In 1960, most everyone who cared about such things knew what a space station was supposed to look like: it would take the form of a revolving wheel. The design, first portrayed in detail by Austrian Hermann Noordung in 1928, was popularized in the United States after the Second World War by Wernher von Braun in the pages of Collier's magazine and in a series of Disneyland "Tomorrowland" programs.

Wheel-shaped stations would revolve to create acceleration, which the crew on board would feel as gravity. This "artificial gravity" would be strongest at the station's outer rim and non-existent at its hub. Use of artificial gravity led to big station designs: this was because artificial-gravity stations of small radius would generate undesirable effects, such as a noticeable variation in the level of acceleration felt along a standing astronaut's body.

Soon after NASA opened for business on 1 October 1958, Langley Research Center (LaRC) took the lead in U.S. civilian space station development. Not surprisingly, the Hampton, Virginia-based laboratory emphasized wheel-shaped artificial-gravity stations. LaRC engineers built and ground-tested donut-shaped inflatable station modules. Meanwhile, several LaRC engineers developed and patented single-launch "self-deploying" or "erectable" large wheel-shaped station designs.

Level. Photo: PedalFreak/Flickr Prototype inflatable space station at NASA Langley Research Center c. 1962. Image: NASA

LaRC engineer Rene Berglund with models of his patented deployable artificial-gravity space station. Image: NASA

As LaRC labored toward space stations, the Space Task Group, an independent team of engineers based at LaRC, began work on Mercury, NASA's first manned spacecraft. NASA Headquarters, meanwhile, solicited proposals from industry for a post-Mercury spacecraft it dubbed Apollo. As originally conceived, Apollo was intended primarily as an Earth-orbital spacecraft capable of conveying astronauts to space stations. An Apollo circumlunar mission was a post-1970 goal.

This plan changed dramatically on 25 May 1961, when new President John F. Kennedy called upon NASA to land a man on the moon by 1970. Space station development was back-burnered, and Apollo became NASA's lunar landing spacecraft. After NASA opted for the Lunar-Orbit Rendezvous (LOR) moon landing mode in July 1962, Apollo's functions were split between two spacecraft: the Command and Service Module (CSM), capable of 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 forbidding surface and back again.

NASA soon recognized a need for a program that would enable astronauts to bridge the yawning spaceflight skills gap separating Mercury and Apollo. The lone Mercury astronaut could, for example, adjust only his spacecraft's attitude (the direction its nose pointed), not its orbit; the three-man Apollo crews would be called upon to conduct multiple significant orbit-changing maneuvers, including capture into and departure from lunar orbit. Apollo would also require rendezvous and docking maneuvers in lunar orbit and, in the event of docking difficulties, spacewalks between the LM and the CSM.

Initially dubbed Mercury Mark II, the two-man skill-building spacecraft was redesignated Gemini in January 1962. Gemini would partner with Agena, a modified upper stage, to provide its crews with rendezvous and docking experience. Gemini astronauts would also conduct spacewalks and remain in Earth orbit for up to two weeks to enable physicians to certify that Apollo crews could remain healthy for the duration of a lunar voyage. NASA planned for Gemini flights to occur in 1963 and 1964.

Drill bits. Photo: photobunny/Flickr Gemini rendezvous and docking with pre-launched Agena target. Image: NASA

Diagram of Gemini spacecraft. Image: NASA Diagram of Gemini spacecraft with modules and sections separated. Image: NASA

NASA tasked McDonnell Aircraft, Mercury prime contractor, with building Gemini. The new spacecraft would comprise two main modules: the Reentry Module bearing the crew and the Adapter Module containing the Orbital Attitude Maneuvering System (OAMS) and solid-propellant deorbit rockets. The latter would be located in the the Retrograde Section, the forward part of the Adapter, up against the Reentry Module heat shield.

Inside the berry. Photo: Ariel Zambelich/Wired Titan Intercontinental Ballistic Missile, the progenitor of the Titan launch vehicle family. Image: U.S. Air Force

As had Mercury and as would Apollo, Gemini would provide its crew with a pure oxygen atmosphere. Unlike Mercury or Apollo, Gemini would feature a jet fighter-style cockpit with forward facing windows and ejection seats. Electrical power would come from fuel cells, which would combine liquid oxygen and liquid hydrogen to produce potable water and electricity. Gemini would reach orbit on a modified U.S. Air Force (USAF) Titan missile. At the end of its mission, the Reentry Module would deploy an inflatable triangular parawing and glide to a controlled land landing on skids.

In the first half of 1961, McDonnell submitted a proposal for a Gemini-based military spacecraft as part of the USAF's Military Test Space Station (MTSS) study. In McDonnell's design, Air Force astronauts would reach a pressurized module attached behind their Gemini spacecraft by opening a hatch above and behind their ejection seats. The hatch would lead through the Gemini Reentry Module heatshield to a bent tunnel passing through the Adapter Module. The military spacecraft would include surveillance cameras and a powerful transtage rocket motor for large orbit changes and fast satellite inspection missions.

High-level uncertainty about the USAF role in manned spaceflight led McDonnell in December 1962 to peddle its Gemini station plans to NASA. The company proposed that the U.S. civilian space agency carry out a low-cost Gemini-based space station program that would include design features it had developed for MTSS. 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 space stations proposed provide. . .early capability to obtain answers to fundamental questions [at] modest cost.

If McDonnell had had its way, Gemini would have become for NASA's eventual large space station what it was already for Apollo. That is, it would have bridged the skills gap between short, weightless missions in small spacecraft and long missions on board large stations resembling, perhaps, LaRC's wheel-shaped artificial-gravity designs.

McDonnell's proposed evolutionary modular station program would include five basic building blocks: the Gemini Transport, which would serve as crew carrier and piloted space tug; the Supply Module; the One-Room Space Station; the Two-Room Space Station; and the Electrical Power Module. To trim costs, the Supply Module and One-Room Space Station would be structurally similar, and the Two-Room Space Station would resemble the Electrical Power Module. In addition, NASA would save money by recovering Gemini Transport Reentry Modules and returning them to McDonnell for refurbishment and reuse.

All these modules would measure 10 feet in maximum diameter, in keeping with the diameter of the Titan-derived rockets that would boost them to Earth orbit. McDonnell assumed two Titan variants for its proposed space station program: the two-stage Gemini Launch Vehicle (GLV) (better known as the Titan II) and the Standard Launch Vehicle (SLV) 624A-C (better known as the Titan III). The latter would comprise a modified two-stage GLV core, twin strap-on solid-propellant booster rockets, and a restartable transtage upper stage.

The GLV, capable of launching 7390 pounds into a 87-by-200-nautical-mile orbit, would loft single spacecraft and modules. The Gemini Transport, Supply Module, One-Room Space Station, and Two-Room Space Station would fall within its capability.

The SLV 624A-C, on the other hand, would be capable of placing 25,280 pounds into a 250-nautical-mile circular orbit or 26,000 pounds into a 100-by-250-nautical-mile orbit. This would permit it to launch module combinations: the Gemini Supply Transport (Gemini Transport plus Supply Module) and the Gemini Transport plus Four-Room Space Station (Two-Room Space Station plus Electrical Power Module).

McDonnell expended considerable in-house time and effort to develop a feasible rendezvous and docking system. The company ultimately settled on having the Gemini Transport "back up" to dock.

Because the Gemini Transport would use the nose-mounted Gemini rendezvous radar, it would first approach with its twin forward-facing windows pointed toward its target. Then, at a distance of 10,000 feet, the co-pilot would unstrap from his seat, twist around in the tight confines of the Gemini Transport cockpit, and open the 27.5-inch-diameter pressure and heatshield hatches above and behind his and the pilot's seats. He would squeeze through a 24.5-inch-diameter opening in the heatshield to enter a 32-inch-diameter tunnel in the Adapter Module. The tunnel would lead to a rear-facing Crew Docking Station.

The pilot, meanwhile, would turn the Gemini Transport end-for-end to point the flat rear of its Adapter Module at the target. The co-pilot would sight the target through a small rear-facing window above the docking control console and then would commence a "semi-manual" final approach employing the OAMS maneuvering thrusters and six docking thrusters. Approach from 10,000 feet would need 10 minutes, McDonnell estimated, during which time the Gemini Transport would slow from a speed of 100 feet per second to zero relative to its target.

McDonnell proposed a "ring-and-fork" docking system. The co-pilot would line up a roughly nine-foot-diameter ring on the rear of the Adapter Module with four equidistantly spaced two-prong forks on the target. The ring would slide along the inner surfaces of the prongs, canceling out any misalignment between spacecraft and target, then would trip latches on the forks to achieve soft docking. Finally, the forks would retract, pulling hatches on the Gemini Transport and its target securely together.

Gemini Transport (left) docked with One-Room Space Station (right). Image: McDonnell Aircraft Corporation/NASA Gemini Transport (left) docked with separately launched One-Room Space Station (right). Image: McDonnell/NASA

McDonnell outlined a series of increasingly complex Gemini-based space station missions. These would begin in 1965, immediately after the baseline Gemini Program was completed, with a series of three two-man One-Room Space Station missions lasting 30, 45, and 60 days, respectively. The company dubbed this series Program A. It based its development schedule on NASA approval in February 1963.

Astronaut activities on board the One-Room Space Stations would emphasize space medicine, station housekeeping, and science, 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 a pressure of five pounds per square inch, 548 cubic feet of pressurized volume, and a ceiling height of seven feet. The station's 36 square feet of clear floor space would be covered with velcro so that the astronauts, who would wear velcro slippers, could anchor themselves in weightlessness.

For the 30-day first mission, a GLV would launch a 7390-pound One-Room Space Station into an initial 87-by-200-nautical-mile orbit, then another would launch a Gemini Transport. The latter would dock with the former, then the combination would maneuver to a 200-nautical-mile circular orbit. This approach - making the Gemini Transport responsible for orbit circularization - would help to maximize the GLV's payload capacity. The two astronauts would work on board the One-Room Space Station for 30 days. They then would undock in their Gemini Transport, cast off the aft section of its Adapter Module, and fire its Retrograde rocket motors to decrease its orbital velocity and fall back to Earth. The Gemini Transport Retrograde section would include five retrograde motors; that is, one more than the standard Gemini. Following a fiery atmosphere reentry, the Reenty Module would deploy its parawing and glide to a land landing.

The second One-Room Space Station mission would see early 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 a 200-nautical-mile-high circular operational orbit.

Artificial-gravity experiment. The "station module" (left) comprises a Gemini Transport and a One-Room Space Station, while the "counterbody module" is the spent Titan II second stage that launched the One-Room Station. Image: McDonnell/NASA

After settling into their new home, the astronauts would detach the GLV second stage and pay out a cable linking it to the One-Room Space Station. Full extension would require between five and six hours, McDonnell estimated. 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 Gemini Transport. Because the mass of the GLV second stage (5800 pounds) would be less than half that of the Gemini Transport/One-Room Space Station combination (about 14,000 pounds), the center of rotation would be located closer to the Gemini Transport/One-Room Space Station (150 feet) than to the GLV stage (362 feet). To halt the artificial-gravity test, the crew would reverse the cable-extension procedure.

McDonnell described other artificial-gravity experiments that might take place in its proposed program. The most complex would involve a pair of Four-Room Space Stations, each with a Supply Module and two Gemini Supply Transports attached. These would be of nearly equal mass and would be separated by approximately 300 feet of cable. The company proposed methods by which a Gemini Transport could safely dock with or undock from a revolving station and calculated the effects on stable rotation of crew movements within the station over time.

The third and final One-Room Space Station mission, which would occur before or during 1966, would last for 60 days, but would otherwise resemble the first. The crew's two-month orbital stay would pave the way for four men to live for 60 days on board a Two-Room Space Station during the Gemini-based station program's second phase.

Altitude sickness: the Himalaya watch, Everest Edition Photo: Courtesy of Kobold Two-Room Space Station. Its first two-man crew would arrive in orbit in the Gemini Transport and would dock with the station's single docking port. After the astronauts entered the station, they would use mooring arms to swing the Gemini Transport to one of a pair of side-mounted mooring ports, freeing the docking port for new arrivals. Image: McDonnell/NASA

McDonnell envisioned that the Two-Room and Four-Room station programs, which it dubbed Program B and Program C, respectively, would both receive preliminary approval in January 1965, and that NASA would in January 1966 choose to fly Program B and Program C in succession or to skip directly to Program C after Program A. If the latter option were selected, McDonnell assumed that NASA would wish to fly a fourth One-Room Space Station in August 1966 to bridge the gap between the third Program A station launched in early 1966 and the Program C station launched in early 1967.

Assuming that NASA opted to fly Program B, however, in mid-1966 a 7390-pound Two-Room Space Station would climb to an elliptical orbit on a GLV. 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 that would increase the Two-Room Space Station's population to four, the first crew would pioneer a new space station technique. They would extend mooring arms to grip fixtures on their spacecraft, disengage the docking fork latches, and swing their Gemini Transport into alignment with one 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. As with the larger docking forks, these would then retract, pulling the Gemini Transport and Two-Room Space Station firmly together.

Like the One-Room Space Station, the Two-Room Space Station would use fuel cells to make electricity; unlike its predecessor, it would be capable of being resupplied. The third GLV launch of the first Two-Room Space Station mission would place the program's first 7390-pound Supply Module into an elliptical initial orbit. Of its mass, 3992 pounds would comprise supplies and equipment for the Two-Room Space Station. The Supply Module would be the key to making possible launch of the Two-Room Space Station on a GLV; it would permit NASA to place the station into orbit with little experiment equipment on board and with supplies adequate only for two men for 30 days, thereby minimizing its launch mass.

The Supply Module's front end would include four docking forks and a hatch, while its aft end would include a docking ring, a hatch, and a rear-facing Crew Docking Station with window. After the Supply Module reached orbit, a Gemini Transport would lift off to rendezvous and dock with it. The Gemini Transport/Supply Module combination would then rendezvous with the Two-Room Space Station. The co-pilot would guide the Gemini Transport/Supply Module to a docking with the Two-Room Space Station using docking controls in the Supply Module. The astronauts would enter the Two-Room Space Station through the Supply Module hatch, then would extend mooring arms to pivot the Gemini Transport/Supply Module combination to the Two-Room Space Station's second mooring port, on the side opposite the Gemini Transport that delivered the first two crewmembers.

Arrival of a third Gemini Transport at the Two-Room Station's docking port would mark the beginning of the first Two-Room Space Station's final operations. After a brief period during which the Two-Room Space Station would house six astronauts, the first crew would undock in their Gemini Transport and return to Earth. The second crew would subsequently undock from the Supply Module, which would remain attached to the Two-Room Space Station to serve as a "pantry" and to provide additional living and working space. Finally, the third crew would undock from the Two-Room Space Station's docking port and return to Earth.

The advent of the man-rated SLV 624A-C rocket would spell important changes for McDonnell's proposed program. The SLV 624A-C would be powerful enough to launch into a circular 250-nautical-mile-high orbit a payload comprising a Gemini Transport with two astronauts, a Two-Room Space Station without fuel cells and fuel-cell consumables, and a two-room Electrical Power Module with twin solar-array wings and storage batteries. The Two-Room Space Station and Electrical Power Module would be bolted together on the ground to create the Four-Room Space Station, which would be capable of supporting a four-man, one-year mission with 60-day crew stays and partial crew rotation every month.

Four-Room Space Station at maximum extent. Image: McDonnell/NASA Four-Room Space Station at maximum extent. Image: McDonnell/NASA

Gemini Supply Transport made up of lightly modified Gemini Transport (left) and Supply Module spacecraft. The stippled area marks the bent tunnel linking the Gemini Transport cockpit with the Supply Module. Image: McDonnell/NASA

Deletion of fuel-cell consumables would permit the Four-Room Station to reach orbit fully equipped with experiment apparatus and loaded with supplies adequate to support four men for six months. The SLV 624A-C could also launch a Gemini Transport/Supply Module together. McDonnell dubbed this combination the Gemini Supply Transport. Modifications to the Gemini Transport for its Gemini Supply Transport role would include deletion of the aft-mounted docking ring, docking piloting station, and docking viewport.

Ten GLV-launched Gemini Transports would dock with the Four-Room Space Station. A single SLV 624A-C-launched Gemini Supply Transport would dock bearing life support consumables, food, and other supplies halfway through the Four-Room Space Station's year-long career. The crew would pivot the Gemini Supply Transport to a mooring port. After its Gemini Transport component undocked from it, the Supply Module docking port would become the second docking port for the Four-Room Space Station.

McDonnell gave special attention to the effects of the space environment on astronauts and equipment. Among features of the space environment it examined was the Earth-circling "artificial radiation belt" that the July 1962 Starfish Prime space nuclear test had created. The company acknowledged that little data existed concerning Starfish Prime radiation, but judged nonetheless that the shielding required to limit astronaut radiation exposure to 1.93 rad per day on a One-Room Station in a 200-nautical-mile-high orbit would weigh 1600 pounds. The 1.93 rad per day radiation exposure limit was based on the exposure 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 crewman.

The company provided detailed cost estimates for its modular station program. If NASA flew Program 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. If it flew A and C only, the development cost would remain the same, and the program cost would total $657.1 million.

NASA's Project Gemini saw 10 manned missions launched 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, March 23, 1965) was a three-orbit manned test of the new spacecraft. At the end of their mission, Grisssom and Young's Reentry Module lowered on a parachute and splashed down at sea: NASA had abandoned the parawing in mid-1964.

The view of Gemini VII from Gemini VI. Image: NASA

During Gemini IV (James McDivitt and Ed White, 3-7 June 1965), Ed White became the first American to walk in space. His successful simple spacewalk deceived planners, causing them to postpone more complex spacewalks in favor of long-duration and rendezvous and docking missions.

Gemini V (Gordon Cooper and Pete Conrad, 21-29 August 1965) remained in orbit for a week and Gemini VII stayed aloft for two weeks (Frank Borman and Jim Lovell, 4-18 December 1965). Following the loss of its docking target (an unmanned Agena rocket stage) when its Atlas booster malfunctioned, Gemini VI (Wally Schirra and Tom Stafford, 15-16 December 1965) performed rendezvous and proximity operations with Gemini VII.

After splashdown: Gemini VIII astronauts Neil Armstrong (right) and David Scott following their harrowing flight. Image: NASA Gemini VIII astronauts Neil Armstrong (right) and David Scott await recovery after their emergency splashdown. Image: NASA

The Gemini spacecraft docked by sliding its blunt nose into a funnel-shaped sleeve 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 OAMS thruster malfunction that forced an emergency landing, scrubbing a planned spacewalk. Gemini IX (Thomas Stafford and Eugene Cernan, 1-11 June 1966) attempted to dock with an ad hoc target vehicle following the loss of its Agena target to an Atlas booster failure, but found its way blocked by a jammed launch shroud. Cernan's attempt to perform a complex spacewalk using a USAF-developed rocket backpack was also less than successful.

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 also drove home again the unanticipated challenges of walking in space. Gemini missions XI (Pete Conrad and Dick Gordon, 12-15 September 1966) and XII (Jim Lovell and Edwin Aldrin, 11-15 November 1966) each performed rendezvous with an Agena and saw astronauts step outside to perfect new spacewalk techniques. During their spacewalks, Gordon and Aldrin each tethered his Gemini to an Agena to perform artificial-gravity and spacecraft stabilization experiments.

Gemini XI launch. Image: NASA Gemini XI launch. Image: NASA

By Gemini's end, NASA had a cadre of astronauts experienced in techniques required for Apollo lunar flights. 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 McDonnell's 1961 MTSS spacecraft.

Six and a half years later (June 1969), with more than $300 million spent, Defense Secretary Melvin Laird cancelled the project in favor of automated surveillance satellites. Eight MOL astronauts subsequently transferred to NASA and went to work at the Manned Spacecraft Center in Houston. Seven formed the seventh group of NASA astronauts, and one (Albert Crews) became a pilot for the Flight Crew Operations Directorate.

Bellcomm, NASA's Washington, DC-based Apollo and advanced planning contractor, sought to revive the concept of a low-cost Gemini-based space station program in 1968, as NASA's attention turned increasingly toward post-Apollo goals. Bellcomm offered its Gemini-based program not as a bridge to a large station, but as a realistic alternative to NASA's plans. At the time, some in NASA aimed to build a six-to-nine-man station despite clear indications that post-Apollo goals of any kind enjoyed little support from the White House, Congress, and public.

A year later, with the political environment no less inimical, NASA sought funding to develop even larger stations serviced by reusable logistics supply vehicles. NASA's station ambitions still received little support, but the Air Force and Nixon White House became interested in the reusable manned spacecraft concept. This marked the genesis of the Space Shuttle. Eventually, all seven Group 7 astronauts would reach orbit on board Shuttle Orbiters.

References:

Modular Space Station Evolving from Gemini, Report No. 9572, Volume I: Technical Proposal, McDonnell Aircraft Corporation, December 15, 1962.

Modular Space Station Evolving from Gemini, Report No. 9572, Volume II: Proposed Program and Available Resources, McDonnell Aircraft Corporation, December 15, 1962.