Space Station Gemini (1962)

Herman Potočnik's 1928 Wohnrad ("living wheel") space station design. Image credit: NASA.

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 in 1928 by Austro-Slovenian Herman Potočnik, was popularized in the United States after the Second World War by Wernher von Braun in the pages of the popular Collier's weekly magazine and through a series of Walt Disney "Tomorrowland" television programs.

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.

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 NASA laboratory emphasized artificial-gravity designs. For example, LaRC engineers built and ground-tested experimental doughnut-shaped inflatable stations.

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.

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

Cutaway illustration of a Gemini spacecraft displaying its forward-facing windows, ejection seats, nose-mounted rendezvous radar and parachutes, retrograde rocket motors for reentry, and propellant tanks for attitude control and orbit-changing maneuvers. Image credit: NASA.

Initially dubbed Mercury Mark II, the two-man skill-building spacecraft was formally named Gemini in January 1962. NASA planned to conduct Project Gemini flights in 1963 and 1964; that is, immediately after Project Mercury's planned conclusion.

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.

NASA partnered the Gemini spacecraft with Agena, a separately launched upper stage with a docking collar, so that U.S. astronauts could gain rendezvous and docking experience. Project Gemini astronauts would also conduct spacewalks and remain aloft in Earth orbit for up to two weeks to permit physicians to certify that Apollo crews could remain healthy for the duration of a lunar voyage.

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.

In the first half of 1961, McDonnell submitted a proposal as part of the USAF's Military Test Space Station (MTSS) study. The McDonnell MTSS design consisted of a Gemini spacecraft and a pressurized module with a powerful transtage rocket motor attached to it. The module would have added volume and functionality to Gemini, much as the Mission Module would have done for Apollo.

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.

All of McDonnell's modules would measure 10 feet in maximum diameter, in keeping with the diameter of the Titan rockets that would boost them to Earth orbit. McDonnell assumed two Titan variants for its proposed program: the two-stage Titan II GLV and the Standard Launch Vehicle 624A-C (Titan III). The Titan III would comprise a modified two-stage Titan II core, twin strap-on solid-propellant boosters, and a restartable upper stage.

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.

The command 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 window above a docking control console, then would commence a "semi-manual" final approach employing the six docking thrusters. Similar thrusters on the One-Room Space Station would ensure its stability during docking. McDonnell estimated that approach from 10,000 feet would need about 10 minutes, during which time the Gemini Transport would slow from a speed of 100 feet per second to zero relative to its target.

Gemini Transport (left) docked with a One-Room Space Station. Image credit: McDonnell/NASA.

McDonnell proposed a "ring-and-fork" docking interface. The co-pilot would line up a roughly nine-foot-diameter ring on the rear of the Gemini Transport 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 where the prongs met to form the forks. Tripping the latches would constitute soft docking. Finally, the forks would retract, pulling hatches on the Gemini Transport and its target securely together to accomplish hard docking.

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.

After settling into their new home, the two 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 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. 

Like Program A's One-Room Space Stations, Program B's Two-Room Space Station would rely on fuel cells for electricity. Unlike its predecessors, it could be resupplied. The third GLV launch of Program B would place the first 7390-pound Supply Module into an elliptical orbit. The Supply Module would be crucial for making possible launch of the Two-Room Space Station on a GLV. Of the Supply Module's mass, 3992 pounds would constitute supplies and equipment for outfitting the Two-Room Space Station in orbit.

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.

The command pilot would turn the combination end-for-end, then the pilot would guide the Gemini Transport/Supply Module combination to a docking with the Two-Room Space Station. 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 Station's first two astronauts.

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.

Deletion of fuel-cells and their reactants would permit the Four-Room Station to reach orbit fully equipped with experiment apparatus and loaded with enough supplies to support four men for six months. Ten GLV-launched Gemini Transports would dock with the Four-Room Space Station during Program C.

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.

Although this image portrays the Gemini Supply Transport used in Program C, it contains details that apply to other modules and to Programs A and B. The stippled area marks the bent tunnel linking the Gemini cockpit with the pressurized part of the Supply Module. Please click to enlarge. Image credit: McDonnell/NASA.

McDonnell gave attention to the effects of the space environment on astronauts and equipment in its proposal to NASA. Among features of the space environment it examined was the Earth-circling "artificial radiation belt" 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 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.

During Gemini IV (James McDivitt and Edward 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 complex spacewalks in favor of Gemini long-duration and rendezvous-and-docking missions.

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 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 another Atlas booster failure, but found their 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 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.

Six and a half years after it began (10 June 1969), with more than $300 million spent, President Richard Nixon cancelled MOL in favor of less costly automated surveillance satellites. Eight MOL astronauts subsequently transferred to NASA and went to work at the Manned Spacecraft Center (MSC) in Houston, Texas. MSC had formed around the STG, which had split away from NASA LaRC and moved to Houston in 1962-1963. Seven of the eight formed the seventh group of NASA astronauts, and one (Albert Crews) became an aircraft pilot for the MSC Flight Crew Operations Directorate.

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.

Sources

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.

More Information

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)

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

President John F. Kennedy messes up NASA's carefully wrought long-range plans, 25 May 1961. Image credit: NASA.

When first proposed in 1959, the spacecraft that would come to be known as the Apollo Command and Service Module (CSM) was envisioned as an Earth-orbital "advanced manned spacecraft" capable of being uprated for circumlunar or lunar-orbital flights. On 15 November 1960, NASA awarded six-month feasibility study contracts for just such an Apollo spacecraft to three contractors: the Martin Company; the Convair Division of General Dynamics; and the General Electric Company Defense Electronics Division, Missile and Space Vehicle Department.

In 1960, the three-man Apollo spacecraft was expected to be the second U.S. piloted spacecraft after the Mercury capsule. It would include a Command Module (CM), a Service Module (SM), and an Orbital Module; the last of these would augment the work and living space available to the crew, in effect making the spacecraft into a mini-space station.

NASA expected that its piloted program in the 1960s would proceed down one or both of two "logical" paths, and that Apollo would be crucial for both. The first path would have Apollo spacecraft transport crews to a temporary "orbiting laboratory." The Orbital Module would be used to transport supplies to the lab in space. The other path would see an Apollo perform a piloted flight around the moon. What might come after 1970 was anybody's guess, though NASA expected that the orbiting lab path would lead to a permanent Earth-orbiting space station and the circumlunar path would trend toward to a piloted Moon landing, piloted Mars and Venus flybys, and a piloted Mars landing.

Apollo as a fork in the road: NASA's plans for piloted spaceflight in 1959. Image credit: NASA.

Martin, General Dynamics, and General Electric submitted their final study reports to NASA on 15 May 1961. Ten days later, new President John F. Kennedy wreaked havoc on NASA's logical plans when he opted to proceed directly to a lunar landing before 1970.

Stinging from the failed Bay of Pigs invasion of Cuba and the first piloted spaceflight by Soviet cosmonaut Yuri Gagarin (12 April 1961), Kennedy had asked Lyndon Baines Johnson, his Vice President and National Space Council chair, to propose a space goal that the U.S. might reach ahead of the Soviet Union. The apparent Soviet advantage in launch vehicle capability would, it was believed, give communist rocketeers a head-start if the goal was anything as modest as the establishment of an Earth-orbiting space station. Landing a man on the Moon, on the other hand, was a goal audacious enough that the U.S. and Soviet Union would start out more or less evenly matched.

Model of the Apollo Command and Service Module atop a conceptual Landing Propulsion Module. Image credit: NASA.

On 28 November 1961, NASA awarded North American Aviation (NAA) the contract to build the Apollo CSM, the design of which included two modules: the conical CM and the drum-shaped SM. The method by which NASA would carry out President Kennedy's bold lunar mandate remained uncertain, though it was widely assumed that the space agency would soon award a contract for a third Apollo spacecraft module: a Landing Propulsion Module for lowering the CSM to a gentle touchdown on the Moon. NAA went so far as to specify in its April 1962 subcontract with Aerojet General Corporation that the CSM's Service Propulsion System (SPS) main engine be capable of generating enough thrust to launch the CSM off of the lunar surface and place it on course for Earth.

As it turned out, however, the Apollo CSM would never land on the moon. On 11 July 1962, as part of an ongoing debate that was not finally settled until November of that year, NASA selected the Lunar-Orbit Rendezous (LOR) mode for accomplishing the Apollo mission. A contract for a third Apollo module was indeed awarded (to Grumman Aircraft Engineering Corporation, 7 November 1962), but it was for the Lunar Excursion Module (LEM), a bug-like two-man spacecraft that would undock from the CSM in lunar orbit and lower to a landing on the Moon. The Apollo CSM thus became the mother ship for delivering astronauts and LEM to lunar orbit and returning astronauts and Moon rocks to Earth.

Despite President Kennedy's new high-priority moon landing goal, space station studies within NASA did not cease. In fact, some believed that NASA might launch its first station into Earth orbit before an astronaut stepped onto the Moon. They reasoned that lunar landing program development costs would peak two or three years before NASA launched its first lunar landing attempt (as in fact they did). If NASA's portion of the Federal purse remained near its peak as Moon program costs declined, then funds might become available for a station in Earth orbit as early as 1968.

At the newly established NASA Manned Spacecraft Center (MSC) in Houston, Texas, engineer Edward Olling headed up space station planning. He informally named MSC's first proposed station program Project Olympus.

In April 1962, Olling circulated a draft planning document within MSC for comment; then, on 16 July 1962, he unveiled to top-level MSC managers his "Summary Project Development Plan" for the Project Olympus space station program. Olling envisioned a series of four 24-man stations launched and continuously staffed over a period of from five to seven years.

Olling explained that the Project Olympus space stations would provide NASA with enough astronauts, scientific equipment, pressurized volume, and electrical power to carry out wide-ranging basic and applied science research in space. Early station research would, however, seek to answer important questions about the efficacy of humans in space; for example, could astronauts work safely and effectively in orbit for long periods?

Image credit: NASA.

Each 138,600-pound Project Olympus station would consist of a 15,000-cubic-foot central hub from which would radiate three evenly spaced arms with a total of about 35,000 cubic feet of volume. The hub would include a hangar for crew and supply spacecraft. Each arm would include a pressurized crew module of oval cross-section with two cylindrical access tunnels. The Project Olympus station would launch atop a two-stage Saturn V rocket with its hub on top and its three radial arms folded below. Once in orbit, the station would separate from the Saturn V second stage and the three arms would hinge upward and lock into place. Pressurized tunnels would link each arm to the station hub.

Small rocket motors at the ends of the arms would ignite to spin the station. The 150-foot-wide Project Olympus station would revolve four times per minute to create acceleration in its arms which the crew inside would feel as gravity. "Down" would be away from the hub.

The crew decks farthest from the hub would experience the greatest acceleration: the equivalent of one-quarter of Earth's gravitational pull, or about midway between lunar and martian surface gravity. Decks closer to the hub would experience less acceleration, so might be used mainly for storage. Olling hinted that the different levels of acceleration experienced at varying distances from the hub might be useful for scientific research, though he did not explain how.

Cutaway drawing of a Project Olympus-type space station. The centrifuge in lower part of the hub would support variable gravity experiments. Not shown is a station power system; NASA MSC proposed both solar- and nuclear-powered station designs. Image credit: North American Aviation/NASA.

New research objectives would be added over time as old stations were retired and new ones launched. The Project Olympus stations would become space-environment research facilities, "national laboratories" for research into meteorology, geophysics, radio communications, navigation, and astronomy, as well as "orbital operations" platforms (that is, shipyards for preparing spacecraft bound for points beyond space station orbit).

Olling advised MSC management that Project Olympus stations should operate in circular 300-nautical-mile-high orbits inclined 28.5° relative to Earth's equator — what he called a "Mercury orbit" because it matched the orbital inclination of the one-man Mercury capsules. Astronaut Scott Carpenter orbited Earth for nearly five hours in the Aurora 7 capsule on 24 May 1962, while Olling prepared his project plan. Olling later lowered his recommended altitude to 260 nautical miles.

The 28.5° latitude of the launch pads at Cape Canaveral, Florida, determined the orbital inclination of the Project Olympus stations. Matching launch-site latitude and station orbital inclination would maximize both station mass and the mass of the payload that could be delivered to the station. Olling also mentioned (albeit briefly) the possibility of a polar-orbiting Project Olympus station that would pass over all points on Earth.

In April 1963, MSC awarded NAA a contract for a seven-month study of a Modified Apollo (MODAP) logistics spacecraft for delivering astronauts and cargo to Project Olympus space stations. The Apollo CSM design had yet to reach its final form. No docking unit design had been selected, for example, though the probe-and-drogue system eventually chosen was already the leading candidate. The overall CSM layout was, however, firmly in place, giving NAA a meaningful point of departure for its MODAP study.

Apollo 15 Command and Service Module Endeavor in lunar orbit. Image credit: NASA.

The Apollo CM included three astronaut couches, control consoles, small windows at strategic locations, a side-mounted hatch with a window, a docking tunnel and parachutes in its nose, thrusters for orienting it for atmosphere reentry, and, at its base, a bowl-shaped reentry heat shield. Umbilicals and cables in a hinged housing linked the CM to the SM.

The Apollo SM included seven major internal bays. A central cylindrical bay housed tanks of helium pressurant for pushing rocket propellants into the SPS main engine. Arrayed around the central compartment were six triangular bays containing tanks of fuel and oxidizer for the SPS and for four attitude-control thruster quads, electricity- and water-making fuel cells, and tanks of liquid oxygen and liquid hydrogen reactants for supplying the fuel cells.

The MODAP CSM would comprise a stripped-down SM and a beefed-up CM. Because it would spend a limited amount of time in free flight before it docked with an Earth-orbiting station, the MODAP SM could dispense with or minimize many Apollo lunar SM systems. Batteries would replace fuel cells, for example, and a compact LEM descent engine could replace the SPS. The LEM engine would draw its propellants from a pair of spherical tanks in the MODAP SM's central cylindrical compartment. These deletions and additions would free up four of the MODAP SM's triangular bays for cargo transport.

The Apollo SM had six roughly triangular bays arrayed around a cylindrical core. The bays contained propellants, fuel cells, and liquid hydrogen and liquid oxygen tanks, among other systems necessary for a lunar mission. For its Earth-orbital station logistics missions, the MODAP SM needed fewer systems and tanks, so could devote four of the six triangular bays to cargo. The section image at right displays the cargo and equipment bays and a possible arrangement for four cargo doors. Image credit: North American Aviation/NASA.

A two-stage Saturn IB rocket capable of placing 32,500 pounds into a 105-nautical-mile circular parking orbit at 28.5° of inclination would launch the MODAP CSM. Pre-launch preparation, launch operations, and ascent to parking orbit would need from five to 10 days, from five to eight hours, and 11 minutes, respectively.

The MODAP CSM would remain in parking orbit for less than five hours before its crew ignited its LEM descent engine to place it into an elliptical transfer orbit with a 260-mile apogee (highest point above the Earth). Upon reaching apogee 45 minutes later, its crew would again ignite the engine to circularize its orbit. Subsequent station rendezvous and docking maneuvers might need up to 17.5 hours.

The company calculated that a 24-man station with crew stays lasting six months would need to receive a MODAP CSM bearing six astronauts and 5855 pounds of supplies eight times per year — that is, every 45 days. The typical cargo manifest would include 1620 pounds of food, 1035 pounds of oxygen, 505 pounds of nitrogen, 1450 pounds of propellants, and 1245 pounds of spare parts. The Project Olympus station would recover and reuse all water launched with it, so would have no need of water resupply.

These cutaway drawings of the Project Olympus hangar display internal (right) and external palletized cargo transfer methods. The internal method assumes that the entire MODAP CSM can fit into the hangar. The drawing at left shows how the protruding MODAP SM would separate from the MODAP CM and pivot into cargo-unloading position. MODAP CMs for Earth-return are docked radially on the dome-shaped docking hub near the floor of the hangar. Image credit: North American Aviation/NASA.

Supplies would reach the Project Olympus station in drum-shaped Cargo Modules, or CAMs, packed in the four empty triangular MODAP SM bays. The mass of the empty CAMs would total 1970 pounds. Liquid and gaseous cargo would fill small CAMs, while solid cargoes would ride on disc-shaped pallets in large CAMs. In all, a MODAP CSM could transport 9127 pounds of cargo and CAMs.

The MODAP CSM would dock with the Project Olympus station via an axial docking unit at the bottom of the station hangar. NAA envisioned that the station would include either a tall hangar for the entire MODAP CSM or a short hangar for the MODAP CM alone (in which case the MODAP SM would protrude into space). If the former, then CAM transfer could occur entirely within the hangar. If the latter, then CAM transfer would occur external to the station. In both cases, after all cargo was transferred, the MODAP SM would be cast off and the hangar closed to protect the MODAP CM.

These cutaway drawings of the Project Olympus station hangar show CAM internal (right) and external transfer methods. Compare with palletized transfer drawings above. Image credit: North American Aviation/NASA.

To free up the single axial docking port for the next MODAP CSM, a manipulator arm inside the hangar would pivot the MODAP CM to one of three radial berthing ports. It would remain parked there, undergoing periodic inspection and maintenance but otherwise dormant, for up to six months.

Discarding the MODAP SM with its LEM descent engine meant that the MODAP CM would need to carry a separate de-orbit propulsion module. NAA proposed a cluster of six solid-propellant retrorockets, any five of which could deorbit the MODAP CM. The retro package would include batteries for powering the MODAP CM during free-flight prior to reentry. NAA expected that, in normal circumstances, the MODAP CM would need 30 minutes for checkout and undocking. The MODAP CM's crew would ignite its retrorockets immediately after it maneuvered clear of the hangar.

The MODAP CM with solid-propellant retropack. Image credit: North American Aviation/NASA.

Twenty-five minutes after retrofire and shortly after retropack separation, the MODAP CM would reenter Earth's atmosphere. Because the MODAP CM would encounter the atmosphere moving at about half the speed of the Apollo lunar CM, its heat shield could be about half as thick. Descent and splashdown would need 11 minutes. With six astronauts on board, the MODAP CM would be heavier than the lunar CM, so would lower on four parachutes; that is, one more than the lunar CM. Its crew could splash down safely if one parachute failed.

Under normal circumstances, the MODAP CM would splash down in the Gulf of Mexico not far from Houston, so crew recovery would take place within a few hours. NAA acknowledged, however, that emergencies might occur. Because of this, the MODAP CM could fly free of the space station for up to 10.5 hours while its inclined orbit and Earth's rotation put it on course for reentry and splashdown at any of three sites. These were the prime site in the Gulf of Mexico, a site near Okinawa in the western Pacific Ocean, and one near Hawaii. To trim costs, fleets of recovery ships would not remain on standby at the landing sites; because of this, the astronauts might need to wait for up to 24 hours for rescue following an emergency splashdown near Okinawa or Hawaii.

An abort during ascent to Earth orbit could cause the Apollo and MODAP CMs to land in southern Africa; that is, to touch down on land. To protect its three-man crew during a land landing, the lunar CM would include shock absorbers in its supporting seat struts. These would enable the crew couches to move vertically up to five inches to dissipate the force of impact.

A tight fit: six-man MODAP Command Module seating arrangement. Image credit: North American Aviation/NASA.

Because the MODAP CM would carry six men arrayed in two rows of three couches each, with one row above the other, NAA found that vertical couch movement would not be an option. The three-man lunar CM would also rely on crushable material behind its heat shield to absorb the force of land impact; this would be inadequate for the greater mass of the six astronauts in the MODAP CM.

NAA proposed to solve the emergency land-landing problem by in effect moving the shock absorbers from the seat struts to the MODAP CM's heat shield and by adding four solid-propellant landing rockets. In the event of a land landing, the bowl-shaped heat shield would deploy downward on shock-absorbing struts and the landing rockets would ignite and pivot out from behind the shield.

NAA envisioned a MODAP CSM design & test program spanning from early 1964 to mid-1968. Operational MODAP CSMs would deliver crews and supplies to 24-man Project Olympus stations between mid-1968 and the end of 1973. The company anticipated that five MODAP CSMs would be used in ground tests and unmanned test flights, and that 40 MODAP CSMs would support the station program. Of these, perhaps two would fail, requiring assembly of at least two backup MODAP CSMs. NAA placed the total cost of the MODAP CSM program including $861 million for Saturn IB rockets at $1.881 billion.

A significant outcome of Olling's Project Development Plan and NAA's MODAP study was the realization that space station crew rotation and resupply would dominate total space station program cost. Summing up his findings, Olling wrote that a "reusable launch vehicle could contribute large economies" (that is, ensure large cost savings) for the station program. Even if four space stations were launched on expendable Saturn V rockets during the Project Olympus program, station cost would total only $1.273 billion; that is, about $600 million less than the MODAP CSM flights.

The Project Olympus and MODAP CSM study teams were not alone in reaching these conclusions; thus, as early as 1963, a reusable logistics spacecraft came to be seen as a desirable component of a large space station program. By 1968, this led to calls by high-level NASA management for a 1970s Space Station/Space Shuttle program.

Sources

Final Technical Presentation: Modified Apollo Logistics Spacecraft, Contract NAS 9-1506, North American Aviation, Inc., Space and Information Systems Division, November 1963.

"Project Olympus: Proposed Space Station Program," Edward H. Olling, NASA Manned Spacecraft Center, 16 July 1962.

More Information

A Bridge from Skylab to Station-Shuttle: Interim Space Station Program (1971)

One Space Shuttle, Two Cargo Volumes: Martian Marietta's Aft Cargo Carrier (1982)

After EMPIRE: Using Apollo Technology to Explore Mars and Venus (1965)

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

Apollo 4, the first Saturn V rocket to fly, departs the Vertical Assembly Building bound for Pad 39A, 26 August 1967. LUT 1 rides beside the rocket on a crawler-transporter; a second LUT in the background awaits its first launch. Image credit: NASA.

A red-painted Launch Umbilical Tower (LUT) was the Saturn V's constant companion from the moment technicians lowered the rocket's 138-foot-tall S-IC first stage into place beside it within a Vertical Assembly Building (VAB) high bay until shortly after the S-IC's engines ignited on one of the twin Launch Complex (LC) 39 pads. At the moment of liftoff, the nine servicing arms linking the 398-foot-tall LUT to the 363-foot-tall Saturn V would retract or swing out of the way; then, between 1.4 and 9.4 seconds after liftoff, the rocket would perform a LUT clearance yaw maneuver, its five F-1 engines bathing the launch pad in flame. After that, the LUT would stand alone, awaiting transport back to the VAB atop one of Kennedy Space Center's two enormous crawler-transporters and assembly of a new Saturn V.

By late 1969, with the Apollo 11 and 12 lunar landing missions successfully accomplished, it had become clear that only a few more Saturn V rockets would depart LC 39 for the Moon. The $25-billion Apollo Program had achieved its goal of humbling the Soviet Union, and many outside of space industry and the fledgling planetary science community saw little cause to continue it.

Meanwhile, NASA Administrator Thomas Paine aspired to replace the Moon program with a large Earth-orbiting Space Station serviced by a fully reusable crew rotation and logistics resupply spacecraft (a "Space Shuttle"). A fully functional 6-man or 12-man core station would reach Earth orbit on a Saturn V rocket; later, Saturn V rockets would launch multiple large Space Station modules which would be brought together to form a 50- or 100-man "Space Base." By the beginning of the 1980s these would, it was hoped, become elements in an Integrated Program Plan that would lead to a piloted lunar surface base and humans on Mars by 1990.

The Nixon White House and the Congress would have none of it, however. By the time Congress passed the $3.75-billion Fiscal Year 1970 NASA budget — the lowest since 1962, the first year of the Apollo Program build-up — space planners had begun to seek tactics that they could use to achieve ambitious goals while spreading out costs. One of those tactics was "series development."

Booster-first development: in this artist concept, a reusable Space Shuttle Booster carries an expendable Saturn S-IVB stage and payload to the edge of space. Image credit: NASA.

As applied to the Space Shuttle, series development could take either of two forms. In the first, the Space Shuttle's fully reusable piloted Booster would be developed and brought into service, then development work would begin on its fully reusable piloted Orbiter.

Until the Orbiter became available, the suborbital Booster would lift off from Cape Kennedy, Florida, carrying on its back an unmanned payload attached to an expendable upper stage based on an existing stage design — the Saturn V S-IVB third stage was one attractive candidate. The upper stage would ignite high over the Atlantic, boosting the payload to Earth orbit — or beyond. The astronauts, meanwhile, would pilot the Booster back to a runway at Cape Kennedy, where it would be refurbished, mated with a new upper stage and payload, and flown again.

Three-stage Saturn V rocket with Apollo spacecraft payload on top, Orbiter with Saturn S-IC first stage, and LUT with nine Apollo Saturn V servicing arms. Image credit: Bellcomm/NASA.

More attractive to space planners eager to see astronauts continue to fly into orbit (that is, almost all of them) was development of the Shuttle Orbiter followed by development of the Booster. In this "Orbiter-first" scenario, an expendable Saturn V S-IC would stand in for the Booster during the first few years of Shuttle flights.

On the last day of 1969, C. Eley, an engineer with Bellcomm, NASA's Washington, DC-based planning contractor, published a memorandum in which he examined how the Orbiter/S-IC combination might be serviced and launched using a LUT "without extensive [and expensive] modifications." Eley assumed that the S-IC would fly virtually unmodified (apart from a 10-foot-long streamlined shroud linking its dome-shaped top to the Orbiter's tail) and that the Orbiter would measure 183 feet long. This would make the combination 331 feet tall, or 32 feet shorter than the Apollo Saturn V.

Eley found that LUT servicing arms 1, 2, 4, 8, and 9 would remain useful for Orbiter/S-IC pre-launch servicing. He recommended that arms 3, 5, 6, and 7 be removed and stored to prevent them from becoming damaged (implying, perhaps, that the LUT might be restored to its original form and purpose — that is, launching Saturn V rockets — at some point). Arms 1 and 2, which would service the S-IC stage, would remain completely unchanged in form and function.

Orbiter-first development: a reusable Shuttle Orbiter with an expendable Saturn S-IC first stage stands beside a modified LUT. Image credit: Bellcomm/NASA.

All Orbiter servicing — for example, propellants loading — would employ arm 4, close by the Orbiter's tail. Arm 8 would provide services — for example, cooling — to the payload in the Orbiter payload bay, but would not enable access to the payload because the Orbiter's top side, where its payload bay doors would be located, would face away from the LUT on the pad. Eley assumed that the Mobile Servicing Structure used during Apollo to reach parts of the Saturn V located out of reach of the LUT arms would not be used with the Orbiter/S-IC. He suggested that a special arm be added to the LUT if payload access on the launch pad were judged to be necessary. Arm 9 would reach out from the LUT to cap the Orbiter's nose, permitting access to its crew cabin.

Eley then examined the probable launch rate of the Orbiter/S-IC stage Space Shuttle. He made three assumptions about the Orbiter and the LUT: that the Orbiter would include an "autonomous checkout capability" that would help to reduce to from five to 10 days the time spent on the launch pad prior to launch; that all three Apollo LUTs would be modified for Orbiter/S-IC launches; and that experience would prove that a LUT could be fully refurbished within 15 days of taking part in a launch.

If these assumptions were shown to be correct, Eley found, then more than 40 Orbiter/S-IC launches could take place in a year. If, on the other hand, only a single modified LUT, a 30-day LUT refurbishment period, and an on-pad preparation time no less than 30 days were assumed, then only six or seven Orbiter/S-IC flights could occur per year.

A little more than two years after Eley completed his memorandum, budget shortfalls forced NASA to postpone Space Station development until after the Shuttle flew — another example of series development. Shuttle Orbiters, not Saturn V rockets, would launch NASA's future Space Station. The Station would be launched in pieces in the Shuttle Orbiter payload bay and assembled in Earth orbit.

Two of the Apollo LUTs were put to use in the Space Shuttle Program, though not as Eley envisioned. NASA partially dismantled them, reducing their height to 247 feet (not counting a new 80-foot-tall lightning mast), then permanently mounted them on the two LC 39 pads. The third LUT was dismantled sometime after 1982 and scrapped in 2004 after its peeling red paint was judged to be an environmental hazard.

Sources

"Feasibility of Shuttle (Orbiter)/S-IC Launches at LC-39 — Case 320," C. Eley, Bellcomm, Inc., 31 December 1969.

Welcome to the Save the LUT Campaign (http://www.savethelut.org/ — accessed 19 November 2015)

More Information

What if an Apollo Saturn Rocket Exploded on the Launch Pad? (1965)

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

McDonnell Douglas Phase B Space Station (1970)

Where to Launch and Land the Space Shuttle? (1971-1972)

Reviving & Reusing Skylab in the Shuttle Era: NASA Marshall's November 1977 Pitch to NASA Headquarters

The Skylab Orbital Workshop as seen by the Skylab 4 crew, the last astronauts to live on the station. Image credit: NASA.

On 14 May 1973, the last Saturn V rocket to fly, designated SA-513, launched the Skylab space station into a 435-kilometer-high orbit about the Earth. Flight controllers soon realized that the 85-ton space laboratory was in trouble. Although they did not know it at the time — Skylab climbed rapidly into dense clouds, so could not be imaged during most of its ascent — 63 seconds after liftoff a design flaw caused its meteoroid shield to rip away. Shield debris jammed one of the workshop's two main electricity-producing solar arrays. The other array remained attached to Skylab's side only at its hinge (forward) end.

Shield debris also pummeled SA-513, tearing at least one hole in the tapered interstage adapter that linked its S-II second stage with the Skylab station. Debris also apparently damaged the system for separating the cylindrical adapter that linked the S-II to the S-IC first stage. The adapter, meant to separate shortly after the spent S-IC, remained stubbornly attached to the S-II all the way to orbit.

Skylab 1 launch, 14 May 1973. Image credit: NASA.

After the S-II's five J-2 engines shut down, forward-facing solid-propellant rockets ignited to push the spent stage away from Skylab. Their plumes blasted open and tore away the loose solar array. Ironically, the jammed array probably survived because it was tied down by meteoroid shield debris.

Without the protection of the reflective meteoroid shield, temperatures within Skylab's 11,303-cubic-foot pressurized volume soon soared, raising fears that its air would become tainted by outgassing from materials on board, film would be ruined, and food and medicines spoiled. Flight controllers soon found to their dismay that maneuvers designed to cool Skylab's interior tended to starve it of electricity, for they turned away from the Sun the four "windmill" solar arrays on the Apollo Telescope Mount (ATM), the beleaguered space laboratory's only functioning sources of power.

NASA immediately began a Skylab salvage effort. Engineers developed deployable sunshields and tools for freeing the stuck main solar array, flight controllers carefully maneuvered Skylab to maximize the amount of electricity the ATM arrays could produce while reducing temperatures on board as much as possible, and the first crew meant to board Skylab (their mission was designated Skylab 2) hurriedly trained to become the world's first orbital repairmen.

Skylab 2 astronauts Joseph Kerwin, Charles "Pete" Conrad, and Paul Weitz. Image credit: NASA.

On 25 May, the Skylab 2 crew of Pete Conrad, Paul Weitz, and Joe Kerwin lifted off in an Apollo Command and Service Module (CSM) atop a Saturn IB rocket. After a failed attempt to pull open the one remaining main solar array with a hook extended from the open CSM hatch, they docked with and entered Skylab, then deployed a sunshield through an experiment airlock. Temperatures began to fall, but the station remained starved for electricity. On 7 June, Conrad and Kerwin succeeded in forcing open the surviving main solar array, saving not only their own 28-day mission but also the planned Skylab 3 and Skylab 4 missions.

The Skylab 3 crew of Alan Bean, Jack Lousma, and Owen Garriott lifted off on 28 July. During their 6 August spacewalk, Lousma and Garriott deployed an improved sunshield. They lived and worked on board the station for 59 days.

The Skylab 4 crew of Jerry Carr, William Pogue, and Ed Gibson boarded the station on 16 November. Carr and Gibson mounted a meteoroid collector on an ATM strut during their spacewalk on 3 February 1974, in the hope that a Space Shuttle crew might retrieve it as early as 1979. When the Skylab 4 crew undocked on 8 February 1974 after a record-breaking 84 days in space, Skylab was expected to remain aloft until 1983, when atmospheric drag would cause it to re-enter Earth's atmosphere. They left Skylab's airlock hatch closed but not latched so that it could provide entry for future visitors.

This pre-launch cutaway illustration of Skylab shows the station as it would have appeared if it had reached Earth orbit undamaged. In addition to two large main solar arrays, it includes the micrometeoroid shield which tore free during Skylab's ascent through the atmosphere. Skylab was the largest single-launch space station ever; astronauts, dressed in brown, look very small inside it. Image credit: NASA.

During the solar-minimum years of the mid-1970s, the Sun was more active than had been anticipated at the time of Skylab's launch. Solar activity heated and expanded Earth's upper atmosphere, subjecting the first U.S. space station to more aerodynamic drag than expected. In March 1977, the NASA Marshall Space Flight Center (MSFC) in Huntsville, Alabama, asked NASA Headquarters to grant it permission by mid-1977 to begin work on a mission to raise Skylab's orbital altitude so that its lifespan could be extended, giving NASA time to consider future uses for the space station.

That MSFC maintained a strong proprietary interest in Skylab should not be surprising. In November 1965, the Huntsville center had proposed that a space laboratory based on a spent Saturn V S-IVB stage be added to the Apollo Applications Program (AAP), at the time NASA's main post-Apollo piloted program. The spent-stage AAP workshop, a low-cost space station, had much greater potential for supporting long-duration astronaut stays in orbit than did modified Apollo CSM and Lunar Module (LM) spacecraft. NASA Headquarters quickly approved MSFC's plan.

For its first three-and-a-half years, the AAP Workshop was the S-IVB second stage of a Saturn IB rocket and, on its top, a small pressurized module with multiple docking ports. During ascent to Earth orbit, it would act as a normal Saturn IB stage. After its single J-2 rocket motor shut down, the four segments of its streamlined launch shroud would open like the petals of a flower, revealing the docking module. Controllers would then command vents in the stage to open so that residual liquid oxygen/liquid hydrogen propellants could escape into space. Meanwhile, solar arrays would unfold from the inside of two of the four shroud segments to generate electricity.

The AAP spent-stage workshop. At left an AAP CSM docks with one of the docking modules four radial ports through the intermediary of an add-on module. Image credit: NASA.

A crew launched on a second Saturn IB would rendezvous and dock with the spent stage in an AAP CSM, enter the docking module, then enter the cavernous liquid hydrogen tank, the largest of the two S-IVB stage tanks. They would pressurize the tank with gaseous oxygen and nitrogen from tanks in the docking module, then install in the tank furnishings, fabric floors and walls, lights, and experiments transferred from the CSM and docking module. Subsequent AAP Saturn IB/CSM flights would deliver Earth-looking and space-looking science modules for attachment to the docking module, including an array of solar telescopes based on the Apollo LM design.

In July 1969, NASA Administrator Thomas Paine approved plans to shift from the Saturn IB-launched "wet workshop" (as it was colloquially known) to a Saturn V-launched "dry workshop." The latter, more capable than the former, would include neither propellants nor an engine and would reach Earth orbit fully outfitted. In February 1970, the AAP workshop (and, indeed, AAP as a whole) was renamed Skylab. NASA Headquarters made MSFC responsible for Skylab Saturn V and Saturn IB rockets, overall Skylab systems engineering and integration, and most onboard experiment apparatus.

On 10 June 1977, former Skylab Deputy Director John Disher, by then NASA's Director of Advanced Programs, requested that MSFC conduct a preliminary in-house study of the feasibility of reusing Skylab in the Space Shuttle era. At about the same time, NASA Headquarters directed NASA Johnson Space Center (JSC), lead center for the Space Shuttle, to study an early Shuttle mission to either boost Skylab to a higher, longer-lived orbit or cause it to safely reenter over an unpopulated area.

In September 1977, JSC informed NASA Headquarters and MSFC that the earliest it could reboost or deboost Skylab was September 1979, as part of the fifth Orbital Flight Test (OFT) Shuttle mission. At the time, NASA envisioned a total of six OFT missions before the Shuttle was declared operational. NASA Headquarters then gave the go-ahead for MSFC and JSC to begin work toward a September 1979 Skylab reboost/deboost mission.

On 16 November 1977, MSFC engineers J. Murphy, B. Chubb, and H. Gierow presented to NASA Associate Administrator for Space Flight John Yardley results of the study they had begun in June. They were addressing a Skylab expert: before coming to NASA in 1974, Yardley had managed Skylab work at McDonnell Douglas, the prime contractor for the OWS.

The MSFC engineers first described Skylab's condition. They reported that when the Skylab 4 crew returned to Earth, the Orbital Workshop's water system contained 1930 pounds of water (enough to supply three men for 60 days). The water, they said, probably remained potable, but might have developed a bad taste. If it was no longer potable, then it might be used for bathing. In any case, the Skylab water system included resupply points, so a Space Shuttle crew could refill it with fresh water if water transfer equipment were developed.

The oxygen/nitrogen supply remaining on Skylab was probably sufficient to supply three men for 140 days at Skylab's standard operating pressure of five pounds per square inch, the MSFC engineers estimated. The station's ventilation and carbon dioxide-removal systems were almost certainly functional. Even if they were not, their most important components were designed to be replaceable in space.

The MSFC engineers also assessed Skylab's electrical power system. They estimated that the main solar array Conrad and Kerwin had freed could still generate between 1.5 and 2.5 kilowatts of electricity, and that the batteries it had charged, located in Skylab's Airlock Module, were probably still usable. The batteries for the four ATM arrays, located inside the ATM, were, on the other hand, almost certainly frozen. The team recommended that controllers reactivate the main array electrical system from the ground before the first Shuttle visit, and that any effort to revive the ATM electrical system be left for a later time.

More problematic than the electrical system was Skylab's attitude control system, which relied on a trio of Control Moment Gyros (CMGs) to turn Skylab so that, among other things, it could reliably point its solar arrays at the Sun. At the time the Skylab 4 crew departed, one CMG had already failed and another showed signs of impending failure. In addition, Skylab's guidance computer was probably dead after being subjected to "extreme thermal cycling" as Skylab passed between daylight and night. The Orbital Workshop's thruster system, on the other hand, was probably operational with about 30 days of propellant remaining.

Finally, the MSFC team looked at Skylab's cooling system, which had leaked while the astronauts were on board and had probably frozen and ruptured since the last crew returned to Earth. They called "serviceability of [the] cooling system. . .the most questionable area" as far as Skylab's reusability was concerned, but added that "any inflight 'fixes' should be well within the scope of crew capability."

The MSFC engineers then proposed a four-phase plan for reactivating and reusing Skylab. The target date for their first Phase I milestone had already passed by the time they briefed Yardley: though it was already mid-November, they made a point of calling for an October 1977 decision on whether Skylab should be reboosted to a higher orbit, extending its orbital lifetime until about 1990, or deboosted so that it could reenter safely over an unpopulated area.

Assuming that NASA decided to reboost Skylab, then a ground-controlled Skylab reactivation test would occur between June 1978 and March 1979. If the test was successful, then the fifth OFT Space Shuttle mission would rendezvous with Skylab. As already mentioned, in September 1977 JSC estimated that the fifth OFT would fly in September 1979. Two months later, when the MSFC team briefed Yardley, the mission had already slipped to February 1980.

Artist concept of Teleoperator spacecraft. Image credit: NASA.

The MSFC team anticipated that the Space Shuttle crew would conduct an inspection fly-around of Skylab, then would deploy an unmanned Teleoperator spacecraft from the Shuttle Orbiter payload bay. Using a control panel on the Orbiter flight deck, the astronauts would guide the Teleoperator, which would carry an Apollo probe-type docking unit, to a docking with the drogue-type docking unit on the front of Skylab's Multiple Docking Adapter. The Teleoperator would fire its thrusters to raise Skylab's orbit; then, its work completed, it would detach, freeing up Skylab's front docking port for Phase II of MSFC's plan.

Astronauts in a nearby Space Shuttle Orbiter stand by as the Teleoperator ignites its thrusters to raise Skylab's orbit and extend its orbital lifetime. Image credit: NASA.

Phase II would begin in March 1980, when NASA would initiate development of Skylab refurbishment kits, a 10-foot-long Docking Adapter (DA) module, and a 25-kilowatt Power Module (PM). The DA would include at one end an Apollo-type probe docking unit for attaching it to Skylab's front port and at the other end an Apollo-Soyuz-type androgynous unit with which Shuttle Orbiters and the PM could dock.

The first refurbishment kit and the DA would reach Skylab on board a Shuttle Orbiter in January 1982, almost two years after the reboost mission. During the 1982 mission, spacewalking astronauts would fold two of the four ATM solar arrays out of the way to improve clearance for visiting Orbiters and would retrieve the meteoroid experiment the Skylab 4 astronauts had left on the ATM. As time allowed, this and other Phase II crews would perform unspecified "simple passive experiments" on board Skylab and would collect samples of its structure for engineering analysis on Earth.

The third Shuttle visit to Skylab would not take place until August 1983. The astronauts would install additional refurbishment kits and would tackle the daunting job of repairing Skylab's damaged cooling system.

The refurbished Skylab station after the start of Phase III of the NASA MSFC reactivation program. The Power Module, Docking Adapter, and Shuttle-carried Spacelab are clearly visible. Image credit: Junior Miranda.

The MSFC engineers told Yardley that Phase III of the Skylab reactivation program would begin in March 1984 with delivery of the PM and any remaining refurbishment kits. Using the Shuttle Remote Manipulator System robot arm, astronauts would lift the PM from the Orbiter payload bay and turn it 180° so that it protruded forward well beyond the Orbiter's nose. They would then dock one of the PM's three androgynous docking units to an identical unit at the front of the Orbiter payload bay. The Shuttle would use another of the PM's docking units to dock with the DA on Skylab.

Following docking with Skylab, the astronauts would deploy the PM's twin solar arrays and thermal radiators, link the PM to Skylab's systems using cables extended through open hatchways or installed on the hull during spacewalks, and power up the PM's three CMGs to replace Skylab's crippled attitude control system. The Orbiter would then undock from the PM, leaving it attached permanently to Skylab. Shortly thereafter, NASA would declare the revived and expanded Orbital Workshop to be fully habitable.

Phase III would continue with the first in a series of 30-to-90-day missions aboard Skylab. During these, a Shuttle Orbiter carrying a Spacelab module in its cargo bay would remain docked with the Orbital Workshop. The astronauts would work in the Spacelab module, take advantage of Skylab's large pressurized volume to perform "simple experiments" requiring more room than Shuttle and Spacelab could provide (for example, preliminary trials of space construction methods), and begin building up stockpiles of food, film, clothing, and other supplies on the revived station.

Another 30-to-90-day mission would see the astronauts refurbish and use selected Skylab science equipment, install new experiments based on Spacelab experiment designs, and stockpile more supplies. Between these missions, the new and improved Skylab would fly unmanned under control from the ground.

The view from the Sun: all of the solar arrays deployed for Phase III of the Skylab reactivation program are visible in this image by Junior Miranda.

The MSFC engineers told Yardley that the volume available to a crew on board a Shuttle Orbiter without a Spacelab module in its payload bay would total only 1110 cubic feet. Adding a Spacelab would increase that to about 5100 cubic feet. This would, however, amount to less than half the pressurized volume of Skylab. For a mission including a Shuttle Orbiter, Spacelab module, and Skylab, the total volume available to the crew would exceed 16,400 cubic feet.

They were not specific about what Skylab would be used for when Phase IV of their program began in mid-1986, though they did offer several intriguing possibilities. Shuttle Orbiters might, for example, attach modified Spacelab modules and experiment pallets to the third docking port on the PM.

A Shuttle External Tank might be joined to Skylab to serve as a strongback for large-scale space construction experiments using a mobile "space crane." These experiments might include construction of a large space solar power module or a multiple beam antenna.

A new "floor" might be assembled within Skylab, enabling it to house up to nine astronauts. As NASA developed confidence in the revived space laboratory's health, manned missions on board Skylab without a Shuttle Orbiter present might commence, leading to permanent manning and "support [of] major space operations."

The MSFC engineers did not estimate the cost of Phases I and IV of their plan, though they did provide (perhaps optimistic) cost estimates for Phases II and III. Their estimates did not include Space Shuttle transportation and contractor study costs.

In Fiscal Year (FY) 1980, NASA would spend $2 million each on Phases II and III. This would increase to $5 million for Phase II and $3.4 million for Phase III in FY 1981. FY 1982, their plan's peak funding year, would see $4.5 million spent on Phase II and $10.2 million spent on Phase III. In FY 1983, NASA would spend $2.5 million to close out Phase II and $12 million to continue Phase III. The following year it would spend $9.1 million on Phase III. Phase III closeout in FY 1985 would cost $4.5 million. Phase II would cost a total of $14 million, while the more ambitious Phase III would total $41.2 million.

In November 1977, the month the MSFC engineers briefed Yardley on their study, NASA awarded Martin Marietta Corporation a small ($1.75-million) contract to begin development of the Teleoperator. The remote-controlled spacecraft was envisioned as a small space tug made up of modular components.

No decision was taken at that time as to whether the Teleoperator would reboost Skylab to make it available for possible future use or would deorbit it in a controlled manner; that decision would await assessment of Skylab's condition and additional study of potential applications. McDonnell Douglas and Martin Marietta subsequently commenced more detailed and extensive Skylab reuse studies under MSFC supervision with inputs from JSC and NASA Headquarters.

Sources

Skylab 1 Investigation Report, Hearing Before the Subcommittee on Manned Space Flight of the Committee on Science and Astronautics, US House of Representatives, Ninety-Third Congress, First Session, 1 August 1973.

"Skylab Reuse Study Presented to Mr. Yardley by MSFC," 16 November 1977.

Living and Working in Space: A History of Skylab, NASA SP-4208, W. David Compton & Charles D. Benson, 1983, pp. 361-372.

More Information

What If a Crew Became Stranded On Board the Skylab Space Station? (1972)

Evolution vs. Revolution: The 1970s Battle for NASA's Future

What Shuttle Should Have Been: NASA's October 1977 Space Shuttle Flight Manifest

A Bridge from Skylab to Station/Shuttle: Interim Space Station Program (1971)

Skylab liftoff on a two-stage Saturn V rocket, 14 May 1973. Had the ISS Program gone ahead as planned, its four station launches in 1976, 1978, 1981, and 1983 would have closely resembled this one. Image credit: NASA.

On 6 April 1971, eight engineers in the Advanced Concepts & Missions Division, NASA Headquarters Office of Advanced Research and Technology (OART), completed a blueprint of NASA's future. Their detailed report was strictly internal and of limited circulation.

Had the OART team's plan become more widely known, it would surely have generated controversy. This was because it proposed to end U.S. lunar exploration with Apollo 15 so that the Saturn V rockets earmarked for missions 16, 17, 18, and 19 could be used to launch into Earth orbit a series of four "interim" space stations, each more capable than the last, between early 1976 and late 1983.

Although the OART plan sounds like an Apollo massacre, it would in fact have deprived the U.S. of two piloted Moon missions, not four. By the time the OART team proposed its program, NASA had already cancelled three Apollos. First was Apollo 20, nixed in January 1970 so that its Saturn V rocket could launch 85-ton Skylab, a temporary space station, into low-Earth orbit (LEO).

Next to go were Apollo 15 and Apollo 19 in September 1970. NASA Administrator Thomas Paine scrapped the two lunar landing missions — an H-class walking mission and a J-class rover mission, respectively — to free up funds for NASA's hoped-for 12-man permanent Space Station and the fully reusable winged Space Shuttle intended to deliver its crews, supplies, and experiment equipment. NASA subsequently renumbered its remaining Apollo missions, so the cancelled missions are more commonly known today as Apollo 18 and Apollo 19.

The Interim Space Station (ISS) Program would have played much the same role for NASA in the mid-1970s/early 1980s as Gemini played in the 1960s. Soon after President John F. Kennedy's 21 May 1961 call for an American on the Moon by the end of the 1960s decade, aerospace engineers realized that they needed an experience-building "bridge" program to link simple Mercury suborbital and LEO missions with complex Apollo lunar orbiter and landing missions. Gemini evolved from Mercury — it was initially called "Mercury Mark II" — to fulfill that role.

The Saturn IB stage served as the Apollo Moon rocket's third stage, the Saturn IB rocket's second stage, and the structural basis of the Skylab station. Image credit: NASA.

OART's ISS Program was envisioned as an evolutionary extension of the Skylab Program. Skylab A and its backup, Skylab B, employed 22-foot-diameter Saturn S-IVB rocket stages as their basic structure. The S-IVB was the third stage of the three-stage Saturn V Moon rocket and the second stage of the two-stage Saturn IB rocket. From top to bottom, the stage comprised the ring-shaped Instrument Unit (the "electronic brain" of the Saturn V or Saturn IB rocket of which the S-IVB stage was part), a large tank for low-density liquid hydrogen fuel, a small tank for higher-density liquid oxygen oxidizer, and a restartable J-2 rocket engine.

Through the addition of metal-grid decks, life-support equipment and consumables, lights and air ducts, a film vault, living quarters, and experiment apparatus, the S-IVB hydrogen tank became the Orbital Workshop (OWS), Skylab A's main habitable volume. The empty S-IVB liquid oxygen tank served as a dumpster, and a radiator replaced its J-2 engine.

The OWS hydrogen tank had bolted to its top the Airlock Module (AM), which in turn linked to the Multiple Docking Adapter (MDA) at Skylab A's front. The AM included a surplus Gemini hatch for spacewalks. The MDA included a main axial (front) docking port and a back-up radial port.

Besides the OWS, MDA, and AM, Skylab A included the Apollo Telescope Mount (ATM), an unpressurized compartment containing instruments for viewing the Sun. The ATM, mounted on a truss attached to the side of the MDA, included four electricity-generating solar arrays arranged in "windmill" fashion. These augmented two large solar-array "wings" on Skylab A's sides.

The Skylab space station as envisioned in 1970. Image credit: NASA.

Skylab A was commonly referred to simply as Skylab, since no firm plan existed to actually launch Skylab B. When the OART engineers completed their report, NASA planned to launch Skylab in late 1972; then, over a period of about nine months, the U.S. civilian space agency would launch to the station three crews in Apollo Command and Service Module (CSM) spacecraft atop Saturn IB rockets. The three-man crews would live and work on board Skylab for up to 56 days. While unoccupied — months might pass between one crew's departure and the next crew's arrival — Skylab would operate under ground control.

The OART engineers applied the term "interim" to their eight-and-half-year program because they intended that it should lead from the Skylab Program to a permanent Space Station through "evolutionary, gradual, and step-wise spacecraft systems development." Beginning about three years after the third and final Skylab crew returned to Earth, a new ISS would reach LEO every two and a half years. Each would be staffed continuously for from 360 to 420 days.

NASA planning was in flux at the time the OART team prepared its report, and would remain so even after President Richard Nixon approved development of a semi-reusable Space Shuttle in January 1972. The ISS Program would span most of a decade, and NASA had in its dozen-year history experienced program instability on the scale of months. These factors caused the OART engineers to avoid making assumptions about the nature of NASA's eventual permanent Space Station when they planned their ISS Program.

They went so far as to suggest, in fact, that the Station/Shuttle Program might be delayed or abandoned in favor of some new space goal before the ISS Program ran its course. For planning purposes, however, they adhered to a timeline which saw NASA's permanent Space Station become operational in late 1987, about six years after the date they gave for the Shuttle's maiden flight and a little more than three years after the last ISS crew returned to Earth.

In keeping with the $3.3-billion Fiscal Year 1972 NASA budget Nixon's Office and Management and Budget had sought from Congress in January 1971, the OART engineers optimistically assumed a steady NASA annual funding stream of $3.3 billion throughout the ISS Program. They estimated that each interim station would cost $2 billion, of which about $330 million would be spent on hardware development, $500 million on experiments, and $1.6 billion on spacecraft hardware. Their program would, they calculated, cost on average about $500 million per year, leaving $2.8 billion for other NASA projects, including Station/Shuttle development.

Interestingly, just 13 days after the OART team completed its report, the Soviet Union launched 20-ton Salyut 1, the world's first space station. The Soviets had during the 1969-1970 period made it known publicly — most prominently in an October 1969 speech by Soviet leader Leonid Brezhnev — that they intended to establish Earth-orbiting stations, so it is tempting to suppose that OART's study was at least in part motivated by Soviet statements.

In January 1970, in fact, the U.S. Central Intelligence Agency had completed a report, classified "SECRET," in which it suggested that the Soviets might construct a series of stations, each larger and more capable than the last, culminating, perhaps, in a $5-billion, 150-ton station between 1976 and 1980. The OART engineers did not, however, mention Soviet space plans in their report.

Interim Space Station design. Image credit: NASA.

Like Skylab, the interim stations would reach LEO atop two-stage Saturn V rockets. The first station in the series, designated Interim Space Station-A (ISS-A), would be mainly outfitted for biotechnology research. It would operate in a a 245-nautical-mile (nm) orbit inclined 28.5° relative to Earth's equator. The OART team envisioned that ISS-A would be built from Skylab B. Like the other three stations in its series, ISS-A would lack an ATM.


Based on Skylab experience, the OART engineers calculated that ISS-A would at launch weigh at least 57.25 tons. They then assumed a 30-ton "growth allowance" which could be wholly or partly used during development and assembly. This meant that ISS-A might weigh as much as 87.25 tons at launch.

NASA would launch the first three-man ISS-A crew — indeed, the first crew of the ISS Program — in a modified CSM within a day or two of the station's launch. No more than 16 hours after they reached LEO, the astronauts would pilot their spacecraft to a docking at one of ISS-A's two MDA docking ports.

The CSMs that delivered astronauts to the interim stations would differ significantly from their Apollo/Skylab predecessors. The most obvious change would be a new-design launch vehicle. The OART engineers considered using either the Saturn IB or the Titan-IIIM to launch ISS CSMs before they settled on a hybrid of the two.

Dubbed the SRM-S-IVB, the new rocket's first stage would comprise a cluster of three 10-foot-diameter, seven-segment Titan-IIIM solid-propellant rocket motors. The Titan-IIIM, never flown, had been meant to launch the U.S. Air Force Manned Orbiting Laboratory, which was cancelled in February 1969. As its name implies, the SRM-S-IVB launch vehicle's second stage would be a lightly modified Saturn S-IVB stage.

The SRM-S-IVB would be capable of launching a 28.7-ton payload from Kennedy Space Center, Florida, to a 245-nm orbit at 28.5° of inclination. For comparison, the Saturn IB could launch about 17.5 tons to the same orbit.

The ISS CSM, like its Apollo and Skylab predecessors, would be a two-part spacecraft. The smaller of the two parts was the conical Command Module (CM), a three-man crew capsule with a reentry heat shield on its broad aft end and an active probe docking unit on its nose. It would lower on parachutes to a splashdown at mission's end. The drum-shaped Service Module (SM) had a Service Propulsion System main engine bell protruding from its aft end.

The 6.3-ton ISS CM would closely resemble its Apollo and Skylab counterparts. The ISS SM, on the other hand, would undergo many changes. Because it would need to carry only enough propellants for Earth-orbital rendezvous and docking maneuvers plus an end-of-mission de-orbit burn, OART proposed to replace its propellant tanks, which were sized for a voyage to lunar orbit and back, with smaller tanks derived from those in the Apollo Lunar Module. Because the ISS CSM would fly independently for a total of less than a day, rechargeable batteries in the ISS SM would stand in for the Apollo SM's trio of fuel cells and tanks of fuel-cell reactants.

These changes would free up for conversion into cargo holds four of the six 175-cubic-foot bays clustered around the SM's cylindrical core bay. The four bays would transport a total of about 10 tons of supplies and equipment. Minus cargo, the ISS SM would weigh 8.6 tons.

The Apollo Command and Service Module (CSM) spacecraft would undergo considerable modification for the ISS Program. Image credit: NASA.

Water, oxygen, and nitrogen stored in tanks in the ISS SM cargo bays would pass through umbilicals to nozzles in the ISS CM. The astronauts would attach hoses to the nozzles to transfer the water, oxygen, and nitrogen to storage tanks inside the ISS.

Solid cargo, on the other hand, could only be transferred from the ISS SM to the ISS by spacewalks. The OART team noted that the spacewalking astronauts would have to travel only about 15 feet to reach the ISS SM from the ISS AM.

The astronauts would hinge open panels in the ISS SM's sides and transfer cargo items to the open ISS AM hatch by attaching them to a clothesline-like "endless line" similar, perhaps, to that used on the Moon to convey sample boxes and film from the base of the LM ladder to the LM ascent stage hatchway. Cargo items as large as 3.5 feet wide by 12 feet long could be removed from the ISS SM cargo bays and transferred through the Gemini-type hatch into the ISS AM, the OART team estimated.

Because it would be cast off to burn up in Earth's atmosphere after it performed the deorbit burn, the ISS SM could transport only "up" cargo. "Down" cargo — for example, biological samples and exposed film — would reach Earth within the relatively small volume of the ISS CM. The OART engineers estimated that, by removing all lunar mission equipment and supplies from the ISS CM, enough room would be freed up to enable it to convey to Earth all experiment cargo a three-man crew was likely to generate during a 90-day stint on board an ISS.

Converting the Apollo CSM into the ISS CSM would cost $100 million, the OART engineers estimated. This price-tag would not include the $80-million cost of developing the SRM-S-IVB launcher.

The Saturn S-IVB rocket stage would form the largest habitable component of Skylab and the ISS stations. While spacious with a crew of three, it would become increasingly crowded as the ISS Program evolved. Image credit: NASA.

Astronauts would occupy ISS-A continuously for 360 days. Four three-man crews would live and work on board for 90 days each. During crew rotations, the replacement crew would dock at the vacant MDA port and six men would temporarily inhabit ISS-A.

OART made biotechnology ISS-A's main research emphasis because its crews would need to demonstrate that astronauts could remain fit and competent throughout a 90-day stay in space. In addition, it would seek to advance medicine on Earth through the study of the human organism in novel conditions. Most of the experiments performed in the ISS series would have a similar dual purpose: that is, to advance the cause of spaceflight and to provide tangible benefits to people on Earth.

ISS-A's mission, the OART team explained, would continue and expand the biomedical research program begun on board Skylab. In addition to copies of Skylab experiment apparatus, experiment equipment launched on board ISS-A would include a 1750-pound "Manned Onboard Centrifuge" — a centrifuge large enough to spin a human — and a 1300-pound Integrated Medical and Behavioral Laboratory Measurement System (IMBLMS). The IMBLMS would be linked to operational control systems throughout ISS-A to monitor crew performance. Centrifuge, IMBLMS, and "peripheral equipment" such as a bicycle ergometer, an experiment airlock, and a sound-proofed work area would together cost $72 million.

Astronauts on board the interim stations would work 10 hours per day, six days per week. At any one time, two-thirds of the crew on an ISS would be focused on its experiment programs, while the rest would maintain systems and perform housekeeping chores. For ISS-A, this meant that, during any particular working day, two of the three astronauts on board would focus on experiments while the third served as space handyman.

Forty-five man-hours per week would be spent on IMBLMS experiments and 55 man-hours per week on centrifuge experiments. Other experiments — for example, assessment of techniques for weightless maintenance of life-support equipment intended for more than a year of continuous use — would require a total of 30 man-hours per week.

The OART team estimated that Skylab's six solar arrays and the batteries it carried for storing electricity for the night part of its orbit would produce about six kilowatts of continuous power and have a total mass of 7.5 tons. The ATM arrays and OWS arrays would each produce about half of Skylab's electricity. The team assumed that the ISS-A arrays and batteries would weigh the same as those on Skylab, but would produce between six and 10 kilowatts of continuous electricity. In the absence of an ATM, the ISS-A solar array configuration would necessarily differ from that of Skylab.

Of the stations in its series, ISS-A would most resemble Skylab. Beginning with ISS-B, larger crews and more complex experiment programs would drive evolutionary modifications to the ISS design, though all would retain the basic MDA-AM-OWS layout.

The AM would have undergone little modification from its first flight as part of Skylab to its last as part of ISS-D. Image credit: NASA.

The first three-man ISS-B crew would arrive for a 90-day stint beginning in July 1978, one-and-a-half years after ISS-A's last crew returned to Earth. A second three-man crew would reach the station a month later. The resulting six-man crew would work together for 60 days, then the first three-man crew would return to Earth. A third three-man crew would arrive almost immediately to replace them. Thirty days later, the second ISS-B crew would return to Earth and a fourth crew would replace them. The seventh three-man ISS-B crew would return to Earth in July 1979 and not be replaced, and the eighth and last three-man crew would splash down a month later, about 390 days after ISS-B reached LEO.

ISS-B's main mission would be to perform experimental Earth surveys, which the OART team placed into five multi-part categories. These were: agriculture/forestry/geography; geology/mineralogy; hydrology/water resources; oceanography; and meteorology. The station would revolve around the Earth in an orbit inclined 50° relative to the equator, so that it would pass over the "most populace [sic] and agriculturally productive areas of the Earth."

ISS-B astronauts would spend 90 man-hours per week testing, calibrating, and modifying a $40-million, 4700-pound suite of 19 experiment sensors covering the spectrum from ultraviolet through visible light to infrared and microwave. They would also continue biotechnology experiments; for example, the OART team allotted 70 man-hours per week to continuation of the IMBLMS program begun on board ISS-A.

ISS-B solar arrays and batteries would produce between seven and 15 kilowatts of continuous electricity for experiments and station operations. As with ISS-A, the OART engineers did not specify ISS-B's solar array configuration, though they implied that it would have a collecting area larger than the ISS-A configuration.

The MDA flown as part of Skylab was more more cluttered than it appears in this NASA cutaway. Skylab crews did not feel comfortable within the MDA because it lacked an obvious "up-down" orientation; no doubt the ISS MDAs would have been modified to take this into account. EREP = Earth Resources Experiment Package. ATM = Apollo Telescope Mount.

ISS-C, scheduled for launch in January 1981, and ISS-D, scheduled for launch on NASA's last Saturn V rocket in July 1983, would have many similarities. Each would have a crew complement of nine, making NASA's reliance on the three-man ISS CSM for crew rotation and resupply somewhat problematic. Somewhat surprisingly, though the OART engineers acknowledged that, based on their own NASA flight schedule, the reusable Space Shuttle would have begun flights in late 1981, they elected (for the sake of "simplicity") not to use it for ISS-C and ISS-D crew rotation and resupply.

ISS CSM launches in January, February, and March 1981 would launch ISS-C's initial nine-person crew. Only a month after its third crew arrived, its first crew would complete its 90-day stint on board the station and would return to Earth. NASA would immediately launch a fourth crew to replace them.

ISS-C and ISS-D would each receive 12 three-man crews. Each station would support nine men for 360 of the 420 days it was occupied. Flights to ISS-C and ISS-D would bring to 36 the total number of ISS CSMs and SRM-S-IVB boosters required for the program.

ISS-C astronauts would "evaluate in terms of direct Earth economic benefits the use of the space environment for materials processing and manufacture." Taking advantage of weightlessness and nearly pure vacuum, the astronauts would devote 95 man-hours per week to manufacturing large crystals, exotic composite materials, and biological compounds impossible (or at least very difficult) to create under terrestrial conditions. Manufactured materials and compounds would splash down with returning astronauts as "down" cargo in the ISS-C CMs.

The Saturn V S-IC second stage would have served as a counterweight for the ISS-C artificial-gravity experiment. Image credit: NASA.

ISS-C would also see a 45-day artificial-gravity experiment that would preempt the space exploitation experiments. The OART engineers provided few details of the experiment, though they did explain that the spent S-II second stage of the Saturn V that launched ISS-C into orbit would serve as an artificial-gravity counterweight. Probably cables would have linked the interim station and the spent stage; as the cables were slowly reeled out, thrusters on ISS-C would have fired to spin the assemblage end-over-end and keep the cables under tension. As the cables reached maximum extension, thrusters would have carefully trimmed the spin rate to ensure the desired acceleration — which the crew would feel as gravity — on board the ISS-C station.

The ISS-C/ISS-D solar array configuration would be identical to that of ISS-B; technological advancements would, however, enable their power systems to provide no less than 15 kilowatts of continuous electricity. The ISS-C and ISS-D astronauts would also evaluate Isotope Brayton nuclear power units for use on NASA's permanent Space Station.

The Isotope Brayton units would not reach space attached to ISS-C and ISS-D; rather, they would be launched separately, possibly atop Titan rockets. The OART engineers did not describe how they would rendezvous and dock with ISS-C and ISS-D. The five-ton ISS-C Isotope Brayton unit would generate six kilowatts of electricity; the more advanced six-and-a-half-ton ISS-D unit would produce 15 kilowatts, doubling that station's electrical supply.

Biotechnology experiments would continue during the ISS-C and ISS-D missions. The ISS-C biotechnology program would, of course, include assessment of the effects of spin-induced artificial gravity. With their nine-person crews, the third and fourth stations of the ISS program would be more crowded than their predecessors, offering an opportunity for study of complex human interactions aboard spacecraft.

ISS-D would include three free-flying astronomy modules in addition to astronomy instruments on the station. How the free-flyers would reach LEO was not made clear. The $50-million Cosmic Ray Physics Laboratory would weigh in at a whopping 26,700 pounds. The $125-million, 6195-pound Solar Astronomy Module would include "larger versions" of the Sun-observing instruments in the Skylab ATM. The $130-million, 6000-pound Stellar Astronomy Module would carry a telescope with a three-meter mirror. For comparison, the Hubble Space Telescope primary mirror is 2.4 meters across. Astronauts would regularly collect exposed film from the free-flying modules, though how they would reach them was not explained.

The OART engineers estimated that, by the time the last ISS-D crew returned to Earth, NASA would have accrued the equivalent of more than two years of permanent Space Station biomedical data and operations experience from its four interim stations. This would, they concluded, constitute the ISS Program's chief benefit to U.S. spaceflight; specifically, it would

enable the [permanent] Space Station to start its effective experimental usefulness almost at initial manning. . . [because] most of the human and operational uncertainties of long duration spaceflight would have been removed by. . .results [from the] four earlier interim space station flights.

Sources

Study of an Evolutionary Interim Earth Orbit Program, Memorandum Report MS-1, J. Anderson, L. Alton, R. Arno, J. Deerwester, L. Edsinger, K. Sinclair, W. Tindle, and R. Wood, Advanced Concepts and Missions Division, Office of Advanced Research and Technology, NASA Headquarters, 6 April 1971.

"Intelligence Report: Aims and Costs of the Soviet Space Station Program," SR IR 70-1-S, Directorate of Intelligence, Central Intelligence Agency, January 1970.

More Information

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

Evolution vs. Revolution: The 1970s Battle for NASA's Future

Skylab-Salyut Space Laboratory (1972)

Dreaming a Different Apollo, Part One