Re-Purposing Mercury: Recoverable Space Observatory (1964)

Launch of astronaut John Glenn on board Friendship 7. Image credit: NASA.

Hermann Potočnik, an Austrian Army officer writing under the pseudonym Hermann Noordung, described the benefits of telescopes in space in his seminal 1929 book Das Problem der Befahrung des Weltraums: der Raketen-Motor. The 1995 NASA-sponsored English translation of Noordung's work includes a brief section titled "Unlimited Visibility." It describes how,

beyond Earth’s blanket of air, nothing weakens the luminosity of the stars; the fixed stars no longer flicker; and the blue of the sky no longer interferes with the observations. At any time, the same favorable, almost unlimited possibilities exist, [and] telescopes of any arbitrary size, even very large ones, could be used.

In 1946, Princeton University astronomer Lyman Spitzer also wrote about the possibilities of space-based astronomy, and it was with him that U.S. efforts to place telescopes into space originated. In 1960, NASA Goddard Space Flight Center (GSFC) in Greenbelt, Maryland, began work on the Orbiting Astronomical Observatory (OAO) series of space telescopes. The Grumman-built satellites would image the cosmos in wavelengths that could not easily penetrate Earth's atmosphere and radio the images they captured to receiving stations on Earth.

Astronomers eagerly anticipated the OAOs, but for the general public NASA in 1960 was all about Project Mercury. The first manned Mercury orbital flight, designated MA-6, took place on 20 February 1962. A modified Atlas missile propelled astronaut John Glenn into space on board the Friendship 7 spacecraft. Glenn orbited Earth three times and, despite a sensor fault which made it appear that his spacecraft's heat shield had come loose in orbit, splashed down safely in the Atlantic Ocean a little less than five hours after launch.

Three more astronauts rode Mercury capsules into orbit. The last Mercury mission, MA-9, saw Gordon Cooper orbit Earth 22.5 times in the Faith 7 capsule. His 34-hour mission spanned 15-16 May 1963.

Final Mercury: Technicians hoist Gordon Cooper's Faith 7 Mercury spacecraft on Launch Complex 14 at Cape Canaveral, Florida. Image credit: NASA.

If Windsor Sherman, an engineer at NASA's Langley Research Center (LaRC) in Hampton, Virginia, had had his way, then Mercury would have found a new role as part of NASA's space astronomy program. In a NASA Technical Note published a year and a half after MA-9, Sherman proposed that NASA modify manned Mercury capsules to serve as recoverable unmanned Earth-orbiting observatories.

Sherman's Mercury-derived observatory would weigh more than the manned Mercury (2150 kilograms versus 1660 kilograms) and would require a higher orbit (at least 500 kilometers) to ensure that it would operate above Earth's atmospheric "airglow." The manned Mercury's Atlas booster would not be up to the task, so the recoverable observatory would launch on an Atlas with an Agena B upper stage. A similar booster-upper stage combination launched Ranger robot explorers to the moon.

Cutaway drawing of a Mercury-derived recoverable space observatory. Image credit: NASA.

Upon attaining orbit, the Mercury-derived observatory's nose would split down the middle and hinge open like a clam shell to clear the light path for a reflecting telescope with a curved primary mirror 76 centimeters in diameter. The telescope would occupy an inverted mushroom-shaped volume one meter wide at its widest point and 2.81 meters long. It would collect the light of astronomical targets such as comets, stars, nebulae, and galaxies, and, using a rotating tilted mirror, direct it by turns to six cameras mounted between the underside of the primary mirror and the Mercury heat shield. The cameras would record images in the gamma-ray, infrared, visible, and ultraviolet (UV) parts of the spectrum on up to 6000 frames (1000 frames per camera) of 70-millimeter photographic film.

Sherman called photographic film "one of the best information storage devices yet devised." A good photographic image of a celestial object would, he wrote, contain 10 times as much information as a good television image of the same object. On the down side, photographic film would require shielding against space radiation lest it become clouded and its information storage capacity degraded.

He acknowledged that, as an alternative to film recovery, exposed film might be developed in space automatically and scanned using a television camera. This technique would be used on board the automated Lunar Orbiter spacecraft. Sherman noted, however, that scanning an photographic image, transmitting it to Earth, and reassembling it would inevitably cause data loss. He estimated that images from scanning would contain half as much information as the exposed film the Mercury-derived observatory would return to Earth.

Sherman estimated that, unless GSFC and Grumman upgraded its systems, OAO would need about 860 days to transmit to Earth the 6000 image frames his Mercury-derived recoverable observatory could collect and return to Earth in 200 days. Upgrades to improve image transmission rate would increase OAO complexity, power consumption, and mass, so that the non-recoverable observatory could not be launched as planned on an Atlas rocket with an Agena upper stage.

As Sherman's Mercury-derived recoverable observatory orbited the Earth, it would rely for stability and pointing on a modified OAO guidance system. Sherman expected, however, that it would be unable to track astronomical targets with sufficient precision for film photography. He offered a preliminary design for a "fine-image stabilization system" meant to compensate for image smear by automatically adjusting the focus of the six cameras. He acknowledged, however, that designing a sufficiently stable pointing system for the recoverable observatory remained an important "problem area."

Sherman only briefly discussed the Mercury observatory's electrical power needs. He noted that non-rechargeable batteries sufficient to power the spacecraft for 200 days could not fit within the tight confines of the Mercury capsule, and would in any case be far too heavy. The LaRC engineer suggested that a deployable solar array might instead be used to recharge batteries, but gave no hint as to its likely dimensions, design, or location.

The Langley engineer also did not contend with the thorny issues of the Mercury spacecraft's demonstrated poor longevity. By the time Cooper manually guided Faith 7 to a splashdown in the Pacific Ocean, all of his spacecraft's automatic piloting systems had failed. He was reduced to timing his retrorocket burn using his wristwatch. Any similar malfunction would have doomed the wholly automated Mercury observatory.

Assuming that its endurance could be extended, at the end of its 200-day mission the Mercury-derived observatory would close its clam-shell nose, orient itself with its broad heat shield pointed approximately in the direction of its orbital motion, ignite its solid-propellant retrorocket pack, and reenter Earth's atmosphere. The Mercury-derived observatory's bifurcated nose would mean that it would deploy two separate main parachutes, each smaller than manned Mercury’s single parachute. Splashdown and recovery would otherwise occur as in manned Mercury missions.

In addition to its superior information capture potential, advantages of the recoverable Mercury-derived observatory would include cost-saving reuse of instruments and spacecraft components during subsequent missions. The Mercury observatory would also permit an ancillary scientific/engineering experiment; because it would return to Earth, any signs of long-term exposure to the space environment that it carried (for example, micrometeoroid pitting) could be subjected to analysis.

Sherman's plan for giving Mercury a new lease on life generated scant enthusiasm. OAO-1 reached orbit on an Atlas-Agena D rocket on 8 April 1966, 15 months after Sherman completed his paper. It carried UV, X-ray, and gamma-ray instruments. Unfortunately, its electrical system overheated, developed arcing, and failed, so that OAO-1's mission ended after only three days. The satellite returned no astronomical data.

Pre-flight artist concept of OAO-1 in Earth orbit. Image credit: Grumman/NASA.

OAO-2, with a suite of 11 UV astronomy instruments, abandoned the Atlas-Agena rocket. It reached orbit atop a more powerful Atlas-Centaur on 7 December 1968. OAO-2 operated for a little more than four years. It revealed, among other things, that enormous haloes of hydrogen gas surround comets and that young stars burn very hot.

The third OAO, launched on 3 November 1970 and retroactively dubbed OAO-B, included a 38-inch UV telescope. Unfortunately, the Centaur upper stage meant to push the satellite into orbit malfunctioned, so that it crashed into the Atlantic minutes after launch.

OAO-3, the last in the series, bore the name "Copernicus" to commemorate the 500th anniversary of the birth of the great Polish natural philosopher. Launched on 21 August 1972, it carried the heaviest NASA scientific payload up to that time (2220 kilograms). This included a Princeton University-built UV telescope and a British X-ray telescope. The non-recoverable observatory explored the cosmos until February 1981.

Sources

Conversion of a Spacecraft Designed for Manned Space Flight to a Recoverable Orbiting Astronomical Observatory, NASA Technical Note D-2535, Windsor L. Sherman, NASA Langley Research Center, December 1964.

The Problem of Space Travel: The Rocket Motor, Hermann Noordung, NASA SP-4026, 1995.

Encyclopedia of Satellites and Sounding Rockets of Goddard Space Flight Center 1959-1969, NASA Goddard Space Flight Center, no date (1970?).

More Information

Solar Flares and Moondust: The 1962 Proposal for an Interdisciplinary Science Satellite at Earth-Moon L1

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

Cometary Explorer (1973)

Gumdrops on Mars (1966)

Exploring Mars in the happy days before Mariner IV. Image credit: Philco Aeronutronic.

The Mariner IV Mars flyby of 14-15 July 1965, marked a watershed in Mars exploration planning. Prior to Mariner IV, engineers and scientists could legitimately propose lifting-body and winged gliding Mars landers that could set down on the planet using almost no propellants. This was because the prevailing scientific opinion gave Mars an atmosphere roughly 10% as dense as Earth's. After data from doughty 261-kilogram Mariner IV finished trickling back to Earth – a process that lasted until 3 August 1965 – such designs were relegated to the dust-bin.

Mars, it turned out, has an atmosphere less than 1% as dense as Earth's. In such an atmosphere, gliders and lifting bodies might still be used – however, they would reach the martian surface traveling at supersonic speeds, not the easily managed subsonic speeds pre-Mariner IV mission planners had assumed. The Philco Aeronutronic Mars Excursion Module (MEM) pictured at the top of this post, for example, would slow only to Mach 2 (twice the speed of sound) before it reached the surface of Mars.

At such a speed, parachute deployment would be problematic, forcing reliance on rockets to slow the MEM below the speed of sound. This would in turn demand substantial quantities of propellants, greatly increasing the MEM's mass, which would generate knock-on mass increases throughout the Mars expedition design.

Less than a year after Mariner IV, Gordon Woodcock, a young engineer in the Advanced Systems Office at NASA's Marshall Space Flight Center (MSFC) in Huntsville, Alabama, proposed what would become the new standard design for MEMs. His four-man MEM was based on the squat conical Apollo Command Module (CM) shape. Two and a half years after Woodcock published his paper, the crew of the Apollo 9 mission (3-13 March 1969), which tested the Apollo Lunar Module in Earth orbit, would name their Command and Service Module spacecraft Gumdrop with good reason.

The Command Module Gumdrop is hoisted aboard the U.S.S. Guadalcanal after the 10-day Apollo 9 mission in Earth orbit, 13 March 1969. Image credit: NASA.

For his Mars atmosphere entry simulations, Woodcock assumed a surface air pressure of 5.69 millibars – that is, a little more than 0.5% of Earth sea-level pressure. He noted that his independently developed Mars atmosphere model compared well with two models the Jet Propulsion Laboratory published just before his paper went to print.

The "semi-ballistic" Apollo CM shape, the MSFC engineer wrote, would have several advantages over lifting-body and delta-winged glider designs. It would, for example, have a low center of gravity and a "wide footprint," making tipping unlikely. The squat shape would enable installation of propellant tanks and payloads with very little wasted internal space.

Furthermore, the Apollo CM-shaped MEM would descend through the martian atmosphere not nose-first, like lifting bodies and gliders, but rather tail-first. This meant that it would not need to accomplish a problematic 180° turn or "flip" at supersonic speeds to point its braking and landing engines toward the ground.

Perhaps best of all, the Apollo Program would generate a large body of experience with use of the CM shape in Earth's upper atmosphere. Much of this experience could be applied to development of the CM-shaped MEM.

Woodcock's 56.1-ton MEM would comprise a descent stage roughly 33 feet across (the diameter of a two-stage Saturn V rocket) and, hidden beneath a protective nose-cone ("separable cap"), a 27.3-ton ascent stage. The ascent stage mass, determined largely by the amount of energy needed to climb to Mars orbit, would size the descent stage, he explained. His MEM would separate from its mother ship in Mars orbit at an altitude of 1000 kilometers, then would fire a retrorocket package to slow down and begin its fall toward the martian atmosphere.

Gordon Woodcock's Mars Excursion Module (MEM) design. Image credit: NASA.

Woodcock advised against MEM separation from the mothership prior to Mars orbit capture. It would relieve the mothership of the MEM's mass, reducing the quantity of propellants it would need to slow itself so that the gravity of Mars could capture it into orbit – thus reducing the overall mass of the expedition – but it would also introduce unacceptable risk. He noted that 10,000 simulations run on an IBM 7094 computer had shown that the safe Mars atmosphere entry corridor for the MEM would be very narrow and thus hard to target during a high-speed entry from an interplanetary trajectory.

The crew would ride in a spherical capsule atop the ascent stage during descent and landing. MEM atmospheric deceleration would cease at a velocity of 0.5 kilometers per second. The MEM's bowl-shaped heat shield would then detach, landing legs would extend, and four landing engines would ignite. Woodcock's MEM design did not include parachutes.

As the landing engines ignited, solid-propellant rockets would blast the separable cap away from the MEM ascent stage. With the conical cover gone, the MEM pilot would see his prospective landing site for the first time.

He would then have 100 seconds of maneuvering time to steer the MEM to a safe touchdown. If rugged terrain made this too short a time to find a safe spot or if a malfunction occurred, the pilot could abort the landing by blasting the ascent stage free of the descent stage and returning to Mars orbit.

MEM mass at touchdown would total 40.9 tons. Following a safe touchdown, the crew would exit an airlock adjacent to the ascent stage cabin and transfer to a Mars surface crew quarters module in the descent stage. The latter would take the form of a segment of a torus with a rectangular cross section.

The MEM descent stage engines would burn non-cryogenic storable propellants drawn from tanks positioned within the MEM to offset its center of gravity, enabling the spacecraft to generate a modest amount of lift during descent. A similar approach would enhance Apollo CM lift characteristics during Earth atmosphere reentry.

By revolving around its offset center of gravity using small thrusters, the CM could halt its descent and climb before descending again. This technique was used during Apollo missions to reduce the deceleration felt by astronauts during reentry at lunar-return speed (39,000 kilometers per hour).

Following the successful completion of their surface mission, the MEM crew would return to the ascent stage cabin and blast off for Mars orbit. The performance advantages of cryogenic propellants led Woodcock to opt for liquid oxygen oxidizer and liquid methane fuel in his ascent stage.

He envisioned a common propellant tank lined with "superinsulation" with a barrier separating the methane and oxygen. Helium stored under pressure in spherical tanks would drive propellants into the three ascent stage engines, any two of which would be sufficient to launch the MEM to Mars orbit.

Logistics MEM. Image credit: NASA.

Shelter MEM. Image credit: NASA.

Much as Apollo engineers envisioned that the basic Lunar Module design would be modified to give it new capabilities (for example, unmanned delivery of cargo to the lunar surface) as the Apollo Program evolved from initial brief sorties to in-depth lunar exploration, Woodcock envisioned that his MEM would form the basis of a long-term, increasingly capable and complex Mars exploration program.

He proposed a design for a one-way logistics MEM in which cargo and a "camper-type" pressurized rover would replace the MEM ascent stage and the surface operations shelter. A crew would arrive separately in a conventional MEM to unpack the cargo and explore widely in the rover.

Woodcock also offered a design for a one-way nuclear-powered MEM that would provide electricity to a long-term Mars surface base built up from one-way shelter MEMs. The nuclear-power MEM would include a shielded reactor, a reactor control room, and a skin-mounted radiator for discarding reactor waste heat.

Each shelter MEM would house five or six astronauts on three levels: communications & control on top; living quarters in the middle; and a laboratory at the bottom. The lab would connect to a "sortie room/decontamination airlock" that would enable access to the surface.

Woodcock calculated that 10.6 tons of water, food, and oxygen with a four-ton reserve could sustain a five-man crew in the MEM on Mars for 500 days. Like the logistics MEM, the power and shelter MEMs would land on Mars unmanned.

The Apollo CM-shaped MEM design became closely identified with piloted Mars missions after NASA MSFC director Wernher von Braun, famous for his 1950s Mars glider lander designs, presented a variation on Woodcock's Apollo-shaped lander theme to President Richard Nixon's Space Task Group in early August 1969. Image credit: NASA.

Sources

"Summary Presentation: Study of a Manned Mars Excursion Module," F. Dixon, Aeronutronic Division, Philco Corporation; paper presented at the Symposium on Manned Planetary Missions, 1963/1964 Status, NASA George C. Marshall Space Flight Center, Huntsville, Alabama, 12 June 1964.

An Initial Concept for a Manned Mars Excursion Vehicle for a Tenuous Mars Atmosphere, NASA TM X-53475, G. Woodcock, NASA Marshall Space Flight Center, 7 June 1966.

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Dyna-Soar's Martian Cousin (1960)

A Forgotten Pioneer of Mars Resource Utilization (1962-1963)

Dyna-Soar's Martian Cousin (1960)

Dyna-Soar spaceplane. Image credit: U.S. Air Force.

In 1960, Philip Bono, a Space Vehicle Design Specialist with the Boeing Airplane Company, envisioned a manned Mars spacecraft which outwardly resembled the X-20A Dyna-Soar single-seat orbital glider his company was at the time developing for the U.S. Air Force. Bono's Mars glider was, however, much larger than Dyna-Soar — large enough, in fact, to hold an eight-man "expeditionary force" and nearly 40 tons of supplies and equipment. The flat-bellied Mars glider measured a whopping 125 feet long and 95 feet across its delta wings.

Though Bono's Mars glider was impressively large, it was part of a Mars expedition plan that was stripped-down and bare-bones by early 1960s standards. It lacked redundancy and provided few abort modes. For those familiar with Wernher von Braun's 1950s plans for Mars expeditions, some of which included 10 or more cargo and crew spacecraft, Bono's plan must have seemed daring, even reckless.

Bono himself acknowledged that his study did not "present the solution to many major problem areas." He nevertheless assured his readers that it was "restricted to the realm of practicality and reflect[ed] a moderate degree of conservatism."

A large crane hoists into place the forward section of Bono's Mars glider. Final assembly occurs on the launch pad. Image credit: Boeing Airplane Company via San Diego Air & Space Museum.

Prior to launch, the forward section of Bono's glider would be lowered into place atop its aft section on the launch pad. All assembly would take place on Earth. In the event of trouble during ascent, the crew would blast free in the glider's forward section. The glider aft section would be mounted atop a living module with an attached small rocket stage which in turn would rest upon a short central booster rocket.

Six tall outboard booster rockets would surround and hide the short booster, living module/rocket stage, and most of the aft section of the glider. Fully assembled, loaded with liquid hydrogen and liquid oxygen propellants, and ready for launch, Bono's massive Mars stack would stand 248 feet tall and weigh in at 4150 tons.

Abort: the forward section of the Mars glider (upper right) blasts free of a malfunctioning booster rocket during first-stage ascent. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

Bono, in common with many Mars exploration enthusiasts of the early 1960s, optimistically targeted his expedition for the favorable 1971 Earth-Mars transfer opportunity, when the energy required to reach Mars would be at a minimum. On 3 May 1971, seven plug-nozzle engines — one per booster — would ignite and power up to generate a total of 10 million pounds of thrust. The advanced plug-nozzle engine design would do without large engine bells, in theory largely eliminating engine cooling requirements and reducing engine mass. The crew would feel a maximum acceleration equal to 5.6 times the pull of Earth's gravity during ascent.

During first-stage operation, four of the outboard boosters would supply propellants to all seven engines. The rocket would climb to an altitude of 200,000 feet, where it would cast off the four expended boosters. These would fall to Earth 60 nautical miles downrange of the launch site.

Bono's Mars spacecraft begins second-stage flight by casting off four outer boosters (lower left). Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

The three remaining engines would continue firing with the two remaining outboard boosters supplying all of their propellants. At 352,000 feet, the two boosters would expend their propellants and detach. The short central booster would continue firing until it placed the glider, living module, and small rocket stage on a trans-Mars trajectory, then would expend its propellants and detach. The Mars spacecraft — two-part glider, living module, and small rocket stage — would have a mass of nearly 138 tons following Earth escape.

Safely on course for Mars, the astronauts would crawl through a tunnel in the glider's aft section to reach the 45-foot-long, 18-foot-diameter living module. They would deploy an inflatable 50-foot dish-shaped antenna for radio communication with Earth (the dish might have been a late addition to Bono's plan, for it is not depicted in any of the illustrations for this post). During the 259-day voyage to Mars, the crew would breathe a 40% oxygen/60% helium air mix, so in their radio reports to Earth they would sound like Donald Duck.

The end of second-stage operation: the remaining pair of outboard boosters exhaust their propellants and separate, leaving to the short central booster the task of placing the glider, living module, and small rocket stage on course for Mars. This image displays the plug-nozzle engines unobscured by exhaust — they are the cones at the bottoms of the two boosters (lower left and lower center). Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

Its job done, the short central booster stage shuts down and fires thrusters to separate from the Mars spacecraft. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

On 17 January 1972, at the end of a 259-day Earth-Mars transfer, the crew would strap into the glider and separate it from the living module. They would discard a 10.4-ton capsule containing human waste accumulated during the voyage to Mars. The small rocket stage, meanwhile, would ignite its four 20,000-pound-thrust Pratt & Whitney-built Centaur engines to slow itself and the living module so that Mars's gravity could capture them into orbit.

After deploying the antenna, the crew would point the glider's nose — which would contain a nuclear reactor for generating the Mars expedition's electricity — at the Sun. This would place the living module in shadow, and would shield the liquid hydrogen/liquid oxygen propellants in the small rocket stage from solar heating. Bono assumed that no course corrections would be necessary so that his spacecraft could maintain its nose-toward-Sun attitude throughout the journey to Mars.

17 January 1972: Arrival at Mars. The unpiloted living module (left) ignites its small rocket stage to slow down so that the planet's gravity can capture it into orbit while the glider bearing the crew enters the martian atmosphere directly. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

The waste capsule — the skinny conical object between the living module and the glider in the image directly above — would strike Mars. Needless to say, this peculiar concept would likely have had few fans among scientists; it would certainly have introduced massive amounts of Earth bacteria into the martian environment, greatly complicating studies of any native martian biosphere that might exist.

The glider, meanwhile, would carry the eight-man crew directly into the martian atmosphere with no stop in orbit. If conditions on Mars were not suitable for an immediate landing — for example, if a planet-wide dust storm were raging — then the crew would have no way of aborting atmosphere entry and descent to the surface. (Such a storm did in fact occur in late 1971, though by January 1972 it had mostly abated.)

The Mars glider casts off its drag parachute as it steers toward a smooth area of martian desert. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

Vertical descent and touchdown. The artist depicts Mars as smooth and dusty, with no obvious rocks on its surface. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

As it descended past 3000 feet of altitude, the glider would deploy a 42-foot-diameter drag parachute to reduce speed. The Mars glider pilot would steer his craft toward a level stretch of ochre desert. At an altitude of 2000 feet — which Bono declared (wrongly, as it turns out) was "adequate to clear the highest mountain of Mars" — three landing engines with a combined thrust of 60,000 pounds would ignite to slow it to a hover. The glider would then lower vertically to the surface in a billowing cloud of yellow dust and sand and touch down on skids with its nose aimed 15° above the horizon. At touchdown, the Mars glider would have a mass of 70.4 tons.

Bono's description of the glider's aerodynamic performance was based on an estimated martian surface air pressure equal to about 8% of Earth's. The true value is, however, less than 1% of Earth's surface pressure. In the actual martian atmosphere, a single 42-foot parachute would not be adequate to slow the heavy glider's descent. In addition, the glider's wing design would not produce sufficient lift to enable effective gliding. In short, Bono's glider would reach the surface while still moving at supersonic speed. Some call this "lithobraking."

Mars Outpost: members of the eight-man crew lower the glider's nose-mounted nuclear reactor onto the expedition truck. In the background (right) stand radio antenna masts and the inflatable dome-shaped shelter. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

During the 479-day "Mars Operational Phase," the eight Mars explorers would set up a 20-foot-diameter, 2000-pound inflatable living dome and relocate the glider's nuclear reactor several thousand feet away so that it could safely generate electricity for their encampment. The crew would have at their disposal about 4.2 tons of scientific gear. They would explore and move equipment using a truck-like two-ton rover.

Near the end of their stay on Mars, the astronauts would reconfigure their glider for launch by moving its landing engines so that they could serve as ascent engines and by returning the reactor to its place on its nose. They would also anchor the aft section of the glider to the surface using stakes and cables. The glider's forward section would then blast off at a 15° angle using the aft portion as its launch pad.

Liftoff from Mars: the forward part of Bono's Mars glider begins the climb to Mars orbit. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

Bono wrote that his Mars glider's delta wings would provide lift, greatly reducing the quantity of propellant and the size of the engines it would need to attain Mars orbit. In the actual martian atmosphere, however, the glider he described would not reach orbit before it expended its propellants.

The crew would dock the glider forward section tail-first with the waiting living module which would have loitered in Mars orbit throughout their surface stay. Several astronauts would spacewalk to join together the glider and living module and detach the empty torus-shaped propellant tanks on the living module's small rocket stage. The tanks would have been retained after the Mars orbit capture maneuver emptied them so that they could protect the small rocket stage and the precious Earth-return propellants it contained from meteoroid punctures.

Members of Bono's Mars crew cast off empty torus-shaped propellant tanks on the small rocket stage (upper right) attached to the aft end of the living module (center) in preparation for Mars orbit departure. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

The forward section of Bono's Mars glider separates from the living module ahead of Earth atmosphere reentry. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

24 January 1974: the forward section of Bono's Mars glider returns to Earth. Image credit: Boeing Aircraft Company via San Diego Air & Space Museum.

The crew would use the living module rocket stage to depart Mars orbit on 21 October 1973, then would discard it. Four months later (24 January 1974), as the home planet shimmered invitingly ahead, the crew would board the glider forward section once more and cast off the nuclear reactor and living module (they would burn up in Earth's atmosphere). Bono's glider, its weight reduced to just 15 tons, would then reenter Earth's atmosphere directly 997 days after launch and glide to a triumphant desert landing on skids.

Sources

"A Conceptual Design for a Manned Mars Vehicle," Philip Bono, Advances in the Astronautical Sciences, Vol. 7, pp. 25-42; paper presented at the Third Annual West Coast Meeting of the American Astronautical Society, Seattle, Washington, 4-5 August 1960.

San Diego Air & Space Museum Image Collection (http://sandiegoairandspace.org/collection/image-collection — accessed 23 November 2017).

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A Forgotten Pioneer of Mars Resource Utilization (1962-1963)

A 1964 Proposal for a Small Lifting-Body Shuttle with "Staged Reentry"

NASA Marshall's 1966 NERVA-Electric Piloted Mars Mission

What If a Crew Became Stranded On Board the Skylab Space Station? (1972)

Image credit: NASA.

On 28 July 1973, the Skylab 3 crew of Alan Bean, Jack Lousma, and Owen Garriott lifted off from Launch Pad 39B at Kennedy Space Center, Florida, bound for the Skylab Orbital Workshop in low-Earth orbit. Despite their mission's numerical designation, they were the second crew to visit Skylab; in a move guaranteed to generate confusion for decades to come, NASA had designated as Skylab 1 the unmanned Workshop launched on 14 May 1973, and had dubbed the first crew to visit it Skylab 2.

The Skylab 3 Apollo Command and Service Module (CSM) separated from the S-IVB second stage of its Saturn IB launch vehicle and began maneuvering to catch up with Skylab. During final approach to the Workshop, one of the four steering thruster quads on the CSM began to leak nitrogen tetroxide oxidizer from its forward-firing engine. The crew dutifully shut off the quad and used the three quads remaining to complete docking without further incident.

On 2 August, a second thruster quad began to leak, raising fears that tainted nitrogen tetroxide might have damaged both quads. If this were the case, then the Skylab 3 CSM's remaining two quads and Service Propulsion System (SPS) main engine might also have been compromised; though the individual quads and the SPS had independent plumbing, all contained oxidizer from the same batch. If the leaks continued and spread, moreover, nitrogen tetroxide might contaminate the inside of the CSM's drum-shaped Service Module, potentially damaging other spacecraft systems.

The leaks did not catch NASA off guard. As was common in the 1960s and early 1970s, NASA had considered potential Apollo and Skylab failures - however unlikely - and had planned ahead. Within hours of the second leak, The U.S. civilian space agency put into motion a variant of a plan Kenneth Kleinknecht, Skylab Program Manager, and Lawrence Williams, Apollo Spacecraft Program Office, had described less than a year earlier at the Fifth Annual Space Rescue Symposium in Vienna, Austria.

In their paper, Kleinknecht and Williams explained that Skylab would provide the first true opportunity for space rescue in the U.S. space program. One-seat Mercury and two-seat Gemini spacecraft had been too small and limited in capability to serve as rescue spacecraft. Apollo lunar CSMs were much more capable; even so, they each carried only a little more breathing oxygen, fuel cell reactants, and food than were needed to support a three-man crew for the duration of a lunar mission (about 10 days). If an Apollo CSM had become stranded in lunar orbit — by an SPS failure, say — then its crew would have perished long before NASA could have attempted a rescue.

The Skylab Orbital Workshop. The red arrow points to the Multiple Docking Adapter's radial port. Image credit: NASA.

If astronauts needed to evacuate Skylab, they could board their CSM docked at Skylab's front port, undock from the Workshop, and splash down in the ocean in less than a day. If, on the other hand, a crew's CSM became unusable while they lived and worked on board Skylab, then the astronauts could await rescue.

Stranded astronauts were unlikely to run out of supplies. Kleinknecht and Williams noted that the Orbital Workshop would be launched with enough oxygen, food, water, and other supplies on board to support three men for eight months. At the time they presented their paper, NASA planned three three-man Skylab visits lasting 28, 56, and 56 days — that is, a total of a little less than five months.

NASA, meanwhile, would prepare and launch a rescue CSM with a crew of two. Skylab, Kleinknecht and Williams explained, had a second, radial docking port on its Multiple Docking Adapter. The rescue CSM would dock at the radial port to pick up the stranded crew.

They proposed that the CSM intended for the next Skylab crew should become the rescue CSM. This would presumably reduce by one the number of long-duration Skylab missions that could be flown. A fourth CSM, which would serve as the backup CSM throughout the Skylab program, would serve as the rescue CSM for Skylab 4, the third and final planned Skylab crew.

Image credit: NASA.

Kleinknecht and Williams estimated that stripping out the rescue CSM's aft bulkhead lockers to make room for a "rescue kit" would require about a day. The rescue kit would include a pair of special astronaut couches, connectors and hoses for linking two additional space-suited astronauts to the rescue CSM's life support and communications systems, and an experiment-return pallet for bringing home a select few of the stranded crew's science results. The rescue CSM's two-man crew would recline in the left and right CSM couches; the three rescued Skylab crewmen would return to Earth in the center couch and in the two special couches mounted below the others in place of the lockers.

The rescue CSM would bring along a special Apollo probe-and-drogue docking unit that would enable astronauts inside Skylab to manually undock and cast off the crippled CSM. This would clear the Workshop's front port for any future CSM dockings. Kleinknecht and Williams did not explain what would happen to the unmanned CSM after it was discarded.

Though the time needed to install the rescue kit was minimal, the time needed to refurbish Pad 39B and prepare the rescue CSM and Saturn IB rocket for launch would depend upon when NASA declared that a rescue was necessary. After each Skylab Saturn IB launch, ground crews would need about 48 days to refurbish Pad 39B and prepare the next Skylab CSM and Saturn IB.

If a rescue were judged to be necessary at the beginning of the 28-day first manned Skylab mission (Skylab 2), then the mission would be extended by 20 days, making the total duration about 48 days. If a rescue were declared to be necessary late in Skylab 2 — say at the time of planned return to Earth — then preparations for the next Skylab CSM launch would be farther along, but would have started later. The rescue CSM and Saturn IB would thus need 28 days before they could lift off, bringing the total Skylab 2 mission duration to about 56 days, or double the duration planned at launch.

Activation of the Skylab rescue capability early in the Skylab 3 or Skylab 4 mission might permit a rescue before the return time planned when the stranded crew left Earth, Kleinknecht and Williams found. A failure near the planned conclusion of Skylab 3 or Skylab 4 would see a rescue CSM launched as little as 10 days after the rescue plan was activated.

Skylab rescue crewmen Vance Brand (left) and Don Lind. Though he never flew to Skylab, Brand would reach space as part of the Apollo-Soyuz Test Project mission in July 1975 and as Commander of Space Shuttle missions STS-5 (November 1982), STS-41-B (February 1984), and STS-35 (December 1990). Lind would reach space as a Mission Specialist on Shuttle mission STS-51-B (April-May 1985). Image credit: NASA.

The 2 August 1973 failure of the second Skylab 3 CSM thruster quad unleashed a storm of activity. NASA prepared the backup Skylab CSM, not the Skylab 4 CSM, as its rescue vehicle, and tapped Skylab 3 backup crewmen Vance Brand and Don Lind to pilot it.

NASA had made other changes to Kleinknecht and Williams' rescue plan. The special probe-and-drogue docking unit for casting off the malfunctioning CSM had become a concave drogue unit that would be installed over the front port. It was launched with Skylab, not in the rescue CSM. After they installed it, the stranded astronauts would "trigger" the drogue to manually release their balky CSM. The rescue CSM would then dock at the front port, not the radial port.

Almost as soon as NASA activated the rescue plan, laboratory analysis on Earth showed that the batch from which the nitrogen tetroxide in the Skylab 3 CSM's propulsion systems had been taken was not tainted. As unlikely as it might seem, the two thruster quad malfunctions lacked a common cause.

Working in the CSM simulator in Houston, astronaut Brand demonstrated that the Skylab 3 crew could maneuver their spacecraft adequately even if they lost a third thruster quad. That is, if they were left with only one functioning quad when time came for them to return home, they could still safely deorbit their CSM.

Though rescue preparations continued as a precaution, by 10 August NASA managers had cleared the Skylab 3 crew for the full duration of their planned 59-day mission on board the Workshop. On 25 September 1973, Bean, Lousma, and Garriott returned to Earth as originally planned, in the CSM that had launched them to Skylab.

Sources

"Skylab Rescue Capability," Kenneth S. Kleinknecht and Lawrence G. Williams; paper presented at the Fifth Annual Space Rescue Symposium Organized by the Space Rescue Studies Committee of the International Academy of Astronautics, 23rd Congress of the International Astronautical Federation, Vienna, Austria, 9-12 October 1972.

Skylab News Reference, NASA Office of Public Affairs, March 1973, pp. IV-6 - IV-8.

"Skylab: Outpost on the Frontier of Space," T. Canby, National Geographic, October 1974, p. 460.

More Information

What If Apollo Astronauts Became Marooned in Lunar Orbit? (1968)

What If an Apollo Lunar Module Ran Low on Fuel and Aborted Its Moon Landing? (1966)

What If An Apollo Saturn Rocket Exploded on the Launch Pad? (1965)

What If Apollo Astronauts Could Not Ride the Saturn V Rocket? (1965)

A Forgotten Pioneer of Mars Resource Utilization (1962-1963)

Sixty-five years ago: the first rocket launch from Cape Canaveral, Florida. A captured German V-2 with an American WAC Corporal sounding rocket on top begins a low-angle flight to a downrange distance of at least 320 kilometers. Image credit: U.S. Army/NASA.

Most Mars expedition plans of the 1950s and early 1960s made little use of martian resources. Apart from using the planet's atmosphere to slow landers for touchdown, either through use of parachutes or, more commonly in the time period, large wings, Mars spacecraft generally depended little on materials or conditions peculiar to Mars. This was because so little was known of the planet.

The potential benefits of using martian resources to make spacecraft propellants, building materials, and life support consumables were so compelling, however, that some planners chose to incorporate them into their mission designs anyway. Chief among the anticipated benefits was a dramatic reduction in spacecraft mass if raw materials for rocket propellants could be found at Mars. Reducing mission mass meant fewer expensive, temperamental rockets would be needed to launch Mars spacecraft components and propellants into Earth orbit for assembly, which in turn meant reduced mission cost and risk.

The Working Group on Extraterrestrial Resources (WGER) was formed in early 1962. Besides NASA, the group included representatives from the U.S. Air Force, the U.S. Army, the U.S. Geological Survey, the Bureau of Mines, aerospace corporations, and universities. The group, which met throughout the 1960s, focused mainly on lunar resources. A few researchers, however, used the WGER as a forum for discussing eventual exploitation of Mars resources.

One of these forward-thinkers was Ernst Steinhoff, representing the RAND Corporation, a think tank created in 1946 to provide advice to the U.S. military services. RAND had performed Mars studies for the U. S. Air Force as early as 1960. Steinhoff, whose specialty was rocket guidance, came to the U.S. in 1945 with Wernher von Braun, Ernst Stuhlinger, Krafft Ehricke, and other members of the Peenemünde rocket team.

After working to launch captured, sometimes modified, V-2 missiles for the U.S. Army — the image at the top of this post shows the 24 July 1950 launch of the two-stage Bumper 8 rocket — Steinhoff went to work for U.S. industry in 1956. He joined RAND in 1961, and was instrumental in the formation of the WGER the following year. In fact, he became the WGER's first chairman.

Mars pioneer Ernst Steinhoff. Image credit: U.S. Air Force.

Steinhoff summed up his Mars work in papers presented at a March 1962 meeting at NASA's Marshall Space Flight Center in Huntsville, Alabama, and at the pivotal June 1963 American Astronautical Society Symposium on the Manned Exploration of Mars in Denver. George Morgenthaler of Martin Marietta Corporation organized the Denver symposium, the first non-NASA meeting devoted to piloted Mars travel. As many as 800 engineers and scientists heard Steinhoff's paper and 25 others. It was the first time so many science and engineering professionals with an interest in Mars had come together in one place, and the last Mars meeting of its size until the 1980s.

Near the end of 1963, soon after he chaired the second annual meeting of the WGER (23-25 October 1963), Steinhoff could not pass up an offer to become Chief Scientist at the Air Force Missile Development Center at Holloman Air Force Base in Alamogordo, New Mexico. When he assumed his new responsibilities, his involvement in the WGER and his work on Mars subjects suffered. This is unfortunate, for in his Huntsville and Denver papers he anticipated and promoted mission concepts which would, with the passage of decades, emerge as highly significant in Mars exploration planning. Had he continued his work at RAND, he might have further promoted his ideas, and that might have changed the course of Mars mission planning in the 1960s and beyond.

Steinhoff's work focused on "autarchic" — that is, self-sufficient — bases on Mars and Phobos. Self-sufficiency would be achieved through mining and processing of local materials, and by equipping the base with regenerable (recycling) life support systems. The Phobos and Mars bases would support scientific research and serve as transportation "terminals" for spacecraft.

Steinhoff estimated that extraterrestrial water could supply over 90% of the logistical needs of space-faring humans. He wrote that the gravitational pull of the Moon — one-sixth that of Earth — would make it an inefficient "interim space base" for fueling Mars-bound ships. Citing Clyde Tombaugh, who had written that the moons of Mars were probably made of the same water-rich materials as Mars itself, Steinhoff proposed that Phobos supplant the Moon as a stepping stone to Mars. Nuclear systems could cook water out of Phobos rocks, then split it into hydrogen and oxygen chemical rocket propellants.

Image of Mars captured at Mt. Wilson Observatory in 1956, the year of the last close Mars opposition at the time Steinhoff wrote his papers. Because Mars has a decidedly elliptical orbit, the Earth-Mars distance during oppositions varies over a roughly 15-year cycle. The next close opposition would occur in 1971; the next after that was in 1988; and the most recent took place in 2003. Another will take place in 2018. When Steinhoff speculated on the nature of martian resources, this was among the best images of Mars available. Image credit: Mt. Wilson Observatory/NASA.

Steinhoff's early Mars expedition would include 18 astronauts and a convoy of three crew and six cargo spacecraft. They would use a conjunction-class Mars mission profile, traveling to Mars in 256 days, remaining in the Mars system for 485 days, and then returning to Earth in 256 days.

Two chemists and two geologists would prospect on Phobos for water-rich rocks. The little moon's weak gravity would enable space-suited astronauts to easily assemble "ready-to-operate" base modules shipped from Earth. Space construction workers, Steinhoff wrote, would be able to carry and connect 50-ton modules by hand. (He neglected to mention that weightless objects retain their mass. Astronauts can move massive objects, it is true, but only through considerable exertion, and only if they have a firm footing and adequate handholds. Stopping a massive moving object in weightlessness requires as much effort as setting it in motion.)

Reusable winged three-man shuttles would transport explorers between the Phobos terminal and the surface of Mars. In common with most Mars planners of his day, Steinhoff assumed, based on the consensus view of Earth-based planetary astronomers, that the martian atmosphere would be about 10% as dense as Earth's — that is, thick enough to support gliding shuttles requiring minimal landing propellants.

The surface of Mars would be rough, Steinhoff expected, so the first gliding shuttle landing would be a difficult proposition. He proposed that early shuttles drop cargo and astronauts using parachutes, then blast back to Mars orbit without landing. Among the early air-dropped cargoes would be a radio-controlled bulldozer, which astronauts on Phobos would remote-control to build a smooth, level runway for the first Mars shuttle landing. This was probably the first time anyone proposed teleoperation of equipment on Mars from Mars orbit.

The runway would be built within 25º of the martian equator so that it could be reached with ease from Phobos, which circles Mars in a near-equatorial orbit. The first Mars surface base would be established near the runway. Inflatable modules would provide living space for early explorers. After the Mars base became operational, shuttles would rely on propellants manufactured from Mars water to return to the Phobos base.

The Mars base would use vehicles and building techniques that Steinhoff's RAND colleagues had proposed in their Air Force studies. Rocket turbine engines tailored to the martian atmosphere — which many expected would be made mostly of nitrogen, as is Earth's atmosphere — would power surface rovers, airplanes, and helicopters with low-mass inflatable parts. Astronauts would manufacture cement from martian materials, construct masonry and cinder-block buildings, and inhabit martian caves.

After the propellant needs of the Mars system were met, Phobos would become a fueling station for interplanetary spacecraft. Steinhoff estimated that enough propellant could be manufactured in just 100 days to launch a spacecraft from Phobos to 300-mile-high Earth orbit, and that Phobos propellants could cut the time required for transfer between Mars and Earth in half.

He added that "use of indigenous resources, combined with more advanced nuclear ferry systems, may . . . pave the way to intensive interplanetary exploration within the limitations of our national resources." Phobos could, for example, serve as a refueling stop for Jupiter-bound piloted spacecraft.

Sources

"Powerplants for Atmospheric and Surface Vehicles on Mars," Research Memorandum RM-2529, W. H. Krase, The RAND Corporation, 10 April 1960.

"Vehicles for Exploration on Mars," Research Memorandum RM-2539, T. F. Cartaino, The Rand Corporation, 30 April 1960.

"A Possible Approach to Scientific Exploration of the Planet Mars," Paper #38, Ernst A. Steinhoff, editor, From Peenemünde to Outer Space, "A Volume of Papers Commemorating the Fiftieth Birthday of Wernher von Braun," NASA Marshall Space Flight Center Technical Report, 1962, pp. 803-836.

"Use of Extraterrestrial Resources for Mars Basing," Ernst A. Steinhoff, Exploration of Mars, George Morgenthaler, editor, pp. 468-500; proceedings of the American Astronautical Society Symposium on the Exploration of Mars, Denver, Colorado, 6-7 June 1963.

"Manned Exploration of Mars?" Raymond Watts, Sky & Telescope, August 1963, pp. 63-67, 84.

Report of the Second Annual Meeting of the Working Group on Extraterrestrial Resources on October 23-25, 1963, at the Air Force Missile Development Center, Holloman Air Force Base, Alamogordo, New Mexico, MDC-TR-63-7, no date (1965?)

More Information

Clyde Tombaugh's Vision of Mars (1959)

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

The Challenge of the Planets: Part One - Ports of Call

What If Apollo Astronauts Could Not Ride the Saturn V Rocket? (1965)

At the time a NASA Marshall Space Flight Center artist created this graphic, the first Saturn V test flight was 17 months in the future. The smaller rocket, labeled "Apollo Saturn I," was subsequently renamed the Saturn IB. The first piloted Apollo flight, Apollo 1, was scheduled for launch on a Saturn IB rocket in early 1967, about six months after this graphic was made. Image credit: NASA.

George Mueller left private industry to become NASA's new Associate Administrator for Manned Space Flight in September 1963. He immediately asked John Disher and Adelbert Tischler, two veteran NASA engineers not directly involved in Apollo, for an independent assessment of the Moon program. On 28 September, they told Mueller that it could not achieve President Kennedy's goal of a man on the Moon by 1970. They estimated that NASA might be able to carry out its first piloted Moon landing in late 1971.

Mueller took drastic action. When he joined NASA, the Apollo flight-test plan was based on the philosophy of incremental testing, which meant that untried rocket stages would launch only dummy stages and dummy spacecraft. On 29 October 1963, Mueller informed his senior managers that Apollo test flights would henceforth use complete systems. Mueller's directive meant that, when the Saturn V S-IC first stage flew for the first time, it would be as part of a complete 363-foot-tall three-stage Saturn V. The new "all-up" approach would, it was hoped, slash the number of test flights needed before the Saturn V could launch astronauts to the Moon.

George Mueller. Image credit: NASA.

All-up Saturn V testing, today hailed as a visionary and heroic step, made many Apollo engineers nervous. The Saturn V was the largest rocket ever developed. It had engines of unprecedented scale and power: the F-1 engines in the 33-foot-diameter S-IC first stage, which burned RP-1 kerosene fuel and liquid oxygen, remain today the largest ever flown. The J-2 engines in the top two stages, the 33-foot-diameter S-II second stage and the 22-foot-diameter S-IVB stage, gulped down temperamental liquid hydrogen and liquid oxygen propellants. Cautious engineers could see many opportunities for trouble, and they were aware that problems they could not foresee might be the most difficult to solve. Many believed that NASA should have in place backup plans in case the Saturn V suffered development delays.

Eighteen months after Mueller's announcement, E. Harris and J. Brom, engineers with The RAND Corporation think tank, proposed one such back-up plan. Their brief report, originally classified "Secret," looked at how NASA might accomplish a piloted Moon landing by 1970 if the Saturn V could not be certified as safe enough to launch astronauts.

Harris and Brom's backup plan would see the Apollo Saturn V lift off without astronauts on board. It would expend its S-IC first stage and S-II second stage in turn, then its S-IVB third stage would place itself plus lunar mission Apollo Command and Service Module (CSM) and Lunar Module (LM) spacecraft into parking orbit about the Earth. Because it would carry no crew, the lunar mission CSM would need no Launch Escape System (LES) tower on its nose.

Three Apollo astronauts would reach Earth orbit separately in a ferry CSM launched atop a two-stage Saturn IB rocket. The ferry CSM would carry a special drogue docking unit on its nose for linking up with the waiting lunar mission CSM's nose-mounted probe docking unit. The special drogue, the only new system required for RAND's backup plan, would need about one year and "perhaps several million dollars" to develop.

The top of the Apollo 13 Lunar Module Aquarius. The red arrow points to the concave drogue docking unit. Image credit: NASA.

The astronauts would dock with and transfer to the lunar mission CSM in Earth orbit, then would cast off the ferry CSM. The remainder of their mission would occur as in NASA's Apollo plan. The astronauts would restart the S-IVB stage to perform Trans-Lunar Injection (that is, to leave Earth orbit for the Moon). After S-IVB stage shutdown, they would detach the lunar mission CSM from the Spacecraft LM Adapter (SLA) shroud that linked it to the top of the S-IVB stage. The SLA, made up of four segments, would peel back and separate, revealing the LM. The CSM would then dock with the drogue docking unit on top of the LM and pull the Moon lander free of the spent S-IVB stage.

The RAND engineers declined to recommend whether the Saturn V or the Saturn IB should be launched first. They noted that liquid hydrogen fuel in the Saturn V S-IVB stage would boil and escape at a rate of 700 pounds per hour; the stage would thus need to be restarted within 4.5 hours of reaching parking orbit if it was to retain enough propellants for Trans-Lunar Injection. They noted that deletion of the 2900-pound LES would make the lunar mission Saturn V that much lighter, so its S-IVB stage could be loaded with an extra 2900 pounds of liquid hydrogen; that is, enough to permit it to loiter in low-Earth orbit for nearly 10 hours. Extending the loiter time further would demand a complex and costly S-IVB stage redesign.

Launching the crew first would avoid the S-IVB stage loiter-time constraint. Harris and Brom noted that, though the Apollo lunar mission was scheduled to last only from seven to 10 days, NASA planned a 14-day Earth-orbital Gemini mission by the end of 1965 to certify that astronauts could withstand long space flights. (That mission, Gemini 7, flew in December 1965. Astronauts Frank Borman and James Lovell returned to Earth after 14 days in good health and high spirits.)

Assuming that the Gemini flight confirmed that humans could endure 14 days in weightlessness, then the ferry CSM crew could in theory wait for from four to seven days for the unmanned Saturn V to join them in Earth orbit. Harris and Brom recommended that, in the event that launch of the Saturn V was delayed so that the astronauts waiting in orbit could not accomplish a lunar mission and return to Earth within 14 days of reaching space, then they should carry out an unspecified backup Earth-orbital mission in the ferry CSM so that their flight would not be wasted.

NASA officials did not take up the Harris and Brom proposal, though for a time in 1968 they might have wished that they had. The first Saturn V test flight, Apollo 4, lifted off without a crew on 9 November 1967. In keeping with Mueller's 1963 directive, it included complete S-IC, S-II, and S-IVB stages, plus a CSM with LES. Because LM development had hit snags, a dummy LM rode inside its SLA. The eight-hour Earth-orbital mission was an unqualified success.

Troubled flight: Apollo 6 Saturn V test, 4 April 1968. Image credit: NASA.

Apollo 6, was, however, another story. On 4 April 1968, two minutes into its automated flight, the second Saturn V to fly began to shake back and forth along its long axis. Dubbed "pogo" by engineers, the violent oscillations tore pieces off the SLA and damaged one of the S-II's five J-2 engines. Following S-II ignition, the engine under-performed and shut down prematurely, then a control logic flaw caused a healthy S-II engine to shut down. The remaining three S-II engines burned for a minute longer than planned to compensate for the two failed engines. The S-IVB's single J-2 engine then burned for 30 seconds longer than planned to reach a lopsided Earth orbit. Two orbits later, the engine refused to restart despite repeated radioed commands from flight controllers.

The pogo oscillations might have injured astronauts, had any been on board the Apollo 6 CSM; the S-IVB failure would certainly have scrubbed their flight to the Moon. Post-flight analysis showed, however, that the pogo and engine failures had relatively simple fixes. After intense internal debate, NASA announced on 12 November 1968 that the third Saturn V would launch Apollo 8 astronauts Frank Borman, James Lovell, and William Anders to the Moon. The giant rocket performed flawlessly, placing the Apollo 8 CSM on course for lunar orbit on 21 December 1968.

Sources

"Apollo Launch-Vehicle Man-Rating: Some Considerations and an Alternative Contingency Plan (U)," Memorandum RM-4489-NASA, E. D. Harris and J. R. Brom, The RAND Corporation, May 1965.

The Apollo Spacecraft: A Chronology, Volume II, NASA SP-4009,  Mary Louise Morse & Jean Kernahan Bays, NASA Scientific and Technical Information Office, 1973, pp. 104-106.

Stages to Saturn: A Technological History of the Apollo/Saturn Launch Vehicles, NASA SP-4206, Roger Bilstein, NASA, 1980, pp. 347-363.

Apollo: The Race to the Moon, Charles Murray & Catherine Bly Cox, Simon & Schuster, 1989, pp. 153-162.

More Information

What If Apollo Astronauts Became Marooned in Lunar Orbit? (1968)

What If an Apollo Lunar Module Ran Low on Fuel and Aborted Its Moon Landing? (1966)

What If An Apollo Saturn Rocket Exploded on the Launch Pad? (1965)