The Real Story Behind the Apollo 11 Computer Error | WSJ

Summary

On July 20, 1969, during Apollo 11’s descent to the moon, a 1202 alarm flashed, causing panic as the computer overloaded and rebooted. Don Eyles, a young programmer responsible for the lunar landing code, was particularly anxious. The revolutionary Apollo computer, with its limited 36k memory capacity, was a feat of engineering but had constraints. When unexpected radar data flooded the system due to a switch error, the alarms sounded. Despite the chaos, mission control determined the computer still handled key functions, allowing Neil Armstrong to land safely. Eyles' code was faultless and continued to be used in subsequent missions.

Highlights

• Apollo 11’s landing was disrupted by the 1202 alarm, triggering panic due to computer overload. 🚨
• Don Eyles, a key programmer, had an unconventional start at NASA with no coding background. 🌟
• The Apollo computer was incredibly compact for its time, relying on just 36k memory. 🧠
• Despite limitations, the race was on to make the Apollo computer functional and precise. ⏱️
• Mission control's composure ensured a safe landing by trusting the essential functions were intact. ✅
• The alarm was caused by a human error with a radar switch, not the computer or code. 🛠️

Key Takeaways

• Apollo 11's 1202 error was due to a radar switch error, not a coding mistake. 😅
• The Apollo computer was pioneering, using integrated circuits to achieve compactness. 🖥️
• Mission Control's steady decision-making under pressure led to a successful moon landing. 🚀
• Don Eyles was critical in programming the lunar module, despite starting with no coding experience. 👨‍💻
• The limited memory forced ingenious coding techniques akin to poetry in motion. 📜
• Apollo's technology laid groundwork for future computing advances, showcasing a lapidary art of coding. 🌌

Overview

In the summer of 1966, Don Eyles found himself unexpectedly joining the MIT Instrumentation Lab, a decision that catapulted him into the heart of the Apollo missions, where he became instrumental in coding the lunar module’s computer system. Despite having no coding experience, Eyles and his team were tasked with programming one of the most advanced computers of the era.

By 1969, Eyles was part of a monumental moment - the Apollo 11 moon landing. This mission was fraught with challenges, including the infamous 1202 and 1201 alarms that caused a near-abort scenario. The Apollo computers, limited by their 36k memory, were innovative yet constrained, pushing programmers to hone their craft into an art form of efficient coding.

During the landing, missteps with a radar switch triggered the alarms, not any fault in the software. Thanks to the trust and quick thinking at Mission Control, and the reliability of the code, Apollo 11 made its historic landing. Eyles’ work was subsequently validated across each Apollo mission, contributing significantly to computing history.

Chapters

• 00:00 - 00:30: Introduction to Apollo 11 Landing and Computer Error On July 20, 1969, during the Apollo 11 mission, the lunar module began its descent to the moon when a computer warning light, 1202, flashed. The computer had overloaded and rebooted, creating an anxious situation. Neil Armstrong requested more information, while Houston scrambled to find a solution.
• 00:30 - 01:00: Introduction of Don Eyles and His Contribution This chapter introduces Don Eyles, a computer programmer who played a crucial role in the Apollo lunar landing. It highlights his involvement in writing important code for the onboard computer used during the landing phase. The narrative emphasizes a tense moment involving a 1202 program alarm, showcasing Eyles' contributions to overcoming challenges during this historic event. The chapter also briefly touches on Eyles' accidental start at NASA at the young age of 23 in the summer of 1966.
• 01:00 - 01:30: Eyles' Unlikely Entry into NASA The chapter titled 'Eyles' Unlikely Entry into NASA' recounts the unexpected circumstances that led Eyles to become part of NASA's workforce. Initially, Eyles was returning from a discouraging job interview at an insurance company, willing to accept nearly any job offer that came his way. Serendipitously, he decided to walk into the MIT Instrumentation Lab and spontaneously inquired about employment opportunities, despite having no prior experience in coding. Surprisingly, he was offered a position, and that marked the beginning of his journey as one among the over 400,000 individuals contributing to NASA's efforts.
• 01:30 - 02:00: The Challenge of Moon Landing and Computer Programming This chapter discusses the monumental task of landing a human on the moon and developing the computer programming skills necessary to achieve it. It highlights the unprecedented nature of the Apollo mission and the vital role played by the MIT Instrumentation Laboratory in designing the guidance and navigation system for the spacecraft. In 1969, this system represented the pinnacle of human technological achievement.
• 02:00 - 02:30: Revolutionary Nature of the Apollo Computer The chapter explores the transformative impact of the Apollo computer, which marked a significant departure from the traditional, large-scale computers that occupied entire rooms. The Apollo computer was revolutionary due to its use of integrated circuits, enabling it to be much smaller and faster, with the entire system fitting into a one cubic foot space. This miniaturization was a groundbreaking development in computer technology.
• 02:30 - 03:00: Physical Attributes and Limitations of the Apollo Computer The chapter 'Physical Attributes and Limitations of the Apollo Computer' describes the physical dimensions and weight of the Apollo computer, mentioning it was roughly six inches by a foot by two feet and weighed about 70 pounds. Despite advancements, it had significant limitations, especially in memory capacity and operation speed. The transcript references the Apollo 11 mission's flight code for the lunar module, which comprised 36,000 instructions.
• 03:00 - 04:00: Significance of Efficient Code for Apollo Computer The chapter delves into the constraints and ingenuity behind the Apollo computer's design, particularly focusing on its limited memory capacity of 36k words. To illustrate the compactness, it's compared to a typical email today, which is around 75k. The necessity for reliability in computation during flight is addressed through the use of core rope memory, a then-novel technology. This form of memory was incredibly reliable and was physically integrated into six modules that fit into the computer's backside slots, highlighting the importance of efficient coding and storage.
• 04:00 - 05:00: The 1201 and 1202 Error Codes During Descent This chapter delves into the 1201 and 1202 error codes encountered during descent, likening it to inserting a CD-ROM into an early Mac. It highlights the importance of concise code, where each part must efficiently fulfill its function using minimal characters. The narrative underscores the necessity for code written by Eyles and his team to perform optimally within severe memory constraints, ensuring successful execution during critical phases like descent.
• 05:00 - 06:00: Mission Control's Decision to Proceed with Landing The chapter "Mission Control's Decision to Proceed with Landing" revolves around a critical moment during the Apollo 11 mission when the lunar module's computer was overwhelmed, triggering error codes 1201 and 1202. This created a tense situation as neither the astronauts nor Mission Control immediately understood what these alarms signaled. Despite the uncertainty, the team had to quickly decide whether to proceed with the landing or abort, underscoring the pressures and complexities of space exploration. The language used evokes a sense of precision and artistry, likening the actions to an art form.
• 06:00 - 07:00: Cause of the Error Codes and Resolution The chapter discusses the unexpected and rapid developments in technology over the past 50 years. It highlights that even the original programmers were uncertain about the outcomes of their creations. This uncertainty is reflected in the mention of error codes 1201 and 1202, which were particularly significant at the time, causing a tense atmosphere. The narrative suggests that while technology has advanced significantly and performs well, there remain significant challenges and dangers associated with its use, particularly in the context of space flights.
• 07:00 - 07:30: Legacy of Don Eyles' Work As the spacecraft began its final descent to the moon, there was a moment of tension and uncertainty. Mission control faced a brief alarm, causing fear and anxiety among the team. Don Eyles, feeling the gravity of the moment, thought the mission might be doomed and considered recommending an abort. However, the flight controllers in Houston had a better understanding of the situation and the perspective needed to handle it. This chapter highlights the intense moments and quick decision-making required during space missions, illustrating the legacy of Don Eyles and the collaborative efforts in mission control.

The Real Story Behind the Apollo 11 Computer Error | WSJ Transcription

• 00:00 - 00:30 - [CAPCOMM] Houston, you're looking good for separation. You're a go for separation, Columbia, over. - [Narrator] On July 20, 1969, just moments after the Apollo 11 lunar module began its descent to the moon a warning light flashed in the cockpit. - [Neil] 1202. - [Houston] 1202 alarm. - It's a 1202. - Standby. - [Narrator] The spacecraft's computer had overloaded and rebooted and no one knew why. As Houston scrambled to find an answer, an anxious Neil Armstrong requested more information.
• 00:30 - 01:00 - [Neil] Give us a reading on the 1202 program alarm. - [Narrator] Back on Earth, few were more nervous than a young computer programmer who had written the code for the lunar landing. - We were landing on the moon the first time. It's not surprising there were problems. My name is Don Eyles, I wrote a good part of the computer code for the onboard computer that was active during the lunar landing phase of the Apollo mission. - [Narrator] Eyles career at NASA began as a happy accident. - This was the summer of 1966, and I'd just turned 23.
• 01:00 - 01:30 I was walking back home from a rather dispiriting interview, I think at an insurance company. At that point I would have taken any job that anyone offered me. When I happened by the MIT Instrumentation Lab and walked in cold and asked for a job. - [Narrator] He had never written a line of code. Even so, Eyles was offered a position. That day he joined an army of over 400,000 scientists, engineers, and technicians
• 01:30 - 02:00 working on the most ambitious engineering project in human history. - No one knew how to land on the moon yet, just as no one knew how to program the computer, and we would figured out both. - Hello, today we're at the MIT Instrumentation Laboratory, which has been given design responsibility for this guidance and navigation system, which will direct our Apollo spacecraft on the way to the moon and back. - [Narrator] In 1969, this was the most sophisticated machine ever created.
• 02:00 - 02:30 Before Apollo, computers had mostly been vast behemoths, often taking up entire rooms or floors of buildings. - When you say this computer is very much like land-based computers, and yet I think of them as occupying whole bays of equipment. You've got all this squeezed into a little box. How did you do that? - [Narrator] What was revolutionary about the Apollo computer was that it was the first use of integrated circuits, which allowed for a much smaller and faster machine. - [Don] The computer was one cubic foot.
• 02:30 - 03:00 It was roughly six inches by a foot by two feet. And weighed I believe about 70 pounds. - [Narrator] Despite these advancements, the Apollo computer's limitations presented formidable challenges. - [Don] We were dealing with a computer that was very limited both in terms of its memory capacity and its operation speed. What this book in front of me is is a listing of the flight code for the lunar module for the Apollo 11 mission. This represents the contents of 36,000,
• 03:00 - 03:30 36k, words of memory. - [Narrator] To give you an idea of just how small 36k of memory is, an average email message today is about 75k. - Alternately for flight the information in a book like this would be woven into a type of memory called core rope that was super reliable. The result of that was six modules like the one in my hand. And these modules would be slid into slots in the back of the computer.
• 03:30 - 04:00 And that would be the code. That was equivalent to plug in the CD-ROM into your early Mac. - [Narrator] Memory was so precious, the code that Eyles and his colleagues wrote had to both do its job and also do so in as few characters as possible. - When you write a piece of code you're writing something that needs to, in as few words as possible, convey an idea. But at the same time it needs to
• 04:00 - 04:30 fall trippingly off the tongue of the central processor. You could call it a lapidary sort of art in the sense that you were dealing with small things and trying to get them just right. (static hissing) - [Computer] 1202 alarm. - [Narrator] So what was happening during Apollo 11's landing when the computer was overloaded. - 1202. - 1202 alarm. - [Houston] It's a 1202, standby. - [Narrator] The computer's display was flashing error codes 1201 and 1202, but the astronauts didn't know what those alarms meant.
• 04:30 - 05:00 And for 50 years, neither has much of the world. It all happened so fast. Not even the programmers who designed it were sure just what was happening. - [Reporter] There are many new things that are happening in this flight. There are big dangers involved, despite the best our technology can do and our technology does do very well. - Right here you see the 1201 and 1202 codes. At the time, we were sort of holding our breath.
• 05:00 - 05:30 You know, what is going to happen next? Is the spacecraft gonna keep flying okay? Or is it gonna somehow go outta control? - [Announcer] They got a momentary alarm on their system. - [Narrator] As the spacecraft began it's final descent to the moon, a terrified Eyles came to the conclusion that the mission was doomed. - There was a pit of the stomach feeling. If it had been up to me, I probably would have recommended an abort. - [Narrator] But flight controllers in Houston had a better perspective. Soon after the alarm started, Mission Control realized
• 05:30 - 06:00 that the computer was still running the critical guidance and navigation systems. - [Houston] Go, same type, we're go. Eagle, Houston, you are go for landing, over. - [Narrator] Rather than abort, they made the courageous decision for Apollo to proceed. Neil Armstrong took over control of the craft and Apollo, of course, landed safely on the moon. - [Neil] Houston, Tranquility Base here. The Eagle has landed. - There was no sense of blame. There was no one calling you and saying, "You fools, what did you do to us?"
• 06:00 - 06:30 but there were questions being asked. It was up to us to figure out what had happened. - [Narrator] The alarm issues were traced to an obscure condition in which a radar accidentally turned on, flooded the computer with unnecessary data. - The alarms were saying there's no more storage space, we're going to flush everything and sort of reconstruct it. Do what you would call a restart. - [Narrator] Eyles code wasn't bad, on the contrary, it had done exactly what it was supposed to do.
• 06:30 - 07:00 The issue was caused by human error in the hardware. Someone had accidentally flipped a switch when it shouldn't have been flipped. - It was determined that in fact the switches were set up in such a fashion that this weird condition could occur. - [Narrator] For his part, Eyles stayed on at NASA and his code was deployed successfully in every Apollo mission. - What was developed was actually extremely advanced for the time and in some ways its more advanced that some of what's being used today in real-time systems.
• 07:00 - 07:30 Because the greater speed and greater memory of today's computers don't force you to be as compact as we had to.