Verbs, Nouns, and the Apollo Guidance Computer


A lot of you guys have asked about the whole Verb/Noun the thing on the Apollo guidance computer. Well, that’s what we’re talking about today – in brief – on Vintage Space. The comparison is often made that a modern cell phone has more computing power than the Apollo guidance computer. Well, yes, that’s true, but your iPhone can’t get you to the Moon; it doesn’t exactly have that software… And really, the beauty of the Apollo guidance computer is in how tightly packed and specifically organized that software really was. When we think of a computer or even a smartphone we think of interfaces that are familiar to us like a screen and a word processor and a keyboard… and even just a basic calculator. Well the Apollo guidance computer had none of those things. It was designed to run a very small set of specifically designed programs needed to run a mission to the Moon, things like checking the guidance platform alignment and firing the engines. Everything on an Apollo mission was done through the computer and it took about 10,500 keystrokes to get one mission to the Moon and back. But because the guidance computer didn’t have those interfaces that we’re used to like keyboards and word processors and all those things, the inputs had to be a little bit different. This is the interface of the Apollo guidance computer, the display and keyboard commonly referred to as the DSKY (diss-key). Now you can see that it does have a screen, it does have keys, but it’s not a typical screen like we’re used to using on our home computers. There aren’t alphabetical keys and the screen doesn’t list information in words. In fact, this keyboard is anything but common to us. So how exactly did the astronauts use the DSKY? Well it actually offered a very simplistic interface for crews. Starting with the warning lights. COMP ACTY lit up when the computer was running a program. UPLINK ACTY was lit when there was data being received from the ground. TEMP lit up when the temperature of the platform was out of tolerance. NO ATT lit up when the inertial subsystem could not provide an attitude reference. GIMBAL LOCK lit up when the middle gimbal angle was greater than 70 degrees signifying that the spacecraft was close to hitting that deadly gimbal lock scenario. STBY lit up when the computer system was on standby. PROG lit up when the computer was waiting for additional information to be entered by the crew to complete a program. KEY REL lit up when the computer needed control of the DSKY to complete a program. RESTART was lit up when the computer was in the restart program.OPR ERR error was lit when the computer detected an error on the keyboard. And TRACKER lit up with one of the obstacle coupling units failed. The lunar module DSKY had three additional warnings: one to signify a problem with the autopilot and two more to signify problems with the altitude and velocity of the lunar module spacecraft. In addition to these 10 warning keys we have other keys: Verb, Noun, Plus, Minus, numbers, and handful of command keys. So there’s no obvious way to write in a command like “run guidance platform alignment program,” so how exactly did the astronauts actually interface with the computer using the DSKY? Well, this is where nouns and verbs come in, but to understand this we actually kind of need to leave the spacecraft for a second and go down to maybe the streets of New York City. So imagine you’re in New York City, you are a tourist, and you don’t really speak any English; you’ve got about five words in your arsenal, none of them include “excuse me, but which way to a lovely restaurant in this fine neighborhood of the city?” So you find a policeman knowing that this is the kind of person who might be able to direct you towards what it is you’re looking for. So you go up to the policeman and you use one of your words to tell him what it is you want to do. That word is “eat,” and that is a verb. But there’s a lot of food in New York City to choose from so you have to define what it is you want to eat, and so you use one of your other words, “pizza,” which is a noun. So do you see where we’re going with this? Just like your awkward, broken English conversation with the New York City policeman, all data going through the Apollo guidance computer used verbs and nouns. The verb is defined as the action being taken and the noun is defined as the data set being acted on. There’s actually a really simple computer-based version of this that we all use but don’t really think about because it’s not expressed as a noun and a verb: printing a document. If you select print, that is the verb. The file name is the noun, which is basically the data set (or in this case document) that that verb is acting on. So the astronauts inputted all their data using nouns and verbs into the Apollo guidance computer. There were 100 sets of noun verb pairs all defining a specific thing that the Apollo guidance computer would do on a mission. So let’s look at an example. Let’s say you enter verb 37 — that tells the computer that you are about to make a change to the program. Then you hit 3-1, and that tells the computer to run noun 31, which is a targeted rendezvous program. And there are a host of others! The crew could request maneuver angles with verb 50 noun 18, the crew could monitor changes while a maneuver was in progress with verb 06 noun 18, or even request velocity change required for the next maneuver using verb 06 noun 84. Once the noun and verb pairing was entered into the computer, the relevant information was displayed on the DSKY. And of course as you can expect when doing something big like going to the moon there were different kinds of programs, so different kinds of nouns and verbs. Regular verbs verbs 00 – 37 were used to display, monitor, or update data meaning they needed a noun; they needed something to be acting on. Whereas extended verbs were verbs 49 – 99 and they didn’t need a noun to execute a program; they told the computer to perform a simple operation. Of course, there is so much more to the Apollo guidance computer than this super quick look at nouns and verbs, and so I would urge you all to check out Frank O’Brien’s book “The Apollo Guidance Computer,” which, as I’ve said before and I always remind Frank is said with love and in jest, it is more than you ever need to know about how the Apollo guidance computer worked! So do you guys have other questions about the Apollo guidance computer? I’m not saying I can answer them off the top of my head but I can read and then figure it out for you! Let me know if any of this makes sense or if none of this makes sense or if you have other things you would just love to figure out about how the Apollo guidance computer worked! Leave all of those and of course any other comments and things you would like to see covered in future episodes down in the comment section. Be sure to follow me on Twitter and on Instagram for new Vintage Space-ish content every day of the week, and things are going to be changing just a little bit on this channel but I’m still doing it classic Vintage Space education episodes every Monday or Tuesday (depending on upload schedule) so if you don’t want to miss any of those be sure to subscribe just so you never miss a video! 🙂

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