[cuSetanta]

As a spacecraft Assembly, Integration and Test (AIT) Engineer, one of my areas of expertise is harness manufacture and routing. So this naturally involves an awful lot of crimping. I am a certified crimping operator and inspector under the ECSS standards (which go a bit overboard at times in their requirements when compared to the NASA standards).

I am lucky to have built a large amount of harness has/is/will fly on many spacecraft for many customers. There are a lot of unique challenges to crimping for spacecraft harnessing, but in almost all circumstances the main issue has be schedule. Very few project managers that I have worked with, even those who have a lot of experience, plan for enough time to complete the harnessing side of a project.

Depending on the number of crimping configurations that are present in a system, it can take days to calibrate all of the crimp tools before starting. Every crimp needs to be inspected before the heatshrink can be shrunk, and often before the next crimp can be performed if the routing is critical. Routing involves labeling, gluing of tie-bases, bundling of harnessing, and the shielding.... jesus christ the shielding can be a nightmare...

Man I love making harness, honestly one of my favourite things to make. Not sure if anyone cares enough to have questions, but happy to answer them if they exist.

[russell_sears]

My grandfather used to work on telephone field network boxes (e.g., the big boxes full of messes of wires in residential areas).

One job was to look for outliers in the network, and they spent time studying areas with an unusually large number of issues and ones with an unusually low number of issues.

There was a part of the phone network that was decades overdue for an overhaul but had no issues, so they inspected it. (This was decades ago, so the replacements for this antique could be modern day museum pieces).

When they took a look, everything was corroded beyond reason, as expected. However, the connections were still low noise / low resistance.

The old boxes used some sort of post connector and a crimp. It had something like two or four points of contact for redundancy (all contact points would need to corrode before it failed).

In the boxes with no failures, the (long gone) technician simply stuck the end of the wire into the post crimp hole, then wrapped slack wire around it a dozen times.

This gave it 100’s of contact points, and (after reverse engineering the technique) it took something like 1/10th as long per connection.

Sadly, we’ll never know if the installer was a genius, lazy or both.

Anyway, the crimp connectors in fig 19-25 and 19-28 of the nasa article look like the same concept but turned inside out.

[nullc]

I'm not sure why more of those didn't use wire-wrap, it's super fast and is really reliable. I've seen some bell terminals that were wirewrap but punchdown was more common in my experience.

[natpalmer1776]

As a young guy who was (un)lucky enough to be exposed to punchdown terminals as a field technician for AT&T…

Fuck punchdowns and everyone who said “good enough for me” when deciding to adopt them.

On a brand new install? Sure it works great!

In a box that has been sitting in the rain for a little over a decade? No.

[figassis]

Laziness tends to be a great catalyst for genius work

[mechhacker]

In my brief stint working on spacecraft in the private sector I worked with guys like you that did beautiful things with wiring that I loved to see.

I hear you on scheduling too. I've given best estimates and they then get chopped up and halved (or worse) by management types, then things start to slip and we end up being closer to what was originally estimated, but somehow everyone then gets surprised.

[cuSetanta]

As you say, things shift around, promises get made, everything gets delayed and all of a sudden there is no margin left. Unfortunately AIT has to do all of the hardware work with no margin so much of the time.

Secretly I love the power that can give us. You can shout at me all you like in the meetings Mr. ESA engineer, but if the holes don't line up, I cant put a bolt through them. Nothing quite like drilling holes in spacecraft on the launch pad.

[jaydeegee]

I once rewired a racecar engine loom with red 18gauge wire and used different colour heatshrink to differentiate power, ground, signal etc.. also happy to answer any questions.

[cuSetanta]

18 gauge! Thats the big leagues. We rarely go that big, 22awg is big for us. I salute you sir.

[jaydeegee]

Haha we had one roll of wire and it was 1am so we made do, I would have much preferred something a little more suitable. But hey you gotta do what you gotta do.

[gravescale]

What is involved in correctly inspecting a crimp? I find it hard sometimes to tell the difference between a crimp that's halfway to severing the wire and one that can come adrift at a moment's notice.

But then those are mostly the cheap ones with the plastic rings so you can't really see what's going on inside them.

[cuSetanta]

The inspection is primarily visual, to ensure that the stands are well aligned in the crimp, with no protrusions. And to check there is no damage to the wire due to stripping or a mis-crimp.

For under/over crimping, thats mostly taken care of with the tool calibration. And every shift (work day or X crimps) samples are taken to check the tool is still performing well.

[gravescale]

Interesting, so it's mostly in the tool setting! I shall have to see if it is practical to find some way of calibrating my (fairly rubbish!) crimp tool and see if they even keep a setting.

[cuSetanta]

If you have a fish scale, you can see what the retention force is fairly easy. Thats the primary method we use for calibration, albeit with a specific testing hardware.

[WalterBright]

During college I had a job wirewrapping circuit boards and putting printed circuit boards together. Most people would make a rat's nest out of the wiring, but I would lay everything out in a pattern. With a pattern, it's much easier to spot errors.

[contingencies]

So as neither an EE nor an ME (nor a qualified SE!) I've been in charge of some fairly complex mechatronic systems development for the last near-decade. IMHO the whole harness thing seems to be on the way out, excepting very specific situations where every last bit of weight really matters. Why? First, cost. Not having point to point means you aren't an off the shelf item, which means costs 10x immediately. Second, communications friction. While numerous providers can create arbitrarily complex harnesses as a commercial service, they generally disagree on everything from the manner by which cable qualities are specified to the sequence by which a termination should be made to what a length means with respect to a radius, etc. especially when crossing national boundaries. Third, complexity. Shared buses are harder to manage from a project evolution standpoint, and make it much harder to isolate and debug misbehaving nodes. Now I can see why all of this is worth it on a spacecraft, where weight matters, or in a car, where volume is assumed, custom connections are probably needed owing to a high vibration environment and every communicating component is probably either relatively well tested (auto grade transceivers) or relatively simplistic (window or door controller) or both, but for the rest of us where a smaller volume is assumed it seems to me harnesses are falling out of favor. Their chief benefit is weight reduction and nominal material cost reduction but the accrued costs in real terms outweigh these savings for the majority of projects, IMHO. Does this echo your own experience?

[cuSetanta]

Space is very slow to change, and traditional harnessing is going anywhere for the time being.

I cannot speak to the newer systems on the market like Starlink, their economies of scale are closer to car manufacture, so for harnessing, they likely do it similar to that industry. Form boards and very repeatable methods for producing a harness that has been well designed into the chassis of the spacecraft to be installed at a specific point. But much of those techniques are relatively unchanged from what I do, just the timing and overall design is more optimised.

Most of the harnessing I have done is very bespoke, and happens at many stages throughout the integration as things are installing, finalised, and what-not.

[contingencies]

Thanks for taking the time to reply. I'm going interpret that as a soft yes with reservation since you seem to be extremely knowledgeable in this specialist area and additionally state that you are doing 'very bespoke' work within that. Interesting stuff, great to hear from someone with such knowledge. I suppose Starlink/SpaceX people are NDA'd to the point they can't comment, maybe we'll hear from them in future. FWIW internally we've achieved autonomous cable production ex termination (length, strip and cut including measured splice-points - rarely used), and custom bus bars which I guess are a nominal harness in a sense. Anything more complex we need pre-terminated still gets sent out.

[cuSetanta]

I would also add that the 'New Space' scene is going to be much more willing to accept autonomous manufacturing methods. People like ESA are much much more resistant to change, and will take a lot of convincing that it is as good as the slow manual method.

Honestly, as things are looking, I am likely to be leaving the space sector in the near future, so I am not too worried about protecting my job or future on that front. The more accessible space is the better, even if that means people like me become less common.

[Pet_Ant]

ECSS... probably this is the "European Co-operation for Space Standardization" and not the top result of "European College for Sport Science"

[1] https://ecss.nl/ [2] https://sport-science.org/

[cuSetanta]

Apologies, yes the crimping standard specifically is here: https://ecss.nl/standard/ecss-q-st-70-26c-crimping-of-high-r...

[goy]

I'd like to know more about the education & career path that lead you there ...

[cuSetanta]

At undergraduate level I studied Physics and Astronomy, and then did a research MSc as an optical astronomer, which I hated and drove me away from Physics and Astronomy as a whole.

I spent a few years working in IT Support before deciding to go back to University to study Spacecraft Engineering at Surrey University. Which was a wonderful course, that gave an incredible overview of how one builds a spacecraft. More than most of the Master programs I have seen in the field since, the guys at Surrey had very real experience building quite a few spacecraft, which shone through in the projects and courses.

After that I started a PhD in Southampton that had an industrial sponsor, who eventually ended up offering me a job to build spacecraft before I finished the PhD itself (which was a little complicated in itself), which I took.

After I started with them, I basically apprenticed under an experienced AIT engineer who was coming up to retirement. This is where I really learned a lot. If you ever get the chance to work under someone in the later stages of their career, you really can learn a lot from them.

That was at OHB Sweden, which was an excellent place to see a broad range of things in the industry. I go to work on multiple spacecraft and various stages of development, from proposal, to qualification, to final assembly and test, and to launch as an operations engineer. Really a super experience I am not sure I could have been luckier ending up there.

After that I joined a very small team building the ispace lunar lander, which I am fairly certain will remain the pinnacle of my career. Never have I worked with such a great team on a great project. Everything just worked between us, and a small team really achieved something spectacular (even if it ended up in a crater on the moon).

Now I am working in Ireland for a data acquisition system developed for flight and launch vehicles. Learning the ins-and-outs of ethernet communication and analog circuitry. So far my complete lack of understanding of electronics hasn't been a problem, somehow.

[goy]

Very interesting. Thanks for the reply.

[hxriv]

What brand of connectors do you favor using professionally and for personal projects? I imagine the list of spacecraft certified companies isn’t that long.

[cuSetanta]

The main brands I would see would be Glenair, Souriau, and ITT Canon. Once you are paying the the space quality hardware, its all much of a muchness really. Glenair would probably be top dogs in this space.

I have used other manufactures with their own propriety connectors, like Harwin, which are a bit awkward.

The various styles of connectors do matter a bit. Micro-DSUB and Nano-DSUB are a bit of a pain, as you generally get the connector with flying leads, so have to inline (butt) splice.

38999 Circular connectors are great to work with the hardware, but order the right parts is a nightmare as they all have phone number part names.

[ThrowawayTestr]

For spring connectors like wago lever nuts, should the wires be tinned?

[cuSetanta]

Havent used them much, but I cant see why they would need to be tinned.

[doubloon]

how good do you think the crimps are nowdays at Boeing and Space-X?

[cuSetanta]

Crimping is essentially quite a low skill method of connecting wires, when compared to the high skill and experience to do it reliably with solder. I would have a lot of trust in the Boeing crimpers, and I have worked with the SpaceX guys, and they were all very good.

[doubled112]

I always thought it was less about skill and more that crimps were more reliable in high vibration situations. Solder often becomes brittle over time.

I'm only coming from shade tree car AV installation though. Nobody (probably) dies when it fails.

[tiahura]

Has a spacecraft ever failed because of a wiring failure?

[cuSetanta]

Hahaha oh yeah, plenty.

Recently the Peregrine Lander had wiring issues that led to using the NASA payload to perform the landing. The Vega-C launcher was lost not long ago as two connectors were swapped, connecting two engines in reverse order.

Wiring issues cause a lot of failures that are found on-ground for the most part. But plenty have made it through to fail on orbit.