Astrogeology Science Center

by David S. F. Portree, 2013

Generalized Photogeologic Map (Sheet 1 of 4)
Generalized Photogeologic Map (Sheet 1 of 4)
Physiographic Divisions of the Moon (Sheet 3 of 4)
Physiographic Divisions of the Moon (Sheet 3 of 4)
Lunar Rays (Sheet 2 of 4)
Lunar Rays (Sheet 2 of 4)

The race to the moon began on August 17, 1958, and the Soviet Union won. This isn't the opening line of an alternate history story; rather, it is an acknowledgment that more than one moon race took place. The first, with the goal of launching a small automated spacecraft to the moon, began with the liftoff of the Able 1 lunar orbiter, a 38-kilogram U.S. Air Force (USAF) probe. (It was later redesignated Pioneer 0.) Just 77 seconds after launch from Cape Canaveral, Florida, Able 1's first-stage Thor rocket exploded, ending the world's first attempted lunar mission.

A month later, on September 23, 1958, the Soviet Union joined the race. A spherical Luna probe intended to impact the moon fell victim to the failure of its upgraded R-7 booster rocket just 93 seconds after liftoff from Baikonur Cosmodrome in central Asia.

On October 11, 1958, USAF launched Able 2, a near-copy of Able 1. It was the first lunar launch conducted under NASA auspices. The civilian space agency had opened its doors on October 1, 1958. NASA absorbed most Department of Defense space projects, though in practice the USAF and Army continued to carry out missions while interagency relations and lines of command became defined.

Able 2, later redesignated Pioneer 1, burned up in Earth's atmosphere on October 13, after its Able second stage shut down early, placing it on an elliptical path that took it about a third of the way to the moon. The Soviets launched their second Luna moon impactor just 16 hours after the U.S. launched Able 2. The Luna's upgraded R-7 launch vehicle exploded 104 seconds after liftoff.

And so it went, with launches from Florida and Kazakhstan alternating and failing. The Pioneer 2 lunar orbiter (November 8, 1958) and another Luna impactor (December 4, 1958) fell victim to premature launch vehicle shutdowns. Pioneer 3 (December 6-7, 1958), the first NASA/Army moon probe, was launched on an Army Juno II, not a USAF Thor-Able, but performed much as had Pioneer 1.

On January 3, 1959, the Soviet Union snatched victory from the jaws of defeat. Their Luna 1 impactor missed the moon by 6400 kilometers, and so failed to accomplish its mission. It sailed on, however, becoming the first human-made object to orbit the Sun. The Soviets nicknamed it Mechta ("dream"). The Army launched the Pioneer 4 lunar flyby spacecraft two months later (March 3, 1959). It failed to return images of the moon, but repeated Mechta's feat.

Another unnumbered Luna impactor fell victim to an R-7 failure on June 18, 1959. Then, on September 14, 1959, on their sixth attempt, Soviet rocketeers succeeded in striking the moon with the Luna 2 impactor. The probe struck near the center of the moon's Nearside, the hemisphere that faces the Earth (figure 1). Three weeks later (October 6, 1959), Luna 3 flew 7900 kilometers over the moon's south pole and imaged the hidden Farside hemisphere.

In a last-ditch effort to steal the Soviet Union's thunder, the USAF and NASA decided to give a planned Pioneer Venus orbiter a new mission: orbit and photograph the moon at close range. Its mission ended 104 seconds after liftoff on November 26, 1959, when its Atlas-Able launcher lost its streamlined launch shroud and tumbled out of control.

As the first moon race ended in Soviet victory, pressure built in the U.S. for a rematch. Though President Dwight Eisenhower had made it clear that the Department of Defense branch services should concentrate on space and rocket projects with immediate military applications, the moon still beckoned to Army and USAF rocketeers.

Even after the creation of NASA, the Army and USAF studied lunar surface bases. The Army Ballistic Missile Agency studied Project Horizon, a lunar fort, while the USAF worked with contractors on the SR-183 Lunar Observatory project. LUNEX was a USAF study of an early manned lunar expedition. The USAF also began lunar mapping using Earth-based telescopes.

The first attempt to map lunar features for scientific and engineering purposes did not, however, originate within the Defense Department. It was begun instead by Arnold Mason of the U.S. Geological Survey (USGS) Military Geology Branch in Washington, DC. According to Don Wilhelms, writing in his 1993 memoir To a Rocky Moon, the peripatetic Mason became interested in lunar geology after the October 4, 1957 launch of Sputnik 1. Mason's boss, Frank Whitmore, soon got caught up in his enthusiasm. Whitmore, incidentally, served as Secretary of the Geological Society of Washington.

Early in 1959 - soon after Luna 1 - Mason proposed to carry out an analysis of the moon's terrains to determine their suitability for spacecraft landings, travel on foot and by rover, and base construction. With Whitmore's blessing, he enlisted Robert Hackman and Annabel Brown Olson of the USGS Photogeology Branch in his project. Mason became project chief, Hackman became Mason's co-author, and Olson (who, according to Wilhelms, received insufficient credit for her labors) assisted Hackman. At first, they had available only meager USGS funds. Soon after Luna 2 and Luna 3, however, the Army Corps of Engineers funded their study.

Mason and Hackman's assessment took in only the Nearside (figure 1). They based their analysis on photographic plates from large telescopes on Earth, which under the best viewing conditions could (they estimated) reveal features on the moon no smaller than about a mile across. In fact, features 10 miles wide were barely discernible in most of the photographic images they used.

Their work soon drew in as consultants lunar experts Gerard Kuiper (McDonald Observatory), Eugene Shoemaker (USGS Menlo Park), and Robert Dietz (Naval Electronics Laboratory). All three supported the impact hypothesis, which stated that most of the moon's craters are asteroid impact scars; not, as some believed, volcanic calderas. At the time, planetary astronomer Kuiper was hard at work on a USAF-funded lunar photographic atlas; Mason and Hackman would use it near the end of their study. Shoemaker, meanwhile, was busy refining a prototype lunar geologic map of the region containing the large, relatively young crater Copernicus; Hackman would later assist him with identification of lineaments in the Copernicus region.

The Army Corps of Engineers published the first edition of Mason and Hackman's four-sheet "Engineer Special Study of the Surface of the Moon" map set in July 1960. The USGS published a second edition with "minor revisions" the following year.

The "Engineer Special Study" was significant in part because its Sheet 1, titled "Generalized Photogeologic Map,” was the first major lunar map to show stratigraphic relationships: that is, it attempted to display the chronological order of the formation of the moon's surface features (figure 2). Mason and Hackman's stratigraphic system centered on the formation of the maria (Latin for "seas"), the relatively smooth, dark-hued plains that mottle the Nearside. They make up about 20% of the moon's surface.

Mason and Hackman colored orange the heavily cratered, light-colored "pre-maria" terrain; that is, landforms that they believed were already in place when the maria formed. They colored maria yellow, while green indicated "post-maria" features; mainly young asteroid impact craters, but also features that they interpreted as being of recent volcanic origin. They used black dots to mark what they identified as volcanic cones and domes and thin black lines to mark what they thought were tectonic faults.

As might be expected, given the quality of the data they had available and the primitive state of lunar science, many of Mason and Hackman's geologic interpretations are known now to be incorrect. Nearly all of the features they identified as volcanic in origin, for example, turned out to be products of impact processes.

Their stratigraphic map, though pioneering, was too simplistic to accurately portray the moon's history. The maria basins formed at different times during the first few hundred million years of lunar history, so features associated with them often overlap. An impact crater blasted into an older mare would, for example, become a pre-maria landform by Mason and Hackman's reckoning if it became engulfed in ejecta and lava from a later basin-forming giant impact. In addition, some prominent lunar features identified as pre-maria (the Apennine Mountains, for example) should have been represented by a fourth color to signify that they are non-maria features created by the same giant asteroid impacts that excavated the maria basins.

By contrast, Shoemaker's nearly contemporaneous prototype Copernicus geology map (figure 3), printed in small quantity by the USAF Aeronautical Chart and Information Center in April 1961, but never formally published, identified five stratigraphic "systems." From oldest to youngest, these were the Pre-Imbrian, Imbrian, Procellarian, Erastothenian, and Copernican systems. Even this would turn out to be simplistic, however, once robot and human explorers began to provide lunar geologists with close-up images of the moon's complex terrain.

In sheet 2 of the "Engineer Special Study," titled "Lunar Rays," Mason and Hackman plotted the source craters and extent of the moon's most prominent ray systems (figure 4). They correctly identified the light-hued rays as ejecta blasted out from young asteroid impact craters.

Mason and Hackman's Sheet 3, titled "Physiographic Divisions of the Moon," was their most ambitious (figure 5). In it, they applied photogeologic principles pioneered on Earth to identify more than 70 different lunar terrain units.

Sheets 1 through 3 laid the groundwork (literally) for Sheet 4, on which Mason assessed in writing the landing, travel, and construction conditions in each of the physiographic regions on Sheet 3. What follows are summaries of his assessments for several regions that have been visited by spacecraft.

Luna 2 struck the southern flank of Autolycus crater in the northern part of Mason and Hackman's Apennines Region. According to Mason and Hackman's analysis, Autolycus is a post-maria impact crater, only lightly rayed, on the western edge of Mare Imbrium, in the extensive Mid Lunar Lowlands. Mason wrote that the surface in the Apennines Region is rough and blocky, so landings there would be very difficult. Movement in the region would, he judged, be the "most difficult on the moon's surface, and possible only by carefully selected routes." Construction would be "very difficult because of blocky material and steep slopes."

Luna 2 was not designed to return images as it plunged toward the moon; however, the Apollo 15 Lunar Module Falcon landed west of the Luna 2 impact site on July 30, 1971 (figures 6 through 9). Astronauts David Scott and James Irwin found the area to be cratered and rolling, but difficult neither to land on nor to navigate on foot and by rover. The surface material was loose to a depth of many meters. The nearby Apennine Mountains, which Mason and Hackman had envisioned as steep and jagged, turned out to have been rounded and partly leveled by micrometeoroid impacts over the nearly four billion years since their formation.

NASA's Ranger 7 probe was designed to return images of the lunar surface as it fell toward destructive impact. On July 31, 1964, Ranger 7 returned more than 4300 photos of the area between Oceanus Procellarum and Mare Nubium. Mason and Hackman called the area containing Ranger 7's impact site the Riphaeus Section. It was a lowland maria divided by the highland Riphaeus Mountains. Mason judged that landing and movement would be "generally easy" if blocky isolated pre-maria highland areas and post-maria craters could be avoided.

Construction, on the other hand, would be a challenge in the Riphaeus Section. Mason expected that, under a thin layer of loose debris, lunar base builders would find basaltic rock hard enough to prevent boring and excavation. Whereas in the Apennines Region he advised lunar base builders to avoid craters and their blocky surroundings, in the Riphaeus Section such asteroid-shattered areas would probably be the only places where digging could occur. This applied to other maria lowlands as well.

Scientists examining Ranger 7 images found that its impact area was cratered down to the scale of inches; however, the craters were almost all eroded, with smooth floors and rims and few large rocks (figure 10). Micrometeoroids had been whittling away at the terrain in the Riphaeus Section for a very long time. In tribute to Ranger 7, lunar mappers named the area where it impacted Mare Cognitum, which means "Known Sea."

Surveyor 7, the last of its series of soft landers, alighted gently on the northern flank of Tycho crater on January 10, 1968. Mason and Hackman identified the area containing post-maria Tycho as the pre-maria Macrocrater Province. Tycho, they wrote, spanned 54 miles from rim to rim. The crater's floor was 12,000 feet below its rim, which stood 7900 feet above the surrounding terrain. They noted that Tycho was the moon's most prominent ray crater, with bright streaks extending up to 500 miles plainly visible to the unaided eye at full moon (figure 11).

Mason judged that landing and movement would be difficult near Tycho. The latter would be possible, however, if a safe route could be selected in advance. Construction would be difficult because of the many large blocks embedded throughout the area.

Surveyor 7 landed blind on Tycho's flank; that is, it included no hazard-avoidance system. Through its scanning camera scientists saw that the area was indeed rougher than those that previous Surveyors had explored (figure 12). They saw loose rocks, boulders, relatively steep slopes, apparent bedrock outcrops, and odd "lakes" of dark gray material, possibly cinders laid down by recent volcanism or rock melted by the colossal energies of the Tycho impact (figure 13). Some of these features could have destroyed Surveyor 7 had it landed on them.

In general, however, Tycho, like the Riphaeus Section and the Apennines Region, was not as rugged as Mason had predicted. In fact, after Surveyor 7, some felt that Tycho's flank was smooth and level enough for Apollo astronauts to visit. A 1969 study based on Surveyor 7 images determined that it was too rough for a manned rover, however.

In early December 1960, Mason and Hackman attended the International Astronomical Union's First Lunar Symposium at Pulkovo Observatory in Leningrad. The meeting was held in the Soviet Union in deference to that country's demonstrated lead in lunar exploration. They displayed the Army Corps of Engineers edition of the "Engineer Special Study."

Upon his return from the historic symposium, Mason presented an informal report on the trip to the January 1961 meeting of the Geological Society of Washington. Mason's boss Whitmore briefly summarized his report in the meeting minutes.

Hackman appeared as co-author on Shoemaker's April 1961 prototype Copernicus geologic map. Copernicus mapping then stalled for several years because Shoemaker had new responsibilities. He had succeeded in launching the NASA-supported Astrogeology Studies Project at USGS Menlo Park, near San Francisco, in August 1960; this became the NASA-supported USGS Branch of Astrogeology in September 1961. In addition, he was busy publishing ground-breaking papers on lunar cratering dynamics and lunar and terrestrial geologic timescales. The Copernicus map was eventually published in 1967 with soon-to-be-astronaut Harrison Schmitt and Newell Trask as Shoemaker's co-authors.

In July 1961, Hackman submitted for review what became after the "Engineer Special Study" the second published USGS lunar map: a geologic study of the Kepler region based on Shoemaker's lunar geologic mapping conventions and five-system lunar stratigraphic column. The Kepler map, published in 1962 under the auspices of the Branch of Astrogeology, was the first NASA-funded USGS lunar map to be published.

Eleven months after the Pulkovo symposium, in November 1961, Whitmore had the sad duty of informing the Geological Society of Washington of Mason's untimely death. The pioneering lunar mapper had taken his own life on October 31, 1961. He was 54 years old.

In his memoir, Wilhelms wrote that Mason committed suicide "for reasons that are not entirely clear and are undoubtedly complex, but which seem to have included non-recognition for his original and ardent pioneering of lunar studies for the U.S. Geological Survey." Pulkovo had marked the high point of Mason's lunar career: after that, Shoemaker's new astrogeology program increasingly sidelined USGS lunar studies in Washington, DC.

Hackman's involvement in lunar geologic mapping was by then also drawing to a close. His steadfast refusal to leave the Washington area proved to be career limiting. Shoemaker transplanted the Branch of Astrogeology from Menlo Park to the small town of Flagstaff, Arizona, during 1963, and soon the name "Flagstaff" became synonymous with lunar and planetary mapping. Hackman completed one more map for the Branch of Astrogeology - a geologic map of the moon's Apennines region, which was published in 1966 - but his pioneering contributions to lunar geologic mapping ceased with publication of the Kepler map.

Although the "Engineer Special Study" remained relatively obscure - and became even more so after data from lunar spacecraft rendered much of it obsolete - it did manage to earn a small place in popular culture. Chapter 12 of Arthur C. Clarke's 1968 novel 2001: A Space Odyssey, titled "Journey by Earthlight," begins with a description of the Macrocrater Province and the crater Tycho extracted from Mason's Sheet 4 of the "Engineer Special Study."

References

  • Engineer Special Study of the Surface of the Moon, Robert J. Hackman and Arnold C. Mason, Army Map Service, Corps of Engineers, July 1960.
  • Engineer Special Study of the Surface of the Moon, Miscellaneous Geologic Investigations Map I-351, Robert J. Hackman and Arnold C. Mason, U.S. Geological Survey, Washington, DC, 1961.
  • Memorial to Arnold Caverly Mason (1906-1961), H. Foster, Geological Society of America Bulletin, Vol. 73, August 1962, pp. 87-90.
  • To A Rocky Moon: A Geologist's History of Lunar Exploration, Don E. Wilhems, The University of Arizona Press, 1993, pp. 37-42 http://www.lpi.usra.edu/publications/books/rockyMoon/ (accessed 5/15/13).