North American DC-3

The DC-3 was a proposed spaceplane designed by Maxime Faget at the Manned Spacecraft Center (MSC) in Houston. The design was nominally developed by North American Aviation (NAA), although it was a purely NASA-internal design.

Unlike the eventual Space Shuttle design that emerged, the DC-3 was a fully reusable launch vehicle two-stage-to-orbit design with a smaller payload capacity of about 12,000 lbs and limited maneuverability. Its inherent strengths were good low-speed handling during landing, and a low-risk development that was relatively immune to changes in weight and balance.

Work on the DC-3 program ended when the US Air Force joined the Shuttle program; they demanded a much greater "cross-range" maneuverability than the DC-3 could deliver, and expressed serious concerns about its stability during re-entry. NAA eventually won the Shuttle Orbiter contract, although it was based on a very different design from another team at MSC.

In the mid-1960s the US Air Force conducted a series of classified studies on next-generation space transportation systems. Among their many goals, the new launchers were intended to support a continued manned military presence in space, and so needed to dramatically lower the cost of launches and increase launch rates. Selecting from a series of proposals, the Air Force concluded that semi-reusable designs were the best choice from an overall cost basis, and the Lockheed Star Clipper design was one of the most-studied examples. They proposed a development program with an immediate start on a "Class I" vehicle based on expendable boosters, followed by a slower development of a "Class II" semi-reusable design, and perhaps a "Class III" fully reusable design in the further future. Although is it estimated that the Air Force spent up to $1 billion on the associated studies, only the Class I program that proceeded to development, as the X-20 Dyna-Soar, which was later cancelled.

Not long after the Air Force studies, NASA started studying the post-Project Apollo era. A wide variety of projects were examined, many based on re-using Apollo hardware (Apollo X, Apollo Applications Program, etc.) Flush with the success of the moon landings, a series of ever-more ambitious projects gained currency, a process that was considerably expanded under the new NASA director, Thomas O. Paine. By about 1970 these had settled on the near-term launching of a 12-man space station in 1975, expanding this to a 50-man "space base" by 1980, a smaller lunar-orbiting station, and then eventually a manned mission to Mars in the 1980s. NASA awarded $2.9-million study contracts for the space stations to North American and McDonnell Douglas in July 1969.

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