30 July 2015

Clyde Tombaugh's Vision of Mars (1959)

Elysium and Tombaugh crater are located near the center of this image from India's Mars Orbiter spacecraft. Image credit: Indian Space Research Organization
Clyde William Tombaugh (1906-1997) was born in Streator, Illinois, and grew up in Burdett, Kansas, where he built his first telescopes. In 1929, Tombaugh joined the staff of Lowell Observatory in Flagstaff, Arizona, to hunt for Planet X, a world which Boston businessman Percival Lowell had predicted should exist beyond Neptune. On 18 February 1930, 24-year-old Tombaugh discovered Pluto.

A little over two weeks ago, on 14 July 2015, the New Horizons spacecraft raced through the Pluto system. The piano-sized probe bore some of Tombaugh's ashes. The New Horizons scientists applied the unofficial name Tombaugh Regio to a prominent surface feature on Pluto.

It is possible that Tombaugh Regio will not win through the formal planetary feature naming process, in part because a feature named for Tombaugh already exists: a crater on Mars, the world to which he devoted far more professional attention than he did Pluto. Tombaugh crater is located at 162° East, just north of the martian equator in Elysium Planitia, a region that Tombaugh believed was important for understanding the surface structure of the Red Planet.

Clyde Tombaugh with a telescope of his own making. Image credit: Wikipedia
Although Pluto became Lowell Observatory's greatest claim to fame, Percival Lowell had founded his observatory in 1894 to find proof of intelligent life on Mars. He had theorized that the aging planet was slowly losing its water, and that the dark lines some astronomers glimpsed on its ochre disk were canals its inhabitants had excavated to distribute melt water from the polar ice caps and stave off encroaching deserts.

Lowell believed that spots strung like beads along the lines were oases, and that irregular dark-colored areas (maria) scattered over the surface were desiccated sea beds. Though rejected by most astronomers (including Tombaugh), Lowell's romantic vision helped to inspire H. G. Wells's novel The War of the Worlds (1898) and the "Barsoom" books of Edgar Rice Burroughs. These tales in turn inspired generations of rocketeers and skywatchers.

In the January 1959 issue of Astronautics, the journal of the American Rocket Society, Tombaugh summarized the prevailing view of Mars surface conditions on the eve of its exploration by spacecraft. He first described three areas where improved data had undermined Lowell's romantic vision.

The first was temperature. Depending on its position in its elliptical orbit around the Sun, Mars receives between 53% and 36% as much solar energy as Earth. Astronomers using telescopes equipped with thermocouples had determined that the temperature on the surface at noon normally barely surpassed the freezing point of water, though it could reach 70° Fahrenheit at noon in the southern hemisphere in summer. Tombaugh added that the temperature regularly swings 200° Fahrenheit from frigid midnight to chilly noon over much of the planet.

Low atmospheric pressure also created problems for Lowell's Mars. Evidence was mounting, Tombaugh wrote, that at its surface Mars had an atmospheric pressure only 10% as great as Earth's sea-level pressure. Enough carbon dioxide was known to exist in the martian atmosphere to give the planet an atmospheric pressure about 1% of Earth's. Many planetary astronomers, Tombaugh added, believed that nitrogen made up the remaining nine-tenths of the martian atmosphere, though none had been detected.

Finally, Mars's surface was likely to be subjected to unhealthy levels of radiation. Planetary astronomers had found no evidence of oxygen in the martian atmosphere, Tombaugh reported. Whatever oxygen Mars had was probably locked up chemically in its crust, giving the planet its characteristic rusty color. Lack of free oxygen meant that Mars would also lack atmospheric ozone, which on Earth creates a shield against solar ultraviolet (UV) radiation. This meant that sterilizing UV radiation from the Sun would reach Mars's surface largely unfiltered.

Tombaugh argued that the dark maria could not be sea bottoms; they would be salt-encrusted if they were, so would appear bright white, not dark. Mars, he added, showed no signs of "a visible dendritic [branching] drainage system" akin to Earth's rivers, so was probably extremely arid. He noted seasonal changes in the maria's color which he attributed to plant life. As the polar cap evaporated in springtime, he wrote, atmospheric moisture would move toward the equator. The martian vegetation in the spring/summer hemisphere would absorb the moisture and change hue.

Tombaugh contended that martian plants had evolved novel ways of withstanding the planet’s cruel conditions. He recounted telescopic observations he made during Mars' close approach to Earth in 1954.
Normally the southern maria range from green to blue in color. The long dark sash, Sabaeus Sinus, running east to west only a few degrees south of the equator, is habitually bluish-green. Amazingly. . .this marking. . .altogether some 2000 miles long. . .suddenly turned to bright lavender or perhaps magenta! The other maria did not. Why? Can vegetation inhabiting this area shield itself by changing pigment to reflect away a sudden influx of lethal radiation?
Sometimes, Tombaugh reported, Mars's cruel conditions could spell catastrophe for even the toughest martian vegetation. He wrote that Syrtis Major,
the principal dark marking on Mars, undergoes some very strange metamorphoses in color. The north half is habitually of a deep blue color, while the southern half is grey-green to blue-green or sometimes a vivid green. I remember. . .when the whole marking became intensely black - totally devoid of color! In the absence of oxygen, dead vegetal matter would not yield to oxidation and decay. Were we seeing dead vegetal matter when the Syrtis turned black?
Tombaugh assured Astronautics readers that he did not believe in Lowell's intelligent Martians, though he hastened to add that he had "seen over 100 of the controversial canals too well, with telescopes of great effective power" to be able to "dismiss them as unreal." He offered an explanation for the planet's linear features that was first advanced by former Lowell collaborator (later Lowell rival) William Pickering in 1904.
Over the ages, Mars must have been hit by many asteroids. Such dreadful collisions must have produced some visible marks. . .Collisions with asteroids a few miles in diameter going at velocities of the order of 15 [miles per second] might well fracture a planet to the bottom of the crust and to radial distances of hundreds or even a few thousand miles. . .Where a fracture line met the surface, a long narrow strip of shattered rock would be produced, and would offer some haven to a hardy form of vegetation . . . [The plants growing in the fracture strip would] make a dark contrast against a light. . .terrain.
Tombaugh theorized that the dark spots Lowell thought were oases are actually asteroid impact craters. The canals, he asserted, divided the planet's entire crust into a "tetrahedron" pattern. As Mars cooled internally and shrank, some faces of the martian tetrahedron slumped. Tombaugh differed from the majority opinion of his time when he argued that other faces had risen to form high plateaus. Many of his contemporaries confidently asserted that Mars lacked any raised landforms. The northern-hemisphere region of Elysium, Tombaugh added, was probably the highest land on the planet. He explained that it
is sharply pentagonal in shape, [and] bounded by five long canals. . .The corners of the pentagon extend 600 geographical miles from the center. During most of the Martian year, Elysium appears much the same as the surrounding desert. By midsummer of the northern hemisphere, this area becomes white with frost except around noon. . .the whitening develops over the entire area, but always stops abruptly at the edges of the pentagon. One is forced to conclude that the five sides represent enormous vertical escarpments - and just where we should expect to see them - along the canals.
After five decades of Mars exploration by robot spacecraft - the first was Mariner IV, which flew past the planet on 14 July 1965, 50 years to the day before the New Horizons Pluto flyby - we know that Elysium is indeed an uplifted region, though not the highest on Mars. That honor goes to the massive Tharsis Plateau, upon which stand the planet's great shield volcanoes. The tallest of these, Olympus Mons, stands some 27 kilometers above the base datum, the martian equivalent of Earth's sea level.

Topographic map of eastern Elysium Planitia showing Tombaugh crater. The image is based on data from  the Mars Orbiter Laser Altimeter (MOLA) carried on the Mars Global Surveyor spacecraft. Low areas are blue and high areas are yellow and red. Image credit: MOLA Science Team/NASA 
We know today that, when Tombaugh's contemporaries detected martian atmospheric carbon dioxide, they had found not a minor atmospheric constituent, but instead virtually Mars's entire atmosphere. We have learned that branching channels are common on Mars, though at a scale invisible to Earth-based telescopes, and that Lowell's canals were products of eyestrain, the mind's tendency to impose patterns on random arrangements of objects, and wishful thinking.

We know also that the dark areas on Mars are mostly sand made from weathering and erosion of volcanic rocks, and that seasonal changes in their color and extent result from obscuring dust storms. We have found cracks in the martian crust, though those associated with asteroid impact craters are only local in extent. The best-known crustal fracture, the 3000-mile-long Valles Marineris canyon system, probably formed through internal stresses associated with the uplift of Tharsis. We know that the planet's overall shape has a pattern, though not one as intricate as Tombaugh's tetrahedron. Rather, Mars has southern highlands and northern lowlands (the latter at least partly underlain by ice, lending credence to the theory that it was once an ocean bottom).

In spite of our improved knowledge, key questions about Mars remain unanswered. We do not know, for example, whether it hosts living organisms. The pitch for piloted Mars exploration which concluded Tombaugh's paper thus remains relevant today.
[W]hy should we be interested in making a trip to Mars?. . .A manned landing on Mars would be a momentous achievement for the human race. It would be a field day for the geologist, biologist, astrophysicist, and meteorologist. They would glean knowledge on the consequences of a set of physical conditions foreign to us. . .Most important, to see at first hand what Nature has done with a world so marginal for life would be of the greatest philosophic and religious value, in helping us to understand our place and our purpose in the Universe.
Astronauts seek signs of past life on Mars. Image credit: NASA/Pat Rawlings

“Mars - A World for Exploration,” Clyde W. Tombaugh, Astronautics, January 1959, pp. 30-31, 86-93.

Mars and Its Canals, Percival Lowell, The MacMillan Company, 1906.

More Information

Pluto, Doorway to the Stars (1962)

27 July 2015

Rocket Belts and Rocket Chairs: Lunar Flying Units

This poor Lunar Flying Unit pilot forgot his PLSS backpack. Image credit: Bell Aerosystems/NASA
Apollo lunar surface exploration was a race against time. The Lunar Module (LM) lander carried only so much cooling water for its avionics, only so much breathing oxygen and carbon dioxide-absorbing lithium hydroxide for its crew, and could coax only so much electricity from its batteries. The Portable Life Support System (PLSS) backpack each Apollo astronaut carried while outside the LM could be recharged, but could contain only so much breathing air and cooling water at one time.

The longest Apollo lunar surface stay and longest period astronauts spent in their space suits on the lunar surface occurred during the advanced J-class Apollo 17 mission (7-19 December 1972), the last manned Moon voyage. During the second of three traverses they conducted during their three-day, three-hour visit to the Taurus-Littrow landing site, astronauts Eugene Cernan and Harrison Schmitt remained outside their LM, the Challenger, for seven hours and 37 minutes.

Operational constraints and conservative mission rules further limited what Apollo Moonwalkers could do with the limited resources at their command. For example, during their travels on board the Lunar Roving Vehicle (LRV) — a four-wheeled electric car — Apollo astronauts could not stray beyond a "walk-back limit." As the term implies, this was the distance beyond which they could not return on foot to the LM before they expended the life support consumables in their PLSS backpacks.

The walk-back limit meant that Apollo lunar surface crews drove to their planned greatest distance from the safe haven of the LM at the start of each LRV traverse, then worked their way back to the LM through a series of pre-planned traverse stops. As they drew nearer to their base camp, the quantity of expendables available in their PLSS backpacks decreased, but then so did the distance they would need to hike if the LRV broke down.

The limited endurance of the Apollo LM and PLSS, combined with the walk-back limit, helped to dictate the list of landing sites Apollo astronauts could explore. During the mid-1960s, proposed Apollo landing sites with scientifically interesting surface features spaced too far apart for "early Apollo" exploration were transferred to lists of candidate targets for more advanced follow-on expeditions. These expeditions would, it was assumed, be carried out in the mid-to-late 1970s within the Apollo Applications Program (AAP).

On 31 July 1967, four years to the day before Apollo 15 (26 July-7 August 1971), the first J-class mission, touched down on the Moon with the first LRV on board, lunar scientists had gathered in Santa Cruz, California, "to arrive at a scientific consensus as to what the future lunar manned and unmanned exploration should be." Soon after their two-week conference, they released recommendations. In their hefty 398-page report, they declared that
[t]he most important recommendation of the conference relates to lunar surface mobility. To increase the scientific return. . .after the first few Apollo landings, the most important need is for increased operating range on the Moon. On the early Apollo missions it is expected that an astronaut will have an operating radius on foot of approximately 500 meters. It is imperative that this radius be increased to more than 10 kilometers as soon as possible.
With this in mind, participants in the Santa Cruz conference recommended "that a Lunar Flying Unit [LFU] be developed immediately to be used in AAP and, if possible, on late Apollo flights to increase the astronaut's mobility range." The workshop participants expected that the LFU would have a range of from five to 10 kilometers, which they stated was "a considerable improvement over the present capability, but not nearly enough."

As space scientists met in Santa Cruz, Congress in Washington debated deep cuts in NASA programs. In part as "punishment" for the Apollo 1 fire (27 January 1967), on 16 August 1967 AAP's Fiscal Year (FY) 1968 budget was slashed from the $455 million President Lyndon Baines Johnson had requested in January to just $122 million. The President, faced with an unpopular war in Indochina, unrest in U.S. cities, and an increasing budget deficit, begrudgingly acquiesced to the cuts.

In his preface to the Santa Cruz conference report, NASA Associate Administrator for Space Science Homer Newell explained that its recommendations had been "prepared under guidelines. . .developed prior to the 1968 Appropriations Hearings by the Congress." Because of this, they were "optimistic in outlook" and "exceed[ed] the capability of the agency to execute." Newell stressed more than once that the report was "NOT an approved NASA program for lunar exploration."

The ambitious Santa Cruz blueprint for lunar exploration died as it was born, yet the LFU concept it touted remained alive. In January 1969, NASA's Manned Spacecraft Center (MSC) in Houston, Texas, issued a pair of seven-month LFU study contracts. In June 1969 — a month before Apollo 11 (16-24 July 1969) carried out the first manned Moon landing — the two competing contractors, Bell Aerosystems (BA) and North American Rockwell (NAR), presented their final briefings to MSC and NASA Headquarters officials.

A Bell test pilot prepares to demonstrate the "rocket belt" at Hopi Buttes, Arizona, in 1966. Image credit: U.S. Geological Survey
BA had studied a "rocket belt" — in reality, a rocket backpack — under contract to the U.S. Army in the late 1950s. The rocket belt used a catalyst bed to decompose hydrogen peroxide into high-temperature steam which it vented through a pair of exhaust nozzles to generate thrust. In 1966, the company demonstrated the rocket belt for U.S. Geological Survey (USGS) lunar scientists among the rugged Hopi Buttes east of Flagstaff, Arizona. Eugene Shoemaker, founding chief of the USGS Branch of Astrogeology, witnessed the demonstration. The following year he co-chaired the Geology Working Group at Santa Cruz, from which emanated the conference's mobility and LFU recommendations.

The BA LFU (image at top of post) was a platform with splayed legs and small (7.5-inch-wide) footpads, not a backpack, but it applied many of the rocket belt's design principles. The astronaut would fly standing, stabilized as he flew by his hold on a pair of handlebar-type hand grips linked mechanically to twin side-mounted rocket nozzles. The grips were based on the Apollo LM hand-controller design. Though safety belts would restrict side-to-side motion, the astronaut would be able to flex his knees, allowing him to absorb the pressure of acceleration and the jolt of touchdown. The BA LFU's simple metal landing legs included no shock absorbers.

Front view of the BA LFU showing astronaut upper torso in flight positions. Image credit: Bell Aerosystems/NASA
BA envisioned that its LFUs would always travel to the Moon in pairs. The company proposed that one 235-pound LFU and Apollo astronaut should stand by at the LM, ready to mount a rescue, while the other LFU and astronaut flew to an exploration target from 10 to 15 miles away from the LM.

Until the midpoint of the LFU study, NASA had asked BA and NAR to design their LFUs to carry 370 pounds of payload. This would enable them to rescue a 370-pound space-suited astronaut stranded beyond the walk-back limit. At the mid-term briefing, NASA directed the contractors to redesign their LFUs so that they would carry at most 100 pounds of payload. BA noted that, if payload were indeed restricted to 100 pounds in the final LFU design, then the second LFU and astronaut could still serve a life-saving function: they could deliver water and oxygen to refill the grounded LFU pilot's PLSS as he hiked back to the LM.

In keeping with NASA ground rules for the study, BA designed its LFU to burn leftover propellants scavenged from the LM descent stage tanks. Grumman, the LM prime contractor, had estimated that from 300 to 1500 pounds of hypergolic (ignite-on-contact) propellants would remain in the descent stage after the LM alighted on the Moon. The astronauts would use three 20-foot-long hoses — one for nitrogen tetroxide oxidizer, one for hydrazine fuel, and one for helium pressurant — to fill tanks in the BA LFUs. The hoses and helium would form part of a 90-pound LFU "support equipment" payload in the LM descent stage.

A BA LFU would carry up to 300 pounds of propellants in its twin tanks, bringing its total mass with a space-suited astronaut and a 100-pound payload to about 1000 pounds. Helium would drive the propellants into the twin throttleable rocket engines, which would each produce from 50 to 300 pounds of thrust. Thrust chamber temperature would peak at about 2200° Fahrenheit. BA expected that during each LFU sortie the amount of time spent in flight would total about 30 minutes. The BA LFU would fly at up to 100 feet per second (about 70 miles per hour).

The company assumed that NASA would fly a total of 10 Apollo lunar landing missions through the end of 1973. It envisioned a staged LFU flight program. An early hydrogen-peroxide-fueled LFU would draw on experience gained from the BA rocket belt, which, the company stated, had flown more than 3000 times on Earth. This would permit short-range test-flights on the Moon with minimum development risk beginning in 1971, during the fifth Apollo lunar landing mission.

During early hypergolic propellant flights - in BA's plan they would commence in mid-1972 - the LFU pilot would fly relatively short distances and climb no higher than 75 feet above the Moon. His flight path would conform to the lunar terrain; BA saw this as a means of avoiding any disorientation exotic lunar flight conditions might cause. Later missions might see high-flying, propellant-saving ballistic trajectories that would extend the LFU's range beyond 15 miles.

BA had other big plans for its LFU. It wrote that, with a special 500-pound propellant package attached, its LFU could climb to lunar orbit. During Apollo missions that lasted longer than the three days planned for J-class missions, its LFU might fly up to 30 times. It might also be flown by remote control or, with engine uprating, eventually propel astronauts through the skies of Mars.

NAR, the other 1969 LFU study contractor, was a relative newcomer to the world of rocket-powered personnel flyers, though it did have some experience. In 1964, the company — then known as North American Aviation (NAA) — had proposed a compact, foldable LFU somewhat similar to the BA design; that is, the astronaut would stand upright on a small platform and grip control handles. The 1964 NAA LFU also featured an "auxiliary payload/rescue tray" for transporting equipment or a recumbent astronaut. Spherical auxiliary propellant tanks could be added to boost range.

The 1964 North American Aviation LFU stressed compactness over range. Image credit: North American Aviation/NASA
Perhaps because it was starting with a relatively blank slate, NAR's 1969 LFU was very different from either its 1964 design or that of its 1969 competitor. NAR rejected LFU designs that had the astronaut standing, having found such a configuration to be unstable in flight and likely to tip during landings. It proposed instead a design which had the astronaut sit at the LFU's center of gravity, much like the recumbent astronaut in its 1964 design, in a seat tipped forward slightly to enhance visibility. He would fly strapped in with his feet on a foot rest that would hinge out of the way to allow easy access to the seat. To attenuate landing shocks, the NAR LFU would rely on shock absorbers in its landing legs.

The NAR LFU would use a cross-shaped cluster of four throttleable rocket engines, each with a maximum thrust of 105 pounds, centered directly under the astronaut. This would, the company argued, offer enhanced in-flight stability as well as redundancy in the event that a single engine failed. The BA design was not flyable if one engine failed; if the NAR LFU lost an engine, the pilot would shut off its opposite number to maintain stability and fly directly back to the LM using the two remaining engines.

Engine redundancy, a seat, and shock absorbers contributed to the NAR LFU's greater mass. The company estimated that it would total 304 pounds without propellants and about 1075 pounds loaded with a space-suited astronaut, a 100-pound payload, and 300 pounds of propellants scavenged from the LM.

NAR's choice of engine position added to its LFU's operational complexity. The low-mounted engines would tend to blast debris from the lunar surface in all directions during LFU landing and takeoff. Dust and rocks thrown out from the LFU might damage the LM, the astronaut's suit and PLSS, or the LFU itself. Because of this, the NAR LFU would take off and land no nearer than 40 feet from the LM. As added assurance against damage, it would take off from and land on a fabric launch pad/landing target laid out on the lunar surface.

Unpacking the NAR LFU from the side of the Apollo Lunar Module. At right is a discarded "thermal cover" for protecting the LFU during flight to the Moon. Image credit: North American Rockwell/NASA

An astronaut drags the NAR LFU to its fabric launch pad/landing target. Note hoses for pumping residual LM propellants into the LFU's tanks after it is positioned on the pad/target. Image credit: North American Rockwell/NASA
Boarding the NAR LFU would necessarily have been more difficult than boarding the BA LFU. Though NAR's illustrations show preparing its LFU for flight to be a one-man job, it probably would have needed both astronauts. Image credit: North American Rockwell/NASA
Following deployment from a compartment in the LM's side, the astronauts would drag the NAR LFU to the center of the fabric target, then use 40-foot hoses to fill its twin modified 20-inch-diameter Gemini spacecraft propellant tanks with scavenged LM propellants. NAR estimated that, on average, it could rely on the LM to contain 805 pounds of left-over propellants; that is, enough to fill its LFU's tanks nearly three times. Helium from an Apollo reaction control system tank roughly the size of a basketball mounted atop one of the two Gemini propellant tanks would push the hypergolic propellants into the four engines.

After loading the LFU's two payload racks with equipment, an astronaut would back into the LFU seat, position the swing-arm-mounted control panel and the foot-rest, and fasten his seat belt and shoulder straps. After a pair of half-mile-long, 200-foot-high test hops that would familiarize the astronaut with LFU flight characteristics under lunar conditions, he would fly at an altitude of up to 2000 feet to a science target up to 4.6 nautical miles from the LM.

That distance was, of course, much less than the 10-to-15-mile operational radius BA promised for its LFU; this was, however, just as well, since NAR expected to fly only one LFU per Apollo mission. Because of this, its pilot would not be immune to the walk-back limit. The company calculated that adding 100 pounds of propellants would increase to 7.8 nautical miles the distance its LFU could fly; it also noted that the LFU could reach science sites high up on the slopes of mountains otherwise inaccessible to Apollo explorers.

The NAR LFU in flight. Note position of control panel (center right) and replaceable helium pressurant tank (upper left). Image credit: North American Rockwell/NASA
NAR LFU swing-arm-mounted control panel. Image credit: North American Rockwell/NASA
During sorties away from the LM, the LFU would land on unprepared lunar ground. This raised the specter of possible damage from engine-tossed debris. To avoid this, NAR proposed turning off the engines some unspecified distance above the surface. This would, the company explained, also decrease the likelihood of tipping; the LFU would land firmly on its four shock-absorbing legs, not slide or skip during touchdown. It acknowledged, however, that accurately judging height above the surface before switching off the engines might be problematic.

After completing work at his science target, the astronaut would unfold a fabric launch pad and drag the LFU onto it before igniting its engines for return to the LM. Between flights, the crew would refill the LFU's propellant tanks, but not the empty helium pressurant tank; they would instead replace it with a spare stored in the LM descent stage.

Though the NAR LFU would reappear briefly in a 1971 NAR lunar base study, the 1969 studies were the LFU concept's last hurrah. In May 1969, as the BA and NAR study teams completed their final reports, NASA Headquarters announced that the Marshall Space Flight Center (MSFC) in Huntsville, Alabama, would direct industry development of the Apollo LRV. MSFC issued a Request for Proposal in July 1969, about a month after NAR and BA engineers briefed MSC and NASA Headquarters officials on their LFU designs. On 28 October 1969, NASA formally opted for wheels over rocket belts by selecting Boeing as the prime contractor for the LRV.

In the images below, a pair of astronauts release the tightly folded LRV from a compartment built into the side of the LM. They pull lanyards in sequence to unfold and lower it; then, after the LRV rests on four wheels on the dusty Moon, they unfold seats and other appendages, such as antennas, by hand. Fully deployed, the LRV measured 10 feet long and 7.5 feet wide. Although its mass was just 463 pounds, it could carry a payload (including two space-suited astronauts) of about 1080 pounds on the Moon.

During Apollo 15, astronauts David Scott and James Irwin drove their LRV a straight-line distance of five kilometers from their LM, the Falcon. Apollo 16 (16-27 April 1972) saw astronauts John Young and Charles Duke drive 4.5 kilometers from the LM Orion. For Apollo 17, the walk-back limit rule was relaxed slightly, so Cernan and Schmitt were able to reach a point 7.6 kilometers from Challenger.

The three LRVs now rest on the Moon where their Apollo astronaut drivers parked them. In a program chock-full of remarkable machines, the LRVs stand out from the rest. Had they not extended the exploration range of the Apollo 15, 16, and 17 lunar surface crews, we would know far less about the Moon than we do today.

Had the LFU flown, however, it seems likely that astronauts could have ranged widely over landing sites more complex and extensive than any Apollo explored. After an Earth-Moon voyage of a quarter-million miles, the LFU could have added a crucial few miles to surface traverses and enabled astronauts to soar up mountainsides and rugged crater rims. What then might we have discovered?

Unpacking the Apollo Lunar Roving Vehicle, steps 1 through 4. Deploying the rover is a two-man task. Image credit: NASA
Unpacking the Apollo Lunar Roving Vehicle, steps 5 through 8. In the bottom right image, astronauts unfold seats and the rover's small control console. Image credit: NASA

"Lunar Surface Exploration Gear Analyzed," Aviation Week & Space Technology, 16 November 1964, pp. 69-71

One Man-Lunar Flying Vehicle Study Contract: Summary Briefing, Space Division, North American Rockwell, July 1969

Study of One Man Lunar Flying Vehicle: Summary Report, Report No. 7335-950012, Bell Aerosystems Company, July 1969

1967 Summer Study of Lunar Science and Exploration, NASA SP-157, NASA Headquarters Office of Technology Utilization, 1967

More Information

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

Dreaming a Different Apollo: Part One

Earth-Approaching Asteroids as Targets for Exploration (1978)

24 July 2015

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 the One-Way Space Man landing site. A rover would also place a radio homing beacon at the site to guide the One-Way Space Man's 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 One-Way Space Man hardware. 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 far 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’s), 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 suit with the joint flexibility of a nylon soft suit that would permit only 0.002 penetrations per four-hour moonwalk.

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, 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 its floor parallel with the lunar surface, and remove its conical nose cone. 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 with the Stars-and-Stripes in one of his suit pockets.

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 manned 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 impatient 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 Krauss's 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 Krauss's proposal illustrated "the decline of moral reasoning."


"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

20 July 2015

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 Garriot) 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 gradually 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.


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)

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

A Forgotten Rocket: The Saturn IB

18 July 2015

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 "Related Posts" 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 moonbase 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 manned 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, thereby 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's surface. They estimated that, lacking adequate prior knowledge of Mars, the first manned 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 manned 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. 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 up 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 astronauts' main job would be to ensure that the probes remained functional until they reached Mars or Venus. The crew 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 repressurized 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 crew's water supply stored between its inner and outer walls. Two 500-pound water reclamation systems (main and spare) would recycle cabin air moisture, wash water, and urine. 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 attach 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's 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 Mars's 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's surface moving at about 11 kps relative to the planet, then would retreat from Mars's 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.


"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