‘Mr. Galileo Was Correct’: The Grand Voyage of Apollo 15 (Part 2)

Haunting view of Jim Irwin with the lunar rover, backdropped by the grandeur of Mount Hadley. Photo Credit: NASA
Haunting view of Jim Irwin with the lunar rover, backdropped by the grandeur of Mount Hadley. Photo Credit: NASA

As July burned into August 1971, three sons of Planet Earth were midway through their exploration of the Moon. Aboard the command and service module Endeavour, astronaut Al Worden operated a sophisticated array of scientific equipment from orbit, whilst his Apollo 15 crewmates Dave Scott and Jim Irwin were on the surface at a place called Hadley—a mountainous region, 400 miles (640 km) north of the lunar equator, characterized by spectacular peaks, football-field-sized craters, and a 25-mile-long (40-km) gorge, known as Hadley Rille. The discoveries made by Apollo 15 revealed more about the history and evolution of the lunar highlands than ever before … and their effects continue to resonate to this day.

Early on 1 August, Capcom Gordon Fullerton woke Scott and Irwin with some unwelcome news. Two days earlier, the lunar module Falcon had touched down at a slight angle—one of its legs had set down in a crater—and this had caused it to lose a sizeable amount of water. Fullerton asked the men to check behind the ascent engine cover. He was right, and the astronauts quickly scooped it into a spent lithium hydroxide canister.

Scott and Irwin’s second Moonwalk was slightly shorter than their first, in order to provide more exploration and less traveling time between geological stops. One relatively low-priority activity had been eliminated and a greater measure of freedom was given to the efforts of the astronauts; Mission Control and the geologists in Houston would depend heavily upon their descriptions and observations, and it would be Scott and Irwin’s choice on exactly where they chose for their major sampling. “We’re looking now, primarily, for a wide variety of rock samples from the [Apennine] Front,” Capcom Joe Allen told them. “You’ve seen the breccias already. We think there may very well be some large crystal[line] igneous [rocks] and we’d like samples of those and whatever variety of rocks which you’re able to find for us—but primarily a large number of documented samples and fragment samples.” Scott was in full agreement; Allen was talking their language, and after two years of geological training he felt ready and confident to explore.

Jim Irwin works with the lunar rover, close to the lunar module Falcon. Photo Credit: NASA
Jim Irwin works with the lunar rover, close to the lunar module Falcon. Photo Credit: NASA

A few minutes before 9 a.m. EDT on 1 August 1971, safely buckled aboard the lunar rover, the astronauts set off due south, heading for Mount Hadley Delta, upon whose slopes they would concentrate their energies. It was a scenic trip, Irwin recalled in his memoir, To Rule the Night. Ahead of them, and all around them, the terrain was literally splattered with craters, right up the slopes of Hadley Delta, and the height of the mountain rivaled the tallest peaks of the Rockies. After passing the vast cavity of Dune Crater, whose rim was littered with large blocks, they started up the mountain. On the plain the going had been rough, but on the slope the surface smoothed out markedly. Near Spur Crater, they swung left and drove across-slope. Looking downslope, they were astonished to realise how far they had come. The lander was a tiny speck on the undulating plain, and the astronauts were now at an elevation of about 350 feet (106 meters). The view, completely unhindered by atmosphere or haze, almost knocked Dave Scott’s socks off.

Their first task was to find a small “drill hole” crater that could have excavated material from the mountain, but the flank was remarkably clean. Scott curtailed the planned drive, and they sampled a small crater and then an isolated boulder which was coated in greenish material. The green hue captivated Jim Irwin, whose Irish descent and birthday on St. Patrick’s Day—and the fact that he had stowed some shamrocks in the lunar module—made this a special find. At first, the two men wondered if their eyes or Sun visors were playing tricks on them, but when it was unpacked a few weeks later in the Lunar Receiving Laboratory (LRL), their initial impressions would be confirmed: It was green, made entirely of minuscule spheres of glass, tiny droplets of magma spewed from a fissure by a “fire fountain.” In time, it and other samples would contribute to making Apollo 15 one of the greatest voyages of discovery ever undertaken in human history.

Finally, they headed for Spur Crater. “As soon as we got there,” Irwin described, “we could look over and see some of this white rock. Immediately, I saw white, I saw light green and I saw brown. But there was one piece of white rock that looked different from any of the others. We didn’t rush over to it; we went about our job the usual way. First I took down-Sun shots and a locator shot about 45 degrees from the Sun-line and Dave took a couple of cross-Sun shots.” Scott and Irwin slowly threaded their way between the craters to the strange white rock. “It was lifted up on a pedestal,” Irwin wrote. “The base was a dirty old rock covered with lots of dust that sat there by itself, almost like an outstretched hand. Sitting on top of it was a white rock almost free of dust. From four feet away I could see unique long crystals with parallel lines, forming striations.” Scott used tongs to pick it up and held it close to his visor to inspect it. The rock was about the same size as his fist and even as he lifted it, some of its dusty coating crumbled away … and he saw large, white crystals.

“Aaaahh!” he exulted.

“Oh, man!” added Irwin.

Dave Scott peers at the Genesis Rock in the laboratory, after the mission. Photo Credit: NASA
Dave Scott peers at the Genesis Rock in the laboratory, after the mission. Photo Credit: NASA

The rock was almost entirely “plagioclase”—an important tectosilicate feldspar mineral used by petrologists on Earth to help determine the composition, origin, and evolution of igneous rocks—and from their expeditions into the hills of the San Gabriels, Scott recognized it as “anorthosite,” which is the purest form of plagioclase. For some time, lunar geologists had suspected that anorthosite formed the Moon’s original, primordial crust; indeed, data from the unmanned Surveyor 7 lander had suggested its presence in the ejecta of the crater Tycho, and tiny fragments of it had actually been found in samples from both Apollo 11’s landing site at Tranquility Base and Apollo 12’s site in the Ocean of Storms. “Explaining why most of the Moon’s crust should be composed of anorthosite,” wrote Andrew Chaikin in A Man on the Moon, “led some geologists to an extraordinary scenario. Within the infant satellite, they proposed, there was so much heat that the entire outer shell became an ocean of molten rock. As this ‘magma ocean’ cooled, minerals crystallized. The heavier species, including the iron- and magnesium-rich crystals, sank to the bottom. The lighter crystals, specifically, the mineral [aluminium-rich] plagioclase floated to the top.”

Recognizing the find as probably a piece of the Moon’s primordial crust, Scott could hardly contain his enthusiasm. “Guess what we just found!” he radioed. “I think we just found what we came for!”

“Crystalline rock, huh?” said Irwin.

Yessir,” replied Scott.

After briefly describing the rock’s appearance, Scott placed it into a sample bag by itself. It would be labeled as sample number 15415, but a keen journalist, inspired by the term “petrogenesis,” the study of the origin of igneous rocks, would later offer it a far more lofty title: “The Genesis Rock,” a sample of the original lunar crust, coming from one of the earliest epochs of the Moon’s history, some 4.1 billion years ago. This date was reached by geologists at the University of New York at Stony Brook and proved to be almost 1.5 billion years older than the oldest rocks found on Earth. If the Moon was any older than that, noted Chaikin, it wasn’t much older; the Solar System itself was thought to have formed only a few hundred million years earlier.

Jim Irwin works on digging a trench to test the bearing capacity of the lunar soil. He "solved a dog's job with a dog's technique". Photo Credit: NASA
Jim Irwin works on digging a trench to test the bearing capacity of the lunar soil. He “solved a dog’s job with a dog’s technique.” Photo Credit: NASA

Back in the vicinity of Falcon, shortly before 2 p.m. EDT and five hours into their second Moonwalk, Scott and Irwin had other chores to finish; first, there was the need to complete drilling the heat-flow hole which had hit resistant soil the previous day. Scott had already noticed inside the lander that his injured fingers were starting to turn black and so had to summon as much strength as he could muster—bringing his hands right up close to his chest just to squeeze the drill’s trigger—to complete the task. He could physically stand only about a minute of the pressure on his fingernails, before breaking off for a breather. At length, both sensor packages were in place to a depth of about 5 feet (1.5 meters). However, when Scott attempted to extract the core sample which, at about 8 feet (2.4 meters) long, was the deepest such sample yet attempted on the Moon, he managed to lift it slightly, but it refused to budge any further. Joe Allen told him to leave it until tomorrow’s final excursion.

Meanwhile, Irwin dug a trench and used a penetrometer to test the bearing strength of its walls and floor. “If you think digging a ditch is dog’s work on Earth,” he wrote, “try digging a ditch on the Moon. The big limitation is the suit and the fact that you are clumsy at one-sixth-G. I had practiced on Earth and come up with a technique that most dogs use. You spread your legs and push the dirt between them. I solved a dog’s job with a dog’s technique. This method worked perfectly on the Moon.” He easily dug through a fine grey material which he likened to talcum powder, and then a coarser, darker soil, but had to give up on reaching a very resistant layer which, although it looked moist, had all the consistency of hardpan.

They wrapped up the second Moonwalk by planting the American flag and loading that day’s rock box aboard Falcon. Not only had most of the equipment operated flawlessly, but the live—and color—images provided by the Earth-operated television camera on the rover was a far cry from the crude black-and-white pictures of Apollo 11. Furthermore, Scott and Irwin had truly done their mentor, Lee Silver, proud through their geological descriptions. “I’m told,” Joe Allen radioed, “that we checked off the 100-percent science completion square time during EVA-1 or maybe even shortly into EVA-2. From here on out, it’s gravy all the way!”

Flight Director Gerry Griffin was a key ally of Scott and Irwin, having worked extensively with them on their geology training expeditions. He knew the intricacies of the timeline, but was also keenly aware of the scientific potential of the troublesome core sample. Photo Credit: NASA
Flight Director Gerry Griffin was a key ally of Scott and Irwin, having worked extensively with them on their geology training expeditions. He knew the intricacies of the timeline, but was also keenly aware of the scientific potential of the troublesome core sample. Photo Credit: NASA

The gravy of the third excursion would be tempered by the fact that it would also be the shortest, scheduled to last barely four and a half hours. It started with the recovery of a core sample from EVA-1. For a few moments, their efforts to extract the core tube from the ground were fruitless, and Scott was almost ready to give up. However, with Irwin’s persuasion, both men hooked an arm under each handle of the drill and after several firm tugs the tube sprang from the ground. Precious minutes were wasted, though, when the vice carried on the rover to dismantle the tube into storable sections proved to have been fitted backward; Irwin broke out a wrench and used that, but Scott’s frustration was evident. He knew that for every minute wasted before the drive started, they would lose at least another two minutes of geological exploration.

Some of the senior NASA managers in Mission Control wanted to abandon the core entirely. However, the astronauts and Joe Allen had an ally in Flight Director Gerry Griffin, who had shared several of their geological trips in the California mountains and knew how important the science was … and how important the deep core sample was to the success of this mission. It was he who persuaded the managers not to abandon the core tube work. After they had partially disassembled the tube, it was decided that they should leave the remainder of the task to later. When the core was finally opened on Earth, it proved to contain several dozen layers which documented some 400 million years’ worth of lunar history. …

At length, Scott and Irwin buckled into the rover and headed west-northwest for a good look at Hadley Rille. After the rille, if time permitted, they hoped to grab an opportunity to inspect the mysterious “North Complex” of craters, which some geologists thought might be a cluster of small, ancient volcanoes. Their arrival at Hadley Rille was truly breathtaking. Its far wall, bathed in the harsh, direct sunlight of the late lunar morning, showed distinct layers of rock pushing through a mantle of dust, lending credence to theories that Mare Imbrium had been built up as a succession of ancient lava flows.

One theory was that the rille was a fracture where the mare surface “opened” like a cooling joint. “But since the scientists have studied the pictures,” Irwin wrote, “the most popular theory is that Hadley Rille was probably a lava tube that collapsed.” All around the two men were enormous slabs of basalt and the geologists in the back room in Houston quickly began pressing for them to move farther downslope, though Joe Allen was becoming nervous. Looking at televised pictures, it seemed to him as though they were right on the edge of a precipice. In fact, the rille had no dramatic “drop”; rather, it resembled the gentle shoulder of a hill, and they were able to walk downslope without difficulty. “In fact,” Scott wrote, “the slope down which we descended was only about 5-10 degrees and the maximum slope of the rille was only 25 degrees—not steep for such a canyon-like formation.” It was steep enough, however, that from their vantage point they were unable to see the floor.

Time was escaping them (it was “relentless,” Apollo 15 backup commander Dick Gordon once said), and any chance to explore the North Complex very quickly disappeared; that would have to await another generation. Both astronauts found this bitterly disappointing: In Irwin’s mind, it left their excursion only half-complete, whilst Scott would wonder for years afterward if the unique data from the deep core was really worth abandoning the chance to visit the North Complex. At the same time, they appreciated the urgent need to get back to Falcon with enough time to prepare for liftoff later that day.

"Mr. Galileo was correct": Dave Scott demonstrates falling objects in gravity fields, with a falcon's feather, during Apollo 15. Photo Credit: NASA
“Mr. Galileo was correct”: Dave Scott demonstrates falling objects in gravity fields, with a falcon’s feather, during Apollo 15. Photo Credit: NASA

Back at the lander, with the minutes of the final Moonwalk rapidly winding down, Scott had one last opportunity to give a scientific demonstration to an audience of millions back home. It came from a suggestion by Joe Allen, who was inspired by the experimental work of the great Italian scientist, Galileo Galilei. More than three centuries earlier, Galileo had stood atop the Leaning Tower of Pisa and dropped two weights of different sizes, proving that gravity acted equally on them, regardless of mass. Now, in front of his own Leaning Tower—the slightly-tilted Falcon—Scott performed his own version of the experiment.

“In my left hand, I have a feather,” he told his audience, “in my right hand, a hammer. I guess one of the reasons we got here today was because of a gentleman named Galileo a long time ago, who made a rather significant discovery about falling objects in gravity fields. The feather happens to be, appropriately, a falcon’s feather, for our Falcon, and I’ll drop the two of them here and hopefully they’ll hit the ground at the same time.”

They did … and applause echoed throughout Mission Control.

“How about that?” Scott concluded triumphantly. “Mr Galileo was correct in his findings!” He originally planned to try it first, to check that it would work, but was worried that it might get stuck to his glove. He decided to “wing it” and, thankfully, it worked. In his autobiography, Irwin would relate that Scott had actually carried two feathers on Apollo 15, one from the falcon mascot at the Air Force Academy. Unfortunately—and much to Scott’s irritation—Irwin accidentally stepped on it! They searched for the feather, but could only find his big bootprints. “I’m wondering,” wrote Irwin, “if hundreds of years from now somebody will find a falcon’s feather under a layer of dust on the surface of the Moon and speculate on what strange creature blew it there.”

Shortly after 9 p.m. EDT on 2 August, a little more than four hours since setting foot on the surface for EVA-3, Scott drove the rover, alone, to a spot a few hundred feet east of the lander. From this place, Mission Control would be able to remotely operate its television camera to record the liftoff of Falcon’s ascent stage. Scott pulled out a small red Bible and placed it atop the control panel of the rover, in order to show those who followed in their footsteps why they had come.

In touching tribute to those who lost their lives in the exploration of space, a tiny plaque, left behind on the Moon by the Apollo 15 crew, honored the (then-known) cosmonauts and astronauts who died during the first phase of humanity's exploration of space. Photo Credit: NASA
In touching tribute to those who lost their lives in the exploration of space, a tiny plaque, left behind on the Moon by the Apollo 15 crew, honored the (then-known) cosmonauts and astronauts who died during the first phase of humanity’s exploration of space. Photo Credit: NASA

Next, he climbed off the machine and strode toward a small crater. He dug a small hollow and dropped a small aluminum figurine of a fallen astronaut onto the lunar soil. The tiny figurine had been arranged by Apollo 15 command module pilot Al Worden. Meanwhile, Jim Irwin had organized a small plaque, planted alongside, listing the names of 14 astronauts and cosmonauts known to have died doing their duty. The list included Yuri Gagarin, the first man in space, together with Vladimir Komarov and the crews of Apollo 1 and Soyuz 11. As he gazed on the plaque, Scott knew he would never come here again.  “I had come to feel a great affection for this distant and strangely beautiful celestial body,” he later wrote in his memoir, Two Sides of the Moon. “It had provided me with a peaceful, if temporary, home. But it was time to return to my own home back on Earth.”

Within the confines of Falcon, they had little time to gaze out at the spectacular site of Hadley; only a few hours remained before their 1:11 p.m. EDT liftoff, bound for a rendezvous with Al Worden in the command module Endeavour. It marked the first occasion on which a crew would complete a Moonwalk and perform the liftoff and rendezvous without a rest period in between the two. Having been outside for less than five hours on EVA-3, Irwin wished that Mission Control could have postponed the inevitable by several hours to have enabled them to drive home by way of the North Complex and gather a few samples. Sadly, it was not to be.

Precisely on time, Scott punched the Abort Stage button and a television audience back on Earth had the chance to actually see an Apollo crew leave the Moon. Falcon’s ascent stage literally “popped” away from the descent stage and shot directly upward with all the speed and accuracy of an express elevator, spraying a shower of fragments of insulation radially outward. One journalist would later compare it to something left over from a Fourth of July celebration. Watching from Mission Control, Chris Kraft—then serving as deputy director of the Manned Spacecraft Center (MSC), today’s Johnson Space Center (JSC) in Houston, Texas—would gape at the speed of the departure. “I had no idea it went so fast,” he wrote in his autobiography, Flight. “We’d been told it was like that by the other Moon crews, but seeing it for real was a thrilling shock.”

Ten seconds later, a strangely familiar sound came into Scott and Irwin’s earpieces: The Air Force Song, courtesy of Worden, which they had intended to play to Houston only, but which somehow ended up being routed to Falcon, as well. “This was kind of surprising,” wrote Irwin, “because Dave had briefed Al to turn on that music at one minute after liftoff (that first minute is rather critical) but here it came at ten seconds. It really caused some consternation in Houston. First, they thought somebody was playing a trick in Mission Control, so they conducted a big search. They asked for radio silence—it was a tense situation. Finally, they realized that probably we had turned it on.”

Several days later, on 7 August, Endeavour splashed down safely in the waters of the Pacific Ocean, bringing the lunar explorers safely back to Mother Earth. The months which followed would be challenging for them all. Initially assigned as the backup crew for Apollo 17—the final lunar landing mission—they were abruptly removed from flight status in April-May 1972 and replaced by John Young, Stu Roosa, and Charlie Duke. The reason stemmed from their carriage of 400 unauthorized first-day covers, the proceeds of which were to be invested into trust funds for their children.

Although the agreement with a German stamp dealer went awry within weeks of splashdown and none of the Apollo 15 astronauts accepted any money, they were harshly criticized by NASA and some members of Congress, who demanded an investigation into what they described as “improper conduct.” Although none of the Apollo 15 crew had done anything wrong or illegal, they were stripped of flight status, and Scott fumed that NASA did nothing to dispel (untrue) rumours that they had been fired. More than four decades after the remarkable scientific extravaganza of Apollo 15—a mission which unveiled more of the Moon’s mysteries than ever before—it is a saddening footnote that this incident continues to resonate. However, the exploration of Dave Scott, Al Worden, and Jim Irwin serves one other purpose: to whet the appetites of future lunar explorers, who may be in college right now, awaiting their chance to visit the mountains of the Moon once again.



This is part of a series of history articles, which will appear each weekend, barring any major news stories. Next weekend’s article will focus on STS-28, a classified shuttle mission from August 1989, which brought not only the experience of space, but also the “taste” of space, back home to Earth.




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  1. The richness of detail in both articles is a testament to Ben’s methodical research and his ability to provide his readers with an important historical perspective of the Apollo 15 mission. I found the description of the “stillness” of the moon and the sounds Scott and Irwin heard inside their suits while on the surface quite interesting.

  2. Another really good piece, but I was a little disappointed it was only two parts, in contrast to the previous four-part Apollo articles. I would enjoyed reading your take on the crew’s heart problems and their difficulties after the rendezvous in lunar orbit, which Chis Kraft later called one the most disturbing crew-ground interactions of any mission.

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