Apollo Moon Landing Computers

To The Moon on 64K

As we celebrate the 40th anniversary of the Apollo 11 moon landing, let's look at the computers that got us there:

Even the simplest software today would far exceed the technical constraints the Apollo team worked under. The so-called Apollo Guidance Computer (AGC) used a real time operating system, which enabled astronauts to enter simple commands by typing in pairs of nouns and verbs, to control the spacecraft. It was more basic than the electronics in modern toasters that have computer controlled stop/start/defrost buttons. It had approximately 64Kbyte of memory and operated at 0.043MHz.

While the astronauts would probably have preferred to fly the spacecraft manually, only the AGC could provide the accuracy in navigation and control required to send them to the Moon and return them safely home again, independent of any Earth-based navigation system.

Along with the APG, mainframes were also heavily used in the Apollo programme. Over 3,500 IBM employees were involved, (pictured below). The Goddard Space Flight Center used IBM System/360 Model 75s for communications across Nasa and the spacecraft. IBM Huntsville designed and programmed the Saturn rocket instrument unit, while the Saturn launch computer at the Kennedy Space Center was operated by IBM.

An IBM System/360 Model 75 was also used at Nasa's Manned Spacecraft Center in Houston. This computer was used by Neil Armstrong and Buzz Aldrin to calculate lift-off data required to launch the Lunar Module off the Moon's surface and enable it to rendezvous with Command Module pilot Michael Collins for the flight back to Earth.

At the time, IBM described the 6Mbyte programs it developed, to monitor the spacecrafts' environmental and astronauts' biomedical data, as the most complex software ever written.