GLAST Proposal Review

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GLAST Large Area Telescope Tracker
Subsystem Robert Johnson Santa Cruz Institute
for Particle Physics U.C. Santa Cruz Tracker
Subsystem Manager johnson_at_scipp.ucsc.edu 831-459-
2125
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Outline

• Overview
• Schedule
• Roadmap to Manufacturing
• Top Issues and Risks

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Design Overview
Multi-Chip Electronics Module (MCM)

• 19 stiff composite tray panels support SSDs on
  both faces with electronics on two sides.
• Converters are on the bottom face, just above the
  SSD plane
• 2-mm gap between trays
• 16 layers of tungsten converter foils.
• 12 layers of 3 X0 converters
• Followed by four 18 layers
• 18 x and 18 y SSD planes.
• Carbon-fiber sidewalls conduct heat to the base
  and stiffen the module.
• Electronics are based on 2 ASICs, PC boards, and
  custom flex cables.
• 31.6 kg mass per module.
• 10.5 W of power per module.

19 Carbon-Fiber Tray Panels
Carbon-Fiber Wall
2 mm gap
Readout Cable
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Production Overview
Module Structure (walls, flexures,
thermal-gasket, fasteners) Engineering SLAC,
Hytec Procurement SLAC
SSD Procurement, Testing Japan, Italy, SLAC
SSD Ladder Assembly Italy
10,368
Tracker Module Assembly and Test Italy
2592
18
Tray Assembly and Test Italy
342
342
Electronics Design, Fabrication Test UCSC, SLAC
Composite Panel Converters Engineering SLAC,
Hytec, and Italy Procurement Italy
648
Cable Plant UCSC
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Near-Term Schedule (?key milestone)
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Near Term Schedule
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Tracker Production Flow
SSD Production and Test 11/01-10/03
ASIC Procurement, Test and Dicing 12/02-5/03
PWB Procurement and Flex Attach 1/03-3/03
Ladder Assembly and Test 11/02-10/03
MCM Assembly Test and Burn-in 3/03-10/03
Tray Panel Fab And test 1/03-11/03
Readout Cable Fab and Assembly 2/03-10/03
Tray Assembly And test 7/03-4/04
Sidewall Fabrication 2/03-10/03
Tower Assembly 10/03-5/04
Tower Testing 11/03-8/04
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Major Procurements
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Progress Since Delta-PDR

• ASIC design and test
• GTFE design is fully functional.
• GTRC is working but needs some logic corrections
  for flight (new logic under test in FPGAs).
• 3 complete MCMs (26 chips each) are under test.
• Mini-MCM connected to full SSD ladder
  demonstrated satisfactory noise performance.
• Radiation testing in progress.
• GTFE wafer probing working.
• MCM production testing is ready for EM
  production.
• Prototype EGSE test stand exercised with multiple
  MCMs.
• EM MCM production
• In progress at Teledyne Electronics Technologies

• Flex cables
• Draft spec in place.
• EM cables nearly finished.
• SSD procurement total
• 4600 delivered.
• 3500 tested by LAT.
• Ladder assembly
• EM ladders completed.
• PRR held for flight ladders.
• Flight ladder assembly begun at GA Engineering
  (30 in test).
• Tray fabrication
• At least 16 EM panels fabricated at Plyform.
• Satisfy dimensional tolerances.
• Fixtures are ready for Kapton, tungsten, and SSD
  mounting.

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Design Status Work Still in Progress

• Electronics
• GTRC/GTFE ASIC designs need some small
  modifications to increase timing margin in data
  transfer between the two.
• Bottom Tray and Tower-Grid Interface
• Invar closeout has been investigated and is now
  only a backup solution.
• Reinforcement of the existing design is being
  followed in work with COI and Hytec. Coupon
  testing and preparation of a prototype tray will
  be completed one month from now.
• Hytec will be updating the tower model,
  completing analysis work, and preparing load and
  vibration tests.

• Tower Sidewalls
• Design in the high-conductivity material exists
  and is being prototyped and tested in Italy.
• Drawings
• 79 design drawings are in Cyberdocs and on the
  Tracker Web drawing tree.
• At least 28 are released and under configuration
  control.
• Assembly Fixtures
• Tower assembly fixture design is in progress (2nd
  iteration). This work includes study of
  alignment of Grid mounts.
• All other fixture designs are complete and in use
  for EM fabrication.

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Tracker Engineering Model

• Full-scale mechanical-thermal tower
• 19 Trays, sidewalls, flexures, etc. to the flight
  design.
• Dummy Si detectors (including some HPK SSD
  rejects).
• Dummy MCMs loaded with resistors to dissipate the
  expected electronics power load.
• Functional mini-tower
• 4 trays loaded with 3 x-y planes of functional
  detectors and electronics and 3 planes of
  tungsten foil.
• 1 bottom dummy tray without electronics for a
  Grid interface.
• Aluminum sidewalls.
• Standard readout cables.
• Functional qualification tray
• Another functional tray for additional
  environmental testing.
• MCMs
• 8 additional functional MCMs for qualification
  and electronics testing.

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Tracker EM Test Matrix
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EGSE and MGSE

• EGSE
• MCM acceptance testing and tray-level electronics
  tests
• Simplified system exists and works well.
• Some software development still needed to
  simplify use interface.
• Some recoding from Python to C needed to speed up
  execution.
• 4 systems needed for production (already exist).
• Tower-level testing
• Standard TEM-based test stand.
• In use already at SLAC with Tracker front-end
  electronics.
• Work beginning in California Italy to develop
  tower-level test scripts.
• 8 systems are needed for production!

• MCM Burn-in
• Special readout cables are in fabrication.
• Control and readout will be done by the TEM-based
  test stand.
• MGSE
• Tower lifting fixture
• Design concept exists but detailed design not
  done.
• Tower vibration fixture
• Design is complete.
• Tower shipping containers
• No design yet.

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Top Issues and Risks

• Bottom tray and Tracker-Grid interface design
• Impact
• Already has delayed the Tracker Peer Review into
  April 03.
• Further delays are possible if the present
  development line doesnt work and invar (or
  another material) has to be used.
• Issue
• We need specifications for realistic input levels
  to use in designing the tower-Grid interface
  stiffness, to ensure that towers do not touch
  during launch.
• Mitigation
• Two engineering firms (COI and Hytec) are engaged
  in the design, analysis, and testing.
• A program of coupon testing is under way at COI
  to prove the redesigned flexure attachment joint.
• Mechanical testing will be carried out on a
  prototype (refitting of an existing tray) prior
  to the engineering model.
• Status
• Invar development on hold after preliminary
  magnetic measurements.
• Received report from Hytec on issues with invar
  and other materials.
• Coupon testing and refitting of the test tray
  will complete by Dec. 15.

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Bottom Tray Reinforcement
Modified Ti Side Fitting to Bond to Sandwich Panel
Concept under study and test for reinforcing the
bottom tray and the flexure mounts.
Double-Lap-Bond Ti Corner Fitting
Carbon-composite angle brackets
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Top Issues and Risks

• ASIC Design and Production
• Issuesome modifications are still needed for the
  flight run
• Several logic errors remain in the latest GTRC
  prototype IC, even though it works sufficiently
  well for EM production and testing.
• Data transfer from GTFE to GTRC works at 2.5V and
  20 MHz, but with no margin to go to lower voltage
  or higher frequency.
• About 20 of the GTFE-G are unstable at low
  threshold.
• Impact a failure of the production run would
  delay the Tracker delivery by about 4 months.
• Mitigation
• A new board with 2 FPGAs and 2 GTFEs is being
  used to verify the modified VHDL code, including
  our corrections of the logic errors.
• The timing issues are being intensively studied
  in simulation to be sure that we understand them.
  A small modification will probably be put in to
  correct it (otherwise VDD will have to be raised
  to 2.8V).
• The GTFE-G stability problem has been understood
  and the correction was tested on actual chips by
  FIB surgery.
• Status the December submission date is tight but
  can be met.

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Top Issues and Risks

• Overlap of Procurements and Tracker Peer Review
  Preparation
• Issue slippage of the Tracker Peer Review
  results in numerous flight Tracker procurements
  occurring prior to it (see page 8)
• SSD procurement and ladder production
• These were always scheduled to occur before CDR
• CDR and PRR have already been completed for these
  items
• Mechanical materials and assembly of tray panels
• ASIC production and other electronics parts
• Impact
• Several item-specific CDRs / PRRs need to be held
  prior to the Tracker Peer Review
• ASIC (December)
• PWB, pitch-adapter flex (January)
• Tray panel fabrication, face sheets, bias
  circuits, etc. (January)
• Flex-circuit readout cables (may be able to delay
  this one beyond CDR)
• Potential manpower conflicts with EM testing and
  CDR preparation.
• Mitigation
• We need to work with management to schedule and
  streamline the PRRs.