MSSR as MEM (1967-1968)

Scary ride: second stage and crew cabin of the Bellcomm minimum Mars Excursion Module (MEM) ascent vehicle. The unpressurized cabin would have included few displays and minimal communications. Image credit: Bellcomm/NASA.
The NASA Planetary Joint Action Group (JAG) saw the addition of the Mars Surface Sample Returner (MSSR) probe to the piloted Mars/Venus flyby mission scenarios it studied in 1966 as a pivotal innovation. Before the advent of the MSSR, the piloted flyby mission appeared to be increasingly threatened by successful robotic flyby missions. The MSSR, members of the Planetary JAG contended, gave the piloted flyby mission an added capability that could not be reproduced by a wholly robotic Mars mission.

The piloted flyby spacecraft would have released the MSSR perhaps 10 days before Mars close encounter. A rocket motor on the MSSR would have boosted it toward Mars, enabling it to reach the planet and land at a preselected site several hours before the piloted flyby spacecraft arrived. 

The crew on board the piloted flyby spacecraft would have used a variety of sample collectors on board the MSSR to gather about two pounds of Mars surface material and air by remote control as the planet grew ever larger in their viewports. These would have been packed into a three-stage ascent vehicle and launched to the piloted flyby spacecraft. 

Partial cutaway of Mars Surface Sample Returner (MSSR) probe. A = Mars intersect trajectory injection stage with toroidal propellant tank; B = sample canister; C = ascent stage with three stages, each with a toroidal propellant tank; D = folded landing leg (one of four); E = aeroshell heat shield; F = toroidal descent stage propellant tank; G = descent stage engine heat shield cap. Image credit: NASA/DSFPortree.
The astronauts on board the piloted flyby spacecraft would have captured the sample canister and ascent vehicle third stage using a boom-mounted docking ring and linked them to a port leading into a hermetically sealed biological laboratory. The MSSR probe would, it was expected, enable analysis of Mars samples within an hour of their collection, helping to ensure that any martian organisms they contained would still be alive. 

Phase 1 of the Planetary JAG piloted flyby study ended with distribution of an NASA report on 3 October 1966. The group then began work on Phase 2 of its piloted flyby study. Some members of the Planetary JAG foresaw a rosy future for the concept — they anticipated that MSSR study contracts might be awarded in Fiscal Year 1968 and the piloted flyby mission might become a NASA new start project in Fiscal Year 1969.

Even before the  AS-204/Apollo 1 fire (27 January 1967), NASA planning for missions beyond Apollo was on shaky ground. Neither the Administration of President Lyndon Baines Johnson nor the Congress supported ambitious plans for post-Apollo spaceflight — for example, a long-term lunar base or humans on Mars. By late summer 1967, the fire, racial and anti-war tensions across the U.S., concerns about the Federal budget deficit, and military setbacks in Indochina had provided opponents of an expansive U.S. future off the Earth with ample justification for curtailing NASA efforts to define its future.

Not all advance planning halted in August/September 1967, however. Bellcomm, NASA's Washington, DC-based planning contractor, continued its efforts as a matter of course. Most Bellcomm studies in 1967-1969 aimed to define the shape of the Apollo Program after the first successful piloted lunar landing, as well as that of Apollo's planned successor, the Apollo Application Program. Work toward more ambitious goals did not, however, stop entirely.

In July 1967, Bellcomm planners D. Cassidy and H. London completed a short technical memorandum in which they explored how the MSSR probe might form the basis for a piloted Mars Excursion Module (MEM) lander. For their study, Cassidy and London assumed a 15,000-pound MSSR with a two-stage ascent vehicle capable of launching 80 pounds to a passing piloted flyby spacecraft launched in 1975, 1977, or 1979 on a Mars Twilight flyby path. The "twilight" mission owed its name to the geometry of its Mars flyby — closest approach to Mars took place over the planet's night hemisphere near the dawn terminator, the line dividing pre-dawn darkness from daylight. 

Cassidy and London calculated that MSSR Mars atmosphere entry velocity would reach 32,500 feet per second (fps) in 1975, 34,500 fps in 1977, and 39,000 fps in 1979. As it passed at a shallow angle through the thin martian atmosphere, the automated MSSR would undergo deceleration equal to up to 40 times the pull of gravity on Earth's surface (that is, 40 Gs). To accomplish rendezvous with the passing piloted Mars flyby spacecraft, the MSSR ascent vehicle would have to boost an 80-pound third stage and sample container to 36,000 fps in 1975, 38,000 fps in 1977, and 42,500 fps in 1979. 

An MSSR-derived MEM released during piloted Mars orbiter approach to Mars — that is, before the orbiter fired its rocket motors to slow down so that Mars's gravity could capture it into an elliptical orbit with a one-day period — would, on the other hand, in 1978, 1982, 1984, 1985, and 1986 enter the martian atmosphere moving at between 20,000 fps and 25,000 fps. It would decelerate at about 10 Gs, which Cassidy and London judged to be acceptable for an astronaut. 

MSSR-derived minimum MEM. Image credit: Bellcomm/NASA.
Two ways of landing on Mars: Direct Entry Mode would see a pair of minimum Mars Excursion Modules (MEMs) and a shelter deployed from a Mars orbiter (labelled "S/C") during approach to Mars. The orbiter would then fire rocket motors to capture into an elliptical Mars orbit. If the orbiter could not capture into orbit, the twin MEMs would abort their landing, fly past Mars, and rendezvous with the orbiter. Entry from Elliptical Orbit would see minimum MEM and shelter separation after the Mars orbiter captured successfully into Mars orbit. Image credit: Bellcomm/NASA.
An equivalent MEM released in Mars orbit would enter more slowly and subject its occupant to a reduced G load while also enabling more precise landing site targeting. The MSSR-derived MEM ascent stage could boost a 900-pound third stage and crew capsule containing a single astronaut to a velocity of 18,000 fps to a rendezvous with the piloted orbiter in an elliptical Mars orbit with a period of one day. 

Cassidy and London wrote that a separate Bellcomm study had determined that a minimum one-person MEM with a crew capsule weighing as little as 600 pounds without an astronaut on board might be possible. Such a MEM would carry only enough life support consumables to remain on Mars for a short time and no scientific exploration equipment. They envisioned that an extended piloted Mars landing mission would employ three MSSR-derived landers: a pair of minimum MEMs, each carrying one astronaut, and an automated one-way cargo vehicle capable of delivering 5,500 pounds of life support supplies and scientific equipment to the surface of Mars.

Compared with the MSSR-derived MEM ascent vehicle, the single-seat Mercury spacecraft — shown here with its retrograde propulsion system (bottom, strapped to bowl-shaped heat shield) and red launch escape tower — was large, heavy, and complex. Image credit: NASA.
The study of a 600-pound MEM crew capsule Cassidy and London referenced was performed by M. Skeer in consultation with Cassidy and McDonnell Aircraft engineers. Skeer, a newcomer to Bellcomm in 1966, summed up results of his study in a technical memo dated two months after the Cassidy and London study. 

Skeer explored whether the design of the one-man McDonnell-built Mercury capsule, which carried six astronauts on suborbital and orbital missions in 1961-1963, might contain weight-saving lessons for designers of an MSSR-derived MEM ascent vehicle. The 4600-pound Mercury capsule, he explained, was a good choice for his study because, like the minimum-mass MEM ascent vehicle, it had relatively simple mission objectives compared with the Gemini or Apollo Command and Service Module (CSM) and Lunar Module (LM) spacecraft.

The minimum MEM would descend from a spacecraft in a highly elliptical Mars orbit with a period of from 24 to 48 hours. A spacecraft in such an orbit would be bound loosely by Mars's gravity, so would require minimal propellant expenditure to depart the planet when the time came to return to Earth. Descent from the highly elliptical orbit to the surface of Mars would last about six hours and return from the surface of Mars to highly elliptical orbit would require about two hours. 

Skeer eliminated 47% of Mercury's weight immediately by deleting the 1119-pound launch escape tower, 315-pound heat shield, 317-pound retrograde propulsion system (used to deorbit the Mercury capsule), landing systems and recovery gear together weighing 343 pounds, and 51 pounds of experiments. He then treated remaining Mercury systems in detail. He wrote, for example, that McDonnell engineers had told him that the 75-pound Mercury couch could be trimmed to 15 pounds. Skeer arrived at a total MEM ascent stage weight of 738 pounds including a 170-pound astronaut. 

Minimum MEM entry and landing. Image credit: Bellcomm/NASA.
Useful payload: two-stage minimum MEM ascent vehicle. Image credit: Bellcomm/NASA.
Minimum MEM liftoff, ascent, and orbital insertion. After rendezvous in Mars orbit the single astronaut would fly the capsule into a hangar on the Mars orbiter or would abandon the capsule and enter the Mars orbiter by spacewalking. Image credit: Bellcomm/NASA.
The MEM cabin would provide just 92 cubic feet of volume for the astronaut — 26 cubic feet less than the snug Mercury cabin. A "plastic shroud" measuring just 30 inches wide by 60 inches long, it would be neither pressurized nor insulated. Skeer estimated that it could weigh as little as 200 pounds, about 415 pounds less than the Mercury cabin structure. The cabin's small volume would prevent the astronaut from moving much; Skeer argued that astronaut immobility would simplify ascent stage guidance and control by avoiding center-of-gravity shifts. 

The astronaut packed into the coffin-like MEM cabin would rely for life support on a 40-pound space suit with a 100-pound life support backpack containing sufficient life support consumables for 12 hours of operations. This combination would replace a Mercury cabin life support system weighing 248 pounds. 

Skeer briefly examined a two-person minimum MEM with a descent stage not based directly on the piloted flyby MSSR. This would, he wrote, have a total weight of less than 35,000 pounds. Of this, 1360 pounds would comprise the MEM ascent stage and crew. He clearly favored the single-person minimum MEM, however. 

Skeer subsequently conducted a pair of follow-on studies of MSSR-derived piloted spacecraft. The first, completed on 8 May 1968, looked at a 4064-pound MSSR-derived two-person surface shelter that would enable a two-week Mars surface stay by astronauts landed separately in a pair of MSSR-derived minimum MEMs. Expendables supporting the two-week stay — mostly for life support and power generation — would account for 1053 pounds of the shelter's weight.

Cutaway view of MSSR-derived Mars surface shelter. Image credit: Bellcomm/NASA.
Plan view of MSSR-derived Mars surface shelter. Image credit: Bellcomm/NASA.
The 575-cubic-foot shelter would include a 60-cubic-foot airlock accessed from the martian surface by a "hoist" (apparently a one-person open elevator platform). A pair of 25-cubic-foot compartments accessed from within the shelter (not from the airlock) contained four complete space suits so each crewmember could have a spare. A laboratory area accounted for 50 cubic feet of the shelter's volume.

Scientific exploration equipment accounted for 1460 pounds of the shelter's weight. This included a single 367-pound one-person surface rover or flyer with a total range of 420 kilometers, 77 pounds of multiband photography/radiometry equipment, a 107-pound shelter-mounted drill capable of reaching a depth of 30 meters, 100 pounds of "surveying tools," a 250-pound "Emplaced Science Station" and three "satellite science stations" (total weight 140 pounds) meant to be left behind on the martian surface, and "local sampling and environmental equipment" weighing a total of 395 pounds. The shelter's pressurized cabin would contain 50 pounds of equipment for geologic analysis. (Skeer made no reference to return of samples in the two minimum MEM vehicles; presumably sample analysis on Mars was meant to replace return of samples to Earth.)

Skeer's second follow-on study, a more detailed examination of the minimum MEM ascent stage dated 8 July 1968, sought to identify "fruitful areas of technological research and development needed for evaluation and future program planning options." He argued for development of new propulsion systems capable of burning new high-energy propellants (for example, fluorine-LOX/methane), compact and lightweight refrigeration systems for long-term storage of such propellants, and development of new lightweight materials to permit further minimum MEM weight reduction. 

He also noted that flights of MSSR probes during piloted flyby missions could be seen as test flights of minimum MSSR technology. Unfortunately, by the time Skeer completed his second follow-on study, work within the NASA Planetary JAG toward a piloted flyby with MSSR probe had been largely abandoned for nearly a year.

Sources

"MSSR/MEM Commonality - Case 233," D. E. Cassidy and H. S. London, Bellcomm, Inc., 19 July 1967.

"Preliminary Sizing of a Mars Excursion Module Ascent Capsule Based on Mercury Spacecraft Design - Case 233," M. H. Skeer, Bellcomm, Inc., 25 September 1967.

"Preliminary Mars Excursion Module Shelter Design - Case 730," M. H. Skeer, Bellcomm, Inc., 8 May 1968.

"Mars Excursion Module Ascent Propulsion Stage Design," M. H. Skeer, Bellcomm, Inc., 8 July 1968.

More Information

A New Step in Spaceflight Evolution: To Mars by Flyby-Landing Excursion Mode (1966)

NASA's Planetary Joint Action Group Piloted Flyby Study (1966)

Triple-Flyby: Venus-Mars-Venus Piloted Missions in the Late 1970s/Early 1980s (1967)

Flyby's Last Gasp: North American Rockwell's S-IIB Interplanetary Booster (1968)

Mars Sample Return Site Selection and Sample Acquisition Study (1980)

The Tharsis hemisphere of Mars. The four large volcanoes are marked by clouds and the western half of Valles Marineris is visible at right. Image credit: NASA.
In 1977-1978, the Jet Propulsion Laboratory (JPL) Mars Program studied a low-cost "minimum" Mars Sample Return (MSR) mission as a potential follow-on to the Viking missions. Late in 1978, JPL Mars Program engineers called upon the NASA-sponsored Mars Science Working Group (MSWG) for aid in defining science requirements to help guide MSR spacecraft design and operations planning. 

The MSWG, chaired by JPL's Arden Albee, included scientists from JPL, NASA, the U.S. Geological Survey (USGS) Astrogeology Branch, universities, and aerospace contractors. Many had participated in the MSWG's July 1977 Mars 1984 study, which proposed a long-range rover, an orbiter, and a penetrator network as a post-Viking/pre-MSR mission (see "For More Information," below).

The MSWG scientists divided into Site Selection and Sample Acquisition teams. The teams held two joint workshops and produced 10 detailed reports before the middle of 1979. Edited by JPL's Neil Nickle, they did not see print until November 1980. 

Publication was delayed in part because Mars planning at JPL slowed markedly in early 1979. It would not begin to emerge from the doldrums again until the following year, after President Jimmy Carter's NASA Administrator, theoretical physicist Robert Frosch, created the Solar System Exploration Committee in an (ultimately successful) effort to revitalize the space agency's flagging robotic exploration program.

Because the MSWG reports were based on limited data, they may appear archaic to some readers. Nevertheless, they remain important, for they capture snapshots of the state of Mars science as the busy first era of robotic Mars exploration ended and the long gap began between the Viking missions, which reached Mars in 1976, and Mars Pathfinder and Mars Global Surveyor, which arrived at the planet in 1997.

The first MSWG report, which looked at polar landing sites for the minimum MSR mission, was authored by J. Cutts, K. Blasius, W. Roberts, and K. Pang of the Planetary Science Institute (PSI) of Science Applications, Inc., and A. Howard of the University of Virginia (UV). They submitted their report to JPL on 30 April 1979.

The PSI/UV team began by pointing out that humans had already explored Mars's poles for more than a decade. Mariner 7 had begun close-up martian polar exploration by imaging the entire southern ice cap at low resolution during its August 1967 flyby. Mariner 9 imaged both caps from Mars orbit during 1971-1972, and the Viking 2 orbiter began high-resolution polar imaging in 1976.

In many respects, polar MSR sites constituted a special case, the PSI/UV team wrote. Whereas missions to the other MSR sites would focus mainly on rock samples, the polar MSR mission would acquire meter-long core samples of ice or dust and ice. Rock samples would be "an unplanned bonus."

The north pole of Mars. Image credit: NASA.
The five scientists looked at two MSR sites near Mars's north pole (image at top of post). Site A, at 86.5° north (N), 105° west (W), included wide "featureless" expanses of undulating perennial ice underlain by layered deposits. Core samples of perennial ice might provide data on ice cap formation processes and time scale, martian climate history, and organic compounds trapped in the ice. They would establish "ground truth" for interpreting polar data from orbital spacecraft.

They assumed that a landing might safely occur anywhere within a target ellipse 25 kilometers wide by 40 kilometers long, and calculated that a lander that set down in the ellipse would stand at least a 99% chance of landing on perennial ice. For this reason, no mobility (that is, no rover) would be required at Site A.

The second polar site, Site B (84.5° N, 105° W), included perennial ice and "partially defrosted" terraced troughs. The latter, the PSI/UV scientists explained, would "form windows through the layered deposits and cross-sections through martian history." The 25-kilometer-by-40-kilometer Site B target ellipse would also overlap the edge of the permanent ice cap. 

Selecting such a varied area would, they warned, reduce the probability of landing on perennial ice to between 60% and 90%. If, however, the Site B mission included a short-range (about 10 kilometers) rover, then the probability of sampling more than one terrain and of sampling perennial ice would increase to greater than 90%.

In discussing the engineering problems of a polar MSR mission, the PSI/UV team cited Purdue University's 1976-1977 Mars Polar Ice Sample Return study (see "For More Information," below), but otherwise left engineering to the engineers. Potential problems identified included acquisition and preservation of ice and permafrost cores, mechanical operations at extremely low temperatures, and water and carbon dioxide frost accumulation and evaporation that might impede a rover.

As a "next logical step" toward a polar MSR mission, the PSI/UV scientists recommended establishment of a science working group with "substantial participation by earth scientists involved with studies of terrestrial sedimentary records[,] particularly those pertaining to climate change." They did not recommend an MSR precursor mission; that is, they judged that the Viking missions had provided data adequate for planning a minimum MSR mission to Mars's north pole.

Arizona State University (ASU) geologists R. Greeley, A. Ward, A. Peterfreund, D. Snyder, and M. Womer submitted the second of the 10 MSWG reports to JPL in March 1979. Their quest for a young volcanic MSR site was hampered, they explained, by a dearth of high-resolution (better than 50 meters per pixel) orbital images. Nevertheless, they located six candidate sites that looked to be volcanic and had few craters, signifying youth. (Planetary scientists count craters to estimate terrain age; the more densely craters pock a landscape, the older it is likely to be.)

Arsia Mons (right of center) is southernmost of the four great Tharsis volcanoes. ASU's "Arsia Mons West" MSR site is located near the center of the left (west) half of the image. Image credit: NASA.
The ASU geologists picked Arsia Mons West, located at 8.5° south (S), 132.5° W, 500 kilometers from Arsia Mons, the southernmost of the four great Tharsis volcanoes, because the site appeared to be both very young and relatively homogenous geologically. The latter, they explained, was a desirable quality because it would facilitate interpretation of sample data. 

The Arsia Mons West site, which had been imaged by the Viking orbiters at 34-meters-per-pixel resolution, included eight overlapping lava flows. The flows measured from eight to 35 kilometers wide and averaged 51 meters thick.

The ASU team found room for two target ellipses 80 kilometers long by 50 kilometers wide on either side of a five-kilometer crater at their site's center. They calculated that a rover with a 14-kilometer range would have a "complete guarantee" of reaching an outcrop of young volcanic rock.

At JPL's request, the ASU geologists also assessed Viking 1's Chryse Planitia landing site as a potential MSR landing site. The volcanic rocks were old at Chryse, a smooth-floored basin at the confluence of several large flood-carved channels. Based on the in-situ evidence provided by Viking 1 lander images, it was clear that no mobility would be needed to acquire a rock sample. 

The ASU team noted, however, that the "value of a returned sample [would be] severely diminished because it may be impossible to determine if the material represents local [lava] flows. . .[or] if it has been deposited from the floods that eroded the channels." The ASU team added that "[w]ithout mobility of at least 200 to 300 kilometers, the [Chryse Planitia] site [would be a] a poor choice to answer basic scientific questions about Mars." For neither site did they recommend an MSR precursor mission.

A Young-Lavas Landing Site Northwest of the Volcano Apollinaris Patera and a Landing Site on the Ancient Terrain Southeast of the Schiaparelli Basin, had a single author: Brown University geologist P. Mouginis-Mark. He argued for mobility at his young Elysium Lavas (5° S, 190° W) and Ancient Terrain (8° S, 336° W) minimum MSR sites. The former, 150 kilometers from the Apollinaris Patera volcano, comprised rolling plains with scattered volcanic domes and shields, stratovolcanoes, and fresh impact craters. He identified a ridge running through the center of the 80-by-50-kilometer target ellipse as the feature most likely to yield a "good sample" (that is, a well-preserved volcanic rock representative of the site).

Mouginis-Mark calculated that without mobility the probability of obtaining a good sample would be nil, while the probability of landing on a sand dune and obtaining no sample at all would be as high as 22%. The probability of obtaining a good sample would increase to 91%, however, if the mission included a rover with a round-trip range of 20 kilometers.

The smooth-floored crater Schiaparelli (top of image, just right of center).  Mouginis-Mark's "Ancient Terrain" MSR site is located near the center of the image. Image credit: NASA.
Mobility would be even more important at Mouginis-Mark's heavily-cratered Ancient Terrain site, located 150 kilometers from the 400-kilometer-diameter crater Schiaparelli. The site, which dated from the Noachian, the earliest identified era of martian geological history, included highly eroded large craters buried under ejecta from Schiaparelli's violent formation. 

Mouginis-Mark expected that a good sample might be found on the rim of a fresh crater more than two kilometers across, five of which occurred in Ancient Terrain target ellipse. He calculated that a rover round-trip range of 50 kilometers would be needed to achieve a 90% probability of acquiring a good sample.

For their contribution, USGS geologists H. Masursky, A. Dial, M. Strobell, G. Schaber, and M. Carr recycled four sites that they had studied in 1977-1978 for a proposed Viking follow-on long-range rover mission. Masursky and Dial were co-authors of the Viking '79 traverse study in 1974, while Carr led the Viking orbiter imaging team (and thus was involved in capturing the high-resolution images the minimum MSR Site Selection Team used in preparing its reports).

The USGS sites represented two martian terrain types. Tyrrhena Terra and Iapgyia Terra included ancient cratered terrain similar to that at Mouginis-Mark's Schiaparelli site, which is perhaps unsurprising given that such terrain covers more than 60% of Mars. The sites contained a jumble of overlapping craters and an intercrater mantle of old lava flows.

Samples collected in Tyrrhena and Iapgyia would permit age-dating of the oldest martian crustal material, the USGS geologists wrote. This would enable calibration of the crater counts used for dating martian terrains. In addition, data from the samples could "be compared to comparable analyses made of ancient lunar crustal materials returned by Apollo 16 and [to] ancient terrestrial rocks in order to make interplanetary comparisons of [how rocks are formed], physical and chemical properties, and age."

Of the two sites, Tyrrhena was "superior as a potential sample site in all respects," the USGS team wrote. They proposed that the minimum MSR lander set down where the old lava flows appeared to be thin, near a six-kilometer-diameter crater - one large enough, they judged, to have excavated ancient crust buried beneath the flows. They calculated that a landing ellipse 30 kilometers long and a rover with a 10-kilometer round-trip range would reach only old lava samples. 

Obtaining an ancient crustal rock sample ("the primary science objective"), on the other hand, would demand a five-kilometer landing ellipse and a 14-kilometer round-trip rover. Achieving such landing accuracy implied that the minimum MSR lander would be capable of automated guidance and precision maneuvers during descent.

The other two USGS sites, Candor Chasma and Hebes Chasma, were both part of Valles Marineris, Mars's great equatorial canyon system. "These sites," the USGS team wrote, would "offer a unique opportunity to sample rock layers and their interbedded soils that would reveal the petrochemical history, age dates[,] and the history of environmental changes that may correlate with episodes of channel formation" on Mars. They might also yield organic material ("if the present red anorganic climate did not exist at times in the past") and a record of "the history of solar variations."

Martian Canyonlands: Candor Chasma. Image credit: NASA.
At Candor, their preferred site, parallel rock layers were exposed in the sloping sides of a 1.3-kilometer-tall mesa standing at the bottom of the four-kilometer-deep canyon. If the MSR lander could set down within a five-kilometer landing ellipse atop the mesa, then a seven-kilometer round-trip traverse would permit sampling of some of the layers. Recalling their 1977-1978 study, which assumed a more capable (and more costly) rover, they noted that a "much longer traverse — more than 200 km — would allow the full thickness of rock layers (~4 km) in the canyon walls to be sampled."

The MSWG's fifth report, the first of the six prepared by members of the MSWG Sample Acquisition Team, looked at the availability of rocks on Mars with emphasis on the equatorial Central Latitude Belt, which spanned between 30° N and 30° S. The report's author, University of Houston geologist E. King, explained that celestial mechanics and MSR lander engineering constraints would probably dictate that the Belt contain the first MSR landing site.

The twin Viking landers had had trouble collecting small rocks on Mars, King noted. This had led some to suggest that what looked like rocks at the Viking sites were in fact soft "clods" of martian dirt. If correct, then this hypothesis would mean that rocks were rare on Mars, which would in turn eliminate the primary motivation for an MSR mission; that is, to collect rocks.

King reported that his "evaluation of all of the presently available relevant data" had eliminated this concern "completely" for large parts of Mars, including for the Central Latitude Belt. Especially encouraging were data from the Viking orbiter Infrared Thermal Mapping (IRTM) experiment, which mapped thermal inertia (that is, how long it takes a given surface to become cool at night). Rocky surfaces need longer to cool down than do dusty surfaces. 

Viking IRTM data indicated that much of the Central Latitude Belt has thermal inertias as high as 12. "It is very difficult to construct a reasonable model of the martian surface that has a thermal inertia of more than about 3 that does not have a substantial percentage of the surface area covered with rocks," King wrote.

He attributed the Vikings' inability to collect small rocks to inadequacies in the Viking sampler design. After it scooped a sample containing small rocks, controllers on Earth commanded the sampler to turn upside-down and shake for up to two minutes to sieve out dust. King noted that shaking the sampler caused its lid to flap open as much as an inch. This would allow any pebbles it contained to escape. 

He advocated collecting rock samples in the form of drilled cores, since drilling could penetrate past any weathered rock rinds. Drilling could also collect uniform cylindrical samples that could be handled easily and stored efficiently in the MSR spacecraft.

King was ambivalent about the need for mobility in an MSR mission; he wrote that, if the objective of the mission were to collect fresh igneous rocks, and if the MSR landing site were similar to the Viking landing sites, then little mobility would be necessary. He added that, while it might be prudent to "build in some additional mobility as a margin of safety and to afford additional possibilities for sample collection. . .such provisions [had to be] traded off against lander science and returned sample weight."

USGS geologist H. Moore wrote the sixth MSWG report, which constituted a tour of the landscape within view of the Viking 1 and Viking 2 lander cameras. Viking 2 landed in Utopia Planitia, near the large impact crater Mie, a region more northerly than Viking 1's site in Chryse Planitia. Like King, Moore wrote that Viking 1 rocks were varied (there were 30 types) and tended to be smaller than Viking 2 rocks. The Viking 2 rock population, for its part, appeared to be dominated by ejecta from Mie. 

Moore then described hypothetical rover traverses at the two sites. In each, the rover would visit 17 sampling stations, traverse about 100 meters, and range up to 20 meters from its lander.

The boulder named "Big Joe" at the Viking 1 landing site in Chryse Planitia. Image credit: NASA.
At the Viking 1 site, the rover would collect samples of cloddy soil, crunchy "duricrust" material, an active dune, and drift material, as well as 10-centimeter-long cores from bedrock outcrops, layered rocks, dark and light rocks, a pink rock, rocks formed by asteroid impacts, and gray-hued "Big Joe" (the largest rock near the lander). The rover at the Viking 2 site would collect samples of "inter-rock drift" material, a "drift dunelet," thick crust near a rock, and small rocks, along with cores from a coarsely pitted rock, planar and rounded rocks, a banded rock, the "massive" and pitted ends of one angular rock, and a ventifact (a rock scratched and carved by wind-blown dust and sand).

Moore estimated that the rover would spend between six and eight days traversing and collecting for each station. Each traverse would thus last from 102 to 136 days. The total mass of samples collected on each traverse would total about two kilograms.

The seventh MSWG report sought to estimate the number of crystalline rocks — that is, volcanic rocks such as basalt — at the Viking landing sites and to plan traverses that would adequately sample them. Its authors, R. Arvidson, E. Guinness, S. Lee, and E. Strickland, geologists in the Department of Earth and Planetary Sciences at Washington University in St. Louis, Missouri, argued that any rock larger than about 10 centimeters in diameter at the Viking sites was a good candidate for being crystalline.

Such rocks, they added, cover 9% of the Viking 1 site and 17% of the Viking 2 site. The former, they wrote, included bedrock exposures and at least four soil types, while the latter included two soil types and no bedrock. They pointed out that, while a sampler arm could probably reach a crystalline rock at either site, it would not be able to sample all of the available materials. For that reason, they proposed that MSR landers at the Viking sites should each deploy a "mini-rover."

The Viking 1 site was "such an interesting place," the Washington University team wrote, that they had planned for it a 40-meter traverse with seven sampling stations (with an option to extend to 50 meters and 10 stations). The basic traverse would collect 10-centimeter core samples from three rocks and four soil samples. The extended traverse would sample two more rocks, including Big Joe, and would gather a total of five soil samples, including very red soil from atop Big Joe.

The Viking 2 site, by contrast, featured minimal variety, so the Washington University team's traverse there would cover only 25 meters and seven stations. The mini-rover would collect four soil samples and core samples from three rocks.

N. Nickle of JPL's Flight Projects Planning Office authored the eighth MSWG report, which was titled Requirements for Monitoring Samples. The report was published originally as a JPL Interoffice Memorandum dated 20 October 1978. Nickle wrote that the "scientific integrity of the returned Martian samples is of prime importance." "Scientific integrity," he explained, meant "the preservation of the physical and chemical state of the acquired samples."

To maintain the scientific integrity of the samples collected during the minimum MSR mission, Nickle recommended that they be kept 20° C cooler than the estimated minimum temperature they had experienced on Mars, and that they be sealed within a container with martian air at typical martian surface pressure. In addition, he recommended that the samples be exposed to no more galactic cosmic and solar radiation than they had been on Mars, and to no magnetic field stronger than Earth's natural field.

The minimum MSR mission sought to control cost in part by avoiding science instrumentation not required for sample collection. In the MSWG's ninth report, J. Warner of NASA's Johnson Space Center (JSC) in Houston, Texas, looked at low-mass, low-power MSR science instruments designed to "provide adequate information to select samples." 

His candidate instrument suite included a steerable imager, a reflectance spectrometer, a chemical analyzer on a boom, a boom-mounted densitometer, and a tool for measuring hardness (this might, Warner suggested, be made a function of the sample scoop; the Viking arm and claw had been used to scratch and chip at rocks to judge their hardness).

Warner also prepared the tenth and last report of the Site Selection and Sample Acquisition Study, which he titled A Returned Martian Sample. In it, he looked at the form the minimum MSR sample should take. He looked at two different landing site types: a Viking-like site "laden with a variety of rocks and soils" and a hypothetical "smooth plains site."

The JSC geologist cited Moore's report when he wrote that, at a Viking-like site, an adequate sample could be "obtained on a traverse of a few hundred meters that never leaves the field of view of the lander." He estimated that an atmosphere sample, a soil core, nine rock cores, four small rock fragments, two duricrust samples, and six scoops of soil would adequately represent a Viking-like site. Together these samples would have a mass of 4.1 kilograms.

An eight-month, 15-station traverse could adequately sample a rock-poor smooth plains site, Warner wrote. The rover would range widely over the smooth terrain. Sampling stations would occur at "obstructions" (for example, craters). The rover would drill two or three rock cores and collect one rock fragment at each station, scoop soil at every other station, and collect duricrust at every fifth station. Adding a soil core and an atmosphere sample would bring the total sample mass to 5.7 kilograms if two rock cores were collected and 6.9 kilograms if three cores were collected.

Sources

Mars Sample Return: Site Selection and Sample Acquisition Study, JPL Publication 80-59, Neil Nickle, editor, NASA Jet Propulsion Laboratory, 1 November 1980.

Detailed Reports of the Mars Sample Return Site Selection and Sample Acquisition Study, JPL 715-23, Volumes I-X, Mars Science Working Group Mars Sample Return Study Effort, NASA Jet Propulsion Laboratory, November 1980. 

More Information

Mars Polar Ice Sample Return (1976-1978)

Prelude to Mars Sample Return: The Mars 1984 Mission (1977)

Safeguarding the Earth from Martians: The Antaeus Report (1978-1981)

NASA's Planetary Joint Action Group Piloted Mars Flyby Study (1966)

Robotic flyby: encapsulated in a streamlined shroud, the Mars-bound Mariner IV spacecraft awaits launch from Florida atop an Atlas-Agena rocket. Image credit: NASA.
The piloted Mars/Venus flyby concept — the hallmark of which was a Sun-centered trajectory intersecting one or more planets and beginning and ending at Earth — was first proposed by Gaetano Crocco in 1956, at a time when robotic probes to other worlds were scarcely mentioned by champions of spaceflight. A decade later, when NASA performed its first high-level NASA-wide study of the piloted flyby concept, that situation had changed markedly — thanks largely to a 261-kilogram (575-pound) spacecraft called Mariner IV.

Launched on 28 November 1964, Mariner IV demonstrated for the first time that a robotic spacecraft could return useful data from the vicinity of Mars. The success of Mariner IV — it captured 21 images of the planet as it flew past on 15 July 1965, and slowly transmitted them to Earth over the following month — gave ammunition to those who called into question the utility of piloted flybys. 

The Mariner IV images revealed a cratered, arid surface, and its radio occultation experiment found an atmosphere only 1% as dense as Earth's. Mars, seemingly so promising for the development of life, suddenly appeared almost as inhospitable as Earth's barren Moon. 

Supporters of Mars exploration were quick to point out, however, that the little spacecraft had imaged only about 1% of Mars at a resolution so low that, had it flown past Earth, it would not have found life. NASA and the planetary science community persisted with plans to launch new scientific exploration missions to Mars in the Mariner and Voyager programs (the latter not to be confused with the late 1970s Voyager originally called Mariner Jupiter-Saturn — please see "More Information," below). 

Cratered planet: One of the sharpest Mariner IV images of Mars. Image credit: NASA.
In like fashion, piloted flyby proponents — such as the participants in the Planetary Joint Action Group (JAG), led by Edward Z. Gray of the NASA Headquarters Office Manned Space Flight (OMSF) — proceeded with their planning meetings in spite of Mariner IV's achievement. The first Planetary JAG meeting, held at the NASA Manned Spacecraft Center (MSC) in Houston, Texas, on 4 May 1966, gave roughly equal priority to piloted Mars/Venus flybys and a piloted Mars landing mission. 

By the Planetary JAG's second meeting, held at NASA Headquarters in Washington on 9 June 1966, piloted flybys had assumed primacy. "The object of the effort," the Group declared, "is a Mars/Venus Fly-by capability by [19]75 with a manned Mars landing in view." 

Ironically, given the negative effect of Mariner IV, a new class of robotic probe was largely responsible for the positive change in the piloted flyby concept's fortunes. The Mars Surface Sample Returner (MSSR), first discussed at the NASA Headquarters meeting, would borrow technology and experience from Mariner and Voyager. It would ride to Mars on board the piloted flyby spacecraft. After carefully checking out and servicing its systems, the crew would release it several days before the flyby. It would reach Mars hours ahead of the flyby spacecraft, land, collect samples of martian air and dirt, and launch them into space. 

The astronauts would capture the sample container minutes after their closest approach to Mars. They would analyze the sample in a lab on board the piloted flyby spacecraft within an hour of its launch from Mars, before any living things it contained could perish. 

More than 50 engineers from across NASA attended the Planetary JAG's third meeting at NASA Kennedy Space Center (KSC) on 29-30 June 1966. By then, the Group had begun work on a pair of documents: a briefing to the high-level managers of the NASA Management Council and a preliminary Program Development Plan (PDP). Bellcomm, NASA's Washington, DC-based planning contractor, provided the Group with technical assistance.

The briefing took place a month later — the Council's response is not recorded, but it was apparently favorable enough for work on the PDP to continue. The completed PDP, labelled "For Internal Use Only," bore the date 3 October 1966. 

The Planetary JAG envisioned that the 1975 Mars flyby, launched out of low-Earth orbit between 5 September and 3 October of that year, would be the first in a series of four Mars and Venus flyby missions. It would last 667 days. The other three were a 715-day Venus/Mars/Venus flyby mission launched in February 1977, a 625-day Venus/Mars flyby mission launched in December 1978, and a 686-day Mars flyby mission launched in November 1979. Regardless of the number of flybys it contained, no piloted flyby mission would require more than modest course-correction propulsion after departure from low-Earth orbit. 

Only the 1975 mission was described in detail in the PDP. It would follow a low-energy twilight trajectory that would take it past Mars and would reach aphelion — its greatest distance from the Sun — on the inner edge of the Asteroid Belt, at 2.2 times the Earth-Sun distance. The term "twilight" referred to the Mars pass geometry; flyby spacecraft Mars periapsis (closest approach) would occur over the line separating the dayside from the nightside. 

Seven years of development and testing would precede launch of the 1975 mission. The flyby program nested within a series of extant and anticipated NASA programs and missions, which the Planetary JAG stated provided "a sound base for the development of a manned flyby system." The piloted flyby spacecraft, for example, would be based on hardware and experience from Apollo and its planned follow-on, the Apollo Applications Program (AAP). Set to begin as early as 1968, AAP was envisioned primarily as an Earth-orbital space station program, but was also expected to include "limited lunar exploration" beyond the Apollo baseline.

AAP astronauts would carry out progressively longer missions on board Orbital Workshops, achieving a one-year stay in weightlessness in 1970 or 1971. The AAP Orbital Workshop would take the form of a converted S-IVB stage, which formed the second stage of the Saturn IB rocket and the third stage of the Saturn V. A third Orbital Workshop launched in 1972-1973 would test prototype piloted flyby spacecraft subsystems.

Major components of the Planetary JAG's piloted flyby spacecraft. A = Propulsion Module (PM) with toroidal propellant tanks and four engines; B = Apollo-derived Earth-Entry Module (EEM) with heat shield tunnel; C = Mission Module (MM) with tunnel to airlock/biological laboratory; D = Experiment Module (EM) with MSSR probe, airlock, telescope, and biological laboratory (probe complement illustrated differs from that described in Planetary JAG PDP); E = deployed high-gain antenna (stowed position also shown); F = deployed solar array. 
In the same timeframe, robotic precursor probes would provide important data to engineers designing piloted flyby mission systems. A Mariner spacecraft would release a probe to plumb the martian atmosphere in 1971 and possibly again in 1973 and probes would assess the meteoroid population between the orbit of Venus and the inner edge of the Asteroid Belt in 1970 or 1971. The former would aid in piloted flyby probe design and the latter might permit reduced piloted flyby spacecraft meteoroid shielding. Weight saved by reducing shielding might permit a heavier scientific payload on board the piloted flyby spacecraft.

Late 1972 would see a test of a Earth Entry Module (EEM) derived from the Apollo Command Module design but capable of withstanding Earth-atmosphere reentry at the end of the piloted flyby mission at up to 50,000 feet per second — that is, 14,000 feet per second more than the maximum planned Apollo lunar-return speed. In 1973-1974, four astronauts — the number planned for the piloted flyby spacecraft crew — would rehearse the piloted flyby mission for a year in low-Earth orbit on board a prototype 180,000-pound (81,650-kilogram) piloted flyby spacecraft. They would ride to Earth orbit and return to Earth in a 51,500-pound (23,350-kilogram) CSM launched with the flyby spacecraft.

The S-IVB stage was the third stage of the Saturn V rocket (shown in silhouette at left) and the second stage of the Saturn IB rocket. It was tapped as the structural basis of the AAP Orbital Workshop. The Planetary JAG expected that three Modified S-IVB stages launched on two-stage Saturn Vs would boost piloted flyby spacecraft out of Earth orbit toward Mars and Venus. Image credit: NASA.
The piloted flyby spacecraft and CSM would reach Earth orbit atop a two-stage "Improved" Saturn V rocket, the workhorse launch vehicle of the piloted flyby program. The Improved Saturn V would comprise an S-IC first stage stretched 20 feet (6.6 meters) to hold additional propellants for its beefed-up F-1 engines. In addition to launching the piloted flyby spacecraft and CSM, it would be used to rapidly launch a series of three 231,400-pound (105,000-kilogram) Modified S-IVB (MS-IVB) stages which would link up with the piloted flyby spacecraft in 485-kilometer (300-mile) assembly orbit to form an Orbital Launch Vehicle (OLV). 

The MS-IVB stages would each contain 195,800 pounds (88,800 kilograms) of cryogenic liquid hydrogen fuel and liquid oxygen oxidizer. Even with added insulation, the liquid hydrogen would boil and escape, so the stages would have to be used within about 50 hours of launch from NASA KSC to ensure that they would contain sufficient fuel to launch the piloted flyby spacecraft out of Earth orbit on flyby course past Mars. 

The Planetary JAG envisioned launching the three MS-IVB stages 12 hours apart. To make possible this "salvo" launch campaign, a third Launch Complex 39 Saturn V launch pad would need to be built beside the two NASA had already built for the Apollo Program. 

Orbital Launch Vehicle (OLV) assembly configurations. Image credit: NASA/DSFPortree.
OLV assembly came in for special consideration in the Planetary JAG PDP. In 1973, a crew in a CSM launched on a Saturn I-B rocket would dock with the prototype piloted flyby spacecraft after the one-year test crew returned to Earth. Shortly thereafter, NASA would launch two MS-IVB stages in rapid succession. The CSM, docked with a special docking collar at the front of the flyby spacecraft, would act as a space tug to push the piloted flyby spacecraft to a rendezvous and docking with the first MS-IVB in assembly orbit, then would push the piloted flyby spacecraft/MS-IVB combination to a rendezvous and docking with the second MS-IVB. The stages would then separate from the prototype flyby spacecraft and ignite in succession to carry out an MS-IVB flight test. The CSM crew would undock from the docking collar and return to Earth.

A full-up OLV assembly rehearsal involving a crew in a CSM, the piloted flyby spacecraft prototype, and three MS-IVB stages would follow in mid-1974. The CSM would dock with the docking collar on the front of the prototype, push it to a docking with the first MS-IVB, push the prototype and MS-IVB to a docking with the second MS-IVB, and finally push the prototype and the two MS-IVBs to a docking with the third MS-IVB. 

After docking with the piloted flyby spacecraft prototype, the crew in the CSM would have difficulty seeing the MS-IVB stages during docking maneuvers. The Planetary JAG proposed that strategically placed TV cameras and a viewscreen in the CSM could enhance visibility. In addition, an astronaut with an Astronaut Maneuvering Unit backpack might position himself where he could see the docking operation and call out directions to the crew in the CSM.

The Planetary JAG suggested that, following CSM separation, the three-stage OLV might launch the piloted flyby spacecraft prototype on an interplanetary trajectory without a crew. Alternately, the OLV might boost it into a high Earth orbit where it could serve as a space station.

The Planetary JAG assumed that the OLV for the 1975 piloted flyby mission would be ready for Earth departure on 5 September 1975, at the opening of its month-long launch window. After OLV assembly and prior to Earth departure, the flyby crew in the CSM would undock from the docking collar on the front of the piloted flyby spacecraft and redock at an airlock port on its side. After entering the flyby spacecraft's drum-shaped, two-deck Mission Module (MM), their home for the next 22 months, they would cast off the CSM and the docking collar. The MS-IVB stages would then ignite, burn to depletion, and separate in succession to commence a 130-day Earth-to-Mars transfer.

During flight to Mars, the flyby crew would operate a 40-inch astronomical telescope almost continuously. The Planetary JAG took pains to stress the value of their research program, which would include multispectral solar, stellar, planetary, and asteroid observations. Solar images were expected to contain details as small as 95 miles (150 kilometers) across. The telescope would be housed when not in use within the flyby spacecraft's tightly packed Experiment Module (EM). 

In total, at launch from Earth the EM would contain 30,190 pounds (13,690 kilograms) of experimental apparatus, including six robotic probes and the biology lab for analyzing the samples collected by the MSSR probe. In addition to the 11,692-pound (5300-kilogram) MSSR, probes would include a 1290-pound (585-kilogram) Lander for surface photography, geology/geophysics, and atmosphere studies, three 100-pound (45-kilogram) Aerodynamic Drag/Impacter probes, and a 10,130-pound (4600-kilogram) Orbiter for planet-wide mapping photography. 

The piloted flyby spacecraft would pass Mars between 23 January and 4 February 1976, the exact date and time depending on the date of Earth departure and magnitude of course corrections required. As the flyby spacecraft approached Mars, the crew would spend an increasing amount of time imaging it using the telescope and relaying the high-resolution images to Earth using the 19-foot-diameter (5.8-meter-diameter) radio dish antenna mounted on a stalk attached to the EM. The images, which would rapidly reveal new details as the piloted flyby spacecraft closed in on Mars, would be of profound scientific interest, but would also serve an operational purpose: they would be used to select targets for the robotic lander probes, which would be released between five and 10 days before piloted flyby spacecraft Mars periapsis (closest approach to the planet).

The MSSR probe would be the first of the six probes to be released. After release, the MSSR would cast off a two-part biological shield. A rocket motor would then ignite to increase the probe's speed by about 500 feet (150 meters) per second. The crew would begin careful tracking the MSSR's course. Twelve hours before landing and about 19 hours ahead of piloted flyby spacecraft periapsis, they would command the motor to perform a final course correction, after which it would be ejected.

The MSSR would enter the martian atmosphere and land in pre-dawn darkness about seven hours ahead of flyby spacecraft periapsis. Immediately after landing it would open like a flower with four fat triangular petals. The petals would contain most of the MSSR's scientific equipment, including two identical sets of four sample collectors on opposite sides of the lander. The MSSR would image the landing site using a panoramic camera and transmit the images immediately to the piloted flyby spacecraft, where the astronauts would use them to select sampling locations. The crew would seek to deploy the collectors outside the zone contaminated by the MSSR's descent rocket engines. 

Partial cutaway of the MSSR probe after biological shell separation. A = course change rocket motor with toroidal propellant tank; B = sample container attached to top of ascent vehicle third stage; C = stowed science compartment (one of four); D = folded landing leg (one of four); E = heat shield aeroshell; F = toroidal descent stage propellant tank; G = detachable heat shield cap covering descent engine bells. Image credit: NASA/DSFPortree.
MSSR descent. A = separation from the piloted flyby spacecraft and Mars targeting course changes; the course change rocket motor (1) is then ejected; B = Mars atmosphere entry and ejection of the protective cap (2) covering the descent engines shortly before ignition of the descent engine cluster; C = ejection of the aeroshell (3) and descent engine (4) operation. Image credit: NASA/DSFPortree.
MSSR after touchdown on Mars. A = sample container attached to ascent vehicle third stage; B = ascent vehicle with three rocket stages with toroidal tanks (numbered in reverse order of use); C = ascent vehicle protective cover/shield protecting deployed science compartment during ascent vehicle liftoff; D = deployed science compartment; E = descent motor cluster. Image credit: NASA/DSFPortree.
The Planetary JAG proposed four sample collectors of different designs in the hope that at least one would successfully sample the unknown surface materials of Mars, plus a single rock drill for collecting subsurface samples and a filter for sampling airborne dust. Of the four collectors, three — two with rotating cylinders intended to scrape the surface and a "vacuum cleaner" — assumed a dry and dusty Mars, while a fourth — the "sticky string" collector — would serve well if Mars turned out to be "tacky or viscous." About two pounds (0.9 kilograms) of material would be collected. A color film camera would automatically photograph the sampling sites then would transfer its film to the MSSR sample container. 

Meanwhile, the other probes would arrive at Mars. The solar-powered Orbiter, with a 200-pound (90-kilogram) camera, would use a three-stage liquid-propellant propulsion system to slow down and capture into a 185-mile (300-kilometer) near-polar orbit four hours before flyby spacecraft periapsis. The Lander would reach Mars two hours before periapsis. An hour after landing it would launch a 50-pound (23-kilogram) solid-propellant sounding rocket to an altitude of about 45 miles (70 kilometers). The three Aerodynamic Drag/Impacters would enter the martian atmosphere six minutes before periapsis. Their missions would end when they struck the martian surface.

The three-stage MSSR ascent vehicle would lift off in daylight 11.5 minutes before flyby spacecraft periapsis. Stage 1 would burn out and separate 5.5 minutes later, when the sample container was about 1540 miles (2480 kilometers) behind the flyby spacecraft. Stage 2 would then burn for 4.5 minutes, closing the distance to about 540 miles (870 kilometers). After a pause, Stage 3 would burn for about a minute, placing the sample container very near the piloted flyby spacecraft over the night side of Mars five minutes after periapsis. The astronauts would extend an arm-mounted docking ring, capture the sample container and third stage, and swing them to a linkup with a port on the biology lab located inside the EM.

Flyby spacecraft periapsis would occur about 125 miles (200 kilometers) above Mars, at which time the spacecraft would be moving at about 30,000 feet per second (9140 meters per second). At that altitude, the spacecraft's telescope would, with motion-compensation slewing, in theory be capable of discerning surface features 1.5 feet (0.5 meters) across. During the flyby, Mars's gravity would bend the spacecraft's course by only 17°.

The MSSR, Lander, and Orbiter probes would continue to explore Mars as the piloted flyby spacecraft moved outward past the planet, at first relaying data at a high rate via the flyby spacecraft and then transmitting directly to Earth at a lower rate. The authors of the PDP hoped that they could continue to return data from Mars for several years. 

Assuming Earth departure on 5 September 1975, the flyby crew would need a further 537 days to return to Earth. Early in that period, they would spend much of their time examining the Mars samples. Later, they would return to their wide-ranging astronomy studies. The Planetary JAG suggested that they could study 12-mile-wide (19.75-kilometer-wide) asteroid 149 Medusa at a distance of about 20 million miles (32 million kilometers) 170 days after Mars periapsis and 75-mile-wide (120-kilometer-wide) asteroid 156 Xanthippe at a distance of about 14 million miles (22.5 million kilometers) 150 days after that. They might also discover new asteroids and comets.

The flyby spacecraft would be on the opposite side of the Sun from the Earth when it reached aphelion at 2.2 times the Earth-Sun distance. The Planetary JAG anticipated that data the astronauts collected from their unique vantage point could be combined with data collected simultaneously on Earth to generate a full Sun portrait for the first time.

During the long flight, the crew could expect to observe many solar flares. Some would be directed toward the piloted flyby spacecraft. At such times, the crew would shelter in the thick-skinned EEM. Toroidal tanks containing PM course-correction propellants and spherical tanks containing MM life support gases and liquids would surround and provide additional radiation shielding for the EEM.

The piloted flyby spacecraft would return to Earth between 18 and 26 July 1977. The four astronauts would enter the EEM with the Mars samples and separate from the piloted flyby spacecraft. They would use the attached PM to nudge their course toward Earth, then would cast it off. The abandoned flyby spacecraft would swing past Earth and enter solar orbit; the EEM, meanwhile, would enter Earth's atmosphere at a speed of 49,100 feet per second, decelerate, and descend on parachutes to a land landing. Solid-propellant rocket motors would soften touchdown.

The Planetary JAG envisioned that its series of four piloted flybys would pave the way for piloted Mars landing and Venus orbital missions using nuclear-thermal rockets. These could begin as early as 1980 and might continue into the 1990s, when a Mars outpost might be established.

With the PDP in circulation, planning began for a new phase of Planetary JAG activity. In the minutes of a meeting held on 12 October 1966 at NASA Headquarters, Edward Z. Gray proposed spending $1.7 million of NASA's $8.45-million advance planning budget on the piloted flyby concept in Fiscal Year (FY) 1967. Of this, $250,000 would be spent to prepare for release to U.S. industry of contracts for an MSSR study in FY 1968. 

The pace of piloted flyby planning picked up in November and December 1966. On 17 November 1966, Gray called an advance planning meeting at NASA Headquarters for 6 December 1966. In a telex message dated 2 December, he explained that "the purpose of continuing activity in the manned planetary area is to be in a position to initiate a flyby project in FY 1969." He wrote that "to accomplish this end, we need to prepare a project proposal by mid-April 1967, in time for consideration in the FY 1969 budget cycle." 

The next Planetary JAG meeting was held at NASA MSC on 17 January 1967. In the early afternoon on 27 January, in response to issues raised during that meeting, Gray dispatched a telex in which he called on participants in the Planetary JAG to address "soft areas" in the 3 October 1966 report by mid-April. He called "experiment return from a flyby mission. . .one of its major attractions and an area which has received many searching questions." A little more than five hours after Gray sent out his message, fire raged through the AS-204/Apollo 1 spacecraft at Cape Kennedy, Florida, killing astronauts Virgil "Gus" Grissom, Edward White, and Roger Chaffee.

Piloted flyby planning became a casualty of Congressional backlash from the fire, which generated searching questions for NASA more pressing and immediate than any associated with the piloted flyby mission. Planetary JAG work did not, however, end immediately. In fact, in May 1967, Edward Z. Gray and his deputy Franklin Dixon felt confident enough to go public with the piloted flyby mission at the 5th Goddard Memorial Symposium in Washington, DC. They called for the 1975 piloted Mars flyby to be made a formal new start program in NASA's FY 1969 budget. 

Gray and Dixon eschewed the term "flyby," which had become closely associated with robotic probes after Mariner IV, in favor of calling the proposed mission a "retriever" or an "encounter." Whatever it was called, the piloted flyby concept — and, indeed, all NASA planning designed to give the space agency a future beyond Apollo — was in deep trouble by the summer of 1967. In September 1967, goaded by a Request For Proposals (RFP) NASA MSC distributed to industry aimed at selecting contractors for the MSSR study, Congress zeroed out all funding for NASA advance planning in FY 1968. NASA MSC collected RFP responses from industry but awarded no contracts.

Meanwhile, the Jet Propulsion Laboratory (JPL), with assistance from the Illinois Institute of Technology Research Institute (IITRI), completed a study of an all-robotic Automated Mars Surface Sample Return (AMSSR) mission. The small study team had begun work toward their 15 March 1967 report, a direct response to the Planetary JAG's 3 October 1966 PDP, on 26 October 1966. The team argued that an AMSSR mission based on Voyager technology and requiring but a single Saturn V launch could be much cheaper than a piloted flyby with MSSR. It was the first U.S. study of an robotic Mars Sample Return (MSR) mission.

If an AMSSR probe ever flew, however, it would not be derived from Voyager, for that program had come to be seen as an expensive foot in the door leading to an even more expensive piloted Mars mission. Congress cancelled Voyager in August 1967, just before it slashed NASA advance planning funding.

In large part because the Soviet Union had declared that it would explore the Solar System with robots, U.S. robotic Mars exploration fared better than did piloted flybys. Negotiations with Congress in September 1967 led to a promise of funding in FY 1969 for a pair of Mariner Mars orbiter missions in 1971 and a pair of reduced-cost Mars lander/orbiter missions in 1973 in a new program dubbed Viking. 

Sources

Memorandum, J. West, AD/Chief, Advanced Spacecraft Planning to Distribution, "Planetary Exploration Program Study — request for review and comments on systems parameters," NASA Manned Spacecraft Center, 9 May 1966.

Memorandum, R. Hock, DP/Chief, Advanced Programs Office (PPR-2) to Distribution, "Minutes of Joint Action Group Meeting on June 29 and 30, 1966," NASA Kennedy Space Center, 8 July 1966.

Planetary Exploration Utilizing a Manned Flight System, NASA Office of Manned Space Flight, 3 October 1966.

Memorandum, MT/Director, Advanced Manned Missions Program to NASA George C. Marshall Space Center, NASA Manned Spacecraft Center, and NASA John F. Kennedy Space Center, "FY 1967 Advanced Studies Planning," 27 October 1966.

Telex, Edward Z. Gray, Dir, Advanced Manned Missions Program, NASA Office of Manned Space Flight, to NASA MSFC Huntsville, NASA MSC Houston, and NASA KSC FLA, 2 December 1966.

Telex [Priority], E. Z. Gray, Director Advanced Manned Missions Program to NASA MSFC Huntsville ALA, Kennedy Space Center FLA, and MSC Houston TEX, 27 January 1967.

Humans to Mars: Fifty Years of Mission Planning,1950-2000, NASA SP-2001-4521, Monographs in Aerospace History #21, David S. F. Portree, NASA Headquarters History Office, February 2001, pp. 23-32. 

More Information






Samuel Herrick's "Outrageously Innovative" Proposal (1971)

Radar image of 1620 Geographos. The white dot at the center of the image marks the axis of rotation, which points toward the viewer. Dots along the left side are a kilometer apart. The image is a compilation of multiple radar returns. Image credit: NASA Jet Propulsion Laboratory. 
The National Geographic Society-Palomar Observatory Sky Survey (NGS-POSS) imaged the sky from the North Celestial Pole to about 30° south declination between November 1949 and December 1958. The NGS-POSS was not conceived as a search for asteroids, but inevitably they appeared as streaks on many of its nearly 2000 glass photographic plates. 

On 14 September 1951, for example, NGS-POSS astronomers Rudolph Minkowski and Albert George Wilson discovered asteroid 1951 RA. By noting its position on plates made as early as 31 August 1951, they were able to determine that it travels around the Sun in an inclined orbit that crosses the orbits of Earth and Mars. It completes an orbit every 508 days.

They determined that their new-found asteroid never comes very close to Mars — when it crosses the Red Planet's orbit about the Sun it is well above the orbital plane. When it crosses Earth's orbit, on the other hand, it is very near the orbital plane. As a result, it can pass very close to Earth. Soon after it was discovered, astronomers determined that 1951 RA would pass near Earth in 1969. 

1951 RA was of sufficient interest to be made the 1620th named asteroid. In 1956, it was dubbed 1620 Geographos in honor of the National Geographic Society, which funded the NGS-POSS. The name Geographos means "geographer" in Greek.

1620 Geographos became a subject of special interest for University of California at Los Angeles astronomer Samuel Herrick. Following the 1969 close flyby, during which he refined knowledge of the parameters of its orbit, Herrick calculated that 1620 Geographos would pass close to Earth in 1994. He believed that its "ominous" orbit meant it stood a very good chance of striking Earth sometime during "the Third Millennium" (that is, in the interval between the years 2001 and 3001). 

Herrick presented his results at the International Astronomical Union's Physical Studies of the Minor Planets colloquium held at Kitt Peak Observatory in March 1971. His contribution did not, however, appear in the colloquium proceedings NASA published later that year. Herrick subsequently passed away at age 62 on 24 March 1974.

According to Dutch-American astronomer Tom Gehrels, editor of the proceedings of the 1971 meeting, Herrick turned his contribution into a proposal to use 1620 Geographos as a planetary engineering tool that might infuse Earth's crust with new mineral wealth. This led the Gehrels and referees of the 1971 proceedings to declare Herrick's contribution to be "premature" and "outrageously innovative" and reject it. 

Before the decade was out, Gehrels had an apparent change of heart. In 1979, he edited the first Asteroids compilation volume. Published by The University of Arizona Press, it included more than 50 papers summing up the field of asteroid studies. Among them was the review draft of Herrick's 1971 paper. 

Herrick proposed a two-phase plan spanning about five years which would, he declared, generate much greater public enthusiasm than the Apollo lunar landings. In the first phase, engineers would used unspecified propulsive means to push 1620 Geographos into a safer orbit and "explosive cleaving" to separate a portion of the asteroid and push it toward Earth. 

The second phase would see the separated portion guided toward an impact on the Isthmus of Panama. Herrick painted a target on the Atrato River in Colombia, which, he explained, had been proposed in the year 1540 as the site for a canal linking the Caribbean Sea and the Pacific Ocean. 

On 25 March 1994, the impactor would streak through midnight skies over the cities of Quito, Bogota, and Medellin on its way to a "rendezvous" with the "jungle wasteland of northwestern Colombia." The resultant impact crater would form a "new canal from sea to sea." The "interocean Crater-Canal" would include no locks — it would be a sea-level passage through the isthmus that would permit the mixing of Caribbean and Pacific waters.

Herrick assumed that 1620 Geographos would be made of "nickel and the heavier elements that are mostly locked in the earth's core: rhenium, osmium, iridium, platinum, gold, etc." The impact would, he estimated, deposit on Earth extraterrestrial minerals worth $900 billion. They would be collected from the water-filled crater as Earth's supply of these valuable minerals became depleted. 

Herrick acknowledged that potential regional and global ecological effects of the 1994 impact would have to be carefully studied. He also acknowledged that 1620 Geographos might not be made of useful metals. He suggested that the techniques developed to deflect most of the asteroid away from Earth and excavate the canal in 1994 could, if necessary, be applied to another, more mineralogically suitable Earth-approaching asteroid. Searching for a new candidate impactor could also reveal future threats to Earth.

In 1994, 20 years after Herrick's passing, 1620 Geographos orbited nearer Earth than it had in two centuries. It did not, however, pose a threat — at its closest approach it passed about five million kilometers away (about 12 times the distance between the Earth and the Moon). The asteroid will not pass as close again until the 26th century. Earth is safe from 1620 Geographos on a time-scale of millions of years.

On 25 January 1994, the Clementine spacecraft lifted off from Vandenberg Air Force Base, California, bound for the Moon and 1620 Geographos. The spacecraft was intended to collect scientific data while demonstrating sensor and miniaturized spacecraft technologies that could be applied to ballistic missile defense systems. After a leisurely one-month transfer, Clementine orbited over the poles of the Moon for about two months (it was the first lunar polar orbiter). 

On 3 May 1994, Clementine began a circuitous transfer to 1620 Geographos. Had it succeeded, it would have become the first spacecraft to fly by a near-Earth asteroid. Unfortunately, a computer malfunction on 7 May caused Clementine to fire one of its thrusters continuously, expending most of its remaining propellant supply and imparting a spin rate sufficient to render most of its instruments ineffective.

During the 1994 close approach Earth-based radar studies showed that 1620 Geographos is five kilometers long by about two kilometers wide. It is probably a "rubble pile" made up of many small asteroids loosely bound by mutual gravitational attraction. Earth-based studies have also revealed that it is a mainly stony asteroid not especially rich in metals. 

Sources

"Voyage to the Planets," Kenneth F. Weaver, National Geographic, Volume 138, Number 2, August 1970, pp. 174-178.

"Exploration and 1994 Exploitation of Geographos," Samuel Herrick, Asteroids, Tom Gehrels, editor, The University of Arizona Press, 1979, pp. 222-226.

Dictionary of Minor Planet Names, Lutz D. Schmadel, Springer-Verlag, 1992, p. 211.

More Information

To Mars By Way of Eros (1966)

MIT Saves the World: Project Icarus (1967)

Multiple Asteroid Flyby Missions (1971)

Earth-Approaching Asteroids as Targets for Exploration (1978)

"A Vision of the Future": Military Uses of the Moon and Asteroids (1983)

Engineer Special Study of the Surface of the Moon (1960-1961)

Engineer Special Study Sheet 1: Generalized Photogeologic Map of the Moon. Please click to enlarge. Image credit: USGS.
The race to the Moon began on 17 August 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 re-designated Pioneer 0.) Able 1's first stage, a Thor missile, exploded just 77 seconds after launch from Cape Canaveral, Florida, ending the world's first attempted lunar mission.

A month later, on 23 September 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 11 October 1958, the 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 1 October 1958. NASA absorbed most Department of Defense space projects, though in practice the USAF and U.S. Army continued to carry out missions while interagency relations and lines of command became defined.

Able 2, later re-designated Pioneer 1, burned up in Earth's atmosphere on 13 October after its Able rocket 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 unnumbered 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 (8 November 1958) and another Luna impactor (4 December 1958) fell victim to premature launch vehicle shutdowns. Pioneer 3 (6-7 December 1958), the first NASA/Army Moon probe, was launched on a U.S. Army Juno II, not a USAF Thor-Able, but performed much as had Pioneer 1.

First attempt: Thor-Able 1 launches Pioneer 0 (17 August 1958). Image credit: Air Force Air & Space Museum. 
On 3 January 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 U.S. Army launched the Pioneer 4 lunar flyby spacecraft two months later (3 March 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 18 June 18 1959. Then, on 14 September 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. Three weeks later (6 October 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 26 November 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 U.S. Army and USAF rocketeers.

The U.S. Army and the USAF studied lunar surface bases even after the creation of NASA. The Army Ballistic Missile Agency emphasized 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.

Moon fort: Project Horizon lunar base. In this painting from 1959, a U.S. Army crew lander arrives at the landing field in the background, beyond which lies a jagged line of mountains. In the foreground, habitat modules are buried in an excavated ditch for micrometeoroid protection. Image credit: National Air & Space Museum.
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 4 October 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 alien 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. 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. USGS published a second edition with "minor revisions" the following year.

The "Engineer Special Study" was significant in part because its Sheet 1 (top of post), 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. 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.

Their stratigraphic map, though pioneering, was too simplistic to accurately portray the Moon's history. Most of the maria basins formed at different times during the first billion or so years of lunar history, so features associated with them often overlap. An impact crater blasted into an older mare (Latin for "sea") 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, 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 and samples of the Moon's complex terrain.

Engineer Special Study Sheet 2: Lunar Rays. Please click to enlarge. Image credit: USGS.

Engineer Special Study Sheet 3: Physiographic Divisions of the Moon. Please click to enlarge. Image credit: USGS.
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. 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. 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 [M]oon's surface, and possible only by carefully selected routes." Construction would be "very difficult because of blocky material and steep slopes."

James Irwin salutes Old Glory at Hadley-Apennine in a photograph captured by Apollo 15 Commander David Scott. The Lunar Module Falcon and the Lunar Roving Vehicle Scott and Irwin used to explore the Hadley-Apennine site glitter in the harsh morning sunlight. The surface material around Falcon is rolling and loose with few large rocks. Mount Hadley Delta, about 4000 meters tall and rounded by billions of years of small meteoroid impacts, stands behind Irwin and Falcon. Image credit: NASA.
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. 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 or 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 31 July 1964, Ranger 7 returned more than 4300 photos of the area between Oceanus Procellarum and Mare Nubium. 

Mason and Hackman had 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.

Mind the crease: the Riphaeus Section from Sheet 3. Ranger 7 impacted the Moon southwest of the heavily degraded Fra Mauro crater, which is marked by a dashed outline at center right. Please click to enlarge. Image credit: USGS.
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. 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 10 January 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.

Closeup of Sheet 2: Tycho and the adjoining Macrocrater Province. Please click to enlarge. Image credit: USGS.
Mason judged that landing and movement would be difficult near Tycho. The latter would be possible, however, if a safe travel 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. 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. 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 rover operations, however.

Tycho's rocky flank: the view from Surveyor 7. Image credit: NASA.
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 U.S. 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 31 October 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 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. Wilhelms, The University of Arizona Press, 1993, pp. 37-42.

More Information

Around the Moon in 80 Hours (1958)

"Essential Data": A 1963 Pitch to Expand NASA's Robotic Exploration Programs

Apollo Science and Sites: The Sonett Report (1963)

An Apollo Landing Near the Great Ray Crater Tycho (1969)

Log of a Moon Expedition (1969)

Could the Voyages in the Film and Novel "2001: A Space Odyssey" Really Happen? (Part 1)