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

Attendees: Dan Pappalardo, Jason Eastman, Mark Derwent, Ross Zhelem, Ray Gonzalez, Tom O'Brien, Bruce Atwood, & Rick Pogge.

Optics

Ross reported on SOML progress on the red corrector lens. SOML has provided us with an analysis of Coordinate Measuring Machine (CMM) profilometry of the aspheric side of the parent. Because the CMM cannot cover the entire 800mm diameter of the parent, measurements are made in 7 runs, clocking the parent in azimuth between runs. A set of 4 reference balls whose absolute positions are known to +/-2um are measured during each run, and used to transform the data from each run and stitch them together onto a common coordinate system that covers the parent.

Features in the raw data that are readily apparent are a deep 200mm diameter depression in the parent where a tooling gouge occurred early in the figuring process. This region has been filled with epoxy for the loose-abrasive grinding stage, but it still appears as a depressed region on the parent. The position of this feature eliminates this region of the parent as a candidate position from which to cut a final lens, but there are enough other candidate regions to not be concerned.

There are a number features appear to be residual data-processing artifacts from the stitching process. After extensive discussion we decided that we want to examine the data ourselves to try to understand them. We have the raw CMM data (roughly 3300 data points), and Ross has been tasked with re-analyzing the data. We will discuss his results next week, and from there decide how to proceed in collaboration with SOML to generate the hit map for the next iteration of figuring.

In other news, we have received dichroic coating test samples from CSIRO for the second coating run. One sample is from the center of the part, the other from about 150mm off-axis. CSIRO also sent us measurements of the coatings made at the design 35-degree angle (something new, the last measures were made at normal incidence). The data look very good. Jerry Mason has been tasked with measuring the transmission and reflection curves of the new samples with our lab monochrometer for next week.

MODS Electronics

Dan reports that he got the WAGO serial I/O software working, and feels it will work very well for us. It will also be a good tool for documentation purposes, since it produces an output of the fieldbus node configuration in a convenient electronic form. The first Instrument Electronics Box (IEB) is now about ready to turn over to Ray Gonzalez for use with qualifing mechanisms in the lab for installation on MODS.

Dan is still working on Revision 2 of the motor board for the IEBs. An issue that has arisen is that the relays used to reset the power of individual MicroLYNX controllers have been frying in about 4 power cycles. The failure mode is for the contacts to fuse on closure, leaving the MicroLYNX powered on. After some discussion, the most likely culprit is in-rush current on the controllers on power up. Dan has installed two more robust relay units for qualification: a heavier-duty DIN-mounted relay designed for Telecomm applications, and an automotive relay. Lifecycle testing is under way, but the Telecomm relay already failed after a few cycles, while the automotive relay is going fine. Dan is trying another DIN-mounted relay, and he and Ray will be testing them through many hundreds of power cycles this week. In the meantime, Dan will include the option of mounting the relay on the Rev2 motor board (rather than on the DIN rail), and will contact IMS (the vendor who makes the MicroLYNX controller) to find out what they know about the problem.

MODS Detector Systems

Bruce reported on cold testing of the black CCD dewar. On the most recent cool-down cycle after fixing leaks from the first run, the exponential cooling time constant is now 6h. The LN2 boil-off rate of 5cu-ft/hr, which translates into 5l/day, meaning a projected dewar hold time of 8/5 of a day (1.6 days) for our 8l reservoir. Bruce fixed a bunch of leaks, and the vacuum vessel pressure is now about one-tenth of what it was before, down to a few microTorr. Another iteration and it should be a few tenths of a microTorr, as good as our best dewars.