GLAST Large Area Telescope LAT Pre-Shipment Review Systems Engineering Pat Hascall

SE Overview 1

GLAST LAT Project September 15, 2006: Pre-Shipment Review

Presentation 3 of 12

GLAST Large Area TelescopeGLAST Large Area Telescope

LAT Pre-Shipment Review

Systems Engineering

Pat HascallSystems Engineering

Stanford Linear Accelerator Center

Gamma-ray Large Gamma-ray Large Area Space Area Space TelescopeTelescope

SE Overview 2



LAT System Engineering OverviewLAT System Engineering Overview

• Requirements Baseline Maintenance– Specifications– Interface Control Documentation– Waiver Requests (See Section 10)

• Design Baseline Maintenance– Design Documentation Configuration Management– Design Changes Since PER

• Requirements Verification Plan (See Section 5)

– Traceability to tests, analysis, inspection– Running Sell Process with GSFC Project Office

SE Overview 3



Documentation StatusDocumentation Status

• The SE related documentation: see next chart (s)

– LAT Specification Current

– Traceability to verification complete

– Verification Cross Reference Matrix Released

– LAT Test Plan Released

– Three pending changes to LAT-S/C ICD: See later chart

– Several Waivers in Process: See NCRs and Waivers– One pending requirement update in 433-IRD-0001

• I&T documentation status: See I&T presentation

• QA documentation status: See QA presentation

No significant documentation liensNo significant documentation liens

SE Overview 4



Documentation Status (continued)Documentation Status (continued)

• RFAs from previous reviews – See Systems Engineering Web site for dPDR, PDR, and

CDR RFA closures• http://www-glast.slac.stanford.edu/

systemengineering/RFAS/RFAS.htm– Two PER RFA’s open

• #1: Alignment Verification– Response: Updated response provided

• #8: NCR/Waiver Review for Unidentified Current and Residual Risks

– Response: LAT project/NASA review and update included in this package

SE Overview 5



Key Documentation Key Documentation

Mission Level Documents433-SRD-0001: GLAST Science Requirements Document 433-IRD-0001: GLAST Science Instrument – Spacecraft Interface Requirements Document 433-SPEC-0001: GLAST Mission System Specification 433-OPS-0001: GLAST Operations Concept 433-MAR-0001: Mission Assurance Requirements (MAR) for GLAST LAT 433-RQMT-0005: GLAST EMI Requirements 433-ICD-0001: GLAST LAT-GBM Burst Interface Control Document1196 EI-Y46311: SC-LAT Interface Control Document 1196 EI-S46310: 1553 Interface Control Document LAT Level DocumentsLAT-SS-00010: LAT Performance Specification LAT-SS-00778: LAT Environmental Specification LAT-SS-00115: Mechanical Subsystem Specification (in final release cycle)LAT-SS-00715: TCS Performance Specification LAT-SS-00019: Trigger & Dataflow Subsystem SpecificationLAT-TD-00399 Software Requirements Specification LAT-SS-00016: ACD Subsystem Specification LAT-SS-00017: Tracker Subsystem Specification LAT-SS-00136: Power Subsystem Specification LAT-SS-00018: CAL Subsystem Specification LAT-MD-00446: LAT SVAC Plan LAT-MD-00408: LAT Performance Verification Plan LAT-MD-02730: LAT Performance and Operations Test Plan LAT-MD-07658: LAT Verification Cross Reference Matrix

SE Overview 6



SC-LAT ICD Pending ChangesSC-LAT ICD Pending Changes

ICN # Title Description Status

-096Unregulated Power Voltage

For shorts periods of time, the SC will be unable to provide the minimum 25V for the unregulated feeds. The voltage may get as low as 23V. GSFC review

-099 LAT IntegrationThis is an appendix to the ICD that is meant to capture agreements for Observatory I&T activities. Approved

-100 LAT ImpedanceIncorporate into ICD the as-measured LAT differential impedance.

Pending SC PRU Measurement

-109 LAT VCHP OvervoltageThe SC limits the voltage on the SIU and DAQ feeds but not on the VCHP feeds. In review

-111 MLI Interface Minor changes to the MLI interface, i.e. velcro size In sign off

– SC-LAT ICD EIY46311-000C is released–The table below lists pending changes

SE Overview 7



Overview of Subsystem Changes Since PEROverview of Subsystem Changes Since PER

• Design Changes Flowed From LAT MRB Process– Changes incorporated in final design documentation– All changes consistent with LAT-SC ICD

• Residual Design Liens Against Flight Software discussed in FSW presentation

• Mechanical– Minor blanket modifications

• Flight Software– Boot code updated

SE Overview 8



LAT End Item Data PackageLAT End Item Data Package

• The LAT Project provides an EIDP consisting of the following documents, data, and other materials– LAT-level subsystem-level requirements specifications

• Acceptance test data packages for subsystems– Requirements verification plans and test plans– LAT-level test procedures and reports, and links to test execution

logs and records– Open nonconformance reports and waivers– Integration and test records

• Assembly and Inspection Data Sheets• Integration records: mate/demate, installation logs, material mix

records– EGSE and MGSE documentation

• All LAT project documentation is maintained in hardcopy and electronic form at SLAC– The EIDP is a subset

• EIDP posted on the Pre-Shipment Review Agenda Page:– http://www.slac.stanford.edu/exp/glast/flight/rdm/sasspreship/

lat_sasspreship_review.html

• EIDP is currently being populated

SE Overview 9



Residual RisksResidual Risks

ID #Risk Rank

Risk DescriptionRisk Mitigation Status

SE - 011

Low

If individual tracker towers do not meet performance requirements due to manufacturing issues (e.g. wire bond breaks) then the LAT may not meet science requirements

•Reduced On Orbit temperature excursions

• Optimized placement of towers A/B based on individual tower performance

•Trending tracker efficiency/dead channels throughout integration testing

• No current concern for mission performance over life expected

Proj Mgt - 009 Low

If Tracker Noise Flares (NCR684), increase an order of magnitude and spread then some risk to overall tracker noise performance

• Monitor for occurrence• Verified no significant change during TVAC•Continue trend in Observatory Test

• Observed noise is an order of magnitude lower than a concern level and isolated

• No increased trend during system test to date

Elect - 005

Low

If spare GASU (AEM) FPGA failure (NCR897) is inherent in the design then mitigation on flight unit could impact schedule

• Complete part failure analysis •Survey of part failure records• Complete assessment of root cause

• Part failure analysis & survey complete

•Root cause identified, no known flight issue

SE Overview 10



Residual Risks (Cont)Residual Risks (Cont)

ID #Risk Rank


Elect - 006 Low

If SIU reboot (NCR 880) is an inherent design flaw then loss of data until reboot completed

• Completed existing data analysis• Additional diagnostics/data gathering plan in place

•Data gathering plan in place should another reboot occur

SE-014

Low

If ACD PMTs become noisy again (NCR626), then ACD ability to perform background rejection may be reduced

• More stringent PMT high voltage screening •All noisy tubes were replaced in the flight ACD• Flight PMTs are operated at voltages less than voltages that produced noise

• No new noisy PMTs have appeared after thousands of tube-hours of screening at high voltage•Conservative Wiebull prediction shows extremely low chance of potentially noisy PMTs making it through the screening.

Elec-007

Low

If the unused QCLK floating pins on PCI FPGA impacts part reliability then mission redundancy may be reduced

• Completed vendor analysis indicating no known failure mode or impact on reliability• Completed LAT analysis indicating no known failure analysis• Consider risk of grounding pins should alternative need to open box occurs

• GSFC Mission Office review and concurrence, no known risk at this time

SE Overview 11




ID #Risk Rank


Elect - 009 Low

If EPU reboot (NCR 881) is an inherent design flaw then loss of data until reboot completed


• Data gathering plan in place should another reboot occur

Elect - 011 Low

If EPU 0 reboot (NCR 902) is an inherent design flaw then loss of data until reboot complete0



Elect-012

LowIf LATC Verify Errors (NCR855) re-occur on orbit then LAT will not execute science run until corrected

• Completed existing data analysis• Additional diagnostics/data gathering plan in place•Consider FSW changes to allow science run with these specific Errors

• No re occurrence reported since FSW 0-6-9

• Data gathering plan in place should another LATC verify error occur

SE Overview 12




ID #Risk Rank


Elect - 014 Low

If EPU reboots (NCR 948) are an inherent design flaw then loss of data until reboot completed



Elect - 015 Low

If EPU reboots (NCR 949) are an inherent design flaw then loss of data until reboot completed



SE Overview 13




ID #Risk Rank


Proj Mgt - 012 Low

If decision to conduct tracker environmental tests with non flight cable configurations (Waiver 433-0360) results in future failure then tracker redundancy may be compromised

• Tracker cables are redundant• Full CPT’s conducted in flight configuration•Trackers to be tested at LAT and Observatory Environmental tests

•No failures to date

•Continue to monitor thru test program

Proj Mgt - 014 Low

If Tracker flex cables/MCM’s fail that had failed coupons (Waiver 433-0367) then Tracker redundancy may be impacted

• Tracker cables/MCMs are redundant•Trackers to be tested at LAT and Observatory Environmental tests

• No failures to date

•Continue to monitor thru test program

Proj

Mgt-

018

Low

If finalization of FSW Science Algorithms is delayed or impacts LAT functional performance then Observatory Test Schedule could be impacted

•FSW build (B1.0) plan in place to add Science requirements

• New Science Algorithms do not impact established LAT performance

• Significant CPU/Memory margin to accommodate minor growth

•Plan to maximize early LAT runtime at SASS

•Well defined build planning with Proj Office involvement in change control

•TVAC eval of CPU peak performance indicate small (acceptable) temperature increase with worst case utilization

•Non interference LAT runtime planning in work

SE Overview 14



LAT Mass Properties LAT Mass Properties LAT Mass Properties Report LAT-TD-00564-12

LAT Mass Properties Summary Effective Date: 24-Apr-06Martin Nordby Print Date: 24-Apr-06

May-06Mass (kg) Estimate Alloc.

TKR 524.5 530.0 (kg) %

CAL 1381.7 1440.0 Parametric 21.4 0.8%ACD 281.6 295.0 Calculated 40.4 1.4%Mech 351.5 386.6 Measured 2727.2 97.8%Elec 242.5 240.0 Total 2789.0 100%Systems 7.1 8.0

LAT Total 2789.0 2899.6Rsrv/Margin 211.0Rsrv/Margin* 7.6%Allocation 3000.0* AIAA G-020 recommended min reserve = 3.8%Allocations per latest mass CCB on 3 Nov 2004

Center of Mass (mm)CMx -1.57 -20 < CMx < 20CMy -1.20 -20 < CMx < 20CMz -65.99 CMz < -51.2Ht off LIP 170.21 Ht < 185

Second Moment of Inertia (kg-m2)Ixx 1039.4 1400.0Iyy 996.8 1350.0Izz 1385.1 1580.0

Mass properties evaluated in LAT Coordinate System

Mass Estimate Breakdown

2400

2500

2600

2700

2800

2900

3000

Oct

-99

Jan-

00A

pr-0

0Ju

l-00

Oct

-00

Jan-

01A

pr-0

1Ju

l-01

Oct

-01

Jan-

02A

pr-0

2Ju

l-02

Oct

-02

Jan-

03A

pr-0

3Ju

l-03

Oct

-03

Jan-

04A

pr-0

4Ju

l-04

Oct

-04

Jan-

05A

pr-0

5Ju

l-05

Oct

-05

Jan-

06A

pr-0

6Ju

l-06

Oct

-06

Date

Mas

s (k

g)

125

150

175

200

225

250

275

300

Cen

ter

of

Ma

ss H

eig

ht

Ab

ov

e L

.I.P

. (m

m)

Mass Budget Review ThresholdTotal Allocated to S.S. LAT Mass EstimateCtr of Mass Est (off LIP)

I-PDR

I-CDR

I-SRR

294.9

I-PSRLAT ReserveLAT Margin 153.7

Prop

dPDR

Subsystem Allocation

CoM Ht off LIP

LAT Est Mass

Page Number 15



LAT Power StatusLAT Power Status

7-Sep-06 Estimate PARA CALC MEAS SPEC

Item (Watts) (Watts) (Watts) (Watts) (Watts)

ACD 11.3 0.0 0.0 11.3 11.5

Tracker 159.2 0.0 0.0 159.2 160.0

Calorimeter 67.8 0.0 0.0 67.8 71.0

Trigger & Data Flow 297.3 0.0 0.0 297.3 327.5

Grid/thermal 26.2 0.0 0.0 26.2 35.0

Instrument Total 561.8 0.0 0.0 561.8 605.0

Instrument Allocation 650.0

% Reserve 15.7%LAT Power

400.0

450.0

500.0

550.0

600.0

650.0

700.0

Jan-99 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06

Po

we

r -

Wa

tts

PDR7/30/02

I

CDR5/1/03

I

PSRR09/06

IGoals estimated using guidelines given in ANSI/AIAA G-020-1992 "Estimating and Budgeting Weight and Power Contingencies for Space Craft Systems"

PDR Reserve Was 15.2%CDR Reserve Was 13.4%

Goal for PSRR Reserve > 5%

PARA - Best Estimate based on conceptual design parametersCALC - Estimate based on Calculated power from detailed design documentationMEAS - Actual power measurements of components

SE Overview 16



LAT Power Status (Continued)LAT Power Status (Continued)

• Survival Power

Component Current Subsystem Power Estimates (W)

Alloc. PARA CALC MEAS Total Margin

On-Orbit Average Power Total1 278.00 0 0 211.3 211.3 31.6%

Regulated VCHP Power Total 58.00 0 0 44.5 44.5 30.3%

Unregulated Passive Survival Power 220.00 0 0 166.8 166.8 31.9%

1Power status reflects the LAT steady state orbit average. Numbers do not reflect transition into or out of survival mode, i.e. early orbit operations.

SE Overview 17



FSW Resource UsageFSW Resource Usage

Resource Total Available Current

Usage

Margin Factor

Source

EPU Boot EEPROM (SUROM)

256 kB 62 kB* 4* B0-6-11

SIU Boot EEPROM (SUROM)

256 kB 62 kB* 4* B0-6-11

EPU EEPROM 6 MB 0.59 MB 10 B0-6-11

SIU EEPROM 6 MB 0.73 MB 8.2 B0-6-11

EPU CPU cycles 200% in 2 EPUs 40% > 5 Estimate

SIU CPU cycles 100% in 1 SIU 25% 4 Estimate

EPU memory 128 MB 16-32 MB 4-8 Estimate

SIU memory 128 MB < 16 MB 8 Estimate

* Storing multiple copies (4 currently to use available memory) for risk mitigation

SE Overview 18



Instrument Bandwidth ResourcesInstrument Bandwidth Resources

Resource Max Total BW limited

by Hardware

Max limited by SC-ground

transmission

Ave current BW at 10 KHz max

trigger rate*

Ave current BW at 2 KHz

nominal trigger rate*

Margin Factor

(for 10 KHz rate)

Detector to GASU-EBM 45 N/A 10 2 4.5

GASU-EBM to EPU-CPU 20 N/A 5 1 4

EPU-CPU to GASU-EBM 2.5 0.075 0.04* 0.02* 2

GASU-EBM to SIU-CPU 5 0.15 0.08* 0.015* 2

SIU-CPU to Spacecraft 5 0.15 0.08* 0.015* 2

EBM: Event-Builder Module

EPU: Event-Processing Unit

SIU: Spacecraft Interface Unit

• LAT communication, bandwidth (BW) in Mbyte/sec

* Present performance of event filter for EPU-CPU, still being optimized. Eventually the physics filter will be adjusted/loosened to take advantage of the max average bandwidh

SE Overview 19



Unit Run TimeUnit Run Time

• These unit run times start after the LAT was completely integrated and cover through the completion of the CPT after TV– Does not include integration testing– Does not include unit testing

SIU-P SIU-R GASU-P GASU-R EPU-P0 EPU-P1 EPU-R Towers ACD ACD HV1

ACD HV2

PDU-P PDU-R

1 949 0 949 0 949 949 0 949 949 949 0 949 02 0 541 0 541 0 541 541 541 541 0 541 0 5413 62 0 0 62 62 62 0 62 62 62 0 62 04 0 30 0 30 30 0 30 30 30 0 30 30 05 0 30 30 0 30 0 30 30 30 0 30 0 306 19 0 19 0 0 19 19 19 19 19 0 0 197 0 3 3 0 3 0 3 3 3 0 3 3 08 0 3 0 3 0 3 3 3 3 3 0 0 39 23 0 0 23 23 23 0 23 23 0 23 0 23

Totals 1053 608 1001 659 1097 1598 627 1661 1661 1033 628 1044 617

Config No.

LAT UNITS ON

SE Overview 20



LAT System Engineering SummaryLAT System Engineering Summary

• Process for verification closure with GSFC in place• SE Review of LAT Environmental Tests and verification status

indicate ready to ship