Minutes of the Tracker Meeting
April 24, 2003
We discussed the virtues of passivating the carbon-carbon with resin versus paint.† The resin was applied with a sponge, while the paint can be sprayed on, filling all areas more reliably and quickly.† Tom stressed the need to test that the paint does not come off.† Sandro will test it with a coupon and temperature cycle it.† We decided that we should use the non-conductive variety of the paint.† The sidewalls will also be painted with the non-conductive variety, as requested in the peer review RFA.
We discussed Sandro's grounding concept.† A wire will be connected to the core and passed through a vent hole in the structural wall and glued to the carbon-carbon with conductive glue.† The closeout walls will also tied together by glued in wires, in this case glued into grooved cut in the carbon-carbon.† Tom suggests welding the wire to the aluminum.† Tom will send Sandro information on parallel gap micro-welders.† Tom will also Fed-Ex a core sample for tests.† We should nickel plate the wire to maintain conductivity in the glue joint to the carbon-carbon.† Tom needs to add the wire to the materials list.
Robert asked about fixturing for MCM mounting.† Sandro wants to replace the screws with pins to align the MCM during gluing.† A tool is being designed that will fix to the thermal boss and clamp the MCM by applying pressure to the pitch adapter.
Pisa is finishing a drawing of the dam to be used for encapsulation of wire bonds from MCM to SSD.† The material is something like Lexan 2000.† Tom will add it to the materials list.† Sandro said that CV-15-2500 is too low viscosity for this application.† G&A will try CV-2502.† Tom will have a sample in a couple of days and will send it to Sandro.† He will also add it to the materials list.† He will also add the conductive epoxy Sandro intends to use for bonding wires to carbon-carbon to the list.† It is a die-attach material that will cure at 80C.† He will also be testing the conductive Nusil for this application.†
Sandro will prepare a plan and schedule for testing these new procedures and send it to Robert.†
We discussed how to retrofit the mini-tower with these new procedures.† For the mini tower we will use M1.6 screws for the MCM mounting but remove the threads.† The MCM gluing fixture needs to be ready for refitting the mini-tower and should first be tested on the mechanical-thermal tower trays.† Sandro thinks that the mini-tower trays can be retrofitted with something nearly equivalent to the planned grounding scheme.
For flight trays BJ will change the closeout drawings to drill to the major diameter of an M1.6 screw, with no tapping of the holes.† The MCM holes will not change.
COI needs the drawings of the bottom-tray closeouts today or tomorrow.† There will be a manufacturing meeting with them on Monday.† We decided to remove the inserts for the MCM attachment, assuming that Sandroís new MCM mounting scheme will be used (and will work).† The hole should be for the major diameter of an M1.6 screw.
Pisa reports that the corner bracket drawings are okay.† Erik said don't drill the alignment pin holes all the way through for Sandro's alignment pins, so that they donít fill with glue.† They can still be about 4mm deep.† Erik will make this change.† This drawing needs to go to Tom soon!† All these drawings need to be released for CDR. Erik will send it Friday or Monday.
Erik reported that he received 2 out of 3 responses to his RFQ for making the titanium pieces and heat straps.† Both vendors requested 6 weeks.† Erik will beg for 5.† Tom said to try to get the corner bracket in 4 weeks for at least 1 tray. Tom & BJ will check for a local shop that can make the brackets faster.
Sandro said that he plans to make Aluminum pieces for dry fit tests.† Tom will send the drawings to Sandro.
We need a tool to press the pins into the corner brackets.† Robert will add this to the plan and schedule.
No responses were received Wednesday on the static test fixture.† Erik will call today.† He has phone messages saying they will be in by noon today.† (The first response was for 8 weeks: Erik will beg for shorter.)
We discussed plans on how to present mechanical margins at CDR but the discussion was rendered irrelevant by subsequent developments (GSFC has approved the new levels for our use, so we will present to them, with generous safety factors and model uncertainty factors).† Erik said that a safety factor of 1.5 and MUF of 1.25 will show positive margin at CDR without force limiting, for the new loads.† Robert asked about plans for static test loads.† Erik suggests testing to the new random-vibe loads (at 3-sigma) plus 5%.
Erik needs to follow up with Bari on the sine-burst test.† This test needs to be added to the CDR presentation, so Robert needs that input.
Robert asked Sandro about the top tray status.† Sandro said that Plyform plans to make the top and bottom trays together.† Robert asked him to make sure in the planning that the top tray does not delay the bottom tray, for which the schedule is critical.
Robert said that work on the drill template design needs to start.† BJ already has modified the vibration fixture drawings.
Sandro described the status of tower assembly tooling.† Drawings are in progress.† The assembly will be like was done for the prototype tower, but upside down.† He will send a copy of the drawings for review as soon as available.† G&A will make the tools.
There was a long discussion of whether the shield plane in the bias circuit is needed.† Sandro is concerned about the extra work and risk needed to align the circuit such that the bias and shield voltages may be wire bonded reliably without shorting.† Robert agreed to draw a diagram of the signal detection circuit and provide an explanation of the reason for the shield plane.† He will also discuss with the engineers and with the reviewer Helmuth Spieler the risks of removing it from the design.†
Tom will check on using the normal SLAC configuration control for electronics design files, as will be done for the mechanical design files.
Erik needs Tom to check on the status of funds for Hytec.† Erik needs to order parts but cannot release POís until this is taken care of.
Tom told Sandro that Nusil is now shipping NASA compliant material to customers, but the old tracker order was canceled.† We need to get a new order into them.† Sandro said that G&A will order it directly.