Today, Travis, Mark and I worked on installing the ETMX lower structure into the chamber. After it was in, while reassembling cables, we noticed that the test mass was really jammed into it's lower stops - upon further inspection, we discovered that both fibers on the left side (viewed from back of the suspension) were gone. We started looking for the debris and found it just outside of the chamber on the floor and on the trolley that the unit had been sitting in overnight last night and this morning. We did not find anything like a bug nearby, but investigation ongoing. Meanwhile, we're revising the schedule to back up a few steps and start the rebuild. History of lower structure after it was welded:
- Welded main chain unit sat on it's trolly in weld room for ~a week before we were ready to install it.
- Yesterday, we rolled the covered main chain on it's trolly ~60ft from weld room cleanroom to the staging cleanroom. We then uncovered it, and lifted it with the genie duct jack and placed it on the reaction chain trolley and mated the 2 units together. The fibers were intact at this point. We then covered it again and rolled the whole unit ~10ft from the staging cleanroom to the chamber cleanroom and parked it near the door. We left the cover on it and the genie duct jack parked around it with the forks loose around the structure to aid in protection.
- This morning we uncovered the unit, and then lifted the unit off of the trolley with the genie lift and set it up on the install arm elevator. We then continued with the installation of the unit into the chamber with the arm. A few hours later we discovered the broken fibers.
All of the above is standard install procedure, with the same equipment (trolly, cover, genie lift, install arm) used in each of the previous QUAD installations.
Since we found the fiber debris all over the trolley and on the ground outside of the chamber on the floor, it must have happened between yesterday late afternoon when we rolled it there and this mornign after we picked it up and set it into the install arm.
We believe that the fibers broke in the morning during the lift out of the LSAT with the genie duct jack lift since we recall specifically NOT seeing debris under the trolley before that. There is a fair amount of jostling that happens to the suspension during this, as the suspension needs to pull free from 8 supporting legs (with 8 nut bars and 8 screws) which are a tight fit around the structure, just above the upper fiber joint. The masses were locked into position, however the test mass was locked with most of the load still on the fibers. Since the lower EQ stops are viton tipped, they must have compressed more during the maneuver (or added up over the course of the previous maneuvers) and the load on the fibers became more than 100%. We will go back to utilizing the rail stops under the mass D060446, a tooling piece abandoned early on due to interferences and difficulty to use (the tooling for the stops we adapted instead has proved sufficient numerous times since, but it only takes one failure).
Attached are pictures of the ear and horns on the PUM and Test Mass. The PUM horns appear to be very short now, so we will take the opportunity to replace the PUM, especially since this is the one with the crack behind the prism which may not survive around of fiber welding.
I'm prepping PUM-ITM03 in the bonding lab. Yesterday the magnet/flag inserts and 1 prism were glued into place. Today the second prism, followed by an overnight low temp out-gassing air-bake.