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

Attendees: Paul Martini, Jerry Mason, Tom O'Brien, Mark Derwent, Dan Pappalardo, Dave Brewer, Dave Steinbrecher, Brad Peterson, Ross Zhelem, Andy Gould, Jason Eastman & Rick Pogge.

MODS Optics

Big news is the safe delivery on Thursday, Feb 22, of the blue corrector lenses and final camera primary mirror. The lenses were very well packaged and protected. They are still coated with the protective film from shipping, and won't be unwrapped until later this week when they are mounted. Each lens has 2 dings near the edge, the best we could manage from the earlier ding damage.

Ross and Tom have started right in on mounting of the first lens. Tom has worked out a temporary bonding method, using epoxy and a cork interlayer that will allow easy cutting later to unmount the lens from its flexures when it is time to ship them for coating (AR coating uses a high-temperature process and cannot have epoxy on the parts). One test has already been done with the aluminum dummy lens and a second will be done tomorrow before proceeding to the real thing.

The blue camera primary is mounted, and the camera is ready to receive the corrector lens. The primary has been successfully pre-aligned using the laser rough alignment system. Current estimate is that the two tilts are within 1-2 milliradians, and the two translations are within 1-2 mm. The corrector will be mounted and pre-aligned using the same system to roughly similar tolerances. This puts them both within range of proper alignment with the small CCD camera. The 230mm collimator has been setup in the student lab and is ready to go. The small CCD camera provides well-sampled images of a pinhole target on-axis and near the 4 corners of the field of view, the latter of which are crucial for measuring focal plane tilt off-axis, which is the most challenging part of the alignment. Alignment tests should begin early next week and proceed until done, with Jason Eastman assisting during the last phases when the alignment progresses from judging image intensity to making detailed measurements of the PSF using the CCD images.

Ross reported that SOML succeeded on the third attempt to create the return sphere for optical testing of the spherical side of the red corrector lenses. The surface of the return sphere is now ~100nm p-v, and so is in principle finished and ready to begin being used for testing the spherical side. There have been some problems with the current SOML interferometer and they have borrowed an interferometer for these tests. The delivery schedule continues to slip later into 2007, and at this point delivery of the red correctors has become one of the primary drivers of the MODS1 assembly and testing schedule.

There was further discussion of the MODS dichroic. CSIRO personnel are getting back from travel (it is high-summer vacation time south of the Equator), and will be sending us test samples from a second coating run, including on- and off-axis samples to meausure uniformity over this large part.

MODS Enclosure

Mark Derwent reports that the parts have arrived for the second phase of the MODS enclosure design work - this time we will be assembling the 1/3-scale model of the top hexagon using what we believe are the final choice of joint parts (the phase 1 model evaluated a variety of different joints). The main goal of this phase is to prove the hexagon is rigid and light-tight, and to refine the side-panel design. About 2 weeks of work will be required for this phase, beginning this week.

Tom is reviewing the performance analysis of the enclosure design, in particularly modeling stiffness and wind survivability. The wind speed specification is 80km/h as the operational limit and 120 km/h survivability limit. These are conservative specs. The stiffness tests are to make sure that as the enclosure flexes it does not come into contact with the interior MODS structure (recall that the enclosure is tied to the telescope at the 6 rotator mounting points and effectively floats over the MODS internal structure).

MODS Electronics

Dan Papallardo has completed rework on the 4 shutter mechanisms, having uncovered an error in the I/O wiring during initial testing. All 4 shutters were fixed and tested with both the 1-axis and 16-axis boxes with the new shutter software and passed all tests.

Dan has worked out the best way to get the extra I/O channels for the MicroLYNX controllers to the DB25 connector, and has finalized that wiring diagram (recall that each 16-axis instrument electronics cabinet has 4 of the MicroLYNX controllers equipped with I/O extender boards to increase the number of I/O channels). At this point, there are no remaining impediments to completing the wiring of all 16 channels within IE cabinet #1 and getting all channels running with full communications. The balance of this work will take about 2 weeks including testing. At that stage, the first IE cabinet will be 85% done except for the outer covers and thermal management system. Since this is not required for immediate mechanism testing, this can be deferred while we get going in making the remaining 4 IE cabinets (2 each for each MODS plus a full spare). Orders are being generated for the ITEM kits. There was some discussion of getting 2 cabinets to the West Campus Birdhouse facility where the enclosures will be assembled initially for fitting.

One of the issues that emerged from last week's review visit by LBTO personnel was the cabling for MODS that will be provided from the Direct Gregorian Rotator cable wrap. Bruce and Rick are tasked with getting a final request for the contents of that cabling to LBTPO next week. However, the services they will provide will be minimal, so we will have to provide our own on-instrument power and ethernet distribution, as well as our own glycol plumbing. Dan and Bruce are tasked with determining the requirements of the services distribution box since it will be shared by both the IE cabinets and the CCD detector head electronics boxes.