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

Attendees: Darren DePoy, Tom O'Brien, Paul Byard, Ray Gonzalez, Jerry Mason, Dan Papallardo, Mark Derwent, Rick Pogge

MODS Optics

Paul Byard reported on the condition of the blue field flattener lenses sent back to OSU for inspection. By way of background, these are fused silica field lenses that were fabricated by SOML, and do double duty as the dewar window for the blue channel CCD cameras. Paul inspected the lenses and found that one of them is better than the other, but neither is made to specification (apparently SOML does not have scratch/dig reference plates to use for measurement of that parameter). Steve Miller at SOML reported that they had examined the lenses in polarized light and he suggests that what we are seeing is relatively deep surface fracturing on at least one of the two pieces. The red field flatteners are only marginally acceptable (they have a few more scratches than our spec), but JML says they can be MgF₂ coated, so we are sending these back to JML for coating and should get them back in a few weeks.

In the mean time, we have requested a quote from JML for the fabrication of 2 new blue field flatteners with coatings. In a pinch, we might have the better of the two SOML-figured field flatteners coated to use as part of blue camera 1 test and integration. Paul will report more once he has more info back from JML.

MODS Gratings

Paul also reported on discussions with Richardson Gratings about higher resolution gratings for modes ("higher" means R=8000-10000). The bottom line in discussions with Richardson may be summarized as follows:

1. A large (e.g., 240x430mm) ruling for R=10000 is out of the question.
2. A mosaic is also not an option as they will not consider doing more than a 1x2 mosaic per substrate, and we would need at least a 2x2 mosaic on a single substrate.

MODS Mechanical Design

Mark Derwent reports that he and Bruce are making excellent progress on the dewar design, which is a two-part LN₂ reservoir (aka "tank"), and detector box architecture. Work on the initial tank design is about done, and they could have detailed drawings for a bid package in a few weeks. Mark will start on the design of the detector box next.

MODS Mechanism Controls

Dan is working on the detailed design of a single-axis motion control box to be used in the lab, and has a basic layout for a 4-axis version. The box will incorporate power, MicroLYNX motor controllers, connectors for the MODS instrument connector cable, and computer interface (single RS232 port for the 1-axis system, 4-port networked serial port server for the 4-axis system). These boxes will be portable for use as benchtop test setups in the lab for test and integration of single mechanism groups.

Ray has been making considerable progress on the software side of the motion control system. He has a test system capable of running multipe MicroLYNX controllers through a network serial port server, and written a manager program that centralizes control of the various modules. The system uses shared memory to provide for efficient interprocess communications and a common "status" block to monitor mechanism control traffic. One issue being worked out is a robust way to protect the communications lines from conflicting traffic, and a robust method of ensuring system synchronization when controlling about 30 axes of motion.

MODS Detectors

Bruce reviewed a basic noise model analysis for a 2-MODS system in "digital beam combination" mode (signals added after the fact). This leads to setting specifications for the eventual MODS detectors. He then outlined a novel scheme, based on something done with circular CCDs (originally developed as curvature sensor detectors) where there are multiple amplifiers per readout register. This lets you either (a) readout a single pixel multiple times and combine the results in quadrature for noise reduction, or (b) read out multiple pixels simultaneously to multiplex the readout and provide a substantial (factor of many) reduction in full-frame readout time. Bruce is generating a more detailed design document to be distributed to his partners in the MODS detector conceptual design (Dick Bredthauer and Mike Lesser).