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

Attendees: Pat Osmer, Darren DePoy, Bruce Atwood, Paul Byard, Tom O'Brien, Jerry Mason, Jen Marshall, & Rick Pogge,

Upcoming PDR (Mar 12)

Darren reported that our PDR presentations have all been collected, edited, converted to PDF format and posted on a a webpage for the PDR. A draft schedule has been circulated that will be forwarded on to Tom Herbst to serve as a framework for the review. The week before the review Pat and Rick will coordinate the preparation of the final preparations wherein each person will respond to questions from the review committee.

Optics

The main part of this meeting was a closed session devoted to the optics bid packages. Public discussion of optics procurement and fabrication will not appear in these reports until after we have reached the stage of placing orders for the optics.

Paul has GSOLVER (back) up and running, and will set about modelling the existing gratings in the Richardson Labs catalog that look good for us. There are 3 potential gratings: Low-dispersion Red and Blue, and a second-order "high" dispersion red grating. We will get a report on the properties of these gratings and the GSOLVER efficiency analysis in a week or so.

Mechanical Design

Tom reported a variety of mechanical issues:

MOS Masks:

Tom discused the virtues of using graphite epoxy for the MOS masks, following what is being done for GMOS on Gemini. Since we need a curved mask, this looks like a very good option for us. GMOS is using a YAG laser to do the machining on flat 200-micron thick sheets of graphite epoxy. Tom has been in communication with James Stilburn at NRCC (Canada) about this, and he will ask them if it is possible to get sample slits to have Jen test in the lab like she is now doing for metal slits.

In the meantime, Tom has ordered raw materials for fabricate mask blanks using a mandrel of the MODS focal plane he has had made in the shop. We will continue to explore this option, but it looks very good for us.

On a related note, we received no replies from the Naranjan Thatte et al. to our questions about the LUCIFER laser machine idea.

Camera Design:

The camera design has been modified to incorporate ball joints. He has finished the corrector cell design, and plans to make that piece first.

Tom derived an alignment sensitivity matrix for the Red camera, and verified that his differential thread approach looks like the right way to go. The lateral sensitivity is 1.5 microns/degree of turn, which means <10-microns for 3-4 degrees. Since we need ~100 microns of tolerance in a 10-20mm range, we are in good shape. He has ordered a set of hardware to evaluate the lock-nut/jam-nut stiffness for this system.

The next MODS meeting will be Tuesday, February 27 at 3pm in the Astronomy Conference Room.

R. Pogge, 2001 February 22