R. Crouch, J. Oberling
This morning we measured the position of the BBSS after the HEPI actuators were installed to see if/how things moved during actuator installation. Short version: Not much movement overall, but there are a couple spots that moved more than expected; there was a slight CW rotation of the BBSS of at most ~170 µrad.
The attached picture shows the position of our measurement points on the BBSS both before and after HEPI actuator installation; Round 5 is from last Wednesday, before the actuators were installed, and Round 6 is this morning. As the deviations in the picture are all related to the CAD nominal, the table below shows the measured positions from Round 5 and Round 6 and the deviation between these 2 measurements, to give an idea of the amount of movement from actuator install (all units are in mm).
| Measurement Point | Before Actuator Install (Round 5) | After Actuator Install (Round 6) | Deviation | |
| +X/+Y Point | X | -111.609 | -111.504 | 0.105 |
| Y | 113.527 | 113.486 | -0.041 | |
| Z | 122.768 | 122.777 | 0.009 | |
| -X/+Y Point | X | -501.049 | -500.998 | 0.051 |
| Y | -274.851 | -274.811 | 0.040 | |
| Z | 122.638 | 122.647 | 0.009 | |
| -X/-Y Point | X | -254.036 | -253.946 | 0.090 |
| Y | -522.848 | -522.663 | 0.185 | |
| Z | 122.791 | 122.837 | 0.046 | |
So all in all, not much motion, as we anticipate. However, there are a couple points that did move: The +X/+Y point moved +X by 0.105 mm, and the -X/-Y point moved +X by 0.09 mm and +Y by 0.185 mm. Overall this appears to indicate a +X shift and a CW rotation, but I can't really square that large +Y move in the -X/-Y point with anything else, it really stands out and doesn't make much sense to me. I'll think on this some more and post any revelations as a comment, but for now everything is still within our position spec and we rotated a little more in the CW direction (which based on Keita's last alog should help the overall IFO alignment), so onward towards chamber closeout we go.
We suspect this is the final FARO measurement of the BBSS that we'll take, but to be on the safe side we have left the FARO set up outside of WHAM3 for now.
