Minutes of the Tracker Meeting
April 22, 2004
1. John Ku: make a priority in the next days to analyze the Grid bushing
2. Sandro and Riccardo: review the top tray closeout/insert drawings tomorrow and send approval back to SLAC
3. Sandro: get lead time for the insert manufacture
4. Sandro: send a sample of facesheet material to Ben Rodini
5. Martin: use the as-built thickness +-50um for the facesheet drawings
6. Sandro: send Martin a fax regarding facesheet drawing issues
7. Arthur: analyze and plot the eccentricity sensitivity vs angle
8. Sandro and Riccardo: review and sign off on the cone/stud drawings with understanding that additional drawings will be made asap for lower-eccentricity cones
9. Robert: make a top-level agenda for next week
10.Nanda: detailed PRR/TRR agendas
11.Riccardo: send mid-tray as-built measurements to Martin
12.Dave: send Tom V the WIP status from Teledyne
13.Sandro: send containers back to Jeff
14.Jeff: send INFN details as to what is needed regarding fastener specs
- Martin/Riccardo: top tray drawing sign-off/resolution of insert counterbore issue
- Jim: 7075-T76 for top/bottom tray inserts
- PRR/TRR planning; Pisa meeting agenda; readiness matrix; expectations
- Mid-tray production status
- Mid-tray "as-built" measurement & verification.
- Mid-tray design- INFN to supply red-line mark-up of design per as-built conditions
- G&A Status: MCM installation & alignment. Wire bonding characterization results
- Menning/Sandro/Ku: grid bushing design and magnitude of eccentric offset.
- Status of bottom tray closeouts, Ti parts, MCMs, BT cores, bias circuits etc. (see the new status chart at http://www-glast.slac.stanford.edu/Tracker-Hardware/Actions/Tracker_SLAC_Status.pdf)
- Jeff: new drawing tree
John Ku presented the status of the static test work. They are starting with the z axis and have run 3 load cases. The main problems are with instrumentation and making sure of recovery of accurate data. They are writing all lessons learned into the procedure. Overall it is progressing well, but they need to work on the LVDTs, which don’t have enough precision. They are now changing to the lateral axis. After finishing they will leave it set up in the lateral case. The work is in the same room as ESPI testing. John estimates that they could do the acceptance test in 1 day in the worst case. Andrea is preparing a procedure for mounting the bottom tray into the fixture to avoid damage to closeouts.
John had some action items regarding the Grid bushing but hasn't had time to look at them.
1. how tight does the fit between stud and bore have to be to give acceptable stress margins in aluminum?
2. how high are stresses in the Grid wall if a bushing is pushed in?
3. can a split bushing be used?
John will make a priority of doing the work himself in the next days. Martin said that a 1.4 mil interference fit is preferred. But is the stress in the Grid too high? Is a split bushing preferred? There will be a meeting Friday on these issues.
Martin said that the insert and closeout drawings are all out for sign-off. The counterbore depth is consistent with the mid-tray design. Inserts are not flush on the backsides. Sandro said that Riccardo was only concerned about 1 particular insert. There would be a small simplification of the tool if this insert flange were increased in thickness. However, at this point the drawings are complete and Martin would not have time to revise them before leaving for Italy. The decision was for everybody to review the drawings as they are and get them released so that work can proceed. Martin and Riccardo will discuss the particular insert again in Pisa.
Sandro said that he and Riccardo will review the top tray closeout/insert drawings tomorrow.
There was general agreement to move forward with using 7075-T76 aluminum for bottom and top tray inserts. The T6 material has not been approved by NASA for that use, and at this point the T76 material is in Pisa. Sandro said that the week after next they will start to make the parts. Sandro needs to get the lead time from the machine shop.
The discussion then turned to face sheet thickness. Sandro said that the actual thickness are 200um for 4 plys and 290um for 6 plys. Sandro also said that the old PCI facesheets were very much the same thickness. That is quite a bit more than what Ben predicted, so he thinks then that the fiber volume must be less than 60%. Sandro will send a sample to Ben for analysis. Ben said that he has seen the prepreg material spec at Plyform. Martin will use Sandro’s numbers and will put +-50 micron tolerance on thickness. Sandro will send Martin a fax with other issues that he has with the facesheet drawings that are out for review. Ben noted a subtle asymmetry in the way the facesheets are made and then put onto the trays, but he thought that it probably was not a big deal.
There was a long discussion of eccentricity. Martin derived the need for the large eccentricity of 20 mils per cone based on tolerance stackup. A major part of the stackup was the tolerance on tilt of the corner-bracket/flexure assembly relative to the bottom tray. Sandro requested an eccentricity less than half as much based on his concern that the angular setting accuracy that could realistically be obtained would result in too much error in offset. Arthur said that even with the large eccentricity the offset is not very sensitive to the angle if the needed offset is small. High sensitivity comes in only when one gets near the full extension with both cones offset the same direction (the dependence of offset on angle is highly nonlinear). But one goes to that extreme position only if needed, in which case a lower eccentricity would not even give a solution. He said that he would perform some more analysis of the adjustment angles and make plots illustrating his points. Sandro suggested making two sets of cones with differing eccentricities. Mike echoed that as a good possibility. However, the first priority is to evaluate the 2 cone/stud sets due to arrive tomorrow. In parallel the existing drawings need to be signed off for release and procurement started. After the evaluation of the first 2 sets that arrive tomorrow Arthur can prepare drawings for cones of reduced eccentricity.
Regarding next week’s meetings, Robert sent out a revised PRR matrix including some comments and also sent comments on several of the procedure drawings. At Nanda’s request he can make a top-level agenda, but the detailed presentation agenda for the individual PRRs need to come from INFN. Robert suggested that prior to the PRRs there should be some discussion of the design to try to close out issues there.
Chris asked when the EM vibe TRR will take place. Robert said that it is gated by the Grid bushing issue, which is preventing a new vibe fixture from being made and by the cone procurement. The TRR should be a week or two before the test, but when we will be ready for the test is unclear at the moment due to the above issues.
Mid-tray production status:
3 mid trays are in Pisa, 1 of them heavy. They have been tested by ESPI and dimensional checks were done. 3 more are at Plyform. Production is going well. A summary of the as-built measurements requested will be sent to Martin tomorrow by Riccardo.
Mid tray drawings still need redlines to be sure they reflect the as-built trays. We will work out a plan next week to get this done.
At G&A the special mock-ups are complete. The tools to align the MCM is ready for the first trays. They need 2 weeks for characterization of the wire bonding. The final procedure should be ready the 2nd week of May.
MCM status: 6 units are to ship from Teledyne today, so thermal cycles and burn-in should start on Friday. 9 more units should ship next week. After the first 6 units there was some delay in the schedule due to a production halt to work on inspection criteria for pitch-adapters. Also, a high than expected chip failure rate has required rework and slowed down completion of the first lot (otherwise 5 more should arrive the next day after the first 6, and etc.) Dave will send Tom V the WIP status.
The new EGSE was successfully tested with the mini-tower. 2 sets should ship in the next days to Pisa.
Jeff reported that the new bottom tray cores are on order as of a few days ago but will have 4-week turn-around, and then they have to go to SLAC for inspection and ship to Pisa.
Jeff asked Sandro to return containers sent to INFN.
INFN (Nanda) will supply specs for the 2.5 and 4mm fasteners so that Jeff can add the info to the procurement spec. He will send an email with specific requests.
Jeff reported that the updated new drawing tree is, as always, available on the Tracker we site.
Bottom tray closeouts are on their way to Pisa.
Titanium flexures and corner brackets and bias circuits should arrive at SLAC tomorrow and will be hand carried to Pisa. That will be 2.5 sets of titanium parts and 45 bias circuits (1/4-oz).