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

Artist concept of Gilruth's 1968 "million-pound" artificial-gravity space station. Visible in this image are the habitat module (left), the hub with space-facing instruments on top and the hangar below, and, in the distance on the right, the S-II stage counterweight linked to the hub by a truss structure. Also visible are a small module maneuvering toward the hangar opening, a small piloted servicing vehicle approaching a free-flying 120-inch telescope, and a docked Gemini-derived crew rotation/logistics resupply vehicle. Image kindly provided by Carmine Rossi. Image credit: NASA.
Engineers often make the mistake of assuming that the course of spaceflight should be logical. Perhaps this is a quirk of the engineer personality (if such a thing exists). In any case, it is an unrealistic expectation. Human enterprise does not follow a logical path. History is about expediency and contingency, rarely do engineers see eye to eye, and, in any case, engineers do not comprise the majority of players in spaceflight decision-making.

In reading various proposals for NASA's post-Apollo future, one often has the sense that engineers wanted earnestly to take back the planning process and put the space agency on a logical track. They understood as well as most people the international and domestic political drivers behind Apollo, but viewed the Moon program as a step out of turn. They were proud of their Apollo accomplishments; as the lunar program's culmination approached, however, many seemed eager for the opportunity to leave the Moon alone in favor of a logical build-up of experience and capabilities back in low-Earth orbit.

At the cutting edge: Robert Gilruth in 1958. Image credit: NASA.
In few places is this as apparent as in Robert Gilruth's 25 June 1968 presentation to the Fourth International Symposium on Bioastronautics and the Exploration of Space. The Symposium took place in San Antonio, Texas, just a few hours' drive from the Houston-based NASA Manned Spacecraft Center (MSC), where Gilruth was director. Gilruth titled his presentation "Manned Space Stations: Gateway to Our Future in Space."

A native of Minnesota, Gilruth had gone to work at the Langley Memorial Aeronautical Laboratory in Hampton, Virginia, in 1937, directly out of graduate school. The National Advisory Committee for Aeronautics (NACA) had established Langley, its first research lab, in 1917, in part to ensure that the United States would not be left behind as the First World War drove aviation advancement in Europe.

Gilruth was no raging conservative when it came to technology. In the 1940s and 1950s he had worked at the cutting edge of high-speed aviation, where conventional aeronautics shaded into the arcane world of rockets and vehicles shaped to endure the pressures and temperatures of hypersonic speeds. He was instrumental in the creation of the rocketry range at Wallops Island, located across Chesapeake Bay from Langley near the tip of the Delmarva Peninsula. His talents were noticed early on; in 1952, before he turned 40, he became Langley's assistant director.

Gilruth's work took on new significance when the Soviet Union launched the first Sputnik satellite into Earth orbit on 4 October 1957. Though President Dwight Eisenhower downplayed the significance of the Sputniks, political pressure orchestrated in large part by Senate Majority Leader and Presidential aspirant Lyndon Baines Johnson forced his hand.

Within a year of Sputnik's launch, NACA became a part of the newly established NASA, Langley was renamed the NASA Langley Research Center (LaRC), and Gilruth became director of the Space Task Group (STG), an ad hoc organization within LaRC dedicated to human spaceflight. He remained director as the STG was elevated in 1962 to the status of a new NASA center, renamed the Manned Spacecraft Center, and transplanted to Vice President Johnson's home state of Texas.

The Symposium held six years later in San Antonio was a high-profile venue for putting across Gilruth's vision of the logical course of post-Apollo spaceflight. Arthur C. Clarke, screenwriter with Stanley Kubrick of the landmark film 2001: A Space Odyssey, was on hand to talk about exotic biology in the clouds of Jupiter. 2001 was released just three months before the Symposium. National Aeronautics and Space Council Executive Secretary Edward Welsh delivered the keynote address. In it, he called upon Congress to cease slashing NASA funding aimed at giving the agency a post-Apollo future.

Planning and building an Earth-orbiting space station would be challenging, Gilruth told his audience, in part because engineers had proposed so many different designs and justifications for space stations. In his presentation, he emphasized designs from MSC in-house and contractor studies. In fact, to prepare for his talk, Gilruth in April 1968 had tasked his engineers with designing a "million-pound station" based on 1966 MSC designs.

A 1966 NASA Manned Spacecraft Center station design with the same general layout as the 1968 "million-pound" design at the top of this post. At upper right is the habitat module. Telescoping arms link it to the zero-gravity hub, to which an Apollo Command and Service Module piloted spacecraft is docked. A spent Saturn V S-II second stage (left) serves as an artificial-gravity counterweight for the habitat. The solar-powered station would permanently point its solar arrays at the Sun as it orbited the Earth so that the spin axis would pass through the center of the cylindrical hub and through the long axis of the docked Apollo. Image credit: NASA.
Gilruth's 1968 station would need three Saturn V rocket launches to get started and two more to reach its full potential as a "location in space. . .developed to support men and equipment on a permanent basis. . .to take advantage of the economies of size, centralization, and permanency." He likened the space station to a base in Antarctica.

He declared that "development of the Saturn V. . .had provided one of the major building blocks for space station design." Gilruth then discussed how the Apollo Applications Program (AAP), NASA's only approved successor to Apollo, would compliment his station program. As its name implied, AAP would apply hardware developed for the Apollo Moon program, including the Saturn V rocket, to new missions on the Moon and in Earth orbit.

In early 1966, as AAP's NASA Headquarters office drew up a roster of more than 30 AAP Earth-orbital and lunar flights after minimal consultation with MSC and the other NASA centers, Gilruth had frank discussions with George Mueller, NASA Associate Administrator for Manned Space Flight, via letter, telephone, and telex. He argued that finding new uses for Apollo spacecraft and rockets was no basis for a post-Apollo space program. This ignored the fact that President Johnson had in 1965 called for a low-cost post-Apollo program based on Apollo technology.

NASA's piloted spaceflight organizations, Gilruth wrote, should aim instead for a "next big program" after Apollo. He mentioned the possibility of casting AAP as a precursor to a piloted Mars/Venus flyby, a class of piloted Apollo-derived mission under active investigation in 1964-1967. While engaged in discussions with Mueller, however, Gilruth initiated the 1966 in-house MSC station studies, thus revealing the form he believed the next big program should take.

In his San Antonio talk, Gilruth explained that AAP would explore the advantages of Earth-orbiting space stations "in a modest way." In particular, the AAP "wet launched" workshop, a modified Saturn IB S-IVB second stage, would enable NASA to study station habitability, biomedical effects of long spaceflights, and, through the addition of a separately launched solar observation module, the ability of humans to perform "a really complex scientific experiment" in Earth orbit.

Cutaway of the AAP Wet Workshop showing the Apollo Lunar Module-derived solar observatory (center left) attached to the docking adapter. The solar observatory would reach Earth orbit atop a Saturn IB rocket, the Saturn V's smaller cousin, which was intended as AAP's workhorse launcher. Image credit: NASA.
The AAP workshop would play the role for which it was intended — that of rocket stage — until it reached orbit. During ascent to orbit, a streamlined launch shroud on top of the stage would separate, revealing a docking module mounted atop the S-IVB stage liquid hydrogen fuel tank.

Ground controllers would command the orbiting stage to open vents in its liquid hydrogen and liquid oxygen tanks to enable residual propellants to escape. They would then close the vents and fill the hydrogen tank with a breathable air mixture from tanks in the docking module. Meanwhile, twin solar arrays would unfold from the workshop's sides. These would generate a total of about six kilowatts of electricity.

A three-man crew would then arrive in a Saturn IB-launched Apollo Command and Service Module (CSM) spacecraft. They would dock at the front of the docking adapter, enter it, and move furnishings stowed inside through a "manhole" hatch into the hydrogen tank. They would, for example, install a grid-work floor, fabric walls, and a galley module. After completing their orbital program, which might last weeks or months, the astronauts would return to Earth in the CSM. Subsequent crews would live on board the AAP workshop for successively longer periods.

Gilruth concluded his discussion of the AAP workshop by noting that it would "neglect what may be one of the major requirements for successful operation of a space station" — namely, artificial gravity. He believed that a practical space station would need to provide its inhabitants with "a high level of artificial gravity."

Artificial gravity would, he explained, enable comfortable movement, easy handling of fluids, and Earth-like "general man/machine interfaces." Because they could move more or less as they did on Earth, with their hands free to hold objects and to work, station crew members would need little special training to move about. Fluids would move as they did on Earth, which would make familiar the basics of personal hygiene, station cleaning, and food preparation. Equipment on the station could be identical to equipment on Earth, improving efficiency.

Artificial gravity would allow many types of researchers to live and work on the station, Gilruth told his San Antonio audience; basically, any who were eager to explore and exploit the economic and scientific benefits the space station would offer. "I, personally, look forward to the day when our space station crews will contain representatives from all the nations of the world," he added.

Gilruth described briefly an intermediate step between the zero-gravity AAP workshop and his large artificial-gravity station. He envisioned that a Saturn IB might launch an Apollo CSM. A drum-shaped multipurpose experiment module Boeing had designed on contract to MSC would ride in the streamlined adapter between the CSM engine bell and the top of the Saturn IB second stage.

Upon reaching orbit, the CSM would detach from the adapter, the four petal-like segments of which would fold back to expose the experiment module. The CSM crew would turn their spacecraft end for end and dock with the top of the experiment module, then would open latches linking the module to the rocket stage. Using the CSM's attitude-control thrusters, they would then pull the experiment module away from the stage.

Artificial-gravity experiment: the counterweight (upper right) is the S-IVB second stage of the Saturn IB rocket that boosted the CSM and experiment module into Earth orbit. Image credit: NASA
The module would, however, remain attached to the spent stage by an "extension mechanism," which might be as simple as a reel and cable. As the CSM/experiment module combination backed away from the stage, the crew would carefully fire the CSM's attitude-control thrusters, causing the CSM/experiment module/cable/stage assemblage to slowly spin end over end. The cable would draw taut and the crew would feel artificial gravity pressing them down into their couches. Separating from the module would end the experiment.

The 1966 MSC station study had looked at three classes of artificial-gravity space station, designated "Y," "O," and "I." The "Y" station would be approximately Y-shaped, with at least three arms. (The Project Olympus station — see the 1963 "Space Station Resupply. . ." link under "More Information" at the end of this post — is a good example of this station type.) The "O" station would take the form of a rotating wheel. The "I" station, which Gilruth favored and described in his San Antonio talk, would be a long cylindrical assemblage. He likened it to a "baton."

Assembling Gilruth's spinning baton (left to right): Saturn V launch 1 boosts the habitat module with its twin telescoping arms into Earth orbit. Saturn V launch 2 places the hub into orbit; the hub then docks with the habitat module. Saturn V launch 3 launches a deployable truss which turns the Saturn V S-II second stage into a counterweight. The station crew then fires rocket motors to spin the station end over end 3.5 times per minute to produce about one Earth gravity in the section of the habitat module farthest from the center of rotation. Image credit: NASA.
One million pounds, the mass Gilruth gave for his station, is equal to 500 tons. Probably this underestimates the likely mass of the station, which he hoped would house 50 people and 100,000 pounds (50 tons) of experiment equipment after its first three assembly launches.

The station would measure 240 feet from the center of rotation at its hub to the farthest part of the multi-deck, 50,000-cubic-foot habitat module and 375 feet from the center of rotation to the engine bells of the spent Saturn V S-II second stage that would serve as an artificial-gravity counterweight for the habitat. Total station length thus would come to about 615 feet.

These dimensions would enable the station to spin at 3.5 rotations per minute (rpm) without any ill effects for the crew, Gilruth explained. Spinning the station at 3.5 rpm would produce artificial gravity in the habitat module about equal to Earth's gravity. He noted that small-radius, fast-spinning systems could, based on Earth-surface studies of rotating rooms, cause crews to become ill and disoriented and produce other undesirable effects: water pouring from a faucet would, for example, curve. Setting his 500-ton baton twirling would require a one-time expenditure of 7000 pounds of propellants, Gilruth added.

The 45,000-cubic-foot drum-shaped hub would include electric motors that would cause it to rotate "backwards," canceling out the station's spin so that it would appear motionless. This would preserve zero-gravity conditions there. Gilruth envisioned that the hub would serve as a laboratory for exploring potential applications of zero gravity and as a hangar.

The hub hangar would receive self-propelled co-orbiting automated modules. Astronauts would service the modules in the hangar; they might collect and replace film, change out experiment equipment, and transfer propellants before releasing them to resume their zero-gravity work near the spinning station. Larger automated modules that could not fit within the hub hangar — for example, a 120-inch telescope — might be visited by astronauts, not returned to the station.

The station would operate in an orbit inclined 50° relative to the equator, enabling its Earth-pointing instruments, mounted on the lower sides of the hub, to survey a large fraction of Earth's lands and seas. Gilruth, an avid sailor, gave special attention to oceanographic observations in his San Antonio presentation. 

Space-pointing instruments would ride on top of the hub. Gilruth explained that many types of astronomical instruments would benefit from a position high above "Earth's dirty and shimmering atmosphere." 

Gilruth was not specific about the station's means of generating electricity, though he expected that it would need "20 or 50 or even 100 kilowatts" if it was to accomplish a wide range of experiments. The station's large size would permit mounting of proportionately large solar arrays; equally, it could enable use of "large nuclear systems" with extensive heat radiator panels, a large separation distance between the crew and the power source, and ample radiation shielding. 

Gilruth envisioned that, some time after the initial 50-person station was complete in Earth orbit, two more Saturn V launches would add another habitat module and a second S-II stage counterweight, bumping the station population up to at least 100. The large number of people would do away with the need for extensive cross-training in multiple skills and would enable specialization impossible in small crews. It would also reduce the amount of time any one station resident would spend performing maintenance and housekeeping chores, thus increasing time available for productive work.

Interestingly, Gilruth barely mentioned the need for a vehicle for transporting supplies and crews to and from his station, let alone any specific vehicle design. He mentioned "flexible crew rotation patterns," but did not explain how they would be accomplished. He did, however, note that the station could serve as a "logistic center" — a kind of warehouse — which would enable "efficient launch schedules for operational and experiment support supplies." He argued that the station's permanency would enable reuse and modification of equipment, reducing the quantity that would need to be shipped up from Earth.

The illustration of Gilruth's million-pound station at the top of this post — sent my way by reader Carmine Rossi — helps to clear up some of the mystery. Visible on either side of the hub are twin "Big Gemini" crew/cargo vehicles. These would have "backed up" to dock with ports on the sides of the non-spinning hub.

Proposed by contractor McDonnell Douglas in 1967, Big Gemini represented a continuation of Gemini contractor McDonnell's efforts to sell NASA and the U.S. Air Force Gemini-derived spacecraft and modular space stations. McDonnell had begun to pitch a broad range of Gemini variants as early as 1962, the year Gemini became the "bridge" program linking Mercury and Apollo.

Each Big Gemini might have launched nine astronauts (12 in its advanced version) and several tons of supplies. The design would have been familiar to many in his audience, so perhaps Gilruth felt no need to call it out specifically in his presentation.

Even in its advanced form, however, Big Gemini was a small crew/cargo spacecraft for a big space station. The concept, spelled out in a detailed eight-volume report submitted to MSC in August 1969, fueled awareness that large stations such as MSC's 1968 design would need sophisticated crew/cargo vehicles. This bolstered plans for reusable winged "Space Shuttle" vehicles.

Gilruth ended his presentation by declaring that a large space station would provide "tens of thousands of hours of operational experience. . .in the space environment." This would, he said, make it "a true gateway into the exciting space programs of the more distant future."


Letter, Robert Gilruth to George Mueller, 25 March 1966.

Letter, Robert Gilruth to George Mueller, 15 April 1966.

Preliminary Technical Data for Earth Orbiting Space Station, Volume 1, Summary Report, MSC-EA-R-66-1, NASA MSC, 7 November 1966.

Status Report: Earth Orbiting Space Station Artificial Gravity Experiment, MSC Internal Note 68-ET-1, NASA MSC, January 1968.

Manned Space Stations: Gateway to Our Future in Space, Robert Gilruth; presentation to the Fourth International Symposium on Bioastronautics and the Exploration of Space in San Antonio, Texas, 25 June 1968.

Astronautics and Aeronautics, 1968: Chronology on Science, Technology, and Policy, NASA, 1969, pp. 141-142.

A Summary of NASA Manned Spacecraft Center Advanced Earth Orbital Missions Space Station Activity from 1962 to 1969, Maxime Faget and Edward Olling, NASA MSC, February 1969, pp. 17-18, 27-28.

Skylab: A Chronology, NASA SP-4011, R. Newkirk, I. Ertel, and C. Brooks, NASA, 1977, pp. 172-174.

NASA Press Release, "Dr. Robert Gilruth, An Architect of Manned Space Flight, Dies," Bob Jacobs, NASA Headquarters, 17 August 2000.

More Information

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

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

McDonnell Douglas Phase B Space Station (1970)

A Forgotten Rocket - The Saturn IB


  1. I hate to nitpick but 1 pound is 0.454 kg, so a million pound is not 500 but 450 tons (metric ! not short tons)

    1. Gilruth used short tons, not metric. I used the units used in the original source. Sort of SOP for history writing, though sometimes I give both.


    2. Thank you so much for this. It would also make a nice cycler..perhaps.

  2. Ben:

    Gilruth makes no mention of any particular kind of logistics/crew spacecraft, just vague thoughts about how handy a station with a big crew and lots of storage would be. Heck, there's not even a docking port for any sort of piloted vehicle. It's a peculiar omission, but not the other one - how to maneuver the various separately launched parts of the station together? What effect would vibration from the counter-spin motor have on experiments in the lab? Where's the power supply? And, as you say, what if you need to evacuate? Some of these omissions can be forgiven - Gilruth was doing a talk, not publishing a technical report. But the logistics/crew issue bugs me.


  3. I have seen illustrations like the first one before, but I don't think I've seen anything like the pictures on the stamps. If they were going to have such large crews, I figure they'd want something like Big Gemini or BALLOS for transportation.

    Perhaps the Space Launch System could someday put something like the basic rotating station in orbit. I do think it's a crying shame the Centrifuge Accommodation Module wasn't installed on the International Space Station. Some people thought it would be like the Hubble Space Telescope of biology.

    1. Phil:

      I expect that you're aware that we almost lost the Hubble Space Telescope multiple times. It was canceled outright at least once when it was the Large Space Telescope. Our approach to space can be really scattershot. Like everything else, I guess!


    2. Well I'll be darned...the new picture does have a Big Gemini docked to the station.

    3. Two Big G's, in fact. I amended the text to reflect the info the new illustration provided.


  4. Ben:

    Oops, forgot to thank you for the correction, which has been made. Thanks!


  5. Tonyon:

    I'm sorry that I had to delete your comment concerning religion. Discussions of such aspects of human activity can be stimulating - as shown by the existence online of plenty of places that welcome such discussions - but they do not relate directly to the topics covered in this particular blog.


  6. "Engineers often make the mistake of assuming that the course of spaceflight should be logical. Perhaps this is a quirk of the engineer personality (if such a thing exists)."

    It does, and it kind of is.

  7. All out of sudden, a rather fictionalized movie about Salyut 7's rescue, coming next year:

  8. Thank you David for writing about my father,Edward Olling's, Project Olympus and his Space Station Resupply reserch.


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