I have learned from my twenty years of service in the U.S. Air Force, significant background knowledge of the history of the space shuttle. In September 1969, two months after the first manned lunar landing, a Space Task Group appointed by the President of the United States to study the future course of U.S. space research and exploration made the recommendation that "…the United States accept the basic goal of a balanced manned and unmanned space program.
To achieve this goal, the United States should …develop new systems of technology for space operation…through a program directed initially toward development of a new space transportation capability…"
According to Cox (1962), many responsible observers felt that we were devoting too many of our resources to increasing an already affluent volume of private consumption and too little for public services, including space-flight programs.
In early 1970, NASA initiated extensive engineering, design, and cost studies of a space shuttle. These studies covered a wide variety of concepts ranging from a fully reusable manned booster and orbiter to dual strap-on solid propellant rocket motors and an expendable liquid propellant tank. Each concept evaluated development risks and costs in relation to the suitability and the overall economics of the entire system.
On January 5, 1972, President Richard M. Nixon announced that NASA would proceed with the development of a reusable low cost space shuttle system. NASA and its aerospace industry contractors continued engineering studies through January and February of 1972; finally on March 15, 1972, NASA announced that the shuttle would use two solid propellant rocket motors. The decision was based on information developed by studies that showed that the solid rocket system offered lower development cost and lower technical risk.
On September 17, 1976, the first orbiter spacecraft, Enterprise, was rolled out. A total of thirteen test flights were performed.
Cited: Donald Cox (1962). The Space Race. Chilton Company Publishers, Philadelphia & New York Louis Rotundo (1994). Into The Unknown. Smithsonian Institution Press, Washington & London The Encyclopedia Americana International Edition, Vol 25, (1998), Grolier Incorporated, Connecticut