From: stephanie snedden
Subject: Re: 2.5m obslog 20090621 (MJD 55004)
Date: Mon, 22 Jun 2009 14:50:59 -0600
Thanks for the sleuthing, Dan. Let's assume the moth goo hypothesis is
correct, and it will be a one-off problem.
Steph
On Jun 22, 2009, at 11:17 AM, Dan Long wrote:
>>                       APACHE POINT OBSERVATORY SDSS 2.5M
>>
>>                                 OBSERVING LOG
>>                              Sunday June 21, 2009
>>
>>                                  (MJD 55004)
>>
>> ---=== OBSERVING TEAM ===---
>>
>> Steph Snedden
>> Dan Oravetz
>>
>> ---=== OBSERVING PLAN ===---
>>
>> SEGUE2 Science!
>>
>> ---=== OBSERVING SUMMARY ===---
>>
>> Added signal to 3459, 3141, and 3395.
>>
>> We lost our field part way through an exposure of cart. 1, 3459,
>> and we're not
>> sure why.
>>
>
>   I went through the TCC, and murmur logs, the guider frames during
> the time, as well as TPM data on the encoders.  The logs helped
> establish a time line, but didn't offer any explanation of the
> apparent telescope shift.  From the guider images it was apparent
> that the telescope rapidly moved on the order of 10 arcseconds while
> taking frame 1314.  The star images in the larger guide fibers were
> doubled indicating a jump rather than a drift.  The flux in the
> stars was about 20% of the previous frame, so it looks like the jump
> happened about 4 seconds into the 20 second exposure.
>
>   From the logs, frame 1314 was started at 08:47:54Z, so this would
> put the jump at 08:47:58 give or take a second.  The jump was large
> enough that guiding could not recover.  The guider stopped making
> corrections after 1314 (although there are no error messages in the
> murmur log saying it couldn't find stars, etc  - unfortunately I
> believe this is normal behavior).
>
>   Checking the encoder plots for this time didn't show anything
> unusual, although tracking rates are fast enough that a 10 arcsecond
> offset would probably not be visible anyway.  The encoder error
> plots however should show a shift of that magnitude.  The rotator
> and azimuth plots showed nothing unusual around that time.  The
> altitude however did show a spike at exactly the predicted time of
> the jump. Before and after the spike, the errors were less than 5
> ticks. During the spike the handful of updates are as follows.
>
>
> 08:47:56.99  -5
> 08:47:57.09  78
> 08:47:57.25   6
> 08:47:57.40  18
> 08:47:57.55 -45
> 08:47:57.71 -18
> 08:47:57.97  -1
>
> At 72 ticks per arcsecond the error is about a tenth of the jump's
> magnitude, but is at exactly the right time, so is an indication
> that something happened in altitude (running over a moth?).
>
>   A check of the drive surfaces did show a repeating moth squish on
> the altitude surface nearest the laptop.  All surfaces have been
> cleaned.
>
>
> 				Cheers,
>
> 				  Dan
>
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