Digital Apollo: Human and Machine in Spaceflight (review)

The subtitle of this book, rather than the title, gives the best description of the volume's contents. Digital Apollo deals with the ways in which the digital computer shaped the role of the Apollo astronauts. It is part of the growing literature on the space programs of the 1960s that strives to understand how these projects operated, how individuals and institutions defined their positions in them, and how specific factors contributed to their success.

Mindell's study builds upon three very different kinds of books. It clearly is based upon technical histories of the US Space program, such as Computers in Spaceflight (NASA History Office, 1988), by former Annals editor James Tomakyo, but it also follows in the tradition of Inventing Accuracy: An Historical Sociology of Nuclear Missile Guidance (MIT Press, 1990), Donald Mac Kenzie's sociological study of inertial guidance systems, and The Right Stuff (Farrar Strauss and Girous, 1979), Tom Wolfe's description of the difference between the public and private persona of the Mercury astronauts. In particular, Mindell analyzes how inertial guidance computers in general, and the Apollo Guidance Computer in particular, shaped the roles of the astronauts.

As chronicled by both Mindell and Wolfe, the early astronauts wanted to fly the Mercury, Gemini, and Apollo spacecraft. They wanted to be at the controls when their rocket left the pad, to direct their machine through its flight, and to guide the spacecraft through its final landing. Many of the first astronauts had done just these tasks as test pilots in the US Air Force X-15 program. Mindell shows that many leaders of the American space program, including Werner von Braun, were opposed to letting the astronauts control the spacecraft. He also suggests that, by describing the training and research exercises conducted with the astronauts, such human control would have been close to impossible to achieve.

The astronauts had sufficient political clout within NASA to prevent the immediate adoption of autonomous digital control for spaceflight. At the same time, they saw engineering demands whittle away at their ability to control the spacecraft. NASA leaders eventually concluded that they would control much of the lunar missions from Houston. On the first trip to the moon, the human pilots devoted most of their effort to verifying computer navigation rather than to navigating the ship itself.

At the same time, NASA engineers did allow the astronauts a certain amount of control over their spacecraft. As a result, the computer became a mediating device, a machine that allowed the astronauts the opportunity to manipulate an idealized model of spaceflight. Once the astronauts had decided where they wanted their ship to go, the computer determined the appropriate sequence of thruster firings to get the machine in the right place and in the right attitude. The Gemini program showed the necessity for such mediation, as the astronauts found that the understanding of motions and forces that they had gained from piloting aircraft did not help them rendezvous with other spacecraft in orbit.

The book culminates in a discussion of the interaction between the guidance computer and the pilot of the lunar lander in the six Apollo landings. On all six flights, the pilot took control of the lander during the final descent. In each instance, NASA argued that the pilot was justified in doing so because human beings were better judges of the landing sites than the computer. Mindell's work suggests that such a conclusion was not always justified. In most cases, the pilots simply wanted to fly their machines to the moon.

Digital Apollo builds upon Mindell's prior work on black box engineering and feedback control loops—see, for example, Between Human and Machine (Johns Hopkins Press, 2002). It contains enough technical description of the Apollo Guidance Computer to satisfy most readers of the Annals and it contains an interesting discussion of the Kalman filter, a mathematical algorithm that greatly simplified navigational and guidance programs. At the same time, the book does not present the detailed design...