Mars Polar Ice Sample Return (1976-1978)

This oblique view of the southern polar ice cap of Mars (bottom) includes the entire permanent cap and a small portion of the adjoining temporary cap. Much of the southern hemisphere is in view; for example, the large Hellas impact basin is visible at center left. At its fullest extent in southern hemisphere midwinter, the seasonal cap expands to touch the southern edge of Hellas. Image credit: NASA.

Mars, like its neighbor Earth, has ice caps at its north and south poles. On both worlds, the polar caps are dynamic; for example, they expand and contract with the passage of the seasons. On Earth, both the permanent and seasonal polar caps are made up entirely of water ice; on Mars, which is generally colder, temperatures fall low enough that carbon dioxide condenses out of the atmosphere at the winter pole, depositing a frost layer about a meter thick on the permanent water ice polar cap and surrounding terrain. 

The three-kilometer-thick permanent caps cover a little more than one percent of the martian surface. In northern hemisphere midwinter, the seasonal carbon dioxide cap expands to about 60° north latitude. Roughly 13 Earth months later, in southern midwinter, carbon dioxide ice covers the cratered landscape to about 60° south latitude.

Confirmation that the permanent polar caps are made up mainly of water ice did not come easily. The polar caps were first glimpsed using crude telescopes during the 17th century, and were widely believed to be made of water ice by the end of the 18th. In 1965, however, data from Mariner IV, the first spacecraft to fly past Mars, indicated that the permanent caps were made of frozen carbon dioxide, an interpretation the Mariner 6 and 7 flybys (1969) and the Mariner 9 orbiter (1971-1972) did little to contradict.

In the late 1970s, however, the twin Viking Orbiters revealed that the northern permanent cap is made of water ice. Confirmation that the southern permanent cap is also made of frozen water had to wait, however, until 2003, when data from the Mars Global Surveyor and Mars Odyssey orbiters became available.
Close-up of the southern permanent water ice cap of Mars in southern hemisphere summer. In winter, the entire image would be cloaked in red dust and carbon ice and frost. Image credit: NASA. 

In 1976-1977, before the composition of either of the permanent caps was known with certainty, a team of students in the Purdue University School of Aeronautics and Astronautics studied a Mars Polar Ice Sample Return (MPISR) mission. Its primary goal was to collect and return to Earth a 50-meter-long, five-millimeter-diameter ice core extracted from the planet's southern permanent cap.

The Purdue students assumed that the permanent ice caps of Mars are, as on Earth, built up of layers of snow or frost deposited annually. They anticipated that each layer would contain a sample of the dust and gases in the atmosphere at the time it was laid down, making it a record of atmospheric particulates and climate conditions. The range of materials captured in the core would enable multiple methods of age determination.

On Earth, ice cores from Greenland record lead smelting in the Roman Empire and vegetation changes in Ice Age Europe. A martian polar ice core, the students believed, might yield a planet-wide record of dust storms, asteroid impacts, volcanic eruptions, flowing surface water, and, quite possibly, the existence of microbial life. 
Section of an ice core collected from deep beneath the Greenland ice cap. Image credit: Greenland Ice Sheet Project.

As the Purdue students carried out their study, the twin Viking spacecraft were en route to Mars. Viking 1 left Cape Canaveral, Florida, on 20 August 1975, and Viking 2 lifted off about three weeks later (9 September 1975). The Vikings were two-part spacecraft — each comprised a Martin Marietta-built 571-kilogram Lander and a 2336-kilogram Orbiter built by the Jet Propulsion Laboratory (JPL).

Viking 1 fired its Orbiter-mounted rocket motor on 19 June 1976 to slow down so that the red planet's gravity could capture it into orbit. The Viking 1 Lander was scheduled to land on the American Bicentennial (4 July), but the landing was postponed after Viking Orbiter images of its prime and backup landing sites, which had been selected using Mariner 9 data, showed them to be too rough. The Viking 1 Lander separated from its Orbiter and performed the first successful Mars landing in Chryse Planitia on 20 July 1976.

Viking 2 reached Mars orbit on 7 August. Its pre-selected landing sites were also found to be too rugged, so touchdown in Utopia Planitia did not take place until 3 September 1976. 

Viking development cost close to a billion U.S. dollars, making it the most expensive automated exploration program of its time. For some planners — possibly unacquainted with the untimely end of the Apollo program — it seemed reasonable to assume that NASA would exploit Viking hardware to the fullest to cash in on its investment. JPL planners, for example, widely expected that a third Viking spacecraft — probably including a rover — would depart for Mars in 1979. For this reason, the Purdue students assumed that Viking hardware would continue to be manufactured into the 1980s and that their MPISR spacecraft could be derived from it. 
Schematic of Viking Orbiter with attached Viking Lander inside protective aeroshell. Image credit: NASA.
Schematic of a Viking Lander deployed on Mars. Image credit: NASA.

The MPISR mission would employ a Mars Orbit Rendezvous (MOR) mission plan equivalent to the Lunar Orbit Rendezvous plan used to carry out Apollo Moon landings. A 5652-kilogram MPISR Orbiter would carry to Mars a 946-kilogram Lander and a 490-kilogram Earth-Return Vehicle/Earth Orbit Vehicle (ERV/EOV). The MPISR Lander would in turn carry a 327-kilogram Ascent Vehicle (AV) for launching the polar ice sample to Mars orbit.

The need for a short-duration flight from Mars to Earth and for south pole conditions safe for landing dictated the MPISR mission's Earth departure date. A long flight back to Earth would place great demands on sample refrigeration equipment, so the Purdue students sought the shortest return opportunity they could find.

Data from the Viking Orbiters had shown the south pole ice cap to be too unstable for landing and sample collection in the spring and summer, when the temperature climbs too high for carbon dioxide to remain solid. At mid-winter, on the other hand, snow and frost accumulation might bury the MPISR Lander. The team proposed, therefore, that the Lander should set down in late summer, about 75 days before southern hemisphere autumnal equinox. 
Schematic of the MPISR spacecraft after Lander separation but before AV third stage arrival. The Earth Return Vehicle near the bottom of the image — which would carry within it the Earth Orbit Vehicle — would be based on the Pioneer Jupiter/Saturn bus design. Image credit: Purdue University.

The MPISR spacecraft would lift off from Cape Canaveral, Florida, on 29 April 1986, in the 15-foot-by-60-foot payload bay of a delta-winged, piloted Space Shuttle Orbiter. It would reach Earth orbit attached to an expendable Tug derived from the U.S. Air Force/NASA Centaur G' upper stage. The Purdue students calculated that the proposed Tug could launch up to 9000 kilograms out of Earth orbit toward Mars during the favorable 1986 Earth-Mars transfer opportunity.

On 16 November 1986, after a flight lasting nearly seven months, the MPISR Orbiter propulsion system would slow the spacecraft so that martian gravity could capture it into a polar orbit. It would then begin a 14-month orbital survey of the martian poles. 

The MPISR Orbiter would map the poles using Viking-type cameras, a Viking-type thermal mapper, and a new-design Radar Ice Sounder for determining ice depth. The sounder, which is not depicted in the MPISR Orbiter image above, would employ an 11.47-meter-diameter dish antenna that would unfold from the Orbiter soon after Mars orbit arrival. Scientists would use data from the Orbiter's instruments to select a safe and scientifically interesting south pole landing site for the MPISR Lander.

On 3 February 1988, the Lander would separate from the Orbiter, ignite solid-propellant rockets to slow down and drop from Mars orbit, then descend through the planet's thin atmosphere to the selected landing site. Because it would have nearly twice the mass of the Viking Lander from which it was derived, the MPISR Lander would lower on six parachutes and six terminal descent rocket engines (in each case, twice as many as Viking). The engines would be arranged in three clusters of two engines each.

Extra engines would complicate deployment of the Lander's most important science system, the 16.3-kilogram Ice Core Drill (ICD). Soon after touchdown, the MPISR Lander would reach out with its modified Viking sampler arm to detach one of the three descent engine clusters to clear the way for ICD deployment.

Sixty-seven times over the next 90 days, the ICD would collect a 75-centimeter-long ice core, raise it to the surface, and deposit it in an insulated 12-kilogram sample container. The final core would sample ice and dust layers hidden 50 meters below the surface. 

The students did not describe ICD operation in detail. No doubt the drilling and core acquisition process would face many challenges. The slender drill might, for example, encounter a patch of compressed crystallized ice and dust at depth and need to start again at a new place within its drill site, which would measure at most two or three square meters in area.

The MPISR Lander's south pole landing site would mean that it could not transmit radio signals directly to Earth. The MPISR Orbiter, for its part, would be able to keep Lander and Earth in view simultaneously for at most 25 minutes per day, sharply restricting radio relay time. This meant that the continuous drilling operation would need to take place autonomously.

Communication limitations, combined with slowly changing, generally unfavorable polar lighting conditions, led the Purdue students to replace the twin Viking scanning facsimile cameras with a simpler vidicon camera akin to that carried on the 1960s Surveyor lunar landers. The camera package would include three strobe lights. This would, they explained, permit the MPISR Lander to capture "snapshots" of the drill site and its novel frosty surroundings for transmission to the Orbiter.

Radioisotope Thermal Generators (RTGs) would power and warm MPISR Lander systems. The Lander's three footpads and underside would be insulated to prevent heat transmitted through its structure from melting the ice, helping to ensure that it would not sink from sight during the three-month sample-collection period. 
Near midwinter: the martian south polar ice cap near maximum extent as viewed from Earth orbit by the Hubble Space Telescope. Image credit: NASA. 

The Mars southern hemisphere autumnal equinox would occur on 17 April 1988. On 2 May 1988, with winter gradually settling in at the martian south pole, the first of the AV's three rocket stages would ignite to blast the ice core samples to Mars orbit. The AV third stage would provide refrigeration in the sample container to keep the ice core sections pristine.

The AV first stage and second stage would burn solid propellants. The liquid-propellant third stage would boost the sample container into a 2200-kilometer circular orbit about Mars, then would commence active maneuvers to perform a rendezvous with the MPISR Orbiter.

On 17 May 1988, the MPISR Orbiter would maneuver to a docking with the AV third stage. A docking collar on the ERV/EOV would dock with the third stage, then the sample container would automatically transfer to the ERV/EOV and the third stage would be cast off.

On 27 July 1988, the ERV/EOV would separate from the MPISR Orbiter and fire its engine to leave Mars orbit for Earth. To reduce the period of time during which the ice core would need refrigeration, the ERV/EOV would expend propellants to speed Earth return. A minimum-energy transfer in the 1988 Mars-Earth opportunity would last 122 days; the ERV/EOV's energetic Mars-departure burn would slash this to as little as 98 days. Arrival in Earth orbit would take place between 2 November and 14 November 1988.

Nearing Earth, the cylindrical 1.5-meter-long EOV would separate from the ERV and fire a solid-propellant rocket motor to slow down so that Earth's gravity could capture it into a 42,200-kilometer circular orbit. The ERV, meanwhile, would speed past Earth into solar orbit.

Discarding the ERV ahead of Earth-orbit capture would slash Earth-orbit insertion mass, dramatically reducing the quantity of propellants needed to place the Mars ice sample into Earth orbit. The Purdue team found that this approach would have mass-saving knock-on effects throughout the MPISR mission design, yielding a 6% reduction in total spacecraft mass at Earth launch.
 
The Purdue students described an EOV with enough refrigerant on board to passively cool the ice sample for up 28 days in Earth orbit, meaning that the it would need to be retrieved no later than 30 November, 1988 if Earth-orbit capture took place on 2 November and no later than 12 December if it occurred on 14 November. During the 28-day period, an automated Tug would climb from low-Earth orbit to retrieve the EOV.

Following retrieval, the Tug would convey the sample container to a waiting Shuttle Orbiter or to a laboratory on board an Earth-orbiting space station. Concerns about planetary protection would drive the selection. If risk of terrestrial contamination were judged to be acceptable, then the Shuttle Orbiter would deorbit and transport the sample container to Earth's surface. If, on the other hand, a more conservative approach seemed warranted, then the Mars sample would be subjected to initial examination on the Station.

Purdue's MPISR concept generated considerable interest and demonstrated surprising longevity for a student project. After a summary of the study appeared in the pages of the British Interplanetary Society publication Spaceflight, two of its authors (Staehle and Skinner) briefed JPL engineers on the concept. They discussed the possibilities of "life indigenous to polar ice" on Mars and the significance of detection of "alternate chemistries" of life.

They also adjusted some of the dates of critical MPISR mission events. Departure from Earth orbit, arrival in Mars orbit, and Mars landing would take place as in the original study, but Mars surface liftoff would take place about two weeks early (24 April 1988). Subsequent dates were adjusted accordingly: the MPISR Orbiter/ERV/EOV combination would dock with the third stage of the AV on 9 May 1988; the ERV/EOV would depart Mars orbit on 20 July 1988; the EOV would capture into Earth orbit on 8 November 1988; and 6 December 1988 was the latest sample retrieval date.

In January 1978, JPL new-hire Staehle pitched the scientific benefits of the MPISR plan at the Lunar and Planetary Institute in Houston, Texas. In his presentation, he called "reasonable" the automated acquisition of an ice core up to 200 meters long made up of segments up to 15 millimeters in diameter.

Sources

"Mars Polar Ice Sample Return Mission - 1," Robert L. Staehle, Spaceflight, November 1976, pp. 383-390

"Mars Polar Ice Sample Return Mission, Part 2," Robert L. Staehle, Sheryl A. Fine, Andrew Roberts, Carl R. Schulenburg, and David L. Skinner, Spaceflight, November 1977, pp. 399-409

"Mars Polar Ice Sample Return Mission, Part 3," Robert L. Staehle, Sheryl A. Fine, Andrew Roberts, Carl R. Schulenburg, and David L. Skinner, Spaceflight, December 1977, pp. 441-445

Mars Polar Ice Sample Return Mission, R. Staehle and D. Skinner, Jet Propulsion Laboratory, September-October 1977

Mars Polar Ice Sample Return Mission - Overview, R, Staehle, Jet Propulsion Laboratory, January 1978

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Chronology: Apollo X, Apollo Extension System, and Apollo Applications Program (AAP) 1.0

Repurposing Apollo: a modified Apollo Command and Service Module (CSM) (upper right) spacecraft moves through space docked with an Apollo Telescope Mount (ATM) derived from the Lunar Module (LM) lander. NASA's Apollo Applications Program (AAP) would have seen ATMs operating alone, with docked CSMs, and docked with AAP Orbital Workshops. Image credit: uncertain, but probably Grumman, makers of the LM.
This is the latest in a series of chronology posts in this blog. I usually write posts separately, with little regard for how they fit with others; these posts enable me to preserve that approach, which I find productive, while also linking separate posts to tell a larger story. This chronology post focuses on the Apollo Applications Program (AAP).

Begun formally in 1965, AAP grew from the Apollo Extension System, Apollo X, Manned Orbital Research Laboratory, and related proposals of the first half of the 1960s. Though backed by President Lyndon Baines Johnson, who saw it as a logical Apollo successor program, AAP suffered from repeated funding shortfalls and internal NASA squabbling.

The Apollo 1 fire (27 January 1967) took place within the main Apollo Program, but it was the final straw for AAP. The program was not formally ended, however, until the Skylab Program took over some of its Earth-orbital objectives in 1970.

AAP evolved into the three J-class Apollo missions (1971-1972) and four Skylab missions (1973-1974). Some have sought to portray the 1975 Apollo-Soyuz Test Project (ASTP) flight as an AAP successor; it is, however, better seen as a spinoff of Integrated Program Plan (IPP) space rescue planning. Nixon-era politics obscured ASTP's link with the IPP.

Apollo Extension System Flight Mission Assignment Plan (1965)

Relighting the FIRE: A 1966 Proposal for Piloted Interplanetary Mission Reentry Tests

Saturn-Apollo Applications: Combining Missions to Save Rockets, Spacecraft, and Money (1966)

"Without Hiatus": The Apollo Applications Program In June 1966

Apollo Applications Program: Lunar Module Relay Experiment Laboratory (1966)

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

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

To "G" Or Not To "G" (1968)

A Forgotten Rocket: The Saturn IB

Rocket Belts and Rocket Chairs: Lunar Flying Units

As originally conceived, AAP would have included many lunar-orbital and lunar-surface missions. Pictured here is an LM-derived, automatically landed LM Shelter designed to support two astronauts during a surface stay lasting 14 days (one lunar daylight period). The astronauts would have arrived separately in an LM-derived "Taxi" spacecraft. Image credit: Grumman.

Chronology: Asteroids, Comets, and Other Small Bodies of the Solar System 1.0

1 Ceres is complex and shows signs of ongoing surface activity. Image credit: NASA.
Chronology is essential to understanding history, yet in this blog I write posts about planned space missions more or less at random, with little regard for the order in which they occurred. Because of this, I occasionally feel moved to publish omnibus chronological posts like this one. So far, I've applied the chronological treatment to groups of posts on Space Stations, catastrophic failure during space missions, missions to Venus, and the Apollo-to-Shuttle Transition

This post's topic is tied to Asteroid Day 2020. It establishes chronology for posts related to some of the Sun-orbiting small bodies of the Solar System: specifically, asteroids, comets, dwarf planets, and Kuiper Belt Objects (KBOs). In this introductory essay, I'll start with the largest members of these four broad classes. 

1 Ceres is an asteroid and a dwarf planet, much as 134340 Pluto is a KBO and a dwarf planet. Ceres, discovered on the first day of the 19th century, is the queen of the Main Belt between Mars and Jupiter, much as Pluto is the king of the Kuiper Belt, which begins just inside the orbit of Neptune. Clyde Tombaugh discovered Pluto on 18 February 1930, at Lowell Observatory.

Ceres is the largest and most massive asteroid. Pluto remains the largest known KBO, though new discoveries could nudge it from the top spot. Pluto is not the most massive Solar System body known beyond Neptune; that honor presently belongs to 136199 Eris, another KBO and dwarf planet, which for a time was thought to be larger than Pluto.

Ceres was not immediately classified as an asteroid when it was discovered. It was widely considered to be a planet until the 1850s, by which time new data — the discovery of more than a dozen other bodies orbiting with it between Mars and Jupiter — had made clear to everyone that it should be classified as the first known example of a new class of small Solar System body. Ceres pro forma became the first asteroid.

In similar fashion, Pluto was widely considered to be a planet until the early 2000s. Beginning in 1992, space scientists discovered that Pluto has siblings. This confirmed the existence of the long-hypothesized Kuiper Belt. The parallel with Ceres was not lost on scientists. Pluto became pro forma the first KBO.

In science, classification is fundamentally about clear communication, which is essential for collaborative research. Classification is not treated as a frivolous matter by most scientists. Only after sufficient data has been obtained, exchanged, and debated is an initial classification changed. 

Since the 1990s, scientific debate has taken place among space scientists via digital communication, enabling far more participation than in the past. The formal in-person poll that reclassified Pluto as a dwarf planet on 24 August 2006 included only a small percentage of the tens of thousands of space scientists scattered around the world; the matter of Pluto's classification had, however, already been widely debated. 

In fact, the vote marked the end of a 76-year-long scientific process. When first discovered, Pluto was assumed to have a mass about six times that of Earth. It had to be that massive to have enough gravitational pull to account for observed deviations in the orbit of Neptune, which is another story (you can read about it among the posts linked below). Pluto did not, however, show a disk, which implied that it was very dark, very dense, or both. 

Pluto's orbit also crossed that of Neptune, which made it unique among the planets. Planet-crossing is common among small bodies such as asteroids, but who ever heard of an asteroid with six times the mass of Earth?

Discovery in 1978 of Charon, Pluto's largest moon, enabled scientists to calculate Pluto's mass accurately for the first time. It has just one-fifth of 1% of Earth's mass, or less than 20% of the mass of Earth's Moon. They then determined Pluto's diameter; it measures less than three times the diameter of Ceres, or about two-thirds the diameter of Earth's Moon. It is astonishing that Tombaugh was able to spot Pluto using the crude astronomical tools available in 1930.

This is as good a place as any to express my view that the term "dwarf planet" should be retired. It is not especially useful to scientists, does not enhance public understanding so is worse than useless for science education, and appears to be moribund. Though perhaps a dozen KBOs discovered since 2006 appear to qualify for the label, none have been added to the initial list of five (in addition to the three I have already mentioned, they include Haumea and Makemake).

Asteroid exploration has advanced rapidly since the 1990s, in part because missions bound for other worlds often can find one or more asteroids to visit along their flight path. Galileo, bound for Jupiter orbit, became the first spacecraft to fly past an asteroid, 951 Gaspra, on 29 October 1991. Two years later, it flew past 243 Ida, in the process imaging Dactyl, the first asteroid moon to be found.

Dedicated asteroid missions began in February 1999 with a bit of a flub; the NEAR Shoemaker spacecraft suffered a computer glitch and missed its first opportunity to enter orbit about the near-Earth asteroid 433 Eros. A year later, NEAR Shoemaker fired its engines to slow itself so that Eros could capture it, making it the first asteroid orbiter. On 12 February 2001, it ended its mission with a bonus rough landing on Eros — the first asteroid landing.

The Dawn spacecraft entered orbit around 4 Vesta in July 2011, thus becoming the first spacecraft to orbit a Main Belt asteroid. It moved on to Ceres, achieving orbit around the largest asteroid in March 2015. 

2015 was a hot year for small-body exploration. NASA's New Horizons spacecraft performed a Pluto fast flyby in July of that year, making it the first spacecraft to visit a KBO. New Horizons flew past a second, smaller KBO, 486958 Arrokoth, in January 2019. Arrokoth is the most distant Solar System body yet explored by a spacecraft.

Dedicated comet missions began in 1985-1986, when a four-spacecraft European-Japanese-Soviet "armada" explorer 1P/Halley, the most famous of the comets. The spacecraft did not try to match orbits with Halley, which revolves around the Sun "backwards" relative to the planets; instead, they carried out fast flybys. In March 1986, Europe's Giotto spacecraft raced past Halley's dark nucleus at a relative velocity of 68 kilometers per second.

Europe's Rosetta spacecraft orbited 67P/Churyumov-Gerasimenko from August 2014 to September 2016. It was the first comet orbiter. Rosetta's time-at-target bracketed the comet's closest approach to the Sun, enabling unprecedented close-up observations of activity triggered by solar heating. Rosetta released the Philae lander on 12 November 2015; though it did not land properly, Philae returned images and other data from the surface for about three days.

An exciting new frontier in small body exploration is now opening. In October 2017, the first asteroid known to have originated outside the Solar System, 1I/'Oumuamua, was discovered. We know that it originated elsewhere in the Milky Way because it is moving too quickly for the Sun's gravity to do more than bend its course before it returns to interstellar space. The first interstellar comet, 2I/Borisov, was found in August 2019.

These new discoveries have inspired proposals for intercept missions. None has so far advanced to the point of serious consideration. Both bodies will, however, remain within range of expected human spaceflight technology for a few decades at least, and the list of known interstellar visitors seems likely to grow, providing new candidate star-roving small bodies for exploration.

The links below lead to posts related to small Solar System bodies dated from 1962 through 2005. In addition, three posts not firmly linked to specific years are included at the bottom of the list.

Pluto, Doorway to the Stars (1962)

To Mars by Way of Eros (1966)

Missions to Comet d'Arrest and Asteroid Eros in the 1970s (1966)

MIT Saves the World: Project Icarus (1967)

Things to Do During a Venus-Mars-Venus Piloted Flyby Mission (1967)

Think Big: A 1970 Flight Schedule for NASA's 1969 Integrated Program Plan

Multiple Asteroid Flyby Missions (1971)

Cometary Explorer (1973)

A 1974 Plan for the Slow Flyby of Comet Encke

Earth-Approaching Asteroids as Targets for Exploration (1978)

"A Vision of the Future": Military Uses of the Moon and Asteroids (1983)

Visions of Spaceflight, c. 2001 (1984)

Catching Some Comet Dust: Giotto II (1985)

New Horizons II (2004-2005)

The Challenge of the Planets, Part Two: High Energy

The Challenge of the Planets, Part Three: Gravity

Pluto: An Alternate History

"Wobble Angle": Characteristics of 11 Apollo-derived Artificial-Gravity Space Station Designs (1963)

"Zero-G and I feel fine" — astronaut John Glenn, the first American to reach Earth orbit, during his five-hour flight on board Mercury-Atlas 6 spacecraft Friendship 7, 20 February 1962. Image credit: NASA.
In early May 1963, Robert Mason and William Ferguson, engineers at the NASA Manned Spacecraft Center (MSC) in Houston, Texas, completed a study of 11 artificial-gravity Earth-orbital laboratory designs. Some might have argued that NASA engineers had better things to do. After all, for two years the space agency's main goal had been to land a man on the Moon and return him safely to the Earth before the Soviet Union did, and the U.S. program still lagged behind its Soviet counterpart.

When the MSC engineers completed their study, the U.S. record for weightless space endurance was held by Wally Schirra, the third American to reach Earth orbit. During the Mercury-Atlas 8 mission (3 October 1962), he racked up a little less than nine hours of weightless experience. About a week after Mason and Ferguson completed their study, Gordon Cooper would set a new record by orbiting the Earth for about 34 hours during the Mercury-Atlas 9 mission (15-16 May 1963).

The world record for weightless space endurance at the time was, however, held by cosmonaut Andriyan Nikolayev, whose Vostok 3 spacecraft lifted off from Baikonur Cosmodrome on 11 August 1962. He orbited the Earth 64 times in 3 days, 22 hours, and 28 minutes, and landed on 15 August 1962. Apart from assurances that Nikolayev was in good health, the Soviet Union shared little information about his physical condition during or after his flight.

Lack of data on human responses to continuous weightlessness goes a long way toward explaining why NASA continued to study Earth-orbiting laboratories two years after President John F. Kennedy made the Moon a major U.S. goal on 25 May 1961. It seemed prudent to some to retain the option to launch a laboratory for studies of human health in weightlessness at least until astronauts could live in space for a period of time equal to the duration of an Apollo lunar landing mission.

Lack of data also explains why Mason and Ferguson studied artificial-gravity laboratory designs. If it were found that humans could not withstand weightlessness for long periods, then it would become necessary to establish a lab in space where the human health effects and engineering requirements of spin-induced acceleration — which is what "artificial gravity" is — could be examined.

There were also policy reasons for studying Earth-orbital laboratories. Before President Kennedy put NASA on course for the Moon, an Earth-orbiting lab had been central to the agency's plans for the 1960s. Some engineers believed that the laboratory should have remained NASA's first priority after Project Mercury, and they looked for opportunities to turn back the clock.

By the end of 1962, the probable cost of the lunar program had become increasingly clear. Grumbling had begun in Congress, placing pressure on Kennedy, who in turn placed pressure on NASA brass to contain space program costs. It seemed possible that the Apollo lunar goal might be found wanting by either Kennedy or, if he lost his bid for reelection in November 1964, by his successor. If so, the reasoning went, NASA might do well to have on hand a plan for an Apollo-derived Earth-orbiting laboratory as a cheap replacement for the lunar program.

In all but one of their 11 designs, Mason and Ferguson had the laboratory and crew reach orbit together; the astronauts would ride in a modified Apollo Command and Service Module (CSM) spacecraft atop the lab's drum-shaped Mission Module (MM). CSM modifications included a much-shortened Service Module (SM) with only enough propulsion, power, and life-support capability for the trip to the lab's 300-mile-high operational orbit and return to Earth.

Mason and Ferguson focused their study on the extent of the shift in the laboratory spin axis that astronaut movement parallel to the spin axis would produce. They called that shift the "wobble angle."

This illustration from Mason and Ferguson's paper depicts the "wobble angle." The line marked "Z" corresponds to the spin axis, which passes through the center of gravity of the orbiting laboratory. The Z at the top would, if the laboratory's spin remained entirely stable, always point directly at the Sun. Astronaut movement parallel to the Z line would, however, cause the spin axis to shift along the curving line labeled "Spin-axis trace." In this design, which corresponds to Laboratory Design 1 below, astronauts would need to contend with a wobble angle of up to 43°. Mason and Ferguson likened this motion to the "rolling of a ship."
The MSC engineers assumed that the orbiting laboratory MM and other structure, habitation and science equipment, and the modified CSM would together weigh about 15 tons. Of that, five tons were allotted to the CSM. All of their designs retained the Saturn IB rocket second stage, the S-IVB, for use as a counterweight. With its liquid hydrogen/liquid oxygen propellants spent, the S-IVB stage would weigh 10 tons.

Mason and Ferguson set the spin rate at a maximum of four rotations per minute. At that rate, and at a distance of 40 feet from the spin axis, the acceleration an astronaut would feel would vary by 15% between their feet and their head, with maximum acceleration being felt at their feet, farthest from the spin axis. Maximum acceleration would be limited to one Earth gravity; minimum acceleration would not fall below one lunar gravity (0.2 Earth gravities).

The 11 images that follow each include two views. The laboratory launch configuration is on the left and orbital configuration is on the right. In all but two of the images, the Z axis/spin axis points at the viewer in both views; for Laboratory Designs 8 and 9, the Z axis in the launch configuration view is turned 90° relative to the orbital configuration view.

Laboratory Design 1: the first Mason and Ferguson artificial-gravity lab design is the simplest, though it also has one of the greatest maximum wobble angles (about 43°). Crew couches in the CSM are at the minimum distance (40 feet) from the spin axis (Z), but the entire two-deck MM is too near the spin axis to avoid a variation in acceleration level between astronaut head and feet greater than 15%. Equipment weight is 12,496 pounds, structure weight is 7504 pounds, and pressurized volume is 2504 cubic feet. Thrusters located at the ends of the lab would expend 52.9 pounds of propellant to start it spinning at a rate of four rotations per minute.
Laboratory Design 2:  An alternate method of solar array deployment improves stability (wobble angle slightly more than 9°) by increasing lab width and mass along the Y axis. Structure weight is 8235 pounds and equipment weight is 11,765 pounds. Pressurized volume is 2505 cubic feet. Unfortunately, no part of the CSM or MM is far enough from the spin axis to avoid a greater than 15% variation in acceleration level between astronaut head and feet. Thrusters expend 55.3 pounds of propellant to spin up the laboratory. 
Laboratory Design 3:  Equipment modules of unspecified function deploy along the Y axis; this helps to reduce maximum wobble angle to about 3.5°. Structure weight including the equipment modules is 12,492 pounds. Equipment weight — 7508 pounds — is the least of any of the designs. Pressurized volume is 2396 cubic feet. No part of the CSM or MM is far enough from the spin axis to avoid a greater than 15% variation in acceleration level between astronaut head and feetThrusters expend just 49.7 pounds of spin-up propellant. 
Laboratory Design 4: A tunnel between the CSM and the MM places the CSM crew couches 43.3 feet from the spin axis. Unfortunately, the maximum distance from the spin axis within the MM is just 18.3 feet. Placing the relatively massive CSM far from the spin axis and relatively narrow structure along the Y axis contribute to a wobble angle of nearly 44°. Structure weight is 8687 pounds and equipment weight is 11,313 pounds. Pressurized volume is 2396 cubic feet. Thrusters expend 50.7 pounds of propellant to spin up the laboratory. 
Laboratory Design 5: The tunnel linking the CSM and MM is extendable, increasing CSM crew couch distance from the spin axis to 52.9 feet. The wobble angle is identical to that of Design 4. Structure weight is 8290 pounds and equipment weight is 11,710 pounds. Pressurized volume is 2400 cubic feet. The MM entirely surrounds the spin axis; in theory, an astronaut at the spin axis would be weightless while the station spun around them. No part of the MM is far enough from the spin axis to avoid a greater than 15% variation in acceleration level between astronaut head and feet. Thrusters expend 65.7 pounds of propellant to spin up the laboratory. 
Laboratory Design 6: Both the CSM and the MM telescope away from the spin axis. The 45° maximum wobble angle is the greatest of the 11 designs. Structure weight is 7505 pounds and equipment weight is 11,765 pounds. Pressurized volume is just 1633 cubic feet, the least of any of the designs. About half the MM is far enough from the spin axis to avoid a greater than 15% variation in acceleration level between astronaut head and feet. Thrusters expend 68.3 pounds of propellant to spin up the lab. 
Laboratory Design 7 is similar to Design 6, but its modified solar array configuration increases its width and mass along the Y axis, reducing its maximum wobble angle to slightly less than 29°. Structure weight is 7869 pounds, equipment weight is 12,131 pounds, and pressurized volume is 1743 cubic feet. Thrusters expend 68.3 pounds of propellant to spin up the laboratory.
Laboratory Design 8 combines features of Designs 3 and 7 to achieve a wobble angle of slightly less than 2.5°. A new feature of this design is a docking porfor a visiting modified CSM at the spin axis (Z). In many artificial-gravity station designs, docking ports at the spin axis rotate spin "backwards" so that they appear to remain still, facilitating docking. Mason and Ferguson gave no indication that their design would include a counter-spun docking port, however. Structure weight is 12,169 pounds, equipment weight is only 7831 pounds, and pressurized volume — without a second CSM — is 2048 cubic feet. All of the CSM and nearly all of the MM are far enough from the spin axis to avoid a greater than 15% variation in acceleration level between astronaut head and feet. Thrusters expend 66.9 pounds of propellant to spin up this design. 
Laboratory Design 9 includes new structural elements: a "fork" and cables that permit the spent S-IVB stage to be pivoted 90° relative to its launch axis. This reduces the wobble angle to slightly less than 1° — the least of any of the 11 designs. Unfortunately, no part of the CSM or MM is far enough from the spin axis to avoid a greater than 15% variation in acceleration level between astronaut head and feet. Structure weight is 8306 pounds and equipment weight, 11,694 pounds. Pressurized volume is 3118 cubic feet. Thrusters expend 64 pounds of spin-up propellants.
Laboratory Design 10 employs a "rigid support" and cables to pivot the spent S-IVB stage 90° relative to its launch axis. Maximum wobble angle is 1°. The CSM crew couches and part of the MM are far enough from the spin axis to avoid a greater than 15% variation in acceleration level between astronaut head and feet. Structure weight is 8120 pounds and equipment weight is 11,880 pounds. Pressurized volume is 2400 cubic feet. Thrusters would expend 71.8 pounds of propellants to spin up this design.
Laboratory Design 11 includes no CSM in its launch configuration view because structure and equipment weight is too great. The large MM is extendible. The CSM is displayed in the orbital configuration view as it would appear after it launched separately and docked with the MM in orbit. The pivoted S-IVB stage and the solar panel arrangement help to compensate for the large MM, yielding a wobble angle only slightly greater than Design 9. Structure weight is 14,047 pounds and equipment weight is 15,953 pounds. Pressurized volume is by far the greatest of the 11 designs (3828 cubic feet), as is the amount of spin-up propellant required (116.1 pounds). Spin-up would take place after the CSM arrived. All parts of CSM and MM are far enough from the spin axis to avoid a greater than 15% variation in acceleration level between astronaut head and feet. 
Source

Project Apollo Conceptual Rotating Space Vehicle Designs Using Apollo Components for Simulation of Artificial Gravity, NASA Project Apollo Working Paper No. 1073, NASA Manned Spacecraft Center, 8 May 1963.

More Information

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

To "G" or Not to "G" (1968)

"A True Gateway": Robert Gilruth's June 1968 Space Station Presentation

A Forgotten Rocket: The Saturn IB

Mars Airplane (1978)

Wings over Mars: the JPL Mars airplane swoops past a martian mountain so that its camera, mounted inside a clear plastic bubble on its belly, can turn sideways to image layers on the mountain slopes. Image credit: Jeff Bateman.
In the 1970s, as U.S. piloted spaceflight retreated to low-Earth orbit, NASA planning for advanced robotic Mars exploration missions came into its own. New information on the martian environment from Mariner 9 and the twin Vikings fueled engineer imaginations.

Many concepts that became actual missions in the 1990s and 2000s first received detailed study in the 1970s. Planners also looked at concepts that have yet to yield NASA missions: Mars sample return, balloons and blimps, small lander networks, and gliders and powered fixed-wing aircraft.

Spacecraft and space mission design and development decisions are complex and influenced by many factors. Scientific efficacy is but one factor considered when planning for a new exploration mission begins, and it is not always the most important one. Nevertheless, scientists are almost always involved at the outset even when they do not originate the mission concept under consideration. Often this involvement is achieved through the establishment of a supportive science working group for the proposed mission.

The Ad Hoc Mars Airplane Science Working Group met at the Jet Propulsion Laboratory (JPL) in Pasadena, California, on 8-9 May 1978, to review mission objectives and propose a possible Mars airplane instrument payload weighing between 40 and 100 kilograms. In its report, the Group noted that a Mars Airplane designed for landings and takeoffs would be able to collect samples in places other types of vehicles might find hard to reach. The plane might also be used to deploy small payloads at scattered locations by airdrop or landing.

Mostly, however, the Ad Hoc Science Working Group limited its deliberations to use of the plane as an aerial survey platform. The Group based its planning on a Mars airplane design derived from NASA Dryden Flight Research Center's "MiniSniffer" pilotless plane, which was designed to sample Earth's stratosphere.

The 300-kilogram airplane would arrive at Mars folded in an lozenge-shaped Viking-type aeroshell. After aeroshell parachute deployment and heat shield separation, it would spread its hinged wings to their full 21-meter span and detach from the parachute and aeroshell in mid-air.

Conceptual Mars airplane design. Image credit: Jeff Bateman.
Normally, the plane would cruise one kilometer above the martian surface, though it would be capable of flying as high as 7.5 kilometers. The 4.5-meter-diameter propeller at the front of its 6.35-meter-long fuselage would pull it through the thin (less than 1% of Earth atmosphere density) martian atmosphere at a speed of between 216 and 324 kilometers per hour.

Mars airplane endurance would depend on the weight of its payload and the choice of power plant. A plane with a 13-kilogram, 15-horsepower hydrazine-fueled piston motor, 187 kilograms of hydrazine fuel, and a 100-kilogram payload could, the Group estimated, fly up to 3000 kilometers in 7.5 hours, while one with a 20-kilogram electric motor, 180 kilograms of advanced lightweight batteries, and a 40-kilogram payload could fly up to 10,000 kilometers in 31 hours.

After it depleted its fuel or batteries, the plane would crash on Mars. The Group noted that the plane's short operational lifetime would dictate that its position after atmosphere entry be determined rapidly so that it could be directed quickly to its survey targets.

The Ad Hoc Group assumed that the Mars airplane would carry an inertial guidance system, radar and atmospheric-pressure altimeters, and terrain-following sensors (laser or radar) for navigation, and that these would serve double-duty as science instruments. The Group's selected science payload was intended to characterize possible landing sites for a follow-on Mars sample return mission and also to perform "topical" studies. The latter would address specific questions about Mars: for example, "Is Valles Marineris a rift valley?"

Visual imaging would be "fundamental" to the Mars airplane mission, so would receive top priority in the instrument suite. The Group determined that the airplane would be well-suited to serve as a camera platform because it would offer image resolution intermediate between orbiter and lander cameras and would obtain valuable "oblique" (from the side) images of the surface.

A Mars airplane might fly down a sinuous martian outflow channel, for example, collecting high-resolution images of layers exposed in its walls. The Mars airplane camera might be mounted on a movable platform inside a transparent dome on the plane's belly.

Other high-priority investigations would include wind speed, air pressure, and temperature measurements at various altitudes, infrared and gamma-ray spectroscopy and multispectral imaging to determine surface composition, and measurements of local magnetic fields. For magnetic field studies, the plane would fly a grid pattern over a selected region. The magnetometer, which might be mounted on a boom or a wingtip to minimize interference from airplane electrical sources, could also be used to seek out iron-rich surface materials and buried iron-rich volcanic structures.

The 1978 Mars airplane conceptual design effort fell victim to post-Viking disenchantment with Mars. Viking, which cost more than $1 billion in 1975 dollars, had been intended to find life, but its three biology experiments did not produce an unequivocally positive result. The Mars community did not at first recognize that it would need to restore support for Mars exploration before it proposed new Mars missions; that is, that Viking had made it more difficult to sell Mars exploration, not easier.

In addition, Space Shuttle development experienced setbacks. It was difficult to justify development of a vehicle for flying in the thin atmosphere of Mars when NASA had difficulty building one to fly in the thin upper atmosphere (and thicker lower atmosphere) of Earth.

Mars missions would resume, but not until 1992, when NASA launched a sophisticated orbiter called Mars Observer. The spacecraft was meant to inaugurate a new era of Mars exploration by providing a new overview of the planet. The loss of Mars Observer as it neared its destination on 25 September 1993 was a major setback; for a time, it appeared that recriminations over the very public failure might halt NASA Mars exploration.

The Curiosity rover landed in Gale Crater on 6 August 2012 and, after a checkout period, began its slow climb up the geologically complex layered slopes of Aeolus Mons (seen here in a color-corrected montage of images captured on 9 September 2015). At this writing, six-wheeled Curiosity has traveled about 22 kilometers. A Mars airplane could provide a perspective on Aeolus Mons, Valles Marineris, and other large features of Mars intermediate between that of a rover and that of an orbiter. Image credit: NASA.
Sources

Final Report of the Ad Hoc Mars Airplane Science Working Group, JPL Publication 78-89, NASA Jet Propulsion Laboratory, 1 November 1978.

Mars Airplane Presentation Material Presented at NASA Headquarters, JPL 760-198, Part II, Jet Propulsion Laboratory, 9 March 1978.

More Information

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

After Venus: Pioneer Mars Orbiter with Penetrators (1974)

Purple Pigeon: Mars Multi-Rover Mission (1977)

Prelude to Mars Sample Return: The Mars 1984 Mission (1977)

Making Propellants from Martian Air (1978)

To "G" Or Not to "G" (1968)

The quintessential space station: Wernher von Braun's revolving artificial-gravity station in Earth orbit. This classic 1952 painting by Chesley Bonestell, the Dean of Space Artists, includes near its hub a pill-shaped piloted space tug. In this view, the station might not be rotating; at least one of the two astronauts visible at center left is floating above its hull (perhaps they have just been tossed away by its spin). Though widely identified with von Braun, the spinning wheel station concept was first described in detail by Herman Poto─Źnik in 1928. Image credit: NASA.
Previously on this blog, I described the 1960s NASA push to make a large Earth-orbiting space station the "new Apollo" of the 1970s. I also discussed plans to exploit Apollo lunar program technology and techniques to conduct a low-cost post-Apollo piloted space program (the Apollo Applications Program, or AAP) that would include temporary space stations.

Both the proposed Space Station Program and AAP had looming over them a potentially crucial question: should NASA spin its future piloted spacecraft, in whole or in part, so that astronauts within could experience artificial gravity? During the longest piloted spaceflight of the era (Gemini VII, 4-18 December 1965), astronauts Frank Borman and James Lovell had orbited the Earth in weightlessness for nearly 14 days, clearing the way for Apollo lunar missions. Their flight encouraged AAP and station planners; it was widely recognized, however, that the meager biomedical results of a single two-week flight by two men in a cramped capsule could not be extrapolated to months-long stays on board a space station.

In a conversational memorandum dated 24 September 1968, E. Marion, an engineer with Bellcomm, NASA's Washington, DC-based planning contractor, examined whether space stations should be designed to provide artificial gravity or should assume that humans could adapt to weightlessness (which he called "abaria"). If the latter were true, then station complexity and cost might be greatly reduced.

Gemini 7 as viewed from Gemini 6, December 1965. Image credit: NASA.
Marion noted that the space medicine community tended to believe that astronauts could adapt to long-term abaria, but cautioned that this was "opinion, nothing more." "In other words," he explained, "it is possible that man can't physiologically adapt to long term abaria, but it is much more likely that he can."

He added that, even if sustained abaria were found to cause health problems, then spinning the entire station might not be necessary. The crew might get by with periodic sessions seated in a spinning centrifuge. Elastic bands in clothing could place limb and torso muscles under continuous tension and "lower body negative pressure boots" could give the heart a workout by pulling blood into the legs.

Marion wrote that artificial gravity might eliminate much astronaut training. Tools, furnishings, and equipment on board the artificial-gravity station — for example, "a plate of food" — could be identical to those used routinely on Earth. Training time reduction might, however, prove elusive; the artificial-gravity station would need to be "designed for abaric operation simply as a contingency" and its crew trained to use its backup abaric systems.

Marion speculated that space travelers might prefer abaria to artificial gravity. He wrote that astronauts — "a strikingly atypical population sample" — might, by virtue of their enthusiasm for new experiences, find that abaria would make "the long confinement of a space voyage" easier to stand. He suggested that, in the interest of astronaut behavioral health, missions might be planned to include both weightless and artificial-gravity periods.

The Bellcomm engineer wrote that astronauts performing work in abaria would probably be less "efficient" than those in artificial gravity — that "you can get more work out of an astronaut if you don't leave him weightless." Artificial gravity might thus enable "a smaller crew and a smaller station."

On the other hand, a major justification for the Space Station Program was the ability to perform experiments in weightlessness. Experiments might be designed to compensate for artificial gravity, Marion wrote, but at the cost of greater complexity and less efficiency. "It doesn't help to have an efficient astronaut running an inefficient experiment," he explained.

Experiments requiring abaria might be mounted in a central hub that would rotate against the station's spin direction to cancel out artificial gravity. Astronauts would enter the counter-rotating hub to operate the experiments. Marion noted, however, that the abaric hub might undercut "astronaut efficiency right when we need it the most — when he's working on the experiments."

Marion then offered three options for determining whether artificial gravity should be incorporated into the Space Station Program, each with "abaria OK" and "artificial-gravity required" alternatives, and provided cost estimates for all. He based these on AAP and Space Station Program schedules under consideration within NASA at the time he wrote his memorandum.

The schedule for AAP in September 1968 began with a mission on board a Workshop in Earth orbit in 1971. The AAP Workshop was called the "wet" Workshop because it would be launched with liquid propellants filling the volume the crew would inhabit in orbit.

AAP wet Workshop concept in 1967-1968. The docked Apollo Telescope Mount at upper left is based on the Apollo Lunar Module design. Image credit: NASA.
It would, in fact, be a modified S-IVB stage, the second stage of a two-stage Saturn IB rocket. The stage would include a long upper tank containing liquid hydrogen, a short lower tank for liquid oxygen, a J-2 rocket engine, and a special docking module bolted to the top of the liquid hydrogen tank. An Apollo Command and Service Module (CSM) spacecraft with a crew of three would ride into space atop the Saturn IB. The spacecraft would detach from the S-IVB second stage upon arrival in Earth orbit.

Controllers on the ground would then vent the S-IVB tanks and J-2 engine to clear them of residual propellants. The CSM would dock with the front (axial) port of the docking module, then its crew would fill the empty hydrogen tank with breathable air and move equipment and furnishings from the module into the tank to outfit it. They would live and work in abaria for 28 days, then would return to Earth.

A second CSM would reach the AAP Workshop at the end of 1971. The astronauts would reactivate it and live on board in abaria for 56 days. Soon after they returned to Earth, a third CSM, the last scheduled to visit the Workshop, would arrive bearing an Apollo Telescope Mount (ATM). The ATM would dock with a radial (side) port on the docking module and the CSM would dock with the axial port. The astronauts would use the ATM to study the Sun during their 56-day abaric mission.

The AAP plan included an option to launch a backup Workshop in mid-1972 if the 1971 Workshop failed. Alternately, the second Workshop might support a new series of missions if NASA received funding to expand AAP.

The Space Station Program artificial-gravity station design in Marion's September 1968 memorandum was barely described, but would probably have shared features with the two designs depicted in the NASA images above. The station at top would have reached Earth orbit atop a single Saturn V; the "million-pound" station at bottom would have required three Saturn V launches and orbital assembly. Both designs include a counter-reporting hub; an Apollo Command and Service Module (CSM) spacecraft is docked to the hub of the station at top.
NASA spacecraft development has generally followed a four-phase system, the details of which have varied considerably. Phase A, from which most proposed programs never emerge, encompasses preliminary analysis; at the time Marion wrote, the proposed Space Station Program was in Phase A. Phase B would see more detailed analysis and early design. During Phase C, detailed design and early manufacturing would take place. Phase D encompassed manufacturing and testing.

At the time Marion wrote, NASA planners anticipated that Space Station Program development Phase B might last six months in 1969. If so, then Phase C would last 18 months in 1970-1971, partially overlapping 42-month Phase D, which would begin in early 1971 and end in late 1974. The station would reach orbit in early 1975 and its first crew would arrive soon after.

The first of Marion's three artificial-gravity development options would assume that prolonged abaria would not pose a problem for station crews. AAP would not be used to confirm this assumption. The first crew would arrive on the station in mid-1975 for a prolonged stay in abaria. If they experienced adverse health effects, then a second crew might fly to confirm that these were caused by abaria.

If, based on their experience, it became clear that artificial gravity was necessary, NASA would halt the Space Station Program and spend two years designing, developing, and building a "G-kit" for attachment to a second station. Thus modified, the second station would reach orbit in early 1978.

Marion estimated that artificial-gravity development option 1 would cost just $700 million if the assumption that long-term abaria was acceptable turned out to be correct; this would make it the cheapest of all the alternatives. If artificial gravity were required, however, then delaying the program to modify the second station while keeping the NASA, contractor, researcher, and astronaut teams together would push total cost to $1.415 billion, making it the most expensive of all the alternatives.

Artificial-gravity development option 2 would see the Space Station Program postponed so that NASA could fly an abaric 120-day AAP mission using the backup Workshop in 1972-1973. Phase B would begin in late 1971, then Phase C would span 1972-1973. Toward the end of Phase C, station design would be finalized based on results of the long abaric AAP mission. Phase D would span from mid-1973 through the end of 1976. The station would reach orbit in 1977.

Marion estimated that artificial-gravity development option 2 would cost $900 million if abaria turned out to be acceptable. It would cost $1.015 billion if artificial gravity were required.

For artificial-gravity development option 3, the station would be built with part of its artificial-gravity hardware in place; specifically, it would include the counter-rotating hub as part of its basic structure. Phase A would begin in 1969, as in option 1, and NASA would launch the station in mid-1975.

At least one crew would then live on board in abaric conditions. If abaria were demonstrated to be acceptable, the Space Station Program could continue without artificial gravity (it might be added later as an experiment, if funds became available). If artificial gravity turned out to be necessary, then systems would be added to the orbiting station to complete its artificial-gravity configuration.

Though Marion did not say as much, it seems likely that artificial-gravity systems added to the station in late 1975-early 1976 would comprise a counterweight — probably a spent rocket stage — and cables or a truss for linking it to the station. The counterweight would be carefully positioned to place the counter-rotating hub at the station's spin center; this would ensure that it could provide an abaric environment for experiments. Astronauts would live on board the artificial-gravity station beginning in 1976.

Marion estimated that, if the Space Station Program continued without artificial gravity, then option 3 would cost $800 million. If artificial-gravity were required, then the cost would reach $915 million. He ended his memorandum by recommending that NASA choose option 3.

Source

"To 'G' or not to 'G'," Bellcomm Memorandum for File, E. D. Marion, Bellcomm, Inc., 24 September 1968.

More Information

Space Station Gemini (1962)

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

Apollo Extension System Flight Mission Assignment Plan (1965)

"Without Hiatus": The Apollo Applications Program in June 1966

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

"A True Gateway": Robert Gilruth's June 1968 Space Station Presentation

McDonnell Douglas Phase B Space Station (1970)

An Alternate Station/Shuttle Evolution: The Spirit of '76 (1970)