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

Attendees: Darren DePoy, Paul Byard, Ray Gonzalez, Jerry Mason, Mark Derwent, Ralph Belville (notes by DDP)

This is the first week of Spring Quarter after spring break. Rick is observing at MDM, and Bruce and Dan are at Mt. Graham for Aluminization activities). We have had no team meetings since the MODS Progress Review on March 7.

Tom reported on the "initial fitting" of MODS components on the structure that has been going on the past 2 weeks. The fitting let them see how each component mounted on the structure, tested out the lifting fixtures, worked out the proper crane procedures, and otherwise gave us our first good idea of what MODS will look like with all of its subassemblies installed. The fitting involved the dark slide, calibration tower, red & blue grating turrets, the blue camera body, slit mask system, and the AGW stage.

Everything went just fine, the only exception was the blue grating turret which was a tricky fit, and will require a minor amount of machining of the structure.

The red camera truss assembly is nearing completion, and a fitting of the red camera will proceed later. The last mechanisms to fit, the dichroic beam selector and the collimator mounts, are still in progress.

The next round of work will involve those mechanism mounts that require drilling relative to the axis of the instrument. Tom, Mark, and Paul are working on designs for the fixturing and optical tests. The goal is to have all mechanisms oriented in the correct axes, and centered to within 1-2 millimeters. This will be done using a laser axis through the central beam of the instrument, and defining the orientations of the mechanisms by making their "faces" perpendicular to this axis.

MODS Optomechanical Systems

The dichroic beam selector is a 3-position rotary mechanism with a dichroic beam splitter, silvered folding flat, and empty position that define the "dual beam", "red-only", and "blue-only" configurations of MODS, respectively. Mark has a near-final design for the dichroic beam selector, and is doing the final load analysis. He should be sending out a request for quote for machining in a week or so.

The sheet-metal mirror covers are in for the collimators, cameras, and red folding flat (fixed flat mounted behind the mask system). We have indentified two good local sheet metal vendors who do good work at a good price. "Buy Ohio" has proven to be a benefit to the project and our local community.

With regards to MODS2 systems, we are fabricating as much as we can in parallel as we go along. All new orders will be for both systems now that the TSIP money is available.

MODS Optics

Paul has put out requests for quote on materials and fabrication costs for the low-dispersion double-pass prism concept. These would provide a wide-band, low-dispersion (few hundred) "survey" option for MODS.

MODS Software

Ray is making progress defining the mechanism control system for MODS, and starting to prototype various modules using a MicroLYNX controller and one of the collimator actuators as a test bed. We expect to have enough infrastructure built to start integrating it with actual mechanisms in early June. In the meantime, lab tests using some simple MicroLYNX-provided engineering tools have been proceeding that are giving us the essential info needed to design the mechanism control routines.

MODS Electrical

Dan has received samples of a custom cable designed to work with the motor controllers. The cable consists of 20AWG wires for motor power, 12 pairs of 24AWG cable for data, and 2 pairs of 20AWG, plus foil shield and drain. We got 1000 feet to start with, and are working on pinouts for the standard CPC connectors we'll use at either end.

[Note: AWG = American Wire Gauge, the standard way of stating wire sizes. Smaller number is larger diameter.]

MODS CCD Detectors

Bruce is assembling a specification for the formal MODS CCDS. We need to identify a series of prioritized options ranging from the minimum specs needed to accomplish MODS science performance all the way through to "gee it would be really cool if it could do X" options. The risks need to be evaluated for each item, and to do this, Bruce will work with Mike Lesser and Dick Bredthauer to establish reasonable metrics for assessing risks.

The dewar design and cooling options are still open questions and will be proceeding over the next few months. On the table for cooling are options for liquid cryogen (i.e., LN2) and Cryotiger refrigerators. Both have attractions, risks, and issues that will be assessed as part of this exercise.

Project Schedule

The schedule has undergone revision including new estimates from SOML for the delivery of MODS optical components. SOML has now introduced a roughly 2-month slip in the schedule. The software schedule has also been revised, and there are no significant changes in that schedule.

The other key feature of the new schedule is the better integration of MODS2 and MODS1 tasks. For example, there is only room for one MODS in the main shop at a time, though we are seeking some non-lab working space where we can do some mechanical work in parallel. Serialized tasks, like optics alignment, are now fully identified and factored in.

Mark Derwent is continuing his analysis of the schedule, but it looks right now like the slip in SOML's delivery date for the red corrector optics does not affect the MODS2 schedule much.