Date: Wed, 1 Oct 2003 07:51:07 -0700
From: Russell E Owen
Subject: Re: 2.5m obslog 20030930 (MJD 52913)
>Secondary oscillation
>---------------------
>
>During observations of plate 1250, around 05:20Z, we lost guide
>stars. When we eventually went to an FK5 star, we saw an ellipse.
>We went to the telescope (left tracking), turned off the fans, and
>realised there was a vibration so strong that you could hear it
>(many hertz) and FEEL it with a hand resting on the altitude drive
>quadrant!  Since we thought we had disconnected the piezo actuators,
>we went and woke French.  He checked the  piezos were indeed
>disconnected.  We found that slewing the telescope back below 45deg
>stopped the oscillation.  After several tests, tracking the Galil
>position through TPM plots, we found that slewing from
>non-oscillation ONLY in altitude up to 65 deg did not start the
>oscillation, but as soon as we then slewed in azimuth, it started.
>
>This was the end of the night, so we have handed the problem
>directly to French and crew who are working on it now.
This sounds like it may be an oscillation induced by the telescope
drives. If so, it's an interesting question whether that matches
earlier episodes. I'm willing to try to help diagnose the problem
when I get into work (later this morning; I'm starting the day at
home).
-- Russell