|Herman Potočnik's 1928 Wohnrad ("living wheel") space station design. Image credit: NASA|
Wheel-shaped space stations would revolve continuously to produce acceleration - so-called "centrifugal force" - which the astronauts inside would feel as gravity. This "artificial gravity" would pull strongest along the station's outer rim and not at all at its hub. Artificial-gravity station designs tend to be large; this is because a spinning station of small spin radius would generate undesirable effects, such as a noticeable gradient in the pull felt along a standing astronaut's body. The astronaut would feel "light-headed" and "heavy-footed."
|An experimental inflatable artificial-gravity space station under development at NASA Langley Research Center in 1961. Image credit: NASA|
As LaRC labored toward artificial-gravity stations, the Space Task Group (STG), an independent team of engineers based at LaRC, began work on Mercury, NASA's first piloted spacecraft. NASA Headquarters, meanwhile, solicited proposals from industry for an "advanced manned spacecraft." The new three-person spacecraft and the program to build and fly it were named Apollo.
As originally conceived, Project Apollo was to have followed immediately after Project Mercury. The Apollo spacecraft would have included three modules, one of which, the Mission Module, would have provided its crew with added living and working volume. The Mission Module could turn an Apollo spacecraft into a small zero-gravity space station or could transport supplies to a large space station. NASA expected that, before 1970, a piloted Apollo spacecraft would fly around the moon without stopping in lunar orbit (that is, it would carry out a free-return circumlunar mission).
NASA's plans changed dramatically on 25 May 1961, when President John F. Kennedy called upon the young space agency to land a man on the moon by the end of the 1960s decade. Faced with this daunting new challenge, NASA out of necessity put most space station planning on the back burner.
Apollo became NASA's lunar landing program. After NASA opted for the Lunar-Orbit Rendezvous (LOR) moon-landing mode in July 1962, Apollo mission roles were split between two spacecraft: the Command and Service Module (CSM) for conveying three men from Earth to lunar orbit and back again; and the four-legged Lunar Module (LM), which would carry two men from the CSM in lunar orbit to the moon's surface and back. The Mission Module was no longer a part of the Apollo design.
The space agency tasked St. Louis, Missouri-based McDonnell Aircraft, Mercury spacecraft prime contractor, with building Gemini. The new spacecraft would comprise two main modules: the Reentry Module bearing the crew and the Adapter Module containing maneuvering thrusters and solid-propellant deorbit rockets. The latter would be located in the Retrograde Section, the forward part of the Adapter Module, up against the Reentry Module's bowl-shaped reentry heat shield.
Gemini, like Mercury and Apollo, would provide its crew with a pure oxygen atmosphere. Unlike Mercury and Apollo, Gemini would feature a jet fighter-style cockpit with forward-facing windows and ejection seats for crew escape in the event of emergency during liftoff, ascent, or landing. Fuel cells in the Adapter Module would combine liquid oxygen and liquid hydrogen reactants to produce drinking water and electricity.
|Artist's concept of a Gemini spacecraft performing rendezvous and docking with a modified Agena upper stage. Image credit: NASA|
Gemini would climb to orbit atop a Gemini Launch Vehicle (GLV), a modified U.S. Air Force (USAF) Titan II missile. At the end of its mission, the Gemini Reentry Module would deploy a triangular Rogallo "parawing" and glide to a controlled land landing on skids.
|The Titan II Inter-Continental Ballistic Missile, progenitor of the Titan family of space launchers. Image credit: U.S. Air Force|
|23 March 1965: twin engines ignite on a Titan II GLV at Cape Kennedy, Florida, marking the start of Gemini III, the first of ten piloted flights in the Gemini series. Image credit: NASA|
Air Force astronauts would have entered the pressurized module by opening a small hatch in the bulkhead above and behind their ejection seats. The hatch, a carefully engineered breach in the Reentry Module heat shield, would have opened on a narrow bent tunnel leading to the aft end of the Adapter Module, where another hatch would have let the astronauts into the pressurized module.
Continuing high-level uncertainty about the USAF role in piloted spaceflight led McDonnell in December 1962 to attempt to hedge its bets by peddling Gemini-derived spacecraft to NASA. The company proposed that while NASA carried out the Apollo lunar program it should also carry out a low-cost Gemini-based space station program. McDonnell argued that
presently programmed launch vehicles capable of placing 20,000 to 200,000 pounds in near earth orbits will be available [in the late 1960s]. Large space station complexes with elaborate facilities and housing large numbers of crewmen will then be technically feasible. However, before undertaking the development of such stations, it is desirable, if not mandatory, to explore at a modest level some of the fundamental design and cost determining operational factors such as, the need for artificial gravity[,]. . . the physiological and psychological effects of long[-]term space operations[,] and appropriate crew tours of duty. The [Gemini-based] space stations proposed provide. . . [an] early capability to obtain answers to fundamental questions [at] modest cost.If NASA had taken up McDonnell's proposal - which the company called "Modular Space Station Evolving from Gemini" - then Gemini would have become for a major NASA space station program what it was already for Project Apollo. That is, it would have bridged the knowledge gap separating short, zero-gravity missions in small piloted spacecraft from long missions on board large artificial-gravity stations.
McDonnell's proposal in fact encompassed a series of up to three programs, each building on and more ambitious than the last. The company designated them Program A, Program B, and Program C. Carrying out Program B would be prudent, McDonnell wrote, but optional.
McDonnell proposed five building blocks that could be combined in different ways to accomplish its three Programs. These were: the Gemini Transport, a modified Gemini spacecraft, which would serve as crew carrier and piloted space tug; the Supply Module; the One-Room Space Station, which was structurally similar to the Supply Module; the Electrical Power Module; and the Two-Room Space Station, structurally similar to the Electrical Power Module.
Structural similarity would yield reduced cost, the company explained. NASA would also save money by recovering Gemini Transport Reentry Modules and returning them to the McDonnell plant in St. Louis for refurbishment and reuse.
|3 November 1966: a Titan III rocket launches a USAF Manned Orbiting Laboratory mockup with the refurbished and modified unmanned Gemini II spacecraft on top. Image credit: U.S. Air Force|
The GLV, capable of launching 7390 pounds into an 87-by-200-nautical-mile orbit, would loft the Gemini Transport, the Supply Module, the One-Room Space Station, and a stripped-down version of the Two-Room Space Station. The Titan III would place 25,280 pounds into a 250-nautical-mile-high circular orbit or 26,000 pounds into a 100-by-250-nautical-mile elliptical orbit. This would enable it to launch module combinations, such as the Gemini Supply Transport (Gemini Transport plus loaded Supply Module).
McDonnell expended considerable in-house time and money to develop feasible rendezvous, docking, and crew/cargo transfer methods for its proposal. Because the Gemini Transport would use the nose-mounted Gemini rendezvous radar, it would first approach its orbital target with its nose and twin windows facing forward, just as would the baseline Gemini when it performed rendezvous and docking with an Agena.
About 10,000 feet from the target, the pilot would unstrap from his seat, twist his body around in the close confines of the Gemini Transport cockpit, and open the 27.5-inch-diameter hatch above and behind his and the command pilot's seats. He would squeeze through a 24.5-inch opening in the heat shield to enter a 32-inch-diameter tunnel in the Adapter Module. The bent tunnel would lead to a rear-facing Crew Docking Station.
|Gemini Transport (left) docked with a One-Room Space Station. Image credit: McDonnell/NASA|
McDonnell proposed that its Program A begin in early 1965, immediately after the baseline Gemini Program supporting Apollo was expected to be completed. It based its development schedule on a February 1963 NASA go-ahead for Program A.
In the first Program A mission, a GLV would launch a 7390-pound One-Room Space Station into an initial 87-by-200-nautical-mile orbit, then another GLV would launch a Gemini Transport. The latter would dock with the former, then would maneuver the combination to a 200-nautical-mile circular orbit. This approach - using the Gemini Transport to circularize the One-Room Space Station's orbit - would help to maximize the weight of useful payload that could be launched in the One-Room Space Station. The two astronauts in the Gemini Transport would then enter the One-Room Space Station and work on board for 30 days.
Astronaut activities on board the One-Room Space Stations would emphasize space medicine and station housekeeping, as well as space sciences, artificial-gravity, and military experiments. The One-Room Space Stations would use improved Gemini-type fuel cells to make electricity and water and would not remain occupied for long enough to need resupply. They would provide their crews with a pure oxygen atmosphere at five pounds per square inch of pressure. With a ceiling height of seven feet, pressurized volume would total 548 cubic feet. The station's 36-square-foot clear floor area would be covered with velcro so that the astronauts, who would wear velcro slippers, could anchor themselves in zero-gravity.
After undocking in their Gemini Transport, the first Program A crew would cast off the aft section of its Adapter Module and fire the solid-propellant rocket motors in its Retrograde Section to decrease its orbital velocity and begin the fall back to Earth. For added redundancy, the Gemini Transport Retrograde Section would include five retrograde motors; that is, one more than the baseline Gemini. Following a fiery atmosphere reentry, the Reentry Module would turn so its nose faced forward, deploy its parawing, and glide to a landing.
The first One-Room Space Station would not be occupied again. McDonnell made no mention of its eventual fate; presumably it would undergo uncontrolled reentry a few years after it was abandoned.
Program A's second One-Room Space Station mission would emphasize artificial-gravity experiments. McDonnell explained that "artificial gravity operations not only constitute new techniques in themselves, but also interrelate with and tend to modify many of the other required space station functions." A GLV would place its own second stage and the second One-Room Space Station into an initial elliptical orbit. The crew would then arrive in a Gemini Transport and boost the combination into its 200-nautical-mile circular operational orbit.
|Proposed Program A artificial-gravity experiment. Image credit: McDonnell/NASA|
At about 75% of full cable extension, the astronauts would begin cautiously pulsing the One-Room Space Station's thrusters. The end-over-end rotation this would produce would create artificial gravity in the One-Room Space Station and the docked Gemini Transport.
Because the spent GLV second stage would have a mass of only 5800 pounds (that is, about a third of the mass of the Gemini Transport/One-Room Space Station combination), the center of rotation would be located nearer the latter than the former (150 feet versus 362 feet). To end the artificial-gravity test, the crew would reverse the cable-extension and thruster-firing procedures. The second Program A crew would return to Earth after 45 days in orbit.
The third and final Program A mission, scheduled for early 1966, would last for 60 days, but would otherwise would resemble the 30-day first Program A mission. The crew's two-month orbital stay would pave the way for crews of four men to live for 60 days on board a Two-Room Space Station during Program B and a Four-Room Space Station during Program C.
McDonnell envisioned that Program B and Program C would receive preliminary approval in January 1965, and that NASA would a year later choose to fly Program B and Program C in succession or elect to skip directly to Program C after Program A. If the latter option were selected, McDonnell assumed that NASA would desire to fly a fourth Program A One-Room Space Station in August 1966 to bridge the one-year gap between the third Program A mission and the first Program C mission launched in early 1967.
Assuming that NASA opted to fly Program B, however, in mid-1966 a stripped-down 7390-pound Two-Room Space Station would climb to an elliptical orbit on a GLV. The GLV-launched Two-Room Station would reach orbit with little scientific equipment on board and only enough supplies to sustain two men for 30 days. A Gemini Transport with two astronauts on board would then lift off on a GLV, rendezvous and dock with the Two-Room Space Station, and circularize the combination's orbit.
To make way for a second Gemini Transport - which, upon its arrival, would increase the Two-Room Space Station's population to its normal complement of four astronauts - the first crew would pioneer a new space station operational technique. They would extend mooring arms to grip fixtures on their Gemini Transport, disengage the docking fork latches, and swing their Gemini Transport into alignment with either of two mooring ports on the Two-Room Space Station's sides. The mooring arms would then retract, causing the Gemini Transport's docking ring to latch on four small mooring forks. Like the larger docking forks, these would retract, pulling the Gemini Transport and Two-Room Space Station firmly together.
|Program B: a Gemini Transport is shifted from the docking port to one of two mooring ports on the Two-Room Space Station to make way for a second Gemini Transport with a Supply Module. Image credit: McDonnell/NASA|
The Supply Module's front end would include four docking forks and a hatch; its aft end would include a docking ring, a hatch, and, within its pressurized volume, a rear-facing Crew Docking Station. Soon after the Supply Module reached orbit, a Gemini Transport would lift off to rendezvous and dock with its front end. The Gemini Transport/Supply Module combination would then rendezvous with the Two-Room Space Station and halt at a distance of 10,000 feet.
|Two-Room Space Station (upper left) with moored Gemini Transport (upper right) and docked Gemini Transport/Supply Module combination (lower left). Image credit: McDonnell/NASA|
Arrival of a third Gemini Transport at the Two-Room Station's docking port would mark the beginning of the end for Program B. After a brief crowded period during which the Two-Room Space Station would house six astronauts, the first two-person crew would undock in their Gemini Transport and return to Earth, ending their 60-day orbital mission.
Thirty days later, the second crew would undock from the Supply Module, which would remain attached to the Two-Room Space Station to serve as a "pantry" and to provide extra living and working space. Finally, the third crew would undock. Their return to Earth 120 days after Two-Room Space Station launch would end McDonnell's Program B.
Man-rating the Titan III rocket would lead to important new capabilities in Program C. The rocket would be powerful enough to launch into a circular 250-nautical-mile orbit a payload comprising a Gemini Transport with two astronauts on board, a Two-Room Space Station with neither fuel cells nor fuel-cell consumables, and a two-room Electrical Power Module with twin rectangular solar arrays and batteries. The Two-Room Space Station and Electrical Power Module would be bolted together on the ground to create the Four-Room Space Station.
Thirty days later, a second two-man Program C crew launched on a GLV would join the two astronauts launched with the Four-Room Station. Thirty days later, the first two-man crew would return to Earth and a third two-man crew would replace them. This staffing pattern - a four-man crew with half the astronauts replaced every 30 days - would continue uninterrupted for a year.
|Program C: the Four-Room Space Station at maximum extent. Note the twin solar arrays extended from the sides of the Electrical Power Module (right). Please click to enlarge. Image credit: McDonnell/NASA|
Titan III could also launch a Gemini Transport and Supply Module together. McDonnell dubbed this combination the Gemini Supply Transport. A single Gemini Supply Transport would dock halfway through the Four-Room Space Station's year-long career as supplies launched with it ran low. The astronauts would pivot the Gemini Supply Transport to a mooring port shortly after it docked.
The Gemini Transport would detach from the Supply Module 60 days after docking. When it departed, it would expose a docking port on the Supply Module. This would become the Four-Room Space Station's alternate docking port.
The company acknowledged that little data existed concerning Starfish Prime radiation, but judged nonetheless that the mass of the shielding required to limit astronaut radiation exposure inside a One-Room Space Station in a 200-nautical-mile orbit to 1.93 rad per day would total about 1600 pounds. The 1.93-rad-per-day maximum exposure was based on limits proposed for Apollo lunar missions. The company also suggested a novel (but probably impractical) method for reducing station shielding mass: "personal shielding" for each astronaut, presumably in the form of a garment. This would weigh 160 pounds per astronaut.
McDonnell provided detailed cost estimates with its "Modular Space Station Evolving from Gemini" proposal. If NASA flew Programs A, B, and C, the cost would come to $194.2 million for development, $194.3 million for Program A, $185.9 million for Program B, and $462.8 million for Program C. The cost of Programs A, B, and C would thus total $843 million. If NASA flew A and C only, the development cost would remain the same, and the cost of the two Programs would total $657.1 million.
NASA's Project Gemini saw 10 manned missions launched on Titan II GLVs between March 1965 and November 1966. This made the program almost two years late if one adhered to McDonnell's optimistic 1962 timeline. Gemini III (Virgil Grissom and John Young, 23 March 1965) was a three-orbit manned test of the new spacecraft. At the end of their mission, Grissom and Young's Reentry Module lowered on a parachute and splashed down into the Atlantic. NASA had abandoned the parawing and land landings amid development difficulties in mid-1964.
|Ed White performs America's first space walk during Gemini IV, June 1965. Image credit: NASA|
|Proximity operations: Gemini VI performs rendezvous maneuvers with Gemini VII, December 1965. Image credit: NASA|
Gemini V (Gordon Cooper and Charles Conrad, 21-29 August 1965) remained in orbit for a week and Gemini VII (Frank Borman and James Lovell, 4-18 December 1965) stayed aloft for two weeks. Following the loss of its Agena docking target to an Atlas booster failure, Gemini VI (Walter Schirra and Thomas Stafford, 15-16 December 1965) performed rendezvous and proximity operations with Gemini VII.
The Gemini spacecraft docked by sliding its blunt nose into a funnel-shaped docking collar on the front of the Agena, triggering latches. Crew movement between the Gemini cockpit and the outer surface of the Agena was by spacewalk. Gemini VIII (Neil Armstrong and David Scott, 16-17 March 1966) became the first manned spacecraft to perform a docking, but then suffered a perilous thruster malfunction that forced an emergency splashdown, scrubbing Scott's planned spacewalk.
|Gemini VIII astronauts David Scott (left) and Neil Armstrong after their emergency return to Earth, March 1966. Image credit: NASA|
Gemini X (John Young and Michael Collins, 18-21 July 1966) docked with an Agena and used its rocket motor to rendezvous with the dead Gemini VIII Agena, thus accomplishing the world's first double-rendezvous. The mission drove home once again the challenges of walking in space.
Gemini missions XI (Charles Conrad and Richard Gordon, 12-15 September 1966) and XII (James Lovell and Edwin Aldrin, 11-15 November 1966) both performed rendezvous with an Agena and saw astronauts step outside to master spacewalk techniques. During their spacewalks, Gordon and Aldrin each tethered his Gemini to its Agena to perform artificial-gravity and spacecraft stabilization experiments.
By Gemini's end, NASA had a cadre of astronauts experienced in techniques required for Apollo lunar flights. NASA did not take up McDonnell's proposal for a Gemini-based space station skills-building program. Meanwhile, Department of Defense and White House interest in a USAF manned space program waxed and waned.
In December 1963, a year to the month after McDonnell sought to interest NASA in its "Modular Space Station Evolving from Gemini" proposal, the Gemini-based USAF Manned Orbiting Laboratory (MOL) program received approval. MOL bore a modest resemblance to both McDonnell's 1961 MTSS spacecraft and its Four-Room Space Station. The USAF selected three groups of MOL astronauts - a total of 17 men - in November 1965, June 1966, and June 1967.
|MOL refugees: NASA's Group 7 astronauts. From left to right they are Karol Bobko, Gordon Fullerton, Henry Hartsfield, Robert Crippen, Donald Peterson, Richard Truly, and Robert Overmyer. Image credit: NASA|
Even as MOL ended, NASA sought funding to develop a six- or 12-man core Space Station and a reusable Space Shuttle to resupply it and change out its crews. The space agency hoped that the Station might evolve into a 50- or 100-man Space Base with artificial gravity. NASA's station ambitions received little support, but the Nixon White House became interested in the Space Shuttle and made NASA accommodation of Defense Department spaceflight needs a condition for its approval as a stand-alone program (that is, with no Space Station). Eventually, all seven Group 7 astronauts would reach orbit on board Space Shuttle Orbiters.
Modular Space Station Evolving from Gemini, Report No. 9572, Volume I: Technical Proposal, McDonnell Aircraft Corporation, 15 December 1962
Modular Space Station Evolving from Gemini, Report No. 9572, Volume II: Proposed Program and Available Resources, McDonnell Aircraft Corporation, 15 December 1962
Gemini Summary Conference, SP-138, NASA Manned Spacecraft Center, Houston, Texas, NASA, 1967
On the Shoulders of Titans: A History of Project Gemini, SP-4203, 1977
The Problem of Space Travel: The Rocket Motor, SP-4026, Hermann Noordung (Herman Potočnik), E. Stuhlinger, J. Hunley, and J. Garland, editors, NASA, 1995
Space Station Resupply: The 1963 Plan to Turn the Apollo Spacecraft Into a Space Freighter
Spacewalks That Never Were: Gemini Extravehicular Planning Group (1965)
McDonnell Douglas Phase B Space Station (1970)