Thursday, July 26, 2012

The Installation details

 You only begin to get an idea of the scale of ODI when you see the pieces being assembled.  Here are a few photos from the installation procedure.  ODI goes on the telescope in 6 pieces - plus all the connections and peripheral systems like power supplies and chillers.  The first part, a shim (1) (machinable if we have to adjust the position or tilt of the overall instrument - ugh) attached to the rotator, was already on when we started on Wednesday. 

The next part is the forward corrector (2).  Here you see Brent and Mark guiding it into the port, where its flange will seat against the shim.  This piece weighs about 300 pounds.  All the optics have covers on them (mostly nice metal plates with handles and hardware for attaching them, but a few are just cardboard disks).  The covers are only removed at the very last minute to avoid damage or dust getting on the surface of the optics.

The next piece to go on is the ISP (3), which holds filter arms and ADC prisms.  This is mechanically the most complex part of the instrument with many motors and the electronics and wiring that drive them, gears, and sensors to monitor the positions of everything.  The ISP has almost all the moving parts in the system.  Here Mark and Brent guide the ISP over to the front corrector, already on the telescope.  The ISP weighs a little over 1000 pounds.  All the lifting was done with the WIYN dome crane, with the addition of an attachment called a Hydra Set Precision Load Positioner.  This hangs between the crane hook and the item being lifted and allows very precise (a few thousandths of an inch) vertical adjustment.  The green strap seen in this photo connects the Hydra Set to the lifting fixture attached to the top of the ISP.

This photo shows Charles and Brent guiding the ISP against the flange of the forward corrector.  The front cover of the ISP, which includes the shutter, has been removed because the bolts to attach it to the forward corrector are only accessible this way.   You can see the hubs for the three sets of filter arms, and the rearmost filter arm in each group.  The filters are held in metal frames that attach to the ends of these arms.  The filter removal and installation process involves removing the outer covers external to each filter arm group (the "chevron-shaped" pieces just counter-clockwise from each hub), running an arm all the way out, and then unclipping or clipping on the filter holder frame.
Now the cover (4) has been attached to the ISP.  The shutter is the rectangular black piece behind the cardboard disk.  At this point we had to do some work on the internal wiring.  One of the modifications necessary during the final lab testing was a redesign and rebuild of some of the worm-gear sets that run the filter arms in order to encase them in grease.  This resulted in our having to change the route of some of the wiring in such a way that we couldn't get the cover housings over the motor-gear assemblies.  Shelby made some cable extenders so that we could route them a different way that allowed us to put the covers on.  Charles here is removing one of those covers so we can add the extenders and connect the cables.  You can also see the hanger above the instrument that guides the wires, cables and hoses between ODI and the telescope.

Also hanging on the telescope is the computer (5) that controls the ISP.  This was assembled and programmed by Shelby Gott, whose back is seen here, while Daniel demonstrates his lifting abilities.  The computer is being attached to a support frame that is behind it.

The last piece to be installed is the Dewar (6).  It weighs about 1200 pounds (if I remember correctly).  It has the focal plane, the vacuum and cooling systems, and the Stargrasp controllers (the two gold boxes on top and bottom).  The Dewar is held by a lifting fixture that keeps it from tilting as it meets the ISP.   The filter arm hubs fit through holes in the flange of the Dewar.  Here Charles, Mark, and Brent (on the far side) guide the Dewar up to the ISP.

In this last picture, Mark and Brent are tightening the bolts that hold the Dewar to the ISP. All the bolts that hold the major parts of the instrument together are tightened with a torque wrench so that they are held securely, but not overtightened.

After finishing up the installation, we ran the field rotator around a few times to make sure that everything would clear and the balance was OK.  No problems.  The entire installation sequence pictured above took about 4 hours.  Mark will spend the next four days completing all the connections.  He's done this a couple of times in the lab, but there will be a few differences on the telescope.  If all goes well, we will begin to turn things on around the middle of next week.


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