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

The quintessential space station: Wernher von Braun's revolving artificial-gravity station in Earth orbit. This classic 1952 painting by Chesley Bonestell, the Dean of Space Artists, includes near its hub a pill-shaped piloted space tug. In this view, the station might not be rotating; at least one of the two astronauts visible at center left is floating above its hull (perhaps they have just been tossed away by its spin). Though widely identified with von Braun, the spinning wheel station concept was first described in detail by Herman Potočnik in 1928. Image credit: NASA.

Previously on this blog, I described the 1960s NASA push to make a large Earth-orbiting space station the "new Apollo" of the 1970s. I also discussed plans to exploit Apollo lunar program technology and techniques to conduct a low-cost post-Apollo piloted space program (the Apollo Applications Program, or AAP) that would include temporary space stations.

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

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

Gemini 7 as viewed from Gemini 6, December 1965. Image credit: NASA.

Marion noted that the space medicine community tended to believe that astronauts could adapt to long-term abaria, but cautioned that this was "opinion, nothing more." "In other words," he explained, "it is possible that man can't physiologically adapt to long term abaria, but it is much more likely that he can."

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

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

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

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

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

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

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

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

AAP wet Workshop concept in 1967-1968. The docked Apollo Telescope Mount at upper left is based on the Apollo Lunar Module design. Image credit: NASA.

It would, in fact, be a modified S-IVB stage, the second stage of a two-stage Saturn IB rocket. The stage would include a long upper tank containing liquid hydrogen, a short lower tank for liquid oxygen, a J-2 rocket engine, and a special docking module bolted to the top of the liquid hydrogen tank. An Apollo Command and Service Module (CSM) spacecraft with a crew of three would ride into space atop the Saturn IB. The spacecraft would detach from the S-IVB second stage upon arrival in Earth orbit.

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

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

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

The Space Station Program artificial-gravity station design in Marion's September 1968 memorandum was barely described, but would probably have shared features with the two designs depicted in the NASA images above. The station at top would have reached Earth orbit atop a single Saturn V; the "million-pound" station at bottom would have required three Saturn V launches and orbital assembly. Both designs include a counter-rotating hub; an Apollo Command and Service Module (CSM) spacecraft is docked to the hub of the station at top.

NASA spacecraft development has generally followed a four-phase system, the details of which have varied considerably. Phase A, from which most proposed programs never emerge, encompasses preliminary analysis; at the time Marion wrote, the proposed Space Station Program was in Phase A. Phase B would see more detailed analysis and early design. During Phase C, detailed design and early manufacturing would take place. Phase D encompassed manufacturing and testing.

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

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

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

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

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

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

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

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

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

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

Source

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

More Information

Space Station Gemini (1962)

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

Apollo Extension System Flight Mission Assignment Plan (1965)

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

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

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

McDonnell Douglas Phase B Space Station (1970)

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