Final Design
While NASA would likely have chosen liquid boosters had it complete control over the design, the Office of Management and Budget insisted on less expensive solid boosters due to their lower projected development costs. While a liquid-fueled booster design provided better performance, lower per-flight costs, less environmental impact and less developmental risk, solid boosters were seen as requiring less funding to develop at a time when the Shuttle program had many different elements competing for limited development funds. The final design which was selected was a winged orbiter with three liquid-fueled engines, a large expendable external tank which held liquid propellant for these engines, and two reusable solid rocket boosters.
In the spring of 1972 Lockheed Aircraft, McDonnell Douglas, Grumman, and North American Rockwell submitted proposals to build the shuttle. The NASA selection group thought that Lockheed's shuttle was too complex and too expensive, and the company had no experience with building manned spacecraft. McDonnell Douglas's was too expensive and had technical issues. Grumman had an excellent design which also seemed too expensive. North American's shuttle had the lowest cost and most realistic cost projections, its design was the easiest for ongoing maintenance, and the Apollo 13 accident involving North American's Command/Service Module demonstrated its experience with electrical system failures. NASA announced its choice of North American on 26 July 1972.
Read more about this topic: Space Shuttle Design Process
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