GLAST Large Area Telescope: Planning Meeting September 3, 2003

1. Gamma-ray Large Area Space Telescope GLAST Large Area Telescope: Planning Meeting September 3, 2003 AntiCoincidence Detector (ACD) Subsystem WBS: 4.1.6 David J. Thompson Thomas E. Johnson NASA Goddard Space Flight Center Subsystem Manager/Instrument Manager David.J.Thompson@nasa.gov Thomas.E.Johnson@nasa.gov

2. CRITICAL MILESTONE CHART 1 1

4. Near Term Milestones - 3 Month Plan

5. Interdependencies • Funding – IPO, availability of LAT resources, GLAST Project, FY03 carryover • ASICs – LAT Electronics group support, Product Assurance (packaging, qual, screen, and test). Status on rapid package as well as flight packaging? • Delivery of FREE Boards and Parts to Electronics • EGSE/G3 – Ongoing development with I&T and electronic groups • ACD/GASU – Cable details and system clock testing. Need signed off and configuration controlled drawing for cables. • Grid to Base Frame installation – Outline drawing and available date for installation

6. Flight Hardware Procurements • TDA’s – December completion, design problem could impact delivery. • ASICs – Receive rapid packaged ASICs on ?, Submit ASICs for flight packaging 1-2 weeks after receiving rapid packaged chips • FREE PWBs – September/October procure, available November • Electronic parts – Completed, problem with HV capacitor • HVBS Assy – August Start – February Completion. Problem with HV capacitor causes minor (~ 1 week) delay. • Shell Panels – Late September completion • PMT parts – All parts procured, all housings completed next week, RN PCB’s due in soon, HV Cap will delay assembly completion. • Base Frame Mechanical Parts– July-August, complete December • TSA Mechanical Parts – July-August, complete December

7. Manufacturing Plans • TDA’s – Completed • ASICs qual, screen and test plan – In review • FREE and HVBS using standard process • PMT Assy Plan– In sign off • Mechanical Parts– Using standard plans • Clear Fiber Cables – Procedure in final review, beginning fab of EU units as well as training techs.

8. Unresolved Assumptions • Thermal Blanket interface (outline drawing) • Grounding (outline drawing and grounding plan) • Rates data (resolved in principle) • Link up date for Grid to Base Frame interface • EGSE cable lengths – GASU to EGSE ~14m • GASU has to work in TVac and Vibration (with isolation)

9. New Issue #1 • TDA design problem Interference between WFS and TDA tiedown at this point • Three Potential Solutions identified. • Move some TDA tiedowns • Reduce bending radius of WSF • Decrease size of TDA tiedown • Potential impact to shell panels and TDA Tiedowns • Good news is that Fermi staffing issue is under control, bad news is they have to refocus their efforts to helping solve this problem.

10. New Issue #2 • High Voltage Capacitor does not meet requirements. Dielectric strength out of spec. • Predicted life time of capacitor would be reduced by a factor of ~2.5 • No life testing results available to verify predictions. Engineers expect that actual would be worse than predicted • Long lead part (original quote of 12 weeks) • Ordered ~16 weeks ago. Parts came in a little late and screening on first batch has just been completed • Manufacture has agreed to replace part at no cost. Negotiating for a shorter lead time (~7 weeks may be possible) as well as keeping 40 of the original parts so that testing program can continue. • Part is used in PMT assembly as well as HVBS’s. • Used on 2nd (middle) resistor network board. This will delay PMT assembly completion. Work-a-rounds include installing all 1st boards as well a reshuffling work for assembly techs. Will assemble qual PMTs using “non-spec” parts. • Impact to HVBS will be minimal. Proceed with qual unit HVBS using “non-spec” part.

11. Issues and Concerns - updates • Need for a final Qualification and Screening Plan for ASICs is a concern • LAT has a general Q&S Plan for ASICs • Issue has been the specific implementation (particularly testing) needed for the ACD ASICs • Working with LAT Parts Control Board in consultation with Goddard parts engineers to finalize details of the plan. Agreed in principle, but documentation is still needed. Test boards are being designed. • Shortage of test equipment at Goddard is a concern • In particular, equipment needed for the ASIC Q&S program seems to be in short supply • Working with Goddard local laboratory and Engineering Directorate to locate or repair needed equipment. Not much success so far. • Requested Goddard funding (~$60K) for additional equipment. None provided yet, requiring unbudgeted expenditures to keep testing program on schedule.

12. Issues and Concerns - new • Reduction of support for ACD TDA production at Fermilab is an issue. • Accelerator shutdown, required vacation, and extended medical leave have seriously reduced the staffing available to continue the TDA fabrication. • Issue appears to be resolved. Axiom operator (actually 2 this week) vacancy has been resolved. They will work a second shift if required to maintain schedule. Have been assured that this job is a high priority, second only to the beam shutdown. Alex and I will be going to Fermi next week. • Reduction of support for ACD mechanical engineering at GSFC is an issue. • Problem in another flight project (XRS on Astro E2) has siphoned off some of the time of ACD mechanical engineers • Working with Goddard management to retain enough support to maintain schedule. Receiving additional support to backfill support lost to XRS • ASIC Yield – 50% yield at ambient temperature prior to thermal cycling or burn-in

13. Issues and Concerns - updated • Late delivery of G3 Test Stand/EGSE from LAT Electronics and I&T is a concern • Scheduled for August, recently slipped to November/December • Planned for testing of multiple FREE cards and Electronic Chassis, scheduled for August - November • Developing workarounds, using older G2 Test Stands and bench electronics. Interfaces are less like the flight interface, but should allow much of the testing. • Developing the G3 software before the arrival of the hardware, to minimize the startup delay once the G3 Test Stands arrive. • G2 will be testing flight hardware, need documentation. • ACD cost increases and availability of FY03 funding is an issue • Cost to Complete exercise identified increased costs for ACD • Goddard Engineering Directorate has provided additional Civil Service support, replacing contractors with CS personnel wherever a qualified Civil Servant could be found. • GLAST Project has offered some support. • Additional ACD funding included in the current LAT request.

14. Open Design Issues - update • OPEN: Outline drawing that defines some interfaces with LAT is still not complete (blanket attachment, grounding, cable tie-downs, optical survey mounts). Action Plan: Work with LAT mechanical design team to resolve open issues by August 29. Status unchanged. • CLOSED: LAT Electronics group requested a change in the backshell of the connector to the ACD. This change requires a change in the bracket that holds the connector, and this bracket is a structural element. Modification should be straightforward, but must be analyzed. Action: Decided to stick with original design. • CLOSED: FREE Board design updates and finalization. Action: Design complete and in fabrication. • OPEN: Need updated interface loads following Grid design changes. Action Plan: Review ACD analysis when updated loads are received. ACD will not delay fabrication of mechanical components due to this open issue (slight risk in doing so). Status unchanged. • OPEN: Discovered interference between some wave shifting fibers and TDA flexures. Action Plan: Re-design and re-analyze to resolve.

15. Mechanical and EEE Parts - update • Mechanical Parts and Materials - ALL APPROVED • PMTs – Qualified, tested, and screened (final report in draft form now) • EEE Parts • FREE - 36 different part types; approximately 830 parts per board. All parts approved by PCB with the following exceptions. • MAX145 and MAX5121 being qualified by GSFC parts group (chips provided by Calorimeter). • ASICs in fabrication. S&Q plan is complete and has been reviewed by members of the PCB. Detailed GARC test procedure in review and draft GAFE test procedure is being circulated • MAX494 was recently approved following radiation testing • HVBS - 38 different parts types; 108 total parts per board • 4 parts are not yet approved (DPA needed on 3 capacitors, screening needed for one wire) • High voltage capacitor was rejected, did not meet specification • Resistor network - 9 different parts types; 26 total parts • One connector is not yet approved, waiting for screening