GLAST LAT Project
March 24, 2003
GLAST Large Area Telescope:
Gamma-ray Large
Area Space
Telescope
Tracker Subsystem
WBS 4.1.4
1A: Introduction
Robert Johnson
Santa Cruz Institute for Particle Physics
University of California at Santa Cruz
Tracker Subsystem Manager
johnson@scipp.ucsc.edu
1A
Tracker Peer Review, WBS 4.1.4
1
GLAST LAT Project
March 24, 2003
Review Outline
1. Introduction
2. Design and modeling
3. Engineering Model
4. Mission Assurance
5. Parts and materials procurements
6. Manufacturing and assembly
7. Testing
1A
Tracker Peer Review, WBS 4.1.4
2
GLAST LAT Project
March 24, 2003
Design Overview
• Stiff composite panels (>500 Hz)
– Allows small gap between x-y SSD
layers
• Tungsten foils on panel bottom
• SSDs on top & bottom faces
• Electronics on panel edges
– Minimizes the gap between towers
(1.59 cm Si to Si)
• Carbon-fiber walls for vertical support
– Very stiff box structure
– Passive cooling to tower base
• New flexure attachment to Grid
– Decouple from thermal expansion
– Lowest frequency >150 Hz
– Greatly reinforced attachment to
the bottom tray.
– Thermal straps couple sidewalls to
the Grid (not shown)
1A
Multi-Chip
Electronics
Module (MCM) 19 Carbon-Fiber
Tray Panels
Carbon-Fiber
Sidewalls
(Aluminum
covered)
CarbonFiber Wall
2 mm gap
Readout
Cable
Tracker Peer Review, WBS 4.1.4
Titanium
Flexure
Mounts
3
GLAST LAT Project
March 24, 2003
Design Overview
Closeup view of the interfaces on the bottom of a Tracker module.
This interface has been substantially redesigned since the May ’02
random vibration tests of the prototype tower module, during which
structural failures occurred in the carbon-carbon closeouts of the
bottom tray.
1A
Tracker Peer Review, WBS 4.1.4
4
GLAST LAT Project
March 24, 2003
Tracker WBS & Interfaces
Thermal
Straps
Interface Control Documents
–Mechanical: LAT-SS-00138
–Electrical: LAT-SS-00176
1A
Tracker Peer Review, WBS 4.1.4
5
GLAST LAT Project
March 24, 2003
Tracker Organization Chart
GLAST LAT IPO
SLAC
R. Johnson, UCSC
Subsystem Manager
H. Sadrozinski, UCSC
Tracker Scientist
T. Ohsugi, Hiroshima
SSD Design,
Testing, Procurement
T. Borden, SLAC
Mechanical-Thermal
System Engineer
O. Millican, SLAC
I&T Supervision
M. Goossens, Teledyne
Manager, MCM assembly
(Contractor)
R. Bellazzini, INFN-Pisa
Italian TKR Project
Manager
A. Brez, INFN-Pisa
Development Engineer,
Production Supervisor
M. Sugizaki, UCSC
Electronics Testing
Nicolla Mazziotta, INFN-Bari
Tracker Production Testing
J. Olson, SLAC
Readout-Controller
ASIC Design
E. Swensen, Hytec
Mechanical Engineering
Design
(Contractor)
1A
D. Nelson, SLAC
Electronics System
Engineer
Tracker Peer Review, WBS 4.1.4
E. Spencer, UCSC
F.E. ASIC Design
6
GLAST LAT Project
March 24, 2003
Action Items from Delta-PDR Review
• Testing of the readout electronics at the multi-ladder level prior to
submission of the ASIC designs.
– 3 ladders were tested prior to the ASIC review (Dec. 6).
– Testing of complete trays is happening now.
• Verify design changes to the bottom tray and Grid interface prior to
the EM test. Also the sidewalls.
– Static pull tests are included in the plan (Presentation 2D).
– YS90 sidewalls are being tested now.
– K13D sidewalls material is being procured and will be tested.
• Complete polyswitch testing and make a decision
– This was done, and the part has been approved and is currently
being procured by SLAC.
• Review schedule and milestones after completing the current round
of ASIC testing. This was done. The electronics remain on the
critical path, but the ASICs have been procured.
• Develop a spares plan: LAT-TD-01379 (released).
1A
Tracker Peer Review, WBS 4.1.4
7
GLAST LAT Project
March 24, 2003
Requirements Flowdown
• The flowdown shown in Foldout D of our NASA proposal is still valid.
• Science Requirements that flow down to the Tracker design:
– Effective Area
– Field of View (aspect ratio)
– Point Spread Function
– Background Rejection
– Dead Time
• These Science Requirements flow down to the Tracker Level-3
requirements, documented in LAT-SS-00017.
• Presentation 1C shows how we have validated that our design
satisfies these Level-3 requirements.
1A
Tracker Peer Review, WBS 4.1.4
8
GLAST LAT Project
March 24, 2003
Science Requirements Flowdown
• Effective Area
– Geometric area: limited by rocket shroud and calorimeter mass
– Conversion efficiency: maximum practical amount of tungsten
– Tracking efficiency:
• Highly efficient detection plane to plane (SSDs)
• Detailed event information (good 2-track separation)
• Excellent signal-background separation
• Field of View (aspect ratio)
– High-precision and compactness of the SSDs allows the
measurement layers to be closely spaced
– Self triggering and high rate capability eliminates the need for a
time-of-flight hodoscope
• Background Rejection
– Depends on detailed event information (good 2-track separation)
• Dead Time
– Goals are readily achieved with solid-state detectors
1A
Tracker Peer Review, WBS 4.1.4
9
GLAST LAT Project
March 24, 2003
Science Requirements Flowdown
• A good Point Spread Function depends on
– Minimizing effects of multiple scattering
• Measurement immediately following tungsten (minimal
moment arm from scattering)
• Nearly 100% detection efficiency, to get two measurements as
close as possible to the vertex
• Highly detailed event information
– Avoid track confusion
– Identify the location of the conversion vertex
– Cull out problematic event configurations (tails in the PSF)
• Many thin converters
– Limited by cost
– The need to support the layers is also a practical limit
• Minimal mass in structural material (carbon fiber)
– Avoid conversions in non-optimal locations
– Avoid unnecessary multiple scattering and Compton scattering
– Good spatial resolution (strip pitch/layer spacing)
1A
Tracker Peer Review, WBS 4.1.4
10
GLAST LAT Project
March 24, 2003
More Requirements
• Mass
– Allocation: 510 kg
– Actual: 509 kg
• Conditioned Power
– Allocation: 155 W
– Actual: 148 W
• Measured on EM prototype
readout modules
• Plus estimate of SSD power
• Radiation hardness
– Presentation 2B
• Reliability
– Presentation 2C
1A
• Environmental
– LAT-TD-778
• Contamination Control
– LAT-MD-404
• Parts Control
– LAT-MD-099
• EMI/EMC
– 433-RQMT-0005
– Presentation 2A
Tracker Peer Review, WBS 4.1.4
11
GLAST LAT Project
March 24, 2003
Critical or Problem Design Areas
• Several design factors and design problems that affect the the
Tracker performance, particularly efficiency and PSF, have been
studied intensively since PDR:
– Low-mass structure (carbon-fiber)
• Pre-EM mechanical prototype
– Prove and debug the detailed design
– Preliminary structural testing
– (failure at GEVS qual. levels)
• EM trays and Tracker module
– Work out all manufacturing issues
– Prove the final design
• Presentation 2D will show how the present design
– Satisfies all structural requirements
– Provides adequate stiffness to accommodate the close spacing of
trays with towers and towers within the LAT
1A
Tracker Peer Review, WBS 4.1.4
12
GLAST LAT Project
March 24, 2003
Critical or Problem Design Areas
•
•
•
•
•
1A
Road to a final bottom-tray design
Originally designed to Delta-II GEVS levels (Appendix A)
Tested to generic GEVS levels (doubled the loads at the transverse
resonance)
– Failure in the carbon-carbon highlighted lack of margin in the original
design and insufficient data on material and joint allowables.
A failsafe design at these generic GEVS levels proved to be difficult and very
expensive ($ and schedule)
– No project input to allow us to use realistic levels or notching despite
apparent common opinion that
• Structure-born levels will be low at the resonance frequency (>100 Hz)
• Acoustic analysis loads will be very low compared with these GEVS
qualification levels
– The GEVS levels produce accelerations >45g at the transverse resonance!
Analysis indicates finally that the present design does have margin with
respect to the GEVS levels.
Margins relative to realistic test levels are now very large.
Tracker Peer Review, WBS 4.1.4
13
GLAST LAT Project
March 24, 2003
1-yr Chronology of the Bottom Tray
Break
COI Joint Pull Tests
Shake
Final
Design
COI/Hytec
Materials Testing
Hytec
Analysis &
Design
COI Reinforced Tray
1A
Tracker Peer Review, WBS 4.1.4
14
GLAST LAT Project
March 24, 2003
Critical or Problem Design Areas
– Electronics Cooling and Thermal Design
• SSDs should not operate above about 30C at end-of-life, to avoid loss
of detection efficiency due to shot noise.
• Presentation 2A: Prototype ICs demonstrated that we can meet our
most optimistic power estimate (0.25 W per SSD layer).
• Presentation 2D:
– The sidewall material was changed to a higher performance fiber
to lower the temperature rise, and the modules will be painted
black (except bottom), to radiate some power to each other and to
the ACD.
– Thermal straps were added to carry the heat directly from the
sidewalls to the Grid.
– Silicon Strip Detectors
• Presentation 5C: no design changes since PDR
• Presentations 6C, 6D: abundant data on flight SSDs and flight ladders
that show that the ladders will more than satisfy all requirements,
especially on the number of bad channels.
1A
Tracker Peer Review, WBS 4.1.4
15
GLAST LAT Project
March 24, 2003
Critical or Problem Design Areas
– Low-Noise, Low-Power Electronics
• At PDR the noise and efficiency requirements were
demonstrated by a full-up system in the beam test and balloon
flight module, except for the problem of retriggering while a
readout is in progress.
• Delta-PDR highlighted problems with the ASIC design process,
with some problems remaining at the ASIC CDR.
• Presentation 2A: tests of the final round of prototype ASICs
with full-length SSD ladders (presented at ASIC CDR)
– Noise and noise-occupancy requirements are satisfied at
threshold levels that should give ~100% efficiency
– There is no longer a problem with keeping the trigger active during
readout
– Power consumption meets our goals and requirements
• Presentation 2A: preliminary results from the flight ASICs,
which have already been manufactured.
– Design problems and bugs all appear to be resolved.
1A
Tracker Peer Review, WBS 4.1.4
16
GLAST LAT Project
March 24, 2003
Manufacturing & Assembly
• Most manufacturing and assembly will be done by commercial
vendors (details in 6A through 6H):
– Mechanical structures: composites vendor in Italy
– Ladders and tray assembly: two electronics assembly vendors in
Italy
– Electronics modules: electronics assembly vendor in L.A.
• Parts and materials are “customer furnished” or specified by us
according to LAT procedures and requirements.
• LAT Tracker controls all design drawings and specifications.
• Development of the processes for fabrication and assembly of the
custom LAT designs was accomplished by close collaboration
between LAT institutes and the commercial vendors.
• Final Tracker tower-module assembly and test will be accomplished
in the clean-room facilities at INFN Pisa.
1A
Tracker Peer Review, WBS 4.1.4
17
GLAST LAT Project
March 24, 2003
Tracker Test Program
• High yield at the tray and tower levels requires an aggressive test
program through all steps of the assembly:
– Receiving and inspection of the SSDs (Presentation 6B)
– Testing of assembled SSD ladders (6C)
– Testing and screening of ICs (5D)
– Testing and screening of other EEE parts (5B)
– Testing and burn-in of MCM electronics modules (6E)
– Testing of assembled composite panels (6D)
– Testing of MCMs on trays prior to ladder attachment (6F)
– Testing of completed trays (7D)
– Cosmic-ray testing of stacked trays (7D)
– Testing of assembled towers (7E)
1A
Tracker Peer Review, WBS 4.1.4
18
GLAST LAT Project
March 24, 2003
Tracker Status Snapshot
• Document list: see the TKR web site for links into Cyberdocs:
– http://www-glast.slac.stanford.edu/Tracker-Hardware/latdocs.html
• Subsystem Requirements Documents
– Level-III: LAT-SS-00017 (released)
– Level-IV: LAT-SS-00134, LAT-SS-00152 (both released)
• Subsystem Interface Control Documents
– Mechanical: LAT-SS-00138 (released)
– Electrical: LAT-SS-00176 (released)
– Interface Definition Drawing: LAT-DS-00851 (draft)
• Design Drawings of Flight Hardware. See the Tracker drawing tree:
– http://www-glast.slac.stanford.edu/Tracker-Hardware/TKR_drawing_tree.html
– ~80 Drawings; ~40 Released
• Drawings of assembly fixtures
– http://www-glast.slac.stanford.edu/Tracker-Hardware/tooling.html
• EEE Parts List: all but one parts (or procurement specs) are approved.
– LAT-TD-00179
1A
Tracker Peer Review, WBS 4.1.4
19
GLAST LAT Project
March 24, 2003
Tracker Status Snapshot
• Materials List: complete, but evaluation of some composites and
adhesives is still in progress.
– LAT-SS-00172
• Mechanical Design (see Presentation 2D for details)
– Mid trays: design complete, released; EM versions fabricated
– Top tray: design complete, released; EM version in fabrication
– Bottom tray and flexures: design complete; EM version in fab
– Sidewalls: design complete; YS90 versions are available; K13d
material on order
– Thermal straps: conceptual design; details in progress
– Modeling and Analysis
• B allowables from testing are now included (with YS90 values
for the sidewalls)
• positive margin everywhere
• A reduced model has been delivered to the LAT
1A
Tracker Peer Review, WBS 4.1.4
20
GLAST LAT Project
March 24, 2003
Tracker Status Snapshot
• Electronics design (see Presentation 2A for details)
– PWB and pitch-adapter flex: designs are complete, with final
prototypes under test and the release process in progress.
– ASICs: designs complete and released. Wafers have already
been procured, several chips have been successfully tested, and
production probe testing is ready to commence.
– Flex-circuit cables: designs are complete. EM versions and burnin system cables are in hand.
– Bias circuit: design is complete. The final prototypes are being
evaluated.
• SSD Design: complete and released, with procurement, including
testing, in progress (Presentations 5C and 6B).
1A
Tracker Peer Review, WBS 4.1.4
21
GLAST LAT Project
March 24, 2003
Tracker Status Snapshot
• SSD Ladder Assembly (Presentation 6C)
– PRR completed for the primary vendor
– >250 flight ladders have been fabricated and tested
• MCM Assembly (Presentation 6E)
– All fixtures and procedures have been developed
– Lessons learned in EM assembly are being applied to improve
the procedures to increase the yield and quality
– A PRR will be held around early June
• Composite Panel Assembly (Presentation 6D)
– All procedures and fixtures have been developed and tested for
mid trays and top trays (only slight variations are needed for the
bottom trays—in progress)
– Testing and acceptance procedures are developed and tested
– A PRR will be held in mid April
1A
Tracker Peer Review, WBS 4.1.4
22
GLAST LAT Project
March 24, 2003
Tracker Status Snapshot
• Tray Assembly (Presentation 6F)
– Includes mounting of SSDs and MCMs onto composite panels.
– Tooling and procedures were very recently tested on the EM to
produce functional trays. A few lessons from that experience are
being applied to finalize those procedures.
• Tower Assembly (Presentation 6G)
– Preliminary tooling was tested with the early prototype tower
– Improved tooling is being designed for EM and flight tower
assembly.
• Test Procedures (Section 7)
– Testing at low levels of integration is well developed and has been
applied to the Engineering Model.
– More experience is now being gained at the tower-module level,
with the Engineering-Model functional mini-tower and the
mechanical/thermal tower.
1A
Tracker Peer Review, WBS 4.1.4
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