NAA eventually won the Shuttle Orbiter contract, based on a very different design from another team at MSC.

Although it is estimated that the Air Force spent up to $1 billion on the associated studies, only the Class I program proceeded to development, as the X-20 Dyna-Soar, which was later cancelled.

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.

NASA awarded $2.9-million study contracts for the space stations to North American and McDonnell Douglas in July 1969.

George Mueller was handed the task of developing plans for such a system, and held a one-day symposium at NASA headquarters in December 1967 to study various options.

On 30 October 1968 NASA officially began work on what was then known as the "Integral Launch and Re-entry Vehicle" (ILRV), a name they borrowed from the earlier Air Force studies.

NASA Houston and Huntsville jointly issued the Request for Proposal (RFP) for eight-month Phase A ILRV studies.

General Dynamics, Lockheed, McDonnell-Douglas, Martin Marietta, and (the newly named) North American Rockwell were invited to bid.

Unlike a conventional aircraft, with separate fuselage and wings, the ILRV designs had blended wing-body layouts.

Re-entry was accomplished in a 60 degree nose-high attitude that presented the lower surface of the spacecraft to the airflow, using a ballistic blunt-body approach that was similar to the one Faget had successfully pioneered on the Mercury capsule.

After re-entry, when the spacecraft entered the lower atmosphere, it would pitch over into a conventional flying attitude, ducts would open, and jet engines would start up for landing.

Although the DC-3 had never been part of the original ILRV plans, Faget's name was so well respected that others at NASA MSC in Houston quickly rallied around him.

In order to clear the logjam developing between the departments, on 23 January 1970 a meeting was held in Houston to study all of the in-house concepts.

Over the next year a number of proposed designs would be dropped, including the entire series of lifting-body-derived vehicles as it proved too difficult to fit cylindrical tanks into the airframe.

Later he demanded that the program be greatly reduced even from the smallest of the Task Group's proposals, forcing them to select either the space base or the shuttle.

However, NASA's estimates of the shuttle development costs were met with great skepticism by the Office of Management and Budget (OMB).

The Air Force's requirements were based on a projected series of large spy satellites then under development, which were 60 feet long and weighed 40,000 lbs.

At almost 35° N, the distance it would move over a single orbit would be slightly smaller than KSC, but critically, the shuttle would be traveling south, not east.

Given existing project budgets, this limited any spending on the shuttle to about $1 billion a year, far less than required to develop any of the completely reusable designs.

Based on these constraints, NASA returned to a Class II-like vehicle with external tankage, which led to the MSC-020 design.

Later that year all straight-wing designs were officially abandoned, although Faget's team continued to work on them for some time in spite of this.

Both were similar to "jumbo jets" in layout in general terms, with their large cylindrical fuselage containing fuel tanks instead of passengers or cargo.

The empennage was a conventional three-surface unit, although in the original MSC-001 design the delta-shaped horizontal stabilizer was located at the bottom of the fuselage and served double-duty in protecting the rear-mounted engines during re-entry.

This arrangement was used in order to center the cargo over the wing, with the heavier oxygen and crew compartment balancing the weight of the engines.

The orbiter would re-enter nose-high at an angle of about 60 degrees above horizontal, decelerating at a peak of 2G until it reached low subsonic speeds at 40,000 ft. At this point the forward speed of the craft would be very low, so the nose was pitched down and the orbiter dove to pick up airspeed over the wings and transition to level flight.