A 3-D rendering of the Apollo 11 Command Module with a view inside the hatch. 

The Tech Behind Apollo 11’s Guidance Computer

Modern smartphones contain millions of times more computing power than the technology that took NASA’s first astronauts to the moon 50 years ago this week.

Fifty years ago this week, on July 20, 1969, the Apollo Lunar Module Eagle landed on the surface of the moon at the culmination of the Apollo 11 mission, and human beings first set foot on the planet’s only natural satellite. 

The technological feat that enabled Neil Armstrong and Buzz Aldrin to bounce around the Sea of Tranquility was the Apollo Guidance Computer, or AGC, and the software that powered it. 

The Apollo space program, and the technical efforts needed to transport astronauts from the Earth to the moon and back safely, helped accelerate technological progress in the United States and the wider world, including the rise of the semiconductor industry. Although the AGC is antiquated by today’s standards (one was briefly brought back to life recently) and modern smartphones have orders of magnitude more computing power, the AGC was a marvel for its time

As the world celebrates the 50th anniversary of the moon landing, it’s worth taking a look back at the technology that made the landing possible and how far modern computers have come since 1969. 

The Marvel That Was the Apollo Guidance Computer

The Apollo program, into which billions of dollars were poured, was perhaps the government program that almost single-handedly kickstarted the semiconductor market. 

The program “became the first and single largest consumer of the semiconductor chips, buying a million or more of them, some 60% of all the integrated circuits produced in the U.S. between 1962 and 1967,” according to The Wall Street Journal.

As The Atlantic notes:

The Apollo Guidance Computer, in both its guises — one on board the core spacecraft, and the other on the lunar module — was a triumph of engineering. Computers had been the size of rooms and filled with vacuum tubes, and if the Apollo computer, at 70 pounds, was not exactly miniature yet, it began “the transition between people bragging about how big their computers are … and bragging about how small their computers are,” the MIT aerospace and computing historian David Mindell once joked in a lecture.

That processing power proved critical. Without it, Armstrong, Aldrin and fellow Apollo 11 astronaut Michael Collins could not have guided their command and service module through space or the lunar module down to the moon’s surface. 

The AGC, was, as the Journal reports, “the first digital general-purpose, multitasking, interactive portable computer” and without it, and the software behind it, the moon mission would have failed. 


The DSKY-Unit of the Apollo Guidance Computer (AGC) mounted on the control panel of the command module. eigene Arbeit/Wikimedia Commons

“They’d put the computer at the center of this hugely ambitious project,” David Brock, director of the Computer History Museum’s software history center, tells the Journal. “It was a real test of that technology and everyone’s beliefs and aspirations for it.”

Apollo’s computer “eventually required about 145,000 lines of code in all, compared with about 62 million lines of code required today to operate Facebook and more than two billion lines of code for Google,” according to the Journal.

Critical to the mission was a piece of code that would allow the lunar module to continue flying and navigating even if the computer was overloaded. An alarm went off signaling that was the case as the lunar module was landing, with only minutes of fuel supply left, but the so-called restart function built into the computer’s code allowed the astronauts to continue flying as the computer restarted itself, as the Journal reports. The code allowed the astronauts to avoid aborting the mission and the moon landing

MORE FROM FEDTECH: Find out how NASA helps astronauts print 3D tools in space. 

Modern Smartphones Are Galaxies Apart from Apollo’s Computers

Today’s smartphones, which fit into most pockets, pack processors and memory that would leave the AGC in the proverbial moon dust. This has been the case for years. 

Michio Kaku, the physicist and popular author, wrote in his 2011 book, Physics of the Future: “Today, your cell phone has more computer power than all of NASA back in 1969, when it sent two astronauts to the moon.”

In terms of memory, the ACG held “2,048 words of erasable magnetic core memory and 36 kilowords of read-only core memory, with a cycle time of 11.72 microseconds,” ExtremeTech reports. That core memory works out to 32,768 bits of RAM or 72KB (equal to 589,824 bits) of ROM.

How does that compare to a modern smartphone? As Cult of Mac notes, an iPhone with 4 gigabytes of RAM (that’s 34,359,738,368 bits) has more than 1 million times more memory than the AGC, and a 512GB iPhone has 7 million times more memory

The AGC did not have a powerful processor by today’s standards, operating at a speed of 0.043 megahertz. University of Nottingham computer science professor Graham Kendall writes for The Conversation that the processor in the latest iPhone is estimated to run at about 2490 MHz, meaning it has over 100,000 times the processing power of the AGC.

Air and Space Museum, Smithsonian Institution
Jul 18 2019

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