Re: Laser ranging to moon begs questions


John C. Polasek <jpolasek@xxxxxxxxxx> writes:
....
[ Markwardt: ]
Why not start with the Science magazine website? I simply went there
and typed "Dickey" into the search box at the top of the screen. Yes,
a price of $30 would have been annoying, but the cost for the Dickey
et al article is far less than $30!

I was not aware of Science magazine or its search feature, and I
looked at it, but even so I am not inclined to pay $10 just to view an
article which may in fact have even less information than the two I
have already read.

Where is your sense of proportion? I already said I was polishing up
the solution to the Dark Matter problem, and I merely posed the lunar
question as a bit of relief. And now you are trying to make me look
totally baffled with this LLR.

I am not "trying" to make you look like anything. You are doing that
for yourself. If you are not "inclined" to be informed, whose problem
is that?

....
But even if you weren't willing
to spend a few dollars, I would be astonished if no libraries in your
region carried Science magazine.
I am even ambivalent about extending my Popular Mechanics subscription
at the unheard of price of $15.97. I may, and then again, I may not.
My own journal article (google Polasek matrix) is available to me or
anyone for $22. Luckily I have the original journal.

I note your non-sequitur. Your willingness to pay for Popular
Mechanics has nothing to do with finding journals at a library.

1967 You have far overestimated my interest in the details of this process.
I simply asked a simple question, expecting a simple answer to how you
can determine fractional cm/s with a few pulses per minute and find
myself drawn into a 70 message harangue.
It is beginning to appear that you are not capable of answering a
simple question.

Actually, your claim is incorrect. As I noted above, I *did* answer
your original simple question with a simple answer, namely the
importance of filtering out noise photons by time, space and
wavelength.

Moralizing about the *importance* of filtering is not a sufficient
answer even for a liberal arts scientist.

I note you did not substantiate your claim. My original reply
discussed the factual issues.


Then *you* proceeded to make your ad hoc and
unsubstantiated calculations of the number of return photons. If you
are willing to make scientific claims, shouldn't you be willing to
substantiate those claims?

I note no response.


...
If you really care about the subject, why not get off of your petard
and find out some facts about the subject you are speculating upon?
Setting arbitrary boundaries about which journals you will or will not
look at is also rather silly. Scientific experiments and results are
published in scientific journals. If you don't look at scientific
journals, then you are pretty much relegated to uninformed observer
status.
I told you my interest in this topic is perfunctory at best and for
all your volubility, neither of you have come close to answering the
original query of this thread.

As noted above, that is not quite true. What actually happened is
that you changed the simple question by starting to ask about the
total efficiency of the system, which is a complicated question.

I note no response.



And finally, while the discussion has focussed on the low quality
McDonald Observatory results, in fact there are other lunar laser
ranging observatories which detect many more photons such as the OCA
(see Samain ref above), and the Apache Point observtory (APOLLO,
Murphy et al 2007). The results from these observatories definitely
do not "beg the question" as your originally post asserted.

CM


References

Murphy et al. 2007, "APOLLO: Apache Point...", PASP, submitted,
arXiv:0710.0890v1

Shelus Ries Williams Dickey, "A Summary of LLR Activity and Science
Results,"
http://geodaf.mt.asi.it/html_old/news/iwlr/Shelus_et_al_LLR.pdf
Thank you for furnishing this reference which however is devoid of
much technical information except that I glean that the OCA can catch
about 30 times the pulses the McDonald can, and that if the moon were
25% further away, ranging would be impossible, and that they consider
the signal loss proportional to 4th power of distance.

OK, sounds promising. Did you try the Murphy reference? (which has
an extensive discussion of the hardware for APOLLO) Did you try the
Samain reference? (which has an extensive discussion of systematic
errors) Did you try the Dickey reference? (which has a good general
discussion and references to other important papers)

I note no response.


[*] the more important question is whether return photons can be
distinguished from non-return photons.
[*]And that is done slam-dunk with time-gating, the only question
whether it can be done on a picosecond basis.

Again, you are missing the point. In an ideal world, there would be
no noise/background, and a *single* photon returned from a 200 ps
pulse would be enough to provide range information at the ~6 cm level.
Actually 12 cm. (Front in, rear out). And, um, Heisenberg's UP.
The challenge is not in measuring range photon return times to
picosecond accuracy, but in excluding the non-ranging photons.
I think you need quite a bit of both, unless I am missing some subtle
nuance.

Apparently you are, but you also appear unwilling to spend a little
effort to learn more about the real issues or substantiate your
claims. Good luck with your "polishing."

CM

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