Date: Sun, 30 Apr 2006 11:26:57 GMT From: observer@apo.nmsu.edu Subject: 2.5m obslog 20060429 (MJD 53855) APACHE POINT OBSERVATORY SDSS 2.5M OBSERVING LOG Saturday April 29, 2006 (MJD 53855) ---=== OBSERVING TEAM ===--- John Barentine Viktor Malanushenko Olena Malanushenko (swing shift help) French Leger (super 2AM phone support) ---=== OBSERVING PLAN ===--- Science! ---=== OBSERVING SUMMARY ===--- Finished 1 plate tonight (2491) and got signal on two others (2140 and 1729). Also imaged SEGUE stripe 1260 N from +105 0.15 pix) COLLIMATE: Predict blue camera ring movement of 5.4 degrees for spectro-2 COLLIMATE: Mean offset = 0.07 pix COLLIMATE: Camera r1 appears to be IN-FOCUS (|mean| < 0.15 pix) COLLIMATE: Predict (red) piston movement of -625 steps for spectro-1 COLLIMATE: Mean offset = 0.06 pix COLLIMATE: Camera r2 appears to be IN-FOCUS (|mean| < 0.15 pix) COLLIMATE: Predict (red) piston movement of -548 steps for spectro-2 We'll call it good and watch SoS returns on b2 just in case it decides to go out of spec on us during the night, but odds are it won't get that cold. (Turns out we were fine...) Bias Percentiles ---------------- Filename 02% 05% 10% 50% 90% 95% 98% ------------------- ------ ------ ------ ------ ------ ------ ------ sdR-b1-00038945.fit -5.7 -4.6 -2.6 2.0 6.8 8.6 10.0 sdR-b1-00038945.fit -5.7 -4.6 -2.6 2.0 6.8 8.6 10.0 sdR-b2-00038945.fit -8.2 -6.4 -4.4 1.0 7.1 8.3 10.7 sdR-b2-00038945.fit -8.2 -6.4 -4.4 1.0 7.1 8.3 10.7 sdR-r1-00038945.fit -7.0 -5.3 -3.8 1.7 6.7 8.2 10.4 sdR-r1-00038945.fit -7.0 -5.3 -3.8 1.7 6.7 8.2 10.4 sdR-r2-00038945.fit -8.0 -6.6 -4.9 0.8 6.7 8.1 10.2 sdR-r2-00038945.fit -8.0 -6.6 -4.9 0.8 6.7 8.1 10.2 The instChange That Almost Didn't Happen ---------------------------------------- Around 07:00Z, after decising that further imaging was a vain effort at best, we headed down to the telescope to switch back to spectroscopy. Viktor decided not to issue the inst change from the control room but rather to track the telescope to (121,90,0) from the laptop at the telescope. I prepared the lindy cart with Cart 6 and got the turtle ready to put the corrector back on the telescope. The telescope reached zenith and the proper azimuth and I went downstairs to switch the tbar latch from telescope to doghouse, thinking that the scope had come to a full and complete stop after putting its seatback up and returning its tray table to the full and upright position. I came back up from downstairs and went round the south side of the telescope, engaging the altitude pin as I went by. At about the same instant, Viktor opened the door to the doghouse. What neither of us noticed was that the rotator was still about twenty degrees out from a rotation of zero degrees. The altitude brake engaged, as it well should have. Thus we found ourselves in a rather curious situation. The doghouse door was up, but the rotator was positioned such that the red camera cold head and assorted attachments from sp2 prevented the door from closing. The clearance was a matter of milimeters, or a couple of degrees of rotation. And now, with the doghouse door open, the altitude brake refused to release. But with the spectrograph camera head in the way, we couldn't lower the door to get the brake to release. We checked everything else we could think of that would restrict altitude motion: stop buttons, the locking pin in the imager cart, disengaged the telescope altitude pin. But it was clear what the problem was, and that was the inability to close the doghouse door. My instinct was to find a way around the restriction of the door being open, preventing the altitude brake from releasing. We tried looking for a kind of limit switch I expected would sense the open/closed state of the doghouse, but without results (there is a strange pushbutton-type switch on the south side of the doghouse, when the scope is parked at stow, that is connected to nothing but an aluminum block... I never noticed it before. What's that all about?) That didn't work, so I thought ot try disabling the interlocks I expected to relate to this situation. I went downstairs and did indeed disable them, but neglected to put in the key that actually causes the bypasses to activate. Needless to say, that accomplished nothing. So we did the next best thing, and that was to get French out of bed in the middle of the night. (Let me use this brief aside to send a shout-out to French, who by the way is *THE MAN*. We would have been stuck stuck STUCK without him tonight.) French walked us through all of the possible/likely reasons for what was happening and ultimately decided to have us move the rotator by hand, such that the doghouse door would clear the spectrograph camera head in the way. We turned off the rotator amplifier and found the rotator easier to move by hand than I expected. With the camera head out of the way, there was plenty of clearance for the doghouse door, and we closed it. Turned the rotator amplifier back on. The altitude pin was already out, so we tried getting back up on our collective horse by issuing an 'axis init' in TCC. That was all fine and well except that the altitude brake would not release. We commanded the rotator back to 0 degrees and verified with the tape mark on the front of the scope that we didn't cause too terrible a slip when we forced the rotator by hand. Yet the al brake would still not release. So then we entered a troubleshooting chain for that problem. Again, we considered all of the factors that would render the altitude axis incapable of moving. No stop buttons in, doghouse door closed, alt pin disengaged, wind baffle powered up, etc. We were nearly stumped when French asked me to look at the "root causes" window in the MCP Interlocks display. That window said something about "sad_mount1" and "sad_mount2", which to French meant the tbar latch was in a bad or wrong state. Since the imager was still on the telescope, we went downstairs and switched the handle back to "telescope", then came upstairs and tried releasing the alt brake again. This time, it worked. We then proceeded with the rest of the instChange as normal, returning the tbar handle to "doghouse" for the protection of the imager. After putting on the corrector and Cart 6, I sent Viktor back to the control room thinking I was just going to do a test slew and then hand the scope over to him. But I had run the counterweights up too far when we put the cartridge on the telescope, and after moving about 20 degrees down in altitude from the zenith, we had an overcurrent on the alt motors because of the out-of-balance condition and the brake came back on. There was also a slip of the altitude axis at this time. I cleared the slip but could not get the brake to release again, so I did the only thing I could think to do, which was to run the counterweights down to their proper values while the scope was not at zenith. While far from ideal cirumstances, it worked. It produced errors too large to correct on the alt axis when we went on to the field of Cart 6, but we forced fiducials and were back in business. Bottom line: Not enough communication between the observers doing the instrument change to make clear who was doing what at what time. We'll try to avoid this in the future. Bad news: We lost almost an hour and forty-five minutes chasing down these somewhat illusory ghosts. Good news: The seeing was no good during this time anyway, at least according to DIMM. Ah, well. It could have been worse.... somehow.