As early as 1961, some within NASA proposed that a Mars expedition be made the space agency's next goal after Apollo. NASA Administrator James Webb was loath to promote such a goal until after Apollo had achieved its politically motivated purpose of placing a man on the moon by the end of the 1960s. In October 1968, Webb retired, leaving his inexperienced deputy Thomas Paine in charge. In January 1969, as Apollo neared culmination, Richard Nixon entered the Oval Office. Nixon appointed the Space Task Group (STG), but otherwise placed a low priority on setting NASA's future course.

In October 1969, Mars supporters within NASA found comfort when the STG endorsed - with reservations - NASA's own proposed blueprint for its future. The NASA plan was based on the Integrated Program Plan (IPP) developed by the NASA Headquarters Office of Manned Space Flight (OMSF). NASA's plan culminated in a Mars expedition in 1981, 1983, or 1986, while the STG report only called for a Mars expedition by the end of the 20th century.

Nevertheless, many hoped that Nixon would follow the STG's advice and declare a Mars expedition to be NASA's next major goal. This optimism led OMSF to establish the Manned Planetary Missions Requirements Group (PMRG), which included representatives from NASA Headquarters and several NASA field centers. The PMRG can be seen as the successor to the Planetary Joint Action Group, which studied Mars landings and piloted Mars/Venus flybys between 1965 and 1967.

The PMRG first met formally in December 1969. Not insignificantly, that same month OMSF chief George Mueller, the driving force behind the IPP, left NASA for private industry. Hoped-for White House support for Mars exploration never materialized, though the Nixon Administration paid lip service to a piloted Mars expedition by the end of the 20th century. At the same time, it slashed NASA's budget, leading Paine to cut three manned lunar landings from the Apollo Program and cancel the Saturn V, the largest and most powerful rocket ever launched. By the end of 1970, Paine also departed NASA, which subsequently shifted most of its efforts to reusable winged spacecraft development. Nixon made the Earth-orbital Space Shuttle NASA's post-Apollo piloted program in January 1972.

NASA's Mars aspirations died with a whimper - a call to NASA centers participating in the PMRG for reports summing up their Mars study activities. PMRG work at the Manned Spacecraft Center (MSC) in Houston, Texas, resided in the Advanced Studies Office, Engineering and Development Directorate, under leadership of Morris Jenkins. The chief guiding principle of MSC PMRG work was "austerity." According to Jenkins,

to improve the probability of a future [Mars] program. . .an austere version should be considered. . .[S]uch a concept would be consistent with an initial expedition. . .[E]verything has been done to make [this study] a useful point of departure when national priorities and economic considerations encourage the mounting of a manned Mars expedition.

A manned Space Shuttle booster releases Image: NASA. A manned Earth Orbit Shuttle Booster releases a Chemical Propulsion Stage with attached manned Mars spacecraft module. Image: NASA.

MSC called for an 11-year development and test period leading to a 570-day initial Mars expedition in 1987-1988. It assumed the existence by that time of a reusable Earth Orbit Shuttle (EOS) consisting of a winged piloted Booster and winged piloted Orbiter with a cylindrical payload bay 15 feet in diameter. The study rejected the notion of launching Mars spacecraft components in the EOS Orbiter payload bay because as many as 30 modules would have to be launched separately and brought together in orbit, yielding a "complex and lengthy assembly and checkout process."

121, "LOW CROSS RANGE LAUNCH ARRANGEMENT" ARTIST UNKNOWN, OIL, BUILDING 4203/1203 ART GALLERY STORAGE. Fully reusable Earth Orbit Shuttle with manned Booster and manned Orbiter. Image: NASA.

MSC proposed instead to launch 24-foot-diameter Mars ship modules on the back of the EOS Booster with help from a Chemical Propulsion System (CPS) upper stage. The CPS, which would have a mass of 60,000 pounds empty, would hold up to 540,000 pounds of liquid oxygen/liquid hydrogen propellants, and would use the same rocket engine and propellant tank designs as the EOS Booster and Orbiter. The EOS Booster would carry the CPS and Mars ship module partway to orbit, then would separate to return to its launch site. The CPS would then ignite to place itself and its payload into assembly orbit. The CPS stages would be refueled in orbit by EOS Orbiters acting as tankers and reused as the Mars ship’s propulsion stages.

Mars ship assembly would require 71 EOS launches. Launch 1 would place CPS #5 and the 110,000-pound Mission Module (MM) into Earth orbit. The MM, the Mars crew’s living quarters, would also serve as the Earth-orbital construction base during Mars ship assembly. Launch 2 would place in orbit CPS #6 and the 33,000-pound Electrical Power System (EPS) module, and launch 3 would place into orbit CPS #4 and the 12,000-pound payload hangar. Launches 4, 5, and 6 would place into orbit CPS modules #3, #2, and #1, respectively. Launches 7 through 71 would see EOS Orbiters pump three million pounds of liquid hydrogen/liquid oxygen propellants into the six CPS modules from tanks in their payload bays.

The assembled Mars ship would include at its front end the payload hangar bearing the mission's 110,000-pound Mars Excursion Module (MEM) lander and 31,000 pounds of automated Mars/Venus probes. Next would come the four-deck MM. Decks 1 and 2 would constitute the MM's primary pressurized volume, while decks 3 and 4 would serve as the backup pressurized volume. Either volume could be sealed off if it lost pressure, became contaminated, or was otherwise rendered uninhabitable. Deck four would also serve as the spacecraft's thick-walled solar flare radiation shelter.

The 65-foot-long EPS module would carry pressurized gas storage tanks and two wing-like solar arrays. The arrays, which together would have a mass of 15,000 pounds, would be of relatively flimsy construction and could be degraded by hard radiation, so would be designed to be retracted during propulsive maneuvers and solar flares.

A tunnel doubling as an airlock would run between an extravehicular activity hatch in the forward payload hangar through the MM to a hatch leading aft into the EPS module. The airlock tunnel would also provide access to docking ports on MM decks 1 and 3.

The front end of CPS #6 would attach to the aft end of the EPS module. The front end of CPS #5 would attach to the aft end of CPS #6, the front end of CPS #4 would attach to the aft end of CPS #5, and the front end of CPS #3 would attach to the aft end of CPS #4. CPS stages #1 and #2 would be mounted on either side of CPS #3, with CPS #1 in starboard position and CPS #2 in port position.

For Earth-orbit departure, the twin solar arrays would be retracted, then a series of propulsive maneuvers would take place over several orbits. Maneuver 1 would see CPSs #1 and #2 ignite and burn to depletion to place the Mars ship into an elliptical "intermediate orbit" with its perigee at assembly orbit altitude. The spent CPSs would then separate. Maneuver 2 would occur at next perigee, when CPS #3 would ignite to boost the Mars ship's apogee, placing it in an elliptical "waiting orbit." For maneuver 3, CPS #3 would ignite at apogee to adjust the plane of the Mars ship's departure path. CPS #3 would then separate. Space tugs would later recover CPS stages #1, #2, and #3 for re-use.

PMRG manned Mars spacecraft. Image: NASA.

Maneuver 4 would see CPS #4 ignite at next perigee, placing MSC's Mars ship on course for Mars. CPS #4 would then separate and not be recovered. The crew would extend the solar arrays, then would spin the Mars ship end over end about twice per minute to produce artificial gravity in the MM equal to one-sixth of Earth's gravity (that is, one lunar gravity). The spin axis would remain located in the forward third of CPS #6 (the CPS stage nearest the EPS module) throughout the expedition.

CPS #5 would perform any necessary course correction maneuvers during the six-month flight to Mars, then would ignite to slow the Mars ship so that the planet's gravity could capture it into a 200-by-10,000-mile orbit. A spacecraft entering an elliptical Mars orbit would need less arrival and departure propellant than one entering a circular Mars orbit, MSC found. CPS #5 would then separate.

The five-person crew would spend the next 15 days in orbit studying Mars and preparing the MEM for landing. The MSC PMRG report proposed a two-stage conical MEM similar to a 1967 North American Rockwell design. The MEM Pilot/Geologist (who would also serve as backup Systems Engineer), Physician (backup Bioscientist), and Bioscientist (backup Med tech/Deputy MEM pilot) would then separate from the payload hangar in the MEM, leaving behind the Commander/Primary Spacecraft Pilot (backup Med tech/Systems Engineer) and Systems Engineer (Deputy Commander/backup Primary Spacecraft Pilot) to mind the mother ship in orbit.

The MEM crew would spend 45 days exploring Mars using a pair of small unpressurized rovers resembling the Apollo Lunar Roving Vehicle. The electric rovers would have a maximum speed of 10 miles per hour. During surface excursions, one crewmember would remain in the MEM at all times while the other two drove one rover each. This "tandem convoy" arrangement would circumvent the onerous "walk back" limitation imposed by single rover use. If both astronauts rode a single rover and it broke down, they would have to walk back to the MEM. Maximum walk-back distance would be limited less by astronaut stamina than by the amount of water and air the Mars suit backpacks could hold. The tandem convoy approach meant that, if one Mars rover failed, the functional rover could return both crewmembers safely to the MEM. The rovers would each include a tow hook for returning the failed rover to the MEM for repairs.

Right at Home in Extreme Conditions ———————————– Basler BT-67s have served in both the Arctic and Antarctic for years. Here a trio of turbine converted DC-3s operated by Kenn Borek Air sit on skis near McMurdo Station. That's Mount Erebus in the background. Photo: Basler Turbo Conversions Mars Excursion Module cutaway. Image: North American Rockwell/NASA.

The area available to two mutually supportive rovers would total 8000 square miles, compared to only 80 square miles for a single rover, MSC determined. Maximum rover range would be 100 miles, but this could be extended by carrying extra batteries. A one-day rover traverse (10 hours outside the MEM) could cover up to 84 mile. Once every 15 days, a 36-hour traverse of up to 152 miles could occur, with the astronauts sleeping overnight on the parked rovers in their hard-shelled aluminum Mars suits.

The astronauts would collect samples of martian rock and soil with emphasis on gathering possible life forms. According to MSC, the "potential for even elementary life to exist on another planet in the solar system may. . .be the keystone to the implementation of a manned planetary exploration program. . .[M]an's unique capabilities in exploration could. . .have a direct qualitative impact on life science yield." The report assumed that equipment and procedures could be developed to prevent the astronauts from contaminating the samples during collection.

After 45 days of exploration, the crew would blast off from Mars in the MEM ascent stage and dock with one of the docking ports (ideally the deck 3 port) on the side of the MM. The MEM crew would use the Backup Pressurized Volume as a quarantine facility until the danger of spreading martian contagion to the other two crewmembers was judged to be past. Any living organisms the astronauts collected would be transferred to a Mars environment simulator in the MM. The spent MEM ascent stage would then be cast off.

CPS #6 would ignite at periapsis to begin the 330-day voyage from Mars to Earth. The astronauts, meanwhile, would begin preliminary studies of the Mars samples to record data on life forms that might not survive the trip to Earth laboratories.

During return to Earth, the Mars spacecraft would fly past Venus. MSC's study favored a Venus swingby-type expedition over an opposition-class short-stay expedition with less than 15 days at Mars and a total duration of less than 450 days. It also rejected a conjunction-class long-stay expedition with a 360-to-560-day stay at Mars and a total duration of 900 to 1100 days.

The opposition-class expedition would have an Earth-return speed of from 50,000 to 70,000 feet per second. This would mean that, if it used no form of aerobraking, it would need to carry up to 30 million pounds of propellants to slow itself enough to achieve an elliptical Earth orbit. Earth return would add nothing to the Mars ship's propellant load if, just prior to Earth arrival, the crew abandoned the Mars ship in a small Earth-return capsule capable of withstanding high atmosphere-reentry speeds. The report pegged the cost of developing and testing such a capsule at more than $2 billion, a pricetag it judged was "certainly not consistent with austerity."

By contrast, propellant needed for the conjunction-class mission, with its long Mars stay, would total only 1.4 million pounds. MSC judged, however, that

to fully utilize the year or more of surface activity, the scientific plan would be extremely complex. Even with the aid of precursor automated programs it is probable that the correct emphasis [for scientific studies] could not be predicted. . .The tendency would be to supply experimental equipment to take advantage of possible discoveries of interest. The cost of covering the scientific equipment, and maintaining monitoring support from earth scientists, would more than offset the economy in propellant. . .it is too expansive for an initial mission.

MSC found that the mission's detour past Venus would permit an expedition with a short stay at Mars and propulsive Earth-orbit capture with the same total propellant load as the opposition-class expedition with high-speed capsule reentry. CPS #6 would slow the Mars ship so that Earth's gravity could capture it into an elliptical orbit. The MM would then separate, and a space tug would be dispatched to dock with it and circularize its orbit at an altitude accessible to an EOS. The EOS would then dock with the MM to retrieve the Mars expedition crew and Mars samples. Upon landing on Earth, crew and samples would be transferred to "appropriate surface quarantine facilities."

MSC's PMRG report received only limited distribution within NASA and virtually no attention outside the agency. Formal studies within NASA aimed at sending humans to Mars would not occur again until the 1980s.

The Mariner 9 spacecraft included a large propulsion module so that it could enter orbit about Mars. . Image: NASA. The Mariner 9 spacecraft included a large propulsion module so that it could enter orbit about Mars and a complex TV imaging package. Image: NASA.

1970s NASA was, however, not through with Mars. Even as MSC completed its report, the robotic Mariner 8 and Mariner 9 Mars orbiters were entering the final stages of preparation for launch. Mariner 8 lifted off on May 9, 1971, and fell into the Atlantic after its Centaur upper stage tumbled out of control. Mission planners activated plans for a one-spacecraft Mars orbiter mission put in place more than a year earlier and launched Mariner 9 on 30 May 1971. The spacecraft took advantage of the extremely favorable 1971 Earth-Mars transfer opportunity, and arrived in Mars orbit on 14 November 1971.

The first Mars orbiter, Mariner 9 waited out a planet-enveloping dust storm that hid nearly all the planet's features; then, as the dust settled in December 1971 and January 1972, it began to map the entire planet in detail for the first time. Scientists viewing Mariner 9 images discovered the great volcanoes of Mars, including Olympus Mons, the largest mountain in the Solar System, and Mars's great equatorial canyon system, which they named Valles Marineris to honor Mariner 9. They also found signs of flowing water in Mars's past: enormous flood channels and smaller branching features. By the time it ran out of compressed nitrogen steering gas and was turned off on 27 October 1972, the robotic spacecraft had exceeded both its own pre-launch mission objectives and those of Mariner 8.

Reference:

Manned Mars Exploration Requirements and Considerations, Morris V. Jenkins, NASA Manned Spacecraft Center, February 1971.

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