The repaired and re-coated secondary mirror was returned from Contraves with essentially the same optical figure as when initially procured according to interferograms provided by Contraves. Intense effort by the electronics and mechanics groups had the system ready at the summit about 1 week before the scheduled July IR observing runs. The system has worked essentially without problem since installation.
Inspection of locking segments on the upper end handler revealed several incorrectly sized bolts which resulted in erratic handling ring operation. These were replaced and re-torqued.
Bird's head clearances were investigated with all three top ends on June 5 and 6. Binding in the locking system at this time precluded provision of adequate clearances in the unlocked position. We currently ensure adequate mounting clearances by detailed visual inspection as the top end is put in place. However this lengthy process is not appropriate for the long term.
A short scheduled 3 day shutdown in early September was used for 'bird's head' lock maintenance and investigation. This is the first time since the telescope was assembled that the locks have been disassembled. Custom handling equipment was designed and fabricated to permit removal of the 400 kg locking segments. This equipment worked extremely well. We also purchased a special 3-man 'basket' with dedicated safety harnesses for work around the top of the telescope. Maintenance however is still very crane- intensive.
During this shutdown we were able to service only one of 4 segments in 3 days. Several of 14 wear plates associated with the SE segment showed signs of heavy wear and cracking. Guide bolts were of non- uniform size. Damaged wear plates were replaced. Guide bolts on all 4 segments were inspected and undersized bolts were fitted with precision sleeves. Although this maintenance was clearly overdue, locking systems clearance problems were not much improved. Clearance problems are accentuated by the design of the handling ring's segments which allows the ends of each segment to swing. The swing results in interference as upper ends are seated.
Clearly these systems require a lot more work. We are planning major upgrade/ repair efforts for next summer. In the mean time detailed documentation of as-built dimensions appears to be the only means for resolving inconsistencies between design and operational clearances.
The primary mirror was liquid washed in mid June resulting in a 4.3 % increase of reflectivity and significant reduction in scattered light.
An initial thought on the cause of the oscillations was that they might originate with contamination in oil-pad bearing clearances. Accordingly all bearing gaps were thoroughly inspected and found to be well within expected limits.
The spare video image integrator unit (known as Leaky2) that was procured many years ago was tested, documented and installed at the summit as a "hot spare" to the main video integrator used by the TCS autoguider system. Now if the main video integrator (known as Leaky1) fails (for which there have been several scares), the telescope operator can bring Leaky2 on-line with only a few minutes of down time before autoguiding is restored. The TCS4 project will replace these custom video integrators with a commercial image processing module.
TCS autoguider cabling: connections between the video integrator unit (Leaky1) and the data acquisition system (CAMAC) required cleaning and rebuilding of cable connectors.