This is the code that sent Apollo 11 to the moon (and it’s awesome)

Science & Technology

Introduction

When we think about the moon landing, the first images that might come to mind are those of the courageous astronauts: Neil Armstrong, Buzz Aldrin, and Michael Collins. Additionally, the Saturn V rocket, a towering 360-foot engineering marvel, often steals the spotlight as it was responsible for transporting the Apollo 11 mission into space. However, the unsung hero of this historic venture lies in the background: the Apollo Guidance Computer (AGC) and its remarkable source code, which played a crucial role in taking humans to the moon.

The Apollo 11 Mission Overview

The Apollo 11 mission, successful on July 20, 1969, marked the first occasion when humans set foot on the lunar surface, an achievement involving a complex orchestration of equipment and personnel. Central to this mission were two spacecraft components: the Command Module and the Lunar Module.

The Command Module, which housed the three astronauts, was responsible for transporting them to the moon and returning them safely to Earth. While Armstrong and Aldrin descended to the lunar surface in the Lunar Module, Collins continued orbiting the moon in the Command Module.

Both modules required navigation capabilities, for which they relied heavily on the Apollo Guidance Computer. The AGC was an advanced component of NASA's guidance system, comprising two identical units—one in the Command Module and another in the Lunar Module—running unique software tailored to their specific tasks. The AGC was groundbreaking for its time, capable of multitasking, thus enabling it to handle multiple programs simultaneously during the mission.

The Apollo Guidance Computer

The AGC was, by modern standards, a relatively underpowered machine. It had a RAM capacity of just 3,840 bytes and read-only memory equivalent to about 69,000 bytes. To put that into perspective, the AGC's RAM was merely 0.45% of the typical RAM found in today's smartphones. Still, this sophisticated piece of engineering had a tremendous impact, showcasing the resourcefulness of its creators.

Margaret Hamilton, a key figure in this story as the director of software engineering at MIT Instrumentation Laboratory, and her team were responsible for developing the source code for not just Apollo 11, but multiple Apollo missions as well. Hamilton even coined the term "software engineer." The AGC software for Apollo 11 primarily consisted of two major programs: Luminary, which controlled the Lunar Module during its descent and landing, and Colossus, which managed the Command Module.

The software was written mostly in Assembly Language, a low-level programming language giving programmers intricate control over computer hardware. The original code, a massive script, was subsequently organized into smaller, manageable components for better clarity and structure.

A Touch of Humor in Code

What is especially fascinating about the Apollo 11 source code is the unexpected presence of humor and personality within the comments and naming conventions. For instance, an ignition routine was dubbed “burn baby burn,” and a section of the code related to the astronauts' interface was titled “pinball game buttons and lights.” One comment even quote Shakespeare, reflecting the programmers' creative spirits while navigating the intense pressure of the mission.

The Known Errors

Although the AGC performed admirably during the mission, it was not without its challenges. During the Lunar Module’s descent, two alarms—1201 and 1202—highlighted an overload of tasks being processed by the AGC. This was due to a radar system inadvertently sending additional signals while the astronauts were attempting to display data about their altitude. When the issue arose, Houston's flight controllers determined that the landing should proceed despite the alarms. Notably, the underlying cause was attributed to a known hardware problem, not a software error, which is often misrepresented in the media.

Conclusion

The Apollo Guidance Computer and its source code reflect an incredible fusion of hardware ingenuity and sophisticated programming in a time long before the conveniences of modern-day computing. The success of the Apollo 11 mission stands as testimony to human creativity, resilience, and the relentless pursuit of exploration. For more detailed insights into this fascinating subject, many resources and links provide further information.

Keywords

  • Apollo 11
  • Moon landing
  • Apollo Guidance Computer (AGC)
  • Command Module
  • Lunar Module
  • Software engineering
  • Margaret Hamilton
  • Assembly Language
  • Source code
  • Multitasking
  • Humor in programming

FAQ

Q: Who were the astronauts involved in the Apollo 11 mission?
A: The three astronauts were Neil Armstrong, Buzz Aldrin, and Michael Collins.

Q: What role did the Apollo Guidance Computer play in the mission?
A: The AGC was responsible for navigation and guidance, enabling the spacecraft to perform various functions during the journey to the moon and back.

Q: What programming language was used for the AGC?
A: The software for the AGC was primarily written in Assembly Language.

Q: What do the errors 1201 and 1202 refer to?
A: These errors indicated that the AGC was overloaded with tasks during the Lunar Module’s descent but were not due to programming errors.

Q: What was notable about the comments in the AGC’s source code?
A: The code included humorous comments and playful remarks from the programmers, reflecting their personalities and creativity amidst a high-pressure environment.