The Ohio State University College of Mathematical & Physical Sciences Department of Astronomy

Attendees: Darren DePoy, Tom O'Brien, Bruce Atwood, Dan Papallardo, Paul Martini, Jen Marshall, Jason Eastman, Andy Krygier, Ray Gonzalez, & Rick Pogge, with Mark Trueblood and Todd Boroson joining from Tucson via video.

Welcome to Jason Eastman, a new OSU graduate student fresh from BU who has joined the group, and Paul Martini, new Assistant Professor at OSU.

MODS Mechanical Systems

Not many meetings, but we were too busy working...

Tom gave a long report on the progress on MODS assembly, testing, and integration. Much of the work is progressing towards a full-dress test of the Image-Motion Compensation System (IMCS) including the full optical path and tilting the instrument in elevation. The highlights of the progress to date in this regard are:

• Mounted hardpoints into two camera primary mirrors

• Silvered the mechanical-sample camera primary for use with the IMCS tests.

• Mounted hardpoints in 1 collimator mirror, and silvered that mirror for the IMCS tests.

• Andy Krygier has designed the elevation drive for MODS, which can rotate from +15 degrees (above the horizon) to -75 degrees (ground-looking). The current upper limit for downlooking is set by the location of the crane during these tests, it should be able to go fully nadir-pointing (elevation -90 degrees). We successfully lifted MODS from its normal mounting position to the nominal CG mounts without problems. It's a big job, but it goes smoothly.

• Assembled 13 collimator drives mechanisms (3 per collimator times 4 + 1 spare), with 3 wired up with motors for the IMCS tests.

• The first camera focus mechanism has been assembled with drives. We will use the first camera without the corrector lens for the IMCS tests (it doesn't matter in this case).

• Built a quad cell detector mounting that mimics where it will be in the final CCD detector "box". One question to be addressed in the testing is how far behind the CCD focal plane works best for the IMCS quad cell.

• Mark is assembling the blue grating-select turret, equipping it with one fixed (imaging flat) and one tiltable position (also a flat, no gratings will be abused in the IMCS tests).

• Jason is mounting the IR/Optical laser dichroic beam splitters (90/60 IR/Vis splitting cubes) in the focal-plane beam launcher. The Optical laser channel is proving to be indispensible for this operation, and will likely prove its worth in the full testing.

• The storage space on west campus for MODS2 has been cleaned out, the floor painted, and an A-frame crane has been ordered. Indian Creek has finished the upper frame, and Tom/Mark are going out on Monday for a final alignment check before the last assembly. We can expect the MODS2 structure in early October. We're all ready for it except for erecting the crane and buying some tools for out there.

• Dewar fabrication packages are complete and we have sent out two RFQs: one for 4 completely assembled packages, and one for 5 "kits" to assemble ourselves. We have 3 good bids in hand so far, and Ralph is busy ordering custom parts (bellows and such) for the dewars.

Slit Masks

Tom has been working with our Rochester electroforming vendor on developing prototype mask materials. The first pieces, made of pure nickel, are in hand, and we'll be getting full pieces covered front/back in copper black/gold foil, as well as some copper/copper and gold/gold samples. Small witness samples of copper black are impressive: the copper black is so black it makes your eyes hurt. So far they've encountered some tool release problems in the first steps, but progress is good. From the point of view of laser machining, this is about the easiest material to machine you can imagine. It looks very promising so far.

Jason Eastman is starting to look into laser machine options, leading up to recommendations for purchase in the coming quarter.

MODS CCDS

Bruce has heard nothing recently from either Steward ITL or E2V regarding MODS post-firstlight detectors, and has been tasked with pinging both groups for info.

MODS Optics

Darren reports that he was in Tucson, but did not get a chance to meet with Steve Miller at SOML, though they did say that tests of the corrector were in progress. Darren will be going back to Tucson in about a week and half, and try to visit then to assess progress on the remaining big optics (3 camera primaries and 4 corrector lenses).

Paul Byard reports that we have taken delivery of the new set of Field Flattener lenses from JML, complete with coatings.

We have started to receive bids on some of the remaining optics. We 3 good bids from vendors for the double-pass prisms which cover a range in prices from $65K to $120K for the set of 4. We also have bids from two vendors for coatings for the red/blue dichroic beam splitter. We will discuss these offline and place orders soon.

Paul has also been working with Richardson Grating Lab (Newport) on designs for a "high-res" R=8000 red grating. The one extant ruling in our large size that delivers this resolution must be used on 2nd order and is not optimal. Instead we are exploring getting a new ruling made. The initial design has some good properties but needs to be explored and refined further, including looking into the possibility that this design might serve as a high-res blue grating when used in 3rd order. The price for a new ruling plus replicas looks about what we expected and is within reach of our budget if we go that way.

In setting up the camera primary mirror and collimator for mounting, we found that the pieces were very dirty on the insides - lots of dried, adhered powdered glass inside the mirrors that took a significant amount of time to clean (many hours) compared to what would be required when the stuff was still damp (an hour). We will talk with SOML about cleaning the parts before shipping them to us.

MODS Software

Ray visited LBTPO in August and met with the software group there and at LBT proper.

The motor control library is nearly finished, and Ray is moving on to the first main application for the IMCS testing. The WAGO units for quad-cell data I/O is working great, and he is working with Tom to get the specs for data logging for the tests. The lab engineering interface is working great and will be used increasingly in the testing and integration of motors with mechanisms. Dan also reported that he's working on the 4-axis control box for lab testing, and should ahve it done in a few weeks (parts are still coming in from vendors). This will be needed for the IMCS testing.

Serial communications with motors through the WAGO, however, is not working so great. Ray was hoping this would be an alternative to using the commercial networked serial port servers (e.g., the Comtrol DeviceMaster RTS units we've been using in the lab). There are lots of issues that greatly complicate the interface when we use the WAGOs as serial port "servers", and we will go back to working with the Comtrol units.

Other Lab Testing and Evaluation

Never ones to let new graduate students off easily, new student Jason Eastman hit the ground running and started out working with Tom characterizing the IR laser system and bypass gratings for the IMCS. The dichroic beams splitter (a 90/60 IR/Optical split) works great: the visible-light laser is a real benefit for alignment. He's been busy mapping out the spot size with focus position, and characterizing the intensity vs. order distribution for the high-order bypass grating. So far the bypass grating is delivering fairly uniform illumination in the various orders, but more work is needed to get more consistent results with his test setup and better quantify this initial impression.

One of the things Jason has looked at is how repeatable the alignment of the IR laser system is with removal and re-installation of the fiber feed. He find about 5mm of motion at the collimator (3500mm away), or about 1-2 arcminutes of angle shift. This projects to about 1mm at the quad cell, which is acceptable, but we might want to look at options for eliminating this, like using a glued fiber adapter at the launch head that won't move between disconnections of the IR laser. In practice, the IR laser once installed will rarely be removed, but we should keep this in mind as testing proceeds with the IMCS.