September 2019 RRRT Update

The RRRT has been offline since early August. This blog entry is a description of what we have been doing over the past many weeks, and where we currently stand.

First, the backstory:
Back in September 2017, we noticed that NSU's Apogee Alta U-42 camera was not cooling properly. Whereas it had been getting down to -20 C on a regular basis, it was struggling to get down to -14 C. A few weeks later, we noticed spots appearing on the edge of the chip, which looked very much like ice/condensation. The camera was 9 years old at time, and clearly had a significant problem.

We removed the U-42 camera from service and replaced it with an SGIB STX-16803 camera borrowed from the UVA Astronomy Department. We sent the Apogee camera back to the factory for servicing. Apogee (now Andor) did a chamber service and returned the camera to us in the spring of 2018.

In the winter of 2017-2018, we decided to manufacture a new tailpiece to connect the camera to the telescope. At the time, we were mounting the camera and filter wheel to the 2-inch eyepiece holder (visual back). This presented some problems. First, there was no set rotation of the camera. Every time it was removed and put back on, it would have a slightly different rotation. Second, the camera and filter wheel were only held in place by set screws. We had our mechanical engineer design a very simple tube that bolts to the telescope, with a plate that bolts to the filter wheel which in turn would bolt to the Apogee Alta U-42 camera. This setup would fix the rotation of the camera, and ensure that everything was securely bolted together.

In the fall of 2018, the Astronomy Department received some funding from the Commonwealth's Equipment Trust Fund, and we purchased a 10 place Finger Lakes Instrumentation filter wheel with a full Sloan filter set, and two narrow band filters (H-alpha and O III). Thanks to a generous donation from Ben Loyola, were were also able to purchase a luminance filter. We designed the new tailpiece so that the new filter wheel could bolt on, with the camera bolted to the filter wheel.

In the spring of 2019, the new tailpiece was complete and was anodized (there was a long delay, in part because of the retirement of Charles Lam, our machinist). We decided not to change the camera in the middle of a semester because classes were using the telescope. Instead, we decided we would wait until the summer to swap back to the NSU Apogee Alta U-42, the new filter wheel and new filter set, and the new tailpiece. This would also require some rewiring at the back end of the telescope, and would offer us the chance to remove some unused wires threading through the tube and mount.

The summer was busier than expected, but by early August we were ready for the swap. In the meantime, during the summer after a thunderstorm, we noted that the Robofocus focuser was no longer working. In early August we took the telescope offline, removed the SBIG camera, filter wheel, and visual back from the telescope. We sent the Robofocus electronics box back to the manufacturer. In the end, they had to replace all the electronics in the box. Jimmy designed and fabricated two plates to mount on the back of the telescope to hold the power supplies for the camera and filter wheel and hold the USB hub. He routed a new USB cable through the mount and removed some unused serial and power cables. We reinstalled the Robofocus electronics, installed the new tailpiece, attached the filter wheel and camera. It took a few days for some clear skies before we could focus the telescope. When the clear skies arrived, we were able to focus the telescope but, unfortunately, the NSU Apogee Alta U-42 camera would not cool to even -10 C (about 35 degrees below ambient). In the past, it had cooled to -20 C (about 45 degrees below ambient). Thus, the cooling problem persists even after the chamber servicing.

In looking at the documentation provided by Andor, it appears that they could not get the camera to cool below about -10 C either. We have since contacted Andor about the camera. Since the camera was recently in for servicing, and since the camera is now over 10 years old, they believe there is nothing else that can be done. We cannot switch back to the SBIG camera as it is needed for the ASTR 5110 course this semester. We also considered switching to an Apogee U9000 that we would borrow from the Astronomy Department, but that camera would need to be returned in the spring. Rather than continue to swap cameras every semester, we have decided to put the U-42 on the telescope and see how it goes for this semester. We will set the cooling target at -5 C.

Thus, the current configuration of the telescope is:
Camera: NSU Apogee Alta U-42
Array size: 2048x2048 with 13.5 micron pixels
Pixel size on sky: 0.57 arcseconds per pixel
Field of view: 19.5x19.5 arcminutes
Filter wheel: Finger Lakes Instruments 10-position filter wheel
Filters: Luminance, Sloan u', g', r', i', Johnson/Cousins B, V, R, H-alpha, O III

We hope to get this running by early next week and will try to keep this configuration static for the 2019-2020 academic year.

The Apogee Alta U-42 is clearly at the end of its life, and we cannot rely on it much longer. The SBIG STX-16803 and Apogee U9000 cameras are general Astronomy Department cameras and cannot be mounted permanently to the telescope. Thus, in the long term, we need to find a replacement camera.