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 ! 
Actually, I don't agree with this in full, and had some time
of self-challenge on how adding a 2nd of something I was
finding deficient could do anything but put some trifling
delayin inevitable failure --that, okay, now the 2nd/last-done
H-Hmust loosen before the given one does, but then it
does !?
Analysis IMO shows that the 2nd
H-H imparts some tightening
and curvature into the first to increase its nip, and in some
cases there is also some friction added by parts now being
adjacent (there being 2 vs. 1).
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 .
///
So, you admit that the manual is (scientific) information-lacking...
That was my point, was nt it ?
As though one should expect any manual to contain such detailed
rationale!!! Still, that wasn't the form/diction of your remark,
but rather a presumption of inferiority --not the mere lack of
some *proof*. Where, btw, do you ever see this given for knots,
so that we might suggest a model for it ? --or do you continue
to wear slippers/loafers, to keep on the safe side?!
it implies that you know better --and would have solved this problem in some other way!
It states that NASA should know better, or 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.
Again, hardly to be expected in a manual of instruction,
and not quite the terms of your point --or in that "should
know better" there is implicit assumption that some "better"
exists, and that begs an answer from who asserts it, not NASA.
And that is a reason you should publish your notebooks before the MANNED NASA trip to Mars !
My notes are now primarily just images of structures.
And I've remarked to myself about my "QRS" so-far format
being nearly entirely graphical vs. verbal, and the loss of
information (tied in what cordage, loaded or what minimal
experience with ...) is bad --a loss. But I have some desire'
for the *purity*/cleaness/objectiveness of presenting just
an image ; let commentary come as it may beyond that ... .
I am not convinced by the quick and dirty, not-clever knotting "solution"
to this non-critical, secondary knotting problem,...
If indeed this is Q&D, and has made the rounds in many
instances w/o hint of problem, why would you devote any
research hours to proving its evident working, or to seek
an alternative? As you note, this binding doesn't have
anything like the importance of those O-rings (which were
functionally noted to be an issue, but overruled --without
consequence, ultimately, but for conscience?-- on other
grounds, tragically. But perhaps NASA has done some
vibration testing of such bindings, to assure themselves
of the working.
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.
And what will which books teach you about hitches?
(Will you find anything about the NASA hitches anywhere?)
--dl*
====
[8/27 edit : "could to" => "could DO" ]
