PGNCS (the Apollo Primary Guidance and Navigation System) generated unanticipated warnings during Apollo 11’s lunar descent, with the AGC showing a 1201 alarm (“Executive overflow - no vacant areas”) and a 1202 alarm (“Executive overflow - no core sets”). The cause was a rapid, steady stream of spurious cycle steals from the rendezvous radar, intentionally left on standby during the descent in case it was needed for an abort. During this part of the approach, the processor would normally be almost 85% loaded. The extra 6,400 cycle steals per second added the equivalent of 13% load, leaving just enough time for all scheduled tasks to run to completion. Five minutes into the descent, Buzz Aldrin gave the computer the command 1668 which instructed it to calculate and display DELTAH (the difference between altitude sensed by the radar and the computed altitude). This added an additional 10% to the processor workload, causing executive overflow and a 1202 alarm. After being given the “GO” from Houston, Aldrin entered 1668 again and another 1202 alarm occurred. When reporting the second alarm, Aldrin added the comment “It appears to come up when we have a 1668 up”. Luckily for Apollo 11, the AGC software had been designed with priority scheduling. Just as it had been designed to do, the software automatically recovered, deleting lower priority tasks including the 1668 display task, to complete its critical guidance and control tasks. Guidance controller Steve Bales and his support team that included Jack Garman issued several “GO” calls and the landing was successful. For his role, Bales received the US Presidential Medal of Freedom on behalf of the entire control center team and the three Apollo astronauts.
Many of you may know that I am a lover of history. However, you may or may not be aware that I am also a lover of medicine. Of several reasons into becoming a medical student, historical medicine is one of them. I am in a constant state of fascination at what it used to be and how far it’s come. That being said, I fell in love with this show that comes on Cinemax titled The Knick.
"In New York City in 1900, the Knickerbocker Hospital operates with innovative surgeons, nurses and staff who have to overcome medicinal limitations to prevent staggeringly high mortality rates" [x]
I recommend that some of you, whether interested in medicine or not, should give this show a try.