Minutes of the Tracker Meeting
- Ben: weigh the tungsten foils before and after etch.
- Sandro: measure tile electrical isolation with a Keithley.
- Sandro: send a dimensioned sketch of his O-ring idea.
- Arthur: send photos of the cable clip fit problems.
- Martin: extract the clearance of the cable clip screw from the model.
- Sandro: send drawings next week of the ideas for resolving the connector clearance problem.
- Travelers to SLAC: bring shipping cases back.
- SLAC: ship cables with connector savers attached.
1) Progress on test articles and coupons & thin tungsten quality
Ben described a new etching process at GSFC
with hydrofluoric acid. About 5um of material is removed. They will try primer
on this surface. Robert asked him to get
the weight before/after the etch. Ben said that the first GSFC etch did not
remove much of the surface at all, but just cleaned it. They are waiting for aluminum pieces for the
Sandro reported that the 3rd test article was
bonded with Kapton today. 2 others were
done earlier and just need trimmed. On
the second article they tried the wire but that failed. The wire moved too much under the
compression. They even tried putting 2cm
bits of wire under each tile near the center, but some of them moved out to the
edge of tray. They had to give up on the
wires. A few tiles remained not grounded
after the tile bonding. T/V test will be
done next Tuesday on the 3 test articles.
They had problems with the peel coupons, with the Kapton peeling loose,
not the tungsten, but all indications were consistent with a good bond to the
tungsten. They are collecting data on the peel tests to make a report. They also experimented with Kapton coupons
and found a times-4 increase in peel strength with brushed Kapton compared with
Kapton that was only cleaned. Discussions
are being held today and tomorrow with the
The 3 test articles are as follows:
1 baseline with room-temperature cure
2 the same but with 35C cure
3 no primer on tiles with 35C cure
The only idea we came up with for handling the grounding problem, in the face of the wire failure, was to calculate and/or measure the resistance without wires. Sandro will look into making a measurement with a Keithley electrometer.
They also completed an inspection of the EM top tray with the ESPI. No evidence was seen of any debonding.
2) Tower-0 assembly progress
Emilio reported that they finished the stacking and the cable assembly. First functional tests will be done by tomorrow morning. They found that it was not easy to attach the tape, and the connector mating was difficult. It requires touching the MCM (with gloves). Emilio said that for the bending of cables 2 and 3 at the top cactus arm they need a special tool.
Meanwhile David Tackes is working on the EM tower to complete his alignment programming.
For the cable restraining, Sandro proposed an O-ring material between cable and sidewall to compress against the double sided tape. Also, it would be used for strain relief for the top connector. This needs a test on Tower-0, and the material will need to be approved. Sandro will make a rough sketch of this concept.
The Tower-A sidewalls are under measurement in Plyform. Nanda will forward the specification document to Robert for release.
INFN will use the Al sidewalls for Tower-0 assembly (they were originally made only to verify the machining program). They don't plan to epoxy in the washers, since no loads will be put on this tower.
Emilio said that there is an issue with sharp edges in the clip for the cable restraint at the top of the tower. There was concern that it may damage the cables. Also, the screw is too close to the the intersection of the 2 cable arms. Martin needs details. Arthur will send photos and so forth. Martin will find the nominal clearance from the model. Nanda expressed concern that the bracket doesn't go under the whole cable, which leaves it more susceptible to handling damage.
3) Progress on resolution of the MCM connector/sidewall interference issue
Sandro is going to G&A tomorrow to resolve this problem. To be successful, the glue thickness under the connectors needs to be maximum 200um. He will make some detailed drawings next week.
4) Non-encapsulation issues: carbon-fiber passivation and EM inspection
Sandro has talked a bit with Plyform on this. Tests of a new procedure to passivate the carbon fiber will be made with the test articles.
5) Plyform closeout, sandwich, and bare-panel production status
Plyform will have 9 bare trays by tomorrow and 20 by the end of next week. Riccardo is making statistics on the closeout production.
6) Next MCM delivery to
MCMs for at least 1 tower should be ready for hand carry by the end of next week. Dave has been working hard on a plan to resolve the conformal coating workmanship issues. These MCMs will be visually scanned for broken pitch adapter traces. An electrical test fixture will be ready to try out by the end of next week. If it works, then it will be applied to all subsequent MCMs.
7) Tower-A schedule
Sandro will send a detailed schedule for Tower-A activities by COB tomorrow (already arrived).
Jeff wants his shipping cases back. Everybody traveling to SLAC from
Sandro reported that from his discussions with the vendor, the CMM calibration is nominally OK from 10C to 40C, but only with software correction. The temperature excursion up to 30C and back should be no problem. In any case, there will be a periodic calibration performed in October, before Tower A assembly.
Sandro said that two flight cables had bent pins. Probably some were bent from extraction, but they also need much better protection during shipping. INFN asks SLAC to leave connector savers attached during shipping. Robert said that this would be possible only if they can be regularly returned to SLAC after tower assembly.