Minutes
of the Tracker Technical Meeting
August
7, 2003
ACTION
ITEMS:
Sidewall
issues: Sandro and Nanda were at Plyform, where some new coupons were being
pulled. Through some miscommunication,
Plyform only made unidirectional K13D coupons (22 plies), so they were not able
to test new coupons of the Tracker design laminate. However, Plyform does have enough prepreg material to make one or
two new panels. That will be done after
the 2-week vacation break, which starts tomorrow.
Sandro
noted a problem with variation of the laminate thickness in the panels laid up
a couple of weeks ago. For example, one
panel with aluminum was only 1.15mm thick, while another panel WITHOUT aluminum
was 1.34mm thick. He noted that the
latter value is actually consistent with COI predictions, given that the panels
has only a single ply of the YS90 fabric on each side. Furthermore, Sandro said that the 22-ply
unidirectional K13d laminates come out at 86 micron thickness per ply, which is
about 20% less than the COI prediction.
Sandro said that the panels were made too quickly, without proper controls
in place. They will repeat the
procedure with remaining material, using careful procedures, after the vacation
break.
Plyform
is cutting coupons from the thicker laminate (1.34mm) for the thermal
testing. Robert and Tom requested that
samples of the thick and thin laminate be sent to SLAC to be analyzed to try to
understand the thickness and resin-content issues.
There
was some discussion to try to understand the Plyform process. Sandro said that the relevant engineer was
not present, so they will have to wait until after the vacation break to get
detailed information. Apparently the
laminates are cured with a Teflon-like foil on both sides. There is no evidence of resin coming off
with those foils. Only a small amount
of resin is lost around the edges. A
5mm thick aluminum plate is put on top of the stack under the vacuum bag during
curing. There was some discussion of
what its purpose might be, but nobody really knew.
Sandro
relayed a few of the pull test measurements during the meeting. The average tension strength was 1200MPa,
whereas 1800MPa was expected (this is for the unidirectional K13d laminate). (For reference, the Tracker allowable is
165MPa, but that is for the design laminate with fibers in all directions and
with YS90 fabric on both surfaces.)
Sandro also said that there was still a problem with some of the pulls
not breaking uniformly.
During
the meeting Sandro also relayed one compression measurement (i.e. very
preliminary) that was 300MPa, whereas 900MPa was expected.
Robert
asked Erik about work on understanding the bottom-tray repair. He needs Steve to do analysis, and Steve
will return next week. They plan to
study the effect of different patch sizes.
Robert requested a written report on the analysis and the proposed
repair plan and procedure.
There
was a discussion of how to proof test the side flexures under the GSFC
specified shear and axial loads. The
plan is for Hytec to analyze the static test with the corner flexures
detached. If the desired loads can be
achieved in the side flexures that way, with still sufficient margins in the
tracker structure, then this will be the easiest way to qualify the flexure
design.
Robert
summarized the situation with Teledyne MCM production. Teledyne received a PO from SLAC to do the
preliminary work needed on process revisions.
This will involve partially assembling 6 MCMs. The will start by attaching flex circuits to 2 existing MCMs
boards from the previous run, which were reworked at SLAC to correct the
dimensions on the raised right-angle-interconnect area. This will verify the alignment of the flex
attach. They will then continue with
those parts by loading capacitors and ICs, doing wire bonds, and then
encapsulating, to test out the process revisions in encapsulation and staking
of the large capacitors. In parallel
they will design and prototype a cover for protecting wire bonds and will add
ground screw holes to the assembly fixtures.
Meanwhile SLAC will machine at least 4 of the new boards from DDI, to
put in the radius and cut the boards to the precise height. SLAC will also get some flex-attach epoxy
mixed with about 1.5% by weight of Cab-o-Sil (treated fumed silica), which
should improve the bondline, squeezout, and peel strength properties of the
flex attach. Those boards and adhesive
will then be used by Teledyne to do 4 more flex attaches. They will also put capacitors on those
boards and vibrate all 6 boards to verify that the capacitors don’t fall off.
SLAC
also expects to receive a proposal from Teledyne for the flight build by
tomorrow. Also, an order should be
going out today for the flex circuits (pitch adapters), with a 2-week delivery
for the first 50 parts. Therefore, the
earliest time to get the flight build started would be about August 25, but
this depends on getting the preliminary work done, as described above, and
getting a contract finalized with Teledyne.