SSO Update
Published in the RSAA Lunations
Vol1 Issue46 1–30 November 2023
The Cassegrain cage (Cass cage) provides a mounting area for instrumentation, electronics, and counterweights for the AAT. It also provides convenient access for people to work on these items. The cage is split into 2 halves, an upper half holding electronic cabinets and a lower half weighing about 7-tonne on which people stand.
In the late afternoon of 13 April, one of the studs holding the lower floor to the upper cage was found to have cracked. This left the AAT unusable overnight for fear of more studs coming loose or braking, which might have resulted in the 7-tonne Cass cage floor dropping off the telescope and falling 5m (we will let you do the calculations, but the end result wouldn’t have been pretty). The next day, the mechanical team rushed to machine a new stud and added safety chains to keep the AAT operational while a permanent solution could be found. The proposed rectification for the fault was to replace the machined studs with off-the-shelf M24 socket head bolts. This would keep the same type of joint design, while improving the rigidity and mitigating the tendency to loosen over time, as well as keeping it easy to remove in the future.
The rectification work started on October 23. The cage was removed from the telescope, split into its two halves, and craned to the ground floor. This proved to be a slow process with the Cass cage trolly suffering a myriad of faults just before it was to be used, but the AAT staff did what they do best and found a workaround to get the ball rolling again. Once on the ground floor, the work went smoothly, and the telescope was back in use right on schedule.
A big thanks go out to all the AAT staff involved, who put in some long days to ensure we stuck to schedule, and to Chris Tinney, who graciously gave up 3 (clear) nights of observing to allow us to perform the work.
Chris Lidman, on behalf of the SSO team
Picture: The upper part of the Cassegrain cage being separated from the lower part
