Knots on Mars (and a few thoughts on NASA's knots) (2012) | Hacker News Reader

Knots on Mars (and a few thoughts on NASA's knots) (2012)

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60 pointsTomte26 comments

On a related note the Museum of Berkshire Aviation near Reading, one hour west of London, has some examples of lacing on display.

They have quite a few parts from a Chevaline / Polaris missile and what struck me the most was the quality of construction. It was just fascinating to see the level of engineering involved, including the cable lacing.

https://www.flickr.com/photos/stevecargill/52524141291/in/al...

https://www.flickr.com/photos/stevecargill/52524425464/in/al...

https://www.flickr.com/photos/stevecargill/52524621525/in/al...

A few years ago when I was starting to do some soldering after a break of many years I came across the NASA Standard. Much like the lacing document another poster linked to, the level of detail is mind blowing.

https://nepp.nasa.gov/docuploads/06AA01BA-FC7E-4094-AE829CE3...

NASA Technical Standard NASA-STD-8739.4 -- Crimping, Interconnecting Cables, Harnesses, and Wiring moved to https://standards.nasa.gov/sites/default/files/standards/NAS...

Found via https://standards.nasa.gov/all-standards?check_logged_in=1&p...

One aspect of knots is missing from these descriptions: suitability for inspections. Wiring on something like a mars rover is going to be inspected dozens of times. So you want a knot that can be easily seen as correct from a variety of angles and without manipulation. Just as climbers want a nice symmetrical knot, if you are inspecting things you want a clean-looking knot rather than one that may have slightly better technical performance, ie figure eights over clove hitches.

Similarly, work with aircraft and you will see safety wire rigged not only to be secure but to be easily spotted and verified from a distance. Safety wire that cannot be verified easily means more work during every future inspection.

It's interesting. It suggests something about software:

- code should be obvious (and obvious about what it does), and where it lives

- tests should be obvious and should surface relevant critical work

- UI should also be 'inspectable from a distance', as in people should be able to glance at it, and grasp the gestalt of how to do what they need (within reason and up to the specific uniqueness of the application)

I once worked with helicopters, very large helicopters. The "UI" in the cockpit involved at least 18 gauges measuring all the basic stuff about the engines and associated sub systems. With the helicopter powered down each gauge seemed installed in a random orientation, a couple were even upside down. But when flying the "normal" needle position would point straight up, allowing the pilots to glance quickly to see that all was good without focusing on each individual gauge.

A lot of car dashboards have this too, where 100km/h, 1500rpm, nominal temperature and battery voltage are all the straight-up position.

People are hardwired to see patterns before details.

Would have been interesting if I could have seen any of the images.

What I find interesting about knots is that different sub-cultures have settled on so different knots. Scouts join rope with a sheet bend, while climbers pretty much would use a double fisherman's knot, etc. ad infinitum.

I think it's the knot application and not the culture driving the requirements. For example, we all know what a square knot is, but it's difficult to untie when stressed and wet. A reef knot on the other hand has a loop for its second half hitch which makes it easy to untie. This is why it was used to reef sails at sea when wet and bouncing.

> I think it's the knot application and not the culture driving the requirements.

Bingo! From article:

"Knots are still used in this high-tech arena because cable lacing has long been the preferred cable management technique in aerospace applications. That it remains so to this day is a testament to the effectiveness of properly chosen knots tied by skilled craftspeople."

If there's a better way (not saying there isn't!), prove it. Knots 'just work', use a minimal amount of material (weight), and are reliable low-tech proven over ages.

Of course, effectiveness / reliability depends heavily on "properly chosen knots" (+materials) and "tied by people who know what they're doing". I'd think NASA has that covered.

Aren’t square and reef knots one and the same?

They are, what GP is describing is called a slipped reef/square knot.

Reef knots without the loop can also be capsized for quick untying. It is a dangerous property of that knot for some situations, and a reason some people think is shouldn't be taught as a general purpose knot. But it can be useful in specific cases like in reefing, as its name suggests.

Check your browser settings, all images are displayed for me.

For me the images work in Firefox, but don't in Chrome. Looks like an issue with https, but i'm not sure how and why.

could be a regional thing, eu here, no pictures

I've built laced wire harnesses for general aviation aircraft, for flight test instrumentation in commercial aircraft, for race cars, and for race motorcycles. I have a particular distaste for zip ties. Some advantages of lacing not discussed here:

The inside diameter of a zip tie is serrated. It can trap particles of dirt, and in a high vibration environment, these particles can abrasively cut through even solid aircraft grades of stainless steel. I saw the results when someone zip tied an instrumentation wire to a 5000PSI 21-6-9 stainless steel hydraulic tube on a GeNX-1B thrust reverser just to secure it out of the way during a test. It sawed through the tube and caused a massive leak after less than than 3000 simulated flight cycles (engine operating cycles on a ground test stand)

Zip ties have an annoying square head, and the tag end is often cut off not quite flush with the head, giving a great jagged edge to lacerate some poor mechanic's hand. I've frequently had my arm buried deep in a mass of spaghetti wiring behind a panel to get at a connector or something, it's very nice to not withdraw it and find deep red scratch marks in my forearms like I've been fighting to trim my cat's nails. They do sell a brand called Cobra Ties that have the tag end parallel to the band, which is a little nicer in this regard.

Zip ties are a hard point and are frequently over-tensioned. It's not uncommon to find damaged/pinched insulation, or even broken conductors in small gauge wires, under a zip tie.

In general aviation maintenance, I frequency (95% of the time inspecting a new to me airframe) encounter previous work that was accomplished with some garbage neon colored zip ties from the home improvement store or Harbor Freight, made of an unknown grade of plastic. When used in an engine compartment, these often cannot withstand long term exposure to high temperatures and fluids, and fail by breaking when you least want them to. When used in the passenger compartment, these can emit hazardous amounts of toxic fumes and smoke in the event of an electrical fire, which can be caused by an over-tensioned zip tie. Shade tree mechanics are too lazy (or ignorant) to mail order the correct MS3367 mil-spec ty-wraps, with guaranteed strength/temperature/flammability performance.

But really, I prefer wire lacing in the cabin, and MS21919 cushioned P-clamps in the engine compartment.

> Zip ties have an annoying square head, and the tag end is often cut off not quite flush with the head, giving a great jagged edge to lacerate some poor mechanic's hand.

In decades past my hands were cut many times in data center racks because of this. Fortunately, zip ties have gone out of fashion and everyone uses Velcro now. The advantages of Velcro over zip ties in data center racks:

- Even pressure and no risk of over tightening

- Trivial to re-work when cables are added/removed

- No more cut hands!

The only downside is that sometimes the loops can be too loose and slide down to the next loop. This is especially common when very few cables are being bound and the Velcro structure does not want to conform to such a tight radius.

Electrical tape. You see this with underwater gear, stuff like hose bundles down to commercial divers. The tape won't last long, nor is it very strong, but it will not damage the cable. You will have to inspect and replace it regularly but its various failure modes wont result in someone's air line being cut through due to vibration..

With images https://archive.ph/20240222110810/https://forum.igkt.net/ind...

Can confirm that the dashboard of an electric airplane made last year has waxed nylon lacing tape and those knots because I did it.

There are three major cable lacing techniques in the United States: USN, USAF and NASA. This video from IMSAI Guy illustrates all three:

https://www.youtube.com/watch?v=EN8dDR4ipBU

I did some harnesses Navy style on our prototype hardware, it turned out nicely!

Makes me wonder if there's an offical "knot tyer" position at NASA.

Never thought a job title could be both so wondrous and wholesome at the same time!

https://www.indeed.com/q-Spacecraft-Assembly-Technician-jobs...

No images shown here. Mobile chrome.

The hitch guide to the solar system

Images work in DDG's browser.

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