
Tindallgrams - thestoicattack
http://tindallgrams.net/
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JadeNB
Any pointers for particularly interesting memos in this collection?

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tomcam
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.

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LukeShu
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)

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danfolkes
Would love to hear someone's experience with using or preparing this kind of
memory.

~~~
thewonderidiot
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/...](https://archive.org/stream/yulsystemforagcr00nasa#page/n485/mode/1up)

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](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](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.

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qznc
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.

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rpvnwnkl
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.

~~~
marcoperaza
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.

~~~
jessriedel
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](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...](https://priceonomics.com/how-the-lumberjack-became-such-a-deadly-
profession/)

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.

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TheSpiceIsLife
> 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...](https://www.nasa.gov/centers/kennedy/about/information/astronaut_faq.html)

