Introduction
There are many publications relating to Mercury, Gemini, Apollo, Skylab, Apollo-Soyuz Test Project, and the Space Shuttle. This paper presents an objective review of some of the technical considerations of the design, development, and operation of these spacecraft. Although there were many triumphs, a number of surprises, and not a few setbacks during the 39-year period covered, such incidents will be mentioned only in the context of technical significance. A little more than 19 years elapsed between 20 February 1962, when John Glenn first rode Mercury into orbit, and 12 April 1981, when John Young and Robert Crip-pen inaugurated orbital flight for the Space Transportation System, or the Space Shuttle as it is commonly called. A comparison of the Mercury capsule and the spaceship Columbia reviews the extent of progress made during these first years of manned flight.
During the early 1920s after approximately 19 years of development, the aviation industry was also entering the transportation phase. But there is a significant difference between the development of airplanes and the development of manned spacecraft. Early airplanes were relatively cheap and easy to build. Often, only one person and at most just a handful would be sufficient to do the entire design job. Consequently, a great number of airplanes was built and flown. This led to a rapid evolutionary process for both the design and the operation of aircraft, and a number of accidents and fatalities provided a strong cooperative influence on any misdirection. The philosophical basis for the design and operation of spacecraft has had to progress without this impartial and unerring guidance of ”survival of the fittest.” As a substitute, we have had to rely on intensive analysis, extensive testing, imperfect simulations, and the judgment and experience of the hundreds of key people working on these programs.
American manned spacecraft by type together with a number of weights, dimensions, and features that characterize them are listed in Appendix A. Mercury was a first of a kind design, and the Gemini and Apollo command and service module (CSM) followed in an evolutionary trend. The Apollo lunar module (LM) and the Space Shuttle, on the other hand, represent new and distinctive designs and have unique features for which no prior art existed.
Project Mercury
The National Aeronautics and Space Administration (NASA) was established in October 1958, and within a few weeks, the first manned spacecraft program, Project Mercury, was initiated (1). To execute the program as quickly as possible, it was deemed desirable to choose an existing rocket for the launch vehicle. The Atlas, considered the most powerful that would be available during the desired time period, was chosen. Conservative estimates indicated that the Atlas could orbit approximately 900 kg (2000 lbm) of payload. The spacecraft grew almost 50% during its development period. When finally developed, the entry weight of the Mercury spacecraft was in excess of 1180 kg (2600 lbm). Fortunately, the Atlas performance also grew sufficiently during this period.
The basic purpose of Project Mercury was to expose several test pilots to orbital flight and to have them evaluate the experience so that future and more substantive programs could be planned (Appendix B). To move the program rapidly and because of severe weight constraints, the design of all systems was as simple as possible and provided only the basic necessities of launch, a short orbital flight, and safe descent and landing. A simple ballistic configuration designed to minimize reentry heating was chosen. Although kept as simple as possible, each active system had at least one level of redundancy. Descent was initiated by firing three solid retrorockets; however, a safe reentry was ensured if only two of these rockets fired. A parachute system that was backed up by a reserve system of identical design provided a safe landing. Redundant sets of hydrogen peroxide monopropellan
