In Their Own Words: James Kernan on Software Testing

James Kernan worked on computer engineering and software during the Apollo Program at MIT/Draper. 

"My name is Jim Kernan. I worked on the software and I always liked the lunar module work so I kind of steered and stayed with the lunar module software from almost its inception up until the lunar landing.

All the software had to be tested rather exhaustively in order to make sure that it met all the the environmental constraints. We had a wonderful simulator which the lab built. So there was a lot of different “ifs,” “ands,” and “buts” thrown at these software to see whether it would behave correctly and under stress. So the designing of that software and those tests was an important problem, an important job.

Apollo 11 was the first lunar landing. The lunar rendezvous radar switch was in the wrong direction. The electronics were not synced up right. The computer was getting a constant stream of pulses from the radar that was eating into the time available for the useful computation. So there was a series of overloads during the landing. The software was not explicitly tested under all those kinds of conditions. That's something we didn't really foresee as happening. But as soon as it did happen we ran all sorts of tests and made sure that the lunar module would be able to do all the tasks that were necessary to bring the crew back. It worked wonderfully and the landing was a success in spite of all those problems."