Closing Mirror Covers

Sunday, December 13, 2015 9:08 AM

Problem(s) Encountered:

The only serious problem was in the afternoon of 12/13, when I was attempting dome flats. The mirror cover petals closed in the wrong order.  Eric G. talked me through the procedure to get them to open again, and I was ready to go before sunset.


Mirror covers were closed when the telescope was pointed over for dome flats, causing them to close out of order.  As stated in documentation, the mirror covers should only be cycled with the telescope pointed at zenith.  Standard procedure for correcting the issue was described, in detail, to the observer.  This can be found in the telescope documentation.  With the proper instruction, and the 1.3m observer acting as spotter, he was able to correct the issue.

From the telescope documentation:

Go out in dome and verify that all four mirror petals are up.

The mirror petals are driven open by a pneumatic air system. If there''s a failure in that (e.g., ice in the lines) they may not come up; also, they barely clear the sky baffle so they sometimes hang on that.

Clearing a hung up mirror cover petal is an intrinsically dangerous operation, but here are the instructions if you wish to try. Alert the 1.3m observer and have them come up to watch, or at least tell them that if you don''t get back to them in 10 minutes they must come up to summon aid in case you injure yourself. Using the control paddle stored on the west side of the telescope, slew the telescope way over so you can get access to the sky baffle. Get the aluminum ladder and a stick about 5 feet long (e.g., a broomstick). Get up on the ladder. That petal is going to open explosively!!! Look out where it''s going to go before you do anything!!!! Once you''re sure you won''t be knocked off the ladder by the opening petal, gently push on the sky baffle to free the cover. BAM! - the cover opens violently. Stop shaking and climb back down. Tell the 1.3m observer that you''re OK.”