largest telescope mirror gets moved

SteveDallas · 11-08-2003, 07:43 AM

Boy, I'd really hate to have a fender bender with this one!!

This is an 8.4 meter mirror for use in the Large Binocular Telescope under construction at Emerald Peak in Arizona. The accompanying article from Sky & Telescope explains that, as you'd expect from the name, there will be a second mirror of equal size coming along in a few months.

xoxoxoBruce · 11-08-2003, 02:33 PM

I didn't see any mention of what the mirror is made of?

SteveDallas · 11-08-2003, 04:21 PM

What else? Glass!

xoxoxoBruce · 11-08-2003, 07:53 PM

Actually, unlike lenses the mirrors can be made of a number of different materials. The last telescope I put together had two mirrors (24" & 12") of ground Beryllium. The big bugaboo is the coefficient of thermal expansion causes most materials to distort the image with temperture changes. Of course all materials move some with temperture changes even concrete.

Elspode · 11-08-2003, 11:15 PM

What kind of telescope uses both a 12" and 24" mirror (I mean besides a damn large amateur scope)?

xoxoxoBruce · 11-09-2003, 06:54 AM

In the 60's we were flying this 24" reflecting scope at about 120,000 feet on a helium balloon to track the moon and venus for the Gumint. I'll have to dig out the pictures.

SteveDallas · 11-09-2003, 08:46 AM

So what kind of optical design was it? I've only ever seen or read about scopes with 2 mirrors where the secondary is much smaller than the primary. (Well, except for Schiefspieglers.... the mirrors are the same size there.)

xoxoxoBruce · 11-09-2003, 09:34 AM

The 24" reflected back to the 12" which reflected back to the camera that was mounted in a hole in the center of the 24".
The camera was a Nikon 35mm that had been much modified and stepping motorized. The mirrors were gold plated because the camera used infrared film and as with all first surface mirrors the surface had to be protected.
The carpenter was nailing up wooden crates to ship all the pieces to New Mexico for flight. He finished one crate and went to throw the hammer up on top of the 24" mirror crate when he realized the top was off the crate. He couldn't stop the throw but managed to deflect it so that it barely missed the mirror crate. Whew! As I recall the 24" was 100k 1964 dollars.

SteveDallas · 11-09-2003, 05:48 PM

So why did the secondary mirror have to be so big? I'm sure I'm missing something important, but with the average reflecting telescope used by amateur astronomers (whether Newtonian or catadioptric), minimization of the secondary mirror size is considered important to minimize loss of contrast.

Elspode · 11-09-2003, 06:56 PM

Yeah, that's the biggest secondary on a cat (or any) design I've ever heard of.

xoxoxoBruce · 11-09-2003, 08:42 PM

OK, '64/'65 I worked as a machinest at Tufts University for the head of the Electrical Engineering Dept, Dr. Howell. Doc was the Chairman of some national balloon research council that handed out government money. One of his favorite tricks was to award say $10 million to an MIT or Cal Tech for a project, then turn around and do the exact same project in parallel for $500k. While the "major" project would have all the bells and whistles like a chase helicopter, we had Gus (the foreman) in a rental car.
This particular package would fly on a helium balloon out of Alamogordo NM. During the day the sun would heat the balloon and it would rise and drift easterly then at night it would sink a few thousand feet and drift westerly. They kept it in the same area for as long as 30 days. If it got too far away they couldn't signal it to drop the package. One flight it caught the jet stream and came down 24 hrs later in Spain.
This picture shows the bare bones framework with the 24" mirror installed (covered with brown paper) and the tripod for mounting the 12" mirror above it.
aside-The guy in the grey shirt was a halftrack driver in the 1st Armored Div. and scheduled for discharge on Dec 20th 1941, just in time for Christmas. Dec 8th they said no dice and he served another 4 years.

xoxoxoBruce · 11-09-2003, 09:08 PM

The mirrors and camera sat on a stepping motorized gimbal ring and platform that I built, shown on the left. The picture on the right shows one of the 2 "saddlebag" boxes that carried the silver batteries and electronics.
The top of the rack attached to a nylon strap which in turn was attached to the bottom of an open parachute. From the top of the 'chute was another nylon strap to a piece of aluminum that was shaped like a Christmas tree. The "tree" plugged into a rather complicated "latch box" and was held in place by "dogs" with explosive bolts that could be fired from the ground to release the package. The "latch box" was tethered to the balloon by another nylon strap.
On the 13th flight Gus the foreman figured why let the difficult to make "latch box" fly away with the balloon and recover the easy to make "tree", so he reversed the setup. The nylon straps between the package/parachute and the parachute/"latch box" plus the nylon parachute cords were stretched out about 30%. When the explosive bolts were fired, the 29 lb "latch box" on the end of these stretched straps shot down through the parachute and wrapped around the package at 113,000 feet. Can you say freefall.

xoxoxoBruce · 11-09-2003, 09:22 PM

Another project they did at Tufts (before I worked there) was sized and shaped like a bomb so it could be fitted into a bomb rack on a plane. When the plane dropped it into the eye of a hurricane, a parachute slowed the "bomb" while an onboard balloon inflated. Then a Sears Craftsman tape measure with an electric motor attached uncoiled to form an antennae for the signal transmitter. They tracked the signal as the hurricane moved across the ocean thus proving for the first time that hurricanes have an eye that moves with it. A couple years later satellites verified it.

zippyt · 11-10-2003, 05:06 PM

29 lb "latch box" x 113,000 feet / terminal velosity = A BIG ASS HOLE IN THE GROUND !!!!

xoxoxoBruce · 11-10-2003, 08:24 PM

They said there was styrofoam insulation from the "saddlebag" boxes, for a quarter mile radius. 29 lbs plus seven hundred or so for the package plus the weight of the chute.

11-08-2003, 07:43 AM	#1
SteveDallas Your Bartender Join Date: Jan 2002 Location: Philly Burbs, PA Posts: 7,651	largest telescope mirror gets moved Boy, I'd really hate to have a fender bender with this one!! This is an 8.4 meter mirror for use in the Large Binocular Telescope under construction at Emerald Peak in Arizona. The accompanying article from Sky & Telescope explains that, as you'd expect from the name, there will be a second mirror of equal size coming along in a few months.

11-08-2003, 02:33 PM	#2
xoxoxoBruce The future is unwritten Join Date: Oct 2002 Posts: 71,105	I didn't see any mention of what the mirror is made of? __________________ The descent of man ~ Nixon, Friedman, Reagan, Trump.

11-08-2003, 07:53 PM	#4
xoxoxoBruce The future is unwritten Join Date: Oct 2002 Posts: 71,105	Actually, unlike lenses the mirrors can be made of a number of different materials. The last telescope I put together had two mirrors (24" & 12") of ground Beryllium. The big bugaboo is the coefficient of thermal expansion causes most materials to distort the image with temperture changes. Of course all materials move some with temperture changes even concrete. __________________ The descent of man ~ Nixon, Friedman, Reagan, Trump.

11-08-2003, 11:15 PM	#5
Elspode When Do I Get Virtual Unreality? Join Date: Dec 2002 Location: Raytown, Missouri Posts: 12,719	What kind of telescope uses both a 12" and 24" mirror (I mean besides a damn large amateur scope)? __________________ "To those of you who are wearing ties, I think my dad would appreciate it if you took them off." - Robert Moog

11-09-2003, 06:54 AM	#6
xoxoxoBruce The future is unwritten Join Date: Oct 2002 Posts: 71,105	In the 60's we were flying this 24" reflecting scope at about 120,000 feet on a helium balloon to track the moon and venus for the Gumint. I'll have to dig out the pictures. __________________ The descent of man ~ Nixon, Friedman, Reagan, Trump. Last edited by xoxoxoBruce; 11-09-2003 at 07:09 AM.

11-08-2003, 04:21 PM	#3
SteveDallas Your Bartender Join Date: Jan 2002 Location: Philly Burbs, PA Posts: 7,651	What else? Glass!

11-09-2003, 08:46 AM	#7
SteveDallas Your Bartender Join Date: Jan 2002 Location: Philly Burbs, PA Posts: 7,651	So what kind of optical design was it? I've only ever seen or read about scopes with 2 mirrors where the secondary is much smaller than the primary. (Well, except for Schiefspieglers.... the mirrors are the same size there.) Last edited by SteveDallas; 11-09-2003 at 08:49 AM.

11-09-2003, 09:34 AM	#8
xoxoxoBruce The future is unwritten Join Date: Oct 2002 Posts: 71,105	The 24" reflected back to the 12" which reflected back to the camera that was mounted in a hole in the center of the 24". The camera was a Nikon 35mm that had been much modified and stepping motorized. The mirrors were gold plated because the camera used infrared film and as with all first surface mirrors the surface had to be protected. The carpenter was nailing up wooden crates to ship all the pieces to New Mexico for flight. He finished one crate and went to throw the hammer up on top of the 24" mirror crate when he realized the top was off the crate. He couldn't stop the throw but managed to deflect it so that it barely missed the mirror crate. Whew! As I recall the 24" was 100k 1964 dollars. __________________ The descent of man ~ Nixon, Friedman, Reagan, Trump.

11-09-2003, 05:48 PM	#9
SteveDallas Your Bartender Join Date: Jan 2002 Location: Philly Burbs, PA Posts: 7,651	So why did the secondary mirror have to be so big? I'm sure I'm missing something important, but with the average reflecting telescope used by amateur astronomers (whether Newtonian or catadioptric), minimization of the secondary mirror size is considered important to minimize loss of contrast.

11-09-2003, 06:56 PM	#10
Elspode When Do I Get Virtual Unreality? Join Date: Dec 2002 Location: Raytown, Missouri Posts: 12,719	Yeah, that's the biggest secondary on a cat (or any) design I've ever heard of. __________________ "To those of you who are wearing ties, I think my dad would appreciate it if you took them off." - Robert Moog

11-09-2003, 08:42 PM	#11
xoxoxoBruce The future is unwritten Join Date: Oct 2002 Posts: 71,105	OK, '64/'65 I worked as a machinest at Tufts University for the head of the Electrical Engineering Dept, Dr. Howell. Doc was the Chairman of some national balloon research council that handed out government money. One of his favorite tricks was to award say $10 million to an MIT or Cal Tech for a project, then turn around and do the exact same project in parallel for $500k. While the "major" project would have all the bells and whistles like a chase helicopter, we had Gus (the foreman) in a rental car. This particular package would fly on a helium balloon out of Alamogordo NM. During the day the sun would heat the balloon and it would rise and drift easterly then at night it would sink a few thousand feet and drift westerly. They kept it in the same area for as long as 30 days. If it got too far away they couldn't signal it to drop the package. One flight it caught the jet stream and came down 24 hrs later in Spain. This picture shows the bare bones framework with the 24" mirror installed (covered with brown paper) and the tripod for mounting the 12" mirror above it. aside-The guy in the grey shirt was a halftrack driver in the 1st Armored Div. and scheduled for discharge on Dec 20th 1941, just in time for Christmas. Dec 8th they said no dice and he served another 4 years. __________________ The descent of man ~ Nixon, Friedman, Reagan, Trump. Last edited by xoxoxoBruce; 04-07-2007 at 06:06 PM.

11-09-2003, 09:08 PM	#12
xoxoxoBruce The future is unwritten Join Date: Oct 2002 Posts: 71,105	The mirrors and camera sat on a stepping motorized gimbal ring and platform that I built, shown on the left. The picture on the right shows one of the 2 "saddlebag" boxes that carried the silver batteries and electronics. The top of the rack attached to a nylon strap which in turn was attached to the bottom of an open parachute. From the top of the 'chute was another nylon strap to a piece of aluminum that was shaped like a Christmas tree. The "tree" plugged into a rather complicated "latch box" and was held in place by "dogs" with explosive bolts that could be fired from the ground to release the package. The "latch box" was tethered to the balloon by another nylon strap. On the 13th flight Gus the foreman figured why let the difficult to make "latch box" fly away with the balloon and recover the easy to make "tree", so he reversed the setup. The nylon straps between the package/parachute and the parachute/"latch box" plus the nylon parachute cords were stretched out about 30%. When the explosive bolts were fired, the 29 lb "latch box" on the end of these stretched straps shot down through the parachute and wrapped around the package at 113,000 feet. Can you say freefall. __________________ The descent of man ~ Nixon, Friedman, Reagan, Trump. Last edited by xoxoxoBruce; 04-07-2007 at 06:06 PM.

11-09-2003, 09:22 PM	#13
xoxoxoBruce The future is unwritten Join Date: Oct 2002 Posts: 71,105	Another project they did at Tufts (before I worked there) was sized and shaped like a bomb so it could be fitted into a bomb rack on a plane. When the plane dropped it into the eye of a hurricane, a parachute slowed the "bomb" while an onboard balloon inflated. Then a Sears Craftsman tape measure with an electric motor attached uncoiled to form an antennae for the signal transmitter. They tracked the signal as the hurricane moved across the ocean thus proving for the first time that hurricanes have an eye that moves with it. A couple years later satellites verified it. __________________ The descent of man ~ Nixon, Friedman, Reagan, Trump.

11-10-2003, 05:06 PM	#14
zippyt LONG LIVE KING ZIPPY! per Feetz Join Date: Mar 2003 Location: Arkansas Posts: 7,661	29 lb "latch box" x 113,000 feet / terminal velosity = A BIG ASS HOLE IN THE GROUND !!!! __________________ "Success is getting what you want. Happiness is wanting what you get. " Brother Dave Gardner

11-10-2003, 08:24 PM	#15
xoxoxoBruce The future is unwritten Join Date: Oct 2002 Posts: 71,105	They said there was styrofoam insulation from the "saddlebag" boxes, for a quarter mile radius. 29 lbs plus seven hundred or so for the package plus the weight of the chute. __________________ The descent of man ~ Nixon, Friedman, Reagan, Trump.

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