Reconstructing the Apollo Guidance Computer

Photo of the Lunar Module console taken in September 1968

Photo of the Lunar Module console taken in September 1968

The Apollo programme is arguably one of the greatest technical achievements of mankind. Of special interest to me, is the Apollo Guidance Computer (AGC) which handled the navigation and control systems in both the Command Module (CM) and the Lunar Module (LM).

The AGC was a remarkable piece of hardware, built at a time when computers occupied entire floors in buildings. Because weight, size and power consumption were critical items on the Apollo program, the designers made a bold decision to use integrated circuits rather than discrete transistors. This critical design decision was made in 1962, only a few years after the first integrated circuit was made.

The initial integrated circuits were extremely expensive ($120 for a single three-input NOR gate!) and unreliable. Over time, the price came down and quality improved. At a certain stage during the Apollo development, NASA consumed almost 80% of all integrated circuits manufactured in the US. Demands from the space program for smaller and more reliable integrated circuits, prompted many electronics manufacturers to invest heavily in this field. This in turn caused prices to drop substantially while newer and more powerful chips became available. Almost 10 years after the first integrated chips were used by MIT in the Apollo Guidance Computer, IBM and many other computer manufacturers also started using ‘chips’ in their designs.

As the first computer to use integrated circuits, the Apollo computer played it’s part in creating the perfect storm that led to the digital revolution.