The Value of the Moon

by Paul D. Spudis

  Next came the question of what to do with the remaining Saturn rockets and Apollo hardware, the surplus equipment that had been procured in the event that more than a single attempt would be needed to successfully land on the Moon. Initially, Apollo engineers planned for more lunar missions and ultimately a human mission to Mars. However, it soon became apparent that the national will was not inclined toward additional human exploration beyond the Moon—or even to it. An ambitious program to push the boundaries of human reach into space was shelved.10 Apollo continued for a few more flights, but lunar bases and Mars missions were not in the cards. Our focus shifted to completing the Apollo program, then to developing a reusable transport-to-orbit vehicle for people and cargo—the flight program that designed, built, and operated the space shuttle.

  Despite the political decision to abandon the capabilities of the Apollo-Saturn system, NASA was able to wrangle permission to fly out part of the remaining original plan for Apollo lunar exploration. Several interesting landing sites were selected for these missions, most of which had advanced capabilities and tools for exploration. Even with some notable mission problems, flight and surface operations steadily improved. Despite being struck twice by lightning during liftoff, Apollo 12 successfully landed on the Moon in November 1969. This mission validated the technique of pinpoint landing by setting the LM Intrepid down within a hundred meters of Surveyor 3, a previously landed robotic probe. This technique allowed us to safely land at future sites of high scientific (but dangerous operational) interest. After the disaster and near-loss of the Apollo 13 mission, following the explosion of an oxygen tank in its Service Module, which cancelled its landing on the Moon, the Apollo 14 crew traveled to the highlands of Fra Mauro in early 1971. Here it was expected that they would find material thrown out from the largest, youngest impact basin, the Imbrium Basin. From this site, the astronauts returned complex, multigenerational fragmental rocks called breccias, parts of which dated to the earliest era of lunar history.

  On the final three Apollo missions (15, 16, and 17), the astronauts spent longer times on the surface and possessed greater capability for exploration.11 The first three lunar landings had no surface transport, so the crews had to stay within a few hundred meters of their LM and could not remain outside the spacecraft for more than four to five hours at a time. The next three landings used more capable spacecraft and each mission carried a surface rover—a small electric cart strapped to the outside of the LM. Once they were on the surface, the cart was taken off, unfolded, and then driven by the crew to locales several kilometers away from the landing points. In addition, a redesigned spacesuit allowed moonwalks of up to eight hours duration. Consequently, an extraordinary amount of high-quality exploration was conducted on these latter missions. Each subsequent mission improved upon the total distance traveled, the amount of samples collected, the experiments performed and the data gathered. These were the “J-missions,” and because of them, the Apollo program wrote great chapters in the history of human exploration.

  Figure 2.1. Oblique view of the Hadley-Apennine region, landing site of the Apollo 15 mission in 1971. The site is at top left; the sinuous channel near the top is Hadley Rille, a channel carved by flowing lava. (Credit 2.1)

  Apollo 15, the fourth manned lunar landing, was sent to the rim of the Imbrium basin, at the base of an enormous mountain range called the Montes Apenninus (Figure 2.1). The mission occurred between July 26 and August 7, 1971. Astronauts Dave Scott and Jim Irwin spent three days exploring the mountains and the mare plain that surrounded them. The landing site was also near Rima Hadley, a winding, sinuous canyon believed to have been carved by flowing lava. With the Apollo 15 astronauts well trained in the sciences, especially field geology, this mission demonstrated a new and growing sophistication in lunar exploration. The astronauts found and returned a fragment of the original lunar crust, the “Genesis Rock,” and an unusual emerald green glass, created by volcanic fire fountains erupting more than three billion years ago. They also used a power drill to recover a core of the upper three-meters of the regolith at the landing site.

  Figure 2.2. Apollo 16 Commander John Young explores the geology of the Descartes Highlands landing site. The samples and data returned from the Apollo missions are the principal sources of detailed information on lunar history and processes. (Credit 2.2)

  Continuing in this mode of surface exploration, the Apollo 16 mission visited the central lunar highlands in April 1972. Veteran astronaut John Young (Figure 2.2) and rookie Charlie Duke explored two large impact craters situated in the mountainous Descartes highlands region, northwest of Mare Nectaris. Against expectations of finding volcanic ash flows, the crew discovered instead that the highlands are made up of ancient rock debris, shattered and broken by eons of cataclysmic, large-scale impacts. Although the astronauts did not find the expected volcanic rocks, the results of this mission led us to a better understanding of the importance of impact in the creation of the lunar highlands. The breccias found at the Descartes site may have come from one of the large multiring impact basins, such as the magnificent Orientale basin on the Moon’s western edge.

  Illuminating the Florida landscape with a brief false dawn, the last Apollo mission to the Moon, Apollo 17, was the first night launch of the program. This mission is renowned for the first flight of a professional scientist to the Moon, LM pilot and geologist Jack Schmitt. He and Gene Cernan spent three days exploring the Moon’s valley of Taurus-Littrow on the eastern edge of Mare Serenitatis, in a low region of smooth mare lavas situated between two enormous basin massifs. They found ancient crustal rocks, old mare lavas, and most spectacularly, orange soil (fine orange and black glass particles, pieces of lunar ash erupted from a lava fire fountain over 3.5 billion years ago). The magnificent scenery of the landing site and the abundant scientific return from the Apollo 17 mission was a fitting conclusion to the Apollo program. The 380 kilograms of lunar rock and soil in the sample vaults at NASA’s Johnson Space Center in Houston are a lasting scientific legacy and testament to the achievement of the Apollo program.

  Post-Apollo Legacies

  Then it was over. When the last crew departed the Moon on December 14, 1972, no one knew when, or if, humans would return. Forty years on, Apollo 17 Mission Commander Gene Cernan remarked that he never would have imagined we would still be looking forward to man’s return to the Moon. Will we go back before the fifty-year milestone, or was it all just a big, one-time stunt? Did Apollo give us something of lasting value? What is the legacy of the Apollo program? And what does it have to tell us about our future in space and about America as a spacefaring nation?

  The scientific legacy of the Apollo program is remarkable. The lunar samples have been studied more intensely than almost any other collection of material in the history of science, with some rocks taken apart atom by atom. These small pieces of another world have a scientific value not present in meteorites because we know exactly where they come from on the Moon, and that information allows us to interpret their history in a broader, regional-to-global context. By reading the historical record found in the lunar samples, we have reconstructed the story of an ancient world, one where entire globes of liquid rock crystallized to form the crust and mantle of the Moon. This episode was followed by an intense bombardment—giant impacts that formed the large overlapping craters and basins of the highland surface. Remelting of the deep interior created magmas that forced their way up through the mantle and crust, erupting onto the surface as extrusive lava flows. In some cases, the amount of volatiles dissolved in the liquid rock were so great that sprays of molten rock shot into space, then quickly cooled into the fine glass spheres that make up the dark ash deposits of the Moon.

  The impact bombardment of the Moon was very intense early in its history, but tapered off drastically around 3.9 billion years ago and continues at a very low intensity to this day. Most of the debris hitting the Moon now consists of micrometeorites that constantly “rain” down upon the surface.
This long-term process has ground the lunar surface into a fine powder. When these tiny particles hit previously made soil, some of the soil grains are fused into a melted mixture of glass and mineral fragments called agglutinates. Because the Moon is exposed directly to space and possesses no global magnetic field, its surface is implanted with solar wind gases—particles emitted by the Sun and galactic cosmic rays, mostly protons, or hydrogen ions, that induce radiation damage in the Moon’s dust grains. Thus, although the geological evolution of the Moon continues to this day, surface erosion happens at an extremely slow pace, about a centimeter every twenty million years.

  From study of the lunar samples, we now understand the telltale signs of hypervelocity impact, which include both chemical and physical effects. Chemically, we can detect the small addition (on the order of a couple percent) of meteoritic debris in the lunar soil in the form of excess amounts of siderophile (iron-loving) elements such as nickel and iridium. Physically, in addition to the shock-melted glass agglutinates (mentioned above), we also see shock damage to the mineral grains of lunar rocks. The common mineral plagioclase is often turned into glass called maskelynite by impact shock, a transition that occurs without melting. Other features, diagnostic of the passage of a shock wave, include cracks, mosaicism (shattered grains that arrange themselves into geometric patterns), and lines of planar deformation. All of these chemical and physical features are found in and around terrestrial impact craters. Their occurrence in lunar samples verifies that the craters of the Moon are of impact origin.

  An interesting and important consequence of this science only became apparent several years after the end of the Apollo lunar missions. Working with marine sedimentary rocks in Italy, geologist Walter Alvarez wanted to know their rates of deposition. His father, physicist Luis Alvarez, suggested that he measure the concentration of the element iridium in the rocks. Iridium is a rare element in Earth’s crust, but it is more abundant in meteorites. His thought was that meteoritic debris constantly rains onto Earth at a known rate and that it could serve as a clock for measuring the rates of carbonate sedimentation on the sea floor.

  When the iridium was measured, surprisingly large amounts were found in the clay layer that marks the end of the Cretaceous Era. This Cretaceous-Tertiary (KT) boundary is demarked by a thin clay layer all over the world and is the youngest horizon below which dinosaur fossils are found. This discovery advanced the idea that a massive meteorite impact sixty-five million years ago was responsible for the extinction of the dinosaurs and several other fossil families.12 Later, small grains of shock-deformed quartz were found within the KT clay layer, supporting the idea of a large body impact occurring at that time. Subsequently, it was found that in some cases, similar boundary layers that marked mass extinctions in the geological record also contained evidence for large body impacts.

  This connection was made by recognizing the critical defining evidence for hypervelocity impact, a process learned from the collection and study of the Apollo lunar samples. It was often claimed in the immediate post-Apollo period that the Moon effort had all been for naught, scientifically. It was thought that we got some rocks and some ages for a few ancient events in the history of the Moon—but so what? That “so what” is now recognized as a revolutionary paradigm shift in our understanding of the significance of impact in Earth history. We now view the process of the evolution of life on Earth from a new and unexpected perspective. Because we journeyed to the Moon, a new concept of how life may evolve was discovered.

  Most of what we now know about the timeline for the origin and evolution of our solar system is tied to facts obtained from our study of the Moon. Results from Apollo scientific work carry over into all of planetary science. The concept of a late heavy bombardment (that is, the apparent increase in the cratering rate between 4.0 and 3.8 billion years ago) and estimates of the timescales upon which events on Mars, Mercury, and other objects have occurred are all reliant on the dates provided by the Apollo lunar samples. Additionally, when requesting lunar samples, investigators had to show they could make their analyses on the smallest amount of material possible. This stringent requirement forced scientists to develop techniques capable of analyzing extremely small amounts of material. This work succeeded to such an extent that fully valid analyses are now done on mere specks of dust. In addition, because some samples were very complex, such as the impact breccias of the highlands, new techniques were developed that can reveal the interior structure of such aggregate rocks using X-ray tomography, a method similar to magnetic resonance imaging (MRI) of the interior of the human body.

  The political legacy of the Apollo program was no less significant than its scientific one. Despite subsequent claims to the contrary, it is now clear that the Soviets had accepted Kennedy’s challenge of sending a human to the Moon and returning him safely within the decade.13 The race to prove the superiority of an ideology had been joined. Each country needed to harness greater technology and science in order to win. This breathless competition in space was conducted with a seriousness that we can scarcely credit these days, with each new “first” being heralded as the key to space success, and, by inference, global domination. The Soviets orbited the first satellite, the first man, the first woman, and were first to hit the Moon with a man-made object. They orbited the first multiple-man crew, and in 1965, one of their cosmonauts, Aleksei Leonov, made the first “walk in space” when he floated outside his spacecraft. America stumbled at first but rapidly caught up, matching most Soviet achievements. Soon we began making our own space firsts—the first rendezvous and docking in orbit, the first long-duration space walks, and the first successful flight of the giant Saturn V booster. But everyone knew the true high-stakes measure of success was to be the first to reach the Moon with people.

  While Americans were enjoying the trill of victory with the epic flight of Apollo 11, the Soviets were having some difficulties. The Soviet Moon rocket, the gigantic N-1, a vehicle comparable in size to the American Saturn V, failed all four times it was launched.14 These disasters, kept secret for twenty-five years, sealed the fate of the Soviet Moon program. Without an operational heavy lift booster to deliver their spacecraft, no Soviet lunar mission was possible. American democracy and free-market capitalism had outmatched the USSR and won the Moon.

  In programs of vast technical scope, particularly those requiring the practical application of high technology such as high-speed computing to very complex problems, Americans had shown the world both dogged determination and technical prowess for accomplishing whatever they set as their goal. The Soviets viewed America as having achieved through a combination of great wealth, technical skill, and resolute determination an extremely difficult technological goal, one that they themselves had vigorously attempted but had failed to achieve. America’s victory of getting to the Moon first and exploring its surface carried over, later figuring in a more serious conflict between the United States and the Soviet Union.

  In 1983, President Ronald W. Reagan called upon the scientific and technical community of the United States and the free world to develop a system to defend the country against ballistic missiles, one that would make America and other nations free from the fear of nuclear annihilation. This program, the Strategic Defense Initiative (SDI), was specifically conceived to counter the prevailing strategic doctrine of mutually assured destruction (MAD), whereby a nation would never start a nuclear war because it would fear its own destruction by retaliatory strikes. The price of peace in a MAD scenario was to live in a permanent state of fear. The promise of SDI was to eliminate that fear by having a system designed to defend countries from nuclear missile attack.

  The Strategic Defense Initiative was roundly criticized and belittled by many in the West who considered it “destabilizing.” Numerous scientists, including those who had previously done weapons work, criticized it as “unachievable.” Arms control specialists decried “Star Wars,” as they called it, as provocative and an escalation of the nuclear arm
s race. Reagan did not retreat and insisted that SDI proceed. The number one foreign policy objective of the Soviet Union in the last years of its existence was the elimination of SDI. The famous Reykjavik Summit of 1986 collapsed on this very point when Reagan would not agree to crippling restrictions on SDI deployment in exchange for massive cuts in ballistic missiles by Gorbachev and the Soviets.15

  If the bulk of academic and diplomatic opinion was so averse to SDI and the very idea of missile defense was so “unworkable,” why then did the Soviet Union fight so long and fiercely against it? Clearly, it was because the leaders of the Soviet Union were convinced that SDI would work—that the United States always achieved its stated goals. Because America had attempted and successfully achieved the difficult and demanding technical goal of reaching the Moon, it made any similar goal that we set out to do seem equally achievable. Moreover, this was a goal that the Soviets themselves had attempted and failed to achieve. With the specter of the American Apollo victory fresh in their minds, the Soviets had no choice but to spend whatever resources were necessary to compete with Reagan’s SDI program. In the end, they went bankrupt, and their communist economy collapsed—a very real and practical consequence of America’s successful Apollo program.16

  Begun as a strategic Cold War gambit under President Kennedy, Apollo and the race to the Moon demonstrated to the world the superiority of America’s free and democratic way of life over that of our communist adversaries, an achievement still not fully appreciated today. America had achieved technical credibility from the amazing success of the Apollo program. When President Reagan announced SDI twenty years later, the Soviets were against it, not because it was destabilizing and provocative, but because they believed we would succeed. That success would render their vast military machine, assembled at great cost to their people and economy, obsolete in an instant. Among other factors, this hastened the end of the Cold War in America’s favor. Thus, the original geopolitical goals of the Apollo program were once again realized, and in a manner undreamed of fifty years earlier.