Author Topic: Knots on Mars! (and a few thoughts on NASA's knots)  (Read 106985 times)

dfred

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Knots on Mars! (and a few thoughts on NASA's knots)
« on: August 25, 2012, 02:20:36 AM »
(NOTE: All photographic images below can be clicked to view at higher resolution.)

In the last few days some of the first high resolution color images of Mars Rover Curiosity's deck have been taken. These included some of the best images yet showing the knots visible on the exposed wire and cable bundles.

While a few of the folks here are no doubt aware, it might surprise most people to learn that knots tied in cords and thin ribbons have probably traveled on every interplanetary mission ever flown.   If human civilization ends tomorrow, interplanetary landers, orbiters, and deep space probes will preserve evidence of both the oldest and newest of human technologies for millions of years..


Image Credit: NASA/JPL-Caltech/Malin Space Science Systems(Original)


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.  It also no doubt has a bit to do with the conservative nature of aerospace design and engineering practices.  Proven technologies are rarely cast aside unless they no longer fulfill requirements or there is something substantially better available. 

While the knots used for cable lacing in general can be quite varied -- in some cases even a bit idiosyncratic -- NASA has in-house standards for the knots and methods used on their spacecraft.  These are specified in NASA Technical Standard NASA-STD-8739.4 -- Crimping, Interconnecting Cables, Harnesses, and Wiring.  As far as I've been able to identify in the rover images below, all of the lacings shown are one of two of the several patterns specified in the standard.




The above illustration shows the so-called "Spot Tie".  It is a clove hitch topped by two half-knots in the form of a reef (square) knot.  In addition to its pure binding role, it is also used to affix cable bundles to tie-down points, as can be seen in many of the Curiosity rover images below.

Knot history buffs might find it interesting that a "Spot Tie"-like knot, with opposite Clove Hitch end orientation and topped only with a single half-knot was illustrated in 1917 by A. Hyatt Verrill under the name "Gunner's Knot".  This was seemingly due to Verrill copying from J.T. Burgess, who had oversimplified "Bowling's" description of what possibly was the first known textual description of the Constrictor knot.  But that's a whole different can of worms!    ;D

So why has NASA standardized on this knot instead others which might serve the purpose?  The following reasons are merely my own musings. I'd be interested to hear others' comments on this knot's strengths and weaknesses.


  • Conservative design
The Reef Knot and Clove Hitch are extremely ancient.  Both were discussed in detail as surgical and orthopedic knots and slings by Greek physician Heraklas in the 1st Century AD.  The Reef Knot is depicted with varying degrees of realism in ancient Egyptian statuary and hieroglyphics as far back as 4000-5000 years ago.  I presume there would be little disagreement here that these two knots must be among the oldest of the purposeful, standardized knots used by humans.   You simply cannot get more field-tested than this!

But why combine these two well-known old knots in a somewhat novel way that, at first, might seem a bit "belt-and-suspenders"?

  • Even pressure
The inner profile of the clove hitch is smooth.  Both turns bear on the bound object evenly throughout their contact.  The contact area is increased by having two turns.  When the reef knot is added, the ends are pulled up and away from the object.  There is some extra pressure exerted by the reef knot on the riding turn, but this is distributed onto the two underlying turns.  Evenness of pressure is important for the same reasons as the next item.

  • Controlled tightening
Overtightening of cable management bindings can cause conductor breakage, insulation damage, excessive chafing, and deformations between the conductive, dielectric, and shield parts of a cable, and no doubt a host of other issues.  It is one of the classic problems with ratcheting plastic cable ties (i.e. "zipties") that they only have quantized adjustment steps and cannot be easily loosened.  While zipties with a metal tooth insert do allow for smoother tightening, the possibility of this tiny metal part coming loose near electronics generally excludes their use.  That zipties cannot easily be loosened or adjusted during tightening makes them more prone to being left in an overtightened state.  Difficulty of adjustment might also be considered a possible strike against using the Constrictor Knot (and similar knots) for this application.

The clove hitch is not known as a particularly good binder alone, but that may be an advantage in this application.  If the clove is initially made too tight it is easily loosened and readjusted.  Once the proper snugness is achieved the addition of the first half-knot produces only a small and predictable amount of additional tightening.  One thing I did notice in my tests is that  if the first half-knot is made in the opposite orientation than shown in the standard, it tends to produce more tightening and also separates the underlying turns of the clove hitch.

  • Resilience to errors in tying
As mentioned above, I did some tests tying the knot incorrectly in different ways.  While these forms generally seemed inferior to the specified knot, they were not obviously destined to fail.    Using these two basic knots in a compound form seems to be a reasonable way to make errors of tying less detrimental to the resulting knot.



Image credit: David J. Fred/Wikimedia Commons (Original)
Above is a high resolution photo taken of these Spot Ties made in Gudebrod Nomex lacing tape.  These types of lacing tapes are often coated or impregnated with materials (e.g. synthetic rubbers) to increase their knot-holding properties.  I'm not sure what the tapes visible on the rover are made of, but I'd suspect the material was chosen for its behavior at extremely low temperatures and pressures as well as very good UV resistance.

The keen observer may note that some of the Spot Ties in the rover images show the ends perpendicular to the cable bundle and some parallel.  Based on general experience with reef and granny knots, one might be tempted to assume the parallel examples are improperly finished with granny knots.  Experimentation with Nomex lacing tape seems to show that it's more a matter of the knot preserving the orientation of the ends as the reef knot was tightened.   I found that when the Spot Tie is finished improperly in the granny form but with the ends kept perpendicular to the wire bundle they tend to stay that way.  While these experiments are hardly definitive, it doesn't seem to me that one can tell from orientation of the ends whether the knot was properly tied or not.

There is also the issue of the handedness of the first half-knot with respect the ends emerging from the Clove Hitch portion.   The relative orientation shown in the NASA spec does appear to be preferable to the alternative.



I won't go into much discussion about these stiches for the moment, but I believe the one on the left (the running clove hitches) appears on the extreme right edge of detail image "1" below.


And now for the pretty pictures...


Image Credit: NASA/JPL-Caltech(Original)
Multi-image panorama giving context of rover, deck, and its suroundings.  The rim of Gale Crater is visible in the distance.


Image Credit: NASA/JPL-Caltech(Original)
Annotated context image showing locations of following five detailed images.   Outlines do not quite align to following image borders due to panorama projection.



Image Credit: NASA/JPL-Caltech/Malin Space Science Systems(Original)
Examples of one of the flat stitching methods (shown above) appear on the extreme right edge of this image.


Image Credit: NASA/JPL-Caltech/Malin Space Science Systems(Original)


Image Credit: NASA/JPL-Caltech/Malin Space Science Systems(Original)


Image Credit: NASA/JPL-Caltech/Malin Space Science Systems(Original)


Image Credit: NASA/JPL-Caltech/Malin Space Science Systems(Original)



[Edited 2013-09-11 to move images back from AWS S3]
« Last Edit: September 11, 2013, 08:29:34 PM by dfred »

SS369

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Re: Knots on Mars! (and a few thoughts on NASA's knots)
« Reply #1 on: August 25, 2012, 03:14:58 AM »
Awesome ! Thank you very much dfred.

X1

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Re: Knots on Mars! (and a few thoughts on NASA's knots)
« Reply #2 on: August 25, 2012, 10:54:03 AM »
   It seems that one can learn how to travel to Mars without knowing much about hitches and - and vice versa... :)
       

knot4u

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Re: Knots on Mars! (and a few thoughts on NASA's knots)
« Reply #3 on: August 25, 2012, 11:31:50 PM »
Cool, thanks!

Dan_Lehman

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Re: Knots on Mars! (and a few thoughts on NASA's knots)
« Reply #4 on: August 26, 2012, 01:44:16 AM »
   It seems that one can learn how to travel to Mars without knowing much about hitches ... :)

Really?  How does it seem so!?

 ???
« Last Edit: August 29, 2012, 06:07:09 AM by Dan_Lehman »

dfred

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Re: Knots on Mars! (and a few thoughts on NASA's knots)
« Reply #5 on: August 26, 2012, 06:30:39 PM »
Quote
Above is a high-resolution photo taken of these Spot Ties made in Gudebrod Nomex lacing tape.
[...]

Indeed : for what is remarkable about what the image shows?!


Didn't intend it for anything other than illustration.  Even these newest images coming down from Mars are still not extraordinarily clear in terms of the knots.  If NASA did not have a published standard, it would likely be very difficult to deduce knots being used.  Since I had the image handy from the Wikipedia cable lacing article, it seemed useful to see the knots tied in similar flat material than as shown on the rover.

Quote
(It looks as though not too much more line would be consumed
in making a binding like commercial fishermen use for headropes
and assorted other things --line running from reversed ground-line
hitch
to next, spiral-wrapping the bound materials between.)

I'm not familiar with that exact knot/technique.   I presume is it akin to marline hitching with RGLHs instead of overhand knots?

Marline hitching, as well as a similar technique of running lock-stitches using figure-eight knots, is used extensively in cable lacing in general.  The figure-eight form is indeed specified in that NASA document.  (Example Wiki photo)  This form is actually quite secure, easy to tighten, and holds tension well while the next stitch is made.   I'd suspect the RGLH form might be even more secure.   Does it tighten-up easily and evenly without much fiddling?

My suspicion as to why they use individual, unconnected knots on the deck and exposed parts of the rover is due to concerns about differential thermal expansion. The rover includes a weather station and recently measured daily low and high air temps at the landing site of -2.2C (28F) / -74.9C (-103F).   Ground temperatures were measured to vary between 2.7C  (37 F)  / -90.9C (-131.8 F).    I don't know how the rover deck transfers heat in comparison, but there are no doubt huge temperature swings each day.  If one of the running lock-stitch style of laces were used, there might be complications with the differential expansion/contraction of long lengths of the lacing material running parallel to the cable bundles.  Just a guess on my part, though.

Much of the inside of the rover has active thermal controls.  It would be interesting know whether that means other lacing styles are available/preferred in that more benign environment.
« Last Edit: August 26, 2012, 06:31:35 PM by dfred »

Dan_Lehman

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Re: Knots on Mars! (and a few thoughts on NASA's knots)
« Reply #6 on: August 26, 2012, 07:30:36 PM »
Quote
Above is a high-resolution photo taken of these Spot Ties made in Gudebrod Nomex lacing tape.
[...]

Indeed : for what is remarkable about what the image shows?!


Didn't intend it for anything other than illustration.  Even these newest images
coming down from Mars are still not extraordinarily clear in terms of the knots.

answer :
 It is remarkable that the knotted/entangled part of the knot
occurs right at the gap between bound parts --i.e., at a point of
least material for clove/constrictor/... binding!  Yes, tying off with the
overhand crossing atop the clove hitch --whose crossing part serves
well to *brace* this half-knotting-- makes the binder independent
of the bound surfaces, but you need to get to that point somehow
without losing tightness of the base knot (whose engagement comes
at this remarkable place).  Hence the point about the nature of the
material helps to understand how this can be done --the compresssion
of the width of the small tape whose surface is (presumed to be)
frictive enables tying over the gap; it probably also makes drawing
the binding tight more difficult --the friction hindering transfer
of tension around the bundle.

Quote
Quote
(It looks as though not too much more line would be consumed
in making a binding like commercial fishermen use for headropes
and assorted other things --line running from reversed ground-line
hitch
to next, spiral-wrapping the bound materials between.)

I'm not familiar with that exact knot/technique.
I presume is it akin to marline hitching with RGLHs instead of overhand knots?

With your points taken about the benefits of individual/independent
at-point bindings, attached is an image of the (what I've taken to calling)
"reverse ground-line hitch --which image might be among some I've
posted previously (but I am not so good w/Search for such things).
nb: The wrapping/tying *flow* is Right-To-Left for both of these
images --a half-hitch first reversing flow, then the 2nd re-reverses
and locks the knot (a duet sometimes repeated, even more than once).

[8/27 edit to add...]  This finish would seem to be a preferable,
more sure one to use on many of the friction-gripping structures
shown by Ashley in #1732..1761 --esp. #1743/47/51/52/54.


--dl*
====

ps : sipping some keemun + barooti tea
« Last Edit: August 27, 2012, 08:38:06 PM by Dan_Lehman »

rusco7614

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Re: Knots on Mars! (and a few thoughts on NASA's knots)
« Reply #7 on: August 27, 2012, 01:03:49 PM »
Thanks dfred - an interesting read.

X1

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Re: Knots on Mars! (and a few thoughts on NASA's knots)
« Reply #8 on: August 28, 2012, 10:19:25 AM »
This finish would seem to be a preferable, more sure one to use on many of the friction-gripping structures shown by Ashley in #1732..1761 --esp. #1743/47/51/52/54

   Really ? Why is this so ? Where are the theoretical or experimental proofs, evidences, or even indications, about this claim ?
   What we have seen is only a manual about how-to, but what about the why-so part on which this manual should have been based on ? Where are the scientific references, the experiments, the theoretical reasoning behind this decision, to use those particular hitches, and not any others ?
   We wish to believe that such a technologically advanced organisation, as NASA, does everything it does the way it does only after a thorough examination of every other possible alternative, based on the most recent theoretical and experimental studies. Wishful thinking - that tends to ignore the fact that there are critical and sub-critical, or even non-critical, parts in every machine, and optimum and not optimum solutions in every technological problem. That there are good and bad solutions, decisions, tasks... and there are disasters as well as triumphs. When a hero like Armstrong dies of natural causes, we should also remember the heroes that have died at accidents because of other people s mistakes - the oxygen in the cabin, the O - ring, the loose tiles.  Heroes that died because somebody told somebody else to "Take your engineering hat off and put your management hat on" . In sub-critical or non-critical parts - as the binding and the attachment of the wires inside the vehicle - this strategy works most of the time, but in some critical parts it might well fail - and it has failed tragically time and again...
   So, until I see something that would really justify the use of the primordial two-half-hitches or two superimposed overhand knots solution to the wire binding and attaching problem, I will continue to see what I see : a so-so, quick and dirty way of dealing with a secondary non-critical problem - and a bureaucratic brochure that attempts to wrap the whole thing within some illustrated pages, using a superficially "scientific"-sounding language, but no scientific method at all. 

   
« Last Edit: August 28, 2012, 07:58:46 PM by X1 »

Sweeney

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Re: Knots on Mars! (and a few thoughts on NASA's knots)
« Reply #9 on: August 28, 2012, 11:59:05 AM »
o, until I see something that would really justify the use of the primordial two-half-hitches or two superimposed overhand knots solution to the wire binding and attaching problem, I will continue to see what I see : a so-so, quick and dirty way of dealing with a secondary non-critical problem - and a bureaucratic brochure that attempts to wrap the whole thing within some illustrated pages, using a superficially "scientific"-sounding language, but no scientific method at all.

Mmmm ...maybe I wouldn't buy a second hand space module from NASA after all! Seriously it's perhaps nice to know that NASA (like other large organisations esp government) have people writing manuals who may not have a clue what they're talking about but once it's in the manual it becomes received wisdom. Perhaps a Martian will see it and give us some scientific analysis (as much chance as NASA responding here I imagine! But maybe it's all secret squirrel?)

Barry

dfred

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Re: Knots on Mars! (and a few thoughts on NASA's knots)
« Reply #10 on: August 28, 2012, 06:13:57 PM »
[...]
Hence the point about the nature of the material
helps to understand how this can be done --the compresssion
of the width of the small tape whose surface is (presumed to be)
frictive enables tying over the gap; it probably also makes drawing
the binding tight more difficult --the friction hindering transfer
of tension around the bundle.

Ah, yes, I misinterpreted your initial comment.  Thanks for the clarification.

In addition to the mock-ups for the Wiki photos, I did the networking in a friend's new house and laced all the permanent cabling in the wiring closet with this tape.  Total overkill, I know, but it was fun/interesting for me and they were the kind of person who appreciates this kind of thing.  I found it was quite suitable for the task, as one might expect.  I mostly used the running figure-eight style, but did use these spot ties for affixing some of the bundles to tie-down points and found there was no problem with the clove hitch maintaining tension while finishing the tie.

BTW, I got a few spools of this tape at Boeing Surplus when I lived in Seattle.  Sadly they closed several years ago, but it was an amazing place to poke around.  Wish I'd bought more of it, as I suspect it is very expensive to buy new.

Quote
[...]
nb: The wrapping/tying *flow* is Right-To-Left for both of these
images --a half-hitch first reversing flow, then the 2nd re-reverses
and locks the knot (a duet sometimes repeated, even more than once).

I do like how these ties flow, and also from one to the next.  One minor concern I'd have about the spiral wrapping on wire bundles is that any torsion would tend to either loosen or tighten the binding against the bundle.  Don't know how likely a scenario that is for most cable lacing, though.

BTW, I really like that second photo -- with the white wraps on the cyan-colored rope -- a very pretty, well-composed shot.


(Tieguanyin oolong for me today... )

SS369

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Re: Knots on Mars! (and a few thoughts on NASA's knots)
« Reply #11 on: August 28, 2012, 08:20:11 PM »
I remember now the cable lacing from my own aircraft maintenance days. It seems that this knotting has been employed since before then (late 60's). If memory serves well I believe the cord/lace was waxed and that aided in the knot retention.

So I wonder if the Mars Rover has waxed tape? It looks quite shiny in the posted pictures.

SS

Dan_Lehman

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Re: Knots on Mars! (and a few thoughts on NASA's knots)
« Reply #12 on: August 29, 2012, 06:06:22 AM »
This finish would seem to be a preferable, more sure one to use on many of the friction-gripping structures shown by Ashley in #1732..1761 --esp. #1743/47/51/52/54

   Really ? Why is this so ? Where are the theoretical or experimental proofs,
evidences, or even indications, about this claim ?

It is so, because the 2nd half-hitch forms a binder
vice the simple half-hitch finish Ashley shows --i.p.,
one of the miller's knots (in the form of the ground-line h.).
(I think that I'm partially misled in at least some of those
images by the spaced helical wrapping, which is done
for clarity but not expected to exist in the tied knot;
but even then, one can work in the 2nd half-hitch.
Otherwise (space intended), it seems to beg for this finish.)


Quote
Where are the scientific references, the experiments, the theoretical reasoning
behind this decision, to use those particular hitches, and not any others ?
...
   So, until I see something that would really justify the use of the primordial
two-half-hitches or two superimposed overhand knots solution ... ,
I will continue to see what I see : a so-so, quick and dirty way of dealing with a
secondary non-critical problem --and a bureaucratic brochure that attempts to wrap
the whole thing within some illustrated pages, using a superficially "scientific"-sounding
language, but no scientific method at all.

Your brief, equally information-lacking criticism cited by me
above (post #4 / reply #2), is stronger than a mere question
for basis : it implies that you know better --and would have
solved this problem in some other way!

Here, you sound as though you won't be going out for a walk
any time soon unless Gauss & Reimann are reincarnated to
prove how to tie shoes validly in any possible geometry!

And yet, meanwhile, things are going far beyond a walk
in the park, into space (& back, sometimes)!


 ;)

Dan_Lehman

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Re: Knots on Mars! (and a few thoughts on NASA's knots)
« Reply #13 on: August 29, 2012, 06:28:42 AM »
Quote
There is also the issue of the handedness of the first half-knot
with respect the ends emerging from the Clove Hitch portion.

Indeed : this essentially makes a squaREef structure.
(And was considered to be the constrictor knot verbally
introduced by "Bowling" as "gunner's knot" --a Verrill mistake
brought into graphics.)

Quote
(the running clove hitches)

Note that the structure implies that the "running"
isn't of cloves but of an orientation of the overhand
binding a pass of the other line --which pair of lines begin
from a clove hitch and finish with a pseudo-cloveness
akin to what I described in another thread about finishing
west country whipping with a (pseudo-)constrictor knot
--i.e., of mimicking the single-strand knot with two strands.


--dl*
====

X1

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Re: Knots on Mars! (and a few thoughts on NASA's knots)
« Reply #14 on: August 29, 2012, 09:47:33 AM »
It is so, because the 2nd half-hitch forms a binder vice the simple half-hitch finish Ashley shows

   I was not talking, of course, about the common knowledge that, most of the time, two good things are better than one good thing !  :) I was talking about the evaluation of all Ashley s and non-Ashley s hitches, that is obviously missing. Unless there are classified knotting secrets, which would be revealed after a century or so - about the time I reckon you will publish your own notebooks  :).

Your brief, equally information-lacking criticism

   So, you admit that the manual is (scientific) information-lacking...That was my point, was nt it ?

it implies that you know better --and would have solved this problem in some other way!

   It states that NASA should know better, of that NASA should tell us about what it knows, about the theoretical or experimental evidence that support the selection of the particular hitches, and not of any other else.
   I am not an expert on knots - but if I were, I would have expected that NASA would have asked my opinion, or refer to my published work. Of course, if knotting solutions are classified, you would nt allowed to tell us that NASA has asked YOUR opinion, would you ?  :) And that is a reason you should publish your notebooks before the MANNED NASA trip to Mars !  :)

you sound as though you won't be going out for a walk any time soon unless Gauss & Riemann are reincarnated to prove how to tie shoes validly in any possible geometry!

And yet, meanwhile, things are going far beyond a walk in the park, into space (& back, sometimes)!

   If I were to walk on Mars, I would expect ( and feel much safer if that has been assured...)  that somebody had examined the shoes I will wear there - and had not put me in his grandfather ( 1915 ?? ) boots !  :) Because if you happen to be into the wrong shoes on Mars, you will not going to be reincarnated on Earth any time soon to publish your notebooks, believe me...

   I am not convinced by the quick and dirty, not-clever knotting "solution"  to this non-critical, secondary knotting problem, and I have not bought the (scientific) information-lacking manual or the glossy pictures. If a similarly quick and dirty, not-clever solution would have been chosen ( should I better say "picked out", without any theoretical or experimental examination ) for a critical, main problem of the mission ( like the oxygen in the cabin, the O-ring, or the lose tiles ), I would not be happy to be on board, because sometimes quick and dirty, not-clever solutions are /were responsible for things/people that are /were NOT going to be back anytime soon - and neither would be you, I suppose.

   There are two philosophies in life : The one says, pay the proper amount of attention to each part of life, according to the value it has in your life. ( A time-saving philosophy ). The other says, give as much attention as you can in every part of your life - because you can not know, in advance, which is, or will be someday proven to be, of the greater value - and because, perhaps, everything deserves to be dealt with our attention, because everything has a value that is related with the value if everything else. ( A soul-saving philosophy).
   We are talking about KNOTS here... in Earth ( or Mars, or everywhere else in the Universe where there might be some form of intelligent life...) 99.99 % of the people do LAUGH when we tell them that we are paying as much attention to knots, as we do. Do knots have a value ? Should we lose our valuable time exploring knots ? Will Ashley congratulate us, when he will come back from his walk ? I do not know. I pay attention to knots, because I like them. That was what Gauss and Riemann did, for the things they did like, and what my grandfather and father did, and what I hope my son will do, too.

   ( My humble advice to knot tyers is to try to learn about hitches by reading books, or tying their own - and not copying and pasting this "solution" NASA has happened to pick out, for unknown reasons.)
 

   
   
« Last Edit: August 29, 2012, 10:04:27 AM by X1 »