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NASA -- the National Aeronautics and Space Administration -- had its own institutional reasons for wanting a large space station. After the Apollo lunar landings in the late 1960s, the agency had fallen on hard times in the 1970s when the space budget was drastically reduced due to the high cost of the Vietnam War and social programs. NASA was barely able to secure funding for the Space Shuttle in 1972 as Apollo was cancelled. The space agency then had to exist on a virtual shoestring budget throughout the 1970s while struggling to complete the Shuttle development program. But the new Shuttle Transportation System (STS) turned out to be more expensive than expected when it finally became operational in 1982. STS was also impopular with the Reagan Administration, who disliked the idea of having NASA rather than private industry run a "national spaceline." The senior NASA managers thus wanted another program to complement the Shuttle; something that would "give STS something to do" while showcasing its versatility and usefulness. At the same time, the new project was going to provide much-needed employment for as many NASA centers and aerospace contractors as possible. NASA had been unable to afford hiring new employees for much of the 1970s, and it was hoped that a large space station would persuade more young engineers to join the agency.
Space stations were part of a very ambitious post-Apollo space program proposed by the Space Task Group in 1969. NASA awarded two $2.9-million Phase-B space station definition contracts to McDonnell-Douglas (McDAC) and North American Rockwell (NAR) in July 1969. The space station contractors reported back in June 1970. McDonnell-Douglas (McDAC) proposed a design consisting of two 10-meter diameter modules, each capable of supporting a crew of six. The basic 12-crew space station would consist of two modules mated to a large nuclear power generator (fig.) . The entire complex would be launched unmanned on a Saturn V heavy-lift rocket (fig.) and deploy its antennas and other equipment in orbit (fig.) . Smaller cargo modules containing supplies and experiments for the crew would be launched by McDAC's Phase-A space shuttle (fig.) . The power generator boom would then extend, putting the nuclear reactor at a safe distance from the crew (fig.) . The space shuttle would then transport crews as well as smaller expansion laboratory modules in its 4.5-meter diameter cargo bay. The laboratory modules would be customized for different kinds of research, including free-flying modules for space-based astronomical observations (fig.) . In compliance with NASA's instructions, McDAC also investigated a larger 50-man space base (fig.) , and a much larger 400-man "space hotel" (fig.) that would have been assembled from 9 and 18 basic 12-man space station modules, respectively. The space base would have been launched around 1980 to support large scale manned space activities in low Earth orbit. Smaller space stations would have been launched into geostationary and lunar orbit during the mid-/late 1970s to support manned lunar exploration (fig.) . The smaller 6-crew space station module would also have housed Mars-bound astronauts in 1982-86 (fig.) . North American Rockwell's Phase-B space station was largely similar, apart from the power generation system (solar arrays rather than nuclear power). Like McDAC, NAR would have developed a smaller 6-man space station (fig.) and a larger 12-man, two-module variant (fig.) . North American Rockwell's primary space base proposal (fig.) would have changed from photovoltaic to nuclear power generators mounted on long booms just like McDAC's configuration, and an alternate space base design (fig.) would have moved most of the equipment from the non-rotating weighless core segment to the rotating arms, where artificial gravity would be generated.
NASA was forced to concentrate all its efforts on the Space Shuttle when Congress and President Nixon's Office of Management and Budget indicated they were prepared to pay for only one project at a time. Work on the space station still continued for some time, but NASA now started to promote a modular design that could be assembled gradually from smaller 4.5-meter modules launched by the shuttle. The initial version might support a crew of six (fig.) , and later grow to a 12-astronaut capability by adding more modules (fig.) . NASA mostly considered using 17.7x4.3 meter cylindrical modules, but a shorter 8.9x4.3 meter design was also investigated. The North American Rockwell (fig.) and McDonnell-Douglas (fig.) space station study contracts were extended until January 1972 to cover modular space station work. NASA was still hoping to launch a smaller space station in 1978, but the budget crunch soon forced the agency postpone its space station plans to the 1980s. Today's International Space Station is basically similar to the early 1971 studies, though.
NASA carried out a number of space station studies while the Shuttle was being developed in the mid-1970s. The first was McDonnell-Douglas' Manned Orbiting Facility (MOF) (fig.) , a small 4-man space station that would have been configured differently (fig.) for various missions, much like the Soviet Salyut stations. Another 1970s design was North American Rockwell's "Austere Modular Space Station" (fig.) . The most important application in those days was constructing large space structures, e.g. extremely large communications satellites (fig.) , giant 20 kilometer-wide solar power satellites (fig.) or even giant orbiting space colonies for millions of people (fig.) . Contemporary space station studies such as Rockwell's (fig.) and Boeing's (fig.) were closely tied to this objective. NASA's Outlook for Spacereport from 1975 recommended a number of possible goals, including development of a 12-man space station in low Earth orbit by 1988 (fig.) and a similar station in lunar orbit by 1994 (fig.)
By 1979, when the Space Shuttle development program was nearing completion, the stage had been set for two detailed space station studies; the NASA/Johnson Space Center's Space Operations Center and NASA/Marshall Space Flight Center's Science & Applications Manned Space Platform