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

Attendees: Bruce Atwood, Paul Byard, Ross Zhelem, Phil Covington, Paul Martini, Jen Marshall, Jerry Mason, Jason Eastman, Tom O'Brien, Mark Derwent, Dan Pappalardo, Darren DePoy, Ray Gonzalez, & Rick Pogge.

Darren began by noting that the LBT Board will be meeting in Columbus on October 16 and 17 this fall. Richard Green and Mark Wagner et al. want to have a brief MODS Progress Review on the 17th, and we should also have as much of MODS assembled to show the Board on the 16th. More later as details become clearer.

MODS Mechanical Subsystem Assembly and Testing

Tom reported on progress in the assembly and testing activities:

Camera Primary Focus

All four Camera Primary Mirror focussing assemblies are completely assembled, wired, and tested. These mechanisms proved very challenging, as the friction was more difficult to control than originally thought, and it was tough to mean the motion specs for the focus (the mirror must both translate and tilt to maintain alignment of the off-axis mirror). In the end, all of the mechanisms meet or exceed our specifications, and are working great. One has passed endurance testing, and two (2) were cold tested (-20C) with no problems.

AGW Camera Stages

The XY stages for both AGW units have been wired and re-assembled (the mirror focus mechanism still uses the lab wiring, and the AGW filter wheel has not yet been integrated). Ray has been exercising them in the lab, and they will be scheduled for cold testing later this month.

Collimator Tip/Tilt/Focus (TTF) Actuators

All 13 TTF actuators (3/collmator times 4 collimators + 1 spare) have bene reworked, primarily to address a problem with the installation of the sensors. The sensors can now be more easily removed for service. All are wired and ready for installation and testing.

Blue Camera 1

Work is proceeding on integrating a complete blue camera #1, except for the corretor lenses. This work includes the following tasks:

• Wiring the shutter and testing low-level shutter software
• Mounting and wiring the 8-position camera filter wheel
• Mounting the detector dewar (w/o detector at this point)
• Designing, fabricating, and mounting the light-tight camera shrouds

This is a lot of work, and will consume most of the month. The other cameras should go quickly.

The next big task will be integration of a complete AGW unit. We have all of the hardware, optics, and most of the software. We will use the AGW unit to align the MODS optical train (see the 2005 Feb 1 Report). This means the entire AGW system, including the AG camera readout electronics, must be fully operational early.

A benefit of getting the AGW unit online early is that a concept for commissioning the f/15 rigid secondary is to ship the MODS2 upper structure (without the collimator arms) to LBT with a fully-operational AGW unit (AG camera and off-axis WFS camera). Of course, this means there also has to be a working direct Gregorian rotator at the same time.

Dave Steinbrecher is working on the final parts for the grating tilt mechanisms following the rework on those units, and should finish their production for both MODS with spares in the next month.

MODS CCD

Mark Derwent reported that the detector box design has been finished except for the mechanical details needed for the 3x8K e2v detectors. Fabrication has already begun, all work is being done in-house, and will occupy Dave Brewer for most of the summer.

Bruce reported on measurements of the temperature distribution in the STA 4Kx4K CCD detector package. The tests are being done with a package without the detector. The main heat loads on the package are ambient thermal radiation coming in through the window and thermal radiation from the window itself.

The first concept tested was to glue a 6mm-thick block of silicon to the gold package (see the 2006 Apr 25 Report) as a heat spreader. This turns out to not be such a good idea after all. The glue bonds the Silicon block to the gold just fine, but on cooling it fractures the silicon, leaving a roughly 2mm-thick layer of broken silicon stuck to the glue (which still holds on real tight). The temperature gradient center-to-corner is about 10C, a bit big.

Bruce is trying a different concept using a fine knit metal mesh used for making Electromagnetic Interference (EMI) gaskets. The mesh is just mechanically pressed (not glued) to the package, making a large number of micro contact points. This cut the temperature gradient down by about a factor of 2. Bruce is working further on developing this concept, but he notes that the knit mesh is still somewhat difficult to procure.

The 4K test dewar (currently slated for field deployment at MDM) has been assembled and has been through multiple thermal cucles. There are still a few trick to be performed to get the hold time up to specs, but progress is good. Bruce pressure tested the window through 10 cycles and the window is still in one piece. It is clear that a critical step is taking care on installation of the window, since it is a bit tricky to not introduce uneven stresses.

Detector electronics development continues apace. The new clock-bias PC boards are expected from the vendor this week. The post-amplifier boards work OK so far. The noise performance is adequate for the 4K CCDs, but some details remain to be worked out to meet the specs for the e2v devices.

Progress on the new PCI-X sequencer card continues. We have all the parts and necessary licenses from Altera for their Stratix-II GX FPGA (FPGA = Field-Programmable Gate Array). It turns out that Altera now makes an assembled Stratix-II demo card that has nearly all of the capabilities we want (except for the amount of static memory), and which would greatly shorten our development time. Bruce and Dan are looking into purchasing one.

MODS Corrector Lenses

Ross reported on progress on the MODS correctors based on the most recent telecon with SOML on Thursday, July 6. Last week was spent measuring the wedge on the blue corrector, and working with the company that provided the software for stitching together the optical tests (recall that their optical test setup only covers about 80% of the diameter of the work piece in a single shot).

The next task is to identify the apertures to be used to cut out the off-axis lenses from the parent, as the optical test can cover these in full. One factor in chosing the aperture is the locations of craters on the spherical side. SOML has provided some possible choices of apertures that Ross is reviewing to minimize their impact on the lenses.

It is clear from the optical data thus obtained far that the blue corrector aspheric side will require at least one more MRF run at QED to achieve the desired surface figure.

Tasks for next week include re-assembly of the step for the final optical test of the data, and creation of the surface map to be used for the MRF run instructions.

MODS Optical Coatings

Ross reported on further progress exploring the optical coating options for MODS.

For the dichroic, we received two more vendor bids, and have decided to iterate once more with one of the vendors on the final dichroic design before letting the contract. As is our practice, we do not discuss specifics of vendor bids in the public webpages during the procurement process.

Coatings for the blue mirrors (Camera Primary and Collimator) were discussed previously at the June 6th meeting. Since then we have learned that one of the proposed "enhanced Aluminum" coatings is a hard protective layer that the vendor claims they have experience successfully removing with a few-day chemical process. We have begun to iterate with this vendor, including how to package the parts for shipping and handling, and will report further when we have a specific contract.

MODS Software

Ray reported on continued progress on the MODS Instrument Control System software. He has written a series of utility routines for setting up shared memory access among the various subsystems and will be distributing that for other programmers to use.

The AGW control system is about done, and he has been working in the lab with the first AGW system to get all the kinks out. The AGW filter wheel control is the only big remaining piece, but that has to await integration of the AGW FW mechanism before he can begin testing.

The main MicroLynx motor control code is basically finished and being documented.

The overall ISL Manager is working very well, and now handles dropped nodes gracefully. Ray thinks he has a robust solution worked out to get the system resynched automatically after one or more nodes are dropped. This is a big step towards integration of the complete instrument control system. The error logger is working, and the error code library is coming together nicely. Overall, the continued integration of the Instrument Control System is proceeding well, and the parts are working well together, validating his basic design.

We are going ahead and purchasing a CentOS server built to the current LBT specifications, to be used for the MODS ICS development in the lab. Now is the time to start using their hardware.

MODS Electronics

Dan reports that Tom and Ed have been working together on wiring up the instrument mechanisms. The last group completed was the camera primary mirror focus mechanism. This puts us about 1/3 of the way through the roughly 60 mechanisms in MODS.

The design iteration on the Instrument Electronics Box (IEB) for MODS has being going well in collaboration with Tom. The most recent iteration is a design that splits the IEB into 2 16-channel boxes that works well with the mechanical envelope of the instrument. Dan is working on the design of a fan-out board for the motor-control boxes, and will have a PCB design soon.

The current outstanding action item is the big order of MicroLynx-7 motor controllers. We are currently planning on ordering 80 controllers. The current mechanism count is 27 per MODS, 54 total for 2 operational MODS instruments, leaving 26 spares. Given this, maybe ordering 81 is the right number, as it provides us with a full set of spares for one whole MODS.