The AGC - An unsung hero

The AGC: Apollo Guidance Computer is the unsung hero in the race to the moon, a visionary piece of hardware that had to work, always, was something totally new, a compact digital computer designed to enable man to navigate in space with no margin for error. 

When Apollo 11 touched down in the Sea of Tranquility on July 20, 1969, it was more than a triumph of the human spirit, it was also the story of a cybernetic wonder called the Apollo Guidance Computer (AGC), which helped the Apollo astronauts safely navigate to the Moon and back. It was a computer so advanced for its time that the engineers who created it said they probably wouldn't have tried to do so if they'd known what they were getting themselves into.

The Apollo Guidance Computer is one of the unsung successes of the Space Race. This is probably because it was so phenomenally successful, having had very few in-flight problems – and most of those were due to human error. Carried aboard both the Command Service Module (CSM) and the Lunar Module (LM), it flew on 15 manned missions, including nine Moon flights, six lunar landings, three Skylab missions, and the Apollo-Soyuz Test Mission in 1975.

At the time it was the latest and most advanced fly-by-wire and inertial guidance system, the first digital flight computer, the most advanced miniature computer to date, the first computer to use silicon chips, and the first onboard computer where the lives of crew depended on it functioning as advertised.

The reason for the AGC.

The reason why all the Apollo missions carried at least one of these computers is that the Moon missions involved navigation problems that would have made Captain Cook go bug eyed. On Earth, navigation is, at its simplest, about finding one's way from one fixed point on the globe to another. For a trip to the Moon, it's like standing with a rifle on a turntable that's spinning at the center of a much larger turntable on which is a third turntable sitting on the rim, with all the tables spinning at different and varying speeds, and trying to hit the target by aiming at where it will be three days from now.

Why it worked ... always.

That was when computer pioneer Halcombe Laning came up with a solution. Instead of timesharing, the AGC was programmed for priority. In other words, each program was numbered in order of importance at any particular point in the mission timeline. If a higher priority program needed the computer, the others would simply stop and wait for it to finish, then resume. Meanwhile, the temporary memory held the data up to the point of stoppage in a way similar to that of a modern computer going into sleep mode. This not only eliminated crashes, but also allowed the crew to interrupt a running program with new data as it came in.

Read the entire New Atlas piece as its exquisitely detailed and utterly fascinating to the max. Without question, you will learn how really creative people invented new tech on the fly that went to where no man has ever gone before.

Click here to run the AGC simulator. Stellar to a fault.