DSKY Simulation

In Their Own Words: Ed Smally on Testing the Apollo Guidance Computer

Edwin Smally
Ramon Alonso with Apollo Guidance Computer in MIT Film
Albert Hopkins

"Dr. Alonso and Dr. Hopkins hired me in December 1959. At that time they had a grant to work on designing a computer that would work in outer space. Sometime in the early 1960's The US government (NASA) gave Dr. Draper of the MIT Instrumentation Laboratory the responsibility to design a guidance system for a spacecraft that would fly to the moon and back. Alonso and Hopkins were natural choices to be involved in designing the computer part of the guidance system. Working for them I was lucky enough to be in the right place to also be part of the team that designed and built the prototype computers. My recollection is that Eldon Hall was in charge of the group that designed the computer and built the prototypes. Alonso and Hopkins were lead engineers in the group.

There came a time when it was realized there was going to be a need for testing the computer. Various methods of testing were discussed with Alonso and Hopkins. They let me design the tests using the approach I wanted to do but said if it didn't work I would have to do it the way they recommended. It worked and AGC-SELF-CHECK was born. A check of the DSKY was added later. An explanation and description of the test for the BLOCK I prototype is explained in MIT Instrumentation Apollo report E-1877 November 1965 and the BLOCK II prototype in report E-2065 December 1966. Both of these reports are in the Apollo and MIT/IL libraries. Designing the tests included using punch cards, where a single instruction was put on a card. A  series of cards (computer instructions like add, store. etc.) were put on a card reader to form a program.

The tests were used to verify the computer was functioning as designed. They were also run at Raytheon facilities in Waltham, MA while the computer was in extremely hot and extremely cold environments to make sure the computer could function as designed in those conditions .Coding for the tests were stored in the fixed rope memory. The tests were normally run as backup when other jobs were not running.

The seven original Astronauts met with some of us when they visited the Lab to train on and learn how the guidance system worked. They were Scott Carpenter, Gordon Cooper, John Glenn, Virgil “Gus” Grissom, Walter Schirra, Alan Shepard Jr. and Donald "Deke" Slayton. They were very interested in learning how the testing programs made sure the guidance system was working correctly and asked many questions. I thought Deke Slayton asked the most probing questions.

After Apollo, I continued to work at the MIT Instrumentation Lab, which later became The Charles Stark Draper Laboratory, designing tests for the computer part of the guidance system for the Poseidon missile. Until this time the guidance system had been made up of 2 separate hardware parts, a computer was one part. Devices that measured and controlled the location and acceleration of the spacecraft were the other part. After Poseidon these two parts were integrated into one piece of hardware. This could be done because digital logic replaced much analog logic in the guidance part. I then was responsible for designing tests for the first 2 iterations of the guidance system for the Trident missile.