1. GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb. 13-15, 2001 J. Ormes/R. Larson 1 ACD Subsystem Jonathan F. Ormes ACD Subsystem Manager Rudolph K. Larsen ACD Project Manager Laboratory for High Energy Astrophysics NASA Goddard Space Flight Center ormes@lheavx.gsfc.nasa.gov

2. GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb. 13-15, 2001 J. Ormes/R. Larson 2 Anti-Coincidence (ACD) Subsystem  Technical overview  Requirements  Status  Organization  Schedule  Budget  Technical issues and mitigations  Summary Outline

3. GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb. 13-15, 2001 J. Ormes/R. Larson 3 Large Area Telescope (LAT) Design Overview 16 towers  modularity height/width = 0.4  large field-of-view Si-strip detectors: 228  m pitch, total of 8.8 x 10 5 ch. hodoscopic CsI crystal array  cosmic-ray rejection  shower leakage correction X Tkr + Cal = 10 X 0  shower max contained < 100 GeV segmented plastic scintillator  minimize self-veto > 0.9997 efficiency & redundant readout Instrument Tracker Calorimeter Anticoincidence Detector Shield 3000 kg, 650 W (allocation) 1.75 m  1.75 m  1.0 m 20 MeV – 300 GeV

4. GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb. 13-15, 2001 J. Ormes/R. Larson 4 ACD: The First Line of Defense Against Background The purpose of the ACD is to detect incident cosmic ray charged particles that outnumber cosmic gamma rays by more than 5 orders of magnitude. Signals from the ACD can be used as a trigger veto or can be used later in the data analysis. Segmented plastic scintillator (Bicron-408) read with wave-shifting fibers (BCF- 91MC) + PMT (Hamamatsu R1635, R4868) readout. Each segment (tile) has a separate light tight housing. Separate tile housings provide resistance to accidental puncture by micrometeoroids. Wave-shifting fiber readout provides light collection uniformity Gaps between tiles are deliberately misaligned with the gaps between tracker towers and covered by scintillating fiber "tapes"

5. GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb. 13-15, 2001 J. Ormes/R. Larson 5 Design Heritage GLAST EGRET Backsplash reduced the EGRET effective area by 50% at 10 GeV compared to 1 GeV. GLAST will be studying photons to above 300 GeV. Anticoincidence Detector for GLAST is subdivided into smaller tiles to avoid the efficiency degradation at high energy. 0.2-2 MeV "backsplash" photons

6. GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb. 13-15, 2001 J. Ormes/R. Larson 6 Design Approach Lip to "hide" thermal blanket and micro-meteorite shield Segmentation for side entry events

7. GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb. 13-15, 2001 J. Ormes/R. Larson 7 Science Requirement: Efficiency SRD Background Rejection requirement: Contamination of the high latitude diffuse gamma rays by background in any decade of energy for > 100 MeV shall be less than 10%. The goal shall be 1%. Charged particle background rejection involves the use of pattern recognition in the tracker and the calorimeter as well as the ACD. For protons, calorimeter and tracker are powerful. 10 5 : 1 at system level Electrons are more problematic. Electrons create showers in the calorimeter identical with photon showers. Worst case is 3 x 10 3 : 1 at 10 GeV The required ACD efficiency for charged particles (detector efficiency + hermeticity) is 0.9997

8. GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb. 13-15, 2001 J. Ormes/R. Larson 8 Additional Requirements Tile segmentation –Efficiency > 80% at 300 GeV relative to that at 1 GeV –Effective area at >60 o ; >0.1 of on-axis value No more than 10% loss of effective area –6% in the plastic and structure –1% from ACD deadtime –1% loss from noise –<5% chance of loss of tile in 5 years (electronics) –<1% per year for loss of tile by micrometeoroid puncture

9. GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb. 13-15, 2001 J. Ormes/R. Larson 9 Physical interface specifications Mass200 kg + 60 kg (30% reserve) = 260 kg Electronics 34 kg + 17 kg (50% reserve) = 50 kg Power 30 watts + 25 watts (80% reserve) Volume - see materials presented by Martin Nordby Electronic signals –Fast VETO Pre-primitives for Trigger thresholds Hi Z trigger for calibration events –Addresses of hit tiles Pulse heights of hit tiles –Rate date from all tiles –Housekeeping data –Command, command verification, and control

10. GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb. 13-15, 2001 J. Ormes/R. Larson 10 ACD Technical Status Detectors: Scintillator tile light output tests have been performed. Tile overlapping and detector tapes are planned to cover gaps Electron background rejection analysis cuts being developed Side tile segmentation is being reevaluated Trade studies are being performed tile thickness, segmentation and PMT placement Electronics: ASIC development proceeding – First prototype submission was in January Higher gain Hamamatsu PMTs are being evaluated Electronic parts have been submitted for acceptance High voltage power supply specs, SOW and cost estimate created – Procurement for prototype sent to identified vendors Mechanical: Tile support structure has been improved over proposal design

11. GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb. 13-15, 2001 J. Ormes/R. Larson 11 ACD WBS Organization Chart Alexander Moiseev, Lead ACD Detectors 4.1.6.3 Robert Hartman John Krizmanic ACD Electronics 4.1.6.4 Dave Sheppard, Lead S. Singh, ASIC design Robert Baker Fabrication William. Daniels Donald Righter ACD Mechanical Components 4.1.6.5 Thomas Johnson, Lead Sharon Seipel 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 ACD management 4.1.6.1 Rudy Larsen - Manager Cristina Doria-Warner - Financial Resources Dennis Wicks - Scheduling Electrical Test Darrin Buck James Odom ACD Flight Software 4.1.6.6 Robert Schaefer, Lead ACD Simulations Heather Kelly Taro Kotani Alexander Moiseev ACD Reliability and Quality Assurance 4.1.6.2 Patricia. Huber, Lead Russell Murray, Quality John Remez, Reliability Peter Jones, Parts Fred Gross, Materials Bo Lewis, Safety Reserved 4.1.6.7 Micrometeroid Shield / Thermal Blanket 4.1.6.B Thomas Johnson, Lead Lou Fantano, Thermal Lead Robert Hartman John Lindsay, Lead Tom Johnson Mission Integration & Test Support 4.1.6.9 John Lindsay, Lead Mission Operation & Data Analysis 4.1.6.A David Thompson, Lead Insrument ACD Subsystem Integration & Test 4.1.6.8 All ACD team members above are GSFC civil service employees or GSFC contractors

12. GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb. 13-15, 2001 J. Ormes/R. Larson 12 Contributing GSFC Lead Organizations WBS 4.1.6 ACD Subsystem - Dr. Jonathan Ormes, GSFC Code 600, Space Science Directorate WBS 4.1.6.1 ACD Management - Rudy Larsen, GSFC Code 700.1, Project Formulation System Engineering - Tom Riley, GSFC Code 730.4, Instrument Systems Office Science Support- Dr. Alexander Moiseev, GSFC/USRA Code 661, Gamma Ray and Cosmic Ray Astrophysics Branch WBS 4.1.6.2 ACD Reliability and Quality Assurance - Patricia Huber, GSFC Code 303, Assurance Management Office WBS 4.1.6.3 ACD Detectors - Dr. Alexander Moiseev, GSFC/USRA Code 661 WBS 4.1.6.4 ACD Electronics - Dave Sheppard, GSFC Code 564, Microelectronics and Signal Processing Branch WBS 4.1.6.5 ACD Mechanical Components - Tom Johnson, GSFC Code 543, Mechanical Engineering Branch WBS 4.1.6.6 ACD Software - Bob Schaefer, GSFC/HSTX Code 664, Data Management and Programming Office WBS 4.1.6.8 Instrument Subsystem Integration & Test - John Lindsay, GSFC Code 568, Flight Systems Integration and Test Branch WBS 4.1.6.9 Mission I&T Support - John Lindsay, GSFC Code 568 WBS 4.1.6.A Mission Operations & Data Analysis - Dr. Dave Thompson, GSFC Code 661 WBS 4.1.6.B ACD Micrometeoroid Shield/Thermal Blanket - Tom Johnson, GSFC Code 543 / Louis Fantano, GSFC Code 545, Thermal Engineering Branch ------------------------------------------------------------------------------------------------------------------------------------ USRA- University Space Research Association EITI - Emergent Information Technologies Inc.

13. GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb. 13-15, 2001 J. Ormes/R. Larson 13 4.1.6 ACD Schedule

14. GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb. 13-15, 2001 J. Ormes/R. Larson 14 ACD Milestones ACD & Thermal Blanket Requirements Review03/21/01 ACD & Thermal Blanket PDR06/27/01 LAT Instrument PDR08/06/01 ACD & Thermal Blanket CDR06/26/02 LAT Instrument CDR08/05/02 ACD Engineering Model (EM) Complete05/15/03 ACD Flight Subsystem Assembly Complete 10/01/03 Thermal Blanket / Micrometeoroid Shield Ready for Integration02/01/03 (with thermal model) Delivery of Calibration Unit ACD to SLAC05/15/03 Flight ACD Ready for Integration01/26/04

15. GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb. 13-15, 2001 J. Ormes/R. Larson 15 Interim ACD Cost Estimate* (Escalated K$) *DOE/NASA funding.

16. GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb. 13-15, 2001 J. Ormes/R. Larson 16 Technical Issues and Mitigations Increase technical margin for light collection –Add reflective termination to fibers or read out at both ends –Monitor and adjust PMT gain in flight –Request 25-30 kg additional mass for thicker tiles on top Required volume for electronics may exceed available –Place PMTs under ACD –Place some of electronics underneath the grid –Reduce side segmentation Parts acceptance and procurement –Prototype HVPS procurement is in preparation –Parts list submitted to Quality Assurance Branch Integration highly coupled to design –ACD I&T manager appointed to work with design team

17. GLAST LAT ProjectDOE/NASA Review of the GLAST/LAT Project, Feb. 13-15, 2001 J. Ormes/R. Larson 17 Summary ACD team is in place and progress is quite rapid –Necessary trade studies underway Optimization of side segmentation Optimization of redundancy Optimization of light collection; tile thickness –Requirements have been established Near term schedule advanced –Received additional funding for FY '01 –Added staff to prepare for PDR –Draft Level 6 schedule is in hand Grass roots costing being scrubbed