Apollo On Board Computer Emulator 166
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."
Re:12-bit Instruction set (Score:5, Informative)
Orbiter (Score:5, Informative)
Already being worked on:
http://mysite.wanadoo-members.co.uk/marui/orbit
Re:Orbiter (Score:3, Informative)
Re:Orbiter (Score:3, Informative)
Source is here [wanadoo-members.co.uk].
Re:12-bit Instruction set (Score:3, Informative)
Why look at the apollo flight computer (Score:4, Informative)
The most recent version of the apollo spacecraft add-on (NASSP 5) has a partial working AGC built into the navigation system.
Re:very simple processor (Score:2, Informative)
Re:very simple processor 1201 (Score:3, Informative)
Re:Why look at the apollo flight computer (Score:3, Informative)
nope Re:Disaster waiting to happen (Score:5, Informative)
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.
you have several pounds of highly combustible aluminum and graphite parts
Aluminum, particularly bulk aluminum is *not* combustible in LOX. It's used on the Space Shuttle main tank fer heavens sake!
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.
LOX only really explodes in contact with greases- it's soluble in them, and they form a contact explosive.
and you have a DC motor with brushes sparking up a storm
Provided the brushes are carefully chosen, this need not be a problem.
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.
Parent is informative, deserves upmod (Score:5, Informative)
Draper Labs built the AGC (Score:4, Informative)
Notes on compiling (Score:5, Informative)
cd yaAGC
./configure
make
sudo make install
cd yaDSKY
./configure
make
sudo make install
yaAGC --core=Validation.bin --debug
In another window, still in the yaDSKY directory: yadsky --cfg=src/LM.ini
(Note lowercase yadsky)
Congratulations, Ronald. Pretty cool. Does the contrast on the LED display have to be so low? The background is very light.
Am I the only one here who actually tried the program?
Re:Curious about the computers back on the ground (Score:3, Informative)
I have no idea what the Prius has as a processor, but a modern laptop would substantially exceed the processing power of the ground installation. Perhaps only if programmed in FORTRAN though (the NASA language of choice at the time).
Re:very simple processor (Score:3, Informative)
While indeed there was actual piloting and people were clearly in the loop to run the spacecraft (and needed!), some of the critical timing issues for orbit insertion and lanuch windows simply have to be run with computers. There is no other way to ensure that you can hit the buttons at the precise time and stop in time.
While analog computers could have been used in this situation, this was the time period (late 1960's) when digital computers were finally widespread enough to be used in applications like this. The AGC was one of the first computers to use integrated circuits (IC's), and even then it was primarily 7400 series chips and a couple of specialized circuits. NASA at the time contracted something like 50%-70% of all IC production, which is where some people seem to think NASA was behind the development of some of the early micros.
BTW, this thread referenced the fact that sailors in the 16th through 19th Centuries used pretty much just a compass, clock, map, and sextant. The poster forgot to mention the clock, but it was indespensible back then...to give longitude data. Clocks still are very important even now, as that is all a GPS satellite really transmits anyway (the current time). All the rest of the positioning info is derived from the clock data.
Anyway, the sextant is actually a fairly sophisticated analog computer that is able to correctly identify your current lattitude with amazing precision. It tended to make the navigator go blind with one eye, which is why you see skippers and naval officers in depictions of the era wearing an eye patch. They litterally looked at the sun too long through the sextant. A good navigator using a sextant could get lattitude down to +/- 1/2 to 1/10th of a degree. Longitude you were usually considered very fortunate if you got it down to +/- 10 degrees (almost 600 miles when near the equator), which is why maps of the 18th Century are very accurate on lattitude but miserable with longitude, causing things like Minnesota's Northwest Angle.
Re:very simple processor (Score:3, Informative)
OI isn't really that critical timewise unless you have to hit *precisely* the orbit you want; a few seconds either way (and there often was during the lunar missions even with the computer running things) meant merely that your orbit would have a few miles or tens of miles discrepancy in perigee/apogee, correctable with a short burn.
The Saturn rockets were pretty reliable wrt to launch windows, but as I recall with the Atlas and Redstone they often couldn't predict exactly how long the rocket would fire sometimes not even to tens of seconds; but they still achieved the trajectories they wanted. So it couldn't have been *that* critical.
De-orbiting to splashdown, now, that's a different matter, a few seconds difference in retrofire and you could under or overshoot your splashdown target by tens of miles.
Given that the Polynesians didn't have clocks (or sextants) they did most of their navigating using dead reckoning and knowledge of their local environment; which shows just how much they understood the local winds and their ability to move their rafts. ( * see below)
Without a clock determining longitude accurately was extremely difficult. One could approximate the time using star set/rise times and seasonal charts, but with the distortion near the horizon causing enormous errors in the actual location of the star, and especially given the inaccuracy of the charts at the time, this was pretty much a crap shoot.
Sextants are certainly incredible! While in college I had the opportunity to learn to use a modern one (with a sun filter) and on my first few tries I located the longitude of the observatory at SCSU to within 14 minutes of arc; not especially astounding by modern standards (see the link below), but astonishing given the basic simplicity of the device and my inexperience.
I didn't know that about the MN NW Angle, do you have a ref? Fascinating!
* There is a good piece available about the Polynesians and modern navigation here [campusprogram.com]
Cheers,
SB
Re:very simple processor (Score:3, Informative)
Gene Kranz's book Failure Is Not An Option talks about simulating the moon landing, and seeing 1201 alarms coming up and the controllers unable to deal with them. Kranz ordered an abort after a 1201 alarm...but it turned out that was the wrong thing to do. Dick Koos, the simulation supervisor, told him, "This was not an abort. You should have continued the landing. The 1201 computer alarm said the computer was operating to an internal priority. If the guidance was working, the control jets were firing, and the crew displays updating, all the mission-critical tasks were getting done." They wound up figuring out rules on which program alarms would terminate descent...and the list did not include the 1201 or 1202 (similar) alarms.
Good thing, too, because both of those alarms occurred on Apollo 11's descent. Buzz Aldrin reported that it seemed to happen when they had a computer display of time, range-to-go, and altitude up. They continued the landing, which was eventually successful; the alarms didn't seem to affect the LM computer performance any.