The 1969 computer game Lunar Lander with text output received a patch from a retired programmer

Retired programmer Martin C. Martin discovered a bug in the original physics code of the 1969 computer game Lunar Lander. Created by then 17-year-old high school student Jim Storer, this «prototype» game only displayed textual status updates on a teletype. In fact, the game is a space simulator.

The legendary game that Storer developed on a computer PDP-8 programming language FOCAL just a few months after Neil Armstrong and Buzz Aldrin landed on the moon. The game allows you to control the descent of the module to the lunar surface. Players must carefully control their fuel usage to achieve a soft landing, making important decisions every ten seconds to spend the right amount of fuel.

In 2009, shortly before the 40th anniversary of the first moon landing, Benj Edwards of Ars Technica decided to find the author of Lunar Lander, which was then known mainly as a graphic game thanks to the 1974 version and the 1979 arcade game for the Atari. He discovered that Jim Storer had created the oldest known version as a teletype game, interviewed him, and wrote a history of the game. Storer later published the source code for the original game.

In 2024, Martin K. Martin, an artificial intelligence expert, game developer, and former MIT graduate student, came across a bug in Storer’s code while researching the optimal landing strategy for a module with maximum fuel efficiency. The optimal method involves free-falling to gain speed, and then igniting the engines at the last possible moment to slow down for safe contact with the surface.

«Recently, I was researching the optimal fuel burn schedule to land as smoothly as possible and with the maximum amount of fuel left. Surprisingly, the theoretically best strategy didn’t work. The game mistakenly believes that the lander does not touch the surface, when in fact it does. As I delved deeper, I was amazed at the complex physics and calculations in the game. Eventually I found the bug: a missing division by two that had gone unnoticed for almost 55 years», — wrote Martin on his blog.

Despite the mistake, Martin was impressed that Storer, who was a high school student at the time, had managed to incorporate advanced mathematical concepts into his game — an achievement that remains exceptional even by today’s standards. Martin reached out to Storer for comment, and the Lunar Lander author said that his physicist father helped him derive the equations used in the simulation.

Mistakes in games don’t always prevent us from enjoying them. But, fortunately for astronauts Aldrin and Armstrong, the real «Apollo» moon landing was calculated without such an error.