Well, folks, it's that time again. This week, as NASA prepares to launch LADEE to the moon, we turn our attention that direction as well. Back in Part II you may recall an offhand mention of the Lunar Reconnaisance Pioneer, the sister probe to the MRP. Well, today, you find out the rest of the story.
This is a bit of "backfilling," in that some events in this post predate the start of Part III, but they then continue into this period and that's where the real action is.
Eyes Turned Skyward, Part III: Post #2
Since the dawn of humanity, the Moon has loomed large in the collective imagination of mankind. The only heavenly body other than the Sun to show a disk to the naked eye, its regular cycles, curious patterns of light and dark, and influence over the tides and, at least in the eyes of early humans, other periodic cycles and patterns made it an object of intense curiosity to early humans. Many made it an object of religious devotion, whether by worshiping lunar gods or goddesses, or by marking time through a lunar calendar, as Jews and Muslims do for religious purposes. Others studied it with all the fervor and attention they could devote to the task, tracking its slow libations and wandering movement. Centuries before the birth of Christ, Greek, Indian, and Chinese astronomers had determined that the Moon did not shine on its own, but only by the reflected light of the Sun, that the Moon was a sphere, and had even made remarkably accurate estimates of the size and distance of the Moon from Earth. Even more sophisticated measurements had to wait on the development of the telescope, which showed the Moon to be a rugged, craggy body, pockmarked with craters and lined with mountain ridges. By the 1950s, highly accurate maps had been made of the entire part of the Moon visible from Earth, and lunar science was, by the standards of the time, a booming, successful field of planetary science.
It was only natural that, even before the successful launch of Soviet and American space probes, some scientists had already started to propose missions to the Moon, as had some military forces. von Braun, of course, described an ambitious crewed lunar expedition in 1952 for
Collier’s magazine, and had undoubtedly begun thinking about lunar exploration much earlier, while for their part Soviet thinkers were considering future lunar exploration long before they began their own satellite program. Within months of Sputnik’s launch, the United States Air Force’s Pioneer program was attempting to launch unmanned satellites to the Moon, mainly to prove the feasibility of launching payloads to escape velocity, while the Soviets were beginning their own Luna program. Although the Pioneer program was an abject failure, scoring only a single successful launch out of ten attempts, the Soviets achieved more success, with Luna 3 in particular returning the first images of the far side of the Moon ever seen on Earth. Encouraged, many American scientists began to imagine more complicated and ambitious robotic lunar probes, with names like Ranger, Surveyor, and Prospector. They would do more than just hit the Moon or loop around it; they would return detailed imagery, go into orbit around it, land payloads, rove the surface as remotely-operated vehicles, and, perhaps, return lunar soil to the Earth.
The beginning of the Apollo program to land men on the Moon was the death knell for these airy fantasies of robotic probes roaming the Moon’s surface, at least in the United States. Programs which did not directly contribute to the overriding goal of putting a man--who anyways was far more intelligent and flexible than any robot--on the Moon were ruthlessly cut. First to go were the advanced Prospectors, but the orbital Surveyors and scientific Rangers quickly followed them to the chopping block. The Surveyor program itself was cut back largely to providing data for the development of the lunar module, and the Lunar Orbiter program, focused on imaging the surface in detail for mission planning, was substituted in place of the scientific orbiters. Although the outstanding success of the Lunar Orbiter program in gathering the crucial site data meant that the final two missions were largely dedicated to more scientific purposes, they simply could not return much of the data lunar scientists wanted. Although the Apollo missions, especially the final four J-class missions, augmented the probe results, they did not and could not provide globally detailed information, leaving scientists unable to answer many questions about the Moon. Therefore, as the Apollo program wound down and NASA began to face a post-Apollo future, many scientists called for a new lunar mission, a Lunar Polar Orbiter, which would carry many of the same instruments that had been flown in the J-class mission’s SIM bays, as well as other experiments to characterize the entire Moon. As NASA struggled with changing responsibilities and falling budgets, their voices went largely unheard, a cry in the wilderness during the difficult 1970s. Nevertheless, they persisted, repeatedly suggesting the mission to the National Academy of Sciences, NASA, and anyone else they thought might help it launch.
In early 1983, their persistence finally paid off. Although American intelligence assets had revealed Soviet modifications of the N-1 pads at Baikonur, fueling suspicion that the Soviets were in the midst of developing their own large rockets--indeed, this knowledge had been a decisive factor in selecting the Saturn Multibody concept over the Titan V during ELVRP II--they lacked certainty on the purpose of the rockets. Were they merely safer replacements for the Proton, which had caused a number of serious accidents and had a poor record of success? Perhaps they were meant to carry large spacecraft, like orbital battlestations, into high orbits? Or were the Soviets more ambitious still...? The CIA concluded that the size and capability implied by what technical data they had and the size of the pads and flame trenches meant that the Soviets could not be merely thinking of new space stations or even orbital weapons platforms, but had to have greater ambitions. In particular, the CIA believed, they must have resurrected their old lunar landing program from the 1960s and given it a modern spin, aiming to land on the Moon sometime “soon,” perhaps establishing bases and going on to Mars by the mid-1990s. This information was leaked to the press in late 1982, where it caused a minor sensation among a public and Congress which had not entirely gotten over the initial shock of the Vulkan. Some kind of response was demanded, which lunar scientists were quick to provide in the form of their old Lunar Polar Orbiter proposal. Almost as quickly, NASA accepted the proposal for further development, while Congress readily provided the necessary funding. At last, just under a decade after the last mission to the Moon, the United States would be returning--albeit with a robotic probe rather than a human landing.
Design and ultimately construction responsibility for the probe were given to NASA Ames Research Center, whose other planetary exploration projects had largely sunk into maintenance mode since the launch of Pioneer Mars in 1979, with the only significant ongoing development program being the Galileo probe project. With a reputation for greater economy than its planetary exploration rival to the south, the Jet Propulsion Laboratory, and less ongoing work, Ames was a natural choice for Headquarters to oversee a program with the profile and importance of what became known as the Lunar Reconnaissance Pioneer, or LRP. Ames set to work with a will immediately, quickly drawing up basic specifications for the spacecraft. In this, they benefited from the work of lunar scientists over the past decade, who had drawn up a firm wishlist of instruments they wanted to see onboard: Spectrometers, like those carried by the J-class missions, to remotely analyze the composition of the lunar surface. A radar altimeter, to map out its height variations. Infrared and visible light imaging to produce more detailed surface maps than available from the old Lunar Orbiters and to provide information about flows of heat to and from the surface. Instruments to explore the magnetic and electric field environments around the Moon. Finally, to make proper use of these instruments, the placement of the vehicle in a polar orbit, to see the Moon’s whole surface. Together, such instruments would perhaps reveal more about the Moon than even the Apollo flights had.
As LRP would be operating in an environment reasonably similar to Earth orbit, it was decided to adapt a new lightweight three-axis stabilized communications satellite design from RCA for the mission. Although this was in some ways a break from the traditional Ames preference for spin-stabilized satellites, necessitated by the demand for high-resolution imagery, in other ways it maintained an essential continuity with Ames’ tradition of lightweight, inexpensive missions, by tapping into the extensive development funds dedicated by RCA to their spacecraft business. Development was slowed by the need to adapt the design to the Mars Reconnaissance Pioneer and Near-Earth Asteroid Pioneer programs while the LRP itself was still being constructed, but by 1988 the probe was ready and launched to the Moon atop a McDonnell-Douglas Delta 4065. After a brief five-day journey, the LRP ignited its own onboard engines, placing itself in a polar low lunar orbit. Over the next few days, it deployed and tested its instruments before beginning its research mission.
From its vantage point just a few dozen miles over the lunar regolith, the LRP obtained a grand vista of the Moon. Whenever it passed within the line of sight of the Earth, a new stream of compositional, altitude, photographic, heat-flow, and magnetic data flowed back to its controllers on Earth. Just as had been predicted by the scientists behind the project, it quickly returned more scientific data than all of the J-class missions put together, at least so far as their orbital instruments were concerned. More experiments were improvised on the fly; an obvious one was to track the LRP’s carrier signal carefully, like with VOIR at Venus, to map the lunar gravitational field. Besides probing the Moon’s interior structure, this would aid management of later low lunar orbit spacecraft by allowing more precise and accurate predictions of orbital perturbations from the infamous mascons. Although the system could, for obvious reasons, only map the Moon’s near side, it was still far better than nothing at all, and revealed a great deal of interest to both future mission planners and lunar geologists.
However, that was not the only unanticipated use that could be made of the probe’s communication system. Since the early 1960s, it had been known that because of the Moon’s rugged topography and small axial tilt, some areas near the poles might be permanently shaded. Even in the lunar equivalent of arctic (or antarctic) high summer, surrounding mountain formations or crater rims might block sunlight from reaching some areas. In turn, this might allow volatile material such as water or carbon dioxide, which would otherwise be vapor under the low pressures and high temperatures of the lunar surface, to gradually collect within the shaded areas. Although budget considerations and the commonly shared belief, stemming from examinations of Apollo lunar samples, that the lunar surface was bone-dry had precluded the inclusion of a dedicated water-sensing device in the LRP’s payload, certain observations by the probe’s spectrometers seemed to indicate that water ice might indeed be present in the shaded regions. To resolve the scientific controversy, an alternate method of detecting water ice was proposed by a team of scientists at the University of Texas several months after the probe reached the Moon. By sending a stream of signals out from its communication antenna towards the Moon, then picking up the resulting signals on Earth, a so-called “bistatic radar” could be improvised. If the polarization characteristics of the probe’s signals were controlled, the radar could, at least in theory, distinguish between a rocky and an icy underlayer to the surface regolith, thereby proving whether or not ice deposits were real or merely the result of overactive imaginations. The resulting observations were duly carried out, and the results were nothing short of astonishing. Rather than the small pools or isolated crystals most scientists thought might be the extent of polar water ice deposits, LRP’s observations seemed, at least at first, to indicate that there might be huge slabs and sheets of ice covering the bottom of many shaded regions, amounting to millions or even billions of tons of water, enough to supply a wealth of critical resources to a lunar base. Although the results were controversial even when published, and only became more so when results from similar Earth-based experiments showing similar data for decidedly non-shaded regions were publicized, in mid 1989 they were the cutting edge of lunar science. Surely they must have contributed to the eventual decision of NASA leaders to focus on a lunar return over a journey to Mars for Project Constellation. After all, not only is water a vital resource for any lunar base, and immensely useful for supporting missions to other worlds, but the simplest and most obvious method of resolving the scientific debate was to send a geologist there to drill cores and take samples in a suspected ice-containing area, then see if he or she actually found any ice.
The discovery of apparent large deposits of ice also invigorated the Lunar Society, which had after all long promoted the establishment of colonies on the Moon as the next logical step in the settlement of space. Ice, together with the other volatiles likely frozen in the putative sheets, would make those colonies far more viable than mining the lunar regolith alone could. The parallel discovery of multiple so-called “skylights,” places where the surface seemed to have collapsed in on lunar lava tubes like those postulated in the wake of Apollos 15 and 18, gave additional vigor to the Society, which had promoted the use of such tubes as locations for its lunar colonies. The one downside to the combination was that few of the permanently shadowed regions seemed to be anywhere close to the lava tubes, raising questions of how lunar colonists were to transport the ice or water from one to the other. The result was a burst of creative, if not always practical, methods for transporting the volatiles hundreds or thousands of miles on a rocky, hot, and airless surface. While they waited on reality catching up to their proposals, meanwhile, the outlook for lunar colonies seemed brighter than it had since the mid-1970s.
When its primary mission ended, the LRP found itself in a very different position than it had been when it launched. With Project Constellation coming up to full steam, once again scientific value was playing a back-seat passenger to human spaceflight requirements, and the probe was press-ganged into serving as a precursor mission. Its powerful imaging system would now be used to examine possible landing sites and occasionally other locations in exquisite high resolution, not only allowing problems like excessive surface roughness to be identified long before any humans would be anywhere near them but also allowing a library of maps to be built up for optical navigation systems like those used in cruise missiles that might be employed on future landers. Its radar altimeter could be used to quantify the slope of candidate sites. And although its other instruments were being sidelined, they, too would benefit from the lower orbit needed to operate to maximum effectiveness, detecting smaller and more localized variations in surface composition, picking up subtler changes in magnetic fields.
Moreover, its low altitude opened up another interesting possibility. Since the United States had landed on the Moon twenty years earlier, a growing strain of thought within the country had claimed that the entire mission had been faked, nothing more than a sham filmed on a Hollywood soundstage. At its new altitude, the LRP would be able to image Apollo’s landing sites in extreme resolution, revealing not just the descent stages and other large markings, as images taken early on in the probe’s career had, but fine detail, like the flags the astronauts had planted around the sites and the tracks of footprints they had made during their EVAs. Although NASA conceded this would not convince the hardcore skeptics, many within the agency still felt the imagery would be worthwhile in persuading the less convinced, and simply as a reminder of the agency’s past achievements. From its lower altitude orbit, the LRP was also able to detect the remains of many of the robotic probes which had been sent to the Moon during the 1960s and 1970s, including the long-lost remains of Lunokhod 1. Besides clearing up a minor mystery of the space age, the first automated rover ever to explore another body’s surface carried a laser retroreflector similar to those carried by its sibling, Lunokhod 2, and by several of the Apollo moon landing missions, actively in use by Earth-based research projects. The new ranging site was quickly pressed into service by those projects, adding another minor scientific accomplishment to the LRP’s total. When the LRP finally depleted its fuel and crashed in late 1993, some five years after launch, it had not only laid the essential foundations of further lunar exploration, but reminded the country of its past on the Moon.
