Computer for Apollo - Page 1
Forum section: electronics / general

author: atferrari
author_rank: Frequent Contributor
timestamp: February 22, 2015, 12:23:05 pm
content: I run across this videohttp://youtu.be/YIBhPsyYCiMI got surprised to learn that still there they used a sextant to measure angles between Earth and starts but looking at the date, no surprise.Incredible the hard work they did to solve one by one all the steps to build such a computer. Wiring the memories...!Starting at around minute 6, the panel of the computer is shown. There are two words "verb" and "noun". Does anyone could tell what they actually mean in this context?

author: John Coloccia
author_rank: Super Contributor
timestamp: February 22, 2015, 12:46:24 pm
content: The "verb" is the command, and the "noun" is a parameter for the command. I don't know much about the Apollo computer, but just as a made up example, let's say you want to recall the last recorded position. Perhaps you might enter a command like this:verb: Displaynoun: Last PositionMaybe you want to see time of flight.verb: Displaynoun: time of flightAgain, I'm just making it up, but that's basically how it used to work.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: February 22, 2015, 12:59:58 pm
content: The sextant was hardly your "olde fashioned" affair, even if they do still have them as backups nowadays.Just looking at the pic I'd love to get my hands on a modern equivalent.

author: atferrari
author_rank: Frequent Contributor
timestamp: February 22, 2015, 01:31:46 pm
content: Quote from: Mechanical Menace on February 22, 2015, 12:59:58 pmBy that time I used them every day on board and I did so, long after the satellites were installed in our vessels. My last voyage using it intensively was from Philippines all the way down to Argentina doing the morning / evening calculations with stars.Since practice makes for perfection I started to compete with myself to see how many fixes (of different starts or even planets) I could take in one period until the horizon did not allow for more. My record, 14.The one in the picture, is it for aeronautical use? I do not recognize much in it. Is it complete? Any link?

author: atferrari
author_rank: Frequent Contributor
timestamp: February 22, 2015, 01:34:55 pm
content: Quote from: John Coloccia on February 22, 2015, 12:46:24 pmGracias for replying. It makes sense now.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: February 22, 2015, 01:47:51 pm
content: Quote from: atferrari on February 22, 2015, 01:31:46 pmThat's the sextant used for the Apollo missions, through the sound of things to compensate for errors in the inertial guidance system.http://www.ion.org/museum/item_view.cfm?cid=6&scid=5&iid=293

author: atferrari
author_rank: Frequent Contributor
timestamp: February 22, 2015, 01:56:43 pm
content: Quote from: Mechanical Menace on February 22, 2015, 01:47:51 pmInteresting site.Gracias MM

author: amyk
author_rank: Super Contributor
timestamp: February 22, 2015, 04:05:53 pm
content: Schematics:http://klabs.org/history/ech/agc_schematics/Imagine designing a whole computer with nothing but 3-input NOR gates...

author: Mechanical Menace
author_rank: Super Contributor
timestamp: February 22, 2015, 04:35:03 pm
content: Quote from: amyk on February 22, 2015, 04:05:53 pmInteresting site, thanks for sharing.I am wondering why they went for 3 input NOR gates instead of 2 input NOR or NAND gates? Will have to get reading.

author: SeanB
author_rank: Super Contributor
timestamp: February 22, 2015, 04:58:33 pm
content: They probably wanted more logic elements, but a 3 input gate is useful and can be used to make any other gate easily. As well you only need 2 to make a RS flip flop, with the extra gate providing a nice clear function for it. As that was likely the most reliable IC that you could make at the time with 3 transistors on it, and used identical value resistors throughout with at least good tolerance for production spread this was probably a big deciding factor.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: February 22, 2015, 06:10:15 pm
content: Quote from: SeanB on February 22, 2015, 04:58:33 pmDidn't think of that one, less wasted transistors than hooking up loads of 2 input gates...

author: albert22
author_rank: Regular Contributor
timestamp: February 22, 2015, 06:26:55 pm
content: Thanks for the very interesting links posted. Definitely the choice of only one IC type was made for reliability.A very important purpose for the sextant was to align the inertial platform to several coordinate systems. This allowed the computer to point the apollo and fire the rockets to the exact trajectory. The computer calculated the position by using stars and relevant point in the earth. But it was more accurately determined from the earth by several tracking stations and by measuring the delay and phase of the radio signals travelling from earth to the spacecraft and back to earth. I read that in this way the error was just a couple of meters when they were near the moon.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: February 22, 2015, 06:39:35 pm
content: Quote from: albert22 on February 22, 2015, 06:26:55 pm370,000,000 metersish and only out by a couple when they got there? Technology has come a long way since the 60's and they managed that and yet we can't even get out of LEO nowadays

author: atferrari
author_rank: Frequent Contributor
timestamp: February 24, 2015, 03:52:41 pm
content: Quote from: Mechanical Menace on February 22, 2015, 01:47:51 pmDigging deeper and wider I came to more info herehttp://timeandnavigation.si.edu/artifacts/search?field_topic_tid=3Impressive.

author: free_electron
author_rank: Super Contributor
timestamp: February 24, 2015, 03:55:56 pm
content: Quote from: amyk on February 22, 2015, 04:05:53 pmMore TTL , less VHDL !

author: AdShea
author_rank: Contributor
timestamp: February 24, 2015, 07:46:53 pm
content: RTL, not TTL. They only used pull down NPNs and resistors there (4 R + 3PNP for one gate).

author: GK
author_rank: Super Contributor
timestamp: February 25, 2015, 03:03:10 am
content: Quote from: amyk on February 22, 2015, 04:05:53 pmOr NAND gates which are logically equivalent depending on interpreting the IO as either positive or negative logic.Not a particularly onerous task in either case......