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[ATM] Is the Celestron 20" R-C telescope a Serrurier truss?
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<div align="left"><font face="Arial"><span style="font-size:10pt">Hi Stuart, </span></font></div>
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<div align="left"><font face="Arial"><span style="font-size:10pt">Vladimir thinks so too. I tried to
send him some JPG's of the
Celestron but both attampts failed. At his suggestion, I've turned
on the Rich Text feature to see if that helps some. If it does, you
both will see some images. Hopefully this won't cause any
problems at the ATM list. Please let me know how the images
arrive.</span></font></div>
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<div align="left"><font face="Arial"><span style="font-size:10pt">Thanks, both of you for the answer
and for the links to more in
depth explanations. It not only answers the question but further
validates my prior arguments to club members for:</span></font></div>
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<div align="left"><font face="Arial"><span style="font-size:10pt">a: NOT using cardboard sonotubes (!!)
for telescopes and</span></font></div>
<div align="left"><font face="Arial"><span style="font-size:10pt">b: using low cost composites even
in simple tube-type OTA's.</span></font></div>
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<div align="left"><font face="Arial"><span style="font-size:10pt">The vastly superior ratios of tensile
strength to weight that
Carbon Fiber provides suggests that the additonal use of a
Serrurier Truss in a modest sized telescope may be overkill.</span></font></div>
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<div align="left"><font face="Arial"><span style="font-size:10pt">The Celestron I saw has a conical
mirror which already gives it a
mass and support structure advantage over conventional
primaries. Carbon fiber trusses are exceptionally strong.</span></font></div>
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<div align="left"><font face="Arial"><span style="font-size:10pt">Without knowing more about the load
paths, it's hard to say.but I
can't help but suspect that part of their motivation may have
been to emulate the appearance of the big boys. Kind of like a
young kid who knowns absolutely nothing about "Down force",
puts a reverse cambered wing on the rear deck of his 60 hp
Datsun and swears to the whole world that the car now handles
better and is faster!</span></font></div>
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<div align="left"><font face="Arial"><span style="font-size:10pt">On 4 May 2004 at 14:17, Stuart Hutchins
wrote:</span></font></div>
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<div align="left"><font face="Arial"><span style="font-size:10pt">Art,</span></font></div>
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<div align="left"><font face="Arial"><span style="font-size:10pt">Serrurier truss? Linear deflection
at the cage equals linear</span></font></div>
<div align="left"><font face="Arial"><span style="font-size:10pt">deflection of the mirror. Pointing
angle then does not change as
the structure sags.
http://astro.umsystem.edu/atm/ARCHIVES/JUL95/0114.html</span></font></div>
<div align="left"><font face="Arial"><span style="font-size:10pt">http://astro.umsystem.edu/atm/ARCHIVES/SEP03/msg00804.html</span></font></div>
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<div align="left"><font face="Arial"><span style="font-size:10pt">Stuart</span></font></div>
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<div align="left"><font face="Arial"><span style="font-size:10pt">----- Original Message ----- </span></font></div>
<div align="left"><font face="Arial"><span style="font-size:10pt">From: <artbianconi@blast.net></span></font></div>
<div align="left"><font face="Arial"><span style="font-size:10pt">To: <Atm@atmlist.net></span></font></div>
<div align="left"><font face="Arial"><span style="font-size:10pt">Sent: Tuesday, May 04, 2004 7:06 AM</span></font></div>
<div align="left"><font face="Arial"><span style="font-size:10pt">Subject: [ATM] Celestron 20"
R-C telescope</span></font></div>
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<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> Why Two Truss
Sections?</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">></span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> Of all the telescopes
at the recent NEAF show, the one that was most</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> memorable for
me was the 18" prototype of Celestrons 20" R-C style</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> telescope. It's
not the conical mirror or size so much that</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> intrigues me
as was their choice to make the OTA out of two seperate</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> truss systems.</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">></span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> Most every open
truss telescope I've seen utilizes one set of tubes</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> to secure the
two mirror assemblies. For some reason, Celestron has</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> a seperate, short
lower cage for the primary and a seperate upper</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> cage that is
about 2-1/2 times longer than the primary one. Then</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> joined them together.</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">></span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> While two cages
break down the truss tubes into something more</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> compact and thus
more transportable, that does not explain it for</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> me. Two sets
of truss tubes of the same length would be shorter and</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> easier to move
about than the tubes resulting from the cage ratio</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> chosen.</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">></span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> I can see no
manufacturing advantage either. In fact the design</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> requires two
additional machined rings of considerable size and</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> twice as many
tube attach points. It's also heavier because of the</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> added components
and fasteners.</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">></span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> With so many
additional fasteners and components, ease of assembly</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> seems hardly
likely although I suspect that machines with this</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> degree of sophistication
do not get packed up and moved very often.</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">></span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> Superior mount
rigidity could explain it but there are simpler ways</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> of accomplishing
that.</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">></span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> Could they be
trying to place a mounting point closer to the CG?</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">></span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> Can any one tell
me what might have been the reasoning?</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">></span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> Thanks</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">></span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> Art Bianconi</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">></span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> _______________________________________________</span></font></div>
<div align="left"><font face="Arial" color="#7f0000"><span style="font-size:10pt">> ATM mailing list
http://www.atmlist.net/</span></font></div>
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