1. GLAST Large Area Telescope:
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
(650)

2. LAT Electronics Physical
TKR Front-End Electronics (MCM)
ACD Front-End Electronics (FREE)
CAL Front-End Electronics (AFEE)
TKR
16 Tower Electronics Modules
DAQ electronics module (DAQ-EM)
Power-supplies for tower electronics
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
GTRC ASIC
GTFE ASIC
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

5. Calorimeter Electronics
GCRC ASIC
GCFE ASIC
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

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 Quantity Cold Current Hot Case Case Estimate
Quantity
Cold
Current
Hot Case
Case
Estimate
Allocation
Total
286.20
313.79
318.00
359.85
Mech On-Board Power 1
38.00
35.00
TEM--Tower Electronics Module
43.20
46.70
48.00
54.32
TEM board 16
2.70
2.92
3.00
3.39
Power Supplies
148.50
163.29
165.00
186.72
TKR,CAL,TEM
9.28
10.21
11.67
GASU--Global Tgr ACD, Signal Dist. Unit
19.80
22.37
22.00
24.90
EP, AEM, Sig Dist & Supplies
Other Boxes
74.70
81.43
83.00
93.92
SIU--Spacecraft Interface Unit
21.60
23.89
24.00
27.16
EPU Total
38.70
42.60
43.00
48.66
EPU--Event Processor Unit 2
19.35
21.30
21.50
24.33
PDU--Power Distribution Unit
14.40
14.93
16.00
18.11

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

20. Temperature Monitoring (SC & PDU)
Location of Sensor
Sensor Type
Sensors by
processed
Spacecraft
PDU
Prime
Redundant
ACD Tiles
Thermal 5
ACD TSA Shell (inside)
ACD TSA Shell (outside) 2
ACD BEA-Grid interface
ACD PMT Rail 4
Calorimeter Baseplate 16
SIU
EPU 3
GASU
TEM DAQ Board
TEM pwr Supply
Radiator Anti-Freeze Htr
Radiators 8 10
Grid-Radiator interface
Grid Make-up Heaters
VCHP-XLHP interface 12
X-LAT Plate
VCHP-DSHP interface
Grid
VCHP's Reservoir Htr 24
VCHP Reservoir Htr Pri/Sec
Voltage
Spare Temp. Channels
SC Action if low or high limit is reached

21. Temperature Monitoring (TEM & GASU)
Sensor processed by
Location
Sensor Type
TEM
GASU
Prime
Redundant
ACD FREE
Thermal 12
CAL AFEE
128
AEM Power Supply 1
AEM DAQ Board
TKR Cables
256
LAT Instrumentation Plan: LAT-SS-00890
Spacecraft ICD: GSFC-IRD-433

22. Voltage/Current Monitoring
Location
Sensor Type
Sensed by Spacecraft
Sensed by PDU
Sensed by TEM
Sensed by GASU
Prime
Redundant
VCHP Reservoir Htr Pri/Sec
Voltage 4
SIU Pri/Sec 3.3/5V V 2
PDU Pri/Sec 3.3V V
GASU Pri/Sec 3.3/28V/3.3VA V 6
EPU 3.3V V
TEM 3.3V V 16
ACD FREE V 12
ACD FREE I
Current 1
ACD HV (I) 24
TKR V 64
TKR I
CAL V 48
CAL I
TEM DAQ V
TEM DAQ I
LAT SIU Bus V Pri/Sec
LAT VCHP Bus V Pri/Sec
Spare Voltage Channels 18
Total 32 20
256 43
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 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