25 December 2015

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

A NASA Manned Spacecraft Center-designed piloted flyby spacecraft departs Earth orbit. A series of three Saturn S-IVB stages would have ignited in turn to place the spacecraft on its interplanetary trajectory. The stylized image above shows two spent S-IVB stages, the third S-IVB with its single J-2 engine firing, and the piloted flyby spacecraft with portholes and a streamlined cover over its large telescope. In most piloted flyby plans, the Earth-departure burns together constituted the only significant propulsive velocity change of the mission. Image credit: NASA
During its first decade (1958-1968), NASA devoted more advance planning study effort to piloted Mars and Venus flybys than it did to piloted Mars landings. Piloted flyby missions to the nearest planets were seen as the most ambitious voyages beyond the moon potentially feasible in the 1970s. Such missions could, many believed, employ modified, upgraded Apollo spacecraft and Saturn rockets to serve as low-cost "bridge" missions linking planned temporary Earth-orbiting space stations of the early 1970s and piloted Mars landings and Venus orbiters of the early-to-mid 1980s. In this respect, they would be as Project Gemini was for Project Mercury and Project Apollo.

Despite the effort spent on them, NASA's 1960s piloted flyby plans are little remembered today. Proposals for piloted flybys in recent years almost never cite the mass of study documents NASA and its contractors generated half a century ago. Even careful historians confuse piloted flyby mission proposals and spacecraft designs with piloted landing proposals and spacecraft.

The NASA Headquarters-led Planetary Joint Action Group (JAG), which included representatives from Marshall Space Flight Center, Kennedy Space Center, and the Manned Spacecraft Center in Houston, proposed in a pivotal October 1966 internal report that the first piloted Mars flyby mission should depart Earth orbit in September 1975. The four-person Apollo-derived flyby spacecraft would swing past Mars in late January-early February 1976 and return to Earth in July 1977.

As it flew past Mars, its crew would release a number of automated probes. At least one would soft-land, collect samples of Mars rocks, dirt, and air, and launch them to a hermetically sealed laboratory on board the piloted flyby spacecraft for initial study and transport to labs on Earth.

Except for modest course corrections, no propulsion would be needed after the piloted flyby spacecraft left Earth orbit. This was one of the mission's great attractions. As they neared Earth, the flyby astronauts would abandon the piloted flyby spacecraft and reenter the atmosphere in a beefed-up Apollo Command Module.

In its report, the Planetary JAG described several candidate follow-on piloted flyby missions for the remainder of the 1970s. Of great scientific interest was a "triple-flyby" mission, in which the piloted spacecraft would fly past Venus, then Mars, then Venus again, before returning to Earth. As with the simpler September 1975 Mars flyby mission, only minor course adjustments would be necessary after the triple-flyby spacecraft left Earth orbit.

Venus flyby: the piloted flyby spacecraft depicted in Earth-orbital launch configuration at the top of this post is shown here with its telescope, solar arrays, dish antennas, and Venus mapping radar antenna deployed. A robotic Venus atmosphere-entry probe - perhaps a lander - is shown departing the flyby spacecraft probe compartment. This NASA Manned Spacecraft Center concept, never described in a formal report, dates from near the end of the 1960s period of piloted flyby planning. Image credit: NASA 
Unfortunately, the only opportunity to begin a triple-flyby in the late 1970s known in 1966 was poorly timed. The spacecraft would need to depart Earth in February 1977, while the 1975 Mars flyby mission was still underway. This would create operational difficulties - NASA would need to operate two piloted planetary missions at once - and would deprive the space agency of the opportunity to apply lessons learned from the September 1975 flyby mission. No other opportunity to begin a triple-flyby mission was known before 1983. Planetary JAG planners assumed that by that date NASA would have moved on to piloted Mars landings and Venus orbiters.

In September 1967, J. Bankovskis and A. Vanderveen, advance planners with NASA contractor Bellcomm, identified a triple-flyby opportunity with an optimum Earth-departure date of 26 May 1981. A spacecraft launched from Earth orbit on that date would fly past Venus on 28 December 1981, past Mars on 5 October 1982, and past Venus again on 1 March 1983. It would return to Earth on 25 July 1983. Mission duration would total 790 days. Departures on other dates within a 30-day launch window would yield mission durations of from 720 days to 850 days.

Discovery of the 1981 triple-flyby opportunity led Vanderveen to look for other triple-planet flyby opportunities researchers had missed. In October 1967, a year after the Planetary JAG completed its report, he announced that he had determined that a previously known November 1978 "dual-planet" (Venus-Mars) flyby mission opportunity could be slightly modified to create a new triple-flyby opportunity.

Vanderveen wrote that, if one assumed a launch from Earth orbit on 28 November 1978, then the triple-flyby spacecraft would pass Venus on 11 May 1979, Mars on 25 November 1979, and Venus again on 29 January 1980. Return to Earth would take place on 31 January 1981. Mission duration would total 800 days. Earth departure on other dates within a 35-day launch window could reduce mission duration to 760 days.

Vanderveen explained that the two Venus flybys would have different qualities, so they would require different scientific programs. In both, the flyby spacecraft would pass about 1200 miles from Venus. On 11 May 1979, the triple-planet spacecraft would race past the center of the dayside hemisphere, its ground track nearly paralleling the Venusian equator. This, Vanderveen wrote hopefully, might permit visible-light mapping through breaks in the dense Venusian clouds.

The southern hemisphere of Venus as imaged by the European Space Agency's Venus Express orbiter. Image credit: ESA
The 29 January 1980 Venus flyby, on the other hand, would see the spacecraft slowly approach the planet's dayside southern hemisphere. It would pass closest to Venus 30° south of the equator near the terminator (the line between day and night), then would recede from Venus's nightside hemisphere. Vanderveen recommended that the flyby crew turn infrared sensors and a mapping radar toward the night side as they flew away from Venus and began their year-long return to Earth.

Piloted flybys did not become part of NASA's 1970s program for several reasons. NASA split over the efficacy of the piloted flyby mission concept, with the Manned Spacecraft Center in particular favoring as bridge missions piloted Mars and Venus orbiters over piloted flybys.

More important was a toxic political climate, which was partly of NASA's making. Increasing U.S. military involvement in Indochina drove up the Federal budget deficit, leading to cuts in many programs, including the space program.

The Apollo 1 fire (27 January 1967) damaged the relationship between NASA and Congress at this critical time, increasing the space agency's vulnerability to funding cuts. The fire broke out during a pre-flight test inside the first Apollo Command and Service Module (CSM) spacecraft scheduled to fly with a crew on board. Astronauts Gus Grissom, Ed White, and Roger Chaffee perished. It emerged that CSM contractor North American had delivered to NASA CSM spacecraft containing many manufacturing flaws, yet NASA had not shared this fact with Congress.

Efforts by NASA Headquarters under Administrator James Webb and the Lyndon Baines Johnson White House to secure substantial funding for post-Apollo piloted spaceflight, including piloted flybys, had switched into overdrive just before the Apollo 1 fire, so became a lightning-rod for Congressional displeasure. In August-September 1967, Congress slashed the Apollo Applications Program (AAP) budget request for Fiscal Year 1968 and heaped scorn on piloted and robotic Mars plans.

AAP, a series of Earth-orbital temporary space station and advanced moon missions based on Apollo hardware, shrank rapidly during the following year. The only U.S. automated probe program planned for the 1970s, the Voyager Mars/Venus program, was cancelled outright in part because the Planetary JAG had relied heavily on Voyager heritage for its piloted flyby automated probe designs.

NASA adapted to adversity, turning AAP into the Skylab Program (three three-man long-duration stays on board one Orbital Workshop space station) and the advanced Apollo J-class missions (Apollo 15, 16, and 17). The space agency also successfully negotiated with Congress for a new program of automated Mars spacecraft based on the low-cost Mariner design (Mariner 9 and Viking 1 and 2).

Piloted flybys would, however, never recover, in part because in early 1969, under the leadership of new NASA Administrator Thomas Paine, NASA advance planning became increasingly grandiose. Paine told NASA Center directors to "think big" in anticipation of riding the wave of spaceflight enthusiasm he expected would follow the first piloted moon landing.

The result was an elaborate Integrated Program Plan (IPP) with a 12-man Space Station evolving into a 100-man Earth-orbital Space Base, reusable winged Space Shuttles, uprated Saturn V rockets, a lunar base, reusable Nuclear Shuttles for transport within cislunar space, and, by 1986 at the latest, a large piloted expedition to land on Mars. A forward step as small as an Apollo-derived piloted flyby mission had no place in the grand IPP.

The post-Apollo 11 wave was short-lived, however. Paine won over Vice-President Spiro Agnew to his plans for men on Mars, but it was a hollow victory, for Agnew had no power in the Administration of Richard Nixon. President Nixon, for his part, for a time considered ending piloted spaceflight.

Unlike the piloted flyby plans of NASA's first decade, the grand-scale plans of 1969-1970 would be long remembered. They would serve mainly to instill in the minds of many the expectation that initial piloted voyages to Mars must land and must be expensive.

Sources

"The Existence of a 1981 Triple-Planet Ballistic Flyby – Case 103-2," A. Bankovskis and A. Vanderveen, Bellcomm, 19 September 1967

"Verification of the Existence of the 1978 Triple-Planet Flyby Opportunity – Case 720," A. Vanderveen, Bellcomm, 19 October 1967

"White House Stand Blocks NASA Budget Restoration," Aviation Week & Space Technology, 28 August 1967, p. 32

After Apollo? Richard Nixon and the American Space Program, John M. Logsdon, Palgrave MacMillan, 2015

More Information

EMPIRE Building: Ford Aeronutronic's 1962 Plan for Piloted Mars/Venus Flybys

After EMPIRE: Using Apollo Technology to Explore Mars and Venus (1965)

To Mars by Way of Eros (1966)

"Assuming That Everything Goes Perfectly Well in the Apollo Program. . ." (1967)

14 December 2015

The Russians are Roving! The Russians are Roving! A 1970 JPL Plan for a 1979 Mars Rover

1984: A Proton-K rocket very similar to those that launched Luna 17/Lunokhod 1 in 1970 and Luna 21/Lunokhod 2 in 1973 lifts off from Baikonur Cosmodrome bearing one of a pair of Vega probes destined for Venus and Halley's Comet. Image credit: Lavochkin Association/NASA
As night fell at Baikonur Cosmodrome in Soviet Kazakhstan on 10 November 1970, a Proton rocket thundered to life and began its climb toward space. Six days later, the rocket's payload, the automated Luna 17 moon lander, soft-landed on broad, flat Mare Imbrium. A team of six operators in the Soviet Crimea - five main operators plus a spare - remotely drove the Lunokhod 1 rover down ramps lowered from the lander onto the moon's dusty surface.

The solar-powered (but nuclear-heated) 756-kilogram rover, measuring 1.35 meters tall and 2.15 meters across its tub-shaped equipment compartment, rolled on eight metal wheels with cleats at a top speed of 0.1 kilometers per hour. A hinged, bowl-shaped lid lined with electricity-generating solar cells opened to expose a thermal radiator atop the tub; as night approached, Lunokhod 1's operators commanded it to close the lid to hold in heat and protect its delicate electronics.

Lunokhod 1. Image credit: Lavochkin Association/NASA
Lunokhod 1 originated in the abortive Soviet piloted moon program, though this would not be revealed until the late 1980s. Its initial role was to have been to certify as safe the landing site selected for the piloted lunar landing.

The rover would then have stood by until a lander bearing a single cosmonaut arrived. If his lander became damaged during touch-down so that it could not return him to lunar orbit, the Lunokhod operator team on Earth would drive the rover to pick him up for transfer to a waiting, pre-landed backup lander. The United States had, incidentally, in the early 1960s considered launching site-survey rovers to Apollo landing sites, and had studied long-range automated rovers that visiting astronauts could board and drive.

Even before the successful Apollo 11 landing (20 July 1969), the Soviets claimed that they never intended to land cosmonauts on the moon. This was, of course, untrue, but it found a receptive audience among those who opposed piloted lunar exploration on the basis of cost or who favored the Soviet Union in the Cold War.

Through their official media, the Soviets declared that they had opted instead for robot explorers that cost much less than Apollo and placed no human life at risk. This message was particularly potent in the months following the near-disaster of Apollo 13 (11-17 April 1970).  They told the world that Lunokhod 1 and its cousins, the Luna automated sample returners, presaged a new era of extensive and intensive robotic lunar and planetary exploration.

U.S. space planners took note. In a report called An Exploratory Investigation of a 1979 Mars Roving Vehicle Mission, completed a timely three weeks after Luna 17 landed on Mare Imbrium and Lunokhod 1 began its traverse, a 12-man design team at the Jet Propulsion Laboratory (JPL) in Pasadena, California, described a NASA Mars rover mission in 1979.

Billed as a "logical follow-on" to the Viking landings planned for mid-1976, JPL's 1127-pound rover would include six wire wheels akin to those on the Apollo Lunar Roving Vehicle, which at the time was scheduled to be driven by astronauts on the moon for the first time in 1971. Mobility would enable "extended" Viking objectives: for example, while Viking would land on a safe, flat plain and seek living organisms only within reach of its three-meter-long robot arm, the 1979 rover could land in a flat area, then enter rugged terrain to seek out biologically promising sites.

Viking 1 launch on a Titan III-C rocket on 20 August 1975. Image: NASA
The Mars rover would leave Earth between late October and mid-November 1979 on a Titan III-C rocket with a Centaur upper stage - the same rocket/upper stage combination that would launch the Vikings in 1975. It would lift off sealed within a Viking-type lander aeroshell and bioshield cap attached to a Viking-type orbiter. The orbiter's rocket motor would perform a course correction burn 10 days after launch.

Assuming a 3 November 1979 launch, Earth-Mars transfer would need 268 days. During the voyage, a door would open in the top of the aeroshell and the rover's cylindrical electricity-generating Radioisotope Thermal Generators (RTGs) would extend into space on a boom. The plutonium-powered RTGs would continually generate heat; if kept sealed within the aeroshell during the flight to Mars, heat build-up would damage the rover.

Mars arrival would occur in August 1980. The orbiter's rocket motor would slow the spacecraft so that the planet's gravity could capture it into orbit. Two days later, it would tweak its orbit so that it would pass over the rover's primary landing site. The JPL team estimated that its Mars rover could reach sites between 30° north and 30° south latitude.

Cutaway of JPL's proposed 1979 Mars rover packed into its Viking-type aeroshell. The arrow points to the rover's twin RTGs, which are extended beyond the aeroshell on a boom to prevent them from overheating the rover's electronic systems during the flight to Mars. Image credit: JPL/NASA
Five days after Mars orbit arrival, the rover would cast off its bioshield cap to expose the aeroshell. Shortly before separation from the orbiter, the rover would retract its RTGs. The aeroshell would then separate and fire thrusters to slow down and fall toward Mars.

The JPL engineers described the rover landing sequence in considerable detail. Two hours after separation from the orbiter and 300 seconds before landing (that is, at L minus 300 seconds), the aeroshell would encounter Mars's thin upper atmosphere. Entry deceleration would peak at about 12 times the force of Earth's gravity.

At L minus 80 seconds, moving at a speed of Mach 2.5, the aeroshell would deploy a compact ballute ("balloon-parachute") 21,000 feet above Mars. Three seconds later, at 19,000 feet and a speed of Mach 2.2, a single parachute would deploy and the ballute would separate.

At L minus 73 seconds, with the rover streaking through the martian sky at Mach 2, the parachute would fill with thin martian air. Six seconds later, the lower aeroshell would separate, exposing the rover's underside and twin landing radars.

JPL's 1979 Mars rover in its landed configuration. Arrows point to the three terminal descent rocket motors. Image credit: JPL/NASA
Three terminal descent rocket motors on the rover would begin firing at L minus 33 seconds. Three seconds later, at an altitude of 4000 feet and a speed of 300 feet per second, the parachute and upper aeroshell would separate from the rover. The rover would then touch down gently on Mars directly on its wheels.

JPL's rover would comprise a train of three compartments, each with one wheel pair. Flexible connectors would link the compartments. The forward compartment (the "science bay") would include a Viking-type soil sampler arm with an attached soil magnetic properties experiment, a new-design "chisel and claw" arm, four biology experiment packages (the number NASA planned to launch on the Viking landers at the time JPL completed its rover report), a mass spectrometer, a weather station, and a seismometer. The forward compartment's wheel hubs would carry one terminal descent rocket motor each, and the front wheel pair would be steerable.

The middle compartment (the "electronics bay") would house the 95-pound dual-purpose (science & rover control) computer.  A telescoping stalk would support a dish-shaped high-gain antenna, a low-gain antenna, a fascimile camera capable of generating a 360° panorama, and a vidicon camera with rangefinder.

The rear compartment (the "power bay") would include the twin externally-mounted RTGs, landing radars on its wheel hubs, and a rear-mounted terminal descent rocket motor. The rear wheel pair would, like the front pair, be steerable.

From some time before Earth launch until its second day on Mars, the three compartments would be squeezed together tightly with their wheels touching. This would enable the rover to fit within the confines of its Viking-type aeroshell.

Controllers on Earth would check out the rover during its first day after touchdown on Mars. On Day 2, they would spread out its compartments, deploy its appendages, and discard the terminal descent motors and landing radars. The JPL design team looked briefly at retaining the terminal descent rockets to enable the rover to "hop" over obstacles, but rejected this capability as being too fraught with risk.

Science operations would commence on Day 3. Mars surface operations would span one Earth year, from August 1980 to August 1981.

Controllers on Earth would guide the rover through its daily program. Operations would occur only during the martian daylight hours, when line-of-sight radio contact with Earth was possible.

Time available for operations during each 24-hour, 39-minute martian day would vary over the rover's one-Earth-year mission, as would radio-signal travel time. On 9 August 1980, for example, a rover at a site on the martian equator would remain in contact with Earth for 10.93 hours, while radio signals would need about 21 minutes to cross the gulf between the planets. In May 1981, Earth and Mars would be far apart - on opposite sides of the Sun - and radio-signal travel time would reach its maximum value of 41 minutes.

Typically, the rover would move from 50 to 100 meters at a time, then halt, image its surroundings, perform one of its science experiments, transmit its data to Earth, and then await new commands. JPL assumed that high-interest science sites would occur on average about 14 kilometers apart along its traverse route, and estimated that early in its mission the rover would travel about 300 meters per day, enabling it to traverse the distance between two science sites in 47 days. Distance traversed would, JPL optimistically assumed, rapidly increase as controllers gained confidence in their remote driving ability: the team estimated that in one Earth year its rover might traverse up to 500 kilometers.

Inspired, perhaps, by Lunokhod 1, the JPL team concluded its study by looking briefly at a lunar variant of its Mars rover design. The team found that the basic design of both rovers could be much the same, though the lunar rover launch vehicle would not need to be as large and powerful (a Titan III/Centaur without strap-on solid-propellant boosters would suffice) and a solid-propellant braking rocket would need to replace the Mars rover's aeroshell, ballute, and parachute because the moon has no atmosphere. In addition, the lunar version could tote an additional 150 pounds of science payload.

As the team's study circulated to a limited JPL audience, Lunokhod 1 continued its slow traverse over dusty Mare Imbrium. The Soviet rover was designed to function for three months, but did not officially cease operations until the 14th anniversary of the launch of Sputnik 1 on 4 October 1971, some 10 months after JPL completed its report (radio contact with Lunokhod 1 was, however, lost on 14 September 1971). During its 10.54-kilometer traverse, it beamed to Earth more than 20,000 images of its surroundings and analyzed lunar surface composition at 25 locations.

Lunokhod 2 included new cameras and instruments and was designed to travel over the lunar surface more quickly than had Lunokhod 1. In this image, the dual-purpose dish-shaped solar array/thermal cover is shown folded open, as it would have been during lunar daytime. Image credit: Lavochkin Association/NASA
The Soviets followed up Lunokhod 1's success a few weeks after Apollo 17 (7-19 December 1972), the final piloted lunar mission. On 17 January 1973, Luna 21 landed inside rugged Le Monnier Crater bearing the Lunokhod 2 rover. The new rover was, the Soviets stated, superior to its predecessor. It would, for example, scuttle across the lunar surface much more rapidly than could Lunokhod 1.

On 9 May 1973, after traversing some 37.5 kilometers in less than three months, Lunokhod 2 rolled accidentally into a dark-floored crater. Its open bowl-shaped solar array/thermal cover apparently brushed against the crater wall, becoming partly filled with lunar dirt.

When, shortly thereafter, controllers in the Crimea commanded the array/thermal cover to shut at lunar sunset, the dirt fell on Lunokhod 2's thermal radiator. Two weeks later, as the Sun rose again at Le Monnier, controllers commanded the array/thermal cover to hinge open in preparation for a new day of lunar driving.

The dirt-covered radiator could no longer reject heat adequately, so Lunokhod 2 rapidly overheated in the harsh lunar sunlight. The Soviets declared its mission ended on 3 June 1973. Lunokhod 2 was the last rover to operate on another world until Mars Pathfinder's Sojourner minirover in 1997.

In March 2010, NASA released high-resolution Lunar Reconnaissance Orbiter Camera (LROC) images of the moon's surface showing the Lunokhod 1 and Lunokhod 2 rovers and the Luna 17 and Luna 21 landers. In the intervening years, the Lunar Reconnaissance Orbiter has orbited lower over the Lunokhod landing sites, enabling higher-resolution imaging. LROC images clearly show the extended Luna 17 and Luna 21 ramps and the tracks Lunokhod 1 and Lunokhod 2 left on the lunar surface.

The last journey of Lunokhod 2: the black arrow points to the crater where the rover accidentally collected a load of lunar dirt. Soon afterwards, the rover parked for the lunar night. The white arrows running up the center of the image highlight tracks Lunokhod 2 left as the Sun rose and the dirt on its radiator caused it to overheat. The white arrow near the top of the image points to Lunokhod 2 in its final resting place. This image from NASA's Lunar Reconnaissance Orbiter shows an area of Le Monnier crater roughly 400 meters square. Image credit: NASA
Proposals for a Viking follow-on robot rover mission would be put forward throughout the 1970s and 1980s, but none would move beyond the stage of proposals and studies. In part, this was because the Soviet Union failed to follow through on its promise (or threat) to launch robot sample returners and rovers to the planets.

Competition with the Soviet Union was rarely mentioned as a motive for robotic exploration after the early 1970s. When it was, it lacked its old punch: for example, it utterly failed to move lawmakers when comet scientists sought to use it as a justification for funding a U.S. mission to Comet Halley during its 1985/1986 apparition.

JPL's proposed 1979 rover bears a passing resemblance to the Mars Science Laboratory (MSL) rover Curiosity launched on 26 November 2011, almost exactly 41 years after Lunokhod 1. Both the JPL 1979 rover design and Curiosity have six wheels, rear-mounted nuclear power sources, stalk-mounted cameras, and front-mounted arms.

The nuclear-powered Mars Science Laboratory Curiosity captured a selfie on 3 February 2013. Image credit: NASA
Curiosity, however, has a single body, solid wheels, and a more elaborate suspension system. Curiosity is also larger and heavier (about 2000 pounds) and depended on a more complex (and, to many observers, more worrisome) landing system known as the Sky Crane. The new system functioned as advertised, however, gently lowering Curiosity onto its wheels in Mars's equatorial Gale crater late in the evening U.S. Pacific Time on 5 August 2012.

Perhaps the most profound difference between the two rovers has to do with expectations. JPL engineers in 1970 assumed that their rover might cover half a thousand kilometers in a single Earth year. Curiosity, by contrast, cautiously traversed about 7.9 kilometers during its first 687-day martian year, which ended on 24 June 2014.

Although it has suffered wheel damage, Curiosity continues to climb the foothills of Aeolus Mons, an immense geologic layer-cake that fills much of Gale crater. Curiosity is expected to continue exploring until it suffers a catastrophic failure or until its electricity-generating nuclear source runs down, whichever comes first.

Sources

An Exploratory Investigation of a 1979 Mars Roving Vehicle Mission, JPL Report 760-58, J. Moore, Study Leader, Jet Propulsion Laboratory, 1 December 1970

Challenge to Apollo: The Soviet Union and the Space Race, 1945-1974, NASA-SP-2000-4408, Asif Siddiqi, NASA, 2000, pp. 532-533, 740-743

Press Kit, Mars Science Laboratory Landing, NASA, July 2012

More Information

Centaurs, Soviets, and Seltzer Seas: Mariner 2's Venusian Adventure (1962)

A 1974 Plan for a Slow Flyby of Comet Encke

Making Propellants from Martian Air (1978)

08 December 2015

Harold Urey and the Moon (1961)

Nobel Laureate and Earth's moon fan Harold Urey. Image credit: NASA
Harold Clayton Urey as born in the small town of Walkerton, Indiana, on 29 April 1893. He taught school in Indiana and Montana, then earned Bachelor's degrees in biology and chemistry from the University of Montana. After a stint at a chemical plant in Philadelphia, he earned a PhD in chemistry at the University of California at Berkeley in 1923. Following a fellowship in theoretical physics at the Bohr Institute in Copenhagen, he joined the Chemistry faculty at Johns Hopkins University in Baltimore, then moved to Columbia University in New York. On Thanksgiving Day in 1931, Urey discovered the hydrogen isotope deuterium, a feat that earned him the Nobel Prize in Chemistry in 1934.

By most accounts, Urey was a generous and humble man. For example, he shared credit for his deuterium discovery with the scientist who manufactured the five liters of liquid hydrogen he used for his research.

Urey left Columbia for the University of Chicago in 1945. While in Chicago, he read Ralph Baldwin's 1949 book The Face of the Moon, which made the case for the impact hypothesis; that is, that the moon's many craters are not volcanic calderas, as was widely believed, but are instead scars left by asteroid impacts. Baldwin's book changed Urey's professional life.

In 1952, Urey published The Planets, which launched the science of geochemistry as applied to extraterrestrial bodies. He christened this new discipline "cosmochemistry." In his book, Urey espoused the "cold moon" theory; that is, that the moon is a primitive body that never became hot enough internally for its rocks to melt. The cold moon hypothesis and the impact hypothesis went hand in hand; Urey expected that a cold, quiescent moon would be necessary to preserve ancient impact craters. Earth's natural satellite, he argued, was little changed from the time it had formed. If humans one day could collect a piece of the moon, it followed, then they would have in hand a "Rosetta Stone" for deciphering the Solar System's early history.

What turned out to be the first steps toward lunar sample return occurred shortly after Urey's book saw print. In late July 1955, the United States announced that it would launch a civilian scientific Earth satellite during the International Geophysical Year (IGY), an 18-month worldwide science campaign that would begin on 1 July 1957. A little more than a month later, in early September 1955, the Soviet Union announced that it, too, would launch a satellite into Earth orbit during the IGY.

President Dwight Eisenhower had little enthusiasm for rockets and satellites except insofar as they had defense applications. The U.S. IGY satellite, though civilian in nature, received his support because it had a hidden military agenda. It was intended to assert the international legal principle of the "Freedom of Space," which was meant to be analogous to the long-established principle of the Freedom of the Seas. The new principle would, Eisenhower hoped, quell Soviet protests when the United States began to launch surveillance satellites into orbits that carried them over Soviet territory.

The Eisenhower Administration believed at first that the Soviet Union did the United States a "good turn" by launching Sputnik 1, the first Earth satellite, on 4 October 1957. The Soviet satellite, which passed over U.S. territory several times each day, made unnecessary American assertion of the Freedom of Space principle.

Sputnik 1 soon turned into a liability for the Eisenhower Administration, however. The old General tried to downplay its significance, but neither an American public fearful of apparent Soviet technological superiority nor Democratic Senate Majority Leader (and Presidential hopeful) Lyndon B. Johnson would stand for it.

One result of Sputnik 1 was the creation of the civilian National Aeronautics and Space Administration (NASA), which opened its doors on 1 October 1958. By then, both U.S. and Soviet rocketeers had begun to launch small probes toward the moon.

During 1958, Urey retired from the University of Chicago and went to work at the University of California, San Diego. On 29 October 1958, at the Lunar and Planetary Exploration Colloquium held at the Jet Propulsion Laboratory in Pasadena, California, he famously predicted that new lunar discoveries would give him a "very red face" in only a few years; that is, that spacecraft would soon collect data that would disprove many of his favorite lunar theories. "Nature can always be more complicated than we imagine," he added.

In November 1958, Urey met newly hired NASA scientist Robert Jastrow, whom he quickly converted to the cause of lunar exploration. The following month, Urey and Jastrow met with NASA Deputy Director for Space Flight Programs Homer Newell at NASA Headquarters in Washington, DC.

At the time, scientists interested in space physics - the study of particles and fields in space - dominated NASA space science. Urey and Jastrow sought to convince Newell that NASA should apply some of its scientific energies (and funds) to the exploration of the moon's geology.

On 5 February 1959, the NASA Working Group on Lunar Exploration, chaired by Jastrow, met for the first time. Urey was an enthusiastic member. He also became a founding member of the influential National Academy of Sciences Space Science Board, which displayed its backing for lunar exploration by forming a "Lunar Committee." The group strongly supported President John F. Kennedy's 25 May 1961 call for a man on the moon by 1970.

Three weeks after Kennedy's "moon speech," Urey responded to an informal request from Newell that he recommend landing sites on the moon. In a 19 June 1961 letter, the polymath Nobel Laureate told Newell that "we should attempt to. . . get as great a variety of objectives as possible in as few landings as possible." In acknowledging that the Apollo landings might be few he was ahead of many of his colleagues. Urey then listed six classes of sites he felt should be explored.

The numbers in the image above are explained in the post text. Image credit: NASA/David S. F. Portree
The first took in sites at high latitudes (that is, close to the lunar poles) (1 on the image above). Urey explained that Harrison Brown, a fellow member of the Working Group on Lunar Exploration, had "presented evidence that water may exist close to the surface in certain high latitude areas." This was, of course, in keeping with Urey's "cold moon" hypothesis.

Urey then called for landings on two of the lunar maria ("seas"), the smooth, relatively dark-hued plains that mottle the moon's Earth-facing Nearside hemisphere. One of these, he explained, should be "of the deep type" - that is, it should be an obvious giant impact basin such as "the great collision area just before Sinus Iridium in Mare Imbrium" (2) or Mare Serenitatis (3). Seismic instruments emplaced on a deep mare would, Urey believed, enable determination of the depth to which the giant impactors that formed them had penetrated the moon's crust.

The other mare landing should occur on a "shallow" mare, Urey wrote. In the shallow category he listed Oceanus Procellarum (4) and Mare Tranquillitatis (5), neither of which displays the distinctive round outline of Mare Imbrium and Mare Serenitatis. Urey told Newell that NASA would probably want to land first on Oceanus Procellarum in any case because it was a wide plain with few mountains or other obstructions to imperil descending spacecraft.

Next on Urey's wish list was the interior of a large impact crater. He suggested Alphonsus (6), an old crater partly filled with "gray material." Soviet scientist Nikolai Kozyrev claimed to have observed there in 1958 a short-lived white cloud. Urey noted also that geologist Eugene Shoemaker, founder and first chief of the U.S. Geological Survey's Branch of Astrogeology in Menlo Park, California, was hard at work studying the young crater Copernicus (7) in "very great detail," and that his work might pave the way for a landing there.

Fourth on Urey's list was one of the "great wrinkles in the maria." He told Newell that the wrinkle ridges, as they are known, might be places where water had escaped from the moon's icy cold interior. He added that Gerard Kuiper, founder of the Lunar and Planetary Laboratory in Tucson, Arizona, had observed deposits of white material atop the ridges. Urey interpreted these to be salts left behind as water boiled away in the lunar vacuum.

A moon lander dispatched to Mare Imbrium near Sinus Iridium could, Urey added, explore both a deep mare and prominent wrinkle ridges (8). Similarly, a landing near Copernicus could explore both the great crater and nearby "little volcano-like things" (9) that Urey believed were related in some way to the wrinkle ridges.

Number five on Urey's list was a mountainous area. His chief candidate were the Haemus Mountains on the south edge of Mare Serenitatis (10), which he believed constituted a mass of material blasted out during the formation of Mare Imbrium.

Finally, Urey listed features that were of interest to him personally. These included an unusual dark gray line in Mare Serenitatis, which he had theorized in the early 1950s was a streak of carbon-rich material similar to that found in primitive carbonaceous chondrite meteorites (11). He also suggested the Aristarchus-Herodotus region (12), which Kozyrev had found to be "luminous," and Lacus Mortis (13), which Urey believed was a graben; that is, a sunken block of lunar crust.

Urey ended his letter by asking Newell to share with him any landing site suggestions he received from other scientists. He argued that site selection was an important matter that "should be considered by many of us."

In his reply of 29 June 1961, Newell told Urey that he had forwarded his suggestions to NASA's Office of Lunar and Planetary Programs and to "the special study groups who have been working out plans for the manned lunar landing." Newell also urged Urey to share with him "any ideas that the Lunar Committee of the Academy's Space Science Board might have."

Urey remained active in lunar exploration throughout the 1960s. In early 1962, he joined the 12-member ad hoc working group NASA’s Office of Space Science created to outline the Apollo science program. He participated in Ranger (1961-1965) and Surveyor (1966-1968) automated missions, as well as the manned Apollo 11 (July 1969) and Apollo 12 (November 1969) piloted missions, which sampled Mare Tranquillitatis and Oceanus Procellarum, respectively. As he predicted, he had occasion to become red in the face: the moon, the Apollo samples and surface experiments showed, was molten throughout its first 1.5 billion years of existence, probably experienced surface volcanism as recently as a billion years ago, and today has a molten inner mantle and outer core.

Urey continued his lunar studies until he was well into his 80s. Among his last scientific papers was one on lunar iron chemistry published in 1977. He died in La Jolla, California, on 5 January 1981.

Sources

Letter, Harold C. Urey to Dr. Homer E. Newell, Deputy Director, Space Flight Programs, NASA Headquarters, 19 June 1961

Letter, Homer E. Newell to Dr. Harold C. Urey, School of Science and Engineering, University of California-San Diego, 29 June 1961

"The Chemistry of the Moon," Harold C. Urey, Proceedings of the Lunar and Planetary Exploration Colloquium, 29 October 1958, Publication 513W3, Vol. 1, No. 3, Missile Division, North American Aviation, 1958

"Harold Urey and the Moon," Homer E. Newell, The Moon, Volume 7, pp. 1-5, 1973

NASA's Origins and the Dawn of the Space Age, Monographs in Aerospace History #10, David S. F. Portree, NASA History Division, September 1998

More Information

He Who Controls the Moon Controls the Earth (1958)

Clyde Tombaugh's Vision of Mars (1959)

Solar Flares and Moondust: The 1962 Proposal for an Interdisciplinary Science Satellite at Earth-Moon L4

Centaurs, Soviets, and Seltzer Seas: Mariner 2's Venusian Adventure (1962)

01 December 2015

Space Station Gemini (1962)

Herman Potočnik's 1928 Wohnrad ("living wheel") space station design. Image credit: NASA 
In 1960, most everyone who cared about such things knew what a space station was supposed to look like: it would take the form of a revolving wheel. The design, first portrayed in detail in 1928 by Austro-Slovenian Herman Potočnik, was popularized in the United States after the Second World War by Wernher von Braun in the pages of the popular Collier's weekly magazine and through a series of Walt Disney "Tomorrowland" television programs.

Wheel-shaped space stations would revolve continuously to produce acceleration - so-called "centrifugal force" - which the astronauts inside would feel as gravity. This "artificial gravity" would pull strongest along the station's outer rim and not at all at its hub. Artificial-gravity station designs tend to be large; this is because a spinning station of small spin radius would generate undesirable effects, such as a noticeable gradient in the pull felt along a standing astronaut's body. The astronaut would feel "light-headed" and "heavy-footed."

An experimental inflatable artificial-gravity space station under development at NASA Langley Research Center in 1961. Image credit: NASA
Soon after NASA opened for business on 1 October 1958, Langley Research Center (LaRC) took the lead in U.S. civilian space station development. Not surprisingly, the Hampton, Virginia-based NASA laboratory emphasized artificial-gravity designs. For example, LaRC engineers built and ground-tested experimental doughnut-shaped inflatable stationes.

As LaRC labored toward artificial-gravity stations, the Space Task Group (STG), an independent team of engineers based at LaRC, began work on Mercury, NASA's first piloted spacecraft. NASA Headquarters, meanwhile, solicited proposals from industry for an "advanced manned spacecraft." The new three-person spacecraft and the program to build and fly it were named Apollo.

As originally conceived, Project Apollo was to have followed immediately after Project Mercury. The Apollo spacecraft would have included three modules, one of which, the Mission Module, would have provided its crew with added living and working volume. The Mission Module could turn an Apollo spacecraft into a small zero-gravity space station or could transport supplies to a large space station. NASA expected that, before 1970, a piloted Apollo spacecraft would fly around the moon without stopping in lunar orbit (that is, it would carry out a free-return circumlunar mission).

NASA's plans changed dramatically on 25 May 1961, when President John F. Kennedy called upon the young space agency to land a man on the moon by the end of the 1960s decade. Faced with this daunting new challenge, NASA out of necessity put most space station planning on the back burner.

Apollo became NASA's lunar landing program. After NASA opted for the Lunar-Orbit Rendezvous (LOR) moon-landing mode in July 1962, Apollo mission roles were split between two spacecraft: the Command and Service Module (CSM) for conveying three men from Earth to lunar orbit and back again; and the four-legged Lunar Module (LM), which would carry two men from the CSM in lunar orbit to the moon's surface and back. The Mission Module was no longer a part of the Apollo design.

NASA soon recognized the need for a program that could bridge the yawning spaceflight skills gap separating Mercury from the moon. The lone Mercury astronaut could adjust his spacecraft's attitude (basically, the direction its nose pointed), but not the shape or altitude of its orbit; three-man Apollo crews would be called upon to conduct multiple significant orbit-change maneuvers, including capture into and departure from lunar orbit. Project Apollo would also require rendezvous and docking in lunar orbit and, in the event of docking difficulties, a spacewalk between the LM and the CSM.

Cutaway illustration of a Gemini spacecraft displaying its forward-facing windows, ejection seats, nose-mounted rendezvous radar and parachutes, retrograde rocket motors for reentry, and propellant tanks for attitude control and orbit-changing maneuvers. Image credit: NASA
Initially dubbed Mercury Mark II, the two-man skill-building spacecraft was formally named Gemini in January 1962. NASA planned to conduct Project Gemini flights in 1963 and 1964; that is, immediately after Project Mercury's planned conclusion.

The space agency tasked St. Louis, Missouri-based McDonnell Aircraft, Mercury spacecraft prime contractor, with building Gemini. The new spacecraft would comprise two main modules: the Reentry Module bearing the crew and the Adapter Module containing maneuvering thrusters and solid-propellant deorbit rockets. The latter would be located in the Retrograde Section, the forward part of the Adapter Module, up against the Reentry Module's bowl-shaped reentry heat shield.

Gemini, like Mercury and Apollo, would provide its crew with a pure oxygen atmosphere. Unlike Mercury and Apollo, Gemini would feature a jet fighter-style cockpit with forward-facing windows and ejection seats for crew escape in the event of emergency during liftoff, ascent, or landing. Fuel cells in the Adapter Module would combine liquid oxygen and liquid hydrogen reactants to produce drinking water and electricity.

Artist's concept of a Gemini spacecraft performing rendezvous and docking with a modified Agena upper stage. Image credit: NASA
NASA partnered the Gemini spacecraft with Agena, a separately launched upper stage with a docking collar, so that U.S. astronauts could gain rendezvous and docking experience. Project Gemini astronauts would also conduct spacewalks and remain aloft in Earth orbit for up to two weeks to permit physicians to certify that Apollo crews could remain healthy for the duration of a lunar voyage.

Gemini would climb to orbit atop a Gemini Launch Vehicle (GLV), a modified U.S. Air Force (USAF) Titan II missile. At the end of its mission, the Gemini Reentry Module would deploy a triangular Rogallo "parawing" and glide to a controlled land landing on skids.

The Titan II Inter-Continental Ballistic Missile, progenitor of the Titan family of space launchers. Image credit: U.S. Air Force
23 March 1965: twin engines ignite on a Titan II GLV at Cape Kennedy, Florida, marking the start of Gemini III, the first of ten piloted flights in the Gemini series. Image credit: NASA
In the first half of 1961, McDonnell submitted a proposal as part of the USAF's Military Test Space Station (MTSS) study. The McDonnell MTSS design consisted of a Gemini spacecraft and a pressurized module with a powerful transtage rocket motor attached to it. The module would have added volume and functionality to Gemini, much as the Mission Module would have done for Apollo.

Air Force astronauts would have entered the pressurized module by opening a small hatch in the bulkhead above and behind their ejection seats. The hatch, a carefully engineered breach in the Reentry Module heat shield, would have opened on a narrow bent tunnel leading to the aft end of the Adapter Module, where another hatch would have let the astronauts into the pressurized module.

Continuing high-level uncertainty about the USAF role in piloted spaceflight led McDonnell in December 1962 to attempt to hedge its bets by peddling Gemini-derived spacecraft to NASA. The company proposed that while NASA carried out the Apollo lunar program it should also carry out a low-cost Gemini-based space station program. McDonnell argued that
presently programmed launch vehicles capable of placing 20,000 to 200,000 pounds in near earth orbits will be available [in the late 1960s]. Large space station complexes with elaborate facilities and housing large numbers of crewmen will then be technically feasible. However, before undertaking the development of such stations, it is desirable, if not mandatory, to explore at a modest level some of the fundamental design and cost determining operational factors such as, the need for artificial gravity[,]. . . the physiological and psychological effects of long[-]term space operations[,] and appropriate crew tours of duty. The [Gemini-based] space stations proposed provide. . . [an] early capability to obtain answers to fundamental questions [at] modest cost.
If NASA had taken up McDonnell's proposal - which the company called "Modular Space Station Evolving from Gemini" - then Gemini would have become for a major NASA space station program what it was already for Project Apollo. That is, it would have bridged the knowledge gap separating short, zero-gravity missions in small piloted spacecraft from long missions on board large artificial-gravity stations.

McDonnell's proposal in fact encompassed a series of up to three programs, each building on and more ambitious than the last. The company designated them Program A, Program B, and Program C. Carrying out Program B would be prudent, McDonnell wrote, but optional.

McDonnell proposed five building blocks that could be combined in different ways to accomplish its three Programs. These were: the Gemini Transport, a modified Gemini spacecraft, which would serve as crew carrier and piloted space tug; the Supply Module; the One-Room Space Station, which was structurally similar to the Supply Module; the Electrical Power Module; and the Two-Room Space Station, structurally similar to the Electrical Power Module.

Structural similarity would yield reduced cost, the company explained. NASA would also save money by recovering Gemini Transport Reentry Modules and returning them to the McDonnell plant in St. Louis for refurbishment and reuse.

3 November 1966: a Titan III rocket launches a USAF Manned Orbiting Laboratory mockup with the refurbished and modified unmanned Gemini II spacecraft on top. Image credit: U.S. Air Force
All of McDonnell's modules would measure 10 feet in maximum diameter, in keeping with the diameter of the Titan rockets that would boost them to Earth orbit. McDonnell assumed two Titan variants for its proposed program: the two-stage Titan II GLV and the Standard Launch Vehicle 624A-C (Titan III). The Titan III would comprise a modified two-stage Titan II core, twin strap-on solid-propellant boosters, and a restartable upper stage.

The GLV, capable of launching 7390 pounds into an 87-by-200-nautical-mile orbit, would loft the Gemini Transport, the Supply Module, the One-Room Space Station, and a stripped-down version of the Two-Room Space Station. The Titan III would place 25,280 pounds into a 250-nautical-mile-high circular orbit or 26,000 pounds into a 100-by-250-nautical-mile elliptical orbit. This would enable it to launch module combinations, such as the Gemini Supply Transport (Gemini Transport plus loaded Supply Module).

McDonnell expended considerable in-house time and money to develop feasible rendezvous, docking, and crew/cargo transfer methods for its proposal. Because the Gemini Transport would use the nose-mounted Gemini rendezvous radar, it would first approach its orbital target with its nose and twin windows facing forward, just as would the baseline Gemini when it performed rendezvous and docking with an Agena.

About 10,000 feet from the target, the pilot would unstrap from his seat, twist his body around in the close confines of the Gemini Transport cockpit, and open the 27.5-inch-diameter hatch above and behind his and the command pilot's seats. He would squeeze through a 24.5-inch opening in the heat shield to enter a 32-inch-diameter tunnel in the Adapter Module. The bent tunnel would lead to a rear-facing Crew Docking Station.

The command pilot, meanwhile, would turn the Gemini Transport end-for-end to point the flat rear of its Adapter Module at the target. The co-pilot would sight the target through a small window above a docking control console, then would commence a "semi-manual" final approach employing the six docking thrusters. Similar thrusters on the One-Room Space Station would ensure its stability during docking. McDonnell estimated that approach from 10,000 feet would need about 10 minutes, during which time the Gemini Transport would slow from a speed of 100 feet per second to zero relative to its target.

Gemini Transport (left) docked with a One-Room Space Station. Image credit: McDonnell/NASA
McDonnell proposed a "ring-and-fork" docking interface. The co-pilot would line up a roughly nine-foot-diameter ring on the rear of the Gemini Transport Adapter Module with four equidistantly spaced two-prong forks on the target. The ring would slide along the inner surfaces of the prongs, canceling out any misalignment between spacecraft and target, then would trip latches where the prongs met to form the forks. Tripping the latches would constitute soft docking. Finally, the forks would retract, pulling hatches on the Gemini Transport and its target securely together to accomplish hard docking.

McDonnell proposed that its Program A begin in early 1965, immediately after the baseline Gemini Program supporting Apollo was expected to be completed. It based its development schedule on a February 1963 NASA go-ahead for Program A.

In the first Program A mission, a GLV would launch a 7390-pound One-Room Space Station into an initial 87-by-200-nautical-mile orbit, then another GLV would launch a Gemini Transport. The latter would dock with the former, then would maneuver the combination to a 200-nautical-mile circular orbit. This approach - using the Gemini Transport to circularize the One-Room Space Station's orbit - would help to maximize the weight of useful payload that could be launched in the One-Room Space Station. The two astronauts in the Gemini Transport would then enter the One-Room Space Station and work on board for 30 days.

Astronaut activities on board the One-Room Space Stations would emphasize space medicine and station housekeeping, as well as space sciences, artificial-gravity, and military experiments. The One-Room Space Stations would use improved Gemini-type fuel cells to make electricity and water and would not remain occupied for long enough to need resupply. They would provide their crews with a pure oxygen atmosphere at five pounds per square inch of pressure. With a ceiling height of seven feet, pressurized volume would total 548 cubic feet. The station's 36-square-foot clear floor area would be covered with velcro so that the astronauts, who would wear velcro slippers, could anchor themselves in zero-gravity.

After undocking in their Gemini Transport, the first Program A crew would cast off the aft section of its Adapter Module and fire the solid-propellant rocket motors in its Retrograde Section to decrease its orbital velocity and begin the fall back to Earth. For added redundancy, the Gemini Transport Retrograde Section would include five retrograde motors; that is, one more than the baseline Gemini. Following a fiery atmosphere reentry, the Reentry Module would turn so its nose faced forward, deploy its parawing, and glide to a landing.

The first One-Room Space Station would not be occupied again. McDonnell made no mention of its eventual fate; presumably it would undergo uncontrolled reentry a few years after it was abandoned.

Program A's second One-Room Space Station mission would emphasize artificial-gravity experiments. McDonnell explained that "artificial gravity operations not only constitute new techniques in themselves, but also interrelate with and tend to modify many of the other required space station functions." A GLV would place its own second stage and the second One-Room Space Station into an initial elliptical orbit. The crew would then arrive in a Gemini Transport and boost the combination into its 200-nautical-mile circular operational orbit.

Proposed Program A artificial-gravity experiment. Image credit: McDonnell/NASA
After settling into their new home, the two astronauts would detach the GLV second stage and pay out a cable linking it to the One-Room Space Station. Full extension would require between five and six hours, McDonnell estimated.

At about 75% of full cable extension, the astronauts would begin cautiously pulsing the One-Room Space Station's thrusters. The end-over-end rotation this would produce would create artificial gravity in the One-Room Space Station and the docked Gemini Transport.

Because the spent GLV second stage would have a mass of only 5800 pounds (that is, about a third of the mass of the Gemini Transport/One-Room Space Station combination), the center of rotation would be located nearer the latter than the former (150 feet versus 362 feet). To end the artificial-gravity test, the crew would reverse the cable-extension and thruster-firing procedures. The second Program A crew would return to Earth after 45 days in orbit.

The third and final Program A mission, scheduled for early 1966, would last for 60 days, but would otherwise would resemble the 30-day first Program A mission. The crew's two-month orbital stay would pave the way for crews of four men to live for 60 days on board a Two-Room Space Station during Program B and a Four-Room Space Station during Program C.

McDonnell envisioned that Program B and Program C would receive preliminary approval in January 1965, and that NASA would a year later choose to fly Program B and Program C in succession or elect to skip directly to Program C after Program A. If the latter option were selected, McDonnell assumed that NASA would desire to fly a fourth Program A One-Room Space Station in August 1966 to bridge the one-year gap between the third Program A mission and the first Program C mission launched in early 1967.

Assuming that NASA opted to fly Program B, however, in mid-1966 a stripped-down 7390-pound Two-Room Space Station would climb to an elliptical orbit on a GLV. The GLV-launched Two-Room Station would reach orbit with little scientific equipment on board and only enough supplies to sustain two men for 30 days. A Gemini Transport with two astronauts on board would then lift off on a GLV, rendezvous and dock with the Two-Room Space Station, and circularize the combination's orbit.

To make way for a second Gemini Transport - which, upon its arrival, would increase the Two-Room Space Station's population to its normal complement of four astronauts - the first crew would pioneer a new space station operational technique. They would extend mooring arms to grip fixtures on their Gemini Transport, disengage the docking fork latches, and swing their Gemini Transport into alignment with either of two mooring ports on the Two-Room Space Station's sides. The mooring arms would then retract, causing the Gemini Transport's docking ring to latch on four small mooring forks. Like the larger docking forks, these would retract, pulling the Gemini Transport and Two-Room Space Station firmly together.

Program B: a Gemini Transport is shifted from the docking port to one of two mooring ports on the Two-Room Space Station to make way for a second Gemini Transport with a Supply Module. Image credit: McDonnell/NASA 
Like Program A's One-Room Space Stations, Program B's Two-Room Space Station would rely on fuel cells for electricity. Unlike its predecessors, it could be resupplied. The third GLV launch of Program B would place the first 7390-pound Supply Module into an elliptical orbit. The Supply Module would be crucial for making possible launch of the Two-Room Space Station on a GLV. Of the Supply Module's mass, 3992 pounds would constitute supplies and equipment for outfitting the Two-Room Space Station in orbit.

The Supply Module's front end would include four docking forks and a hatch; its aft end would include a docking ring, a hatch, and, within its pressurized volume, a rear-facing Crew Docking Station. Soon after the Supply Module reached orbit, a Gemini Transport would lift off to rendezvous and dock with its front end. The Gemini Transport/Supply Module combination would then rendezvous with the Two-Room Space Station and halt at a distance of 10,000 feet.

The command pilot would turn the combination end-for-end, then the pilot would guide the Gemini Transport/Supply Module combination to a docking with the Two-Room Space Station. The astronauts would enter the Two-Room Space Station through the Supply Module hatch, then would extend mooring arms to pivot the Gemini Transport/Supply Module combination to the Two-Room Space Station's second mooring port, on the side opposite the Gemini Transport that delivered the Station's first two astronauts.

Arrival of a third Gemini Transport at the Two-Room Station's docking port would mark the beginning of the end for Program B. After a brief crowded period during which the Two-Room Space Station would house six astronauts, the first two-person crew would undock in their Gemini Transport and return to Earth, ending their 60-day orbital mission.

Thirty days later, the second crew would undock from the Supply Module, which would remain attached to the Two-Room Space Station to serve as a "pantry" and to provide extra living and working space. Finally, the third crew would undock. Their return to Earth 120 days after Two-Room Space Station launch would end McDonnell's Program B.

Man-rating the Titan III rocket would lead to important new capabilities in Program C. The rocket would be powerful enough to launch into a circular 250-nautical-mile orbit a payload comprising a Gemini Transport with two astronauts on board, a Two-Room Space Station with neither fuel cells nor fuel-cell consumables, and a two-room Electrical Power Module with twin rectangular solar arrays and batteries. The Two-Room Space Station and Electrical Power Module would be bolted together on the ground to create the Four-Room Space Station.

Thirty days later, a second two-man Program C crew launched on a GLV would join the two astronauts launched with the Four-Room Station. Thirty days later, the first two-man crew would return to Earth and a third two-man crew would replace them. This staffing pattern - a four-man crew with half the astronauts replaced every 30 days - would continue uninterrupted for a year.

Program C: the Four-Room Space Station at maximum extent. Note the twin solar arrays extended from the sides of the Electrical Power Module (right). Please click to enlarge. Image credit: McDonnell/NASA
Deletion of fuel-cells and their reactantss would permit the Four-Room Station to reach orbit fully equipped with experiment apparatus and loaded with enough supplies to support four men for six months. Ten GLV-launched Gemini Transports would dock with the Four-Room Space Station during Program C.

Titan III could also launch a Gemini Transport and Supply Module together. McDonnell dubbed this combination the Gemini Supply Transport. A single Gemini Supply Transport would dock halfway through the Four-Room Space Station's year-long career as supplies launched with it ran low. The astronauts would pivot the Gemini Supply Transport to a mooring port shortly after it docked.

The Gemini Transport would detach from the Supply Module 60 days after docking. When it departed, it would expose a docking port on the Supply Module. This would become the Four-Room Space Station's alternate docking port.

Although this image portrays the Gemini Supply Transport used in Program C, it contains details that apply to other modules and to Programs A and B. The stippled area marks the bent tunnel linking the Gemini cockpit with the pressurized part of the Supply Module. Please click to enlarge. Image credit: McDonnell/NASA
McDonnell gave attention to the effects of the space environment on astronauts and equipment in its proposal to NASA. Among features of the space environment it examined was the Earth-circling "artificial radiation belt" the July 1962 Starfish Prime space nuclear test had created.

The company acknowledged that little data existed concerning Starfish Prime radiation, but judged nonetheless that the mass of the shielding required to limit astronaut radiation exposure inside a One-Room Space Station in a 200-nautical-mile orbit to 1.93 rad per day would total about 1600 pounds. The 1.93-rad-per-day maximum exposure was based on limits proposed for Apollo lunar missions. The company also suggested a novel (but probably impractical) method for reducing station shielding mass: "personal shielding" for each astronaut, presumably in the form of a garment. This would weigh 160 pounds per astronaut.

McDonnell provided detailed cost estimates with its "Modular Space Station Evolving from Gemini" proposal. If NASA flew Programs A, B, and C, the cost would come to $194.2 million for development, $194.3 million for Program A, $185.9 million for Program B, and $462.8 million for Program C. The cost of Programs A, B, and C would thus total $843 million. If NASA flew A and C only, the development cost would remain the same, and the cost of the two Programs would total $657.1 million.

NASA's Project Gemini saw 10 manned missions launched on Titan II GLVs between March 1965 and November 1966. This made the program almost two years late if one adhered to McDonnell's optimistic 1962 timeline. Gemini III (Virgil Grissom and John Young, 23 March 1965) was a three-orbit manned test of the new spacecraft. At the end of their mission, Grissom and Young's Reentry Module lowered on a parachute and splashed down into the Atlantic. NASA had abandoned the parawing and land landings amid development difficulties in mid-1964.

Ed White performs America's first space walk during Gemini IV, June 1965. Image credit: NASA
Proximity operations: Gemini VI performs rendezvous maneuvers with Gemini VII, December 1965. Image credit: NASA
During Gemini IV (James McDivitt and Edward White, 3-7 June 1965), Ed White became the first American to walk in space. His successful simple spacewalk deceived planners, causing them to postpone complex spacewalks in favor of Gemini long-duration and rendezvous-and-docking missions.

Gemini V (Gordon Cooper and Charles Conrad, 21-29 August 1965) remained in orbit for a week and Gemini VII  (Frank Borman and James Lovell, 4-18 December 1965) stayed aloft for two weeks. Following the loss of its Agena docking target to an Atlas booster failure, Gemini VI (Walter Schirra and Thomas Stafford, 15-16 December 1965) performed rendezvous and proximity operations with Gemini VII.

The Gemini spacecraft docked by sliding its blunt nose into a funnel-shaped docking collar on the front of the Agena, triggering latches. Crew movement between the Gemini cockpit and the outer surface of the Agena was by spacewalk. Gemini VIII (Neil Armstrong and David Scott, 16-17 March 1966) became the first manned spacecraft to perform a docking, but then suffered a perilous thruster malfunction that forced an emergency splashdown, scrubbing Scott's planned spacewalk.

Gemini VIII astronauts David Scott (left) and Neil Armstrong after their emergency return to Earth, March 1966. Image credit: NASA
Gemini IX (Thomas Stafford and Eugene Cernan, 1-11 June 1966) attempted to dock with an ad hoc target vehicle following the loss of its Agena target to another Atlas booster failure, but found their way blocked by a jammed launch shroud. Cernan's attempt to perform a complex spacewalk using a USAF-developed rocket backpack was also less than successful.

Gemini X (John Young and Michael Collins, 18-21 July 1966) docked with an Agena and used its rocket motor to rendezvous with the dead Gemini VIII Agena, thus accomplishing the world's first double-rendezvous. The mission drove home once again the challenges of walking in space.

Gemini missions XI (Charles Conrad and Richard Gordon, 12-15 September 1966) and XII (James Lovell and Edwin Aldrin, 11-15 November 1966) both performed rendezvous with an Agena and saw astronauts step outside to master spacewalk techniques. During their spacewalks, Gordon and Aldrin each tethered his Gemini to its Agena to perform artificial-gravity and spacecraft stabilization experiments.

By Gemini's end, NASA had a cadre of astronauts experienced in techniques required for Apollo lunar flights. NASA did not take up McDonnell's proposal for a Gemini-based space station skills-building program. Meanwhile, Department of Defense and White House interest in a USAF manned space program waxed and waned.

In December 1963, a year to the month after McDonnell sought to interest NASA in its "Modular Space Station Evolving from Gemini" proposal, the Gemini-based USAF Manned Orbiting Laboratory (MOL) program received approval. MOL bore a modest resemblance to both McDonnell's 1961 MTSS spacecraft and its Four-Room Space Station. The USAF selected three groups of MOL astronauts - a total of 17 men - in November 1965, June 1966, and June 1967.

MOL refugees: NASA's Group 7 astronauts.  From left to right they are Karol Bobko, Gordon Fullerton, Henry Hartsfield, Robert Crippen, Donald Peterson, Richard Truly, and Robert Overmyer. Image credit: NASA
Six and a half years after it began (10 June 1969), with more than $300 million spent, President Richard Nixon cancelled MOL in favor of less costly automated surveillance satellites. Eight MOL astronauts subsequently transferred to NASA and went to work at the Manned Spacecraft Center (MSC) in Houston, Texas. MSC had formed around the STG, which had split away from NASA LaRC and moved to Houston in 1962-1963. Seven of the eight formed the seventh group of NASA astronauts, and one (Albert Crews) became an aircraft pilot for the MSC Flight Crew Operations Directorate.

Even as MOL ended, NASA sought funding to develop a six- or 12-man core Space Station and a reusable Space Shuttle to resupply it and change out its crews. The space agency hoped that the Station might evolve into a 50- or 100-man Space Base with artificial gravity. NASA's station ambitions received little support, but the Nixon White House became interested in the Space Shuttle and made NASA accommodation of Defense Department spaceflight needs a condition for its approval as a stand-alone program (that is, with no Space Station). Eventually, all seven Group 7 astronauts would reach orbit on board Space Shuttle Orbiters.

Sources

Modular Space Station Evolving from Gemini, Report No. 9572, Volume I: Technical Proposal, McDonnell Aircraft Corporation, 15 December 1962

Modular Space Station Evolving from Gemini, Report No. 9572, Volume II: Proposed Program and Available Resources, McDonnell Aircraft Corporation, 15 December 1962

Gemini Summary Conference, SP-138, NASA Manned Spacecraft Center, Houston, Texas, NASA, 1967

On the Shoulders of Titans: A History of Project Gemini, SP-4203, 1977

The Problem of Space Travel: The Rocket Motor, SP-4026, Hermann Noordung (Herman Potočnik), E. Stuhlinger, J. Hunley, and J. Garland, editors, NASA, 1995

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Space Station Resupply: The 1963 Plan to Turn the Apollo Spacecraft Into a Space Freighter

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21 November 2015

Space Station Resupply: The 1963 Plan to Turn the Apollo Spacecraft Into a Space Freighter

President John F. Kennedy messes up NASA's carefully wrought long-range plans, 25 May 1961. Image credit: NASA
When first proposed in 1959, the spacecraft that would come to be known as the Apollo Command and Service Module (CSM) was envisioned as an Earth-orbital "advanced manned spacecraft" capable of being uprated for circumlunar or lunar-orbital flights. On 15 November 1960, NASA awarded six-month feasibility study contracts for just such an Apollo spacecraft to three contractors: the Martin Company; the Convair Division of General Dynamics; and the General Electric Company Defense Electronics Division, Missile and Space Vehicle Department.

In 1960, the three-man Apollo spacecraft was expected to be the second U.S. piloted spacecraft after the Mercury capsule. It would include a Command Module (CM), a Service Module (SM), and an Orbital Module; the last of these would augment the work and living space available to the crew, in effect making the spacecraft into a mini-space station.

NASA expected that its piloted program in the 1960s would proceed down one or both of two "logical" paths, and that Apollo would be crucial for both. The first path would have Apollo spacecraft transport crews to a temporary "orbiting laboratory." The Orbital Module would be used to transport supplies to the lab in space. The other path would see an Apollo perform a piloted flight around the moon. What might come after 1970 was anybody's guess, though NASA expected that the orbiting lab path would lead to a permanent Earth-orbiting space station and the circumlunar path would lead to a piloted moon landing, piloted Mars and Venus flybys, and a piloted Mars landing.

Apollo as a fork in the road: NASA's plans for piloted spaceflight in 1959. Image credit: NASA
Martin, General Dynamics, and General Electric submitted their final study reports to NASA on 15 May 1961. Ten days later, new President John F. Kennedy wreaked havoc on NASA's logical plans when he opted to proceed directly to a lunar landing before 1970.

Stinging from the failed Bay of Pigs invasion of Cuba and the first piloted spaceflight by Soviet cosmonaut Yuri Gagarin (12 April 1961), Kennedy had asked Lyndon Baines Johnson, his Vice President and National Space Council chair, to propose a space goal that the U.S. might reach ahead of the Soviet Union. The apparent Soviet advantage in launch vehicle capability would, it was believed, give communist rocketeers a head-start if the goal was anything as modest as the establishment of an Earth-orbiting space station. Landing a man on the moon, on the other hand, was a goal audacious enough that the U.S. and Soviet Union would start out more or less evenly matched.

Model of the Apollo Command and Service Module atop a conceptual Landing Propulsion Module. Image credit: NASA
On 28 November 1961, NASA awarded North American Aviation (NAA) the contract to build the Apollo CSM, the design of which included two modules: the conical CM and the drum-shaped SM. The method by which NASA would carry out President Kennedy's bold lunar mandate remained uncertain, though it was widely assumed that the space agency would soon award a contract for a third Apollo spacecraft module: a Landing Propulsion Module for lowering the CSM to a gentle touchdown on the moon. NAA went so far as to specify in its April 1962 subcontract with Aerojet General Corporation that the CSM's Service Propulsion System (SPS) main engine be capable of generating enough thrust to launch the CSM off of the lunar surface and place it on course for Earth.

As it turned out, however, the Apollo CSM would never land on the moon. On 11 July 1962, as part of an ongoing debate that was not finally settled until November of that year, NASA selected the Lunar-Orbit Rendezous (LOR) mode for accomplishing the Apollo mission. A contract for a third Apollo module was indeed awarded (to Grumman Aircraft Engineering Corporation, 7 November 1962), but it was for the Lunar Excursion Module (LEM), a bug-like two-man spacecraft that would undock from the CSM in lunar orbit and lower to a landing on the moon. The Apollo CSM thus became the mother ship for delivering astronauts and LEM to lunar orbit and returning astronauts and moon rocks to Earth.

Despite President Kennedy's new high-priority moon landing goal, space station studies within NASA did not cease. In fact, some believed that NASA might launch its first station into Earth orbit before an astronaut stepped onto the moon. They reasoned that lunar landing program development costs would peak two or three years before NASA launched its first lunar landing attempt (as in fact they did). If NASA's portion of the Federal purse remained near its peak as moon program costs declined, then funds might become available for a station in Earth orbit as early as 1968.

At the newly established NASA Manned Spacecraft Center (MSC) in Houston, Texas. engineer Edward Olling headed up space station planning. He informally named MSC's first proposed station program Project Olympus.

In April 1962, Olling circulated a draft planning document within MSC for comment; then, on 16 July 1962, he unveiled to top-level MSC managers his "Summary Project Development Plan" for the Project Olympus space station program. Olling envisioned a series of four 24-man stations launched and continuously staffed over a period of from five to seven years.

Olling explained that the Project Olympus space stations would provide NASA with enough astronauts, scientific equipment, pressurized volume, and electrical power to carry out wide-ranging basic and applied science research in space. Early station research would, however, seek to answer important questions about the efficacy of humans in space; for example, could astronauts work safely and effectively in orbit for long periods?


Each 138,600-pound Project Olympus station would consist of a 15,000-cubic-foot central hub from which would radiate three evenly spaced arms with a total of about 35,000 cubic feet of volume. The hub would include a hangar for crew and supply spacecraft. Each arm would include a pressurized crew module of oval cross-section with two cylindrical access tunnels. The Project Olympus station would launch atop a two-stage Saturn V rocket with its hub on top and its three radial arms folded below. Once in orbit, the station would separate from the Saturn V second stage and the three arms would hinge upward and lock into place. Pressurized tunnels would link each arm to the station hub.

Small rocket motors at the ends of the arms would ignite to spin the station. The 150-foot-wide Project Olympus station would revolve four times per minute to create acceleration in its arms which the crew inside would feel as gravity. "Down" would be away from the hub. The crew decks farthest from the hub would experience the greatest acceleration: the equivalent of one-quarter of Earth's gravitational pull, or about midway between lunar and martian surface gravity. Decks closer to the hub would experience less acceleration, so might be used mainly for storage. Olling hinted that the different levels of acceleration experienced at varying distances from the hub might be useful for scientific research, but he provided no specifics as to how.

Cutaway drawing of a Project Olympus-type space station. The centrifuge in lower part of the hub would support variable gravity experiments. Not shown is a station power system; NASA MSC proposed both solar- and nuclear-powered station designs. Image credit: North American Aviation/NASA
New research objectives would be added over time as old stations were retired and new ones launched. The Project Olympus stations would become space-environment research facilities, "national laboratories" for research into meteorology, geophysics, radio communications, navigation, and astronomy, as well as "orbital operations" platforms (that is, shipyards for preparing spacecraft bound for points beyond space station orbit).

Olling advised MSC management that Project Olympus stations should operate in circular 300-nautical-mile-high orbits inclined 28.5° relative to Earth's equator - what he called a "Mercury orbit" because it matched the orbital inclination of the one-man Mercury capsules. Astronaut Scott Carpenter orbited Earth for nearly five hours in the Aurora 7 capsule on 24 May 1962, while Olling prepared his project plan. Olling later lowered his recommended altitude to 260 nautical miles.

The 28.5° latitude of the launch pads at Cape Canaveral, Florida, determined the orbital inclination of the Project Olympus stations. Matching launch-site latitude and station orbital inclination would maximize both station mass and the mass of the payload that could be delivered to the station. Olling also mentioned (albeit briefly) the possibility of a polar-orbiting Project Olympus station that would pass over all points on Earth.

In April 1963, MSC awarded NAA a contract for a seven-month study of a Modified Apollo (MODAP) logistics spacecraft for delivering astronauts and cargo to Project Olympus space stations. The Apollo CSM design had yet to reach its final form. No docking unit design had been selected, for example, though the probe-and-drogue system eventually chosen was already the leading candidate. The overall CSM layout was, however, firmly in place, giving NAA a meaningful point of departure for its MODAP study.

Apollo 15 Command and Service Module Endeavor in lunar orbit. Image credit: NASA
The Apollo CM included three astronaut couches, control consoles, small windows at strategic locations, a side-mounted hatch with a window, a docking tunnel and parachutes in its nose, thrusters for orienting it for atmosphere reentry, and, at its base, a bowl-shaped reentry heat shield. Umbilicals and cables in a hinged housing linked the CM to the SM.

The Apollo SM included seven major internal bays. A central cylindrical bay housed tanks of helium pressurant for pushing rocket propellants into the SPS main engine. Arrayed around the central compartment were six triangular bays containing tanks of fuel and oxidizer for the SPS and for four attitude-control thruster quads, electricity- and water-making fuel cells, and tanks of liquid oxygen and liquid hydrogen reactants for supplying the fuel cells.

The MODAP CSM would comprise a stripped-down SM and a beefed-up CM. Because it would spend a limited amount of time in free flight before it docked with an Earth-orbiting station, the MODAP SM could dispense with or minimize many Apollo lunar SM systems. Batteries would replace fuel cells, for example, and a compact LEM descent engine could replace the SPS. The LEM engine would draw its propellants from a pair of spherical tanks in the MODAP SM's central cylindrical compartment. These deletions and additions would free up four of the MODAP SM's triangular bays for cargo transport.

The Apollo SM had six roughly triangular bays arrayed around a cylindrical core. The bays contained propellants, fuel cells, and liquid hydrogen and liquid oxygen tanks, among other systems necessary for a lunar mission. For its Earth-orbital station logistics missions, the MODAP SM needed fewer systems and tanks, so could devote four of the six triangular bays to cargo. The section image at right displays the cargo and equipment bays and a possible arrangement for four cargo doors. Image credit: North American Aviation/NASA
A two-stage Saturn IB rocket capable of placing 32,500 pounds into a 105-nautical-mile circular parking orbit at 28.5° of inclination would launch the MODAP CSM. Pre-launch preparation, launch operations, and ascent to parking orbit would need from five to 10 days, from five to eight hours, and 11 minutes, respectively.

The MODAP CSM would remain in parking orbit for less than five hours before its crew ignited its LEM descent engine to place it into an elliptical transfer orbit with a 260-mile apogee (highest point above the Earth). Upon reaching apogee 45 minutes later, its crew would again ignite the engine to circularize its orbit. Subsequent station rendezvous and docking maneuvers might need up to 17.5 hours.

The company calculated that a 24-man station with crew stays lasting six months would need to receive a MODAP CSM bearing six astronauts and 5855 pounds of supplies eight times per year - that is, every 45 days. The typical cargo manifest would include 1620 pounds of food, 1035 pounds of oxygen, 505 pounds of nitrogen, 1450 pounds of propellants, and 1245 pounds of spare parts. The Project Olympus station would recover and reuse all water launched with it, so would have no need of water resupply.

These cutaway drawings of the Project Olympus hangar display internal (right) and external palletized cargo transfer methods. The internal method assumes that the entire MODAP CSM can fit into the hangar. The drawing at left shows how the protruding MODAP SM would separate from the MODAP CM and pivot into cargo-unloading position. MODAP CMs for Earth-return are docked radially on the dome-shaped docking hub near the floor of the hangar. Image credit: North American Aviation/NASA
Supplies would reach the Project Olympus station in drum-shaped Cargo Modules, or CAMs, packed in the four empty triangular MODAP SM bays. The mass of the empty CAMs would total 1970 pounds. Liquid and gaseous cargo would fill small CAMs, while solid cargoes would ride on disc-shaped pallets in large CAMs. In all, a MODAP CSM could transport 9127 pounds of cargo and CAMs.

The MODAP CSM would dock with the Project Olympus station via an axial docking unit at the bottom of the station hangar. NAA envisioned that the station would include either a tall hangar for the entire MODAP CSM or a short hangar for the MODAP CM alone (in which case the MODAP SM would protrude into space). If the former, then CAM transfer could occur entirely within the hangar. If the latter, then CAM transfer would occur external to the station. In both cases, after all cargo was transferred, the MODAP SM would be cast off and the hangar closed to protect the MODAP CM.

These cutaway drawings of the Project Olympus station hangar show CAM internal (right) and external transfer methods. Compare with palletized transfer drawings above. Image credit: North American Aviation/NASA
To free up the single axial docking port for the next MODAP CSM, a manipulator arm inside the hangar would pivot the MODAP CM to one of three radial berthing ports. It would remained parked there, undergoing periodic inspection and maintenance but otherwise dormant, for up to six months.

Discarding the MODAP SM with its LEM descent engine meant that the MODAP CM would need to carry a separate de-orbit propulsion module. NAA proposed a cluster of six solid-propellant retrorockets, any five of which could deorbit the MODAP CM. The retro package would include batteries for powering the MODAP CM during free-flight prior to reentry. NAA expected that, in normal circumstances, the MODAP CM would need 30 minutes for checkout and undocking. The MODAP CM's crew would ignite its retrorockets immediately after it maneuvered clear of the hangar.

The MODAP CM with solid-propellant retropack. Image credit: North American Aviation/NASA
Twenty-five minutes after retrofire and shortly after retropack separation, the MODAP CM would reenter Earth's atmosphere. Because the MODAP CM would encounter the atmosphere moving at about half the speed of the Apollo lunar CM, its heat shield could be about half as thick. Descent and splashdown would need 11 minutes. With six astronauts on board, the MODAP CM would be heavier than the lunar CM, so would lower on four parachutes; that is, one more than the lunar CM. Its crew could splash down safely if one parachute failed.

Under normal circumstances, the MODAP CM would splash down in the Gulf of Mexico not far from Houston, so crew recovery would take place within a few hours. NAA acknowledged, however, that emergencies might occur. Because of this, the MODAP CM could fly free of the space station for up to 10.5 hours while its inclined orbit and Earth's rotation put it on course for reentry and splashdown at any of three sites. These were the prime site in the Gulf of Mexico, a site near Okinawa in the western Pacific Ocean, and one near Hawaii. To trim costs, fleets of recovery ships would not remain on standby at the landing sites; because of this, the astronauts might need to wait for up to 24 hours for rescue following an emergency splashdown near Okinawa or Hawaii.

An abort during ascent to Earth orbit could cause the Apollo and MODAP CMs to land in southern Africa; that is, to touch down on land. To protect its three-man crew during a land landing, the lunar CM would include shock absorbers in its supporting seat struts. These would enable the crew couches to move vertically up to five inches to dissipate the force of impact.

A tight fit: six-man MODAP Command Module seating arrangement. Image credit: North American Aviation/NASA
Because the MODAP CM would carry six men arrayed in two rows of three couches each, with one row above the other, NAA found that vertical couch movement would not be an option. The three-man lunar CM would also rely on crushable material behind its heat shield to absorb the force of land impact; this would be inadequate for the greater mass of the six astronauts in the MODAP CM.

NAA proposed to solve the emergency land-landing problem by in effect moving the shock absorbers from the seat struts to the MODAP CM's heat shield and by adding four solid-propellant landing rockets. In the event of a land landing, the bowl-shaped heat shield would deploy downward on shock-absorbing struts and the landing rockets would ignite and pivot out from behind the shield.

NAA envisioned a MODAP CSM design & test program spanning from early 1964 to mid-1968. Operational MODAP CSMs would deliver crews and supplies to 24-man Project Olympus stations between mid-1968 and the end of 1973. The company anticipated that five MODAP CSMs would be used in ground tests and unmanned test flights, and that 40 MODAP CSMs would support the station program. Of these, perhaps two would fail, requiring assembly of at least two backup MODAP CSMs. NAA placed the total cost of the MODAP CSM program including $861 million for Saturn IB rockets at $1.881 billion.

A significant outcome of Olling's Project Development Plan and NAA's MODAP study was the realization that space station crew rotation and resupply would dominate total space station program cost. Summing up his findings, Olling wrote that a "reusable launch vehicle could contribute large economies" (that is, ensure large cost savings) for the station program. Even if four space stations were launched on expendable Saturn V rockets during the Project Olympus program, station cost would total only $1.273 billion; that is, about $600 million less than the MODAP CSM flights.

The Project Olympus and MODAP CSM study teams were not alone in reaching these conclusions; thus, as early as 1963, a reusable logistics spacecraft came to be seen as a desirable component of a large space station program. By 1968, this led to calls by high-level NASA management for a 1970s Space Station/Space Shuttle program.

Sources

Final Technical Presentation: Modified Apollo Logistics Spacecraft, Contract NAS 9-1506, North American Aviation, Inc., Space and Information Systems Division, November 1963

"Project Olympus: Proposed Space Station Program," Edward H. Olling, NASA Manned Spacecraft Center, 16 July 1962

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