Begun in 1965, AAP grew from the Apollo Extension System and Apollo X 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 squabbling internal to NASA.
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
|1 Ceres is complex and shows signs of ongoing surface activity. Image credit: NASA.|
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 to science educators, 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
|"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.|
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."
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.
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.
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
|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.|
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.|
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.
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.
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)
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.|
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.|
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.
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.
"To 'G' or not to 'G'," Bellcomm Memorandum for File, E. D. Marion, Bellcomm, Inc., 24 September 1968.
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)
|Climbing toward reusability: liftoff of the Space Shuttle Orbiter Columbia at the start of mission STS-2 (12-15 November 1981). Image credit: NASA.|
When Columbia glided to a landing for the second time, the form the STS would eventually take was still poorly defined. It would remain so at least until the destruction of the Shuttle Orbiter Challenger (28 January 1986) at the start of the STS-51L, the 25th flight of the Shuttle Program. The loss of Challenger and her seven-member crew marked the end of the optimistic first phase of the Space Shuttle Program.
Before that, however, the STS seemed ripe for augmentation. It would, of course, include expendable rocket stages attached to satellites carried to low-Earth orbit (LEO) in the Shuttle Orbiter Payload Bay; these "upper stages" were meant mainly to boost payloads from LEO to geosynchronous orbit (GEO), but could also launch robotic spacecraft from LEO on interplanetary trajectories. In addition, the STS would include Spacelab, a European-built system of Payload Bay-mounted laboratory modules and scientific instrument pallets. Development of upper stages and Spacelab had commenced in the 1970s, shortly after Space Shuttle development began.
Many saw the stages and Spacelab as interim steps toward more complex and competent STS elements. The former, it was expected, would lead to a reusable Orbital Transfer Vehicle (OTV); the latter, to a Space Station assembled in LEO from Orbiter-launched components. The OTV and its "little brother," the Orbital Maneuvering Vehicle (OMV), were typically seen as auxiliary vehicles based at the Space Station.
NASA Johnson Space Center (JSC) in Houston, Texas, anticipated that the Space Station would support ambitious space construction projects; for example, large communications platforms in GEO. In 1979, inspired in part by its involvement in joint Department of Energy/NASA Solar Power Satellite studies, JSC studied a Space Station concept it called the Space Operations Center (SOC). After an initial flurry of planning activity, Shuttle delays put the SOC on the back burner; immediately after STS-1, however, JSC efforts to promote the assembly base in LEO kicked into high gear.
At the time, JSC was called the Manned Spacecraft Center (MSC). It was renamed in 1973 after the death of President Lyndon Baines Johnson. The LSC was renamed the Lunar and Planetary Science Conference (LPSC) in 1978.
Michael Duke was on hand when the Apollo 11 samples arrived at the LRL; he was Lunar Sample Principal Investigator for the mission. In July 1969, he had been working for the U.S. Geological Survey (USGS) Branch of Astrogeology for six years. In 1970, he left USGS to become Lunar Sample Curator at MSC, a post he held until 1977, when he became Chief of the JSC Planetary and Earth Sciences Division.
Shortly after STS-2, Duke and another geologist in his division, Wendell Mendell, became concerned that developing the SOC and other proposed STS elements might mean reduced funding for NASA science programs. Space science at NASA was already hurting; the new Administration of President Ronald Reagan had made deep cuts. Rather than oppose new STS elements, Duke and Mendell sought ways that the SOC, OTV, and other proposed hardware could advance scientific exploration. Specifically, they sought to make the case for a base on the Moon.
Their efforts in some ways paralleled those of lunar scientists at the dawn of the Apollo Program, when lunar science barely existed as a field of study. Much like those early pioneers, Duke and Mendell sought to find and bring together individuals and organizations to build a constituency. Initially, they found prospective lunar base allies through informal, low-profile contacts. By late 1982, however, it was time to go public.
This they did by organizing three public special sessions at the 14th LPSC, which was held at NASA JSC in March 1983. The lunar sessions were titled "Return to the Moon" and "Future Lunar Programs." The third session, "Prospects for Planetary Exploration," sought to tie their lunar base efforts to the interests of the broader Solar System exploration community.
In their introduction to the lunar special sessions abstract volume, Duke and Mendell explained that "very little vision is required to see the [STS] reaching to the Moon." They argued that "the lunar option requires decisions today — but not dramatic ones." They pitched a Fiscal Year (FY) 1985 start for the lunar base program, but took pains to stress that the lunar base would need little or no new dedicated funding before FY 1991 or FY 1992.
In fact, they expected that lunar capability would grow more or less naturally from the STS in the late 1990s, several years after the SOC, OTV, and OMV were in place to support GEO missions. The amount of energy required to put a satellite into GEO is, after all, very nearly the same as that needed to put a payload into low-lunar orbit (LLO).
The lunar special sessions abstract volume included 22 abstracts by more than 30 authors and co-authors. The abstracts covered topics ranging from philosophy, law, and economics to geology, physiology, and energy. Of particular interest was an abstract by Hubert Davis, Senior Vice President of Houston-based Eagle Engineering, Incorporated (EEI). In it, he proposed to extend the STS to the Moon. His aim: to make the STS more economical by mining, refining, and using as rocket propellant oxygen chemically locked in lunar dirt.
EEI had been established by retired NASA JSC engineers. Davis, a co-founder of the company, began his career as an aircraft maintenance engineer in the U.S. Air Force during the Korean War. Inspired by President John F. Kennedy's May 1961 call for a man on the Moon, he went to work for the MSC Power & Propulsion Division in March 1962. He oversaw the test program for Lunar Module 5; better known as Eagle, it bore Apollo 11 astronauts Neil Armstrong and Edwin "Buzz" Aldrin to the lunar surface on 20 July 1969.
As Apollo ended, Davis transferred to the MSC Special Projects Office, where he studied new STS elements — cheap solid-propellant STS upper stages and a Shuttle-derived heavy-lift launcher — as well as Solar Power Satellites manufactured from lunar materials. He took early retirement in 1978 after being made the JSC Engineering Directorate representative to the Space Shuttle Program Office; in a 2009 NASA JSC oral history interview, Davis explained that he had left the space agency at age 48 because he found the Shuttle oversight job to be boring.
The industry magazine Aviation Week & Space Technology made his presentation the centerpiece of its coverage of the LPSC lunar base special sessions. Two months following the special sessions Davis published an expanded version of his abstract and presentation as an EEI report called Lunar Oxygen Impact Upon STS Effectiveness.
Davis acknowledged that his study was incomplete and preliminary. He did not, for example, examine how his oxygen mining and refining facility would be established on the Moon. That the study was preliminary explained why it was incomplete; if it could not provide an early indication that lunar oxygen would enhance STS capabilities, Davis argued, then there would be little point in conducting a more detailed study of the concept.
To illustrate how lunar-produced liquid oxygen might enhance the STS, Davis used as an example STS-40, which was scheduled to place the Galileo spacecraft into LEO on 30 May 1986. Galileo would reach LEO attached to an expendable Centaur G' upper stage which, following release from the Orbiter payload bay, would launch it out of LEO on a direct trajectory to Jupiter.
The Galileo spacecraft was expected to weigh 2510 kilograms and the Centaur G' without propellants, 2650 kilograms. Support equipment for maintaining Galileo and Centaur G' in the payload bay would weigh 470 kilograms and 3640 kilograms, respectively. Filling the Centaur G' large tank with low-density liquid hydrogen fuel would add 3310 kilograms to STS-40's payload weight; filling the Centaur G' small tank with dense liquid oxygen oxidizer would increase payload weight by a whopping 16,570 kilograms. STS-40 payload weight thus came to 29,480 kilograms, with liquid oxygen making up 56% of the total.
The Shuttle Orbiter would carry a 660-kilogram tank containing 3310 kilograms of liquid hydrogen for fueling the OTV in LEO. The propellant dump in LEO near the SOC would provide the OTV with lunar liquid oxygen. Support equipment in the payload bay for the spacecraft and hydrogen tank would bring the total Shuttle payload weight to just 7280 kilograms, or about one quarter of the STS-40 total.
A chemical process called hydrogen reduction of ilmenite formed the basis of the lunar oxygen STS infrastructure. Ilmenite (chemical formula FeTiO3), a titanium ore, is a mineral common in the basaltic rocks, dirt, and dust that form the dark-hued lunar plains known as maria (Latin for "seas").
Davis focused on ilmenite rather than lunar polar ice — which can provide both hydrogen and oxygen — because in 1983 no one knew that water ice exists at the lunar poles. Though the lunar polar ice hypothesis was by then more than 20 years old, the first evidence that it might be correct would not be found until 1994, when Clementine became the first spacecraft to explore the Moon from lunar polar orbit.
Mining robots would continuously gather ilmenite-rich lunar dirt at a rate of 28 metric tons per hour and deliver it to a separation facility. The dirt would first be sieved to remove large dirt particles, clods, and rocks. The resulting fine-grained dirt and dust would then be heated and subjected to an electrostatic process that would separate the ilmenite at a rate of 2.27 metric tons per hour.
The ilmenite would be moved to the hydrogen-reduction unit, where it would be exposed to hydrogen gas at 700° Celsius (C) and 2.7 Earth atmospheres of pressure. The hydrogen would bind with and free the oxygen bonded to the iron. This would yield water vapor at a rate of 0.26 metric tons per hour, which would be cooled, condensed, and subjected to electrolysis, splitting it into oxygen and hydrogen.
The oxygen would be chilled until it condensed into dense liquid, then stored in spherical tanks. The hydrogen would be returned to the reduction unit for reuse and the powdery titanium oxide and iron left over from the reduction process — about 90% of the original mass of the lunar dirt — would be stacked out of the way for possible future use.
The facility would use a little more than six megawatts of electricity continuously; this might be reduced if waste heat from the refining process could be exploited effectively. Davis estimated that his mining and refining facility could produce 150 metric tons of liquid oxygen per month.
Normally, the ET would separate from the Orbiter as it neared orbital velocity, tumble and break up in the upper atmosphere, and fall into the Indian Ocean. When the ACC was attached, however, the Shuttle Orbiter would boost the ET/ACC combination to LEO and separate. A remote-controlled OMV based at the SOC would then detach the hydrogen tank from the ACC and move it to the propellant dump, where refrigeration and high-tech insulation would ensure that no hydrogen was lost to boil-off.
Zero liquid hydrogen boil-off was, Davis explained, critical to making his lunar oxygen STS infrastructure viable. He wrote that the Centaur G' stage was expected to lose about 3% of its liquid hydrogen to boil-off per day. A similar boil-off rate at any point in his lunar oxygen STS infrastructure would be "intolerable."
Davis assumed two types of modular OTVs, each of which could be tailored to carry out several types of missions. The OTVs, clusters of spherical propellant tanks linked by struts, would perform roundtrip missions between LEO and GEO and between LEO and an LLO SOC and propellant dump. The OTVs could operate with or without a pressurized module containing a crew.
The smaller OTV, which would burn 25 metric tons of liquid hydrogen and liquid oxygen during a voyage from LEO to LLO and back, would include a rigid aerobrake heat shield 18 meters wide. The heat shield, which would include thermal protection tiles akin to those attached to the Space Shuttle Orbiter, would enable the OTV to use atmospheric drag to capture into LEO with minimal propellant expenditure. The smaller OTV could transport nearly 43 metric tons of liquid hydrogen from the LEO propellant dump to its counterpart in LLO.
A single-stage Lunar Module lander based on the smaller OTV design would burn 28 metric tons of liquid hydrogen/liquid oxygen propellants to travel from LLO to the lunar surface and back. It would be capable of lifting 41 metric tons of liquid oxygen from the lunar surface to the LLO propellant dump.
Davis used Lunar Module landing gear as an example of how hardware in his lunar oxygen STS infrastructure would need to be optimized to reduce mass. The Apollo Lunar Module's four landing legs and foot pads accounted for 3.3% of its landed weight; the small OTV-based Lunar Module would exploit new materials and improved understanding of the lunar surface to reduce the figure to 2%.
One might be forgiven for asking why such a large lunar oxygen cargo was necessary; that is, why Davis did not propose transporting it to LEO using several smaller OTVs spaced out over time. He explained that minimum-energy opportunities for travel from the LLO propellant dump to LEO would occur less than once per month. They would be infrequent because the OTV could only depart LLO as its orbital plane coincided with that of the LEO propellant dump. To do otherwise would demand plane-change maneuvers that would contribute toward making the lunar oxygen STS infrastructure uneconomical.
During aerobraking, the OTV would pass through Earth's upper atmosphere at an altitude of between 50 and 100 kilometers so that atmospheric drag could reduce its speed. The OTV would then climb back into space toward an apogee (orbit high point) near SOC altitude (about 400 kilometers). At apogee, it would ignite its engines to raise its perigee (orbit low point) out of Earth's atmosphere. For the perigee-raise maneuver, Davis budgeted only enough propellants to change OTV speed by 100 meters per second. He suggested that, if further analysis showed this to be insufficient, then an SOC-based OMV might retrieve the OTV and lunar oxygen payload at apogee.
In neither the small OTV nor the large OTV case could aerobrake heat shield mass exceed 3.5% of OTV mass at the time of Earth atmosphere entry. Davis focused on heat shield mass reduction because other OTV systems were already optimized, OTV propellants had been trimmed to the bare minimum required, and reducing the liquid oxygen cargo would defeat the purpose of the exercise. He conceded that cutting aerobrake heat shield mass so dramatically might constitute a significant technical challenge; most OTV studies, he explained, had assumed that the heat shield would make up at least 10% of OTV mass at Earth atmosphere entry.
Davis used computer models to attempt to determine the Mass Payback Ratio (MPR) of his proposed lunar oxygen STS infrastructure. An MPR of 1 would mean that the mass of resources (mainly propellants) expended to exploit lunar oxygen would equal the mass of the lunar oxygen supplied to LEO. NASA would thus gain nothing from putting lunar oxygen to work in the STS. If, on the other hand, the mass of the lunar oxygen delivered to LEO exceeded the mass of the resources needed to exploit it, then more detailed study might be justified.
Davis cited a computer model that included 25 roundtrip OTV flights between LEO and LLO and 103 roundtrip Lunar Module flights between LLO and the lunar surface. He wrote that, in exchange for 983 metric tons of liquid hydrogen, hydrogen tanks, and OTV attitude-control system propellant dispatched to the Moon, 2414 metric tons of lunar liquid oxygen would arrive in the LEO. He judged that this quantity could support 90 OTV flights between LEO and GEO over a period of about five years.
This indicated a preliminary MPR of 2.45, which, Davis wrote, justified additional study. He anticipated, however, that it probably would not provide enough margin to maintain a positive MPR if the mass of hardware and propellants required to establish and maintain the lunar oxygen STS infrastructure were taken into consideration.
Davis did not provide weight estimates for the LEO propellant dump, the LLO propellant dump and LLO SOC, and the Lunar Modules. Neither did he estimate the weight of the Earth-launched liquid hydrogen and liquid oxygen propellants needed to initiate the lunar oxygen STS infrastructure, nor the weight of Earth-launched liquid hydrogen needed to fly resupply and crew rotation missions after lunar oxygen became available. He assumed that the OTVs and LEO SOC would be built for LEO and GEO operations even if NASA did not return to the Moon, so disregarded their weight in his model.
He did, however, provide a weight estimate for the lunar surface mining and refining facility. Mining robots, a habitat for housing 10 facility caretakers, refining equipment, storage tanks, a nuclear reactor for generating electricity, radiator panels, and other equipment would have a combined weight of 437 metric tons. Adding this to the 983 tons of hydrogen, tanks, and attitude-control propellant would lead to an MPR of only 1.7.
If, somehow, the MPR remained sufficiently favorable after more detailed technical studies yielded credible complete weight estimates, then complex economic analyses would follow. These would, Davis explained, be based on real-world dollars and would take into account societal factors such as "affordability."
Davis conceded that extending the STS to the Moon probably could not be justified solely on the basis of economics. He argued that lunar resources should nevertheless be developed. He cited a January 1982 Los Alamos National Laboratory (LANL) proposal for an international research laboratory on the Moon; it promised wide-ranging scientific, economic, political, and defense benefits. With a nod to the political language of the 1980s United States, Davis declared that the "vitality of Free World commerce and physical security would be greatly increased by the presence of. . .resources in space."
This post is the first in a series on lunar base planning in the 1980s centered on activities at NASA JSC. The next installment will examine NASA JSC's March 1984 in-house Lunar Surface Return study.
Space Operations Center presentation materials, NASA Johnson Space Center, 18 January 1982.
"NASA Conference to Highlight Return to the Moon," NASA News Release 83-007, Steve Nesbitt, no date (March 1983).
"Economic Benefits of Lunar Base Cited," E. Bulban, Aviation Week & Space Technology, 18 April 1983, pp. 132-133, 135-137.
Fourteenth Lunar and Planetary Science Conference Special Sessions Abstracts — Return to the Moon — March 16, 1983, Future Lunar Program — March 17, 1983, LPI Contribution 500, Lunar and Planetary Institute, 1983.
Lunar Oxygen Impact Upon STS Effectiveness, Report No. 8363, Hubert Davis, Eagle Engineering, Inc., May 1983.
"Return to the Moon," Andrew Chaikin, Sky & Telescope, June 1983, p. 493.
NASA Johnson Space Center Oral History Project Edited Oral History Transcript: Hubert P. Davis, 28 July 2009 (https://historycollection.jsc.nasa.gov/JSCHistoryPortal/history/oral_histories/DavisHP/DavisHP_7-28-09.htm — accessed 20 March 2020).
Harold Urey and the Moon (1961)
Apollo Science and Sites: The Sonett Report (1963)
Electricity from Space: The 1970s DOE/NASA Solar Power Satellite Studies
One Space Shuttle, Two Cargo Volumes: Martin Marietta's Aft Cargo Carrier (1982)
"A Vision of the Future": Military Uses of the Moon and Asteroids (1983)
Mission to the Mantle: Michael Duke's Moonrise (1999-2009)