R. Crouch, J. Oberling, B. Weaver, I. Abouelfettouh
We have completed the BBS test stand alignment. After several rounds of yaw adjustment and figuring out the mechanics and what was rubbing where, we finally arrived at a yaw alignment within tolerance with everything torqued down and no rubbing in the SUS chain. In comparison, pitch alignment was a few twists on the adjustable mass in the PUM, maybe 20 minutes in total. The final pointing alignment deviations (yaw direction assuming a top-down view):
After the pointing alignment was complete we then moved back to the AR side to check that the position had not changed. The BBS cage has not been moved on the ISI, so our alignment of the cage reported here is still valid. The results (tolerance for all is +/- 1.0 mm):
Rotating from our IAS equipment basis to the IFO axes, shifting the deviations from the AR to the HR surface, and adding the pointing alignment, the final test stand position of the BBS HR surface is shown in the below table (CW = clockwise; CCW = counterclockwise; reported assuming a top-down view):
| Target | Actual | Deviation | Tolerance | |
| X | -202.6 mm | -202.3 mm | +0.3 mm | +/-1.4 mm |
| Y | -184.1 mm | -183.8 mm | +0.3 mm | +/-1.4 mm |
| Z | -83.1 mm | -83.2 mm | -0.1 mm | +/-1.0 mm |
| Pitch | -446 µrad (up) | -431 µrad (up) | +15 µrad (down) | +/-55 µrad |
| Yaw (from -X axis) | -785.918 mrad (CW) | -785.758 mrad (CW) | +160 µrad (CCW) | +/-190 µrad |
I've kept the yaw angles in radians for consistency, but converting them to degrees gives a target yaw from the -X axis of 45.0298° CW and an actual yaw of 45.0206° CW, with a deviation of 0.0092° CCW.
We've left the IAS equipment in the West Bay near the test stand in case we need to take a look at alignment again, but as of now the test stand alignment is complete.