May 2016

Volume 31 Number 5

[Don't Get Me Started]

Left Brains for the Right Stuff

By David Platt | May 2016

David PlattI’ve been reading Apollo astronaut memoirs lately. The very best is Michael Collins’ “Carrying the Fire” (Rowman & Littlefield, 2001) in which he vents his frustrations on the guidance computer in the command module simulator:

I lost my temper. Flash an “operator error” light at me, will you, you stupid goddamned computer, and I would sputter and stammer until the soothing voice of [the simulation operator] came over the earphones and unctuously explained how I had offended their precocious brat.

Intrigued, I decided to dig deeper into those earliest spacecraft computers. That meant looking up an old comrade-in-arms. Hugh Blair-Smith hired me in 1987, for a startup that imploded two years later (not his fault). He was also my student in 1992, in my first Windows class at Harvard Extension (16-bit SDK in C, because you ask). But long before all that, he had worked at MIT’s Instrumentation (later Draper) Lab, helping to develop both hardware and software for the Apollo Guidance Computer. The same machine, with different software, was used in both the Command Module and the Lunar Module ( in its more advanced “Block II” configuration.

I hadn’t talked with Blair-Smith since writing “Why Software Sucks” 10 years ago (he’s in it, but not by name). Hugh has now written a book about his Apollo days, entitled “Left Brains for the Right Stuff: Computers, Space, and History” (SDP Publishing, 2015). He describes the hardware, such as the rope memory that held the ferrite core ROM (, and the software, down to the microcode of the divide instruction (and in a geeky endnote, even the nanocode of the multiply instruction).

Not only does Blair-Smith’s book cover technical topics, he also discusses the social and political context of the space race within which all this engineering took place. And he does so in beautiful language. Here he recounts watching Apollo 8’s TV broadcast on Christmas Eve 1968, from the first humans to orbit the moon:

The spacecraft coasted on toward the darkness that only the shadow of an airless world can produce. “And now, from the crew of Apollo 8, we close with, good night, good luck, a Merry Christmas, and God bless all of you, all of you on the good Earth.” And to you, Frank and Jim and Bill, I thought. And to you, little computer.

I found the UI especially fascinating. The astronauts entered verbs and nouns through a numerical keypad. For example, “Verb 88, enter,” told the computer to ignore input from the VHF rangefinder, while “Verb 87, enter” told it to start paying attention again.

“This was only intended as a stopgap until they could think of something better,” says Blair-Smith. “But it turns out the astronauts sort of liked it. ‘Even a pilot can use this,’ Dave Scott (Apollo 15 commander) said, so it stuck.” (See Scott’s article, “The Apollo Guidance Computer: A User’s View,” downloadable as a PDF at

The computer would prompt the astronauts to take actions, but couldn’t initiate a rocket engine burn on its own. Blair-Smith says, “The philosophy is that no significant action can be taken without an overt command from the crew—the astronauts insisted that, ‘If we kill ourselves, it will be our fault, not some goddamn computer’s.’”

Naturally, I wanted to hear more. Blair-Smith was kind enough to invite me to the quarterly lunch of the surviving Apollo engineers, in Cambridge near MIT.

Of course I had to bring my daughter Annabelle, a budding space geek. For her imminent 16th birthday (and how the heck did that happen?), she wants a Buzz Aldrin T-shirt that says, “Get Your Ass to Mars.” The old men loved meeting a fresh newcomer to pass the torch. One said, “I’m the Rope Mother for Apollo 12,” (the single engineer with ultimate responsibility for the ROM), with pride that hasn’t dimmed, and won’t while the gentleman lives.

Annabelle and I saw the full moon rising over the salt marshes near our home a few nights later. Bright, smiling, mithril-colored, but oh so lonely, with no footprints for going on 50 years. “We could do that, you know,” Annabelle said to me. She’d caught the spark.

I wondered what the Apollo veterans see when they look at the moon. As always, Blair-Smith sums it up pithily: “Notice something? For us who lived Apollo, everything about it remains in present tense, and always will.”

With one exception: a phrase I heard them use to each other, to me and Annabelle, and to themselves. I now pass those words to you, dear reader, as their challenge to us all, and as their epitaph when they come to need one: “We didn’t know what we couldn’t do. So we just went ahead and did it.”

David S. Platt teaches programming .NET at Harvard University Extension School and at companies all over the world. He’s the author of 11 programming books, including “Why Software Sucks” (Addison-Wesley Professional, 2006) and “Introducing Microsoft .NET” (Microsoft Press, 2002). Microsoft named him a Software Legend in 2002. He wonders whether he should tape down two of his daughter’s fingers so she learns how to count in octal. You can contact him at

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