Friday, July 11, 2014

140702 TimC: From the Workshop...#7

From the Workshop...#7 (from SBAU July newsletter):
by Tim C
    I believe we are at a point where we talk about polishing and testing. Before we do, I am going to take a brief aside and tell a good story - the story of the Hubble Space Telescope and what happened to it. I will not go into specifics of how the testing
was done. Instead, I'm going to tell you what happened and how a "shower" solved a giant problem. The Hubble telescope became a political football for a time as the huge cost was viewed as wasted money because the main mirror was flawed, and seemingly beyond correction. 
    The Hubble mirror was finished and figured on a ground floor room. Above this was a small, rather awkwardly situated room. This small upper room housed the testing equipment. This design made it possible to test the mirror in place, so there was no need to pick up the heavy mirror and put it on a testing rack. Instead, they only needed to open access to the test apparatus. The “Null Corrector" was an arrangement of mirrors and lenses held to each other with specific-length rods. The only problem was the "field caps" covering the ends of the rods. Reflections from these field caps introduced a 1.3 mm error into the optics. This error was overlooked due to pressures to finish the mirror. The damage was done. The outer edges of the mirror were over-corrected or too flat. 
    So, when the Hubble Space Telescope saw “first light” there was much consternation as to what happened. The views were terrible. How do you go about fixing something like this? Replace the main objective, or replace the corrector mirror, or use a series of corrective mirrors with the instruments on board? Any of these techniques should work but there was no way to get it done. Think of the spacesuits of the astronauts with their big bulky gloves. In principle there was no way to delicately replace the mirrors.
    In Europe a Strategy Panel met to address the different ways of fixing the problem. Jim Crocker, an engineer by training, thought if they could fix the cameras it would solve the problem. Maybe they could place corrective mirrors in front of the camera? But there were several instruments on board. One mirror would not fit all of the instruments’ needs. He went back to his room one night thinking hard on the subject and went to take a shower. The European shower system was unlike those found in America. A rod holds a showerhead in place. The showerhead can slide up or down to adjust to the height of the person in the shower.  During the day, the maids slid the showerhead all the way to the bottom of the rod. As Crocker slid the shower head up and pivoted it outward to be over his head, he had a vision of several different
“showerheads” swinging into position with their corrective mirrors in the light path between Hubble’s secondary and the science instruments. If they sacrificed one of the first generation instruments in place and plugged in this corrective mirror unit, it would fit the simple kind of maintenance the Hubble team had planned for decades. It would work. In fact, and as you may recall, it worked perfectly. Moral of this story: you just never know when or where a solution to a problem will present itself!
see also...

Wednesday, July 2, 2014

140701 TimC's dilemmas

140701 SBAU Telescope Workshop
Attendees: Angela, Paul, Tim, Jerry, Chris, TomT, Mike

> On Tue, Jul 1, 2014 at 10:40 PM, Tim C wrote:
>     Okay guys,   
bulge plus TDE insideR?
It happened again.  I put the mirror up on the stand tonight.  It tested out that it has a slight dome overall but it looks like I am also introducing a very small turned edge.  That's okay. 

major scratch...what caused it?
But afterward I decided to check my new flashlight on the mirror surface.  I found the mother of all scratches on the mirror.  This time I can feel it with my nail.  Wow, at first I was bummed out (for some time).  Now I'm just frustrated.  I have never had a mirror come I with so many problems.  I have gone backwards 3 times so far and I was at first thinking I would be unwilling to go back again.  If all you guys think it's okay, I'd like to continue polishing for a while.  Hey, what can it hurt.  I was trying to get this done so the donor could see the results.  Now, I'm kind of thinking I'd like to see the results.  Could be many reasons for tonight's debacle.  Without boring you all with the rundown, I'd like to see if a particle has lodged in my pitch.  That will make it easy. 
indent on pitch lap
Dump the pitch, go back to 320 and bring it on back one more time.  If this is the course I take,  I will definitely keep this sucker.  I'd deserve it.  It owes me.  (Only kidding).  It is a learning experience and as such I am delighted to take on this challenge.  I hope you all will join me to try to figure out what keeps going on.  It is a mystery right now.  Like I said earlier, this has never happened before.  Are there sub-surface bubbles that chip up onto the surface?  Am I dislodging grit from my workplace from under my fingernails?  Am I just not taking care to keep a "clean room" atmosphere around my workplace?  All good questions.  I am really sorry you guys for screwing this up over and over.  I am trying to be patient.  I hope you will be patient with me.
>     T
On 7/1/2014 10:52 PM, Dmitrii Z wrote:
> Tim, I am sorry to hear that! How frustrating! Hang in there, though. We must not let each other give up.

TT: see more photos/vids, full size, at Flickr link.
JerryW analyzing TimC iris adapter...let's see what happens if we take it apart!
peg holes for tool mirror holding on work board

Chris asking Jerry for star hopping help

Paul showing Starry Night Pro Plus

PaulW Seahorse nebula astrophotography