"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."

Sources

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

The Last Days of the Nuclear Shuttle (1971)

Image credit: NASA.

In July 1969, as the Apollo 11 moon landing brought the Apollo Program to its culmination, Lockheed Missiles and Space Company (LMSC), McDonnell Douglas Astronautics Company (MDAC), and North American Rockwell (NAR) began the Nuclear Flight Systems Definition (NFSD) study on contract to NASA’s Marshall Space Flight Center (MSFC) in Huntsville, Alabama. The NFSD study occurred against a backdrop of great change in the U.S. civilian space program, and its evolution through three phases reflected this.

Cutaway of a typical NERVA nuclear-thermal rocket engine. The explanation of its operation that follows is simplified. Turbopumps push liquid hydrogen propellant from a large insulated propellant tank (not shown) through the reactor core. A reflector focuses neutrons radiated from uranium fuel rods back into the core, causing nuclear fission to occur. Liquid hydrogen picks up heat generated by the fission reaction in the core, helping to prevent the fuel rods from melting. The hot hydrogen then expands outward from the nozzle skirt extension, producing thrust. Liquid hydrogen also cools the nozzle. During engine shutdown, a control drum blocks the reflector, damping nuclear fission in the core. Propellant flow is maintained for a "cool-down" period after fission is halted to prevent fuel rods melting. Note the external and internal radiation shields which reduce crew radiation exposure. Image credit: NASA.

In Phase I of the NFSD study, MSFC charged LMSC, MDAC, and NAR with producing a "detailed analysis [and] conceptual design" of an expendable nuclear-thermal rocket stage equipped with a 200,000-pound-thrust NERVA II engine. The NERVA II was expected to be flight-ready in late 1977. The contractors were directed to study "development requirements of a nuclear propulsion system, including its evolution from a flight test stage to an operational. . .stage."

The Phase I nuclear stage was envisioned as a NERVA II with a single 33-foot-diameter propellant tank sized for launch from Earth atop a two-stage, 33-foot-diameter Saturn V rocket. Its main purpose would be to push piloted spacecraft out of low-Earth orbit (LEO) toward Mars.

Phase II commenced in October 1969, immediately after President Richard Nixon's Space Task Group (STG) endorsed (with reservations) NASA's aggressive Integrated Program Plan (IPP) for future U.S. spaceflight. The IPP was the brainchild of George Mueller's NASA Headquarters Office of Manned Space Flight, which supervised NASA's manned spaceflight centers, including MSFC.

In NFSD Phase II, MSFC directed its contractors to design a reusable nuclear rocket stage equipped with a 75,000-pound-thrust NERVA I engine. The stage, dubbed the Reusable Nuclear Shuttle (RNS), was intended mainly for roundtrip crew and cargo flights between space stations in LEO and lunar orbit. In January 1970, MSFC presented the contractors with an ambitious RNS traffic model calling for 157 Earth-moon flights between 1980 and 1990 by a fleet of 15 RNS vehicles, each toting 50 tons of cargo. Piloted Mars missions, though still considered a part of the IPP, were in NFSD Phase II relegated to secondary importance.

Image credit: NASA.

As in Phase I, the Phase II nuclear stage would reach Earth orbit on top of a Saturn V rocket. Its liquid hydrogen propellant would, on the other hand, climb into orbit in the payload bay of the proposed reusable winged Earth-to-Orbit Shuttle (EOS). NASA envisioned that more than 40% of EOS flights would be devoted to delivery of propellants. The EOS would pump liquid hydrogen/liquid oxygen propellants it carried directly into the tanks of chemical-propulsion Space Tugs. Most propellant carried in the EOS would, however, be liquid hydrogen meant for RNS propulsion. MSFC engineers envisioned that the EOS would cache RNS liquid hydrogen in LEO at an Orbital Propulsion Depot.

Electricity from twin nuclear reactors arranged in a "Y" configuration (right) powers refrigeration systems that keep liquid hydrogen stored in the Orbital Propellant Depot from turning to gas and escaping. Image credit: NASA.

A Reusable Nuclear Shuttle tanks up at the Orbital Propellant Depot using a soft-docking Refueling Adapter. Image credit: NASA.

That same month, NASA Administrator Thomas Paine permanently terminated Saturn V production and canceled Apollo 20 so that its Saturn V could launch the Apollo Applications Program (AAP) Dry Workshop (DWS). In February 1970, NASA gave the AAP DWS the new name Skylab and redesignated AAP as the Skylab Program.

Soon after, MSFC directed LMSC to examine launching the RNS inside the Space Shuttle payload bay, which was expected to measure 15 feet wide by 60 feet long. LMSC's Shuttle-launched "modular" RNS would comprise a NERVA I engine and multiple hydrogen tanks launched separately into LEO and joined together through a labyrinth of pipes. NAR continued work on a single-tank RNS sized for launch on a future heavy-lift rocket, while MDAC divided its study efforts between the two launch options.

Phase II segued into Phase III in May 1970, when MSFC directed the NFSD contractors to assume a 1978 or 1979 NERVA I flight readiness date. The postponement reflected an anticipated Fiscal Year 1971 NERVA funding cut. MSFC also directed the contractors to limit to 150 tons the amount of liquid hydrogen propellant each RNS would carry.

In February 1971, with the NFSD study set to conclude in less than two months, D. J. Osias, an analyst with NASA Headquarters planning contractor Bellcomm, summarized and critiqued reports prepared by the three contractors. He began by examining the ways that the contractors had approached the problem of radiation shielding. "Nuclear propulsion," he wrote, "complicates in-space operations by introducing a radioactive environment."

All the RNS designs included a 3000-pound radiation shield on top of the NERVA I to create a conical radiation "shadow" for crew protection, but also relied on the vehicle's propellants and structure for supplemental shielding. Osias asserted that "in regard to radiation shielding. . .the most optimistic results are being accepted and attention to the problem is diminishing."

He also noted that, as liquid hydrogen was expended as propellant, it would cease to be available to serve as radiation shielding. As the RNS tank or tanks emptied, crew radiation dose would thus steadily increase. To solve this problem, NAR had developed a "stand-pipe" single-tank RNS concept, in which a cylindrical "central column" running the length of the main tank stood between the crew and the NERVA I engine. The central column would remain filled with hydrogen until the surrounding main tank was emptied. MDAC, for its part, had developed a "hybrid" RNS shielding design that included a small hydrogen tank between the bottom of the main tank and the top of the NERVA I engine.

 Image credit: NASA.

The proper way to load cargo onto a Nuclear Shuttle: I = Use Space Tug robot arms to remove cargo module from Space Shuttle payload bay; II = stack cargo module on Space Tug; III = ignite Space Tug chemical rocket motors to rendezvous with Nuclear Shuttle, taking care to approach within the conical shadow created by the NERVA engine's radiation shields; IV = transfer cargo to Nuclear Shuttle. Image credit: NASA.

Crew transfer from the Earth-to-Orbit Shuttle to the Nuclear Shuttle might take place at the Orbital Propellant Depot. In this image, the crew of the Earth-to-Orbit Shuttle takes care to remain within the shadow of the NERVA engine's radiation shields. Image credit: NASA.

Osias postulated a maximum allowable radiation dose for an astronaut from sources other than cosmic rays of between 10 and 25 Roentgen Equivalent Man (REM) per year. Astronauts riding an RNS would, however, receive 10 REM each time its NERVA I engine operated. An astronaut 10 miles behind or to the side of an RNS operating at full power would receive a radiation dose of between 25 and 30 REM per hour. Osias noted that the NFSD contractors had recommended that no piloted spacecraft approach to within 100 miles of an operating NERVA I engine.

Radiation would create other operational problems, Osias wrote. Spacecraft could dock with an RNS by approaching through the cone-shaped radiation shadow that protected its crew. Docking an RNS to a large vehicle that protruded beyond the shadow — for example, a space station or a liquid hydrogen propellant depot — would, however, generate obvious problems. The large vehicle's crew might be exposed to radiation from the NERVA I; more insidious, the large vehicle's structure would reflect radiation back at the RNS, endangering its crew.

The NERVA I engine would emit radiation not only while it was in operation; it would also generate spent nuclear fuel that would emit harmful levels of radiation for decades or centuries. Osias noted that NAR had "repeatedly emphasized [that] maintainability is essential to economic operation of the RNS." A spacewalking repairman who approached to within 400 feet of the side of an RNS 10 days after its tenth (and, going by MSFC's traffic model, final) Earth-moon round-trip would, however, receive one REM per hour from the spent fuel it contained. Maintenance robots might replace the servicing capabilities of astronauts, Osias noted, but such systems would need costly development before they could become available.

Osias also reported that the "NFSD contractors. . .devoted little effort to [studying] emergency operations and malfunctions," adding that "[n]uclear systems, more than chemical propulsion vehicles, have the ability to involve the general population of the [E]arth in a space accident." A NERVA I explosion in LEO, for example, could lead to "random reentry of large pieces of radioactive material" that would probably survive reentry heating and strike Earth's surface. He urged that prevention of "return of the NERVA engine to the [E]arth's surface. . .be a basic rule of nuclear propulsion planning."

In NFSD study Phase II, LMSC estimated that, after just one Earth-moon round-trip, enough spent fuel would have accumulated within a NERVA I engine that it would need to remain in a safe high-altitude disposal orbit for 135 years. By the end of its operational life — after ten Earth-Moon flights — the "most desirable method of disposing of an engine" would, Osias wrote, be to "send the RNS on an unmanned, one-way mission to deep space."

The same month Osias completed his critique of the PFSD contractor studies, veteran New Mexico Senator Clinton Anderson, a close friend of former President Lyndon B. Johnson and a long-time nuclear rocket supporter, called a hearing to highlight the Nixon Administration's plan to slash NERVA funding from $110 million in Fiscal Year 1972 to only $30 million. At the hearing, Acting NASA Administrator Robert Seamans, an STG member, explained that Space Shuttle development had priority over NERVA development because the Space Shuttle was the essential transportation element that would launch into space all other IPP elements, including the RNS. He told Anderson that "NERVA needs the Shuttle, but the Shuttle does not need NERVA."

Six months after the NFSD contractors completed their reports, the Nixon White House unveiled its Fiscal Year 1973 budget request. As many had feared, it contained no funding for continued NERVA development. Anderson was ill and no longer able to adequately defend NERVA. A group of more than 30 pro-NERVA congressmen sought to sway the Nixon Administration, but to no effect. The final NERVA ground tests occurred in June and July 1972, after which the program was terminated, ending nearly 20 years of U.S. nuclear propulsion development.

Sources

"Status of Nuclear Flight System Definition Studies — Case 237," B71 02018 (NASA Contractor Report 116601), D. J. Osias, Bellcomm, Inc., 9 February 1971.

Humans to Mars: Fifty Years of Mission Planning, 1950-2000, Monographs in Aerospace History #21, NASA SP-2001-4521, David S. F. Portree, NASA, February 2001.

More Information

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

Series Development: A 1969 Plan to Merge Shuttle and Saturn V to Spread Out Space Program Cost

Apollo's End: NASA Cancels Apollo 15 & Apollo 19 to Save Station/Shuttle (1969)

Humans on Mars in 1995! (1980-1981)

Starfish and Apollo (1962)

9 July 1962: An artificial aurora lights the sky over the Pacific Ocean following the Starfish Prime space nuclear explosion. Image credit: U.S. Air Force.

Since I first posted a less detailed version of this post on my old Romance to Reality website (1996-2006), the Starfish Prime nuclear test has become a popular topic on the Internet. On 9 July 1962, the U.S. Air Force launched a 2200-pound W-49 nuclear warhead into space on a Thor rocket from Johnston Atoll in the Pacific Ocean. The warhead exploded with a yield of 1.44 megatons of TNT at an altitude of 248 miles above the Pacific.

The Starfish Prime nuclear blast produced a flash of light visible over much of the Pacific basin. For seven minutes after the explosion, an artificial red aurora danced in the skies over island groups as widely separated as Hawaii, Tonga, and Samoa. The blast's electromagnetic pulse damaged electrical systems on the Hawaiian island of Oahu, 800 miles away from the explosion.

Starfish Prime, a follow-on to U.S. high-altitude nuclear tests conducted in 1958, was publicized in advance. Many widely scattered aircraft and naval vessels, as well as sounding rockets, were used to observe its effects.

Though it sought answers to scientific questions, it was intended also to test whether nuclear explosions in low-Earth orbit (LEO) could augment and expand the Earth-girdling Van Allen radiation belts to create a barrier that would incapacitate Soviet intercontinental missiles launched against the United States. The test series of which it was part, Operation Dominic, was partly a response to the Soviet Union's August 1961 decision to end a three-year nuclear testing moratorium.

Schematic cross-section of the inner and outer Van Allen Belts based on James Van Allen's 1958 model. In February 2013, NASA announced that data from the two Van Allen Probes indicated that a third radiation belt can sometimes form beyond the outer belt. Image credit: Wikipedia.

High-energy particles Starfish Prime pumped into the belts probably contributed to the failure of Telstar 1 just four months after its 10 July 1962 launch. Telstar 1 was the first active communications satellite, meaning that it received and re-transmitted incoming radio signals. The satellite was reacquired in January 1963, but failed permanently on 21 February. Six other satellite failures have been traced to Starfish Prime.

No one knew how long the beefed-up radiation belts might persist. Some feared that the increased radiation might last until 1967-1968, when NASA hoped to carry out the first Apollo expedition to the Moon. The Apollo spacecraft, launched from Cape Canaveral on Florida's east coast, would have to traverse the augmented Van Allen Belts, and no one could say what effect their radiation would have on Apollo crews.

A Bell Labs technician puts the finishing touches on the experimental multi-national Telstar 1, the world's first privately sponsored satellite. A Thor-Delta rocket boosted the 170-pound satellite into a 592-by-3687-mile Earth orbit the day after the Starfish Prime nuclear explosion. Image credit: Bell Laboratories.

D. James and H. Schulte, researchers with NASA's newly created advance planning contractor, Bellcomm, analyzed the effects of Starfish Prime on NASA Moon plans in a memorandum they sent to NASA Headquarters on 5 October 1962. It was among the first of many memos and reports Bellcomm would supply to NASA over the decade that followed.

James and Schulte based their analysis of the LEO radiation environment during the first Apollo mission on a model of the post-Starfish Prime Van Allen belts developed by NASA Goddard Space Flight Center scientist Wilmot Hess. His model placed the lower limit of the expanded inner Van Allen belt at an altitude of about 600 miles.

Just two days after Starfish Prime, NASA announced that, after more than a year of sometimes heated discussion, it had selected the Lunar-Orbit Rendezvous (LOR) mission mode for accomplishing Apollo Moon landings. LOR would see lunar mission functions split between two manned spacecraft — a large command ship and a small Moon lander. The command ship would come no closer to the Moon than lunar orbit. The lander would operate independently only during descent to the Moon's surface, on the surface, and during ascent to lunar orbit.

LOR mission plan. Please click to enlarge. Step 10 shows the lunar lander separating from the command ship; 11 and 12 show the lander descending and on the surface; 13 and 14 show the lander ascent stage climbing to lunar orbit and docking with the command ship; and 15 shows the ascent stage being cast off and the command ship firing its engine to leave lunar orbit and fall back to Earth. Image credit: NASA.

LOR had won out over Earth-Orbit Rendezvous (EOR) because it promised to reduce the mass of the lunar spacecraft, enabling launch on a single Saturn C-5 rocket (as the Saturn V was known in 1962), and because it would make the moon lander small compared to the EOR lander and thus safer to land. EOR needed multiple Earth launches and landed the entire piloted lunar spacecraft on the Moon.

Despite NASA's decision, James and Schulte examined the radiation environment for both LOR and EOR Apollo missions. This reflected lingering anxiety both inside and outside NASA concerning LOR.

Many worried that the LOR mission mode's namesake maneuver, the post-lunar landing rendezvous and docking between the command ship and the Moon lander in lunar orbit, might prove too challenging. They worried in particular that, with Earth's ground-based tracking stations too far away to be of use, the spacecraft in lunar orbit would have difficulty finding each other. If, during Apollo development, this were found to be so, then an EOR backup plan would become necessary.

In James and Schulte's EOR scenario, NASA would launch a single large piloted lunar spacecraft with mostly empty propellant tanks into LEO. There it would rendezvous and dock with a separately launched automated tanker containing its LEO departure propellants.

James and Schulte assumed that, before an EOR Apollo spacecraft could set out for the Moon, it would need to orbit the Earth at least six times in a 252-mile-high parking orbit inclined 28.5° relative to Earth's equator (28.5° is the latitude of launch facilities on Cape Canaveral). During its first orbit after launch, controllers on the ground would track the piloted EOR Apollo to determine its precise path.

Rendezvous and docking with the tanker would need up to 2.5 orbits, then propellant transfer and final orbit determination/spacecraft checkout would require two more. After a final half-orbit, the EOR Apollo's orbital motion would have caused its orbital plane to become aligned for launch to near-equatorial landing sites on the Moon. It would then ignite its engines to depart LEO.

The Bellcomm planners determined that, based on the Hess model, the EOR Apollo astronauts would receive a radiation dose of four rad in LEO before setting out for the Moon. They would experience most of their LEO radiation exposure during orbits five and six, when they would begin to pass through a magnetic field anomaly that spans the Atlantic from Brazil to South Africa.

NASA Goddard Space Flight Center illustration of the South Atlantic Anomaly.

Within the South Atlantic Anomaly, as it is known today, the Van Allen belts dip to within 100 miles of Earth's surface. If the EOR Apollo astronauts could not depart LEO on schedule, then they would pass through the widest part of the South Atlantic Anomaly during orbits seven, eight, nine, and 10, and would receive up to six rads per orbit.

LOR Apollo would, by contrast, not linger in LEO. James and Schulte assumed that the LOR Apollo spacecraft/LEO-departure booster combination would circle Earth once in 252-mile-high LEO while controllers precisely tracked it to determine its orbit. It would then complete half an orbit more so that its orbital plane would align for departure to near-equatorial landing sites on the Moon.

The LOR Apollo crew would stay far from the South Atlantic Anomaly during their one and a half orbits of the Earth. Because of this, their radiation dose in LEO from the augmented Van Allen belts would amount to only 0.02 rad.

In both the LOR and EOR modes, the astronauts would receive a dose of 16 rad while crossing the Starfish Prime-augmented Van Allen belts en route to the Moon. Thus, the minimum dose the EOR astronauts would receive would be 20 rad, while LOR astronauts would receive 16.02 rad.

The Bellcomm planners noted that future nuclear explosions in LEO could dramatically boost the dose Moon-bound astronauts would receive during Van Allen belt passage. They added that a nuclear bomb packed with Uranium-238 could increase radiation in the belts "a hundredfold."

James and Schulte noted that the Van Allen belts are inclined relative to Earth's equator and do not cover its poles. If the belts became impassable, they wrote, NASA would have little choice but to launch Apollo astronauts through the Van Allen belt gaps over the poles.

Unfortunately, Cape Canaveral was poorly placed for polar launches because rockets launched due south or north would pass over populated areas. These included Cuba and Brazil to the south and the major cities of the U.S. eastern seaboard to the north.

James and Schulte wrote that a country with polar launch capability might explode nuclear weapons in space to bar a nation without such capability from launching men to the Moon. They did not mention the Soviet Union specifically, nor did they point out that the Soviet Union, with its extensive Arctic Ocean coastline, was well placed to carry out polar launches.

The Van Allen radiation belts returned to normal a few years after Starfish Prime. Nuclear explosions in space never menaced Apollo astronauts, in large part because on 5 August 1963, representatives of the U.S., Great Britain, and the Soviet Union met in Moscow to sign the Treaty Banning Nuclear Weapon Tests in the Atmosphere, Outer Space, and Under Water.

Conclusion of the treaty, which needed more than eight years to negotiate, very likely received some impetus from Starfish Prime. The treaty, which permitted only underground nuclear tests on Earth and sought to curtail spread of nuclear test fallout, entered into force on 10 October 1963, and has subsequently been signed by nearly all United Nations member countries.

Sources

Memorandum, D. James and H. Schulte, Bellcomm, to W. Lee, NASA Headquarters, "Radiation environment of EOR and LOR," Bellcomm, October 5, 1962.

"The Artificial Radiation Belt Made on July 9, 1962," W. Hess, Journal of Geophysical Research, Volume 68, Number 3, 1 February 1963, pp. 667-683.

Wikipedia - "Starfish Prime" (https://en.wikipedia.org/wiki/Starfish_Prime - accessed 9 January 2016).

Wikipedia - "Telstar" (https://en.wikipedia.org/wiki/Telstar - accessed 12 January 2016).

U.S. Department of State - "Treaty Banning Nuclear Weapon Tests in the Atmosphere, Outer Space, and Under Water" (http://www.state.gov/t/isn/4797.htm - accessed 12 January 2016)

More Information

What If Apollo Astronauts Became Marooned in Lunar Orbit? (1968)

What If Apollo Astronauts Could Not Ride the Saturn V Rocket? (1965)

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

Solar Flares and Moondust: The 1962 Proposal for an Interdisciplinary Science Satellite at Earth-Moon L4

He Who Controls the Moon Controls the Earth (1958)

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

 24 July 1969: Richard Nixon and Thomas Paine (left), NASA's third Administrator, wait on board the aircraft carrier Hornet for splashdown of the Command Module Columbia at the end of the Apollo 11, the first mission to land men on the Moon. At the time, Paine was lobbying hard for Nixon's acceptance of the IPP. Image credit: NASA.

When one reads of NASA's 1969 Integrated Program Plan (IPP), it is often difficult to know whether to laugh or cry. The IPP, a product of George Mueller's NASA Headquarters Office of Manned Space Flight, began to evolve as early as 1965, but not until May 1969 did it take on the grandiose form NASA Administrator Thomas Paine stubbornly advocated to President Richard Nixon.

Paine, a Washington neophyte who had replaced the politically wily James Webb in late 1968, expected that the IPP would be NASA's reward for vanquishing the Soviet Union in the race to the Moon. He urged his Center directors across the country to "think big" in their plans for post-Apollo space projects.

Had NASA gained approval for its Integrated Program Plan in 1969, a vast network of space transportation systems, space stations, and surface bases might have been in place by 1984. Image credit: NASA.

In its various versions, the IPP included space stations in low-Earth orbit (LEO), geosynchronous orbit (GEO), and near-polar lunar orbit; Saturn V and Saturn V-derived rockets for launching them; a fully reusable Earth-to-LEO Space Shuttle for launching astronauts, cargo, and propellants; a reusable modular Space Tug that could operate with or without a crew and do double-duty as a Lunar Module-B (LM-B) Moon lander; a reusable Nuclear Shuttle for LEO-GEO and LEO-lunar orbit transportation; and lunar and Mars surface bases. All of this complex and expensive infrastructure was meant to become operational by the mid-1980s at the latest.

The IPP is sometimes wrongly attributed to Wernher von Braun, director of NASA's Marshall Space Flight Center (MSFC) in Huntsville, Alabama. Von Braun was in fact skeptical about the IPP. He did not expect an Apollo-level commitment to spaceflight following Apollo's culmination, let alone one several times larger. He had spent the 1960s seeking opportunities to expand U.S. piloted spaceflight using his Saturn rocket family. By the time Apollo 11 Commander Neil Armstrong set foot on the Moon (20 July 1969), however, it was abundantly clear to the pragmatic German-born rocketeer that this would not happen.

Nevertheless, with his position rapidly eroding in the new political climate, von Braun at Paine's request tasked MSFC's artists with pumping out IPP illustrations and its advance planners with grafting a piloted Mars mission onto the up-to-then cislunar IPP. He then touted the Mars plan to Nixon's high-level Space Task Group (STG) on 4 August 1969. Paine called von Braun NASA's "Big Gun" and expected the STG to be bowled over by anything he put before them. The first NASA piloted Mars mission could leave Earth as early as 1981, von Braun told the STG in a 30-minute presentation.

Nixon had appointed the STG in February 1969 to provide him with alternatives for NASA's future. Paine, a member of the STG, had won over Vice President Spiro Agnew, the STG's chairman, enabling him to put forward the IPP as the only choice for NASA's future. The STG's September 1969 report offered Nixon three schedules for accomplishing the IPP, but that was not the same as providing the three program alternatives Nixon had requested. Paine might have offered Nixon a choice between an LEO space station, a lunar base, or a man on Mars. Instead, he insisted on a package containing all three.

This was, of course, an ill-considered move. Nixon's Office of Management and Budget had made it clear that NASA should expect rapidly declining annual budgets, not rapidly increasing ones. Nixon interpreted Paine's stubborn advocacy of the ambitious IPP as a clumsy effort at bureaucratic empire-building, not as a sincere proposal for a bold ("swashbuckling" was a term Paine used) American space program.

Paine's inflexibility created a vacuum that the Nixon Administration filled. NASA had supplied a single plan for its future that was unacceptable, so the White House made its own plan that served the President's political ends.

First, before accepting the STG report in September 1969, the White House added a fourth IPP schedule with no fixed dates. Nixon then adopted the line that IPP development would proceed as funding became available with the goal of a man on Mars by the year 2000, a date so far in the future as to be meaningless.

Next, in July 1970, a year after Apollo 11, Nixon accepted Paine's resignation effective on the first anniversary of the STG report's public release (15 September 1970), and replaced him with the much more pliant James Fletcher. Finally, on 5 January 1972, Nixon made the Space Shuttle the sum total of NASA's post-Apollo piloted program. He touted the aerospace jobs it would create in California, a state vital to his 1972 reelection bid.

5 January 1972: President Richard Nixon and NASA's fourth Administrator, James Fletcher, in California with a model of the Space Shuttle. The Space Shuttle was the only element of the IPP to fly, and then only in a partially reusable form. It first reached orbit on 12 April 1981. Image credit: NASA.

Before that fateful announcement, however, NASA expended considerable effort on planning the IPP's execution. Paine's resignation did not stop the study efforts immediately. The LEO Station and Shuttle received more attention than the other elements because they were viewed together as the IPP's first step, but planners continued to look at all elements of the IPP well into 1971.

In June 1970, E. Grenning, an engineer with Bellcomm, NASA's Washington, DC-based advance planning contractor, developed a "traffic model" (basically, a flight schedule) based on a modified version of Paine's IPP Option I (the so-called "Maximum Program"). Grenning's model spanned the years 1970 through 1984.

Grenning explained that the IPP was based on two fundamental principles. These were "the systematic establishment of semi-permanent manned bases in various locations in cislunar space and eventually in interplanetary space" and the "parallel introduction of low cost transportation systems. . . for the purpose of economically moving cargo and personnel to and from the bases."

A major change from the IPP as submitted to Nixon was that the piloted Mars program, which would span seven years, was not tied to any specific dates. Grenning explained, however, that, when the decision was taken to proceed with the piloted Mars program, its seven-year schedule would need to be tied to existing Earth-Mars minimum-energy transfer opportunities, which occur every 26 months.

Another change was that Grenning listed proposed automated planetary exploration missions. This was a response to protests from scientists, who were understandably eager to explore the many types of worlds in the Solar System. The "Balanced Base" planetary program would include 21 missions, all of which would leave Earth between 1976 and 1984.

In addition, Grenning stretched the pre-Mars IPP over a slightly longer period, so that its elements would not all be in place until 1984. Combined with not providing a specific date for its man-on-Mars program, this made Grenning's traffic model for Option I somewhat more conservative than the one in the STG report. It was, however, more conservative only relative to the grandiose Option I Paine championed.

Until 1975, Grenning's model was based wholly on Apollo spacecraft and Saturn rockets, none of which were reusable. Because it used no reusable vehicles and established no permanent bases, it was simple in execution compared with the traffic model that began to take hold in 1975.

The year 1970 would see three Apollo Moon-landing missions, Grenning wrote, each with three astronauts, a Command and Service Module (CSM), and a Lunar Module (LM) launched on a three-stage Saturn V rocket. They would constitute the continuation of the Apollo lunar landing missions that had begun with Apollo 11. It is interesting to note here that Grenning's model, dated June 1970, seemed to exist in a parallel universe; after the Apollo 13 accident in April 1970, Apollo was grounded until January 1971.

The year 1971 would see the first two Extended Apollo missions. An uprated Saturn VB rocket would launch three astronauts, an Extended CSM (XCSM) capable of 16 days of flight, and an Extended LM (XLM) capable supporting two astronauts for three days. The XLM would have a landed payload capacity of 1000 pounds. NASA would fly two Extended Apollo missions per year from 1971 through 1974, plus one in 1975, for a total of nine missions and 54 man-days on the Moon.

Once again, Grenning's model did not match up with reality. In January 1970, Paine had announced that, far from being uprated, Saturn V production would go on standby. He had also cancelled Apollo 20, at the time the last planned Moon-landing mission.

The IPP would have seen two-stage Saturn V rockets (designated Int-21) launch many payloads. Int-21 would have remained operational as late as the mid-1980s. This image shows the only two-stage Saturn V; it launched the Skylab space station in May 1973. Image credit: NASA.

In Grenning's traffic model, 1972 would see the first two-stage Int-21 Saturn V derivative launch the first Apollo Applications Program (AAP) Orbital Workshop (OWS). The AAP OWS was a 22-foot-diameter Saturn V S-IVB third stage converted into a temporary space station. The Int-21, of which a whopping total of 41 were meant to fly between 1972 and 1984, would be capable of placing up to 250,000 pounds into LEO.

Saturn IB rockets would launch three CSMs, each bearing a three-man crew, to the first AAP OWS between mid-1972 and early 1973. NASA would launch a second AAP OWS at the beginning of 1974. A total of nine CSMs would deliver crews to the the second AAP OWS by early 1976.

Paine had cancelled Apollo 20 so that its Saturn V could be used to launch the first AAP OWS. In February 1970, NASA announced that the AAP OWS program would be called the Skylab Program, a name that Grenning did not use in his June 1970 traffic model document.

Reusable IPP spacecraft and semi-permanent bases would make their debut in 1975, overlapping with missions using Apollo-Saturn systems and helping to ensure that there would be no gap in U.S. piloted spaceflight. As already indicated, these would increase the complexity of NASA piloted space operations. Spacecraft and bases would need to be assembled, refueled, and resupplied using other spacecraft and bases that would themselves need to be assembled, refueled, and resupplied.

Cutaway of a Saturn Int-21-launched Space Station Module with docked and docking research modules and, at its far end, a transfer module for transporting Station crews and supplies from a Space Shuttle Orbiter payload bay to the Station. Image credit: NASA.

In 1975, NASA would launch on an Int-21 its first LEO Space Station Module (SSM), the prototype for all subsequent SSMs. Grenning wrote that the LEO SSM, which would orbit between 200 and 300 nautical miles above the Earth, would be used to conduct science, applications, and technology research. It would also serve as a depot for cargo bound for GEO and the Moon, a satellite repair base, and an assembly and launch control center for automated and piloted planetary missions.

Soon after the LEO SSM reached space, the fully reusable Space Shuttle would take wing for the first time. In the LEO SSM's first year, winged Shuttle Orbiters would visit it three times. The 12-man Shuttle Orbiter would lift off vertically on the back of a winged, piloted booster larger than a 707 airliner, then would separate and ignite its own cluster of engines to complete the climb to LEO. It would carry up to 50,000 pounds of payload in its 15-by-60-foot payload bay. A Shuttle Orbiter would be good for 100 flights before it would need to be replaced.

The cislunar portion of the IPP architecture. Space Station Modules, color-coded blue, appear in low-Earth orbit, in synchronous Earth orbit, in lunar orbit, and on the lunar surface. The Shuttle is depicted as the only Earth-to-orbit transportation system, though the Saturn V would have remained in service into the 1980s. Image credit: NASA.

In 1975, NASA would also conduct a test flight of the Saturn VC, a beefed-up three-stage Saturn V with a Space Tug/LM-B fourth stage. The Saturn VC, an "interim system" for bridging the gap between Apollo and more advanced IPP lunar systems, would be capable of placing 100,000 pounds into lunar orbit. The LM-B, a Space Tug with landing legs, could operate on the lunar surface for up to 14 days at a stretch.

Early in 1976, a Saturn VC would launch a 50,000-pound SSM and a fully fueled Space Tug/LM-B to near-polar lunar orbit. During 1976, 1977, and 1978, nine Saturn VCs would launch four Space Tug/LM-Bs and five four-man "QCSMs" to the lunar-orbit SSM, enabling a continuous lunar population of four astronauts. The QCSM, which Grenning did not describe, would be an interim system like the Saturn VC. Two-person crews would land on the Moon in Space Tug/LM-Bs four times in 1976, five times in 1977, and four times in 1978. Each trip to the lunar surface and back would expend 50,000 pounds of liquid hydrogen/liquid oxygen (LH2/LOX) propellants.

One design concept for the Space Tug/LM-B. Image credit: NASA.

A slightly different design concept for the Space Tug/LM-B. Both the Tug/LM-B in this illustration and the one shown above it would have had similar capabilities. Image credit: NASA.

The Space Tug would have an important "Space Shuttle Augmentation" function. Among augmentation missions considered was satellite servicing beyond Space Shuttle/Space Station operational altitude. Image credit: NASA.

The American Bicentennial year of 1976 would see an Int-21 boost a stack of five fully fueled Space Tug/LM-Bs into LEO. With a full load of LH2 fuel and LOX oxidizer, each Tug/LM-B would have a mass of about 50,000 pounds. Space Tug/LM-Bs would be designed for a one-year in-space lifetime. Beginning in 1976, one Space Tug/LM-B would be based at the LEO SSM at all times for use in satellite servicing, spacecraft assembly, Earth-orbital rescue, and other missions.

The lunar-orbit SSM would have on hand two fully fueled Space Tug/LM-Bs at all times. One would land on the Moon and the other would stand by to rescue the surface astronauts in the event that their Space Tug/LM-B malfunctioned. After a year of operations, Space Tug/LM-Bs based at the lunar-orbit SSM would be stripped down and turned into tankage for a propellant depot in lunar orbit.

Also in 1976, the Space Shuttle would fly eight times. Six Shuttle missions would deliver astronauts, supplies, and cargoes, including two automated planetary spacecraft, to the LEO SSM. The remaining two missions would see the Shuttle orbiter serve in a "tanker" role. Each Shuttle Orbiter would carry 50,000 pounds of LH2/LOX propellants, enough to refuel one Space Tug/LM-B.

The Space Shuttle Orbiter in one of its chief IPP roles: that of tanker supplying propellants to other IPP spacecraft. Image credit: NASA.

A piloted Space Tug removes a cargo module from the Shuttle payload bay using robot arms, stacks it on its top (center left), performs rendezvous with a waiting Moon-bound Nuclear Shuttle (upper right), and transfers the cargo module. Image credit: NASA.

The first two missions of the Balanced Base planetary program, the Venus Explorer Orbiter and the Comet d'Arrest flyby, would depart Earth in 1976. Automated planetary missions would each need two fully-fueled Space Tug/LM-Bs. When the planetary launch window opened, Space Tug/LM-B #1 would ignite its rocket engines to accelerate Space Tug/LM-B #2 and the planetary probe, then would shut down its engines, undock from Space Tug/LM-B #2, turn end for end, and fire its engines again to return to LEO for refueling and reuse.

Space Tug/LM-B #2 would fire its engines to further accelerate the planetary probe, then would shut down its engines and release the probe onto its interplanetary trajectory. Space Tug/LM-B #2 would then turn end for end and fire its engines to slow itself and return to LEO.

Grenning's IPP included many Space Tug-launched robotic probes. The probe above resembles the Voyager Mars/Venus orbiter/lander design cancelled in 1967. Image credit: NASA.

In 1977, the Space Shuttle would fly 10 times and the Int-21 would fly twice. The Space Tug/LM-B could not carry enough propellants to change from near-equatorial LEO SSM orbit to polar Earth orbit, so two Shuttle Orbiters would launch directly from Earth's surface into polar orbit to perform sortie (non-Space Station) missions. Polar sorties would occur at a rate of two per year through 1984.

Eight Shuttle missions would transport crews and cargoes bound for the LEO SSM. One of those would deliver to 50,000 pounds of LH2 propellant for the first NERVA nuclear-thermal rocket engine-equipped Nuclear Shuttle, and four would deliver 50,000 pounds of Space Tug/LM-B propellants each.

The Nuclear Shuttle would extend the IPP's reach to the Moon and Mars, enabling establishment of Moon and Mars bases. Note the crew cabin (upper right). Image credit: NASA.

One Int-21 would launch the first Nuclear Shuttle and another would launch five fully fueled Space Tug/LM-Bs (four for the robotic planetary program and one for the LEO SSM). The Int-21 would not have the lift capacity to launch the Nuclear Shuttle to LEO fully fueled, so it would reach space with room in its tank for an additional 50,000 pounds of LH2. Before a newly launched Nuclear Shuttle departed LEO for the first time, a Shuttle Orbiter tanker would rendezvous with it to top off its tank.

Nuclear Shuttles would each be good for 10 missions from LEO to GEO or lunar orbit and back, then would be launched into disposal orbit around the Sun. Some would carry a cargo of worn-out Space Tug/LM-Bs into solar orbit with them.

Each Nuclear Shuttle mission would expend 240,000 pounds of LH2. Six Space Shuttle tanker flights would be required to refuel the Nuclear Shuttle once. The Nuclear Shuttle would transport to the lunar-orbit SSM six astronauts and 90,000 pounds of cargo, or 100,000 pounds of cargo in automated mode. It could return 10,000 pounds of cargo and six astronauts from the Moon to the LEO SSM.

The Nuclear Shuttle could deliver 90,000 pounds of cargo and six astronauts to GEO and return six astronauts from GEO to the LEO SSM. After the GEO SSM was established in 1980, all Nuclear Shuttles would perform a shakedown cruise to GEO before traveling to lunar orbit for the first time. If it malfunctioned during its maiden flight to GEO, a Space Tug/LM-B could rendezvous with it to make repairs or return it to the LEO SSM.

The first Nuclear Shuttle would operate only in automated mode; its 10 missions would serve as an extended flight test. The first piloted Nuclear Shuttle, the second launched, would reach LEO on an Int-21 in early 1979. Four piloted and six automated Nuclear Shuttle flights would occur each year beginning in 1981, by which time one new Nuclear Shuttle would reach LEO and one old Nuclear Shuttle would be disposed of in solar orbit each year.

In 1977, four Tug/LM-B pairs would launch the Mars Explorer Orbiter, the Mars High Data Orbiter, and two Jupiter-Saturn-Pluto Mariner-class flyby spacecraft. The Tug/LM-Bs would burn the propellants with which they were launched to send the two Mars missions on their way, then would be refueled to launch the twin Jupiter-Saturn-Pluto missions. Grenning noted that dispatching automated spacecraft to destinations beyond the Main Asteroid Belt would need so much energy that the second Tug/LM-B could spare no propellants to return to LEO. It would, therefore, be expended.

The year 1978 would see a Mercury-Venus Mariner flyby, a Venus Mariner Orbiter, and a Solar-Electric Asteroid Belt Survey depart the LEO SSM. All Space Tug/LM-Bs used to launch these missions would be recovered. In 1979, NASA would launch the 6,000-pound Mars Soft Lander/Rover and two more Jupiter-Saturn-Pluto Mariner-class flybys, expending two Tug/LM-Bs.

In 1980, a second Venus Explorer Orbiter would leave Earth, as would two Jupiter Flyby/Atmosphere Probe spacecraft. The latter would expend two Tug/LM-Bs. The year 1981 would see a second Mars Explorer Orbiter, two Saturn Mariner-class Orbiter/Atmosphere Probes, and two more expended Tug/LM-Bs.

NASA would launch only one automated planetary mission, the 8,000-pound Mercury Solar Electric Orbiter, in 1982. Venus would get another Venus Explorer Orbiter and a Venus Mariner Orbiter/Rough Lander in 1983. NASA would also launch its second comet mission, a Mariner rendezvous with Comet Kopff. With a mass of 8500 pounds, it would be the heaviest of the 21 automated probes in the Balanced Base program. Mars would get a second High Data Orbiter and a second Soft Lander/Rover in 1984.

Back in NASA's piloted program, between 1979 and 1981 Int-21s would launch three more LEO SSMs. These would be combined with the first LEO SSM to form a "Space Base" with a permanent crew of from 50 to 100 astronauts. In 1980, an Int-21 would launch into LEO an SSM that would be mated to a Nuclear Shuttle and boosted to GEO. Early in 1979, Space Shuttle missions would begin to fly at a rate of 30 per year; by mid-1980, Grenning had the number of flights ramping up to 90 per year.

One proposed Space Base configuration. This three-armed design, which would have a permanent crew complement of 50 astronauts and scientists, would spin about its axis to produce acceleration in the habitat arm (left). The crew would feel the acceleration as gravity. The other two arms would each hold a nuclear reactor at a safe distance from the crew in the habitat module and core section. Also visible to the right of the Space Base is a small free-flying science module; these would dock with the non-spinning core section for servicing. Image credit: NASA.

As indicated earlier, Grenning tied piloted Mars missions to no particular year. Probably the piloted Mars program would not begin until NASA had ample experience with long-duration spaceflight, orbital assembly, and Nuclear Shuttle operations. The Bellcomm planner did, however, lay out a seven-year plan encompassing two complete piloted Mars missions and the first half of a third. The first and second missions and second and third missions would overlap.

All three would follow a conjunction-class mission profile; that is, they would reach Mars in about six months, remain there for about 18 months, and return to Earth in about six months. For safety, two identical six-person Mars spacecraft would travel as a convoy. At launch from the Space Base, each would comprise three Nuclear Shuttles, a mission module housing the crew, a payload module bearing unmanned probes and supplies, and a two-stage piloted Mars Excursion Module (MEM) lander. Both Mars spacecraft would be capable of supporting the entire 12-person mission complement in case one failed catastrophically.

Nuclear Shuttle IPP mission applications would culminate with Mars missions in the 1980s. Each Mars expedition would include two piloted Mars spacecraft and each piloted Mars spacecraft would include one Nuclear Shuttle with strap-on tanks (as shown here) or a cluster of three Nuclear Shuttles (as shown in the next image). Image credit: NASA.

The IPP Mars mission would have seen two Nuclear Shuttles used as interplanetary boosters. After they set a third Nuclear Shuttle, a Space Station Module-based crew module, and a piloted Mars Excursion Module lander on their way, each would have separated, turned end-for-end, and fired its NERVA engine to slow down and return to low-Earth orbit for reuse. Image credit: NASA.

A pair of IPP interplanetary spacecraft en route to Mars. The bulbous forward section (right) would have housed sample-returner probes and the Mars Excursion Module piloted Mars lander. Image credit: NASA.

Eighteen months before the first mission was set to depart the Space Base, NASA would launch four Nuclear Shuttles on Int-21 rockets and then launch four Space Shuttles to top off their tanks. The following year, the space agency would launch two more Nuclear Shuttles. These would each have a half-load of LH2 propellant because the Int-21s that launched them would also carry one MEM each. Topping off the Nuclear Shuttle tanks would need three Space Shuttle flights. Six Shuttle flights would fuel Space Tug/LM-Bs used for Mars spacecraft assembly. A final pair of Int-21s would launch the twin SSM-derived Mars spacecraft mission modules; a final Space Shuttle would launch the Mars spacecraft crews.

As the countdown clock reached zero, the NERVA engines in the two outboard Nuclear Shuttles on each spacecraft would fire to place the third Nuclear Shuttle, mission module, payload module, and MEM on course for Mars. They would then shut down, separate, turn end for end, and fire their engines again to slow themselves and return to LEO. The center Nuclear Shuttle on each spacecraft would perform course corrections and slow the spacecraft so that martian gravity could capture them into orbit.

The Apollo Command Module-shaped MEM was designed to descend through the thin martian atmosphere found by the 1960s flyby Mars Mariners. It would have comprised two main parts: the descent module with Mars surface living accommodations and an airlock/garage with Mars surface rover; and the cramped ascent module, where the crew would ride during descent, landing, and ascent after the surface mission was complete. Image credit: NASA.

MEM ascent stage liftoff. The ascent stage was a stage-and-a-half design with a cluster of approximately conical expendable propellant tanks and integral tanks in its cylindrical core feeding a single engine. Image credit: NASA.

After 18 months at Mars, during which at least one MEM would land on the planet for about a month (the second might be held in reserve in Mars orbit as a rescue vehicle), the twin center Nuclear Shuttles would fire again to put the mission modules on course for Earth. They would be used to perform course corrections; then, as the Mars spacecraft neared Earth, they would fire for the last time to slow the mission modules for capture into Earth orbit. Space Tug/LM-Bs would retrieve the Mars crews and the center Nuclear Shuttles.

The second and third Mars missions would be carried out in much the same way. The four outboard Nuclear Shuttles from the first mission would be reused for the second and third missions and the two center Nuclear Shuttles from the first mission would be reused for the third mission. The second mission would leave LEO before the first mission returned, so would need two new center Nuclear Shuttles. Grenning wrote that the third mission, preparations for which would begin in the fifth year of the seven-year program, might establish the first semi-permanent Mars surface base.

Grenning forecast that the seven-year piloted Mars program would need four Space Shuttle flights and four Int-21 flights in its first year to place Mars spacecraft components and (especially) propellants into LEO. Year 2, toward the end of which the first two piloted Mars spacecraft would depart from Earth orbit, would need four Int-21s and 13 Shuttles.

Year 3, during which preparation for the second Mars expedition would begin, would need just one Int-21 and 13 Shuttle flights. NASA would launch 20 Space Shuttle flights and three Int-21s in the Mars program's fourth year, 10 Shuttle flights and no Int-21s in its fifth, and 24 Shuttle flights and four Int-21s in its sixth. The final year of the program would see no Int-21s and 13 Shuttle flights.

Grenning also summed up the number of flights required to carry out the Maximum Rate cislunar program from 1975, when IPP stations and spacecraft began to replace Apollo-based stations and spacecraft, to 1984. The Space Shuttle fleet would accomplish 518 missions to LEO. The Saturn VC would fly 11 times between 1975 and 1979, when it would be phased out in favor of piloted lunar flights via the Space Shuttle, LEO SSM, Nuclear Shuttle, lunar-orbit SSM, and LM-B. The Int-21 would fly 25 times in the cislunar IPP, with a peak annual launch rate of five in 1981.

Was the Mueller/Paine IPP in any sense realistic? It depends on the judgement criteria one uses. Certainly, it was not a realistic option for 1970 America due to domestic political and economic considerations, the opposition of the Nixon White House and the Congress, and public disinterest.

In addition, one might take issue with its confident assertion that its network of reusable space systems and permanent and semi-permanent bases would save money. Complex reusable space systems require either costly development or costly maintenance and refurbishment. A single failure can take down an entire network of interdependent complex systems, and pioneering systems are more prone to failure than well-established ones. If, for example, a Space Shuttle had exploded, then crew and propellant transport would have ground to a halt throughout the IPP infrastructure for an indeterminate period of time.

One might, on the other hand, argue that the IPP's scale was not adequate for the challenges of piloted space exploration. Even the IPP would have permitted astronaut access only to cislunar space, the Moon, and Mars. Perhaps we find the IPP grandiose in part because we have been conditioned to "think small" about space exploration. If our plans took in our entire local neighborhood — the Solar System — and sought to be realistic, then they would of necessity demand a scale orders of magnitude beyond that of the IPP.

Sources

"Integrated Manned Space Flight Program Traffic Model Case 105-4," E. M. Grenning, Bellcomm, 4 June 1970.

The Next Decade in Space: A Report of the Space Science and Technology Panel of the President's Science Advisory Committee, Executive Office of the President, Office of Science and Technology, March 1970.

"Statement About the Future of the United States Space Program," Richard M. Nixon, 7 March 1970.

"An Integrated Space Program for the Next Generation," George Mueller, Astronautics &  Aeronautics, January 1970, pp. 30-51.

"Integrated Space Program - 1970-1990," Internal Note-PD-SA-69-4, Terry Sharpe & Georg von Tiesenhausen, Advanced Systems Analysis Office, Program Development, NASA Marshall Space Flight Center, 10 December 1969.

America's Next Decades in Space: A Report for the Space Task Group, NASA, September 1969.

The Post-Apollo Space Program: Directions for the Future, Space Task Group Report to the President, September 1969.

"Manned Mars Landing Presentation to the Space Task Group," Wernher von Braun, 4 August 1969.

"Integrated Manned Space Flight Program: 1970-1980," NASA Office of Manned Space Flight, NASA Headquarters, 12 May 1969.

Astronautics and Aeronautics, 1970, NASA SP-4015, 1972, pp. 77-79, 82-84.

Astronautics and Aeronautics, 1969, NASA SP-4014, 1970, pp. 266-269, 304-305, 308.

After Apollo? Richard Nixon and the American Space Program, John M. Logsdon, Palgrave MacMillan, 2015.

More Information

Triple-Flyby: Venus-Mars-Venus Piloted Missions in the Late 1970s/Early 1980s (1967)

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

McDonnell-Douglas Phase B Space Station (1970)

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