wielded rakes, scoops, cameras and sample bags, hammered a double section of core tube into the soil, and even turned the boulder over so that they could obtain samples from beneath it, samples which might tell just how long the rock had been lying where they found it.

The view from the slopes of Hadley Delta can only be described as spectacular. Thanks to the Rover-mounted TV camera, Scott and Irwin could share the view with watchers back on Earth. Off in the distance, Mount Hadley and the hills west of the rille gave the horizon a distinctive personality - missing at the earlier landing sites - and provided visual balance to the winding, sinuous rille which trends north away from the mountain. Because it was still early morning at Hadley, the eastern wall of the rille was in shadow. In contrast, the western wall and, in places, parts of the floor were fully lit. Because of the relatively low resolution of the TV camera, the audience back on Earth couldn't see all of the detail that the astronauts could see; but, still, it was beautiful and, everywhere in the bottom of the rille, the floor was littered with boulders big enough to be seen by all.

By the time they were done, Scott and Irwin had spent fifty minutes at St. George. It was, by far, the longest and most productive geology stop that had yet been performed by an Apollo crew. Well-trained and well equipped, Scott and Irwin were able to make the most of the limited time and, as well, had the help of people back in Houston who could, for the first time, not only hear what they were saying but also see what they were doing. The geologists on Earth couldn't see minerals and textures in the rock but they could see how the work was going and, thereby, offer credible, real-time advice.

Return to the LM

As they climbed back on the Rover, Scott and Irwin had three options for getting back to the LM. When they first reached the St. George station, CapCom Joe Allen had asked if they could see their outbound tracks, wondering if they'd be able to do the "Hansel and Gretel trick" and follow the tracks home. Scott laughed and reported that he'd already checked at Elbow and had no trouble seeing where the Rover had disturbed the otherwise pristine lunar surface. On this first visit to the site, with no other tracks to confuse the picture, there would be no doubt about finding the LM. And even without tracks, the surrounding mountains provided enough landmarks that they could have gotten close enough to the LM to see it. However, everyone was interested in putting the Rover navigation system to the ultimate test and, as Scott pulled away from the St. George station, he planned to drive as straight a line back to the LM as the craters and other obstacles would let him.

For the first part of the drive, Scott had to drive downhill. That meant that he had a clear view of the ground ahead of him and, therefore, a chance to comment on things a bit farther afield. In particular, he was eyeing the slope off to his left. When he and Irwin got their first look into the rille, it was quite obvious that the rille wall below Hadley Delta was covered with fine debris. There seemed to be few, if any, boulders and Scott thought that it might be a place where someone could drive down into the rille - if not back out. From this closer vantage point on the hill side, Scott reported that the slope still seemed to be smooth and boulder-free, and he told Houston that "if anybody ever comes back, Joe, and wants to go down into the rille, have them come talk to us, because there's a good place to do it here." Perhaps he could have driven out of the canyon by making a series of switchbacks, but this wasn't the time to try. Indeed, it wasn't a minute later that he found out just how much there was to learn. On the way down from the St. George, as he crossed a slope only a little bit flatter than the one he'd just been eyeing, he got going a bit too fast, tried to avoid an obstacle, and "did a 180". When the Rover finally came to a stop, Scott found himself facing uphill and, thinking back to Irwin's comment about Sun Valley, the Idaho ski resort, he announced that he'd just done the first lunar "christie" - a high-speed skiing turn made by throwing the weight forward an skidding into the turn on parallel skis. It was a longish moment or two before he and Irwin stopped laughing and got going again.

If there was any residual doubt about the Rover navigation system it was answered just five minutes out of St. George when Irwin spotted a reflection off the LM. The spacecraft was dead ahead, a sharp little gleam on the horizon. It was a comforting sight out in the middle of the wilderness.

Drilling Troubles

Scott and Irwin got back to the LM at about four hours and twenty minutes into the EVA and planned to spend the remainder of the EVA deploying the ALSEP experiments. In all, they planned to be out for a total of seven hours. However, for unknown reasons, Scott was using oxygen faster than had been expected and, once he was back at the LM, Houston suggested that he "do as little unnecessary moving around as possible". Scott was quick to point out that, for most of the remaining time, he was supposed to drill three deep holes into the lunar surface - two for a heat flow experiment and one for a deep core - and, as everyone knew from training, the drilling promised to be hard work. Indeed, it was probably the most demanding physical work that either of them expected to do. Houston would keep a close watch on his oxygen supply.

In most respects, Scott and Irwin had relatively little trouble with the ALSEP deployment and, with the exception of the drilling, they completed the work in about an hour and a half. If things had gone according to plan, Scott would have spent about a half hour doing the drilling, emplacing the heat flow thermometers, and disassembling the six deep core sections; but almost nothing about the drilling seemed to go right. On Apollo 16, Charlie Duke drilled his first heat flow hole to the full 2.5 meter depth in one minute flat; and, on Apollo 17, Gene Cernan drilled his in a bit under three. However, both Duke and Cernan had the advantage of equipment which had been extensively modified as a result of what turned out to be a very frustrating experience for Scott.

At the start, the drilling went well enough but, after getting down 20 or 30 centimeters, Scott reported that the ground was getting 'stiffer" and that his rate of progress was slowing dramatically. After about five or six minutes of effort, he only had the drill stem about 170 centimeters into the ground and, as far as he could tell, it seemed as though he'd run into hard rock. Unbeknownst to Scott or anyone else, the problem wasn't hard rock but, rather, a fundamental flaw in the design of the drill-stem flutes. When the drill stem was turning and cutting, the flutes weren't carrying the cuttings to the surface but, rather, were getting clogged, thereby binding the stem tightly in the hole. When Scott said that he didn't think he would be able to get any deeper, Houston decided that this first heat flow hole was deep enough and told him to emplace the probes before moving on to the second hole. In order to do that, Scott first had to detach the drill from the stem and, when he tried to turn the drill counter-clockwise to break the connection, the stem twisted freely in the hole. He then took hold of the stem with one hand and tried to turn the drill with the other, but it soon became obvious that the two were virtually frozen together. Scott struggled for a couple of minutes before Houston suggested that he get the "wrench" off the Rover and use it to get a better grip on the drill stem. It took a minute or so before Scott and Irwin figured out that the "wrench" was the piece of equipment they knew as the "vise" intended for the separation of core sections. Much to everyone's delight, the vise did the trick. Scott offered heartfelt congratulations to the people in the Backroom, obviously glad to have finished this surprisingly difficult hole. The first hole should have taken no more than five minutes, but it consumed a quarter hour of precious time.

Any hopes that Scott may have had about the second hole were quickly dashed. As with the first hole, he managed to get the drill stem down about 170 centimeters but then no farther. With time running out, Houston told Scott that they wanted him to abandon the effort, at least for this EVA, so that he could help Irwin set up one last piece of ALSEP equipment and then head back to the LM for closeout. Tomorrow, after they had finished their second traverse and the drill experts had had a chance to think things through, they could give it another try.

By the time they were ready to leave the ALSEP site, Scott and Irwin were about six hours into the EVA and, because of the status of Scott's oxygen supply, Houston wanted them back inside the LM in about thirty minutes more. Scott was eager to make the best use of that time as he could and suggested that they not bother with the seatbelts for the short drive back to the LM. He would drive slowly, he promised. Minutes were precious; and they would gain about three minutes by not fiddling with the belts and only lose one or so by driving at a slower speed. Back at the LM, Scott saved a little more time by not turning the TV on.

In all, these little economies probably saved about five minutes, which Scott then put to good use at the very end of the EVA. Once he'd finished all his planned closeout activities and had sent Irwin up the ladder, Scott asked Houston if there was anything else he might do. Rarely at a loss for suggestions, Houston was quick to ask that he erect the solar wind experiment. This was a job that Irwin was scheduled to do at the start of the second EVA and, indeed, when Scott reminded Allen that he hadn't handled the equipment since he and Irwin had finished their Apollo 12 backup training two years before, Houston backed off the suggestion. However, Scott was not about to waste precious EVA time by dawdling or by climbing the ladder early. So he asked Irwin, who was up in the LM getting sample bags out of the way, if he could look out the right-side window and talk him through the procedure. Why not get the equipment deployed now, he said, and give the experimenters lots of data?

"Okay," Irwin told him. "Just take it out about 50 feet."

"Okay. Right about here, huh?"

"Farther, if you want. Yeah. And just pull the tube out full. Careful when you get to the end, that little thing popped off the end."

"Okay"

"Just pull it on out."

"Okay."

"And (be) careful, when you rotate the screen, that you rotate in the right direction, so it doesn't pop off. Just extend the tube several sections."

Because of the thick gloves, Scott couldn't feel the sections lock, but he should see red marks come into view at the proper extension.

"Okay. Red. Red. Red. Red," he said. "Okay. That's easy enough."

Now he had to extend the actual collecting screen like a window blind.

"And make sure you get the bottom of the screen - not the wire - over the loop," Irwin told him.

"Okay I see that. The bottom of the screen is over the loop. It says 'Sun', Scott said, obviously pleased with himself. "I guess that means that's what you face the Sun, doesn't it?"

"Isn't that a neat experiment?", Irwin asked him.

"Yes, that's the kind of experiment I like. Okay, we're out here at good distance where it won't get any dust on it from the Rover. And I'll turn it into the Sun here; stick it in the ground."

After the drilling, it was nice to have a job so simple and satisfying. The lightweight pole, Scott told Houston, would make a "good core tube". It went into the ground easily. And with that he was done.

" Okay, Joe, solar wind is deployed." The five minutes were gone.

The day hadn't quite gone the way Scott would have preferred. There had been problems and he and Irwin had been forced to delete planned activities. What Scott really wanted to do was some geology and some driving, and the oxygen situation was getting in the way. Was there anything he could do about the oxygen use, he asked Houston? Was there a zipper that could use some extra lubrication, just in case there was a small leak? No, said Houston, it didn't look like a leak. It looked as though he was burning oxygen at higher than expected rates both while he was working and while he was driving.

"Okay," he said, "I'll breathe a little less tomorrow".

But there wasn't a need for anything so extreme, Joe Allen told him. He and Irwin had just set a bundle of new EVA records: six hours on the surface and a productive, two-hour, three-kilometer geology trip. If they managed another couple of EVAs like the first, then nobody was going to complain.

Getting Out of the Suits

As Jim Irwin mentioned later in the mission, "the secret of living up here (in the LM) is getting out of these suits. It really makes a difference." After a full day's EVA, it was a great relief to be rid of the constant chafing and rubbing, free to stretch arms and legs and flex fingers without constant backpressure from the suit, and free to let your underwear dry out. Like most things, freedom from the suit came at a price, and that price was the loss of elbow room. One-sixth g can be fun and restful but, except when they were in the hammocks, it was difficult to make much use of the low gravity within the confines of the LM. The cabin was a place to eat, a place to repair and prepare equipment with unencumbered fingers, and a place to sleep.

It was nice to be out of the suit; but, in the morning - rested and dry - they were eager to get going again. During training, Dave Scott had developed a real love for geology and the new day promised to be the sort he could really enjoy. As it turned out, it was one of the more memorable days of the whole Apollo program.

The need to finish the second heat flow hole hadn't gone away, nor had the deep core; but, as had been discussed before Scott and Irwin bedded down, Houston was willing to defer those tasks to the end of the EVA. As planned, they would spend the first part of the day driving south again in the Rover for about four hours of exploration and sampling. Scott believed that he'd gone to the Moon primarily to take advantage of the Rover, and the less time the Rover spent parked at the LM or the ALSEP site, the better he liked it.

The Second EVA

By the time Scott and Irwin were out on the surface and were ready to drive off, it may have seemed as though their luck had turned a bit. They had been forced to spend a little extra time prior to depressurization cleaning up a few gallons of water that had spilled on the floor the previous night after a plastic bacteria filter broke off their water gun; and they'd had to use tape to re-attach Irwin's backpack antenna which had broken off when he crawled back into the LM the previous night. But they'd been able to take care of both problems in short order and now, much to Scott's delight, they found that the formerly inoperative front steering was now working.

"You know what I bet you did last night, Joe?" said Scott to his CapCom. "You let some of those Marshall guys come up here and fix it, didn't you?" Perhaps, he suggested, Boeing had built a secret launcher so that engineers from Boeing and from Marshall could come up to the Moon "to fix their Rover".

Three and a half hours after wake-up and an hour after depressurization, they were rolling. It took Scott a little while to adapt to the new steering and indeed, after a few minutes, he decided to stop and switch to front-wheel steering alone. The vehicle, he said, was much too responsive, especially when he was going downhill. However, he soon discovered that, with front-wheel steering, the rear wheels seemed to be drifting rather than centering properly. Four-wheel steering was better than two, it seemed, and it wasn't going to take long to adapt.

To start this second trip, Scott drove almost due south toward one of a handful of medium-sized, fresh craters on the lower slopes of Hadley Delta. With luck, they might find some of the unaltered samples of the ancient crust that had eluded them at St. George. The chances of finding fragments of bedrock depended, of course, on finding a crater both big enough that the impactor would have penetrated through the regolith and young enough that the fragments hadn't been re-buried by the same downhill movement of material that had smoothed the rille walls below St. George.

As they drove south, the mountain dominated the view. To Scott, it seemed "as big a mountain as I ever looked up." The lower slopes averaged about 8 to 10 degrees but, above them, the mountain sides steepened and rose nearly as far and nearly as fast as the slopes of Mt. Fuji in Japan. It was a rise of three-and-a-half kilometers in a horizontal distance of no more than seven, a slope of about 30 degrees. Because most of the mountain is so steep, any material dislodged by impacts will tend to tumble at least a short distance downhill and, as Scott and Irwin approached the place where the mountain and the mare meet, they noticed a clear change in the nature of the surface. About three hundred meters before they reached the base of the mountain, they noticed that the number of deep craters was dropping dramatically and that there seemed to be far fewer small rocks lying on the surface. Burial by talus that had tumbled down from the mountain - or by ejecta from impacts on the mountain slopes - seemed the most likely explanation.

Right at the base of the mountain, Scott and Irwin drove into a shallow east/west trough, a depression which can be interpreted in at least two different ways. According to one theory, during the mare-filling period the cooling lava shrank and pulled slightly away from the mountain. The resulting gap was then smoothed by impact erosion and partially filled by material tumbling down off of Hadley Delta. According to the second theory, the mountain has been subsiding ever since it was raised in the Imbrium impact and, therefore, the theory says, the depression marks the bounding fault, a moat that is partially filled in as it opens - again - by debris tumbling off the mountain.

As they had from the LM, Scott and Irwin kept an eye out for fresh craters and boulders on the hillside but, even as they got closer and could pick out more detail, there was little more detail to see. Other than Spur Crater, a fresh, 40-meter feature where they planned to do most of their sampling, the only striking object that they saw while driving south from the LM was a large boulder a short way upslope from Spur. Otherwise, the hillside had the appearance of a dry, sandy, well-used beach covered with soft hummocks and with poorly-defined, shallow craters.

The mission plan called for Scott and Irwin to climb the hillside a bit west of Spur and then turn to the east and make a three-kilometer drive roughly along a contour line. That would give them a chance to see what variety of samples were available before making a sampling stop at the far end of the traverse. They then planned to retrace their tracks, stopping once about halfway back to Spur and then, finally, at Spur itself. However, because the drilling wasn't done and because of Scott's oxygen use rate, time was at a premium and Houston asked them to think about the relative value of driving versus sampling. It wasn't very long before Scott and Irwin satisfied themselves that, except near the few fresh craters already marked on the map, any one part of the hillside was going to look pretty much like any other. They had been angling up slope - having passed Spur Crater on their right - and now were on about the same level as the boulder and about three hundred meters east of it. There didn't seem to be much point in driving farther east. It looked as though they could get representative samples here as well as anywhere else. So, they parked the Rover and got busy with what proved to be a long and very productive geology stop.

A Green Boulder on Mt. Hadley Delta

Working on the hillside took some practice. Without the suits, they might well have spent much of their time standing sideways to the slope, with the uphill leg bent a little to keep themselves upright. However, in the stiff suits it was difficult to stand sideways for very long and, most of the time, they had to stand facing into the mountain and leaning into it. As they soon discovered, work on the hillside was possible only because the soil was soft enough that their boots sank in a way, giving them extra purchase. In addition, they could sometimes use a small crater as a step or bench on which to stand . Indeed, they made life a good deal easier for themselves when, about twenty minutes into the stop, they moved downslope about 15 meters from the Rover - and about three meters vertically below it - to a flat-floored, 12-meter crater where they could work without fighting for balance.

After an hour's worth of basically pleasant, rewarding work, Scott and Irwin were ready to move on. They had collected a large number of samples, most of them reminiscent of the Fra Mauro breccias. They had dug a trench, and had taken panoramas and telephoto pictures of Mount Hadley and of the LM. Scott had even had the novel experience of getting a core from the rim of the 12-meter crater merely by pushing the tube with his hand into the soft, loose soil. The only really difficult part of the experience, they found, was climbing back up to the Rover. Scott, who has been described to me as a "moose", bulled his way up the slope while Irwin took his time. When Scott laughingly said that "I'd sure hate to have to climb up here (from the base of the hill),", Irwin seconded the thought and suggested that they "work above the Rover from now on." Fortunately, once they were back on the Rover, both of them could relax for a few minutes before they had to climb off and work on the slope again.

As they approached the big boulder a few minutes later, Irwin decided that, here at least, it might not be such a good idea to park downhill of the work site. The rock was about a meter high, a meter wide, and about three meters long and, although it was partially buried and obviously had been sitting right where it was for millions of years, it was still easy to imagine the rock sliding down on them or the Rover. The rock was perched on a slope of about 15 degrees, the steepest they'd encountered, and prudence seemed in order. Scott parked about 15 meters west and slightly uphill from the boulder, but it wasn't long before the slope made them think again.

They both had difficulty getting out of the Rover and, once he was on his feet, Scott had trouble finding a good place to stand as he tried to point the high gain antenna at Earth. Houston began to wonder if, once they got down to the boulder, they could get back up to the Rover. CapCom Joe Allen urged caution.

"Hey, troops", he said, "I'm not sure you should go downslope very far, if at all, from the Rover."

"No," Scott told him, "it's not far."

The only way to find out if they could make it was to try, but Scott wanted Irwin to stay with the Rover while he scouted the slope.

Irwin offered encouragement. "I think we can sidestep back up," he said.

"It's not that hard," said Scott, still edging down toward the boulder.

Houston was usually cautious about offering advice to the crews but this was clearly an unusual circumstance and Allen firmly suggested that Scott try climbing back up before he got too far. Scott agreed that was a good idea. "Okay; I'm halfway, and I'll go back first. Why don't you just stay there, Jim?"

"Okay," said Irwin. "Come back up."

"The Rover makes (this slope) feel so easy (to climb)," said Scott.

"I know it," Irwin said. "(We) should have parked right beside it."

And that sounded like the best idea. Scott came back up to move the vehicle. Irwin decided that it would be easier for him to walk down to the new parking place rather than try to climb into his seat. Because of the stiffness of the suit, getting on board meant standing at the side of the Rover and jumping sideways into the seat and, on this slope, that wasn't going to be easy. Irwin had been watching Scott carefully and was confident that he could get downhill without trouble. Once Scott had gotten himself on the Rover, Irwin started down but, before he'd moved more than a few steps, Scott told him to stop. It was going to be easiest for Scott to put the Rover in reverse gear and back up for a few feet before he turned downhill and he wanted Irwin to watch and wait until he had the Rover securely parked again.

Again, Allen urged caution. "Proceed very carefully now, please, " he said.

"Oh, we are", said Scott. "We're doing it really cool."

"Super cool," suggested Allen.

"Super cool," agreed Scott.

"How am I doing, Jim?," he asked as he backed.

"Doing okay. Want me to come over there and get on?"

"No, no. Stay there."

Slowly, Scott turned downslope, first headed west and then looping east below Irwin's position. He drove along the hillside a bit further until he was past the boulder, still above it slightly, and then turned down the hill again to complete an S-shaped path. He parked the Rover just a bit below the rock and to the east.

Scott still wasn't too sure that they'd be able to work around the boulder. The Rover was perched so precariously that the left-rear wheel was a good six inches off the ground and Scott decided that it wouldn't be prudent to leave the vehicle, just in case it decided to roll downhill on its own. He suggested that they abandon the effort.

No matter what they did next, Irwin had to pass the boulder on way down, so he stopped to take a picture. Then he noticed that the boulder seemed to be light-green in color and offered to come down and hold the Rover so that Scott could go up to take a look. A green rock was novel enough that Irwin wanted to make sure that the better geologist of the pair had a good look at it. Scott agreed instantly. Irwin climbed down and, once Scott was sure that Irwin was standing comfortably and had a firm hold on the Rover, he climbed up.

The boulder was green, all right, and a breccia as well. Scott grabbed a few fragments which, once they were examined back on Earth, proved to be full of iron-rich and magnesium-rich glass which produced the green tint. Scott also collected some of the surrounding soil which, as Irwin had noticed, also had a greenish cast. For about six minutes, Scott worked around the rock and then, gingerly, made his way back to the Rover. The slope made the work strenuous and, in hindsight, not much of scientific value would have been lost if they had abandoned the boulder. As it turned out, they found similar rocks once they got downhill at Spur. However, from an operational point of view, it was useful to know that, with some care taken in parking the Rover, it would be possible for crews to work on slopes at least as steep; and, indeed, the Apollo 17 crew spent most of their third EVA working on steeper slopes.

As he re-parked the Rover, Scott had taken care to point it downhill, in hopes that it would make getting on easier. Irwin suggested that Scott get on first while he kept his grip on the Rover. Scott made it on the first try but suggested that Irwin wait where he was until Scott had driven downhill a short ways to a small crater where he could get the Rover level enough that Irwin could jump on easily. Irwin even said that he'd be willing to walk the whole 300 meters down to Spur, but Scott vetoed the idea and, indeed, with the Rover level, Irwin had no trouble. For a second time, the crew of Apollo 15 proved the operational value of small craters.

The Genesis Rock

Spur Crater is big enough that the north (downslope) rim provided a big, nearly-level parking pad and the work at this stop was relatively easy. It was also very rewarding.

One of the first things that Scott and Irwin noticed was that they were standing on more of the greenish soil. Irwin began to wonder if the greenish appearance might not be due to their dark visors. What if they got the rocks home and they weren't green after all? The ribbing would be merciless.

"I've got to admit it really looks green to me, too, Jim, but I can't believe it's green," said Scott.

"Oh, it's a good story," said Irwin, laughing. "Something about green cheese? Who would ever believe it?".

Independently, Scott and Irwin decided to try the obvious experiment and raised their visors. As their eyes adjusted to the brighter light, the greenish tint faded a bit but, as Scott said, it was definitely "a different shade of gray." Two soil samples went into bags - samples that still had a greenish cast when they were examined after the mission - and then the astronauts turned their attention to other matters.

About fifteen minutes into the stop, as they were scanning the rim to make sure that they were getting a full suite of samples, Irwin spotted a four-inch rock that glinted in the Sun, sitting up by itself on a pedestal of breccia. It seemed to beckon, Irwin thought, and to say "come and sample me." As they looked more closely, there was no doubt about what they had found. Here was a crystalline rock made up almost entirely of the mineral plagioclase; and it was very different in character from the breccias and mare basalts that they had collected so far.

"I think we found what we came for," Irwin told Houston.

"I think we might have (found) ourselves something close to anorthosite," Scott said with some satisfaction, "because its crystalline, and...it's just almost all plag(ioclase). What a beaut."

Back on Earth, while Scott and Irwin were carefully bagging what came to be known as the Genesis Rock, commentators lost no time in trying to come to grips with the significance of the find. Once the great Moon Race had been won, America's interest in Apollo had declined fairly quickly and, by this time, all that was left in the public mind was a question of the Moon's early history. The Apollo 11 and 12 crews had brought back the mare samples with which geochemists dated the great lava floods that made the mare; and the 14 crew had brought back the breccia samples which confirmed general impressions about the age and composition of the ejecta from the large basins like Imbrium. What remained to be found was a pristine fragment of the ancient crust and, in laymen's shorthand, this became the search for the "oldest rock." In some ways, the "oldest rock" took on characteristics of the Holy Grail and the Rosetta Stone and its discovery was seen by many as the final Apollo task. There would be two more flights to fill in a bit of the detail; but, in the public mind, the quest was now over. Fortunately, NASA had no plans for Scott and Irwin to rush home if they did find an "oldest rock". One anorthositic rock from one site could not tell the whole story. As it turned out, even the Genesis Rock had been shocked at least twice in the four billion years or so since it slowly solidified deep within the lunar crust and, at the Apollo 17 landing site, Cernan and Schmitt found an even older fragment of the Moon. Still, the Genesis Rock was an important piece of the puzzle and Scott and Irwin were well pleased with themselves. They had spent time during training learning to "sort the unusual from the usual," as Dave Scott later said; and, in particular, had learned how to recognize anorthosite. They had been primed to look for it; and, after only three hours in the field, they found some.

During their stop at Spur, Scott and Irwin actually collected four pieces of anorthosite, with the Genesis Rock being the first and largest. Along with other tools, the astronauts had a large rake which looked and worked like a clam rake. Here at Spur, Irwin dragged it through the soil several times, trapping rock fragments of walnut size and bigger in the basket and letting the soil and smaller fragments flow out between the tines. In one two-foot-long swath, he got a remarkable total of 15 fragments - a real "jackpot" as Joe Allen called it - and his total collection proved to include not only three more pieces of anorthosite but also samples of breccia, some fragments of basalt which had probably been tossed up to Spur from the mare below, and also some "exotic" fragments thrown onto the site from even farther away.

Return to the LM

The stop at Spur was one of the highlights of the entire Apollo program and, during the trip back to the LM, Scott and Irwin got a momentary fright when, during a hurried stop at the South Cluster, Scott noticed that Irwin didn't have a sample collection bag on his backpack. Convinced that Irwin's bag had dropped off somewhere back along the track, Scott quickly reassured himself that he'd been careful to put the collection bag with the "good rocks" under the Rover seat before they left Spur.

"Oh, well, win a few lose a few," he said.

There was certainly no time to go back and look for a dropped bag, even though the Rover tracks would show exactly where they had been. And, as it turned out, Scott was mistaken about the "lost" bag. As they were preparing to mount the Rover once more, Scott remembered that he hadn't bothered to put a fresh bag on Irwin's back before they left Spur.

"Boy, you had me worried," said Irwin.

"I had me worried too. I knew (I hadn't lost) the one with the good rocks because I stuck that in the seat pan. But I thought I had put (a new) one on you, and now I remember I started to put it on you, and your harness looked loose, so I stuck it on the (back of the Rover) where its got a lock. So we're okay."

And then Joe Allen offered a bit of apology. "And we knew all the time, Dave," he told them. "We should have told you. Wanted to keep you honest though."

The drive back to the LM was uneventful and, indeed, was a nice break in an otherwise busy and productive day. There were plenty of descriptions to pass along to Houston - descriptions of the samples, of their impressions of the sites, and of Mount Hadley out beyond the LM, but it was hardly physical work.

"Gee, it's nice to sit down, isn't it?," Scott prompted Irwin.

"Oh, it is."

"It's a good deal," Scott said, laughingly. "You hop off and work like mad for 10 minutes and hop back on, sit down, and take a break." It was a great way to do lunar geology, especially with more drilling awaiting them back at the LM.

From time to time during the drive, Scott and Irwin could see the LM out in front of them. From their station at Spur - about 60 meters above the spacecraft and, of course, nearly five kilometers to the south - they could see sunlight glinting off of it and were pleased to note that, with the nose of the Rover pointed at the LM, the bearing and heading indicators agreed precisely. Neither of them felt comfortable judging distance yet. Without familiar objects to help them - trees, telephone poles, houses, and the like - it was almost impossible to judge sizes and distances and, during the drive home, Scott threw in the towel. "I don't know how large 'large' is anymore," he said. But at least there wasn't any doubt about the Rover navigation system. At 2.4 kilometers out - according to the navigation system - they began to see details on the LM. Four hours after they set off for the mountain, they were back at "home, sweet home", 85 pounds of rocks and soil richer.

Penance

If the first part of the EVA made for the sort of geology-rich day that Dave Scott could really enjoy, the drilling promised to be his penance. And for Jim Irwin, the cost of the honor of having spotted the Genesis Rock was a set of soil mechanics experiments that he would perform while Scott did the drilling. Irwin almost wished that he could trade jobs; the instructions for the soil mechanics experiments filled five full pages on the cuff checklists. In comparison, the tasks for a geology stop usually only filled two pages.

As Scott told Allen: "Before we got out this morning, we figured you guys had a conspiracy against us, having Jim doing...(the soil mechanics experiments) and me drilling at the same time."

The soil mechanics experiments were designed to give the engineers detailed information on the stability and load-bearing characteristics of the regolith, information that would be useful in planning for an eventual lunar base. The engineers had, of course, been able to deduce a good deal of such information from the depth of footprints and Rover tracks, the depth to which core tubes could be pushed and/or hammered, and the stability of the walls of trenches dug by the crews of Apollos 12 and 14. Here at the Apollo 15 site, Irwin would supplement those inferences with quantitative measurements made with an instrument which recorded the amount of force that he needed to exert to penetrate the soil with a thin, cone-tipped rod. As it turned out, the soil was about as hard and compact at any encountered by Apollo crews and that fact, in hindsight, suggests that Scott was not only fighting a poor drill stem design, but was also drilling into intrinsically stiff dirt.

Not surprisingly, NASA's experts had been thinking about the drilling problems ever since Scott abandoned the effort the night before and now suggested that he run the drill for a short while without pushing down on it. Then, if he noticed it starting to bind again, they wanted him to try raising the stem a little bit to clear the flutes. Unfortunately, even with Scott just holding the drill as lightly as he could, it bound up almost immediately and, as well, he found that it took a great deal of effort to pull the stem up even a short distance. With the power on, he said "it pulls me right on down with it." By straining for all he was worth, Scott managed to lift the assembly a few inches; that seemed to help for a few seconds, but then the drill bound up again, even tighter than before, like a "steel vise."

Scott's hands were beginning to give out and it wasn't long before Houston decided to call it quits again. Perhaps, they all thought, they'd made a little extra depth. However, when Scott tried to insert the heat flow probe, it wouldn't go deeper than about 100 centimeters. What had happened was that, when he lifted the stem part way out of the hole, the bottom section stayed bound in the hole and separated from the next one up. And when he started drilling again, the second section deflected to the side and became firmly wedged against the first section. In short, Houston's suggestion had only made matters worse. Fortunately, although the heat flow experimenters had to take extraordinary care in interpreting the data from the second hole, they were eventually satisfied that they were getting good measurements. The results of the Apollo 15 heat flow experiment were consistent with those made on Apollo 17.

After finishing the second heat flow hole, Scott took a short break to help Irwin with a trenching experiment. While Irwin dug, Scott took pictures. Irwin got down to about a one-foot depth, but then had to stop because the soil was so compact that he was almost sure he'd reached bedrock. Scott then helped Irwin seal a trench sample in a vacuum-tight can before getting back to what he facetiously called his favorite task. There was, after all, still the deep core to be obtained and Houston wasn't at all sure that the drill's power supply would last out the rest period between EVAs. It was now or never.

This time, mostly because of a good stem design, the drilling itself went fairly smoothly and Scott got the six sections of core tube in their full depth of 2.4 meters after only a few minutes of effort. However, although the core stems would turn in the hole when Scott pulsed the drill, once again, cuttings filled the flutes enough that he was unable to pull the core out of the ground. The hole had been drilled and, presumably, the core tube now held a detailed section of soil nearly half way down to the top of the lava below; but Scott was rapidly running out of oxygen and it was time to get back into the LM. The core tube would have to stay in the ground for a few more hours. Tomorrow, they would try to pull it out.

The Cost of Drilling

Because of the drilling problems and number of tasks new to this mission, by the end of the second EVA, Scott and Irwin were running an hour and forty minutes behind the mission timeline. When they climbed back into the LM at the end of the EVA, they had only twenty-two hours left before they were scheduled to go back to orbit; and, in that short period, they still had to complete their post-EVA tasks, get some sleep, conduct the third EVA, and then, four hours after climbing back in the LM for the last time, launch and rendezvous with Al Worden. They were short on time and, because Houston was insisting, sensibly, on both an on-time lift-off and a full night's rest, the third EVA had to be shortened. Nonessential activities - like a scheduled science debriefing - were dropped; but there wasn't much padding in the schedule. By morning, Scott and Irwin had only been able to catch up by about ten minutes and were looking at an EVA that would last "somewhere between four and five hours" rather than the nominal six. Allen tried to put things in perspective and noted the highest priority mission goals had already been achieved. With only slight exaggeration, he said that "we checked off the 100 percent science-completion square sometime during EVA-1 or maybe even shortly into EVA-2. From here on out, it's gravy all the way, and we're just going to play it cool, take it easy, and see some interesting geology. "It should be", he said, "a most enjoyable day."

Two and a half hours after wake up, Scott and Irwin had finished breakfast and, as they listened to Houston's plans for the day, were well into their preparations for the EVA . For the first three hours they would follow the flightplan and drive west to the rille for sampling and photography. But, then, they would have to turn for home without going to a cluster of craters called the North Complex where, from slim evidence seem in orbital photography, the geologists hoped that evidence of post-mare volcanic activity might be found. Inevitable as it was, the deletion of the North Complex stop was something of a disappointment and Scott asked Houston to hold open the possibility of at least a quick foray. Joe Allen told him that the request had been noted. "We copy that, and it may well be that we can get up there. We'll just see how it goes."

Three hours after wake-up, Scott and Irwin were out on the surface. They made good time loading their backpacks and the Rover with tools and sample bags and, just forty-three minutes after depressurization, they were ready to leave the LM. However, before they could drive to the rille, there was the not so minor matter of retrieving the deep core and they could only hope that the bad luck they'd been having with the drilling had ended.

But it was not to be. The drill stem wouldn't budge - even with both of them lifting on the drill handles. At Houston's suggestion, they tried running the drill for a few seconds, but all it did, Scott said - laughing at the humor of the situation - was that it "sucked me right back down". There was power left in the battery pack after all and, Scott described the situation: "What happens, Joe, is that, when I turn the drill on, the drill drills - like all drills should."

What they needed was a jack of some sort, a way to gain some mechanical advantage, but that would have to wait for Apollo 16. For now, all they had was their own muscles and gradually, by getting elbows and then shoulders under the drill handles, they pried it up a few inches at a try. Time and time again they counted off, straining together on the count of three. Ten minutes into the effort there were some real signs of hope.

"Okay," said Scott, "it's coming. It's coming. Let me get underneath it here. 1, 2, 3."

"One more," said Irwin.

"1, 2, 3. Okay. I've got it. Okay. Let me have it now."

Scott pushed once more with his shoulder; and the core came out. Unbeknownst to anyone else, he badly sprained his shoulder in the effort. However, a shoulder would heal faster than a memory of a core tube left stuck in the lunar surface. They'd gotten the job done, and that was what mattered. Sore as he was, Scott would be able to get the rest of the day's work done without any problem. There certainly wasn't any point in calling the sprain to Houston's attention. Once he was back in the cabin he would take some aspirin to ease the pain but, for now, there was a final EVA to complete.

As he and Irwin struggled to remove the core, what Dave Scott wanted most for Houston to tell him was that the effort was worthwhile. It would be a while yet before he said anything, but his frustration showed up occasionally in his tone of voice. For one brief moment after they'd gotten the core out, he was even a bit abrupt with Houston when Allen asked Irwin to go ahead and take some pictures of the trench. Somewhat pointedly and certainly uncharacteristically, he said, "Joe, just standby until we get this settled down; and then we'll come at you for what is our next task. You're going to have to just hold off on jumping ahead of us, because we always have to come back and ask you what you said anyway."

Allen, who surely ranks as the most diplomatic of all the people who served as EVA CapComs, backed off immediately. "Read you loud and clear," he said.

And there the matter might have ended, but for the fact that, despite having worked superbly as a stand in "wrench" at the end of EVA-1, the vise on the back of the Rover wouldn't work. The vise was designed specifically to grip a section of core so that it could be separated from the other sections. However, as Scott discovered, the vise would hardly grip at all. By grasping the core tube tightly in one hand, Scott managed to remove each of the top three sections but then couldn't separate the bottom three. As he worked, he realized that the vise was mounted on the Rover backwards, a remarkable discovery since the mounting hardware ensured that the vise could be put on only one way. As it turned out, the error originated in an engineering drawing which hadn't been caught because, during assembly of the training version of the Rover - either accidentally or for the obvious reason that the vise wouldn't work as drawn - the mounting hardware had been installed backward from the drawing. However, that information wasn't passed on to the people who assembled the flight Rover, nor was the drawing changed; and, consequently, Scott and Irwin found themselves with a tool that wouldn't work. Because the lower sections of the core tube had been turning in the ground longest, they were stuck together too tightly for Scott, even with Irwin's help, to separate by hand.

Finally, after Scott and Irwin had spent a half hour on the core, Houston advised them to lay the remaining sections on the ground and proceed with the traverse. Irwin noted that the remaining three-section piece was short enough that they might be able to take it into the LM as it was, although Scott wondered where it would fit in the Command Module. Houston had nothing, as yet, to say on the matter and, indeed, Scott finally decided that it was time to remark on the amount of time they spent on the core.

'Hey, Joe, you never did tell me that (core) was that important. Just tell me that it's important, and then I'll feel a lot better."

"It's that important, Dave," Joe Allen said.

"Okay. Good. Because then I don't feel like I wasted so much time".

"No," said Allen. "Quite seriously, Dave and Jim, that's undoubtedly the deepest sample out of the Moon for perhaps as long as the Moon itself has been there."

After the mission, the Apollo 15 core tube was promptly x-rayed and Scott had the pleasure of showing the pictures at a press conference. During the drilling, he had penetrated over fifty distinct layers, an extraordinary record of the multiple events which created this particular column of soil. Studies of the deep cores obtained on Apollos 15, 16, and 17 provided details that were critical to an understanding of the processes that produce the soil layers. When combined with more qualitative observations about the depth of craters that bring blocks of bedrock to the surface, these details give some confidence in predictions of such things as the prevalence of rocks at depth, a matter of some importance to civil engineers designing buried or partially buried structures for a lunar base and to mining engineers interested in processing large quantities of regolith in order to extract such things as the hydrogen, carbon, and helium-3 implanted by the solar wind. From this point of view, the extra effort - that undoubtedly cost Scott and Irwin the chance to visit the North Complex - was worthwhile. And of course, as the first crew to attempt so ambitious a mission, it would have been extraordinary if Scott and Irwin had not run into difficulties at some point. Compared with the troubles that cost the Apollo 13 crew a landing, the loss of an hour's worth of time was a relatively minor matter. It would have been nice to get to the North Complex; but, then, none of the Apollo crews had time enough on the Moon to do all they could have done with the equipment at hand. A brief stay dictated compromise.

The series of minor troubles that had been plaguing Apollo 15 hadn't quite ended yet. With the core out of the ground, Scott's next task was to mount the Rover and, with Irwin standing by with a movie camera, put the Rover through its paces for the Boeing and Marshall engineers. Unfortunately, as Scott drove by for the first time, Irwin found that the movie camera wasn't working. On his own initiative, Scott decided that they would abandon the Grand Prix. The engineers would have to wait for Apollo 16 to get a movie and, for now, it was obvious that the Rover was working beautifully. Verbal descriptions of its performance would have to be enough.

Houston lost no time in supporting Scott's decision.

"That was a good try," Joe Allen said. "Let's press on to Station 9. Let's take a good, clean, comfortable look at that rille."

"Yeah, that's a good idea, Joe," said Scott, eager to be off. "Best idea you've had all morning."

Hadley Rille

An hour and a half into the EVA, they were finally on their way. Now that they knew almost exactly where they had landed, they knew that the drive to the rille would be a quick one: a trip of about two kilometers that would take ten to fifteen minutes, depending on the sort of terrain they encountered. During the Stand-up EVA, Scott had gotten a pretty good look at the countryside in all directions except the west. For the same reason that the Apollo 12 crew had been slow to recognize that Head Crater sat just down-Sun of them, Scott hadn't been able to see much detail in the direction of the rille and, now that he was driving toward west, he and Irwin could only assume that they would find the same sort of terrain that they had found south of the LM. Consequently, their encounters with a series of three large depressions came as something of a surprise. On their own scale, the depressions were shallow - with inner slopes of only about three degrees or so. However, each of them was up to two hundred feet deep and that was enough to send Scott on a detour.

The surface, Scott said, "is smooth but rough. Smooth on a small scale" but rough enough on the large scale that "you really could get lost. Up and down."

"It's like driving over the big sand dunes in the desert," Irwin added. It wasn't at all like driving up to Hadley Delta, he said. There, "you could always look back and see the LM."

Along the section of the rille that Scott and Irwin were approaching, the western rim is about 30 meters lower than the eastern rim, and it was only at high points on the traverse that Scott and Irwin caught glimpses of the far wall. Ten minutes into the drive, at a point about half a kilometer short of the near rim, they got a momentary look at it. And then they saw it again when they got to a brief sampling stop at a small, fresh, soft-rimmed crater.

Over the last 200 to 300 meters of the approach to the rille, the surface slopes gently down toward a line of light-grey boulders that marked an apparent edge and, as Scott and Irwin approached, the number and size of rocks they saw sticking up through the soil increased steadily. Long before Apollo 15, a number of clues had suggested to geologists that Hadley Rille was a lava drainage channel - or drainage tunnel - left over from the time when the mare were being filled. Or, perhaps, the Rille had begun its life as a fault, or a series of faults, running roughly parallel to the western slopes of Hadley Delta which was then eroded - rather than filled - by the thin, liquid mare lavas. Whatever the rille's origin, once the flow of lava stopped, the steady rain of impactors gradually eroded roofs, rims and walls and slowly filled the bottom of the channel with debris, building up talus slopes, and moving the edges of the canyon outward. With luck the talus wouldn't be piled all the way to the rim and, from their perch on the edge, Scott and Irwin would be able to see, describe, and photograph layering in the far wall, layering produced by the sequence of mare-filling lava flows. Limitations of time and equipment would prevent them from making the equivalent of a trip down the trails into the Grand Canyon for a close look at mare history; but at least, it was hoped, they would be able to see and photograph enough to give the geologists insight into the history of mare deposition.

Although pictures that Scott and Irwin took toward the south along the rille suggest that, along much of its length, the talus slopes have built up nearly to the rims, when they looked across the canyon - a distance of no more than a kilometer - they could see obvious layering within the occasional outcrops that had been preserved. In the upper 60 meters of the far wall, they could pick out at least a dozen distinct layers; and, because of the winding nature of the rille, to the south they could see suggestions of similar layering in a section of the near wall.

[During a review of this Apollo 15 summary, I asked Jack Schmitt why there were outcrops visible. Was it that the rille wasn't old enough for the talus to have built up to the rim?

Jack told me, "Those rille walls are working away from the centerline due to impact. And, because they're steep walls, the debris has a statistical tendency to go down to the bottom, rather than lying on the walls. So they are going to maintain exposure, unless hit by an impact big enough to destroy the whole section of wall. The original configuration was probably a lava tube. Sometimes lava tubes are open and sometimes they're roofed over, depending on the dynamics of the individual flow episode. It's amazing how they tend to maintain themselves. There's probably melt erosion that helps to maintain them - and which coats over the walls and hides any layering in the surrounding rock. But, as soon as all the eruptions stop, impacts break through any roof that might have been present - which would be relatively thin - and start to erode the wall cover back. After that happens, you start to see the exposed layers."

I asked if the persistence of the vertical faces was evidence of hardness variations, like we see in New Mexico mesas. "That's why you see the layers. The interior of the flows are probably softer than the exteriors, because they haven't been quenched (by radiative cooling). The exteriors tend to be denser and harder, although that depends on how vesicular they were. So every flow is a different story. If you look at the Apollo 12 material that seems to have come from deep down in the flow - and actually some of the Apollo 11 rocks that I called gabbro to distinguish them by texture from basalt - when you get coarse crystals, they just tend to be more friable (breakable)."]

The visit to the rim of Hadley Rille not only provided glimpses into the structure of the bedrock underlying the landing site, but also a new perspective on the structure of the regolith. Although the thickness of the soil layer undoubtedly varies from place to place around the landing site, evidence from the seismic signals generated by the astronauts as they walked around the LM/ALSEP area and evidence from the depth of craters that brought up bedrock fragments suggests that the regolith is typically about five meters thick. However, as Scott and Irwin approached the rille, they had seen clear evidence of a thinning of the soil layer. The thinning was a simple consequence of the presence of the canyon. Away from the rim, crater ejecta is scattered in all direction; the crater dug by one impact is gradually filled with ejecta from later impacts and, except for the effects of the occasional, larger impacts, the net result is that the average depth of the layer isn't influenced at all. However, near the rim, ejecta thrown toward the canyon tumbles onto the talus slope and isn't replaced by anything being thrown back out. Slowly, the canyon is filling and, the closer one gets to the rim, the thinner the soil layer. This thinning produces both a surface that slopes down toward the rille and an increase in the prevalence of rocks lying on the surface. Close to the edge, in a strip extending up to 25 meters back from it, there is hardly any soil at all and the surface is littered with boulders lying practically on bedrock. And it was bedrock that they were after.

Because the Rover had only 14 inches of clearance, Scott and Irwin parked on soil well back from the edge of the rille. Then, once they finished describing and photographing the far wall, they moved down to the boulders. Scott was quite confident that these were bedrock boulders; and Houston was so interested in them that they readily agreed to drop a more conventional mare sampling site scheduled for the trip back to the LM in favor of an extension here. Scott and Irwin took pictures, sampled boulders, raked the soil near the Rover for a collection of small rocks, bagged soil samples, and drove two short core tubes into the ground. In all, they collected over a hundred pieces of rock - all fragments of the bedrock basalt, excepting only six breccia fragments which were, themselves, made up mostly of bits of basalt.

The station was both productive and fun. Scott and Irwin had clear objectives for the site and, because of the value of the station, were given extra time so that they could work without undue haste. They didn't have any appreciable slopes to content with, so the work wasn't physically demanding. And, finally, the site offered enough interesting detail that they were able to put their geology training to very good use. It was a fitting climax to the mission and indeed, as they prepared to drive off, Scott neatly summed up his pleasure and his buoyant mood. "Man, am I going to miss one-sixth g. This is neat."

Time was running out. Fifty-five minutes after they stopped, Scott and Irwin were headed north, going to a spot another 200 meters along the rim so that Scott could take a second series of photographs for a stereo view of the far wall. It would be a very short stop - for photography only. Houston wanted them back at the LM in no more than 45 minutes. Lift-off was only five and a half hours away and there was a good deal still to be done. Scott understood the situation perfectly, but was still a bit disappointed. "Okay," he said. "Shoot! No time to go to the North Complex, huh?"

Allen recognized the question as rhetorical and maintained an appropriate silence while Scott and Irwin went about the business at hand. Fourteen minutes after they stopped, they were moving again. They were still faced with the prospect of separating the bottom sections of core, but were determined that, somehow, they would get the entire core home. In the end, Houston decided that there would be room for the three connected section of core in the Command Module; and that is the way it was done.

In some ways, Apollo 15 was the last of the engineering flights. Armstrong and Aldrin proved that a landing could be made, and that a pair of astronauts could go out on the surface and do useful work. Conrad and Bean proved that the LM could be flown to a predetermined target, and that there was no real problem in working for several hours at a time. Shepard and Mitchell showed that, in the event of a Rover breakdown, a crew could walk back to the LM from a considerable distance. And it remained, then, for Scott and Irwin to put the Rover through its paces and to demonstrate that the LM, the suits, the backpacks, and they, themselves, could handle a three-day visit to the lunar surface.

By the end of Apollo 15, it was clear that, after three very active days, Scott and Irwin had not exceeded any practical limits to the length of an Apollo mission. There had been a number of minor problems with the equipment and, as was further demonstrated on Apollo 16 and 17, an accumulation of small failures was inevitable. Perhaps they were approaching a limit. At the end of the first EVA, Scott forgot to stow the small antenna on the top of Irwin's backpack, and it broke off as he crawled through the hatch. They were able to tape it back on, but the accident illustrated what could and would happen over time. Dust was a continual problem and, despite their best effort to clean each other off at the end of the EVAs, the cabin got dirtier and dirtier. They put the suit legs in bags to help to control the dust and, each night, they cleaned and lubricated their zippers and neckrings and wristrings. Nonetheless, the closures got balkier with each passing day. Outside, the dust got into all unsealed moving parts and, although the 15 crew didn't experience nearly as many dust-related Rover or tool problems as did the later crews, they accumulated scratches on their visors and, because the dust covered almost everything, had trouble reading gauges.

These small problems - and the inevitability that they accumulate - should serve as warnings for those planning more ambitious missions. However, in the context of Apollo, Scott and Irwin demonstrated that three days were manageable and that there was every reason to expect even greater success from the remaining missions. The drill stems could be re-designed, the vise could be mounted properly, and other lessons could and would be learned so that Apollo 16 and 17 would be even more productive.


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