Serious knot history buffs may know that a "Spot Tie"-like knot, with opposite Clove hitch end orientation and topped only with a single overhand 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!

I find it quite interesting that yet another hitch knot (not a Clove nor a Gunner's) topped with a single overhand knot was recommended for cable lacing in both a 1905 Popular Mechanics article entitled "Cable Sewing Knots", and also two 1907 Telephony magazine articles: (Part 1, Feb 1907) and (Part 2, Mar 1907). The frequent use of the Double Strap Hitch (ABOK #1695) and also an unusual usage of the reef knot as a stopper knot for a tensioned doubled cord are both shown in the Telephony articles. Some of these specific patterns can still be seen in the NASA specification, as well those of the Australian Civil Aviation Safety Authority. Telephone companies also still use knots related to those used by linemen more than 100 years before, such as seen in this 2007 Qwest Corporation document, pp. 5-19 - 5-24.

All of these references, both old and new, share patterns of knot usage that are not often seen in general knotting literature. This seems to provide evidence that cable lacing knots have evolved somewhat independently, in isolation from other knot tying traditions.

So, that's some of the history, but what about the knots on Curiosity? Why might NASA have standardized on this particular knot, the Spot Tie, to use so extensively instead of the many others which might serve the purpose? The following reasons are merely my own musings:

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 from knot experts that these two 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, without consideration, might seem a bit "belt-and-suspenders". Why not simply use a single more aggressive binding knot?

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.

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. Zipties cannot easily be loosened or adjusted after tightening and they may not conform to the cable bundle as well as lacing cord or tape. 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 hitch is initially made too tight it is easily loosened and readjusted. Once the proper snugness is achieved the addition of the first overhand produces only a small and predictable amount of additional tightening. One thing I did notice in my tests is that if the first Overhand 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.

As discussed below, I performed 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.

Here is a high resolution photo taken of these Spot Ties made in Nomex lacing tape. These types of aerospace 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. Outgassing is also probably a concern, especially inside the rover and/or near the scientific payload.