Tindallgrams(tindallgrams.net)
tindallgrams.net
Tindallgrams
http://tindallgrams.net/
3 comments
Any pointers for particularly interesting memos in this collection?
Does anyone know what he meant by “rope” in these memos? By context it appears to be supporting but not primary code? I could be completely wrong on this.
The ROM that the code was stored in was rope.
https://en.wikipedia.org/wiki/Core_rope_memory
https://en.wikipedia.org/wiki/Core_rope_memory
Would love to hear someone's experience with using or preparing this kind of memory.
I haven't used or prepared rope memory, but I have done quite a bit of research and planning to potentially construct some in the future.
Using it wasn't terribly exciting; the rope memory for a program was broken up into six rope modules that could be installed into and removed from the back of the AGC pretty easily with a screwdriver. Dedicated rope modules were only really used for flight and for completed test programs. For the most part during development they made use of "core rope simulators", that simulated the electrical properties of a core rope memory, but read data from a traditional coincident current ferrite core stack. This let them much more easily and quickly test programs out on hardware, without going through the pain of shipping a release out to the factories to manufacture.
The long and expensive assembly process caused last-minute changes before mission to be, in some cases, a bit hacky. They would do their best to localize changes to a single module, if possible, so that they would only have to re-manufacture one of them instead of all six. The Apollo 11 LM thus flew with 3 modules of Luminary 97, 2 from Luminary 99, and 1 from Luminary 99 Rev. 1. And this page from the Apollo 5 software Sunburst 120 shows how messy that could get: https://archive.org/stream/yulsystemforagcr00nasa#page/n485/...
Rope memory led to one of the most interesting "binary" output formats from an assembler that I've ever come across. The assembler (https://archive.org/details/yulsystemsourcec00hugh), upon successfully assembling a program, could punch a paper tape for manufacturing. The tape didn't contain the words of the program, directly. Rather, it contained commands for a special machine that was designed to help with the construction of the rope modules. The machine would position a small loop in front of the next core a wire was supposed to be threaded through. One of the two operators would pass a needle and wire through the loop and through the core to the operator on the other side, and the loop would then be repositioned in front of the next core the wire was to pass through. This video describes the process in more detail and shows it being done: https://www.youtube.com/watch?v=YIBhPsyYCiM
Preparing it nowadays is a bit challenging. Contrary to most descriptions you'll find online, rope memory is not "just" simple transformer coupling between the drive lines and the sense lines. The operation is a lot closer to the concept of coincident current ferrite core memory. Just like regular ferrite core memory, rope memory relies on the switching action of cores with "square" hysteresis loops. When a particular word is being read out of memory, a single core is addressed (each core stores the data for twelve 16-bit words). This core is "set", or driven to one magnetic polarization, by a set current, with all other cores being held by a series of inhibit lines. After a short time, the core is then "reset" to its original polarization by flowing current through the other direction. The changing magnetic field of the core couples into the sense lines that go through the core (and not onto those that don't), which are run into a traditional sense amplifier circuit.
Anyways, the cores used were (as far as I've been able to gather) metal tape cores, wound with 1/8mil thick 4-79 molybdenum permalloy tape. Similar stuff is still made today, but it's not super easy to come across. Each of the six modules contains 512 of them, so you'd need 3072 cores total if you wanted to weave one of the full manned flight programs.
Using it wasn't terribly exciting; the rope memory for a program was broken up into six rope modules that could be installed into and removed from the back of the AGC pretty easily with a screwdriver. Dedicated rope modules were only really used for flight and for completed test programs. For the most part during development they made use of "core rope simulators", that simulated the electrical properties of a core rope memory, but read data from a traditional coincident current ferrite core stack. This let them much more easily and quickly test programs out on hardware, without going through the pain of shipping a release out to the factories to manufacture.
The long and expensive assembly process caused last-minute changes before mission to be, in some cases, a bit hacky. They would do their best to localize changes to a single module, if possible, so that they would only have to re-manufacture one of them instead of all six. The Apollo 11 LM thus flew with 3 modules of Luminary 97, 2 from Luminary 99, and 1 from Luminary 99 Rev. 1. And this page from the Apollo 5 software Sunburst 120 shows how messy that could get: https://archive.org/stream/yulsystemforagcr00nasa#page/n485/...
Rope memory led to one of the most interesting "binary" output formats from an assembler that I've ever come across. The assembler (https://archive.org/details/yulsystemsourcec00hugh), upon successfully assembling a program, could punch a paper tape for manufacturing. The tape didn't contain the words of the program, directly. Rather, it contained commands for a special machine that was designed to help with the construction of the rope modules. The machine would position a small loop in front of the next core a wire was supposed to be threaded through. One of the two operators would pass a needle and wire through the loop and through the core to the operator on the other side, and the loop would then be repositioned in front of the next core the wire was to pass through. This video describes the process in more detail and shows it being done: https://www.youtube.com/watch?v=YIBhPsyYCiM
Preparing it nowadays is a bit challenging. Contrary to most descriptions you'll find online, rope memory is not "just" simple transformer coupling between the drive lines and the sense lines. The operation is a lot closer to the concept of coincident current ferrite core memory. Just like regular ferrite core memory, rope memory relies on the switching action of cores with "square" hysteresis loops. When a particular word is being read out of memory, a single core is addressed (each core stores the data for twelve 16-bit words). This core is "set", or driven to one magnetic polarization, by a set current, with all other cores being held by a series of inhibit lines. After a short time, the core is then "reset" to its original polarization by flowing current through the other direction. The changing magnetic field of the core couples into the sense lines that go through the core (and not onto those that don't), which are run into a traditional sense amplifier circuit.
Anyways, the cores used were (as far as I've been able to gather) metal tape cores, wound with 1/8mil thick 4-79 molybdenum permalloy tape. Similar stuff is still made today, but it's not super easy to come across. Each of the six modules contains 512 of them, so you'd need 3072 cores total if you wanted to weave one of the full manned flight programs.
I just read the first memo. I also entered the automotive world a few months ago. It seems that nothing has really changed since 1966 on the management level. Also automotive and spaceflight is probably more alike than I previously thought.
Take a peek at the change of tone in the early May 1967 memo (after the Jan Apollo fire that killed three crew members)
”...it’s almost unthinkable to fly with any known deficiencies in the program - even those which would only affect very low probability contingency situations...”
Reminds me a bit of the work being done with self-driving cars. Unfortunate that it sometimes takes tragedy to give management perspective.
”...it’s almost unthinkable to fly with any known deficiencies in the program - even those which would only affect very low probability contingency situations...”
Reminds me a bit of the work being done with self-driving cars. Unfortunate that it sometimes takes tragedy to give management perspective.
The obscenely expensive obsession with safety in space flight has always seemed misguided to me. Plenty of people are willing to take the risk. Millions of people take bigger risks in their lines of work every day, with much less upside. The frontier of human capabilities seems like an odd place to renounce risk taking.
I agree with the first part, but I don't think it's the case that millions of people take astronaut-level risk in their work every day. 4% of everyone who has gone into orbit were killed in a mission or during training.
https://www.quora.com/What-is-the-astronaut-fatality-rate
The most dangerous jobs in the US, logging, has only 60k workers and a mortality risk of about 2.7% over a 30-year career.
https://priceonomics.com/how-the-lumberjack-became-such-a-de...
The reason it's bad to spend so much on astronaut safety is because the cost is so enormous and because the people at risk are very well-informed and participate voluntarily.
https://www.quora.com/What-is-the-astronaut-fatality-rate
The most dangerous jobs in the US, logging, has only 60k workers and a mortality risk of about 2.7% over a 30-year career.
https://priceonomics.com/how-the-lumberjack-became-such-a-de...
The reason it's bad to spend so much on astronaut safety is because the cost is so enormous and because the people at risk are very well-informed and participate voluntarily.
> The reason it's bad to spend so much on astronaut safety is because the cost is so enormous and because the people at risk are very well-informed and participate voluntarily.
That 4% fatality rate would likely be much higher if safety was lower priority.
Since astronauts don't oversee the entire build process, nor all of the maintenance, nor do the review all of the source code, etc etc etc, they aren't really well informed.
I believe you mean to say they are well informed of the risks, but the risk (4% fatality rate) is only that low due to astronaut safety being a high priority.
Also, as far as I understand, astronauts are usually paid[1], so they participate voluntarily only insofar as I participate voluntarily at my job: sure, I choose to go, but it's not volunteering for tax purposes.
1. https://www.nasa.gov/centers/kennedy/about/information/astro...
That 4% fatality rate would likely be much higher if safety was lower priority.
Since astronauts don't oversee the entire build process, nor all of the maintenance, nor do the review all of the source code, etc etc etc, they aren't really well informed.
I believe you mean to say they are well informed of the risks, but the risk (4% fatality rate) is only that low due to astronaut safety being a high priority.
Also, as far as I understand, astronauts are usually paid[1], so they participate voluntarily only insofar as I participate voluntarily at my job: sure, I choose to go, but it's not volunteering for tax purposes.
1. https://www.nasa.gov/centers/kennedy/about/information/astro...
I feel like a lot of it also has to do with the political origins of the space race. If we got to the moon but treated our astronauts as disposable, it wouldn't look as good.
Mission failure was also extremely expensive in monetary terms. ;)
Manned spaceflight is a publicity exercise, and killing people is bad publicity.