Apollo On Board Computer Emulator

frankk74 writes "For those of you interested in Historical Computing and the Apollo manned spaceflights Ron Burkey has created a open source emulation of the Apollo Guidance Computer called vAGC. I use it as my desktop clock of choice. Note it only keeps mission time so after 24 hours you have reset the time :-). P.S. Another cool Apollo toy free and payware can be found here."

Comments

Warning

[poofyhairguy82]

From site: For Win32 users, it's much more work to get your computer set up to build Virtual AGC than it is in Linux, and the steps needed will be less familiar.

That made me feel good seeing as how this is the first week I've tried linux.

very simple processor

[ndevice]

Took a quick scan at the architecture of the machine, and I'm suprised that it's so simple.

People say over and over again that simple handheld calculators are more powerful than that thing, and it seems that the oft-parroted line is more accurate than they realize.

Add to that: RTL (before TTL) and magnetic core memory bring up the nostalgic value.

Re:very simple processor

[thhamm]

some of the "moon hoaxers" think thats why they could never get to the moon at all.
"though much faster, my pentium can barely run [insert 3d shooter here] at good FPS. how could it fly to the moon? so they never did."

logic?
clavius explanations.

Re:very simple processor

[Edward Teach]

In the Apollo 11 descent to the moon, you hear someone say "twelve oh one alarm." This was the alarm that told the LM crew that the computer reset because it ran our of memory.

Re:very simple processor

[TheHawke]

Eh, Brute force. They needed the AGC to be as simple, yet programmable with all the steps necessary to get the boys on the moon and back.
So they took the PDP8 and squeezed it down into the size of a early 80's era Kaypro portable (now that's saying something about my age) and managed to get it to draw as much power as your coffeemaker.
THEORETICALLY, they could have done it with a sextant and a good clock, BUT! Their navigation skills had to be dead-bang on every time to the fraction of a minute.
So it was easier to shoehorn this colossus into the spacecraft and let it do the driving.

Simulation - emulation environment

[Anonymous Coward]

What I would like to see is a complete Apollo computing system simulator, consisting of the hardware simulator, where you could realistically simulate the effects of increased core voltage, heat, power surges, fluctuations, etc. coupled with the hardware emulator capable of running native Apollo code, just like vAGC.

Do they have this at NASA? For them it must be easier and more reliable to just use an identical environment for testing purposes, but some Apollo enthusiasts would enjoy tinkering with such a combined simulation-emulation environment (SEE).

Re:Simulation - emulation environment

[thhamm]

then integrate the whole thing into Orbiter.
this would be incredible. not just simulating the whole spacecraft in such detail, but actually doing the whole flight.

i wasnt my fault. i they tell me to stir the tanks, i stir the tanks.

Space Shuttle computers

[Veteran]

An engineer I work with at JSC has an actual - legally obtained Space Shuttle flight computer. The government declared it surplus, and he bought it from the surplus section, so he has the paperwork documenting that he is the legal owner. His box is an actual flight unit, which was in space, not a ground test unit or engineering sample. He has the paperwork documenting its complete history.

Every once in a while you can find some incredible things in government surplus.

Re:Space Shuttle computers

[Veteran]

I believe he has powered it up, and it does work.

Not comparable in any way to calculators

[panurge]

This machine is optimised for the acquisition of fairly real-time data; read the architectural description. Multiple channel counters are implemented in hardware, partly because in the days of discrete logic this was relatively easy to do (and, of course, the tube calculators with which people had gained experience used lots of counters, because it is relatively easy to make a counter tube, while binary tube logic is very hardware inefficient.)

Calculators have absolutely minimal I/O and need hardly any interrupt handling capability, and general purpose CPUs like the PDP-8 require a great deal of external hardware to give efficient programmed I/O. It was only really with integrated electronics that general purpose CPUs became appropriate for real time instrumentation and control.
It's also important that in a space environment, every added gate is a hazard because it can get flipped by radiation. The ideal is to have the minimum gate count, minimum memory cell count, and the shortest possible path between phyical I/O and computing. The computers used in the Apollo meet this requirement.

Sorry to restate what may be obvious to some people, but a lot of people here will never have had to implement a rad-hard design, and will not understand why simplicity and directness are such virtues in design for space use.

Re:Not comparable in any way to calculators

[Anonymous Coward]

Uh, so the MacIntosh that I flew on STS 46, 57, and 63, without any Radiation optimization was crap?

Ran OS-7 along with Labview to run an experiment in a mid-deck locker for 8 days.

Proved that a lot of the Rad hard design crap, is just that, crap. :)

Re:Disaster waiting to happen

[peawee03]

Not posting this as troll, flamebait, or anything other than a matter of engineering: could you do better?

Re:Anyone get a good look at the code yet?

[Quatloo]

And its nice to see octal again too!

Re:Disaster waiting to happen

[Beryllium Sphere(tm)]

Maybe a capacitive measurement? Liquid oxygen must have a different dielectic constant from gaseous oxygen.

Re:nope Re:Disaster waiting to happen

[Veteran]

They didn't use artificial gravity to seperate the LOX; quite the opposite.

In fact, in zero gravity LOX tends to divide up into regions of gas and liquid. If the gas happens to float past the sensor, then they get an incorrect reading of the density, and hence they don't know how much is in there. This was a big problem on previous flights. Stirring the tank mixes it all up and makes it the same density; allowing a reliable reading to be taken.

Yes and no. In zero g the bubbles and liquid have no reason to separate. In a gravity field the bubbles float just like the do in water - so you get a liquid without voids in it - which you can measure.

Aluminum, particularly bulk aluminum is *not* combustible in LOX. It's used on the Space Shuttle main tank fer heavens sake!

Aluminum will burn in air if there is enough energy to break through the surface layer of aluminum oxide which builds up on the surface. In fact aluminum is so reactive with oxygen that this layer forms instantly when the metal is exposed to oxygen. Anything which will burn in air will really burn in LOX.

Graphite can't really burn either; for it to burn it needs to reach ~3000K, and the LOX is pretty keen on it not reaching that temperature.

There was an experiment where a scientist used LOX and charcoal to see how fast it would burn - it esentially flashed in less than a second. DO NOT ATTEMPT THIS. IT IS RIDICULOUSLY DANGEROUS. Your statement is like saying Nitro Glycerin is safe to have in your house. NOTE FOR THE YOUNG AND INEXPERIENCED: DO NOT STORE NITRO GLYCERIN IN YOUR HOUSE. IT WILL BLOW UP AND KILL YOU!!!

Provided the brushes are carefully chosen, this need not be a problem.

This is exactly the sort of thinking which resulted in the original disaster. Brushes are mechanical devices - there is inductance in a motor - when the brush connection is broken the inductance of the motor will cause a spark. We have studied the ignition properties of such sparks in LOX in my group. There is a statistical probability of a given spark igniting the brush material.

That's not actually what caused the explosion anyway.

During testing a relay welded itself shut due to incorrect voltages. In flight, the wiring overheated- and the insulation burnt in the LOX. That caused the LOX tank to overpressure, and it blew away half the side of the vehicle

That is the official theory which was reached by people who knew nothing about the spark ignition problem. The voltage in the GFE power supply used in the test was not enough to weld contacts - the LOX would have cooled the wires so that they wouldn't have reached ignition temperature. The explosion didn't happen until the tank was stirred. The thinking behind reaching that official theory was "Well none of the other tanks blew up so the design was OK so it must have been someing which was done to that particular tank that caused the problem."

Thanks for demonstrating the "Whirr click, whirr click " mind set to everyone.

Re:nope Re:Disaster waiting to happen

[Veteran]

No argument there! Of course this would not have been news to the tank designers either.
It may have been. There is currently a discussion between various groups at NASA on this very subject - is there some minimum value of spark energy which is safe in a pure oxygen athmosphere? We say no, others say there is.

This entire thread is highly instructive of how memory and the human brain work in the real world: When I read the original reports about a year and a half ago I knew and understood the cause of the actual accident - but I remembered the dangerous design of the tank better than I did the pedestrian causes of the actual incident. Why? as a design engineer the design problems were of more interest to me. Over time I forgot the actual cause of the incident and substituted what I did remember about it.

Learn from this error lest it happens to you at some point.As you get older this happens more since you have much more information stored as an older person than you do as a young person. This makes you slower to respond (it takes longer to search through more stuff), and the chances of 'bit errors' increase with the number of bits stored.

Nevertheless my original point can be modified to: "it was a poor design decision to have live electrical circuits inside of a LOX tank".
I think most of us can agree with that.