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News & ArtsMonday, July 20, 2009
Science The Apollo Guidance Computer
Posted by Jonathan Golob on Mon, Jul 20, 2009 at 7:09 PM
Let's say you're a NASA engineer in the 1960s, wearing your snazzy black plastic glasses, thinking of landing a man on the Moon and returning him safely to the Earth. You start thinking navigation. Getting into the right orbits is going to take a fair bit of computation—plus some fine control of rocket engines and navigation jets. Really, you're going to need a computer.
But this is the 1960's. Computers are HUGE. Yes, yes, transistors had been invented years before—and are now in wide use. So, at least we're not talking vacuum tubes. Egads. Tubes! Building computers means wiring a whole bunch of these transistors together. With wire. In other words, the world's finest computers look a bit like that box of Christmas lights you don't want to think about in the basement: tangled, ugly, mean and prone to failure if jostled. Not exactly conducive to placement in a rocket.
No biggie, you think. You'll just have the computer on Earth—nice solid earth—radioing back and forth to the sensors and engines in the rocket. You can even correct for the speed-of-light delays! Problem solved! Light up some Lucky Strikes and call it a day.
But then you think of the return burn. If the Apollo craft are going to get out of lunar orbit and return to Earth, they're going to need to fire the rocket engine on the far side of the Moon—you know, where radio waves can't reach. Crap. I guess you'll have to figure out a way of wiring together all those (4000 or so, egads!) transistors in a way that is small, light and durable enough to survive being rocketed into space. Time to create the first integrated circuit computer—father of every damn computer most of us have used, ever.
Better call MIT.
(Happy Moon Landing day!)
1
An ipod has more computing power than all the computers NASA used combined for the Apollo missions.
3
@1, and yet, if the US *had* to land on the Moon again within 50 years for some reason, I bet we wouldn't be able to do it anymore.
5
@3 I agree. The space program has stagnated. We are still largely using technology developed during the '70s (the shuttle). I bet it will take China putting a man on the moon for the US to wake up again, and by then, it will be too late.
7
@5: I agree with 4. The fireworks of the moon landing of '69 don't really compare with the technological firepower of what we're doing today. Less glamor, yes, but more information.
8
Shame your typical Slogger would have been smoking pot and protesting for mixed-sex dorms if they'd been back in the day......
10
Jonathan, great post. I have been in awe of the Apollo program and all the hardware ever since I was little.
Any chance you could describe for me and other laypersons exactly how the celestial navigation worked? I know how latitude & longitude works, and have a rudimentary knowledge of how navigation on earth works.
How does it work in space? When there's no up or down, how, for example, did they know which way to orient the spacecraft for the farside burn? How did NASA track their progress and determine if they were on course or not?
Any chance you could describe for me and other laypersons exactly how the celestial navigation worked? I know how latitude & longitude works, and have a rudimentary knowledge of how navigation on earth works.
How does it work in space? When there's no up or down, how, for example, did they know which way to orient the spacecraft for the farside burn? How did NASA track their progress and determine if they were on course or not?
12
@3 According to David DeLong in his book Lost Knowledge: Confronting the threat of an aging workforce, NASA managed to lose the drawings for the Saturn 5. Nothing like reinventing the wheel.
13
There's an old DSKY simulator you can play with here.
@10:
Almost all the navigation tasks on Apollo missions were handled using ground-based radars, then feeding the information into computers at Mission Control in Houston to plot relative position. Although there was an optical sextant aboard the Apollo CM, it was used almost exclusively as a lunar telescope when in orbit around the moon.
I think Lovell took some sightings during the Apollo 8 mission, and did pretty well IIRC, but they were totally on his own initiative, and not required by the mission profile.
The on-board sextant could of course have been used in an emergency, if communication and telemetry transfer had been lost with the ground, but that would have been the only case when the astronauts would have needed to depend on it.
@10:
Almost all the navigation tasks on Apollo missions were handled using ground-based radars, then feeding the information into computers at Mission Control in Houston to plot relative position. Although there was an optical sextant aboard the Apollo CM, it was used almost exclusively as a lunar telescope when in orbit around the moon.
I think Lovell took some sightings during the Apollo 8 mission, and did pretty well IIRC, but they were totally on his own initiative, and not required by the mission profile.
The on-board sextant could of course have been used in an emergency, if communication and telemetry transfer had been lost with the ground, but that would have been the only case when the astronauts would have needed to depend on it.
14
And yes, the computational power of the on-board computers was pathetically small, but they weren't used to do any heavy number-crunching or multi-tasking. Essentially it was a fancy, compact routing switch that controlled the mechanical actions of the guidance and navigation system, and designed primarily to instruct the main engines to fire for a certain amount of time, at a certain rate of thrust and monitor the results. All the strings of numbers and "noun/verb" entries were simply codes to tell the GNC to perform specific sequences of preset commands already programmed into the system, or to request specific information from it.
15
@13 -- re: the sextant -- some of my coworkers were debating why the caption to a photo of the Earth from Apollo 11 that was on the Boston Globe's "Big Picture" blog listed the distance in "nautical miles", and we theorized that it was because absent an actual geographical location on the Earth's surface, the astronauts had to figure out their position using triangulation, the same way sailors used to sight stars through their sextant and plot their position...
@7, I am a huge, huge fan of unmanned space probes like Messenger, New Horizons, Cassini, the Mars rovers and the LRO, that just sighted the Apollo landers on the Moon's surface (I was geeky enough to submit my name to NASA to be put on a microchip onboard that craft). Even though I know intellectually that there's much more bang for the buck in those missions without having to keep people alive and return them to Earth, it still seems like the challenges and the courage involved in sending men up there and bringing them back may never be something we're capable of doing or willing to figure out how to do, again, and that seems like a tremendous loss.
It's weird to grow up after the future already happened and ended.
@7, I am a huge, huge fan of unmanned space probes like Messenger, New Horizons, Cassini, the Mars rovers and the LRO, that just sighted the Apollo landers on the Moon's surface (I was geeky enough to submit my name to NASA to be put on a microchip onboard that craft). Even though I know intellectually that there's much more bang for the buck in those missions without having to keep people alive and return them to Earth, it still seems like the challenges and the courage involved in sending men up there and bringing them back may never be something we're capable of doing or willing to figure out how to do, again, and that seems like a tremendous loss.
It's weird to grow up after the future already happened and ended.
16
@3 well the current plan is to do it by 2020-2030.
Also we might be sending humans about in space but we are doing some impressive things. The space station, the Hubble repairs, rovers on mars, etc.
Also we might be sending humans about in space but we are doing some impressive things. The space station, the Hubble repairs, rovers on mars, etc.
17
What's the point fo all this blaoney in outer space when we still have Americans going bankrupt due to medical bills, kids in Africa going blind due to that bug in the water, and our infrastructure is crumbling (for a pathetic example, look at Seattle Parks' handling of MAgnuson....huge areas of vacant buildings and space totally going to waste...we don't even have enough money and sense of prioritization to keep Colman pool open but a few weeks in summer).
18
Scientists have found evidence that another object has hit Jupiter, exactly 15 years after the first impacts by the comet Shoemaker-Levy 9.
Following up on a tip by an amateur astronomer, Anthony Wesley of Australia, that a new dark "scar" had suddenly appeared on Jupiter, this morning between 3 and 9 a.m. PDT, JPL scientists at the summit of Mauna Kea, Hawaii, gathered evidence indicating an impact using NASA's Infrared Telescope Facility ...
http://www.jpl.nasa.gov/news/news.cfm?re…
POW!
Following up on a tip by an amateur astronomer, Anthony Wesley of Australia, that a new dark "scar" had suddenly appeared on Jupiter, this morning between 3 and 9 a.m. PDT, JPL scientists at the summit of Mauna Kea, Hawaii, gathered evidence indicating an impact using NASA's Infrared Telescope Facility ...
http://www.jpl.nasa.gov/news/news.cfm?re…
POW!
19
Not to be that guy, but the integrated circuit was invented in the late 50s at Texas Instruments. Not that MIT isn't awesome.
21
The ACG was really, really cool.
But let's not forget that the real development that made it possible had already taken place behind closed doors. 800 Minuteman-I ICBMs were delivered by 1965, each with an Autoneteics D-17B Guidance Computer. Each computer had 1500+ transistors and 6000+ diodes, soldered into 75 conformal coated double clad copper-on-fiberglass circuit boards. Each radiation-hardened system had a primitive hard drive for memory.
http://en.wikipedia.org/wiki/D-17B
But let's not forget that the real development that made it possible had already taken place behind closed doors. 800 Minuteman-I ICBMs were delivered by 1965, each with an Autoneteics D-17B Guidance Computer. Each computer had 1500+ transistors and 6000+ diodes, soldered into 75 conformal coated double clad copper-on-fiberglass circuit boards. Each radiation-hardened system had a primitive hard drive for memory.
http://en.wikipedia.org/wiki/D-17B
22
Sometimes I daydream about traveling back in time and making Jules Verne watch my VHS copy of Apollo 13. Of course I'd have to do it after he had already written most of his books, because immediately after seeing the movie he'd have an orgasm and die.
24
@15:
I'm guessing NASA has continued to use nautical mileage because it's traditionally been the standard unit-of-distance measurement for aviation and is still recognized by international aviation and aerospace bodies. Also, since a nautical mile equals one minute of terrestrial latitude, it might have some relevance to that as well, I'm not sure.
I'm guessing NASA has continued to use nautical mileage because it's traditionally been the standard unit-of-distance measurement for aviation and is still recognized by international aviation and aerospace bodies. Also, since a nautical mile equals one minute of terrestrial latitude, it might have some relevance to that as well, I'm not sure.
26
For the tech geeks out there, Science Channel had a series last summer on the making of the machines and programs that flew the Apollo program. You can get it on DVD -- search for "Moon Machines DVD" on Amazon.
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YEs, we have people here in the USA that need help with medical, That,s not up to the USA, Let the other countries worry about their own people. The USA can't feed or medicat the whole damn world.Time to get that threw to some people. We need to take care of our own, ONLY. Now, Lets shoot for the stars and go to the Moon and Mars. Ignore the idiots that think that the Apollo missions never went to the moon, I bet they even think that the space station is empty. You can please some of the people some of the time and Get rid of the oxygen wasters the rest of the time.. Count down in 5.........
28
YEs, we have people here in the USA that need help with medical, That,s not up to the USA, Let the other countries worry about their own people. The USA can't feed or medicat the whole damn world.Time to get that threw to some people. We need to take care of our own, ONLY. Now, Lets shoot for the stars and go to the Moon and Mars. Ignore the idiots that think that the Apollo missions never went to the moon, I bet they even think that the space station is empty. You can please some of the people some of the time and Get rid of the oxygen wasters the rest of the time.. Count down in 5.........
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