MIT Analog Computer Laboratory

Space Engineers and Simulations

Portrait of Tom Fitzgibbon
Draper Engineer Bill Robertson
George Schmidt
Phillip Felleman
Lance Drane
Malcolm Johnston
Ain Laats

How can we practice going to the moon? 

There was no rule book; there was no example to follow. Before anyone could walk on the moon, the Apollo space engineers first had to invent a way for mankind to navigate there. With no internet, no personal computers and no smart phones, the team at Draper labs had to invent a compact digital system to navigate millions of pounds of material (and some very VIP astronauts!) hurtling through space. 

With an initial design for an Apollo Guidance Computer in place the next step was to test it out – run it through every possible situation it would encounter during it’s maiden voyage. But the team was stuck. How could they thoroughly test a space navigation tool while stuck on Earth? The answer they hacked was to invent a computer simulation, a technology and concept that had never been used in this way before.

"We had an actual mock up cockpit with the Apollo computer and the keyboard. And one of the mockups was actually open to the air and that they could look through the telescope and see the stars," recalls Bill Robertson, Draper Engineer. 

In the 1960s these engineers were building the computers, piece by piece, wire by wire, and coding the computer programs to mimic the launch and orbit line by line. 

Tom Fitzgibbon, remembers how real these simulations were for the astronauts: "And as far as they were concerned they were in the spacecraft. They didn't know they were on the third floor of 75 Cambridge Parkway and the computer didn't know. The computer thought it was 150,000 miles out in space. 

The Apollo missions were really at the forefront of computer simulations and took the minimal existing technology to a whole new level. Before any of the astronauts were launched into space they flew in the simulator [or sim] hundreds if not thousands of times. NASA engineers loaded the programs with every hazard and emergency they could think of. This was really the beginning of the "what if" scenario engineers and scientists use today when developing new technologies. "They lived in the simulator, I mean literally lived in those simulators. That seems to be their most vivid memory is the relentless time in the simulator. " said team engineer David Mindell. 

The sim programs were very complicated because the actual Apollo spacecraft was controlled by small mini engines called reaction control jets. Add to that the dynamics of a rotating body in space that is often unbalanced and it makes for a very challenging environment to recreate, especially with 1960's computer technology. 

Giant sim computers filled entire labs strung together in a maze of thousands of wires. In the early days of the program the sim technology was all analog technology, just as the Apollo Guidance Computer evolved into a digital system, so did the simulation computers. Once they were using digital simulation technology the engineers were able to create the most realistic experience for the astronauts in training, a hybrid system, where actual flight hardware parts were used with digital analog accessory elements. This allowed the engineers to run the simulations in real time creating the most advanced and realistic sim program to date. 

Today the legacy of early sim technology developed for the Apollo program is immense and can be seen in the most popular video games, flight simulators for aviation and spaceflight as well as virtual reality technology.