27 July 2017

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

Stacking a Saturn V rocket: inside the Vertical Assembly Building at Kennedy Space Center, a giant crane gingerly lowers an S-II second stage onto an S-IC first stage. Image credit: NASA
NASA abandoned work toward piloted Mars and Venus flyby missions based on hardware developed for Apollo and its planned successor, the Apollo Applications Program, during the final months of the pivotal year 1967. Until August of that year, however, the concept was viewed by many as a plausible interim step between 1960s Apollo moon landings and 1980s piloted Mars landings.

Though NASA awarded no new piloted flyby study contracts, studies performed in 1965, 1966, and 1967 continued to report out at aerospace conferences and in NASA briefings during 1968 and 1969. In March 1968, for example, North American Rockwell (NAR) engineers W. Morita and J. Sandford summed up a study they completed in April 1967 for NASA's Marshall Space Flight Center (MSFC) in Huntsville, Alabama. Their study looked at how a modified NAR-built S-II rocket stage might be used to boost a piloted flyby spacecraft out of Earth orbit (that is, "inject" it onto an interplanetary trajectory). They presented results of their study at the Fifth Space Congress in Cocoa Beach, Florida.

Image credit: NASA
The 33-foot-diameter, 81.5-foot-long S-II, the second stage of the Apollo Saturn V rocket, weighed about 40 tons empty. A single propellant tank divided by a dome-shaped "common bulkhead" held a total of more than 400 tons of liquid oxygen (LOX) and liquid hydrogen (LH2) propellants. LH2 is of low density, so the LH2 section in the top/front part of the tank measured more than twice as long as the LOX section.

The propellants fed a cluster of five J-2 rocket engines, each producing 200,000 pounds of thrust. Together they consumed more than a ton of propellants per second during their 6.5 minutes (390 seconds) of operation, boosting the Saturn V's speed from 6000 miles per hour at separation from the Saturn V S-IC first stage to 17,400 miles per hour (just short of Earth-orbital velocity) at S-II shutdown.

NAR proposed to launch the S-II interplanetary boost stage, which it designated the S-IIB, into Earth orbit on a two-stage Saturn V. The S-IIB would include two or three improved J-2S engines in place of the S-II's five J-2s. After separation from the spent S-II, the J-2S engines would fire briefly to place the S-IIB into an elliptical Earth orbit. An auxiliary propulsion system made up of three solid-propellant motors would perform orbit circularization, and eight thruster modules based on the Apollo Command and Service Module (CSM) attitude control system would carry out orbit corrections and rendezvous and docking with the piloted flyby spacecraft.

Proposed North American Rockwell-built piloted flyby payloads are shown in red. Image credit: NAR/DSFPortree
The S-IIB would reach orbit with about 76 tons of LH2 fuel on board. NAR's analysis determined that, if only standard S-II thermal insulation were employed, boil-off caused by solar heating in orbit would reduce this to only 25 tons in less than five days. NAR proposed to reduce boil-off by installing a hydrogen gas-filled "vapor barrier" between the LH2 and LOX sections of the propellant tank and by applying "super-insulation" panels to the stage exterior. These modifications would reduce total LH2 boil-off over 10 days - the rated orbital lifetime of the S-IIB - to less than five tons.

The S-IIB would need to lift off with its LOX tank empty if the two-stage Saturn V was to place it in Earth orbit. Separately launched automated LOX tankers would then dock with it to fill the tank. The NAR engineers examined S-II-based tankers, tankers based on the Apollo Saturn S-IVB stage, and a wholly new tanker Lockheed Corporation designed in a separate study for MSFC.

LOX tankers considered in the North American Rockwell study. Green represents each design's LOX cargo volume. Image credit: NAR/DSFPortree
Morita and Sandford described two S-II-based tankers. The first, the S-IIB/TK, would measure about 25 feet shorter than the standard Saturn V S-II stage. It would separate from the S-II second stage of the two-stage Saturn V that launched it, fire its twin J-2S engines for 3.5 minutes to attain a 100-nautical-mile-by-263.5-nautical-mile orbit, then fire them again at apogee (the high point in its orbit about the Earth) to raise its perigee (the low point in its orbit about the Earth). The circularization burn would leave the S-IIB/TK into a 263.5-nautical-mile-high parking orbit.

The 92 tons of LOX remaining after the circularization burn would constitute the tanker's payload. Solar heating would cause the LOX to boil off over time, so after 163 days - the longest period the tanker would need to loiter in Earth orbit before transferring its payload to the S-IIB injection stage - 75 tons would remain.

NAR's second S-II tanker variant, the S-II/TK, would have a LOX tank four feet longer than that of the standard Saturn V S-II. It would serve double-duty as a Saturn V second stage and a tanker. After it separated from the S-IC first stage, its five J-2S engines would boost it into a 100-nautical-mile-by-263.5-nautical-mile orbit, Earth orbit, then two engines would fire a second time at apogee to circularize its orbit. The S-II/TK would retain about 105 tons of LOX after the circularization burn and about 82 tons after 163 days in orbit.

Sandford and Morita next examined tankers based on the Douglas Aircraft Company-built S-IVB stage. The 22-foot-diameter S-IVB served as the the second stage of the Saturn IB rocket and the third stage of the Saturn V moon rocket.

The first S-IVB tanker design would trim cost by retaining - but leaving empty - the S-IVB stage LH2 tank. The second would delete the LH2 tank, making for a tanker that was shorter and lighter, but more heavily modified and thus more costly. The first design would deliver 110.5 tons of LOX to 263.5-nautical-mile orbit, of which about 99 tons would remain after 163 days. The second S-IVB-based design would deliver 107.5 tons to a 263.5-nautical-mile circular parking orbit. Of this, 92.5 tons would remain after 163 days.

The third tanker Morita and Sandford investigated was Lockheed's Orbital Tanker. Because it would be purpose-built to serve as a tanker, it would be more efficient than the NAR S-II and Douglas S-IVB tankers, but also more costly. Efficiency in this case would be measured in terms of the expected amount of LOX boil-off.

After launch on a two-stage Saturn V, the Orbital Tanker would fire LH2/LOX or solid-propellant rocket motors to place itself into a 263.5-nautical-mile-high parking orbit. The Orbital Tanker would reach orbit bearing 114.9 tons of LOX in an insulated spherical tank. Of this, 110.9 tons would remain after 163 days.

Sandford and Morita looked at Mars and Venus flybys, but emphasized a Mars flyby that would leave Earth orbit in late September 1975. Their proposed Mars flyby launch schedule took into account the narrow range of Earth-orbit departure dates, the planned 10-day lifetime in Earth orbit of the S-IIB injection stage, and the existence of only two Launch Complex 39 Saturn V launch pads at NASA's Kennedy Space Center in Florida.

Assuming an Earth-orbit departure date of 20 September 1975, the piloted Mars flyby mission would begin with three LOX tanker launches in April-May 1975. They would lift off between 153 and 130 days before the scheduled launch to Earth orbit of the S-IIB injection stage. A Saturn V bearing a fourth, backup tanker would be held in reserve.

Following the launch of the third LOX tanker in May 1975, KSC ground teams would refurbish the twin Launch Complex 39 pads for launch of the backup tanker (if necessary), the piloted flyby spacecraft, and the S-IIB injection stage. NAR estimated that KSC workers would need no more than one eight-hour shift per day to ready the pads in time for the piloted flyby spacecraft and S-IIB stage launches in September 1975. More shifts would be added if the backup tanker became necessary; that is, if one of the first three tankers failed to reach orbit or malfunctioned in orbit while awaiting arrival of the spacecraft and S-IIB stage.

On 15 September 1975, the S-IIB injection stage would lift off, followed within 24 hours by the piloted flyby spacecraft. Spacecraft and stage would rendezvous and dock within 12 hours, then the combination would set out in pursuit of the waiting tankers.

The piloted flyby spacecraft/S-IIB combination would dock with the three LOX tankers about 12 hours apart. Each would in turn link up with the aft end of the S-IIB, transfer its LOX cargo, and detach.

The piloted flyby astronauts and mission controllers on Earth would then perform a detailed systems check of the piloted flyby spacecraft/S-IIB stage combination. If all checked out as normal, they would be certified ready to depart Earth orbit on 20 September, just as the launch window opened for a minimum-energy Earth-Mars free-return transfer.

The quantity of propellants required to depart Earth orbit on a Mars flyby trajectory would increase steadily from the moment the launch window opened. At the same time, boil-off would cause the quantity of propellants in the S-IIB stage to steadily decrease. Morita and Sandford calculated that the S-IIB stage would retain sufficient LH2 to boost the Mars flyby spacecraft out of Earth orbit toward Mars for five days after the launch window opened; that is, until 25 September 1975.


"The S-II Injection Stage for the Mars/Venus Flyby Mission," W. H. Morita and J. W. Sandford, Proceedings, Fifth Space Congress: The Challenge of the 1970s, pp. 10.1-1 – 10.1-22; paper presented in Cocoa Beach, Florida, 11-14 March 1968

More Information

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

Apollo Ends at Venus: A 1967 for Single-Launch Piloted Venus Flybys in 1972, 1973, and 1975

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

Two for the Price of One: 1980s Piloted Missions with Stopovers at Mars and Venus (1969)

23 July 2017

Plush Bug, Economy Bug, Shoestring Bug (1961)

President John F. Kennedy, flanked by Vice President Lyndon Baines Johnson (right) and NASA officials, addresses employees of the Manned Spacecraft Center (MSC) in Houston, Texas, on 12 September 1962. The Apollo lunar lander mockup in this image is a North American Aviation design. Image credit: John F. Kennedy Library/NASA
Following President John F. Kennedy's 25 May 1961 "Moon speech" before a joint session of Congress, NASA re-directed Project Apollo. When first conceived, Apollo was to have been the next U.S. piloted spacecraft program after Mercury. In a plan drafted in 1959-1960, the Apollo spacecraft was described as an Earth-orbital vehicle designed for independent flight or ferry flights to an Earth-orbiting space station.

NASA planners hoped that eventually - by about 1970 - Apollo might lead to a circumlunar or lunar-orbital flight. Following JFK's speech, however, the program's goal became to land a man on the Moon by 1970 and return him safely to the Earth. Almost immediately, many asked the obvious question: how would Apollo accomplish this epic feat?

As many as six lunar mission modes received consideration in 1961-1962, though two - Earth-Orbit Rendezvous (EOR) and Direct Ascent - emerged as early favorites. Both modes included several variants.

In the EOR mode, one or more propulsion stages and a piloted Moonship (and sometimes tankers for filling the propulsion stages with propellants) would be brought together in Earth orbit. The propulsion stage or stages would then be ignited to place the Moonship and its crew on course for the Moon.

In Direct Ascent, a single large rocket would boost the piloted Moonship from Earth's surface directly to the Moon. After the piloted spacecraft was placed on course for the Moon, the EOR and Direct Ascent mission modes would be essentially identical.

The process by which the Apollo lunar mission mode decision was taken was complex and involved many players at NASA Headquarters and the NASA field centers, some of whom backed different modes at different times. Throughout the entire untidy 14-month-long process, however, engineer John Houbolt of the NASA Langley Research Center (LaRC) in Hampton, Virginia, staunchly advocated Lunar-Orbit Rendezvous (LOR). Houbolt did not originate the LOR mode: it dates back at least to 1948, when H. E. Ross described it in London before a meeting of the British Interplanetary Society.

John Houbolt at the chalkboard. He points toward an "LEV" (Lunar Excursion Vehicle); this would become the Apollo Lunar Module. Image credit: NASA
Houbolt gave briefings on LOR to several of the groups involved in the Apollo mode decision, including the Lundin Committee, the Ad Hoc Task Group for Study of Manned Lunar Landing by Rendezvous Techniques (the Heaton Committee), and the LaRC-based (but otherwise independent) Space Task Group. The Large Launch Vehicle Planning Group (the Golovin Committee) requested a detailed written report on LOR after Houbolt briefed it in August 1961.

Houbolt and his colleagues at LaRC explained in their 31 October 1961 report to the Golovin Committee that LOR would differ from EOR and Direct Ascent in the nature of its spacecraft. As noted above, in EOR and Direct Ascent a single Apollo spacecraft would accomplish all phases of the lunar landing mission. It would bear its occupants from the Earth to the Moon, land them on the Moon, and then transport them back to Earth. LOR, on the other hand, would see lunar mission phases divided between two distinct piloted vehicles. In the LOR scenario LaRC described, these spacecraft were the Apollo and the single-stage "Bug" lunar lander.

The three-man Apollo spacecraft, which in the LOR mode would come no nearer to the Moon than lunar orbit, would include the mission's Earth-atmosphere reentry vehicle and a pair of propulsion modules for performing major maneuvers. The Bug would detach from the Apollo in lunar orbit, descend toward the Moon's surface, land one or two astronauts gently on the Moon, and then return to the Apollo mothership in lunar orbit. The crew would cast off the spent Bug, then the Apollo would return to Earth.

LaRC examined three Bug designs, which it dubbed "Shoestring," "Economy," and "Plush." The first, with a dry (no propellants or other expendables) mass of only 1270 pounds, would land one man on the Moon for only a brief period and return no more than 50 pounds of lunar samples to the orbiting Apollo for transport to Earth. Of the three designs, the Shoestring Bug would come closest to fulfilling the strict letter of President Kennedy's mandate - that "a man" land on the Moon.

The second design, the Economy Bug, would support two men on the Moon for 24 hours. The lander's dry mass would total 2234 pounds; it would transport up to 100 pounds of rock samples from the Moon's surface to the orbiting Apollo.

The Plush Bug, the scientists' favorite, would support two men on the Moon for one week, providing them with adequate time to perform field geology at the lunar landing site. Plush Bug dry mass would total 3957 pounds; it could lift 150 pounds of samples to the orbiting Apollo.

According to Houbolt's team, an LOR landing would be safer than either a Direct Ascent or EOR landing because the Bug would be designed only for that function - in other modes the landing function would be compromised by the need to take into account other functions, such as Earth atmosphere reentry. Houbolt also proposed a spacecraft configuration that would further enhance astronaut safety: an Apollo with two Shoestring Bugs. If the first Shoestring Bug became trapped on the lunar surface, then the second would be used to mount a rescue.

John C. Houbolt's concept drawing of a Lunar Orbit Rendezvous spacecraft with twin Shoestring Bugs. The stack depicted would reach Earth parking orbit atop a Saturn C-3 rocket. Weights (in pounds) are for "wet" hardware (that is, loaded with propellants and expendables). Image credit: NASA 
As with the other proposed Apollo modes, many preparatory and precursor missions would lead up to LaRC's LOR Moon landing. LaRC's proposed five-year "Master Flight Plan" would begin with 11 Ranger automated lunar rough-landing missions before October 1963. These would help engineers and scientists characterize the lunar surface so that they could design the Bug, lunar surface space suits, and surface exploration equipment.

Meanwhile, NASA would fly four Mercury manned Earth-orbital missions, each completing 18 Earth orbits. The missions, flown between February and August 1963, would enable doctors to gather basic data on human performance in space.

NASA would launch 15 Surveyor automated soft-landing missions to the Moon between August 1963 and March 1966. Meanwhile, back on Earth, the space agency would drop Apollo reentry vehicles from aircraft 20 times between September 1963 and June 1964 to test glide characteristics, parachutes, and land landing systems (the LaRC engineers assumed a landing on U.S. soil).

Astronauts would practice rendezvous and docking using maneuverable Mercury Mark II spacecraft launched into Earth orbit atop modified Titan missiles. The two-seater Mercury Mark II, which was renamed Gemini in January 1962, would dock with separately launched unmanned Agena upper stage target vehicles during five missions spanning October 1963 to June 1964.

Six manned Mercury Mark II missions between August 1964 and June 1965 would see astronauts practice docking with Bug landers in Earth orbit. For each mission, the Bug and the Mercury Mark II would be launched together on a Saturn C-1 rocket. Saturn C-1 was envisioned as the first NASA launch vehicle designed specifically for piloted spaceflight.

The Mercury Mark II/Bug Saturn C-1 missions would overlap with eight Saturn C-1-launched Apollo suborbital and Earth-orbital flight tests spanning September 1964 through August 1965. A pair of Saturn C-1-launched manned Apollo/Bug test missions in Earth orbit would follow in September-October 1965, laying the groundwork for four piloted Apollo high-elliptical Earth-orbit and circumlunar/lunar-orbit missions between November 1965 and February 1966.

LaRC suggested that the high-elliptical and circumlunar/lunar-orbit missions, each of which would leave Earth on a Saturn C-3 or C-4 rocket, might be converted into manned lunar landing attempts if necessary: for example, if the Soviet Union were believed to be on the verge of launching its first piloted lunar landing attempt. Assuming, however, that they were not turned into landing missions, then the first four manned lunar landing attempts of the Apollo Program would occur between March and June 1966.

LaRC's LOR missions would begin with launch on a Saturn C-3 or C-4 from Cape Canaveral, Florida. The LaRC team noted that a direct flight to the Moon from a fixed site on the Earth's surface could begin only during a short period each month if it sought to land at a specific lunar landing site. To circumvent this limitation, LaRC's Apollo mothership/Bug lander stack would enter low-Earth parking orbit before setting out for the Moon. This would in effect give the mission a mobile launch site, providing planners with "complete freedom" in selecting lunar landing mission start time.

The first and largest of the two Apollo propulsion modules would burn all of its propellants to push the Apollo mothership with its small propulsion module and a Bug lander out of Earth orbit, then would separate. LaRC opted for an Earth-Moon transfer lasting from 2.5 to three days.

LaRC noted that the mission could follow "a free return circumlunar trajectory" that would enable the Apollo/Bug stack to swing around the Moon and return directly to Earth without additional propulsion. This would come in handy if the Apollo/Bug stack suffered a propulsion malfunction after Earth-orbit departure.

Assuming, however, that all occurred as planned, the astronauts in the Apollo/Bug stack would turn the small propulsion module forward (that is, in its direction of motion) as it looped behind the Moon. Over the center of the lunar Farside hemisphere, they would ignite the module so that the Moon's gravity could capture the Apollo/Bug stack into lunar orbit.

LaRC recommended a 50-mile-high circular orbit over the Moon's equator, "especially if the exploration time on the lunar surface [was] to be of the order of a week." A spacecraft in such an orbit would pass over all points on the Moon's equator every two hours. This meant that every two hours the Bug would have an opportunity to descend to a specific equatorial target landing site or to lift off from an equatorial site and perform a rendezvous with the orbiting Apollo.

If, on the other hand, the Apollo entered an orbit inclined relative to the lunar equator so that the Bug could descend to a non-equatorial landing site, the Moon's slow rotation would gradually take the site out of the Apollo's orbital plane (that is, the mothership would no longer pass over the Bug landing site). The Bug or the Apollo (or both) would then need to expend propellants to perform a plane-change maneuver to match orbits before rendezvous and docking could take place. LaRC noted, however, that the plane change necessary after a one-day stay at a non-equatorial site would be "insignificant."

LaRC proposed that the Moon landing occur close to local lunar midnight under a full Earth, "thus avoiding the bright glare and black shadows of the sunlit side." Prior to Bug separation, the crew would examine the Moon from orbit to make their final landing site selection. One or two astronauts would then enter the Bug, undock, and fire its engines briefly to move away from the Apollo. This would prevent the Apollo from being enveloped in the Bug's engine plume when the more powerful "lunar letdown" maneuver began. The Bug's engines - LaRC recommended two for redundancy and improved maneuverability - would be capable of being throttled and gimbaled (that is, pivoted for steering).

Halfway around the Moon from the selected landing site - over the Farside, out of view of Earth - the Bug pilot would fire the engines to slow the lander by 60 feet per second. This would nudge its orbit so that it would intersect the surface at the landing site. The Bug would then coast for an hour, steadily losing altitude. Bug and Apollo would remain in visual and radio contact throughout the descent.

About 100 miles from the landing site, the Bug pilot would fire the twin engines to reduce speed, then would commence landing maneuvers. The Bug would gradually tip so that it would reach the landing site with its engines and landing leg footpads pointed down. The pilot would then have one minute of hover time to choose a safe spot for final letdown.

All of LaRC's Bug designs would employ a single pair of engines for descent and ascent. If landing proved impossible, the pilot could throttle up the engines and abort back to orbit. Assuming that all went as planned, the Bug would gently settle on the surface at the target landing site as its pilot throttled back to zero.

Following a period of surface activity, the astronaut or astronauts would prepare the Bug for liftoff. Just before liftoff, the orbiting Apollo mothership would climb into view above the Bug's horizon. The Bug pilot would spot it visually and with radar, then would ignite the Bug's engines. The lander would climb 10 miles high at 0.5 gravities of acceleration, then would coast along an arcing course for up to 33 minutes. Meanwhile, the Apollo spacecraft would orbit over the landing site and pull ahead of the Bug.

A gyroscope-equipped "inertial attitude reference" would provide guidance data to the Bug pilot; if electronic aids failed, however, he could complete rendezvous and docking using visual cues. The Bug pilot would start homing on the Apollo's blinking light beacon about 250 feet out. Docking would take place over the lunar night hemisphere to avoid Sun glare and improve beacon visibility. After docking, the astronaut or astronauts would transfer to the Apollo and cast off the Bug.

The Apollo mothership's small propulsion module would ignite for a second time to push it out of lunar orbit, then would be cast off. LaRC reported that studies of optimum Earth-return trajectories for accomplishing land landings in the U.S. were in progress.

NASA formally adopted LOR in July 1962. The Apollo spacecraft became known as the Command and Service Module (CSM) and the Bug was designated the Lunar Excursion Module (LEM - later changed to Lunar Module, or LM). On 7 November 1962, NASA awarded the LEM contract to Grumman Aircraft Engineering Corporation in Bethpage, Long Island, New York. The Grumman design featured separate descent and ascent stages.

Grumman's winning November 1962 LEM concept featured five landing legs, two docking ports, and large curved glass windows. The design would evolve rapidly as the company and NASA confronted the challenges of landing a man on the Moon. Image credit: NASA
Early LM designs took as their design inspiration small helicopters, so featured curved surfaces and large windows; as the LM design evolved, however, it became faceted and asymmetrical, with small triangular windows. These changes reduced the LM's mass; large, curved, multi-pane glass windows were, it was found, heavier square centimeter for square centimeter than the LM's metal skin.

No LM was as light as the heaviest LaRC Bug - the Apollo 11 LM had a dry mass of 9271 pounds, or about 2.5 times the dry mass of the Plush Bug. It is unlikely that Houbolt and his colleagues knowingly low-balled their mass estimates; rather, most Apollo systems ended up heavier than at first estimated because no one had built piloted lunar spacecraft before.

20 July 1969: The Apollo 11 LM Eagle pirouetted in lunar orbit so that Command Module Pilot Michael Collins, alone on board the Command Module Columbia, could inspect and photograph it. At Eagle's controls were Apollo 11 Commander Neil Armstrong and Lunar Module Pilot Edwin Aldrin. Less than two hours after Collins took this photograph, Eagle touched down on the Moon's Sea of Tranquility, an ancient dusty plain pocked by impact craters. Image credit: NASA
In preparation for the first manned Moon landing, the NASA carried out robotic Ranger, Surveyor, and Lunar Orbiter missions. They mainly focused on equatorial and near-equatorial areas of the lunar Nearside hemisphere. Three Rangers imaged small areas close-up as the fell toward destructive impact, five Surveyors soft-landed and imaged, analyzed, and dug into the lunar surface, and five Lunar Orbiters imaged large regions and small candidate LM landing sites. Meanwhile, 10 two-man Gemini missions in Earth orbit gave astronauts rendezvous and spacewalk practice.

The LM reached space for the first time atop a Saturn IB (an uprated Saturn C-1 variant) during the unmanned Apollo 5 mission in January 1968. Apollo 7, also launched on a Saturn IB, was a piloted CSM test in Earth orbit.

Apollo missions 8 through 17 each launched on a three-stage Saturn V rocket; originally designated Saturn C-5, the Saturn V was more powerful than the Saturn C-3 and Saturn C-4 rockets described in LaRC's report to the Golovin Committee, which were never built. Apollo 8 was a CSM-only piloted lunar-orbital flight. Apollo 9 was a piloted test of the CSM and LM in Earth orbit. Apollo 10, which included a CSM and an LM, was a lunar-orbital dress rehearsal for the first lunar landing attempt scheduled for Apollo 11. Astronauts used the LOR mode to land successfully on the Moon six times between July 1969 and December 1972 (Apollos 11, 12, 14, 15, 16, and 17).

In April 1970, the LM served as a lifeboat for Apollo 13 astronauts James Lovell, Fred Haise, and Jack Swigert after an oxygen tank explosion crippled the CSM Odyssey en route to the Moon. Odyssey's propulsion, electricity generation, and life support systems were all compromised. Fortunately, they had an undamaged spacecraft at their disposal.

The Apollo 13 crew used LM Aquarius's single descent engine and navigation aids to change their course to a free-return path and speed their docked CSM and LM spacecraft back to Earth. They relied on the LM's life support system to provide oxygen and scrub exhaled carbon dioxide from their cabin air. Had an EOR or Direct-Ascent Apollo spacecraft suffered a similar mishap, its crew would almost certainly have perished through asphyxiation, collision with the Moon (if Moon-bound), or uncontrolled Earth-atmosphere reentry (if Earth-bound).


"Manned Lunar Landing Via Rendezvous," NASA Langley Research Center, presentation materials, 19 April 1961

Manned Lunar Landing Through Use of Lunar-Orbit Rendezvous, NASA Langley Research Center, 31 October 1961

The Apollo Spacecraft: A Chronology, NASA SP-4009, The NASA Historical Series, I. Ertel and M. Morse, Vol. I, pp. 81-202

Enchanted Rendezvous: John C. Houbolt and the Genesis of the Lunar-Orbit Rendezvous Concept, Monographs in Aerospace History #4, J. Hansen, NASA History Office, December 1995

More Information

Starfish and Apollo (1962)

The Spacewalks That Never Were: Gemini Extravehicular Planning Group (1965)

If an Apollo Lunar Module Crashed on the Moon, Could NASA Investigate the Cause? (1967)

"Still Under Active Consideration": Five Proposed Earth-Orbital Apollo Missions for the 1970s (1971)

09 July 2017

SEI Swan Song: International Lunar Resources Exploration Concept (1993)

In the top image, the Soviet Union's two-stage Energia heavy-lift rocket and Buran reusable shuttle orbiter ride a transporter to a launch pad at Baikonur Cosmodrome in Kazakhstan. A sturdy armature designed to hoist the combination upright on the pad obscures Energia's lower half. In the bottom image, 59-meter-tall Energia stands on a launch pad bearing Polyus, an experimental military payload developed in response to the U.S. Strategic Defense Initiative. After the Soviet Union crumbled and Russia became a potential international supplier of rockets and spacecraft, hopeful NASA advance planners tentatively tapped Energia to launch hardware for piloted moon and Mars missions. Image credit: NPO Energia
By the close of 1992, the handwriting had been on the wall for the Space Exploration Initiative (SEI) for more than two years. President George H. W. Bush had launched his moon and Mars exploration initiative on the 20th anniversary of the Apollo 11 lunar landing (20 July 1989), but it had almost immediately run headlong into a minefield of fiscal and political difficulties. The change of Presidential Administration in January 1993 was the final nail in SEI's coffin. Nevertheless, exploration planners across NASA continued to work toward SEI goals into early 1994.

In the same period, the Soviet Union was falling apart. Even as Bush called on NASA to return astronauts to the moon and launch them onward to Mars, Soviet domination in eastern Europe collapsed, then the Soviet Union itself began to disintegrate. A bungled coup d'etat in August 1991 undercut the authority of Soviet President Mikhail Gorbachev and led to the official demise of the Soviet Union on 26 December 1991. The largest state on Earth divided into more than a dozen countries, with the Russian Federation under President Boris Yeltsin emerging as the most significant.

The end of the U.S.-Soviet Cold War created dangers and opportunities. Some feared that, impelled by economic chaos in the former Soviet Union, scientists and engineers would sell their skills and knowledge abroad, leading to unprecedented global nuclear proliferation.

Others noted that high-level Soviet space officials had begun to peddle their space hardware at important aerospace meetings in the late 1980s. They saw an opportunity to, among other things, save the U.S./European/Japanese/Canadian Freedom Space Station from cancellation. Yeltsin and Bush agreed to wide-ranging space cooperation in June 1992, partly in the hope that NASA money might help to forestall an exodus of Russian aerospace talent.

In February 1993, Kent Joosten, an engineer in the Exploration Program Office (ExPO) at NASA's Johnson Space Center (JSC) in Houston, Texas, proposed a plan for lunar exploration which, he hoped, would take into account the emerging realities of post-Cold War space exploration. His International Lunar Resources Exploration Concept (ILREC) would, he wrote, reduce "development and recurring costs of human exploration beyond low-Earth orbit" and "enable lunar surface exploration capabilities significantly exceeding those of Apollo." It would do these things by exploiting the abundant oxygen in the lunar regolith (that is, surface material) as oxidizer for burning liquid hydrogen fuel brought from Earth, shipping most cargo to the moon separate from crews, employing Earth-based and moon-based teleoperations, and cooperating with the Russian Federation.

Joosten's concept was a variant of the Lunar Surface Rendezvous (LSR) mission mode. The Jet Propulsion Laboratory (JPL) in Pasadena, California, put forward LSR in 1961 as a candidate mode for achieving President John F. Kennedy's goal of a man on the moon by the end of the 1970s. In 1962, after NASA selected Lunar Orbit Rendezvous (LOR) as its Apollo lunar mission mode, the LSR scheme faded into obscurity. Joosten's concept was not inspired by the early 1960s scenario; instead, his work drew upon contemporary In-Situ Resource Utilization (ISRU) and Mars surface rendezvous techniques proposed for use in NASA's Mars Design Reference Mission 1.0 and Martin Marietta's Mars Direct scenario.

The Apollo LOR mode was designed to permit the U.S. to reach the moon quickly and relatively cheaply, not to support a sustained lunar presence. It split lunar mission functions between two piloted spacecraft, each of which comprised two modules. Modules were discarded after they fulfilled their functions.

Joosten's ILREC piloted moonship would be roughly intermediate in size between the Apollo Lunar Module (LM) (left) and the Apollo Command and Service Module (CSM) (right). This NASA artwork from 1966 is a partial cutaway showing two blue-clad astronauts moving from the CSM to the LM in preparation for undocking and landing on the moon. A third astronaut, who will remain in lunar orbit, awaits LM undocking strapped into his CSM couch.
At the start of an Apollo lunar mission, a Saturn V rocket launched a Command and Service Module (CSM) mothership and a Lunar Module (LM) moon lander. The mighty rocket's S-IVB third stage boosted the CSM and LM into a parking orbit about the Earth; then, about 90 minutes later, reignited to push itself, the CSM, and the LM out of Earth orbit toward the moon. This maneuver, called Trans-Lunar Injection (TLI), marked the real start of the lunar voyage.

After TLI, the CSM separated from the spent S-IVB, turned end-for-end, docked with the LM, and extracted it from the S-IVB. The S-IVB then vented propellants to change its course so that it would not interfere with CSM/LM navigation. Beginning with Apollo 13, the S-IVB was intentionally crashed on the moon to trigger seismometers left behind by previous Apollo expeditions.

As they neared the moon, the Apollo crew fired the CSM engine to slow down so that the moon's gravity could capture the joined Apollo spacecraft into lunar orbit. The LM then separated from the CSM bearing two of the astronauts and descended to the lunar surface using the engine in its Descent Stage.

After a maximum of three days on the moon, the Apollo lunar crew lifted off in the LM Ascent Stage using the Descent Stage as a launch pad. The astronaut in the CSM performed a rendezvous and docking with the Ascent Stage in lunar orbit to recover the moonwalkers - hence the name Lunar Orbit Rendezvous - then the crew discarded the LM Ascent Stage and fired the CSM engine to depart lunar orbit for Earth. Nearing Earth, they cast off the CSM's drum-shaped Service Module and reentered Earth's atmosphere in its conical Command Module (CM).

According to Joosten, a spacecraft that flew from Earth to the lunar surface, arrived on the moon with empty oxidizer tanks, and reloaded them for the trip home with liquid oxygen mined and refined from lunar regolith, could have about half the TLI mass of an equivalent LOR spacecraft. The Apollo 11 CSM, LM, and spent S-IVB stage had a combined mass at TLI of about 63 metric tons; the ILREC spacecraft and its spent TLI stage would have a mass of about 34 metric tons. This substantial mass reduction would permit use of a launch vehicle smaller than the Apollo Saturn V, potentially slashing lunar mission cost.

Lunar regolith is on average about 45% oxygen by weight. According to Joosten, literally dozens of lunar oxygen (LUNOX) extraction methods are known. He listed 14 as examples, including one, Hydrogen Ilmenite Reduction, for which the U.S. Patent Office had issued a patent to the U.S.-Japanese Carbotek/Shimizu consortium.

Joosten assumed that an automated LUNOX extraction process involving "solid-state high-temperature electrolysis" could produce 24 metric tons of LUNOX in cryogenic liquid form per year. He estimated that the process would need between 40 and 80 kilowatts of continuous electricity, and suggested that a nuclear reactor would be the best power-supply option. Such a reactor would have ample reserve power for charging electrically powered teleoperated mining vehicles and could supply crew electricity needs when astronauts were present.

Joosten acknowledged that ILREC emphasized technologies "in somewhat different areas than most exploration scenarios." Among these were teleoperated surface vehicles and surface mining and processing. On the other hand, the technological areas it emphasized had a "high degree of terrestrial relevance," a fact which, he argued, might prove to be a selling point for the new piloted lunar program.

Automated exploration missions would precede the new piloted lunar program. These might take the form of Lunar Scout orbiters and Artemis Common Lunar Landers, both JSC-proposed projects. The automated missions would have some "science linkages," Joosten explained, but would serve mainly to locate landing sites with abundant oxygen-rich regolith, perform ISRU experiments under real lunar conditions using real lunar materials, and map candidate landing sites to enable mission planners to certify them as safe for landings and rover traverses.

The NASA JSC engineer envisioned a three-phase piloted lunar program, though he provided details only for Phases 1 and 2. In Phase 1, three cargo landers would deliver equipment to the target landing site ahead of the first piloted mission. Flight 1 of Phase 1 would deliver the nuclear reactor on a teleoperated cart and the automated liquid oxygen production facility (the latter would remain attached to its lander); flight 2 would deliver teleoperated diggers, regolith haulers, oxygen tankers, and carts for auxiliary fuel-cell power and consumables resupply; and flight 3 would deliver a pressurized moon bus exploration rover and science equipment for the astronauts who would reach the moon on flight 4.

Following launch on an Energia rocket, translunar injection, and an Earth-moon voyage lasting up to about a week, a U.S.-built cargo lander bearing a self-deploying LUNOX regolith processing payload descends toward the lunar surface on a direct-descent trajectory. The lander is arranged horizontally, not vertically, to reduce the risk of tipping and, as important, to provide the astronauts who will follow it to the moon with easy access to its cargo. Image credit: NASA
After touchdown, the LUNOX regolith processing payload pivots into vertical operational position and deploys ramps so that teleoperated regolith hauler rovers (two are shown on the left side of the image) can reach its screen-covered input hopper. Meanwhile, a teleoperated tanker rover (right) collects and stores LUNOX in preparation for the arrival of a piloted ILREC spacecraft. Image credit: NASA
An Energia-launched cargo lander slowly lowers a U.S.-built pressurized moon bus lunar rover to the surface ahead of the arrival of the first two-person ILREC crew. Image credit: NASA
The one-way automated cargo landers, each rectangular in shape and capable of delivering 11 metric tons of payload to the moon's surface, would be assembled and packed in the U.S. and shipped to Russia in C-5 Galaxy or Antonov-124/225 transport planes, then launched on Energia rockets from Baikonur Cosmodrome, a Russian enclave in independent Kazakhstan. The Soviet Union's Energia heavy-lift rocket and Buran reusable shuttle were developed beginning in 1976 in response to the planned U.S. Space Shuttle. Energia replaced the Soviet answer to the U.S. Saturn V rocket, the N-1, which was cancelled in 1974 after four failed test flights. 

In contrast to the N-1, Energia flew successfully both times it was launched. Energia payloads were required to perform a short burn after they separated from the rocket so that they could achieve a stable orbit about the Earth. Polyus, launched 15 May 1987, did not orient itself properly ahead of the burn and did not reach orbit, while the unpiloted Buran completed a single orbit as planned and landed on a Baikonur runway on 15 November 1988. 

Based on data Russia provided to NASA, launch teams at Baikonur could prepare two Energia rockets for launch simultaneously. Three Energia launch pads were available - two originally built for the Soviet N-1 moon rocket and an all-new pad. Energia could launch a 5.5-meter-diameter canister containing a U.S.-built cargo lander attached to a Russian "Block 14C40" upper stage. Following an Earth-orbit insertion burn, the upper stage would perform a TLI burn, boosting the cargo lander toward the moon.

Shuttle-derived heavy-lift boosters would launch Joosten's piloted landers from the twin Kennedy Space Center (KSC) Complex 39 pads. The pads, monolithic Vehicle Assembly Building, and other KSC facilities, most of which were originally constructed in the 1960s for the Apollo moon program, were modified in the 1970s to serve the Space Shuttle. They would require new modifications to support the ILREC program; Joosten assured his readers, however, that no wholly new facilities would need to be constructed at the Florida spaceport.

Joosten considered both Shuttle-C and in-line Shuttle-derived launchers. The Shuttle-C design had a cargo module with attached Space Shuttle Main Engines (SSMEs) mounted on the side of a Shuttle External Tank (ET) in place of the delta-winged Shuttle Orbiter. The in-line design, a conceptual ancestor of the Space Launch System presently (2017) under development, would place the cargo module on top of a modified ET and three SSMEs underneath. The tank would have attached to its sides twin Advanced Solid Rocket Motors more powerful than their Space Shuttle counterparts. Joosten appears to have favored the Shuttle-C design.

The image above is slightly confusing: it displays a piloted ILREC lander and, below that, a conical TLI stage with three engines, but does not make clear that, except for the white, black, and gray conical crew capsule at the top, both lander and stage would be hidden from view under a streamlined white launch shroud. Missing from this illustration is the solid-propellant launch-escape system tower mounted on the crew capsule's nose. Image credit: NASA
A piloted ILREC lander descends toward a landing near the regolith processing lander and the teleoperated tanker rover. The aft compartment, located between the two rear landing gear, holds up to two tons of cargo. Image credit: NASA
Shortly after touchdown, the teleoperated tanker rover moves into position beside the ILREC crew lander and extends an umbilical so that it can refill the lander's empty liquid oxygen tanks with LUNOX for the trip home to Earth. Note the position of the crew hatch and two of the lander's four engines. Image credit: NASA
The Shuttle-derived heavy-lift rocket would launch the piloted lander, bearing an international crew and about two tons of cargo, into Earth orbit. About 4.5 hours after liftoff, following a systems checkout period, the TLI stage would place the piloted lander on a direct trajectory to the moon. The stage would then be cast off.

Joosten's crew lander design outwardly resembled the fictional "Eagle" transport spacecraft from the 1970s Gerry Anderson TV series Space: 1999. The crew compartment, a conical capsule modeled on the Apollo Command Module (but lacking a nose-mounted docking unit), would be mounted on the front of a horizontally oriented three-legged lander. The three landing legs would fold against the lander's belly beneath a streamlined shroud during ascent through Earth's lower atmosphere.

On the moon, the crew hatch would face downward, providing ready access to the surface via a ladder on the lander's single forward leg; on the launch pad, the hatch would permit horizontal access to the capsule interior much as did the Apollo CM hatch. The crew compartment windows would be inset into the hull and oriented to enable the pilot to view the landing site during descent. The crew spacecraft would land on and launch from the moon using the same set of four belly-mounted throttleable rocket engines.

During descent to the lunar surface, the engines would burn Earth oxygen and hydrogen. Soon after lunar touchdown, the lander would be reloaded with liquid oxygen from the automated lunar oxygen plant.

During return to Earth, Joosten's spacecraft would burn Earth hydrogen and lunar oxygen. The entire crew lander would lift off from the moon; only descent stages that delivered automated payloads would remain on the moon to clutter up the site. After a brief period in lunar parking orbit, the ILREC lander would ignite its four engines again to place itself on course for Earth.

Nearing Earth, the crew capsule would separate from the lander section and orient itself for reentry by turning its Apollo-style bowl-shaped heat shield toward the atmosphere. The lander section, meanwhile, would steer toward a reentry point well away from populated areas. The crew capsule would deploy a steerable parasail-type parachute. Joosten recommended that NASA recover the capsule on land - perhaps at Kennedy Space Center - to avoid the greater cost of an Apollo-style CM splashdown and water recovery. Most of the lander section would burn up during reentry.

The first piloted ILREC lander, with a U.S.-Russian crew of two on board, would spend two weeks on the moon. The crew would inspect the automated mining and oxygen production systems and explore using the moon bus rover. In Phase 1, the moon bus would be capable of traveling away from the crew lander landing site for two or three days at a time.

Several Phase 1 piloted missions to the site would be possible; alternately, NASA and Russia could skip immediately to Phase 2 - establishment of a temporary lunar outpost - after only a single Phase 1 piloted flight. In ILREC Phase 2, three more cargo flights would deliver to the same site a second moon bus rover, a rover support module with an attached airlock derived from Space Station hardware designs, consumables in a cart-mounted pressurizable Space Station-derived module, and science equipment.

An Energia-launched cargo lander would deliver the U.S.-built airlock/rover support node to the outpost site and lower it to the lunar surface. Astronauts in the pressurized moon bus rovers would drive it to a flat area using teleoperations techniques, then would use robot arms on their rovers to lower stilt-like supports. These would level and raise the airlock/node. After the airlock/node's wheels became raised off the ground, they would be removed, clearing the way for the twin rovers to "dock" with the node's two round side ports (one port is visible below the observation cupola just right of center). Image credit: NASA
Phase 2 ILREC temporary lunar outpost. Two pressurized rovers are docked tail-first to the support node, as is a pressurized consumables cart (at the end of the node opposite the airlock). Hanging regolith-filled bags on the node provide added protection from ionizing radiation. Wheels removed from the airlock/node are stacked to the left of the surface access gangway; they serve as spares for the pressurized moon bus rovers. A buried electrical cable (visible as a curved line in the lunar dirt running from center to lower right) leads toward a nuclear reactor (out of view). Image credit: NASA
Phase 2 outpost with components identified. The lower image is turned 90 degrees relative to the top image. Image credit: NASA
A piloted flight would then deliver a four-person crew for a six-week lunar surface stay. The crew would divide up into pairs, with each pair living in and operating a moon bus rover. The support module/airlock would include docking ports so that the two moon buses and the consumables module cart could link to it, forming a small outpost.

The moon buses would tow auxiliary power carts in Phase 2 to enable longer traverses across the lunar surface. The moon bus/cart combinations might travel in pairs along parallel routes or one moon bus might remain at the outpost while the other moon bus and its power cart ventured far afield. In the event that a moon bus rover failed beyond walking distance from the outpost and could not be repaired, the other moon bus could rescue its crew.

ILREC Phase 3 was poorly defined: it might see larger lunar crews venturing further afield, or NASA might change direction and use technology developed for the lunar program to put humans on Mars (perhaps still in partnership with Russia). Joosten identified the piloted moon lander crew capsule, Shuttle-derived heavy-lift rocket, pressurized moon bus rovers, and Energia as candidate Mars mission hardware. Both Energia and the Shuttle-derived rocket might be upgraded for piloted Mars missions; they might even be merged to create a single international heavy-lift rocket more powerful than either Energia or the Shuttle derivative.

Joosten envisioned that in Phases 1 and 2 Russia would pay for Energia and the Block 14C40 TLI stage, while NASA would pay for the Shuttle-derived rocket and its TLI stage, the crew and cargo landers, moon bus rovers and teleoperated carts, and lunar oxygen production systems. In exchange for Russia's participation, its cosmonauts would walk on the moon in the early years of the 21st century. If U.S.-Russia space cooperation were for any reason curtailed, NASA could continue the moon program by using Shuttle-derived launchers to launch moon-bound cargo - provided, of course, that U.S. policy makers determined that an all-U.S. moon program was worth the added cost.


Mir Hardware Heritage, NASA Reference Publication 1357, NASA Johnson Space Center Reference Series No. 3, David S. F. Portree, March 1995, pp. 168-170

"International Lunar Resources Exploration Concept," Kent Joosten, Low Cost Lunar Access Conference Proceedings, 1993, pp. 25-61; paper presented at the AIAA Low Cost Lunar Access conference, Arlington, Virginia, 7 May 1993

International Lunar Resources Exploration Concept, Presentation Materials, Kent Joosten, Exploration Programs Office, NASA Johnson Space Center, February 1993

Press Kit: Apollo 11 Lunar Landing Mission, NASA, 6 July 1969

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