Secondary Visual Inspection August 2000

( By Mac Cooper, 16 Aug 2000)

A visual inspection of the new chopping secondary was performed as part of engineering shutdown activities this month (August 2000). The results are very good with only one exception, and that is the corrosion found on the secondary mirror itself.

First the flexpivots were checked and found to be in good shape with no signs of deterioration. The pictures show the upper(near 0 degrees of theta) and lower flexpivots (near 180 degrees of theta)
All the chopping motion limit switches were actuated and functioned okay. The rubber hard stops were found to have some cracking and rubber deterioration, but all are still in place and functioning okay at this time.
A small amount of lubricant had dripped onto the lower back of the secondary and collected a significant amount of dust and dirt. The dust and oil was approximately 1/8 inch thick at the worst point. This was cleaned up with solvent and then rinsed with methanol.
Next, the small cog belts that couple the stepper motors to the gearboxes were inspected for signs of cracks, wear, and streaching. All were in great shape - no signs of cracking or loosness.
The flexible wiring leads that connect to the torque motor were inspected and found to be in great shape with no sign of looseness or deterioration of the insulation. A visual inspection of all the other wiring (especially the moving leads) showed no wear at all. The wiring is still well suspended in the center of the theta rotation axis.
The V-roller supports for the theta axis showed almost no signs of wear eventhough we operate in the same position almost all the time.
And finally regarding the corrosion that was found on the secondary mirror surface. The following pictures show the corrosion on the left side of the mirror, the right side, and a right side closeup, and then an overall distant shot. These corrosion spots are more than just visual as the worst of them can easily be felt with the finger as you move across them. I estimate that about 5% of the secondary mirror is covered by this corrosion at the present time.