Studying the Moon from Orbit
Although the Ranger and Surveyor missions had sent back many close-up views of the lunar surface, they were never intended to provide all the photographs we would need to select the Apollo landing sites. That was to be the job of Lunar Orbiter. Conceived in 1963, its objective was to obtain detailed photographs of the whole Apollo landing zone. We needed high resolution in order to pick areas free of large boulders or small craters that would be a hazard to the astronauts guiding the lunar module to a safe landing. Obstructions of this size could not be seen on photographs taken from Earth, even by the largest telescopes. The Lunar Orbiter program was managed by the Office of Space Science (later the Office of Space Science and Applications), but the photographic design requirements were dictated by the Office of Manned Space Flight and in particular the engineers at the Manned Spacecraft Center. Langley Research Center (LaRC) was selected to be the day-to-day manager, and the request for proposal was released by LaRC. The RFP called for building six to eight orbit – ers; it was possible that the final ones in the series would include other experiments in addition to cameras. OSSA released an announcement of flight opportunities to solicit experiments for these last missions and received over one hundred proposals or inquiries.
The competition to build the spacecraft and cameras was won by the Boeing Company as the prime contractor, supported by two major subcontractors, RCA and Eastman Kodak. Langley’s program manager, Clifford Nelson, put together a superb team to oversee the program; many years later, when NASA management called for a review of lessons learned from all the completed programs, Lunar Orbiter was judged the best managed. If for some reason it had not been successful, the entire Apollo project would have been in jeopardy or, at the very least, delayed beyond the date President Kennedy had called for. Lunar Orbiter was successful far beyond our hopes based on our experience with Ranger and Surveyor. Lunar Orbiter 1, which flew in August 1966, did not perform completely to specifications, but it returned a total of 422 medium and high resolution photographs of potential lunar equatorial landing sites as well as some photographs of the Moon’s farside. After correction of the problem that degraded some of the first mission’s photographs, Orbiter 2 and Orbiter 3 were so effective that all the Apollo landing site photographic requirements were completed; the engineers and mission planners had enough photographs in hand to permit detailed landing site analysis, and they released the final two spacecraft for science and site selection for potential post-Apollo missions. (The last three Lunar Orbiters were eventually canceled, and the experiments solicited for those missions were put on the shelf to be resurrected later.)
The first three spacecraft had concentrated primarily on photographing the nearside equatorial zone, where the upcoming Apollo landing sites would be. Lunar Orbiter 4 expanded the coverage on the nearside, including many of our high priority post-Apollo exploration sites. The final mission, Lunar Orbiter 5, completed the coverage of the poorly known farside. By the time Lunar Orbiter 5 snapped its last picture, the five Lunar Orbiters had sent back 1,950 pictures of the Moon covering most of the lunar surface, nearside and farside. The resolution of these photographs ranged from approximately sixty-five meters to five hundred meters, although much higher resolution photographs of the potential Apollo landing sites were taken on the first three missions. To obtain this higher resolution (two meters), the first three missions took their photographs at lower orbital altitudes than the final two.
Thus Lunar Orbiter equaled the best Earth-based photographs, and it bettered many of them by a factor of 250. Only a small area of the Moon was covered by the high resolution photographs, but the coverage had been judiciously distributed by the planning teams. An added benefit was that by closely tracking the spacecraft’s orbits, we were able to map the Moon’s gravity field at a resolution not achievable from Earth.
Both the Falmouth and Santa Cruz summer conferences devoted considerable thought to recommending experiments that could be done in lunar orbit to complement the study of the Moon from the lunar surface as part of the comprehensive, post-Apollo exploration program. In 1964 and 1965 Peter Badgley had attempted to interest NASA management in a remote sensing program to be conducted in Earth and lunar orbit, and eventually a program titled Lunar Mapping and Survey System was initiated.1 This program, designed to use Apollo hardware, was canceled in early 1968 in a cost-cutting move.
But the recommendations from the summer conferences did not die. In March 1968, ignoring the just announced program termination, Sam Phillips sent a memo to Bob Gilruth requesting that MSC look into providing scientific and operational photography during the landing missions.2 With planning proceeding for the final missions, and following up on the Phillips’s request, Lee Scherer sent Bill Hess a memo in early May 1968 asking that MSC begin to study how to integrate experiments into the command and service module to take advantage of the longer staytime in lunar orbit. Hess agreed, prompting our office to write a memo for Phillips’s signature asking MSC to expand the study he had requested in March to identify other orbital experiments that would take advantage of the ‘‘overall CSM science potentialities.’’3 This memo resulted in MSC’s adding $100,000 to its Martin Marietta Apollo Applications Program integration contract and marked the beginning of a program to develop a suite of sensors that would be flown in the CSM.
While this analysis was under way, OSSA dusted off the experiments that had been submitted earlier for Lunar Orbiter and began to assemble the rationale for including different suites of cameras and sensors that could fit into the CSM. George Esenwein, who had been the headquarters project officer for the Apollo command and service module mechanical systems, transferred to our office at this time and was put in charge of the orbital science and photographic team. Floyd Roberson was named program scientist, and David Winterhalter was program engineer. Noel Hinners, at Bellcomm, assigned several members of his staff to work with this team, notably Farouk El Baz and Jim Head, both of whom had played prominent roles in analyzing Lunar Orbiter photographs and recommending targets for photography on Orbiter 4 and Orbiter 5.
As an extension of these studies, Esenwein’s team, working with MSC, determined that it would be possible to include in a service module (SM) bay a small subsatellite that could be left in lunar orbit, and an announcement of flight opportunities was released soliciting experiments that could utilize the subsatellite. In April 1969 OSSA and its advisory panels reevaluated the Lunar Orbiter proposals, and the new proposals to place experiments on the subsatellite, and selected a final suite of experiments.4 In June OMSF directed MSC to proceed with the modifications of the CSM and to procure the experiments. Eventually the science payload carried in the command and service module, including cameras, experiments, and the subsatellite, totaled almost 1,200 pounds. Most of the experiments were housed in one quadrant of the service module in what was named the scientific instrument module (SIM), and a few were carried in the command module (CM).
For the experiments that did not send their data back by telemetry but recorded them on film or in some other form, the film and data would have to be retrieved by the CM pilot during extravehicular activity. After much debate concerning the safety of the CM pilot during the retrieval operations, it was finally agreed to schedule this EVA after leaving lunar orbit, when the astronauts were safely on their way back to Earth. Imagine floating outside your spacecraft somewhere between the Moon and Earth attached by an umbilical cable and a slender wire! The three CM pilots who carried out this risky maneuver would all comment on the strange sensation of seeing the Earth from so far away while floating in space.
Starting with the flight of Apollo 8 at Christmas 1968, the astronauts began making their contributions to studying the Moon from lunar orbit. Armed with the ever present hand-held Hasselblad cameras, the crew of Apollo 8 and all the crews that followed (except Apollo 9, which remained in Earth orbit) took pictures of the Moon from various altitudes above the lunar surface. Many of the photographs taken during the early missions were meant to improve our understanding of future landing sites by augmenting the Lunar Orbiter photographs. Apollo 12, as an example, took 142 multispectral photographs of the designated Apollo 13 landing site, Fra Mauro, and other equatorial sites. These photographs were used to help decipher the geology and to improve the productivity of the astronauts after they landed by identifying sampling sites that probably had different mineralogical compositions. After Apollo 13’s failure, Fra Mauro became the landing site for Apollo 14, and the information obtained from the multispectral photography helped, in a small way, in planning the Apollo 14 surface traverses.5
Apollo 14 carried out a variety of experiments, including photography, while on the way to the Moon, in lunar orbit, and on the return to Earth. Three types of cameras were used: a 16 mm data acquisition camera, Hasselblads, and the Hycon lunar topographic camera. (The Hycon malfunctioned during the mission, but almost two hundred usable photographs were recovered.) These experiments included measurements of gegenschein and heiligenschein (rather arcane observations, the former possibly related to Earth-Moon-Sun libration points6 and the latter related to reflected light, which had potential application for the interpretation of the Moon’s fine-scale surface roughness). An S-band transponder experiment provided new information on the Moon’s nearside gravity field by permitting close tracking of the CSM’s orbits and a bistatic radar investigation that yielded information on the lunar crust.7 The final missions, Apollos 15, 16, and 17, had much more extensive orbital science payloads than any of the previous missions.8
Because I was not closely involved with developing the experiments carried in lunar orbit, I will not further describe them or their principal investigators, but for completeness in covering the scientific results of Apollo, in chapter 13 I briefly discuss the scientific information returned from some of the experiments.