1. GLAST Large Area Telescope: Jonathan Ormes / Rudolph Larsen
Gamma-ray Large Area Space Telescope
GLAST Large Area Telescope:
LAT Quarterly Review
ACD Subsystem
Jonathan Ormes / Rudolph Larsen
NASA GSFC
ACD Management

2. ACD Subsystem Outline LAT and ACD Design Overviews
ACD Organization and WBS Charts
Tile Detector Assemblies (TDA) Design Status
Tile Shell Assembly Design Status
Base Electronics Assembly Design Status
Studies Requested from February Review
Issues, Risks and Mitigations
ACD Near Term Milestones
Conclusions

3. LAT Design Overview Instrument Tracker Calorimeter
16 towers  modularity
height/width = 0.4  large field-of-view
Si-strip detectors: 228 mm pitch, total of
8.8 x 105 ch.
hodoscopic CsI crystal array
 cosmic-ray rejection
 shower leakage correction
XTkr + Cal = 10 X0  shower max
contained < 100 GeV
segmented plastic scintillator
 minimize self-veto
> efficiency & redundant readout
Tracker
Calorimeter
Anticoincidence Detector
3000 kg, 650 W (allocation)
1.75 m  1.75 m  1.0 m
20 MeV – 300 GeV

4. ACD Design Overview
Lip to "hide" thermal blanket and micro-meteorite shield
Tile Shell Assembly (TSA) X Y
Base Electronics Assembly (BEA)

5. ACD Organization Chart
ACD Subsystem
Code 600
Jonathan Ormes - Lead Investigator
ACD management
Code 700
Rudy Larsen - Manager
Cristina Doria-Warner - Financial
Resources Code 400.1
Dennis Wicks - Scheduling
ACD Design and Science support
Code 661
ACD System Engineering
Tom Riley
Code 740
Alexander Moiseev,Lead
David Thompson, Robert Hartman
David Bertsch, Jay Norris
ACD Reliability and Quality Assurance
Code 303
ACD Simulations
Code 661
Patricia. Huber, Lead
Tavi Alverez, Quality
Tony DiVenti, Reliability
Nick Virmani,Thom Perry, Parts (560)
Fred Gross, PilarJoy, Materials (543)
Bo Lewis,Jim Anderson, Safety
Chris Lorantson, Contamination
Heather Kelly
Taro Kotani
Alexander Moiseev
Ground Support
Facilities & Equipment
Code 543/564
Thomas Johnson /
TBD Electronics Lead
Tile Shell Assembly
Code 543
Base Electronics
Assembly
Code 564
Micrometeroid Shield /
Thermal Blanket
Code 543/ 545
Flight Software
R. Schaefer
Code 664
moved to
LAT Flight Electronics
SLAC
Hardware/Software
Integration & Test
Code 543
T. Johnson, Lead
LAT Insrument
Integration & Test
Code 568
Mission Integration
& Test Support
Code 568
Mission Operation
& Data Analysis
Code 661
Thomas Johnson, Lead
TBD, Lead
Thomas Johnson, Lead
Lou Fantano, Thermal
Lead
D.Sheppard, S. Singh,
John Lindsay, Lead
Scot Murphy
John Lindsay, Lead
David Thompson, Lead
Robert Baker
Tile Detector
Assemblies
Code 661
A. Moiseev, Lead
Code
543 - Mechanical Engineering
Branch
545 - Thermal Engineering
564 - Microelectronics and
Signal Processing Branch
568 - Flight Systems Integration
and Test Branch
Code
600 - Space Sciences
Directorate
661 - Gamma Ray and
Cosmic Ray Astronomy
663 - Instrument Development
664 - Data Management
& Programming
Code
302 - Systems Reliability
and Safety Office
303 - Assurance Management
Office
Code
STAAC Business
Management Office
Code
Systems Technology,
And Advanced Concepts
Directorate
740 - Flight Instrument
Division

6. ACD Work Breakdown Structure
Tile Shell Assembly
Base Electronics
Assembly
TBD, Lead
D.Sheppard, S. Singh,
Robert Baker
Micrometeroid Shield /
Thermal Blanket
Thomas Johnson, Lead
Scot Murphy
ACD Design and Science support
Alexander Moiseev,Lead
David Thompson, Robert Hartman
David Bertsch, Jay Norris
ACD System Engineering
Tom Riley
ACD Subsystem
4.1.6
Jonathan Ormes - Lead Investigator
ACD management
Rudy Larsen - Manager
Cristina Doria-Warner - Financial
Resources
Dennis Wicks - Scheduling
Tile Detector
Assemblies
Flight Software
moved to
4.1.7
LAT Flight Electronics
ACD Simulations
Heather Kelly
Taro Kotani
Alexander Moiseev
ACD Reliability and Quality Assurance
Patricia. Huber, Lead
Tavi Alverez, Quality
Tony DiVenti, Reliability
Nick Virmani,Thom Perry, Parts
Fred Gross, PilarJoy, Materials
Bo Lewis,Jim Anderson, Safety
Chris Lorantson, Contamination
Hardware/Software
Integration & Test
T. Johnson, Lead
Ground Support
Facilities & Equipment
4.1.6.B
Thomas Johnson /
TBD Electronics Lead
Lou Fantano, Thermal
Lead
John Lindsay, Lead
Mission Integration
& Test Support
Mission Operation
& Data Analysis
4.1.6.A
David Thompson, Lead
LAT Insrument
A. Moiseev, Lead

7. Tile Detector Assembly (TDA) Design
Flat Tile TDA
Bent Tile TDA
Wave Shifting Fibers
Clear Fibers
Mirrored on this end
PMT Connector
Wave Shifting/Clear Fiber Connector
Wave Shifting Fiber
Groove detail for bent tiles
(holds fibers in place
during gluing process)
Key Hole Grooves

8. Tile Detector Assembly (TDA) Design
Descoping of Tile Array
Bottom row replaced on each of four sides with single 15 cm x 170 cm tile
Configuration is 89 tiles (each with two PMTs), 12 scintillator ribbons
Simulations confirmed 4 hole mounting scheme not impacting efficiency
Laboratory tests for light collection were performed
fiber spacing mm
wrapping material Tetratec
two scintillator manufacturers comparable product
Fabrication testing proved keyhole grooves best
Two flight-like tiles fabricated
Now under test
Light efficiency better than expected

9. Tile Shell Assembly Design
Top TDA’s (25)
Side TDA’s
Fiber Ribbons
Bent Tiles
Top Panel
Side Panel (4 Places)
Corner Flexure (4 Places)
Middle Flexure (4 Places)
Doubler (8 Places)
Corner Flexure

10. Tile Shell Assembly Design
Worked on minimizing the volume of the ACD. This was in response to an increase in LAT Grid size and an increase in the height of the LAT Trackers.
Refined the TDA placement on the sides to minimize the overall volume of the ACD.
Continuing to work on routing of the fibers in the tiles.
Optimized the design of the shell to increase its overall stiffness to >50 Hz
Performed several trade studies to determine the optimum mounting interface between the shell and base frame

11. Base Electronics Assembly+X
Event Board Module (single row)
Event Board Module
(double row)
Closeout
Connector Bulkhead (24 places)
Channel (4 places)
Machined Aluminum
Corner Fitting (4 places)

12. Base Electronics Assembly Design
Photomultiplier tubes competitive procurement action initiated
baseline tube identified with flight heritage
10 Qual units 1/02; 40 EM units 6/02; 210 FM units 3/03
Level IV Requirements Document recently drafted
Reliabilty Requirements balanced against cost have driven the Electronics Design
Topology of the Event Processor Board established with each board servicing 18 PMTs
Boards are no longer interconnected
Trigger Primitives are generated in the LAT
ACD Science team is investigating tile / electronics channel failure modes, effects and mitigations
Progress was made in the ACD to LAT electrical interface definition

13. Studies Requested at February Review
R&D Testing: Identify optimum design in terms of tile efficiency and light collection and map the response (light yield, efficiency) of a fiber/tile configuration in detail.
Determine testing methodology and construct test configuration -complete
Determine optimum fiber spacing in tile -complete
Determine optimum groove depth -complete
Determine tile thickness effects on light yield (linear with thickness?)
Determine edge effects -complete-no measureable effect
Determine tile uniformity
Determine effects of fiber end treatments (Al’ized ends)
Determine fiber length effects -complete, using low attenuation light transmission fibers
Determine MIP light yield, # of PE’s, and PMT gain requirements -complete
Production Testing: Develop and implement test procedure and fixture to verify performance of every tile.
Experience derived from R&D Testing will determine testing methodology and requirements
Milestones:
Remaining R&D Testing Completed: September 1
Production Test Plan Completed: September 1

14. Issues, Risks and Mitigations
Accelerated schedule - Issue: risk to readiness for the LAT Preliminary Design Review. Mitigation: hold the ACD Design Peer Review as scheduled and work all action items assigned.
Revised cost estimate - Issue: threat to LAT budget
We are still over the proposal cost. Mitigation: Complete redesign of ACD electronics; shared use of LAT resources; further ACD descope.
Mass constraint - Issue: risk to efficiency, redundancy, and margin of the Anticoincidence Detector. Mitigation: careful design; additional mass request
Thermal blanket/micrometeoroid shield performance - Issue: risk to durability of ACD over its lifetime. Mitigation: agreement for design help from Johnson Space Center, which specializes in protection against penetrations.
Light collection from scintillator tiles - Issue: affects efficiency throughout the life of the mission. Mitigation: Tests to optimize the light collection and use of clear optical fiber transmission lines.

15. Issues, Risks and Mitigations
Gaps between scintillator tiles - Issue: Lowers Background rejection efficiency. Mitigation: cover gaps with scintillating tapes in one dimension and overlap detector tiles in the other.
Electronics Cost - Different cost estimates within GSFC and between GSFC and SLAC. Mitigation is all parties meet to understand differences and reach agreement.
Reliability Requirements - To yield higher reliability number Micrometeoroid Shield may need thickening which could lead to higher background. Mitigation is more analyses are needed.
Background entering at the edge of the bottom of the ACD - Mitigation
is further analyses needed. Preliminary look says its not a problem.
LAT other subsystems’ ability to compensate for loss of effective area - Mitigation is also further analyses.

16. ACD Near Term Milestones

17. Conclusions
ACD Design Peer Review shows significant progress in preparing for the October LAT Instrument Review
Respondees to the Peer Review Action Items have been identified along with an internal GSFC due date of September 21.
Major open issue is ACD cost.