

NASA Technical Standard: Crimping, Cables, Harnesses, and Wiring (2011) [pdf] - GuiA
http://www.hq.nasa.gov/office/codeq/doctree/87394.pdf

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ceequof
Page 50: Hey, that's how you're supposed to use heatshrink! Wow, I've been
doing it wrong for years.

Page 62: Mildly surprised that they don't want crimped connections soldered,
but I suppose that compromises flexibility, and shouldn't add all that much
strength if they're properly crimped.

Page 76: Wow, had never heard of "connector saver" jumpers before. Sounds
bananas, but I suppose if you're going to test everything ten times for every
launch, it's mostly reasonable.

~~~
engi_nerd
I currently work as an aircraft telemetry and instrumentation engineer, and
have also done similar engineering on rockets. So I spend a lot of time
thinking about (and have been trained very thoroughly about) connections and
how to do them.

> Hey, that's how you're supposed to use heatshrink! Wow, I've been doing it
> wrong for years.

Out of curiosity, how have you been doing it? The way shown in this manual is
the standard way to do it in my world.

> Mildly surprised that they don't want crimped connections soldered

I'm confused as to why you would think about soldering a crimped connection.
Properly crimped connections will stand up to a good deal more vibration (and
are pretty much gas-tight, staving off corrosion) than soldered connections.
Plus, crimping is quick and easy with the right tools. Maybe there are some
niche applications where you'd do both. I've never seen it.

> Wow, had never heard of "connector saver" jumpers before. Sounds bananas

Totally not bananas when you look at the spec sheet for something like a
D38999 series connector. Connector savers are a normal thing in the aerospace
world. Most connectors are only rated for a few hundred mate/demate cycles
(Usually 250 or 500). Every time you mate or de-mate a connector you run the
risk of damaging a pin or socket. So the connector savers are sacrificial for
when you test. They get mated to the real connections once at the beginning of
your tests, and demated at the end. Then you give your real connections a
thorough check at the physical level and hook them up.

~~~
HeyLaughingBoy
_I 'm confused as to why you would think about soldering a crimped connection_

Because most crimped connections (at least in the hobbyist/DIY world) are
_crap_. So after crimping, the only way they hold together is with solder.

There are no applications where this is better. Every connector manufacturer I
know recommends against doing it. You can get away with doing it if you
support the soldered end against vibration, but you should do that anyway.

It's really a training issue. People haven't been taught better and there is a
lot of bad advice floating around hobbyist forums. I have only been using good
crimping tools for the last few years since I started making a product with a
50-conductor harness. Until I spent $200 on a crimping tool and took the time
to research how to make good crimps (Molex has an excellent document), I never
realized how they were supposed to look. Now most of my tools are used,
purchased at auctions of dead companies, but I have $400 crimping tools I paid
pennies on the dollar for. Even so, I normally farm out crimping to a company
that does it with automated machinery, better and faster than I can do by
hand.

~~~
asynchronous13
Most of the crimpers I use are $1000+. I was totally shocked at the expense
when I first switched from home hobby to professional work, but the quality of
the crimps is simply incomparable. Very much worth it for reliability.

~~~
HeyLaughingBoy
I don't think I've seen a manual tool that was so expensive. Are you using
some kind of pneumatic crimper? I thought of getting even better tools, but I
found an outfit that will cut and strip wire to my spec. and crimp on any
contacts I need, and they do it cheaper and faster than I can.

~~~
engi_nerd
No, that's about how much a good manual crimper costs. But man, the results
you can get out of them are fantastic.

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raymondh
Technical standards would be vastly improved by adding a because-clause to all
of the do-this and don't-do-that requirements.

Section 9.5: "NOTE: Do not use spiral wrap sleeving on mission hardware
including launch vehicles."

If you knew why, then you could make intelligent decisions for cases to
specifically covered by the standard. Possible reasons: Poor strength to
weight ratio, unreliable under high-g load, makes visual inspection difficult,
there is a better but more expensive substitute, etc.

~~~
TeMPOraL
From a point of view of a person not employed at NASA manufacturing plant who
would like to learn something from that document, I agree. But my guess is
that this standard is created for people who are paid to obey, not to think,
because there are decisions made higher up the chain that depend on the
components being deterministic.

This reminds me of an anecdote I saw on HN once, about Apple hardware team
sending boards back to Chinese manufacturers who replaced a capacitor (or some
other part) with a cheaper one without realizing it was vital for the product
to work for reasons they were not aware of.

------
noir_lord
Years ago I trained as an (industrial) electrician with a particular focus on
hazardous environments (flour mills etc, lots of suspended flammable dust),
lots of the stuff in here is familiar :).

Working with armoured cable all day was enough to make me decide to go do
something else as a career.

