After LHO's BBSS drift issues was "fixed" by lowering the blades by -4mm from nominal, we noticed that the PUM flags were low and somewhat too low even at their max adjustment. One of the ways to try and fix this was to increase the entire BBSS by 5mm. This maintains the Top Mass blade heights while raising the PUM flags into a centerable position for the PUM BOSEMs.
We increased BBSS Height Increased by 5mm, bringing the PUM flags back to nominal. Once this was done, we needed to move the Top Mass tablecloth upwards to compensate, so we did (by 5mm as well). Below is a table with the Mass-to-Structure gaps. Take note that the Top Mass Gap isn’t an absolute measurement since the tablecloth/structure it is measured from can also move.
|
Date |
Dummy Test Mass Gap |
PUM Gap (mm) |
Top Mass Gap (mm) |
Context |
|
Nominal Dimensions (DWG) |
25 |
17 |
19.90 |
Nominal - what the drawings in D1900628 tell us. |
|
Feb 22 2024 |
25 |
14-15 |
17-18 |
First article build measurement (pre-drift investigation). |
|
Oct 17 2024 |
20.5 |
12.5 |
18.55 |
After “fixing” drift by lowring Top Mass blades -4mm BP (nominal blade position) |
|
Oct 29 2024 |
25.5 |
17.5 |
21 |
After raising entire BBSS by raising Top Stage Blades +5mm |