R. Crouch, J. Warner, J. Oberling, M. Robinson
We made some more HEPI moves today to better position the BBS SUS cage. The results are shown in the 1st attachment. The deviations listed in the attachment are the deviations from nominal, but that is not our target here. To better position the BBS optic we are trying to match our position and yaw from the test stand. As a reminder, I've attached the final SUS cage alignment from the test stand (2nd and 3rd attachments). The table below shows our current deviations from the test stand alignment (all units in mm):
| SUS Alignment Points | Target from Test Stand | Actual In-Chamber | Deviation | |
| +X/+Y | X | -110.809 | -111.450 | -0.641 |
| Y | 113.819 | 113.392 | -0.427 | |
| Z | 122.562 | 122.801 | 0.239 | |
| -X/+Y | X | -499.759 | -500.327 | -0.568 |
| Y | -275.102 | -275.519 | -0.417 | |
| Z | 122.669 | 122.660 | -0.009 | |
| -X/-Y | X | -252.295 | -252.875 | -0.580 |
| Y | -522.581 | -523.013 | -0.432 | |
| Z | 122.616 | 122.811 | 0.195 | |
We wanted to bias to the negative by ~0.3 mm in both X and Y since our BBS test stand alignment had a +0.3 mm deviation in both X and Y position, so this looks pretty good. The Z axis indicates a potential off level in the cartridge assembly, but one has to be very careful in assessing level based on these measurements. These measurements are all done in the LHO Global coordinate system, which is tilted w.r.t. the local level in the WBSC2 chamber (see T0900340), so you cannot level to global coordinates; if one did then the suspension would then hang weird as it doesn't care about our different coordinate systems, it just hangs along the local gravity vector. Jim is planning on using an autolevel to measure the top of the keel mass of the ISI's Stage 2 to see how that looks (similar to what LLO did).
In addition, the yaw of the SUS cage also closely matches our test stand alignment. Our target, from the 3rd attachment, is 44.9979° from the +X axis and we are currently measuring 45.0025°. This is a difference of 0.0046°, or ~80 µrad, in the CCW direction, so pretty close to our target. We won't know for sure how good the pointing alignment is until we can use the BBS OpLev, which is not currently available (the channels do not yet exist, per Oli the plan is to add them next week), but my hope from today's work is that we'll be pretty close.
So next steps are to have the BBS OpLev available so we can assess our pointing alignment and the attachment of the HEPI actuators. We'll have to measure position again after the HEPI actuators are attached, so we aren't quite done yet.
