Five options for NASA's future (1970)

The NASA Headquarters Office of Manned Space Flight created its Advanced Manned Missions Program as part of its efforts to put in motion the Integrated Program Plan (IPP) set out in its September 1969 report to Nixon's Space Task Group (STG) and endorsed (with reservations) in the STG's report to the President. In January 1970, Philip Culbertson became the program's director. In an April 29, 1970 memorandum, Lee Scherer, director of the Apollo Lunar Exploration Office, laid out five "tentative" post-Apollo lunar program options for Culbertson to present to the NASA Manned Space Flight Management Council in May 1970.

The first three options assumed no restart of the Saturn V assembly line, which NASA Administrator Thomas Paine had declared to be permanently closed on January 13, 1970. Option 1 was to continue with NASA's plans as of April 1970 without change. Apollo missions would end with Apollo 19 in early 1975. Apollos 18 and 19 were, however, "under review," so the Apollo Program might conclude as early as 1972. The IPP had NASA bringing online its Earth Orbit Space Station (EOSS) and winged reusable Earth-to-Orbit Shuttle (EOS) by 1977. The EOSS would serve as base for reusable piloted Tugs and reusable Nuclear Shuttles. When mated to a Nuclear Shuttle, a Tug would be capable of reaching the moon. NASA planned to use this infrastructure in 1981 to establish a Lunar Orbit Space Station (LOSS) with a propellant depot. A Lunar Surface Base (LSB) would follow no earlier than 1985 (see images at the top of this post).

This baseline program would, Scherer explained, create a "large gap" in lunar exploration lasting from seven to nine years, during which interest in the moon would "atrophy." "Reusable hardware generally may be expensive to build, to use and to refurbish," Scherer noted, adding that "lunar science objectives do not need the heavy traffic that would support such reusability." He told Culbertson that the LOSS might not be needed, and that his office viewed neither the Nuclear Shuttle nor the LOSS propellant depot "as clear requirements."

Scherer's Option 2 was a "Shuttle/Tug lunar program." The EOS and a reusable piloted Tug without EOSS, LOSS, and Nuclear Shuttle would enable piloted lunar orbit and landing missions by 1979, he told Culbertson. He stressed that, to enable this option, lunar mission requirements would need to play a role in the drafting of Shuttle and Tug sizing and performance requirements. As envisioned by Scherer, two Tugs would suffice to place astronauts in lunar orbit, while four Tugs would allow astronauts to land on the moon. A pair of landings at a single site would be sufficient to establish a temporary "minibase" by 1982.

Option 3 was for NASA to pursue a wholly automated lunar program. Humans would cease to travel to the moon in 1974 with Apollo 18. NASA would follow Apollo with a series of five automated lunar exploration missions spanning 1976-80. Each would include an orbiter and a rover capable of long-distance traverses. If based on Viking Mars technology, which was under development at this time, the automated lunar program might cost a total of $1.3 billion. It would "extend lunar exploration & fill gaps left by Apollo," "provide precursor data for [a] Lunar Surface Base," "contribute data toward Mars exploration," and "offer [an] opportunity for international cooperation," Scherer explained.

Scherer's final two options assumed that the Saturn V assembly line would be restarted. His "Stretched-Out Apollo Program" would need two or three additional Saturn V rockets. Beginning with Apollo 18 in 1974, "gap-filler" missions would occur annually, though Apollo 19 might be delayed by the launch of the Skylab II space station. The program would end with Apollo 21 in 1978, or Apollo 22 in 1979. Designated "J-class," each mission would carry a small open rover. They would also include technology experiments with application to the LSB, which would be established in 1981.

Scherer's final option was to turn back the clock to the Johnson Administration. From the early 1960s on, NASA and its contractors had proposed a range of Apollo-derived vehicles for advanced space missions, including post-Apollo moon flights. In 1965, these studies had become the basis for the Apollo Applications Program (AAP), which for a time in 1966 included about 40 piloted Earth-orbital and lunar missions. That Apollo-derived spacecraft might reach the moon in the 1970s was believed likely in some quarters as late as 1968. AAP devolved into the wholly Earth-orbital Skylab Program in 1970. Reviving AAP lunar plans would require a NASA budget increase, Scherer told Culbertson. Apollo 19 would fly in early 1975, then a series of five annual dual Saturn V launches would begin in 1976. In each of these, the first Saturn V would place an unmanned shelter/cargo lander, a long-traverse rover, and rocket-powered flyers on the moon; the second Saturn V would then deliver a crew for a lunar stay lasting from two to eight weeks. The program would culminate with an LSB in 1981.

Memorandum with attachment, MAL/Director, Apollo Lunar Exploration Office, to MT/Director, Advanced Manned Missions Program, Post-Apollo Lunar Missions - Input to your May Management Council Presentation, April 29, 1970.

NAR MEM (1968)

In October 1966, NASA's Manned Spacecraft Center in Houston, Texas, awarded North American Rockwell (NAR), prime contractor for the Apollo Command and Service Module (CSM), a contract to study designs for a Mars Excursion Module (MEM) lander. In its January 1968 final report, the company proposed a 30-foot-diameter lander shaped like the Apollo Command Module. NAR's least massive MEM design (65,800 pounds), which would carry only enough life support consumables to support two astronauts on Mars for four days, would operate from a mothership in a low circular Mars orbit. The most massive, a four-person, 30-day MEM with a mass of 108,990 pounds, would operate from a mothership in an elliptical orbit.

NAR described a MEM mission using a four-person design. After the mothership arrived in its assigned Mars orbit, four astronauts would enter the MEM ascent capsule through a docking unit in its nose and strap into couches arranged in two tiers. The MEM would separate from the mothership, point the retropack mounted on its heatshield in its direction of flight, and fire its seven advanced beryllium-fueled solid-rocket motors to slow down and begin descent to the martian surface. After exhausting its propellant the retropack would jettison.

The MEM's blunt, bowl-shaped heat shield would protect it from atmospheric entry heating through ablation; that is, it would char and erode, carrying away heat. The astronauts would experience seven Earth gravities of deceleration during entry. A drogue parachute would open after the lander's speed fell to between Mach 1 and Mach 4.5, creating drag and further slowing the MEM's descent. The drogue would then withdraw a larger ballute ("balloon-parachute"). At an altitude of 10,000 feet, the ballute would detach, taking with it a section of the MEM's upper hull and exposing the ascent capsule windows.

At the same time, a round panel would drop out of the center of the heat shield to expose the descent engine. NAR favored a "plug-nozzle" engine design because it would be smaller and lighter than an equivalent "bell" design. Eight spherical tanks would hold the MEM's liquid oxygen/liquid methane descent propellants. NAR favored this combination because it offered both high performance and "stability" (that is, it would not readily boil off or decompose).

After descent engine ignition, the two astronauts in the top tier would climb from their couches and stand at flight controls located just below the ascent capsule windows. Two minutes of hover time would enable the MEM commander and pilot to inspect their designated landing site before touchdown or move up to 3.6 miles to an alternate site. NAR's MEM could land safely if maximum wind speed at the landing site remained below 340 feet per second (230 miles per hour - in the thin martian atmosphere, the equivalent of a 23-mile-per-hour wind on Earth). Six landing legs would extend with heat shield segments serving as skids. NAR calculated that its MEM could alight safely on a 15° slope.

The MEM would contain two habitable areas: the ascent capsule and the descent stage lab compartment. The latter would include an airlock for access to the martian surface. During their surface stay, the astronauts would rely on fuel cells that would combine hydrogen and oxygen to make electricity, yielding drinking water as a by-product. Breathing oxygen would be stored in cryogenic liquid form, and lithium hydroxide canisters would scrub exhaled carbon dioxide from the MEM's atmosphere.

When the time came to return to the mothership, the MEM ascent stage would blast off from the descent stage using a liquid oxygen/liquid methane plug-nozzle engine. It would climb vertically for five seconds before pitching over to steer toward orbit. The ascent engine would draw propellants from eight conical strap-on tanks. Once exhausted, the propellant tanks would fall away; the ascent engine would then draw on a pair of internal tanks to complete orbit insertion. If the mothership were in elliptical Mars orbit, the MEM ascent stage would first enter an intermediate circular orbit, then would fire its engine a second time to raise its apoapsis (orbit high point) to match orbits. After rendezvous and docking, the astronauts would transfer to the mothership and discard the ascent stage.

NAR's MEM development program assumed a 1974 decision to send people to Mars and a first Mars landing in 1982. The program would include ground tests employing six MEM test articles. Three fully configured MEMs would be needed to carry out the extensive flight-test program, along with three two-stage Saturn V rockets, two uprated Saturn Is, one Saturn IB, a Little Joe, and three Apollo CSM-based Logistics Support Vehicles (LSVs).

In one of the last (and most dramatic) tests of the series, a fully configured MEM would reach Earth orbit in 1979 on a two-stage Saturn V with a piloted LSV on top. In orbit, the LSV would detach, turn end for end, and dock with the MEM to permit crew transfer. The crew would then abandon the LSV and fly the MEM to an Earth landing. NAR placed the total MEM development cost at $4.1 billion.

Definition of Experimental Tests for a Manned Mars Excursion Module: Final Report, Volume I, Summary, SD 67-755-1; Volume II, Design, SD 67-755-2; Volume III, Test Program, SD 67-755-3; Volume IV, Briefing Brochure, SD-755-4; North American Rockwell Corporation Space Division, January 12, 1968.

On the habitability of Mars (1976)

Mars is often thought of as the planet in the Solar System most like Earth, but only because the other planets are even less hospitable. A human placed unprotected on Mars's red sands would gasp painfully in poisonous carbon dioxide air only one percent as dense as Earth's air, pass out in seconds, and perish within two minutes. The corpse would freeze rapidly - the global average temperature of Mars is minus 53° Celsius (-64° Fahrenheit) - then would mummify as the parched atmosphere leached out its moisture. Unshielded ultraviolet (UV) radiation from the Sun would then blacken the desiccated corpse - unless, of course, the ever-present wind-blown dust and sand buried it first.

Most, if not all, of these perils were understood by the authors of this report, six Stanford-Ames Faculty Fellows from universities across the United States. R. D. MacElroy of NASA's Ames Research Center in Mountain View, California, coordinated their study. Its chief product was the 1976 report On the Habitability of Mars: An Approach to Planetary Ecosynthesis, probably the first detailed discussion of terraforming prepared under NASA auspices.

The Stanford-Ames Fellows justified their study, which drew on data gathered by the Mariner 4, 6, and 7 Mars flybys and the Mariner 9 Mars orbiter, by arguing that "there is a distinct possibility that technological developments or the needs of society may make the utilization of Martian resources economically feasible or socially desirable." Permanent Mars settlements might thus become necessary in order to "exploit Mars more efficiently." "The question thus arises," they concluded, "as to whether Mars is a habitable planet or can be made into one."

The Stanford-Ames Fellows noted that the harshest, most Mars-like environment on Earth - the Antarctic Dry Valleys - are far better suited to terrestrial life than the most hospitable environment on Mars. They found, nevertheless, that "specific martian microhabitats" could be habitable by cold-adapted anaerobic bacteria and some forms of blue-green algae and lichen. They cautioned that "[e]ven a most optimistic appraisal suggests that. . . the growth of even these forms would be quite restricted in vigor and extent." Water loss and cold would limit photosynthesis (the conversion of water and carbon dioxide into starch and oxygen using energy from the Sun) in these organisms to a period of about four hours each day, and solar UV radiation would stunt their growth.

Given sufficient time - on the order of 140,000 years - mats of blue-green algae could cover more than a quarter of Mars’ surface and place in its atmosphere the minimum amount of oxygen humans need for respiration. Earth-adapted lichen would need 10 times longer to accomplish the same feat because lichen grows more slowly than blue-green algae. As occurs on Earth, solar UV radiation would then interact with oxygen in the upper atmosphere to produce an ozone layer, largely shielding the surface from further UV influx.

The authors then proposed more aggressive techniques for making Mars habitable. Genetic engineering could, they wrote, tailor terrestrial algae and lichen to existing martian conditions - "in effect, transforming currently available 'best fit' organisms into 'ideal' organisms." Such modifications would be possible, they judged, by "utilizing methods of gene manipulation currently known or under development." At the same time, planetary engineering could "increase enormously the area of the planet available for growth and would optimize the conditions under which such growth would occur."

Job number one for planetary engineers would be to raise Mars's temperature. The Stanford-Ames Fellows cited papers by Carl Sagan, Owen Toon, and others when they proposed that this be accomplished by vaporizing the martian polar ice caps. They noted, however, that the composition of the caps remained poorly understood. Mixing dust or sand into the ice would probably reduce its reflectivity by a few percent, boosting the amount of solar heat it absorbed. Boosting solar heating of the caps by 20% for "about a hundred years or so" would vaporize carbon dioxide ice. The freed carbon dioxide would then produce a modest greenhouse effect on Mars.

More importantly, they stated, the freed gas would thicken the martian atmosphere, improving heat transport from the equator to the poles. Raising polar temperature would melt water ice, placing water vapor - a more powerful greenhouse gas than carbon dioxide - into the air.

As atmospheric temperature and pressure increased, liquid water ("the necessary catalyst for Earth-like planetary evolution") would begin to persist on the surface. The Stanford-Ames Fellows noted, however, that, while theory predicted that Mars outgassed large quantities of water, known or suspected reservoirs - the polar caps, water combined chemically with martian dirt, and permafrost - could account for only a fraction of the water expected. "The unsettled nature of the question of water [on Mars]. . . reveals a serious gap in current knowledge, a gap that is especially significant when trying to project the fate of living terrestrial organisms implanted on the martian surface," they wrote. They also noted the lack of data on other chemical elements essential for life - for example, nitrogen. The Stanford-Ames Fellows concluded that

No fundamental, insuperable limitation to the ability of Mars to support terrestrial life has been unequivocally identified. However, important data are not available. . .These data must be acquired before a more accurate assessment of the habitability of Mars can be made.

On the Habitability of Mars: An Approach to Planetary Ecosynthesis, NASA SP-414, M. M. Averner and R. D. MacElroy, editors, NASA Ames Research Center, 1976.