Space Race: The Notorious 1962 Proposal to Launch an Astronaut on a One-Way Trip to the Moon

Mercury suborbital flights were considered a prudent first step in U.S. piloted spaceflight. The Soviet Vostok missions upstaged suborbital Mercury, leading NASA to accept more risk by moving on to Mercury orbital missions. Image credit: NASA.

When the seven Mercury astronauts were presented to the world on 9 April 1959, it was expected that, before any reached for Earth orbit, each would fly a suborbital "training" flight. These short flights, launched on modified Redstone missiles, would subject the astronauts to preflight preparations, liftoff and acceleration, a brief period of weightlessness, fiery reentry and rapid deceleration, and splashdown and recovery — in short, all of the stresses of an orbital mission. This was judged to be a prudent approach to preparing America’s astronauts for the rigors of orbital spaceflight.

Cosmonaut Yuri Gagarin's launch into Earth orbit in the 10,420-pound Vostok 1 capsule three years later (12 April 1961) consigned this plan to the dustbin. On 5 May 1961, astronaut Alan Shepard flew a 303-mile-long, 116-mile-high suborbital hop lasting 15 minutes, 22 seconds in the 4,040-pound Mercury-Redstone 3/Freedom 7 spacecraft. The flight was widely compared with Gagarin's 108-minute single orbit and derided as proof that the Soviet Union remained far ahead of the United States in space — and that it was, perhaps, superior in other ways.

Before a joint session of Congress on 25 May 1961, President John F. Kennedy called on NASA to land an American on the Moon and return him safely to Earth before 1970. NASA tapped Apollo, previously planned as an Earth-orbital program with circumlunar potential, as its new lunar landing program.

As for suborbital Mercury training flights, prudence went out the window. NASA flew only one more suborbital mission — Gus Grissom's Mercury-Redstone 4 flight (21 July 1961), which ended with the loss of the Liberty Bell 7 spacecraft during recovery — before terminating Mercury-Redstone to concentrate on Mercury-Atlas orbital flights. Two weeks after Grissom's 15-minute, 37-second flight, Gherman Titov orbited the Earth 17.5 times in 25 hours on board Vostok 2 (6-7 August 1961), adding to feelings of humiliation and desperation in the United States.

By the time John Glenn became the first American in orbit (20 February 1962), NASA and several advisory committees were debating how the U.S. should reach for the Moon. At the same time, the U.S. civilian space agency began planning a program to bridge the gap between Mercury and Apollo. On 7 December 1961, NASA announced plans for a two-man "Mercury Mark II" spacecraft that would surpass Vostok's achievements beginning in 1963 and 1964. In January 1962, Mercury Mark II was renamed Gemini. The Gemini missions would expose astronauts to space conditions for up to two weeks (roughly the duration of a lunar mission) and give them spacewalk and orbital maneuvering practice.

Many feared, however, that Gemini, like Mercury, would be upstaged. Though the Soviets remained cagey about their space plans, it was widely assumed that their apparent lead in powerful booster rockets would permit them to launch a man to the Moon and return him to Earth in about 1965.

Against this backdrop, John M. Cord, a Project Engineer in the Advanced Design Division at Bell Aerosystems Company, and Leonard M. Seale, a psychologist in charge of Bell's Human Factors Division, developed a plan for a desperate mission to put a man on the Moon ahead of the Soviets. They unveiled their "One-Way Manned Space Mission" proposal in Los Angeles at the Institute of Aerospace Sciences (IAS) meeting in July 1962.

Cord and Seale explained that, since neither propellants for departing the Moon nor parachutes and an Earth-atmosphere reentry heat shield would be required, their new approach would slash lunar spacecraft mass. This would enable a rocket with between 450,000 and 1.1 million pounds of thrust — perhaps a near-relative of the Saturn I rocket, a Saturn I with an advanced upper stage, or a Titan missile derivative — to launch a one-man Moon lander on a Direct-Ascent path to the Moon. Such a rocket would, they estimated, be ready in the United States in 1964 or early 1965.

The Saturn I rocket was mainly a test vehicle for Saturn IB and Saturn V systems. Rockets only a little more powerful might have launched the One-Way Space Man cargo capsules and crew capsule during 1964. Image credit: NASA.

Though they termed it "one-way," Cord and Seale did not propose a suicide mission. They estimated that a rocket capable of launching a three-man Direct-Ascent Apollo mission to retrieve the One-Way Space Man — that is, a rocket with between 1.1 million and 3.5 million pounds of thrust at liftoff — would become available in the U.S. in the 1965-1967 period, between 18 and 24 months after his arrival on the Moon. Nevertheless, the mission would be "extremely hazardous." This was due to the fact that, after its boost phase — the period between Earth liftoff and injection onto an Earth-Moon path — the astronaut would be unable to abort if some technical malfunction or unknown environmental danger threatened his life. If, on the other hand, the mission were a success, it would be "significant both scientifically and politically."

Cord and Seale viewed their mission as part of a series of increasingly capable lunar missions. First would come automated lunar flyby and orbiter missions to assess radiation hazards and photograph the Moon for terrain roughness assessment. Automated Ranger spacecraft would then photograph selected small areas up close as they plummeted toward destructive impact. A slightly different Ranger design would hard-land sturdy instruments, such as seismometers, on the Moon.

Next, automated Surveyor soft landers would visit potential One-Way Space Man landing sites to return images and perform soil experiments so that scientists could determine whether the One-Way Space Man would be able to land safely. Automated rovers would follow to gather detailed data on his landing site. A rover would also place a radio homing beacon at the site to guide the One-Way Space Man crew lander and cargo landers to safe landings.

The One-Way Space Man mission would come next, then round-trip Apollo missions would begin. The first Apollo would, of course, set down near the One-Way Space Man's lunar base; one of the One-Way Space Man's tasks would be to select a safe site for the three-man Direct-Ascent Apollo lander that would take him home. The Apollo Program might then lead to a permanent lunar base — a goal made more attainable, Cord and Seale argued, by the One-Way Space Man's experiences on the Moon.

While the flybys, orbiters, hard and soft landers, and rovers explored the Moon, engineers would develop hardware for the One-Way Space Man mission. In addition to a suitable man-rated booster rocket, they would develop a "minimum" crew capsule, a cargo capsule, a retro stage with extendible "alighting gear" for soft-landing both capsule types, and a layout for the One-Way Space Man's lunar base.

Testing would then begin. This would include Earth-orbital crew capsule tests bearing primates, much like those conducted ahead of the Mercury-Redstone and Mercury-Atlas manned flights. A boilerplate cargo lander fitted out with engineering sensors and telemetry transmitters would land on the Moon, then four cargo landers would home in on the rover-emplaced homing beacon at the One-Way Space Man landing site. The four cargo flights would test systems common to the crew lander and would pre-land supplies and equipment the One-Way Space Man would use to build his base. Finally, the One-Way Space Man would depart Earth for the Moon.

The One-Way Space Man crew capsule. Image credit: Bell Aerosystems.

Cord and Seale's crew capsule would measure 10 feet across its base and about seven feet tall. It would provide 345 cubic feet of living volume for the One-Way Space Man. The capsule would have an empty mass of just 1735 pounds — less than half that of Mercury — and a fully loaded mass of only 2190 pounds. Its low mass was in large part attributable to its lack of an integral Earth-reentry heat shield — the heat shield would be discarded at the end of the boost phase along with other launch-abort systems. In addition to the 180-pound astronaut, the capsule would carry food and water for 12 days (90 pounds), breathing oxygen for 12 days plus an 18-day emergency supply (60 pounds), a space suit with rechargeable life-support backpack (90 pounds), tools and tool supplies, such as solder (25 pounds), and health, first-aid, and safety gear (10 pounds).

The thin-skinned crew capsule would not provide adequate radiation protection during the One-Way Space Man's 2.5-day Earth-Moon journey, nor while he lived in it while setting up his lunar base. This was because providing adequate shielding would add so much mass to the capsule that it would scuttle the entire One-Way Space Man plan. Cord and Seale noted that the next period of high solar flare activity would not begin until 1967, by which time, if all went well, the One-Way Space Man would have returned to Earth; they admitted, however, that more than 25 flares had occurred during the three years prior to their Los Angeles talk.

One-Way Space Man lunar base. The nuclear reactor providing electricity to the base is located at the far left edge of the image; overhead cables link it to One-Way Space Man's shelter. A large dish antenna on the shelter links the One-Way Space Man to Earth. Image credit: Bell Aerosystems.

Immediately upon landing, the One-Way Space Man would set to work establishing his base. His would be a race against time; in addition to the constant threat of a solar flare, his crew capsule's fuel cells could provide electricity for no more than 9.5 days by the time he landed.

The One-Way Space Man would exit his crew capsule through one of two hatches. The capsule would include no airlock; to exit or enter, the astronaut would depressurize or re-pressurize the entire capsule. The capsule atmosphere would consist of pure oxygen at a pressure of seven pounds per square inch.

The environment into which the One-Way Space Man would step would be extremely hazardous, Cord and Seale warned. In fact, they forecast lunar surface conditions harsher than actually exist. They expected that the One-Way Space Man would find few level places and many sharp rocks. The irregular surface and knife-like rock shards would be especially hazardous during the One-Way Space Man's clumsy first days on the Moon, when he would be unaccustomed to the low gravity (17% of Earth surface gravity), harsh sunlight (almost twice as bright as on Earth), and deep shadows of the lunar surface.

Micrometeorite dust would cover portions of the surface to a depth of about a yard, Cord and Seale reported. The One-Way Space Man would stir up the dust with his feet as he moved. They told their audience that each disturbed dust grain would ricochet off the surface and stir up additional grains. Combined with dust kicked up by micrometeorite impacts, the astronaut would walk in a veritable dust storm that would at times obscure vision. Inevitably he would carry dust into his shelter; Cord and Seale anticipated that this would place strain on the air filtering system and might damage other systems.

One-Way Space Man space suit. Cord and Seale envisioned a harsh, dusty lunar surface covered with sharp rocks, but this image displays a benign surface. Image credit: Bell Aerosystems.

Cord and Seale attempted to estimate how often the One-Way Space Man's space suit would be penetrated by micrometeorites. These would, they reported, travel at an average velocity of 40 kilometers per second. They found that a pressure suit made of sewn three-ply nylon would experience on average 1.3 punctures every four hours. Adding a suit-sealant layer would reduce the decompression danger, but would do nothing to protect the One-Way Space Man's body from the bullet-like impacts of the micrometeorites.

Adding a one-tenth-centimeter-thick woven-aluminum layer would slash the average number of punctures to 0.007 per four-hour Moonwalk and would attenuate impacts. It would, however, hamper movement. Cord and Seale recommended that the One-Way Space Man be fitted instead with a rigid aluminum-skinned suit that would permit only 0.002 penetrations per four-hour moonwalk. They hoped that clever engineers would be able to build a rigid suit with the joint flexibility of a nylon soft suit.

During his first 9.5 days on the Moon, the One-Way Space Man would unload the four cargo capsules, each of which would measure 10 feet wide and about 13 feet long. Each 2190-pound cargo capsule would carry 910 pounds of supplies and equipment. Two capsules, each equipped with a floor, pre-installed life support systems, and start-up supplies, would become his shelter. He would tip each onto its side, placing their floors parallel with the lunar surface, and remove their conical nose cones. He would then winch the two capsules together, forming a living space about 25 feet long.

One-Way Space Man cargo capsule.
Image credit: Bell Aerosystems.

If left unprotected, the One-Way Space Man's shelter would suffer on average 1.4 micrometeorite punctures per year. Cord and Seale noted that burying the shelter under "lunar rubble" would provide protection from micrometeorites and reduce its interior radiation level. Moving enough surface material to adequately bury the 25-foot-long, 10-foot-tall shelter would, however, be beyond the capabilities of a lone astronaut, so they suggested instead that the One-Way Space Man ward off meteorites by installing on his shelter's hull thin metal micrometeorite shields carried inside one of the cargo capsules. The shields, which would stand several inches off the hull, would break up and vaporize micrometeorites that struck and penetrated them, blunting their impact on the shelter's hull.

For radiation protection, Cord and Seale proposed a separate small radiation shelter that could be easily buried or moved to a "void" in a crater wall. They assumed that six feet of lunar rubble would be sufficient to protect the One-Way Space Man from solar flares. When detectors registered a sharp increase in radiation at the base site, the One-Way Space Man would hurry to the radiation shelter to wait out the flare. As his range of operations increased, he would establish other small shelters at strategic locations around his base site.

The One-Way Space Man would bring along his own potentially hazardous radiation source: a nuclear reactor for generating electrical power. Unlike solar cells, the reactor could make electricity during the frigid two-week lunar night and, unlike fuel cells, it would not require expendables. The astronaut would move the reactor from one of the cargo landers to a small crater and, after running overhead cables back to the shelter and activating it, bury it to protect himself from its ionizing radiation.

One-Way Space Man shelter (foreground); in the background, the buried radiation shelter (left) and an abandoned cargo capsule descent stage and nose cone are visible. Image credit: Bell Aerosystems.

Cord and Seale estimated that 13 cargo landers per year would be required to deliver life support supplies. Three more cargo landers would deliver parts for a multi-purpose rover and construction equipment, and one would deliver the nuclear reactor and radio equipment, including a large dish-shaped high-gain antenna. Three more would deliver "utility" payloads; these would include scientific gear. Establishing the shelter would need two cargo landers. In all, the One-Way Space Man would need 22 cargo landers during his first year on the Moon.

In addition, he might occasionally need emergency supplies, such as medicines, at short notice. Cord and Seale suggested that a small booster with a special rough-landing cargo lander — perhaps derived from Ranger — be kept on standby.

On 11 July 1962, a few weeks after Cord and Seale presented their paper, NASA announced that it had selected the Lunar Orbit Rendezvous (LOR) mode for Apollo lunar missions, not Direct-Ascent. LOR would see an Apollo mothership with a lone astronaut on board remain in lunar orbit while two astronauts descended to the surface in a minimal "bug" lander. The bug became known first as the Lunar Excursion Module and later as the Lunar Module (LM). As already noted, Cord and Seale based the One-Way Space Man plan on the Direct-Ascent mode. They conceded that it could also include Earth-Orbit Rendezvous, another Apollo mode contender. They argued, however, that any form of rendezvous would complicate their mission plan unnecessarily.

Although never seriously considered, Cord and Seale's proposal excited considerable interest. For example, it led off a 25 June 1962 news story on the Los Angeles IAS meeting in the pages of Missiles and Rockets magazine. Its headline read, "One-Man, One-Way Moon Trip Urged." Cord and Seale, perhaps feeling the heat for proposing such a risky mission, took exception to the word "urged" — in a letter printed in the 30 July 1962 issue of the magazine under the title "Morality and the Moon," they called their proposal "inconsistent with our moral values" as a nation. That did not stop them, however, from publishing a summary of their proposal in the publication Aerospace Engineering in December 1962. After that, technical discussion of the One-Way Space Man concept ended.

The concept remained intriguing to many, however. In 1964, novelist Hank Searls published a thriller called The Pilgrim Project based on Cord and Seale's plan. The novel had the flavor of alternate history even as it saw print.

In Searls' novel, the U.S. has fallen far behind the Soviet Union in the race to the Moon. The Soviets have built an Earth-orbiting shipyard and have begun manned circumlunar flights while the U.S. struggles in Earth orbit to perfect rendezvous and docking using Apollo spacecraft. Searls implies that more Mercury orbital flights took place than in our timeline, but his book makes scant mention of Gemini, the program NASA used to develop rendezvous techniques.

The lone Project Pilgrim astronaut leaves for the Moon in a modified Mercury capsule soon after the Soviets have launched a three-man one-way mission. His target is a pre-landed shelter called Chuckwagon. The radio homing beacon on the shelter fails, forcing the Pilgrim astronaut to rely on visual sighting to find it on the lunar surface. Unlike Cord and Seale's One-Way Space Man, Searl's Pilgrim astronaut could swing around the Moon and return to Earth if Chuckwagon or his capsule suffered a malfunction.

The cover art for this edition of The Pilgrim Project is mostly stylized, but the Mercury-derived piloted lunar spacecraft is discernible (lower right). Image credit: McGraw Hill Book Company.

The Pilgrim astronaut spots an object on the lunar surface near Chuckwagon's expected position, so he ejects his heat shield and Earth-landing systems to reduce his spacecraft's mass for the retro maneuver. He lands successfully, exits the Mercury capsule, and moves cautiously over the stark alien surface toward the object he spotted from space. It turns out to be the Soviet lander, which has crashed in a crevasse, killing its occupants. One cosmonaut hangs out of the spacecraft hatch gripping a Soviet hammer-and-sickle flag; the Pilgrim astronaut places it in one of his suit pockets, which already contains a U.S. flag.

The modified Mercury is not designed to serve as a temporary shelter and the Pilgrim astronaut has only a limited supply of oxygen in his suit backpack. Having no idea where Chuckwagon is, he sets out at random after laying out the Soviet and American flags side by side. His unexpected exertions as he moves over the rugged surface soon cause him to overheat. Then, just as he is about to accept his fate, he notices a slowly blinking star on the horizon; it is the flashing locator beacon on top of Chuckwagon. The novel ends as the Pilgrim astronaut sets out toward his refuge.

Searls' novel became the basis for the 1968 Robert Altman film Countdown. In the film, a Gemini capsule on an Apollo LM descent stage replaces the modified Mercury. The story is simplified, but closely follows the novel. According to space historian and NASA biomedical researcher John B. Charles, Altman filmed the launch of Gemini 11 (12-15 September 1966), the penultimate Gemini mission, so that it could represent the launch of the Pilgrim astronaut. A Gemini-Titan rocket was, of course, not powerful enough to put a Gemini and LM descent stage on a Direct-Ascent path to the Moon. The Gemini 11 scenes do, however, constitute rare cinema-quality footage of a Gemini launch.

By the end of the Gemini program in November 1966, the U.S. was well ahead of the Soviet Union in the race to the Moon. For a time it appeared that the Apollo 1 fire (27 January 1967) might set back the U.S. space program and reignite the Moon race; however, the Soviet space program suffered the Soyuz 1 disaster three months later (23-24 April 1967). The closest NASA came to a desperation mission in the Moon race was Apollo 8, which orbited the Moon 10 times on Christmas Eve 1968. The mission, intended originally to test the LM in high Earth orbit, was dispatched to the Moon without an LM to head off the threat to hard-won U.S. prestige of a possible Soviet piloted circumlunar flight.

At the end of their IAS paper and their Aerospace Engineering article, Cord and Seale explained that the One-Way Space Man concept could be applied throughout the Solar System. When next the concept of a one-way manned space mission was proposed, it was aimed at Mars, and it was envisioned as a truly one-way mission.

At the Case for Mars VI conference in July 1996, George William Herbert of Retro Aerospace proposed that middle-aged scientists be dispatched on a one-way journey to the Red Planet to cut costs and increase scientific payback. His scenario had the scientists living out their natural lives while exploring the planet to which they had dedicated their careers. Herbert's was a new kind of desperation mission. He and his fellow Mars enthusiasts were not desperate to beat another country to Mars; rather, they were desperate to see humans on Mars.

The one-way Mars concept remains of interest to some, though it has not gained widespread acceptance. In 2009, Lawrence Krauss, Director of the Origins Initiative at Arizona State University, told The New York Times that "To boldly go where no one has gone before does not require coming home again." He explained that a one-way approach would reduce the cost of piloted Mars exploration and compared the journey to that of the Pilgrims.

Science News picked up and published the Krauss statement, and the magazine's readers quickly reacted. One noted that the Pilgrims traveled to a place where they knew that they could survive. One-way Mars explorers would have no such assurance. Another complained that the proposal illustrated "the decline of moral reasoning."

Sources

"The One-Way Manned Space Mission," IAS Paper No. 62-131, John M. Cord and Leonard M. Seale; paper presented at the Institute of Aerospace Sciences National Summer Meeting held in Los Angeles, California, 19-22 June 1962.

"At IAS meeting. . . One-Man, One-Way Moon Trip Urged," W. Wilks, Missiles and Rockets, 25 June 1962, pp. 16-17.

"Morality and the Moon," John M. Cord and Leonard M. Seale, Letters, Missiles and Rockets, 30 July 1962, p. 8.

"The One-Way Manned Space Mission," John M. Cord and Leonard M. Seale, Aerospace Engineering, December 1962, pp. 60-61, 94-102.

The Pilgrim Project, Hank Searles, McGraw-Hill Book Company, 1964.

Countdown, directed by Robert Altman, screenplay by Loring Mandel, Warner Bros. Pictures, 1968.

"One-Way to Mars," George William Herbert, AAS-96-322, The Case for Mars VI: Making Mars an Affordable Destination, Kelly R. McMillen, editor; proceedings of the sixth Case for Mars Conference held at the University of Colorado at Boulder, 17-20 July 1996.

"Science Observation," Lawrence M. Krauss, Science News, 20 October 2009, p. 4.

"Feedback — One-way ticket to Mars," Science News, 21 November 2009, p. 29.

More Information

Around the Moon in 80 Hours (1958)

"He Who Controls the Moon Controls the Earth" (1958)

Apollo Science and Sites: The Sonett Report (1963)

Moon Suit: 1949

Skylab-Salyut Space Laboratory (1972)

Image credit: NASA.

On 14 May 1973, the five F-1 engines at the base of the last Saturn V rocket to fly ignited, engulfing Pad 39A at Kennedy Space Center in orange flame and gray smoke. Seconds later, the hold-down arms on the launch pad swung clear, and the giant white-and-black rocket began its thundering ascent.

The last Saturn V bore aloft the Skylab Orbital Workshop, a temporary space station. Skylab was the last vestige of NASA's ill-fated Apollo Applications Project. It comprised the nearly 22-foot-diameter cylindrical Orbital Workshop (OWS) with two wing-like solar arrays, the cylindrical Airlock Module (AM) and Multiple Docking Adapter (MDA), and the truss-mounted Apollo Telescope Mount (ATM) with four solar arrays arranged in a "windmill" formation. The OWS, for which McDonnell Douglas was prime contractor, was a converted Apollo Saturn S-IVB stage.

Fully deployed in 435-kilometer-high orbit inclined 50° relative to Earth's equator, the 77-metric-ton OWS measured about 36 meters long. It included 347 cubic meters of living and working space pressurized to 5 pounds per square inch (psi). Skylab reached orbit unmanned and fully stocked with oxygen, nitrogen, water, food, clothing, film, spare parts, and other expendables. Apollo Command and Service Modules (CSMs) launched on two-stage Saturn IB rockets delivered to Skylab three-man crews and a small amount of cargo.

Never mind what it says; this is the mission patch for the Skylab 2 crew. Image credit: NASA.

In a move that immediately generated confusion, NASA designated the unmanned Saturn V mission to launch the Skylab Orbital Workshop Skylab 1 and the program's first piloted mission Skylab 2. The Skylab 2 crew then wore a mission patch, designed by fantasy & science fiction artist Kelly Freas, that bore the designation "Skylab I." The Skylab 3 crew's mission patch had "Skylab II" emblazoned upon it, and the Skylab 4 patch included a stylized numeral "3." Prior to launch, Skylab 1 was designated Skylab A; had it failed, a backup OWS designated Skylab B might have been readied and launched, though in retrospect it seems unlikely that NASA would have allocated funds to complete and launch it.

Skylab 1 was in fact nearly lost; it suffered damage about a minute after launch as its meteoroid shield deployed prematurely and peeled away, then lost one of its twin OWS solar array wings shortly after attaining orbit. The other wing array was stuck shut, leaving Skylab starved for power. With the reflective meteoroid shield gone, temperatures on board soared, threatening to spoil food, medicines, and film.

NASA engineers hurriedly fashioned a sun shield and specialized tools and trained Skylab 2 astronauts Pete Conrad, Joe Kerwin, and Paul Weitz in their use. They reached Skylab on 25 May 1973, and succeeded in making it habitable and functional, then spent a total of 28 days in space. The Skylab 3 crew (Alan Bean, Jack Lousma, and Owen Garriott) spent 59 days on board the repaired station. After 84 days in space, the Skylab 4 crew (Gerald Carr, Edward Gibson, and William Pogue) undocked from Skylab on 8 February 1974.

A repaired Skylab 1 orbits the Earth. Image credit: NASA.

Skylab 1 was not Earth's first space station; that honor belongs to the Soviet Union's Salyut 1. Salyut 1 had reached orbit on top of a Proton rocket, the Soviet equivalent of the Saturn IB, on 19 April 1971. The station was much smaller than Skylab, with a mass at launch of only about 20 metric tons.

Built from parts developed for the Almaz military space station and the Soyuz piloted spacecraft, Salyut 1 measured 15.8 meters in length and contained 90 cubic meters of living and working space pressurized to 15 psi (that is, approximately Earth sea-level pressure). Like Skylab, Salyut 1 reached orbit unmanned and stocked with expendables. Soyuz ferries delivered three-man crews and a limited quantity of cargo to a single port at Salyut 1's front end.

Only one crew — the Soyuz 11 crew of Georgy Dobrovolsky, Vladislav Volkov, and Viktor Patsayev — succeeded in docking with and entering Salyut 1; they lived on board from 7 to 30 June 1971. During return to Earth, a valve accidentally opened in their reentry capsule, venting their air supply into space. The crew wore no pressure suits, so perished.

At the time Salyut 1 flew, the U.S. and the Soviet Union were negotiating toward a U.S. spacecraft docking with a Soviet spacecraft. By the end of 1971, the sides had settled on an Apollo CSM docking with a Salyut station. The two spacecraft would each carry a new-design International Docking Mechanism (IDM). The mission was meant to be a test of the IDM ahead of its routine use on future Soviet and American spacecraft.

In April 1972, however, Soviet negotiators declared that the Salyut design could not easily be modified to include a second docking port. They suggested that a CSM dock instead with a modified Soyuz. On 24 May 1972, at a summit meeting in Moscow, U.S. President Richard Nixon and Soviet Premier Alexei Kosygin signed the Space Cooperation Agreement, an international treaty that called for a wide range of cooperative ventures, including an Apollo-Soyuz docking. On 30 June 1972, NASA named the new cooperative program the Apollo-Soyuz Test Project (ASTP). The Soviets called it Soyuz-Apollo.

A week earlier, a McDonnell Douglas Astronautics Company team had pitched to NASA a cooperative space mission much more ambitious than either Apollo-Soyuz or Apollo-Salyut. The team proposed a docking between the Skylab B, a Salyut, an Apollo CSM, and a Soyuz ferry. The resulting "cooperative space laboratory" would "address world needs" and "provide identifiable benefits from space [and] mutual technological benefits and cost savings."

The U.S.-Soviet crew would perform solar, stellar, and Earth observations, communications technology development, and biomedical studies. Perhaps most important for NASA, Skylab-Salyut would serve as "an evolutionary step between Skylab A and Space Shuttle/Station" that would permit the U.S. space agency to keep its spaceflight teams mostly intact during the projected gap in U.S. piloted flights between ASTP in 1975 and the planned first Shuttle flight in 1979.

McDonnell-Douglas illustration of Skylab-Salyut space laboratory.

The company proposed a 140-day Skylab-Salyut mission in mid-1976. The Skylab B OWS would launch into a 435-kilometer-high orbit inclined 51.6° relative to the equator; that is, at Skylab A’s orbital altitude but at the Soviet Union's preferred orbital inclination. A CSM bearing three astronauts would launch the following day and dock with an Apollo-type port on the side of the Skylab B MDA. The Soviet Union would then launch a Salyut into a 240-kilometer-high orbit at 51.6° of inclination, followed by an IDM-equipped Soyuz ferry bearing three cosmonauts. The Soyuz would dock with the Salyut forward port, which would also carry an IDM.

McDonnell Douglas cited published Soviet data when it assumed that the Salyut's propulsion system could be used to match orbits with Skylab B. As the Salyut-Soyuz combination approached the U.S. station, two cosmonauts would undock from the Salyut in the Soyuz and dock with an IDM-equipped port on the side of the Skylab MDA opposite the CSM. The lone cosmonaut on board the Salyut would then pilot it to a docking with the IDM-equipped Skylab forward port.

The cosmonauts and astronauts would work together on board Skylab-Salyut for at least 24 days (the longest period a Soyuz had operated in Earth orbit as of June 1972). The three cosmonauts would then undock in the Soyuz and return to Earth. The Soviets could then launch at least one more crew to the station. After up to 70 days in orbit, the first U.S. crew would return to Earth in its CSM. A second CSM would then deliver a second crew. If they docked immediately after the first crew departed, the second crew could remain on board Skylab-Salyut for up to 70 days.

Image credit: Junior Miranda.

As noted above, U.S. and Soviet spacecraft provided their crews with different gas mixes and pressures. Astronauts and cosmonauts passing between the two parts of the Skylab-Salyut station might prebreathe to adapt their bodies to the change in pressure and gas mix, though the time required would probably become onerous very quickly. Alternately, the sides could adopt a common atmosphere.

If the international station adopted Skylab's oxygen-rich 5 psi atmosphere, the Salyut and Soyuz would require improved fireproofing and beefed-up thermal control systems to keep its electronics cool in the thin air. If, on the other hand, the Soviet 15 psi pressure were adopted, Skylab B would need substantial structural changes to withstand the increased pressure and extra tanks of oxygen and nitrogen to make up for air lost through accelerated leakage. The CSM could not withstand 15 psi without suffering damage, so would need to remain isolated from the Skylab/Salyut/Soyuz cluster. McDonnell Douglas suggested that a small airlock for pre-breathing be placed in the MDA for CSM access.

Image credit: Junior Miranda.

The company then proposed a compromise 8 psi atmosphere slightly rich in oxygen. The CSM could withstand this pressure, it explained, and the modifications both sides would need to make would be roughly equivalent in magnitude.

Some modifications would be required no matter which atmosphere was adopted. McDonnell Douglas assumed that Skylab B would provide all attitude control for the international station. To meet this requirement, NASA would need to equip it with control moment gyros 30% more capable than those planned for Skylab A. The Skylab B MDA structure would have to be beefed up to handle greater docking loads, as would its ATM trusses. In addition, a new thermal radiator would be needed to dissipate the heat produced by the three Soviet cosmonauts when they worked on board Skylab B. McDonnell Douglas proposed that this be added to the Fixed Airlock Shroud at the front of the OWS, close to the MDA.

Possible Salyut changes would include enlarged solar arrays; these might be needed because the four arrays on the Skylab B ATM would shade the Salyut's forward pair of arrays, reducing the Soviet station's electricity supply by up to a quarter. McDonnell Douglas assumed that Skylab B and the Salyut would not share electricity, so the U.S. would be unable to make up the difference. The company added, however, that, by relieving the Salyut of attitude control responsibilities, Skylab B might save it as much electricity as it took away.

Apollo-Soyuz crews pose with a model of their docked spacecraft. At left in brown are Deke Slayton, Thomas Stafford (standing), and Vance Brand; at right in green are Alexei Leonov (standing) and Valeri Kubasov. Image credit: NASA.

A little more than a three years after McDonnell Douglas completed its study, the ASTP mission commenced. On 15 July 1975, the Soyuz 19 spacecraft ascended to Earth orbit, followed seven hours later by the final Apollo CSM, which had no official numerical designation. On board Soyuz 19 were Alexei Leonov, the first man to walk in space, and Soyuz 6 veteran Valeri Kubasov. The ASTP Soyuz carried an "APDS-75" international docking unit with three outsplayed guide "petals." Gemini and Apollo veteran Thomas Stafford and rookie astronauts Vance Brand and Donald Slayton rode aboard the ASTP CSM.

After reaching an unusually low 188-by-228-kilometer orbit — required because the Soyuz could not climb higher — the ASTP Apollo CSM detached from the Saturn IB S-IVB stage that had injected it into orbit and turned 180°. It then docked with an Apollo-type port on the Docking Module (DM). The DM, which had reached orbit within a streamlined shroud between the CSM's large engine bell and the top of the S-IVB stage, included an international docking system and an airlock to enable the ASTP crews to move between the U.S. and Soviet spacecraft atmospheres without harm. After they extracted the DM from the spent S-IVB, the American ASTP crew maneuvered their spacecraft toward a rendezvous with Soyuz 19.

The ASTP CSM docked with Soyuz 19 on 17 July 1975. Following two days of ceremonies and mutual experiments, the two spacecraft undocked, redocked with Soyuz 19 playing the active role, and then went their separate ways. Soyuz 19 landed in Soviet Kazakhstan on 21 July and the ASTP CSM splashed down in the Pacific Ocean on 24 July, six years to the day after Apollo 11 returned from the moon. It was the last time American astronauts flew in space until the first Space Shuttle flight in April 1981.

In 1974, NASA studied a 1977 ASTP mission. At about the same time, work began toward a Shuttle-Salyut docking in the early 1980s. New cooperation was hampered by U.S. domestic politics: the Administration of Gerald Ford felt unable to commit to a new international piloted flight ahead of the November 1976 presidential election.

Shuttle-Salyut concept. Image credit: Junior Miranda.

President Jimmy Carter renewed the Space Cooperation Agreement in May 1977. In November of that year, NASA and Soviet engineers met in Moscow to discuss the Shuttle-Salyut mission. The sides examined using the Shuttle to deliver an experiment module to a Salyut and traded engineering data. By then, Salyut 6 was in orbit. The new station included a second, aft-mounted, docking port. In January 1978, NASA completed a preliminary Shuttle-Salyut mission plan which saw the Shuttle dock with the Salyut front port while a Soyuz was docked at its aft port.

U.S.-Soviet relations rapidly soured, however. A Shuttle-Salyut technical meeting planned for April 1978 was indefinitely postponed. In September 1978, NASA ceased Shuttle-Salyut planning pending the outcome of an U.S. government interagency review of U.S.-Soviet space cooperation in which the Department of State played the central role. The Soviet invasion of Afghanistan in December 1979 subsequently halted for a decade almost all discussion of dockings between U.S. and Soviet piloted spacecraft, though superpower space cooperation with a lower profile — for example, the Cosmos biosatellite program — continued.

Skylab B never reached orbit; it became an exhibit in the National Air and Space Museum in Washington, DC. NASA studied reboosting Skylab 1 into a higher orbit and reusing it in the Space Shuttle era, but Shuttle delays and a faster-than-expected rate of orbital decay meant that it reentered Earth's atmosphere on 11 July 1979.

Sources

Basic Data of the Scientific Orbital Station “Salyut,” USSR, no date (1971?).

US/USSR Cooperative Space Laboratory (Skylab/Salyut), McDonnell Douglas Astronautics Company Eastern Division, 23 June 1972.

Skylab News Reference, NASA Office of Public Affairs, March 1973.

Apollo-Soyuz Test Project Information for Press, USSR/NASA, 1975.

Thirty Years Together: A Chronology of U.S.-Soviet Space Cooperation, NASA CR 185707, David S. F. Portree, February 1993, pp. 9-26 (http://ntrs.nasa.gov/search.jsp?R=19930010786 - accessed 15 July 2015).

Mir Hardware Heritage, NASA RP 1357, David S. F. Portree, March 1995, pp. 33-35, 65-72 (http://history.nasa.gov/SP-4225/documentation/mhh/mhh.htm - accessed 21 July 2015).

More Information

NASA's 1992 Plan to Land Soyuz Space Station Lifeboats in Australia

A Forgotten Rocket: The Saturn IB

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

Skylab 1 liftoff, 14 May 1973. Image credit: NASA.

Between August 1963 and November 1964, a 13-member team at NASA's Marshall Space Flight Center (MSFC) in Huntsville, Alabama, conducted a detailed in-house study of Mars and Venus flyby missions. These would see a flyby spacecraft bearing a crew depart Earth orbit, coast past its target planet, and return to Earth. Only small course-correction maneuvers would be necessary after Earth-orbit departure.

The study, led by Harry O. Ruppe of the MSFC Future Projects Office (FPO), was a follow-on to the Early Manned Planetary-Interplanetary Roundtrip Expeditions (EMPIRE) study, which had lasted from May 1962 to February 1963. MSFC FPO had directed EMPIRE contractors Ford Aeronutronic, Lockheed, and General Dynamics to study manned Mars and Venus flyby and orbiter missions in the early 1970s as a means of justifying early development of nuclear-thermal rockets and launch vehicles more powerful than the Apollo Saturn V (see "More Information" below). MSFC FPO stressed these technologies in EMPIRE because MSFC was NASA's lead center for large rocket development and because it was involved in the joint NASA/Atomic Energy Commission nuclear propulsion program through the Reactor In-Flight Test (RIFT), which sought to launch a nuclear rocket into space in 1967.

The new manned planetary flyby study acknowledged changes in the advance planning environment within NASA. Whereas the EMPIRE contractors had been instructed to "attempt" to use Apollo hardware in their spacecraft designs — and had responded by designing all-new systems with little Apollo heritage — the MSFC in-house study adhered strictly to the rule that Apollo technology should be used everywhere possible.

This reflected increasing restrictions placed on NASA advanced technology development by President John F. Kennedy and his successor, President Lyndon Baines Johnson. Expressed succinctly, NASA planners had begun to realize that a commitment to the goal of a man on the Moon did not imply a commitment to the goal of a man on Mars.

The MSFC team declared, nevertheless, that it was "inconceivable" that the "tremendous" technology that NASA had developed for Apollo would not lead eventually to a manned Mars landing. It was simply a matter of which course NASA should follow to get there. An Earth-orbiting space station or a lunar base were 1970s goals that could use Apollo hardware and provide "training" for manned Mars landings; like Apollo, however, these would operate "within the Earth's 'sphere of activity.'" Manned Mars/Venus flybys in the mid-to-late 1970s, on the other hand, could be based on Apollo systems, yet would venture beyond the safe harbor of the Earth-Moon system.

Little was known of Mars's atmosphere or surface conditions when Ruppe's engineers performed their study. A piloted Mars flyby in the 1970s could, they argued, provide data they would need to design a 1980s Mars landing mission. They proposed that, in addition to exploring Mars closeup with remote-sensing instruments mounted on their spacecraft, flyby astronauts should serve as caretakers for a small armada of automated probes. These would include "landers, atmospheric floaters, skippers, orbiters, and possibly probes. . .to perform aerodynamic entry tests [of spacecraft] designs and materials."

Automated probes would need caretakers, the MSFC team believed, because they had had a checkered history. Mariner II had flown past Venus successfully in December 1962, near EMPIRE's end, confirming what astronomers had already begun to suspect: that the planet's dense clouds hid a hellish surface. The Ranger VII Moon probe had returned images of southeast Oceanus Procellarum as it plunged toward planned destructive impact in July 1964, providing engineers designing the Apollo Lunar Module lander with essential data on the Moon's surface.

Mariners I and III had, however, failed, as had the first six Rangers. Mariner IV had been launched toward Mars on 28 November 1964, as editing began on the Ruppe team's study report. As it saw print in February 1965, the 261-kilogram solar-powered robot remained healthy. It was, however, anyone's guess whether Mariner IV would survive until its planned Mars flyby in July 1965.

The MSFC engineers believed that "the major emphasis of the manned flyby-unmanned probe combination" should "be focused on assisting later [Mars] landing missions." Engineers who lacked data on Mars conditions would, they explained, have little choice but to design the Mars landing spacecraft for "worst conditions." This would tend to increase its mass and thus the number of costly booster rockets necessary to place its components into Earth orbit for assembly.

In the first half of 1965, this 1962 U.S. Air Force Mars map remained the best available to Mars mission planners. Image credit: U.S. Air Force/Lunar and Planetary Institute.

Conversely, adequate knowledge of Mars would enable engineers to cut costs by taking advantage of the conditions there. Of particular importance, they wrote, would be probes that would test propellant-saving aerodynamic braking maneuvers in the martian atmosphere and prospect for "usable indigenous materials. . .such as water" on Mars.

They estimated that, lacking adequate prior knowledge of Mars, the first piloted landing mission "would probably transport 2 or 3 men to the surface of Mars for a few days. . .[at a cost of] a billion dollars per man-day on Mars." If on the other hand, "the physical properties of Mars were well known, we could think. . .of the first landing as a long-duration base, reducing cost to less than 10 million dollars per man-day."

The MSFC team consulted Ruppe's previously published launch opportunity tables to determine that several Mars and Venus flyby launch windows would open in the mid-to-late 1970s. Because Venus has a nearly circular orbit around the Sun, opportunities to reach it would vary little in terms of amount of energy required, mission duration, and Earth-return velocity (all critical factors in interplanetary mission design). Mars, on the other hand, has a noticeably eccentric (elliptical) orbit, which means that these factors vary considerably from one launch opportunity to the next. For their detailed analysis, the MSFC engineers opted for a "typical" Mars flyby that would leave Earth orbit in September 1975, and a corresponding "typical" Venus flyby that would depart Earth orbit in August 1978.

An "improved" two-stage variant of the Apollo Saturn V would serve as the piloted flyby program's workhorse Earth-to-orbit booster. The first payload it would place into orbit for any flyby mission would be the 125-ton flyby spacecraft with a multipurpose "aft skirt assembly." Stacked atop the two-stage Saturn V and covered with a streamlined launch shroud, the flyby spacecraft/aft skirt assembly would outwardly resemble the Skylab Orbital Workshop, which was launched on a two-stage Saturn V in May 1973, eight years after Ruppe's team completed its study (image at top of post).

The three-stage Saturn V configured for Apollo Moon flights stood 363 feet tall, while the two-stage Saturn V with Skylab on top measured 333.6 feet tall. The two-stage Saturn V with the flyby spacecraft/aft skirt assembly combination on top would stand 332 feet tall. Skylab measured 84.5 feet long at launch, while the flyby spacecraft/aft skirt assembly would measure 89 feet long with its launch shroud (A in the drawing below) and 81.6 feet long in orbit, after its shroud completed its task and was discarded.

Cutaway drawing of the Ruppe team's piloted flyby spacecraft. Letters on the drawing are called out in italics in the post text. Please click on the image to enlarge. Image credit: NASA.

The MSFC engineers tapped as their rocket engine for course corrections the Apollo Lunar Module Descent Engine (B). It would draw hypergolic propellants (that is, fuel and oxidizer that ignite on contact with each other) from four spherical tanks (I). The tanks would be designed to hold enough propellants to change the flyby spacecraft's speed by 500 meters per second (mps). The 0.5-kilometer-per-second course change would need 26,272 pounds of propellants for the 1975 Mars flyby and 20,583 pounds for the 1978 Venus flyby.

A pair of 5000-pound "radioisotope power supply systems" would be mounted to the flyby spacecraft near the course-correction engine, well away from the spherical, 20-foot-diameter Lab/Crew Living area (M). During ascent to Earth orbit, these would remain folded inside the launch shroud (C). Some time after shroud separation, they would pivot outward to their flight positions (D) and begin to make electricity.

The flyby spacecraft's pressurized Hangar (E) would fill the space between the course-correction engine and the course-correction propellant tanks. The three-man flyby crew would reach the Hangar from their main living area via an airlock tube (J). The Hangar would contain at its center a modified Apollo Command and Service Module (CSM). The Ruppe team felt it necessary to cocoon the CSM within the Hangar to protect it from "micrometeoroids, outgassing, and other detrimental effects" of long space exposure.

The CSM warranted special protection for two reasons. First and foremost, it was the flyby crew's end-of-mission Earth-atmosphere reentry vehicle. The astronauts would ride in its conical Command Module (CM) (F) and would use the Service Propulsion System (SPS) engine (H), a part of the Service Module (SM) (G), to slow to Apollo lunar-return speed of 11 kilometers per second (kps) before they reached Earth's atmosphere. Cocooning the CSM in the Hangar would also limit the amount of costly redesign and retesting the CSM would need before it could be used for manned Mars/Venus flyby missions.

The CM for flyby missions would lack a nose-mounted docking unit, but otherwise would closely resemble the Apollo lunar CM. It would, therefore, need no new testing beyond that required for lunar missions.

For Venus flybys, the SM also could remain unchanged. The Mars flyby SM, on the other hand, would approach Earth moving fast enough that its SPS engine would need to fire for up to 536 seconds longer than the Apollo lunar SPS and would burn as much as 2790 pounds more propellants than the Apollo lunar SM could hold. The Mars flyby SM would thus need longer propellant tanks and either a redesigned SPS or a pair of conventional SPSs operating in tandem or in series. A new engine rated for a longer burn time was also a possibility, though that option would not be in keeping with the MSFC team's goal of reliance on Apollo hardware.

In addition to the Earth-atmosphere reentry CSM, the flyby spacecraft Hangar would house five tons of automated probes destined for release near the mission's target planet. As noted above, the crew's main job would be to ensure that the probes remained functional until they reached Mars or Venus. The astronauts would thus have available within the Hangar 1000 pounds of tools and supplies for servicing the probes. The MSFC engineers also placed in the Hangar an airlock for spacewalks (they doubted that it would see much use), and a stock of emergency life support provisions.

When not attending to their cargo of probes, the three flyby astronauts would live and work in the Lab/Crew Living Area, where they would breathe a half-oxygen, half-nitrogen atmosphere at a pressure of 10 pounds per square inch. The Lab/Crew Living Area and the Hangar could each be re-pressurized 12 times during a Mars flyby mission and eight times during a Venus flyby mission.

Repressurization would occur in the event that a meteoroid punctured the spacecraft hull and Lab/Crew Living Area pressure vessel or after scheduled periodic air dumps that would purge the atmosphere of toxic trace gases outgassed from furnishings and equipment and generated by experiments and cooking. Each repressurization would need 1885 pounds of gases, bringing the total breathing gas carried to 22,650 pounds for the typical Mars flyby spacecraft and 15,050 pounds for the Venus flyby spacecraft. A system for recycling air between purges would have a mass of 1800 pounds on both the Mars and Venus flyby spacecraft.

The Ruppe team's engineers cited a study by the MSFC Research Projects Laboratory (RPL) when they rejected specialized radiation shielding for the flyby spacecraft's bottle-shaped emergency shelter (K). The RPL had found that solar flares powerful enough to harm flyby crews were unlikely to occur in the mid-to-late 1970s.

In place of 1000 pounds of shielding, the MSFC team proposed a double-walled shelter with the flyby spacecraft life support water supply stored between its inner and outer walls. Equipment and food would be arranged around the shelter's exterior to provide additional radiation protection. The crew would sleep inside the shelter to minimize their exposure to cosmic rays. In the event of fire, catastrophic pressure loss, or other emergency, the shelter, which would contain a duplicate set of spacecraft controls, could be sealed off from the rest of the flyby spacecraft.

The MSFC engineers calculated that building the flyby spacecraft so that it could spin to create artificial gravity would add 69,000 pounds to its total mass. The engineers rejected this approach in favor of providing a small centrifuge (L) capable of holding two astronauts at a time (one at either end). Support arms would link the twin centrifuge gondolas to a motorized ring around the hatch leading into the emergency shelter.

The Lab/Crew Living Area would nestle in a bowl-shaped recess in the aft skirt assembly (O). At its front end, the aft skirt assembly would match the 22-foot diameter of the flyby spacecraft; at its aft end, it would match the 33-foot diameter of the S-II second stage of the Saturn V that would boost it and the flyby spacecraft into 185-kilometer-high Earth orbit. S-II separation would reveal twin RL-10 rendezvous and docking rocket motors (P) and a large socket-like docking structure (N) on the aft skirt assembly's aft end.

At its front end, the aft skirt assembly would contain a ring-shaped, 22-foot-diameter Saturn V Instrument Unit (IU) (not shown). In addition to guiding the Saturn V carrying the flyby spacecraft during its ascent to Earth orbit, the IU would provide guidance control for Earth-orbital assembly maneuvers and for flyby spacecraft Earth-orbit departure.

The number of two-stage Saturn V rockets required to place into Earth orbit the flyby spacecraft, its S-IIB Orbital Launch Vehicle (OLV), and liquid oxygen (LOX) for the S-IIB OLV would depend on the amount of energy required to place the flyby spacecraft on course for its target planet. Even in the least demanding opportunities, Mars flybys would require more energy than Venus flybys, so would need more Saturn V rockets.

The MSFC engineers described in detail the assembly campaign for the Mars flyby mission that would leave Earth orbit in September 1975, during a launch opportunity lasting 28 days. The first two-stage Saturn V in the assembly campaign would lift off from one of the two Complex 39 Saturn V launch pads at Cape Kennedy, Florida, on 28 April 1975. If the Saturn V failed and the flyby spacecraft/aft skirt assembly it carried was destroyed, then a backup would lift off on 24 June 1975.

The next Saturn V in the series would launch on 28 June 1975, bearing the first of four LOX tankers to 185-kilometer orbit. The Ruppe team's tanker could transport about 95 tons of LOX. Three more successful tanker launches would be needed; these would occur on 6 July and 7 July and 3 September 1975. A single backup tanker would stand by in case of a tanker launch failure; if it were needed, it would launch on 6 September 1975.

With a Mars flyby spacecraft/aft skirt assembly and four LOX tankers safely orbiting the Earth, the sixth and last Saturn V would launch the S-IIB OLV into a 485-kilometer-high orbit on 13 September 1975. As its name implies, the S-IIB OLV would be a derivative of the Saturn V S-II second stage.

Modifications would include deletion of two of its five J-2 engines and improved insulation to retard boil-off and escape of the roughly 80 tons of liquid hydrogen it would carry into orbit. The MSFC engineers expected that an S-IIB OLV could be developed that would retain enough liquid hydrogen for flyby spacecraft Earth-orbit departure 72 hours after its launch from Complex 39, but aimed for an Earth-orbit departure just 50 hours after S-IIB OLV launch.

Using the twin RL-10 engines in its aft skirt assembly, the unmanned flyby spacecraft would climb to a 485-kilometer circular orbit and rendezvous with the S-IIB OLV as soon as the latter was confirmed to be safely in orbit. It would then back up and dock with the S-IIB OLV. Next, the four LOX tankers would climb to 485-kilometer orbit and dock one at a time with the S-IIB OLV. Each would pump its cargo into the S-IIB OLV's LOX tank, then would undock and move away, clearing the way for the next in the series.

The astronauts would board the Mars flyby spacecraft 20 hours before planned launch from Earth orbit. If NASA had a space station in Earth orbit in 1975, they might board from that. An alternate plan would see the flyby astronauts reach their spacecraft on board an Apollo CSM launched from Earth on a Saturn IB rocket. After entering the flyby spacecraft and checking out its systems, they would cast off the CSM.

The S-IIB OLV's three J-2 engines would burn for about eight minutes on 26 September 1975 to push the flyby spacecraft/aft skirt assembly combination out of 485-kilometer Earth orbit and place it on course for Mars. The burn would add about five kps to its speed. After the flyby spacecraft/aft skirt assembly combination separated from the S-IIB, the RL-10 engines in the aft skirt assembly would be used to fine-tune the flyby spacecraft's course. The aft skirt assembly, its work done, could then be cast off or retained for at least part of the mission to provide additional radiation/meteoroid shielding for the Lab/Crew Living Area.

Image credit: NASA.

Ruppe's team provided an example heliocentric orbital plot for a manned Mars flyby mission leaving Earth on 26 September 1975. The dashed line on the plot represents the flyby spacecraft path around the Sun. Flight to Mars would require 130 days.

Halfway to Mars, on 30 November 1975, the crew would adjust their spacecraft's course using the course-correction engine. The MSFC engineers budgeted enough propellants for the first midcourse burn to change the flyby spacecraft's speed by 150 mps. The crew would eject "consumed life support" (that is, body and food waste, saturated absorbent charcoal, used filters, and other trash) shortly before the course-correction burn so that it would continue on the flyby spacecraft's original course and not intersect Mars.

Mars flyby would occur on 3 February 1976, when Mars and the flyby spacecraft were 0.86 Astronomical Units (AU) — that is, 0.86 times the Earth-Sun distance — from Earth. The flyby spacecraft would approach the day side, reaching a distance of 200,000 kilometers from the planet's center 6.5 hours before closest approach. It would pass 792 kilometers from Mars moving at about 11 kps relative to the planet, then would retreat from the night side. During approach to the planet, the astronauts would release 2.5 tons of robot probes and carry out continuous observations. Near closest approach, they would ignite the course-correction engine a second time.

During retreat from Mars, the astronauts would release the remaining 2.5 tons of probes. While the flyby spacecraft remained close to Mars, it would relay data from the probes to Earth at a high data rate. The flyby spacecraft would, however, spend only one hour within 18,250 kilometers of Mars's center. Five and a half hours after closest approach, it would pass beyond 164,000 kilometers from the planet's center, and shortly after that the Mars probes would switch to direct transmission to Earth at a low data rate. The crew would then begin a grueling 539-day journey home.

A few weeks later, the crew would become the first humans to enter the Asteroid Belt. Maximum distance from Earth (3.21 AU) would be attained on September 13, 1976, about one year into their mission. At about the same time, Earth would move behind the Sun as viewed from the flyby spacecraft. The crew would then perform the mission's final course-correction burn, changing their spacecraft's speed by up to 200 mps.

The flyby spacecraft would pass inside of Mars orbit on 31 May 1977 at a distance of 0.353 AU from Earth. Over the following two months, it would gradually catch up with the homeworld. On 19 July 1977, six days before planned Earth atmosphere reentry, the crew would transfer to the modified Apollo CSM in the Hangar and check out its systems.

Two days before reentry, the CSM would emerge from its cocoon and abandon the flyby spacecraft. On 25 July, with Earth looming outside its small windows, the crew would turn the CSM so that its engine or engines pointed in its direction of flight. A burn lasting up to 19.4 minutes would reduce the CSM's speed from up to 15.8 kps to Apollo lunar-return speed of 11 kps, then the conical CM would detach and, using small rocket motors, orient its bowl-shaped heat shield for reentry. Minutes later, the CM would deploy three parachutes and lower gently into the ocean.

Image credit: NASA.

The Ruppe team also prepared an orbital plot for the Venus flyby mission departing Earth in August 1978. A shortened S-IIB OLV would add about 3.8 kps to the Venus flyby spacecraft's speed. The mission would be of shorter duration than the Mars mission — only one year — with Venus flyby occurring low over the planet's day side on 11 December 1978. The spacecraft would attain its greatest distance from Earth — 0.674 AU — on 15 April 1979. After leaving the Hangar, the CSM's main engine would trim about 2.6 kps from its Earth-approach speed. Reentry and splashdown would occur on 16 August 1979.

The MSFC engineers outlined a hardware development schedule based (inexplicably) on a Venus flyby in late 1975 and a Mars flyby in 1978 (that is, the exact reverse of the program detailed in their report). They also estimated the probable cost of the flyby program. They assumed that no new-start funding for the program would become available in NASA's budget before Fiscal Year (FY) 1969, after the first successful Apollo lunar landing, which in 1965 was scheduled to take place during early 1968. Detailed flyby program planning would begin in mid-1968 and last a year.

LOX tanker, flyby spacecraft, and interplanetary avionics development would commence in the last quarter of 1968. LOX tanker development, at a cost of $380 million, would be completed in late 1974. A pair of LOX tanker flight tests would launch on two-stage Saturn V rockets in 1973 and mid-1974. A flyby spacecraft development test unit would reach Earth orbit on a two-stage Saturn V in 1974; among other things, it would be used for crew training. The flyby spacecraft would cost more to develop than any other hardware element ($1.563 billion). Avionics development (total cost: $325 million) would include a Saturn IB-launched flight test.

S-IIB OLV development (total cost: $425 million) would start in late 1969 and conclude in 1974. S-IIB OLV flight tests would take place in 1973-1974. Apollo SM modifications (total cost: $115 milion) would begin in mid-1970 and end in 1974, and aft skirt assembly development (total cost: $165 million) would span late 1970 through early 1975. An aft skirt assembly flight test using a Saturn IB launch vehicle would take place in 1974.

Science probe development for the 1975 Venus flyby would begin in mid-1970 and continue through the last quarter of 1975. Mars probe development would start in the last quarter of 1973 and run through 1977. Probe development would cost $220 million for each mission.

The MSFC engineers based their operational cost estimates on learning curves developed through the many Saturn V and Saturn IB launches that they expected would occur by the mid-1970s. They estimated that 62 three-stage and two-stage Saturn Vs would be launched prior to the first Venus flyby Saturn V launch, so that each Saturn V for the Venus flyby would cost $70 million. Fifty-two Saturn IB launches would take place before the first Venus flyby Saturn IB launch, leading to a cost of $22 million per Venus flyby Saturn IB. They assumed that 70 Apollo CSMs would have flown before the first Venus flyby CSM, leading to a Venus flyby CSM cost of $72 million.

For the 1978 Mars flyby, the MSFC engineers assumed that NASA would already have launched 98 three-stage and two-stage Saturn V rockets by the time the first Mars flyby Saturn V lifted off, reducing the cost per Mars flyby Saturn V to only $65 million. Seventy Saturn IB launches would have taken place, reducing the cost for each Mars flyby Saturn IB to $20 million. One hundred CSMs would have flown ahead of the first Mars flyby CSM, reducing the flyby CSM cost to $69 million.

Design and development cost would peak in FY 1972 at $895 million. Operational cost would peak at $497 million in FY 1974. The peak funding year for the program would be FY 1973, when operational and development costs would total $1.222 billion. Development costs would total $3.75 billion between FY 1969 and FY 1978. Operational costs would total $2.671 billion between FY 1971 and FY 1978. The entire piloted flyby program would thus cost $6.421 billion. The MSFC team estimated that, by providing data to engineers, the flyby program would reduce by about $4 billion the cost of a follow-on Mars landing mission.

The MSFC engineers also conducted what they called a "mission worth analysis." They first assumed an undefined "basic space program" for the 1970s and 1980s. Manned Venus flyby missions could, they calculated, be deleted from the program with only a 2% impact on total space program worth and only a 10% reduction in planetary program worth because "it is not possible to land on Venus." Leaving the Venus flybys in place but deleting the Mars flyby and landing missions would reduce total space program worth by 9% and planetary program worth by half. Deleting all piloted planetary missions and relying only on robotic probes would reduce total space program worth by 12% and planetary program worth by 63%.

Artist concept of Mariner IV at Mars. Image credit: NASA.

Mariner IV flew triumphantly past Mars on 14-15 July 1965, five months after the MSFC team's study report saw print. It returned 21 black-and-white images of the planet's cratered surface and, as it flew behind the planet, conducted a radio-diffraction experiment that indicated a martian atmospheric pressure ten times less than had been expected — about 1% of Earth sea-level pressure. Mariner IV revealed a Mars apparently inhospitable to life. The mission also showed that robots could cross the gulf between Earth and Mars and return useful data without help from astronaut caretakers.

Oddly enough, neither Mariner IV's success nor its discouraging Mars findings undermined the manned flyby concept. The flyby program goal of putting Saturn-Apollo hardware to new uses remained attractive to many in NASA.

In April 1966, NASA Associate Administrator for Manned Space Flight George Mueller launched a new piloted flyby study under the auspices of the Planetary Joint Action Group (JAG). The group, which drew members from MSFC, the Manned Spacecraft Center in Houston, Kennedy Space Center in Florida, NASA Headquarters, and NASA planning contractor Bellcomm, had been assembled in April 1965 to study piloted Mars landing missions. The new study, which emphasized the 1975 piloted Mars flyby opportunity, sought to flesh out automated probe and on-board instrument designs and to further explore the interplanetary potential of Apollo technology and techniques.

Sources

"Future Effort to Stress Apollo Hardware," Aviation Week & Space Technology, 16 November 1964, pp. 48-49, 51.

Manned Planetary Reconnaissance Mission Study: Venus/Mars Flyby, NASA TM X-53205, Harry O. Ruppe, Future Projects Office, NASA Marshall Space Flight Center, 5 February 1965.

"Photos Point to Mars Landing Difficulty," R. Pay, Missiles and Rockets, 26 July 1965, pp. 13-19.

"Manned Planetary 'Swing-Bys' Proposed," D. Fink, Aviation Week & Space Technology, 30 August 1965, p. 30.

More Information

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

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

A Forgotten Rocket: The Saturn IB

New Horizons II (2004-2005)

Artist concept of the New Horizons spacecraft in the Pluto system. From bottom left to top right: New Horizons, Pluto, and Charon. Image credit: NASA.

The New Horizons II (NH II) mission was originally conceived in mid-2002 as a backup for the New Horizons (NH) mission to Pluto, its moons, and other bodies of the Kuiper Belt. The brainchild of Southwest Research Institute (SwRI) scientist and NH Principal Investigator Alan Stern, NH II was meant to ensure that, should NH fail, NASA could still satisfy the stated desires of the planetary science community.

In their 2002-2003 Decadal Survey of future goals for planetary exploration, planetary scientists rated Kuiper Belt Object (KBO) exploration as their highest scientific priority. Nevertheless, the planetary science community, NASA, and the Congress have many competing priorities, so the NH II mission was judged to be a reach too far.

NASA had approved the NH mission proposal in November 2001. The compact 478-kilogram spacecraft was scheduled to launch atop a hefty Atlas V 551 rocket in January-February 2006. A Jupiter gravity-assist flyby in March 2007 would accelerate it toward Pluto with a flight time of only about eight years. If all went well, NH would bring to bear on Pluto and its satellites a suite of seven science instruments in July 2015. NH would then fly past one or more additional Kuiper Belt Objects (KBOs) in the 2016-2020 period.

For a time in 2004-2005, however, it appeared that it would leave Earth with a minimal supply of plutonium in its electricity-generating Radioisotope Thermal Generator (RTG). (In the image at the top of this post, the RTG is the black vaned cylinder at lower left.) The plutonium shortage stemmed from a security breakdown at the Department of Energy (DOE) laboratory that produced the plutonium New Horizons needed. Without an RTG fully loaded with plutonium, it was unlikely that NH could operate for long enough to reach any KBO beyond Pluto.

The shortage caused SwRI to propose a modified version of NH II. In its purest form, the new NH II would aim exclusively to explore one or more KBOs. It would leave Earth at least a year after NH, hopefully enabling it to launch with a topped-off RTG.

To cut costs, NH II would be a "clone" of New Horizons. SwRI estimated that, by avoiding new development and by drawing on the experience it had gained from NH, the NH II mission would cost only $472 million; that is, at least $200 million less than NH.

SwRI found that NH II could launch to one or more of the hundreds of KBOs known in 2004-2005 any time that a launch window for Jupiter opened (that is, every 13 months). The March 2008 and April 2009 launch opportunities were especially attractive, however, because they would permit a Uranus flyby in the 2014-2017 period en route to the target KBO without dramatically increasing mission duration. This would make NH II only the second spacecraft to explore the Sun's seventh planet; the first was Voyager 2 in January 1986.

This Hubble Space Telescope image shows Uranus approaching equinox in 2005 and at the time of equinox in 2007. The image also shows bright clouds, bands, and other signs of atmospheric activity absent when Voyager 2 flew through the Uranus system during southern hemisphere summer in 1986. Image credit: NASA/Space Telescope Science Institute.

All of the planets except Uranus rotate on an axis more or less perpendicular to the plane of their orbit around the Sun. Earth, for example, is tilted at 23.44° relative to the plane of its orbit. Uranus is tipped on its side relative to the other planets, meaning that its rotational axis is nearly parallel to the plane of its orbit.

Uranus has at least 27 moons, of which five (Miranda, Ariel, Umbriel, Titania, and Oberon) range from 450 to 1600 kilometers in diameter. It also has a system of at least 11 rings. The rings and moons revolve around Uranus in the plane of its equator, which means that the entire Uranus system appears to pivot around the Sun on its side. Uranus needs a little more than 84 years to circle the Sun once.

When Voyager 2 flew past Uranus, the planet's south pole was pointed toward the Sun; that is, its southern hemisphere was near the middle of a 21-year summer. Its northern hemisphere was pointed away from the Sun, so was locked in dark winter. The same applied to its moons; their southern hemispheres were fully lit and their northern hemispheres were cloaked in cold darkness. This meant that Voyager 2 could not image their northern hemispheres. The Uranian equator would be turned more toward the Sun when NH II flew past, so the spacecraft would be able to observe the Uranus system in its entirety.

Uranus appeared bland to Voyager 2, and the visible parts of its largest moons showed many intriguing features but no signs of present-day activity. In 1998, however, the Hubble Space Telescope revealed about 20 bright clouds in the Uranian atmosphere, and more bright clouds have since been observed. In addition, astronomers have spotted glowing aurorae at its magnetic poles, which do not match its rotational poles.

Small worlds similar to the Uranian moons in size and mass have turned out to be surprisingly active. Saturn's 500-kilometer-diameter moon Enceladus, to cite the best-known example, has squirting from warm areas at its south pole jets of water vapor laden with salt and organic compounds.

Binary Kuiper Belt Object 1999 TC36, Image credit: NASA/Space Telescope Science Institute.

After flying past Uranus, NH II would zoom onward to its primary destination. If launched from Earth in March 2008, the spacecraft could zip past the binary KBO 1999 TC36 as early as September 2020. Launch in April 2009 could lead to a flyby no later than April 2023. 1999 TC36, currently orbiting the Sun at about 31 times the Earth-Sun distance, comprises two close KBOs, one about 285 kilometers across and the other about 265 kilometers in diameter. Circling the close pair is a moon about 140 kilometers wide.

NH II might instead be directed toward a flyby of 2002 UX25, a roughly 680-kilometer-diameter KBO with a 205-kilometer satellite. If launch took place in March 2008, the flyby could occur as early as July 2022. Earth departure in early May 2009 would yield a 2002 UX25 flyby in July 2023. 2002 UX25 currently orbits the Sun at about 41 times the Earth-Sun distance. With a fully fueled RTG, additional KBO flybys after the 1999 TC36 or 2002 UX25 flyby would be possible.

In late 2004, as the plutonium shortage became apparent, the NH team appealed to Congress for funds for an NH II mission study. NASA's Fiscal Year 2005 budget appropriation called for such a study, though Congress declined to fund it. Nevertheless, in early 2005 NASA Headquarters tasked NASA Goddard Space Flight Center in suburban Washington, DC, with an independent study of the NH II concept.

The DOE subsequently was able to resolve its security problems and provide a full load of plutonium for the NH RTG, so NASA dropped the NH II concept. NH left Earth on 19 January 2006, flew past Jupiter on 28 February 2007, and flew through the Pluto system in mid-July 2015.

Seven months after NH left Earth, Pluto's classification as a planet, long tenuous, was updated to take into account new knowledge of the outer Solar System. The NH flyby made Pluto both the first KBO to be discovered and the first to be visited. NH flew past a second KBO, provisionally designated 2014 MU69, in January 2019. In November 2019, the 35-kilometer-long KBO was named Arrokoth.

Sources

New Horizons 2: A Journey to New Frontiers, presentation materials, A. Stern, Southwest Research Institute, 10 June 2005.

New Horizons II Mission Design, presentation materials, Y. Guo, 16 June 2004.

“New Horizons II: Doubling UP in the Outer Solar System,” L. David, Space.com (no longer online), 17 June 2004.

“New Horizons Set to Launch with Minimum Amount of Plutonium,” B. Berger, Space News, 4 October 2004.

More Information

The Challenge of the Planets, Part Three: Gravity

The Seventh Planet: A Gravity-Assist Tour of the Uranian System (2003)

A Forgotten Rocket: The Saturn IB

Image credit: NASA.

The Saturn V Moon rocket, the largest, most powerful launcher ever built, commands much attention, but not everyone knows that the giant had smaller, lesser-known relatives, including one that launched men into space. Had the Apollo Applications Program (AAP) gone ahead as planned in mid-1966, that other piloted Saturn rocket, the Saturn IB, might have become more familiar than the Saturn V. It would have become the AAP workhorse rocket, with more than two dozen flights to its credit. Of all the human spaceflight systems that the U.S. has produced, only the Space Shuttle has flown more missions than that.

The detailed 1971 NASA Marshall Space Flight Center graphic at the top of this post is a good point of departure for describing the Saturn IB. As the graphic indicates, the Saturn IB was a two-stage rocket. The eight H-1 engines in its Chrysler-built S-IB first stage burned liquid oxygen (LOX) and RP-1, a kind of kerosene used as aviation fuel. The single J-2 engine in the S-IVB second stage burned LOX and liquid hydrogen (LH2). Both stages were expended in launching their payload. The S-IVB stage also served (in slightly modified form) as the Saturn V Moon rocket third stage.

The ring above the second stage, the Instrument Unit (IU), was the Saturn IB's IBM-built electronic brain. It controlled the rocket's flight path and various in-flight events, such as first-stage separation and second-stage ignition. The outwardly similar Apollo Saturn V IU was located in the same position on the Saturn V S-IVB stage.

The tapering part above the IU, labeled "Apollo spacecraft," was in fact composed of several major systems. The skinny Launch Escape System (LES) tower on top contained a solid-propellant rocket motor designed to pull the conical Apollo Command Module (CM) to which it was attached to safety in the event that the Saturn IB malfunctioned.

The three-man CM was one part of the two-part Apollo Command and Service Module (CSM) spacecraft. The CSM also included the drum-shaped Service Module (SM), which housed propulsion and attitude-control systems, life-support consumables, and electricity-generating fuel cells.

Finally, the Spacecraft Lunar Module Adapter (SLA) was a segmented, streamlined shroud that linked the bottom of the CSM to the top of the IU. Though shown empty in the graphic, it could serve as a cargo volume. The SLA housed a Lunar Module (LM) Moon lander when it formed part of an Apollo Saturn V stack.

The first piloted Apollo mission: Apollo 7 liftoff from Launch Complex 34 on 11 October 1968. Image credit: NASA.

The first four Saturn IB rockets were test vehicles without crews. SA-201 (26 February 1966), the rocket's maiden flight, launched a Block I Apollo CSM on a suborbital path. The second, SA-203 (5 July 1966), was the first Earth-orbital Apollo flight. Its objective was to enable study of the behavior of liquid hydrogen in weightlessness. This was important for the development of an S-IVB stage that could restart in Earth orbit, as it would be called upon to do when it served as the Saturn V third stage during Apollo lunar missions. Next came SA-202 (25 August 1966), another suborbital Block I CSM test.

Finally, there was SA-204, which launched a test version of the LM into Earth orbit. SA-204 had originally been intended to launch the Apollo 1 crew of Gus Grissom, Ed White, and Roger Chaffee into Earth orbit in early 1967. Sadly, they perished on 27 January 1967, when fire broke out in their CSM during a countdown test at Launch Complex 34, located at Cape Canaveral Air Force Station, just south of NASA's Kennedy Space Center. The SA-204 Saturn IB did not contribute to the disaster.

Saturn IB rockets boosted Apollo CSM spacecraft bearing astronauts into low-Earth orbit just five times. The first piloted Saturn IB, designated SA-205, launched the Apollo 7 crew of Wally Schirra, Donn Eisele, and Walter Cunningham from Launch Complex 34 on 11 October 1968. The astronauts tested their CSM in orbit for 11 days — long enough to reach and return from the Moon — and splashed down in the North Atlantic Ocean on 22 October 1968.

The next Saturn IB rocket to fly, SA-206, did not launch until 25 May 1973, nearly five years after Apollo 7. By then, Apollo lunar landings were already a thing of the past and the Space Shuttle was at an early stage in its development. SA-206 launched the Skylab 2 CSM to the Skylab Orbital Workshop. Skylab, a converted S-IVB stage taken from the SA-212 Saturn IB rocket, reached orbit without a crew on 14 May 1973 atop the last Saturn V to fly. Though officially designated Skylab 2, crew atop SA-206 was the first to visit Skylab. Similarly, Skylab 3 was the second mission to visit the temporary space station and Skylab 4 was the third. The Skylab Program was the shrunken remnant of AAP.

The first Skylab crew, made up of moonwalker Pete Conrad and rookies Paul Weitz and Joseph Kerwin, had to fix Skylab before they could begin their program of scientific research; it had become damaged during launch. They worked in space for 28 days and returned to Earth on 22 June 1973.

The second crew to visit Skylab lifted off atop Saturn IB SA-207 on 28 July 1973. Moonwalker Alan Bean and rookies Jack Lousma and Owen Garriott lived on board for 59 days and splashed down on 29 September 1973. The all-rookie third crew, made up of Gerald Carr, William Pogue, and Edward Gibson, launched on SA-208 on 16 November 1973 and splashed down on 8 February 1974.

The last piloted Apollo mission: Apollo-Soyuz Test Project Apollo on Pad 39B, July 1975. Image credit: NASA.

The last Saturn IB to fly, SA-210, lifted off on 15 July 1975, bearing Gemini and Apollo veteran Thomas Stafford and rookies Vance Brand and Donald Slayton. Their mission, called the Apollo-Soyuz Test Project, was ostensibly an international space rescue test, but was in fact the poster child for President Richard Nixon's policy of detente with the Soviet Union. (By the time SA-210 lifted off, however, Nixon had been out of office for nearly a year.) On 17 July, the three astronauts docked their Apollo CSM, designated simply "Apollo," with the Soviet Soyuz 19 spacecraft.

The Apollo 7 and Skylab 2, 3, and 4 Saturn IBs had carried no spacecraft or cargo in their SLAs; SA-210, on the other hand, carried a Docking Module designed to circumvent incompatible docking units and an airlock that permitted the U.S. and Soviet spacefarers to move safely between the two spacecraft, which had different air mixes. Apollo astronauts breathed pure oxygen at low pressure; Soyuz designers opted for a more Earth-like, higher-pressure oxygen-nitrogen mix. Handshakes, ceremonies, and science experiments with Soyuz 19 cosmonauts Alexei Leonov and Valeri Kubasov followed the docking. Stafford, Brand, and Slayton splashed down in the Pacific Ocean on 24 July 1975, six years to the day after Apollo 11 returned from the Moon.

SA-206, -207, -208, and -210 all launched from the Launch Complex 39B Saturn V pad at NASA’s Kennedy Space Center. NASA planning contractor Bellcomm realized in late 1968 that launching AAP missions from Launch Complex 39 would allow Launch Complex 34 and its twin, Launch Complex 37, to be abandoned, thus saving NASA a considerable sum of money.

The decision to launch Saturn IB rockets from a Saturn V pad led to what was probably the most unusual launch pad arrangement of the Space Age. Called the "milk stool," it was a platform that raised the Saturn IB so that its S-IVB stage and CSM were at the same height as their Saturn V counterparts. This enabled the Skylab and Apollo-Soyuz Saturn IBs to use the existing Launch Complex 39B S-IVB and CSM umbilicals and crew access arm.

A total of 14 Saturn IB rockets were at least partly constructed. Besides four unmanned Saturn IB test missions that flew before Apollo 7 and the five Saturn IB-launched missions described above, there were SA-209, SA-211, SA-212, SA-213, and SA-214. SA-209 was actually prepared for a possible launch – for a short time in July 1973, it appeared that it would launch a two-man rescue CSM to recover the Skylab 3 crew, whose CSM had developed attitude-control system leaks soon after launch. It also stood by to launch the Apollo-Soyuz backup CSM. SA-209 is now on display at the Kennedy Space Center visitor center. As mentioned above, the SA-212 S-IVB stage became Skylab. The other Saturn IB rockets were turned into displays of various kinds or scrapped.

Sources

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

More Information

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

Dreaming a Different Apollo, Part One