The following typescript might be useful. Filmed or videoed in back-and-white in the olden days of television, this is a quaintly amusing programme to watch but it has some incredibly good information for those who don't know much about the AGC. It has blackboards and chalk in place of graphics, and shows engineers who are as stiff as a board and look utterly terrified to have a movie or TV camera pointing at them — a bit like possums caught in the headlights or bad actors in a B-grade horror movie.
Spacecraft Films DVD Set — Mission to the Moon — Disc 1
Computer For Apollo
0:00:00 Chapter 1.
0:00:02 John Fitch: These test engineers are checking out a sophisticated collection of telescopes, gyroscopes and electronics for Project Apollo. This guidance and navigation system will be mounted in an Apollo spacecraft, to aid our three astronauts on their voyage to the moon and return.
0:00:20 Fitch: The miniaturised computer at the very heart of this system is our story today on Science Reporter.
0:00:29 NASA Presents
0:00:33 Science Reporter
0:00:37 Computer For Apollo
0:00:41 Reporter: John Fitch, MIT
0:00:47 Fitch: Hello, I'm John Fitch, MIT Science Reporter. Today we're at the MIT Instrumentation Laboratory, which has been given design responsibility for this guidance and navigation system, which will direct our Apollo spacecraft on the way to the moon and back.
0:01:04 Fitch: At one time, the direction of the rising sun or perhaps a winding riverbed was all that man needed in his restless search for new land. Centuries later the quadrant and the magnetic compass guided his way, even across the open sea, even after familiar landmarks had long since disappeared.
0:01:23 Fitch: But today we speak of traversing a million miles of empty space, where there is no north nor south, no rising nor setting sun, not even any up or down. It's an extremely complicated path requiring many, many measurements and millions of calculations.
0:01:41 Fitch: As you can see from this Apollo flight plan, there are several critical manoeuvres that have to be performed. After the Apollo spacecraft reaches its earth orbit, it must be injected into a translunar trajectory at just the right place in time and space.
0:01:58 Fitch: Someone has compared it to shooting at a moving target from a revolving platform, which is mounted on a train, which is going around a curve.
0:02:08 Fitch: Then at the half-way point, along about here, the programmed course must be examined for errors and possibly a mid-course correction made. There are many other similar manoeuvres, and to learn about the guidance and navigation system which will make this possible, we talk with Mr Eldon Hall, Deputy Associate Director of the Instrumentation Lab.
0:02:30 Eldon Hall: The guidance and navigation system consists of two measurement elements, controls, the computer, and the computer display and control. The inertial measurement unit, shown up here but normally down at the back, consists of gyros and accelerometers. It measures the angles and velocity of the spacecraft in this fashion.
0:02:56 Hall: The spacecraft rotates and the inertial measurement unit holds the reference, so the angles can be measured. The sextant is an instrument very similar to that used by the sailors to navigate on the surface of the earth.
0:03:10 Fitch: Now what kind of a problem might you have to solve on the way to the moon?
0:03:14 Hall: The most basic problem is to determine the position at any point in time, and that can be illustrated in these charts. The sextant shown here represents the spacecraft, and to determine the position an angle must be measured, between a point on the earth and a star. And you can see that as you move away from the earth, this angle would narrow down, thus giving the distance between the earth and the spacecraft.
0:03:48 Hall: The astronaut first positions the spacecraft so that a point on the earth, a landmark, is visible through the sextant. Then he positions the sextant angle so that the star is superimposed upon this landmark.
0:04:05 Fitch: Now what kind of a landmark might this be?
0:04:07 Hall: This one is San Francisco Bay, as you can see here. However, the Great Lakes, or Cuba, or Cape Cod, the tip of Florida — any of these points make suitable landmarks.
0:04:20 Fitch: Then through some system of mirrors you actually superimpose the star on that feature.
0:04:24 Hall: That's right. The mirrors inside the sextant will bring the star within the field of view so that we can superimpose it on the landmark.
0:04:33 Fitch: Now how is this angle actually measured?
0:04:36 Hall: It's done automatically by the computer. The astronaut must first identify to the computer the star and the landmark he is planning to use. Then, as he's positioning the spacecraft and the sextant, the computer is measuring the angle between the two.
0:04:54 Hall: When the astronaut is satisfied that the star is superimposed upon the landmark, he pushes the Mark button, telling the computer to record these angles and the time of the measurement. From that information the computer can compute the position of the spacecraft in space.
0:05:04 Chapter 2.
0:05:11 Fitch: Well, now that you know the position, what can you do about it if it isn't right?
0:05:15 Hall: The computer can position the spacecraft, turn on the motors and steer it, and shut the motors off.
0:05:23 Fitch: So you'll be coasting on a new and corrected path.
0:05:26 Hall: That's right.
##########
0:05:27 Fitch: To see the Apollo guidance and navigation system in operation, we visited the Systems Test Laboratory, and talk with Mr Ramon Alonso, Assistant Director of the Instrumentation Laboratory.
0:05:39 Ramon Alonso: One of the interesting aspects of the guidance system is the way in which the astronaut controls the guidance equipment through the computer. And he does so by means of the display and keyboard, which is a subsystem.
0:05:52 Alonso: There are two instances of the display and keyboard. One is with the rest of the navigation equipment in the lower equipment bay, and the other is near the couches where the astronauts can operate the computer without leaving their couches.
0:06:04 Alonso: The system of codes used is reasonably simple. It consist of a numeric verb and a numerical noun.
0:06:12 Fitch: These are little sentences made of numbers?
0:06:14 Alonso: Essentially, that illustrates it. An example of it might be a verb 16, which is Continuous Display, in decimal, and a noun, which is Time. I pick these, and they're at work. I've now told the computer what I want, but I have not yet told it to go ahead and do what I want.
0:06:34 Alonso: When I press Enter, the computer proceeds to display time, and it does so, giving me times from launch, perhaps, in hours and hundredths of hours, 98.56 hours from launch. And it also gives me a fine view of the low order part of the time in seconds and hundredths of seconds. That is useful occasionally.
0:06:55 Fitch: I should think it around launch time would be interesting.
0:06:57 Alonso: Yes. The computer will continue to display this information until told otherwise, and it is told otherwise by another verb. In this case the verb is Terminate — 34. It's now forgotten that command.
0:07:11 Alonso: Another example of the use of the computer might be to position the optics. Now, that is something that can be done manually and usually would be, but it affords us a good view as to how the computer is operated.
0:07:22 Alonso: The optics are now pointing in a certain direction and I want to change that direction to another target. And I will invoke a verb which is Point, verb 41, and a noun, which is Optics, noun 55.
0:07:34 Fitch: Point the telescope.
0:07:36 Alonso: Point the telescope. When I press Enter, the computer then proceeds to request the angle to which I wish the optics pointed.
0:07:43 Fitch: Well, the numbers have changed and now they're flashing, aren't they?
0:07:46 Alonso: That's right. The flashing indicates that action is requested of the operator, and the verb and noun have changed to tell the operator what it is that is expected of him.
0:07:54 Alonso: Verb 21 is Load, load the first component, first angle. And noun 57 — it used to be 55 — is the angle. Fifty-five was the telescope and 57 is the angle which the telescope makes. In this case the angle I want is 180 degrees. And I enter that, and now it asks for the second angle.
0:08:13 Fitch: Verb 22. I see.
0:08:15 Alonso: Second angle is plus 325. Now when I press Enter, the camera, which will come close to the eyepiece, will see the telescope slew and point to another target.
0:08:30 Alonso: As you can see, the crosshairs were lined up on the edge of the rightmost of the two targets, and the computer is now driving the optics telescope, with relation to the spacecraft, and it's aligning it on the rightmost of this pair of targets. Now you can see the crosshairs right in the middle of the target.
0:08:49 Alonso: Suppose now that we had done the optical sighting by hand rather than by the computer, then we'd be wanting to inform the computer that we are on target. This is part of the procedure that is done when star sightings are made, as Mr Eldon Hall mentioned previously.
0:09:05 Alonso: That is done by means of a Mark button, which is located in the lower equipment bay. When the telescope is on target, the astronaut presses the Mark button and the computer changes the display to Display — that's the verb — Mark Information, number 56. And what it displays are the two angles that the telescope is making and the time at which that measurement was made. Notice that these angles are very close to the ones that were commanded originally in our earlier effort.
0:09:34 Alonso: This information is part of what is necessary for the computer to then estimate the present position and velocity of the spacecraft. To estimate what the velocity correction is that ought to be performed, and then to execute that velocity correction.
##########
0:09:50 Fitch: To learn more about the remarkable little computer at the heart of the guidance and navigation system, we talk with Mr Albert Hopkins, Assistant Director of the [MIT] Instrumentation Laboratory.
0:10:01 Hopkins: This computer is similar to its ground-based big brothers that are dominating our lives so much today, in that it's fundamentally a high-speed adding machine, with the additional feature of having a memory into which it can write results and some which it can take data, very much as an accountant has his ledger.
0:10:08 Chapter 3.
0:10:24 Hopkins: And also it has a self-contained list of instructions, analogous to an accountant's training, so that this tells the computer what to do in sequence. If we look over here I can show you more about how the computer operates.
0:10:40 Hopkins: The adding machine of this computer is a high-speed arithmetic unit which carries out the fundamental arithmetic processes. All of the complex operations that we've seen today can be broken down into long lists of arithmetic.
0:10:55 Fitch: I see.
0:10:58 Hopkins: The arithmetic unit receives its data from a memory divided into two sections and it puts its results back into the erasable portion of that memory. This is the portion which is similar to the accountant's ledger.
0:11:10 Fitch: What is the fixed memory?
0:11:12 Hopkins: The fixed memory is unique to the space age. It is a memory which cannot be written into by the arithmetic unit and it contains information which must last the entire mission. It's here for safety.
0:11:23 Fitch: The location of stars and things it wouldn't want to forget.
0:11:26 Hopkins: That's right. This contains a list of instructions which are fed one at a time to the sequence generator which generates all of the controls necessary to operate the entire computer.
0:11:38 Hopkins: Input data which comes from the angle-measuring devices that we saw earlier, or the keyboard, comes in through input conditioning circuits and is available in the erasable memory.
0:11:48 Hopkins: The arithmetic unit can operate upon this input data and compute results designed to be output. These results are placed in a particular portion of the erasable memory where they are sent to output conditioning circuits, out to other instruments which need this data, such as for instance the displays or, perhaps, a rocket motor.
0:12:13 Fitch: When you say this computer is very much like land-based computers, and yet I think of them as occupying whole bays of equipment. You've got all of this squeezed into a little box. How did you do that?
0:12:23 Hopkins: Miniaturising a computer like this requires a judicious choice among many quantities. It's first necessary to minimise the number of circuits which are used. It's necessary to minimise the size of the components which you use, and it's necessary to package them as tightly as possible.
0:12:44 Hopkins: Now this must not be carried too far. If it's carried to far it can endanger the reliability of the computer, so that a compromise must be sought.
0:12:52 Fitch: Now what kinds of circuits are involved?
0:12:55 Hopkins: In the memory and also in the power supplies and in the input/output of the computer, conventional components are used, with the exception of the fixed memory, a piece of which we see here. This fixed memory is actually composed of magnetic cords with wires woven in and out — sewn in with a pattern, for the information here is in the patterns of the sewing.
0:13:18 Fitch: I see.
0:13:19 Hopkins: The remainder of the computer — the arithmetic unit, the sequence generator, the so-called connective tissue — the logic section, so-called, of the computer is made up of a single type of unit. This is a micro-circuit gate. Forty-three hundred of these are used in the computer to make up this entire segment.
0:13:40 Hopkins: These are packaged together tightly — they fit in a fairly small space and are interconnected in separate modules in one side of the computer.
##########
0:13:51 Fitch: The Apollo computers are manufactured by the Raytheon Company in Waltham, Massachusetts. The computer itself consists of two trays, one containing logic modules, the other memory modules.
0:14:04 Fitch: To learn how these modules are put together, we talk with Mr Jack Poundstone, Raytheon's Apollo engineering manager.
0:14:12 Poundstone: In this room, John, we run all of the electrical components through a screening and burning process. You know there are over 30,000 parts that go together to make this machine.
0:14:23 Poundstone: Every part is put through an electrical test and then a series of environmental stresses. Now, as an example, this girl is placing the micrologic units into a fixture that will be used in this centrifuge.
0:14:37 Poundstone: Here the fixture is spun at a very high speed and 20,000 g's of force is placed on each component.
0:14:43 Fitch: That's a lot more than it will ever experience, isn't it?
0:14:45 Poundstone: Yes, that's true, but we put more forces on, more stresses than we really expect, to ensure the high reliability.
0:14:51 Fitch: So this is really sort of a torture chamber.
0:14:53 Poundstone: That's right. In addition, we run all the parts through a leak test, to make sure there is no leaks in the can. The part is put into a high-pressure helium tank, and if there is a leak, the helium will be forced into the can.
0:15:05 Chapter 4.
0:15:08 Poundstone: Then we put it in a vacuum chamber and evacuate and test for the amount of helium coming out.
0:15:14 Poundstone: In the final phase of the screening and burning process, the girl puts the parts, as she's doing here, into a test socket. Then those parts are placed on this burning rack.
0:15:28 Poundstone: Here they will be operated for almost a week at a over-voltage stress condition.
0:15:34 Fitch: You actually are operating them.
0:15:35 Poundstone: Yes, we are operating the parts. Now any failure, any significant failure of any of our tests is cause for rejection of the entire lot of 5,000 parts.
0:15:46 Poundstone: After we've ensured that we have good components, then we want to make a module.
0:15:50 Poundstone: Now, the little cans, here, are placed in these holes in a component holder. Then we take a matrix, which is a complex wiring pattern. It's placed on the back, and the wires are folded over and welded to the leads of the micrologic unit itself. I'd like to show you now, how we make a matrix.
0:16:15 Poundstone: Here we see an operator who is placing a piece of Mylar insulator that has been heated on both sides, and this insulator has previously had a pattern of holes punched onto it. Now this is placed on this longitudinal wire winder. Now as the piece advances, strips of nickel ribbon are laid down in a longitudinal direction on the Mylar.
0:16:39 Poundstone: Next, it's taken to the vertical wire winder. Here the operator is placing it on the machine, and as the drum rotates, wires are laid down on the opposite side of the Mylar in a vertical direction. The wires will be laying down right over the areas where the holes have been punched.
0:16:57 Fitch: Some running one way on one side and others running the other way on the other side.
0:17:00 Poundstone: That's right, John. Now the next operation is to perform the welding. This is done on a automatic welding machine. With this machine we are advancing the matrix underneath these weld heads, and whenever a hole appears under a weld head the weld is commanded to drop and perform a weld, and this makes a feed-through connection from one side of the insulator to the other.
0:17:27 Poundstone: In the final operation, this girl uses a cutting tool to remove the excess pieces of wire, to give us the final configuration of our precise wiring pattern.
0:17:41 Fitch: This matrix, then, is the wiring that sort of connects one little micro-electronic circuit to another.
0:17:47 Poundstone: That's right, John. This wiring diagram shows you how the matrix can be used to interconnect the micrologic elements. See here, a wire will run from this can, down here were it's welded through to the other side, run down, break out to another can, and up here to another.
0:18:03 Fitch: I see, yes.
Continued next post...
