GLAST Large Area Telescope: Electronics, Data Acquisition & Flight Software

1. Gamma-ray Large Area Space Telescope GLAST Large Area Telescope: Electronics, Data Acquisition & Flight Software LAT Electronics Design Engineering Gunther Haller Stanford Linear Accelerator Center Manager, Electronics, DAQ & FSW LAT Chief Electronics Engineer haller@slac.stanford.edu (650) 926-4257

2. LAT Electronics Physical TKR Front-End Electronics (MCM) 16 Tower Electronics Modules • DAQ electronics module (DAQ-EM) • Power-supplies for tower electronics ACD Front-End Electronics (FREE) TKR CAL Front-End Electronics (AFEE) CAL Global-Trigger/ACD-EM/Signal-Distribution (GAS) Unit* 3 Event-Processor Units (2+1 spare) • Event processing CPU • LAT Communication Board (LCB) • Storage Interface Board (SIB) Spacecraft Interface Unit • Storage Interface Board (SIB): EEPROM SC MIL1553 control & data • LAT control CPU • LAT Communication Board (LCB): LAT command and data interface Power-Distribution Unit (PDU)* • Spacecraft interface, power • LAT power distribution • LAT health monitoring * Primary & Secondary Units shown in one chassis

3. LAT Electronics • TKR: Tracker • CAL: Calorimeter • ACD: Anti-Coincidence Detector • EPU: Event Processor Unit • SIU: Spacecraft Interface Unit • GAS Unit: Global Trigger-ACD-Signal Distribution Unit • TEM: Tower Electronics Module • There are • 2 prim EPU’s, 1 redundant EPU (not shown) • 1 prim SIU, 1 redundant SIU (not shown) • 1 prim GAS, 1 redund. GAS (not shown) • 1 prim PDU (not shown), 1 redundant PDU (not shown)

4. Tracker Electronics • TKR sub-system electronics • Si-Strip Detectors • 24 GTFE (GLAST Tracker Front-End) ASICs (1,536 signal channels) • 2 GTRC (GLAST Tracker Readout Controller) ASICs • MCM (Multi-Chip Module) • Flex-cables • Presented in tracker sub-system presentation GTRC ASIC GTFE ASIC

5. Calorimeter Electronics • CAL sub-system electronics • Diodes • 48 GCFE (GLAST Calorimeter Front-End) ASICs • 4 GCRC (GLAST Calorimeter Readout Controller) ASICs • AFEE (Analog Front-End Electronics) board • Presented in calorimeter sub-system presentation GCRC ASIC GCFE ASIC

6. ACD Electronics • ACD sub-system electronics • PMT’s • 18 GAFE (GLAST ACD Front-End) ASICs • 1 GARC (GLAST ACD Readout Controller) ASIC • FREE (Front-End Electronics) board • High-Voltage Supply board (not shown) • Presented in ACD sub-system presentation GAFE ASIC GARC ASIC

7. DAQ Electronics • DAQ sub-system electronics • SIU, EPU, GASU, PDU, TEM, Harness, Instrument Software • Example shown is Tower Electronics Module Engineering Unit • Presented in DAQ & Instrument Software presentations

8. Changes since PDR • Spacecraft Selection and Meetings: • PDU was moved to opposite side of SIU to match SC power/C&DH physical partitioning • Signal levels (discretes, 1 PPS, Science Interface, GBM GRB signal) were officially changed to LVDS (before undefined or RS422), March 03 • Recently finalized power, analog monitoring, and discrete interface to SC • Defined MIL1553 command set/interface • Separated SIU prime and redundant into separate (and identical) crate assemblies since cross-connection to SC prime and redundant was solved on the SC-LAT interface level and lead to removal of direct SIU-SIU inter-connections Before SC selection After SC selection

9. Changes since PDR (Con’t) • Event-Builder was moved from CPU crates to GAS unit • Reduced complexity of inter-connections • Reduced hardware from 3 event-builder blocks to 2 (1 prime, 1 redundant), and power dissipation from two event-builder blocks to one • SIU crate was modified to be the same as EPU crate • Removes mechanical, thermal, electrical design effort for one assembly • Moved SC science interface from Spacecraft Interface Board in SIU to event-builder in GASU (renamed SIB to Storage Interface Board) • Additional benefit that SIB board is almost identical to existing SECCI version (both boards are designed by NRL/Silver Engineering), major simplification • Science interface on GASU is small change since GASU already transmits event data to LAT CPU’s, so additional target is incremental • Added SIB board in each EPU crate to provide local EEPROM • Simplification in software effort. • No remote booting code development/testing required.

10. LAT Spacecraft Interface • Power (to SIU, PDU, Heaters) • 28V regulated and unregulated • MIL1553 (to/from SIU) • Commanding, house-keeping • Science Interface (from GASU) • Transport of science data to spacecraft solid-state recorder 1-PPS timing signal (to GASU) • Timing pulse • GBM GRB Candidate signal (to GASU) • Notification of candidate Gamma-Ray Burst (GRB), from GBM routed through SC • Discretes (to/from SIU)) • Pulsed and level digital signals from and to spacecraft • Analog Monitoring (from entire LAT) • Temperature and voltage monitoring by SC; available even when LAT is off • Two sets of power & signals: Prime and redundant • Spectrum Astro SC-LAT Interface Document

11. Power Interface to Spacecraft • All power feeds from spacecraft can be turned off/on via ground • Heaters are on separate power feeds • Each SIU is powered via one dedicated SC power feed • Rest of LAT power is on main feed • One primary, one redundant • Cross-connected in LAT PDU • Can use either SC main feed to power either PDU • Spacecraft turns off SIU/DAQ feeds when going to survival mode • LAT start-up ICD: LAT-TD-01536 • Describes process of cold and warm boot (bring-up) of LAT

12. Spacecraft 1-PPS and GRB Candidate Signal (to GASU) • 1-PPS signal from spacecraft (prime and redundant) are connected to both GASU boards (prime and redundant) • GASU selects which SC signal to use • Result is fanned out to all processor crates (SIU’s as well as EPU’s) • prime and redundant signals are connected to discrete RAD750 processor inputs (PID’s) • Software select which 1-PPS to use • SC-LAT components are fully cross-connected • Same for GBM GRB candidate signal • LAT needs to know which SC-port or GBM-port to listen to • Ground commanding

13. Spacecraft Discrete Signals & MIL1553 (to SIU) • Discrete Signals from SC to LAT: • Discrete LVDS-signals from spacecraft prime and redundant are connected to both SIU crates (prime and redundant) • Reset discrete: P and R SC signal is logically Or’ed and used as CPU reset • Spare discretes: CPU selects whether to use P or R input and result is routed to CPU discrete inputs (3 prime and 3 redundant) • Discrete Signals from LAT to SC (not shown) • Discrete LVDS-signals from LAT SIU P and SIU R are driven to both, prime and redundant, spacecraft C&DH (Control & Data Handling) systems • MIL1553 Command/Data (not shown) • Command & Data interface to both, SIU P and SIU R

14. LAT-SC Science Interface (from GASU) • GASU event builder • Directs data from TEM’s to any of the CPU’s (not shown) • Directs data from CPU to CPU • Directs data from CPU to spacecraft • Any CPU can direct data via either GASU Event-Builder (P or R) to SC • Data is driven to both SC sections (P and R) • SC needs to select which GASU to listen to • LAT GASU needs to know which SC port (P or R) flow-control line is active • All configured via ground commanding

15. Connections LAT/Spacecraft and to LAT EMI Shield ACD HTR EGSE EPU SIU P GASU PDU SIU R TEM HTR LAT EMI shield Heater & Monitoring Box Spacecraft

16. Grounding and Shielding • EMI/EMC: GSFC-355-RQMT

17. Shielding

18. Power Allocation

19. Monitoring • Spacecraft monitors • Voltages & Temperatures • PDU, SIU, GASU, VCHP switches • Temperatures • Locations outside LAT EMI shield • PDU monitors • Voltages & Temperatures • TEM, EPU, SIU • Temperatures • Locations outside LAT EMI shield • GASU monitors • Voltages & Temperatures • ACD • TEM monitors • Voltages & Temperatures • CAL, TKR

20. Temperature Monitoring (SC & PDU) SC Action if low or high limit is reached

21. Temperature Monitoring (TEM & GASU) Sensor processed by • LAT Instrumentation Plan: LAT-SS-00890 • Spacecraft ICD: GSFC-IRD-433

22. Voltage/Current Monitoring Note: LAT does not monitor currents or voltages on SC-LAT feeds

23. Heater Control • Survival Heaters (GRID & VCHP Anti-Freeze) • Powered by SC unregulated feed • Block redundant prime and redundant set • Thermostat control, not controlled by LAT electronics • Survival & Operational Heaters (VCHP) • Powered by SC regulated feed • Block redundant prime and redundant set of 12 heaters • Controlled by LAT SIU • Temperature monitoring • Software algorithm in CPU • 12 hardware switches in SIB • Hardware watchdog to power heaters as default • Final responsibility of not exceeding low or high survival temperatures lays with SC • LAT-SS-00715 Thermal Control System ICD

24. Instrument Protection: High and Low Temperatures • GRID/Anti-freeze heaters • turn on when T is below thermostats • no LAT active control • VCHP heaters • LAT responsible for operational control • Survival T • if T too high or too low • SC puts LAT into safe mode • SC turns-off LAT SIU and Main DAQ power • SC may need to switch heater feeds in cold case • SC responsible for LAT • Document: LAT-TD-01553

25. Instrument Protection: ACD PMT Protection • LAT turns down PMT high-voltage levels during SAA passage to protect PMT’s • In response to SC SAA notification, or • When SC heard-beat is lost • PMT’s are hardware protected within ACD in case of DAQ mishap • ACD HV supplies have built-in protection to limit current to PMT’s • Document: LAT-TD-01553

26. Instrument Protection: Over-Current • LAT does not monitor current on SC feeds • SIU power feed not fused on LAT, SC has current limit switch • Main DAQ feed power not fused on LAT, SC has current limit switch • LAT PDU distributes 28V to about 20 LAT loads. Each sub-feed is fused on PDU via poly-switches • Tower Electronics Modules convert and distribute power (+1.5V, 2.5V, 3.3V, 0-100V, 0-150V) to TKR & CAL: Feeds are fused on TEMs via poly-switches

27. Summary • Interface to SC defined • Grounding and shielding of LAT defined • Monitoring of temperatures, voltages, and currents defined • Heater control defined • Instrument protection tree documented • SC, not LAT has final responsibility to protect instrument from damage in respect to temperatures • SC has to meet power quality specifications to not damage LAT • LAT is responsible for SAA PMT survival • First layer of protection software controlled • Second layer (back-up) protection: hardware • Over-current protection of electronics components via poly-fuses