NLSI Lunar Science Conference (2008)
Robotic Lunar Precursors to Apollo. G. E. Bugos1 and J. W. Boyd2, 1 2NASA Ames History Office, MS207-1, NASA Ames Research Center, Moffett Field, CA 94035, Glenn.E.Bugos@nasa.gov.
Introduction: In one four year period—1964 through 1968--humans learned far more about the Moon than had been learned before, and perhaps more than during the four year period that followed. This enormous increase in knowledge was driven by NASA’s three series of small robotic spacecraft: Ranger, Surveyor and Lunar Orbiter. Some of these spacecraft had started their programmatic lives as remote laboratories, designed to do lunar science. All of them were repurposed as “precursors” to the Apollo missions. That is, they were focused on gathering data needed to validate the engineering decisions needed for a successful lunar landing. It is worth remembering how quickly and efficiently they laid an experimental foundation for lunar science. This paper focuses on four questions. First, what did we know with any degree of certainty about the Moon prior to the first of the American robotic encounters in 1964? Second, what did we learn about the Moon as a result of Ranger, Surveyor and Lunar Orbiter series of spacecraft, and which commmunities of scientists generated that lunar science? Third, how well did that information guide engineering decisions made for the Apollo landings of humans on the Moon? Fourth, how does revisiting this period help NASA today bring lunar science to a new generation, and garner the data to guide engineering decisions in America’s return to the Moon? Historians Revisit the Precursors to Apollo: The history of the early lunar robots is often misinterpreted because of the shear mass of the Apollo program in the historiography of lunar exploration. The historian revisiting Ranger, Surveyor and Lunar Orbiter--using documents from that time--becomes aware of several ways in which this history of the lunar robots has been misconstrued. First, it is unfair to cast the history of these programs in terms of failure rate, as a way to suggest how dismally NASA started in 1958 as an engineering enterprise, and how abundantly they had learned in accomplishing Apollo. The failure rate prior to 1965 was discouraging. However, the failures all resulted from problems with the launch vehicles or the general design of spacecraft systems and not from presumptions made about the actual encounter with the Moon. Notably, the robots launched from January 1965 to January 1968, the latest before the Apollo 7 launch in October 1968, had a good success rate of 10 out of 13. Second, we should remember how quickly the robotic precursors to Apollo did their work, and how
close in time to the Apollo landing. There were 13 successful American encounters with the Moon prior to Apollo, the first of which happened less than 5 years prior to the July 1969 Apollo 11 landing. Time scales this compressed would be almost inconceivable in NASA today.
Third, there was little that was international about the early robotic exploration of the Moon as precursors to Apollo. Though the lunar science community was well-dispersed around the world, non-Americans generated little data used in Apollo engineering decisions. The Soviet Luna missions, though early and notable successes, had little impact in verifying or changing any of the engineering decisions made for Apollo.
NLSI Lunar Science Conference (2008)
Fourth, in the 1960s everyone involved expected that these spacecraft--whether conceived initially as scientific missions or later redefined as precursors-would always be a series of small spacecraft. There is no real discussion of any missions being planned for large, complex spacecraft. This was not because of launch vehicle limits on the size of payloads. The lunar science community advised NASA to design the spacecraft to generate overlapping or redundant data sets. These robots were designed as three common platforms, on which NASA mission planners could hang complementary families of instruments. Most important, these were not in fact precursor programs. Through the early 1960s, the Ranger, Surveyor and Lunar Orbiter programs were each defined as scientific missions. The experiment packages hung on them were design to help planetary scientists understand the geophysical characteristics and evolution of the Moon. Only after the start of work on the Apollo lander were the mission profiles tweaked to collect data that might be useful to Apollo engineers. Even after this redefinition, the data returned was far more useful to the nascent lunar science community. Notably, contemporaneous literature never called the Rangers, Surveyors, and Orbiters “precursors.” That terminology was not applied to them until the 1990s, as lunar scientists began to think analogously, and contemplate what sort of data needed to be collected robotically before NASA planned an extended return to the Moon. Furthermore, during the 1960s, both the NASA headquarters public affairs staff and the press considered the actual precursors to Apollo to be the manned Mercury and Gemini programs. Learning to live and work in space seemed more relevant to Apollo than learning more about the Moon. The literature generated by the Ranger, Surveyor and Orbiter program offices seldom discuss their work as something the Apollo planners would rely upon. Where precursor data mattered most to Apollo was in selecting the landing sites. Potential sites had all been selected using the 1 kilometer resolution available from telescopes at the start of the Apollo program; final site selection and astronaut training benefited greatly from the 1 meter resolution maps generated by the Orbiters. Still, none of the major decisions about the Apollo program were revised because of information returned from the precursors. The lunar model was largely defined in December 1964, before the first encounter with the Ranger 7, and the Apollo landing gear was finalized before the first Surveyor landed. Ten days before the landing of Apollo 11, NASA published its final version of its lunar surface model derived from the robotic precursors.
And indeed, the primary result of these three robotic programs was to invigorate a lunar science community. Above all, these robotic explorers showed that the Moon was not a changeless, dead planet. Rather, its surface had undergone dramatic change and evolution across eons. While there was still much debate over precisely how the lunar surface was shaped, there emerged some consensus on the broad trends. The maria were vast lunar flows, flooding over older features. They resembled terrestrial basalt, with some distinct differences. Meteoroids, both large and small, played a big role in shaping the surface of the Moon. In many ways lunar geology was similar to terrestrial; in other ways quite different. Furthermore, data from robotic explorers did nothing to resolve the debates over the origins of the Moon and the evolution of its surface. Indeed, all camps found some evidence to support their positions. To the community of lunar scientists, by 1969, the lunar sample return goal was looking like the most vital part of the Apollo program. Looking Ahead: Landing site selection remains a major difference between the Apollo program and every lunar landing conceived since. The Apollo sites were specifically selected for ease of landing, above all else. They were mostly along the equator, in areas determined to be free of rocks and rough terrain. The time on the lunar surface was fairly short, so everything the astronauts needed was packed aboard the lander. Since then, plans for returning to the Moon assume some in-situ resource use to support an extended stay. That places emphasis not only on imaging to locate usable resources, but also in defining a lander that can reach mineral-rich areas even when those happen to be located on rough terrain. Future Moon missions will be more heavily driven by the findings of lunar science than by spacecraft engineering decisions. The robotic program NASA undertakes to support future human missions to the Moon likely will look quite different from those that supported Apollo. And while this next generation of lunar precursors may look dramatically different than the Apollo era, they will all share a palpable sense of possibility. Every encounter with the Moon prior to and including Apollo, garnered incredibly rich data about the Earth and planetary science. It also confirmed that the Moon offered little easy pickings. Now that NASA has redefined the goal as staying on the Moon, and now that technology has generally advanced 40 years, and now that scientific questions are being posed by a new generation of explorers with fresh eyes, the Moon now seems to be full of chemical possibilities. In the coming decade, as with the pre-Apollo years, a precursor program may lend some reality to those visions of possibility.