GLAST Project Science Requirements Document (SRD) Table 3 ... · Objective For This Presentation:...

1

GLAST ProjectScience Requirements Document (SRD)

Table 3. Science Requirements on the GLAST Mission

Systems Engineering

Norman RiouxChris ConnorJulie McEnery

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SRD In Context of Mission RequirementsGLAST

Program Plan

433-PLAN-0008

(Level I Rqmts

Document)

MOC Funct &

Perf Rqmts

492-MOC-0002

LV-OBS ICD

LEVEL 1 NASA HQ

LEVEL 4 Subsystems

GBM Inst. Ops

Center Rqmts

GBM-REQ-1021

GROUND SYSTEM REQUIREMENTS

LEVEL 2 GLAST Project

LEVEL 3 SC, Instruments, LV

NASA HQ

GLAST Project

NASA/KSC

Spectrum Astro

SLAC

NASA/MSFC

MOC

NASA HQ

GLAST Project

NASA/KSC

Spectrum Astro

SLAC

NASA/MSFC

MOC

To LAT & GBM

Level 3

Science Rqmts

Document

433-SRD-0001

Science Rqmts

Document

433-SRD-0001

Mission System

Specification

433-SPEC-0001

Mission System

Specification

433-SPEC-0001

Ops Concept

Document

433-OPS-0001

Ops Concept

Document

433-OPS-0001

LAT Mission

Assurance Rqmts

433-MAR-0001

LAT Mission

Assurance Rqmts

433-MAR-0001

EMI Rqmts

Document

433-RQMT-0005

EMI Rqmts

Document

433-RQMT-0005

SC Performance

Specification

433-SPEC-0003

SC Performance

Specification

433-SPEC-0003

LAT-SC

IRD

433-IRD-0001

LAT-SC

IRD

433-IRD-0001

GBM-SC

IRD

433-IRD-0002

GBM-SC

IRD

433-IRD-0002

SSC Functional

Rqmts Document

433-RQMT-0002

SSC Functional

Rqmts Document

433-RQMT-0002

GBM Mission

Assurance Rqmts

433-MAR-0002

GBM Mission

Assurance Rqmts

433-MAR-0002

LAT Inst. Ops

Center Spec.

LAT-SP-00015

LAT Inst. Ops

Center Spec.

LAT-SP-00015

SC Mission

Assurance Rqmts

433-MAR-0003

SC Mission

Assurance Rqmts

433-MAR-0003

LAT-SC ICD

1196 EI-

Y46311-000

LAT-SC ICD

1196 EI-

Y46311-000

Detailed SC

Rqmts Document

1196 EO-R46502

Detailed SC

Rqmts Document

1196 EO-R46502

GBM-SC ICD

1196 EI-

Y46312-000

GBM-SC ICD

1196 EI-

Y46312-000

1553 Bus Protocol

Doc. 1196 EI-

S46310-000

1553 Bus Protocol

Doc. 1196 EI-

S46310-000

SAS Subsystem Spec

LOF Subsystem Spec

SAS Subsystem Spec

LOF Subsystem Spec

SAS Subsystem Spec

LOF Subsystem Spec

- Baselined Document

- In CM Process

- Baselined Document

- In CM Process

GDS Mission

Assurance Rqmts

433-MAR-0004

GDS Mission

Assurance Rqmts

433-MAR-0004

Ground System

Rqmts Document

433-RQMT-0006

Ground System

Rqmts Document

433-RQMT-0006

GBM Rqmts

Database

GBM-REQ-1007

GBM Rqmts

Database

GBM-REQ-1007

LAT Instrument

Performance Spec.

LAT-SS-00010

LAT Environ. Spec

LAT-SS-00778

LAT Instrument

Performance Spec.

LAT-SS-00010

LAT Environ. Spec

LAT-SS-00778

LAT Instrument

Performance Spec.

LAT-SS-00010

LAT Environ. Spec

LAT-SS-00778

LAT-GBM ICDLAT-GBM ICD

Mech. Subsystem Spec

TCS Performance Spec

Power Subsystem Spec

T&D Subsystem Spec

ACD Subsystem Spec

TKR Subsystem Spec

CAL Subsystem Spec

LAT-TKR ICD

LAT-CAL ICD

LAT-ACD ICD

LAT-ELEC ICD

LAT-TKR IDD

LAT-CAL IDD

LAT-ACD IDD

LAT-ELEC IDD

LAT-RAD IDD

Mech. Subsystem SpecMech. Subsystem Spec

TCS Performance Spec

Power Subsystem SpecPower Subsystem Spec

T&D Subsystem SpecT&D Subsystem Spec

ACD Subsystem SpecACD Subsystem Spec

TKR Subsystem SpecTKR Subsystem Spec

CAL Subsystem SpecCAL Subsystem Spec

LAT-TKR ICDLAT-TKR ICD

LAT-CAL ICDLAT-CAL ICD

LAT-ACD ICDLAT-ACD ICD

LAT-ELEC ICD

LAT-TKR IDD

LAT-CAL IDDLAT-CAL IDD

LAT-ACD IDDLAT-ACD IDD

LAT-ELEC IDD

LAT-RAD IDDLAT-RAD IDD

IMU SOW

CSS SOW

GPS SOW

PROP MOD SOW

SSR PFS

PDE PFS

GPIO PFS

LGIO PFS

RAD750 CPU PFS

SW Rqmts Spec

GDE PFS

PACI PFS

UDL PFS

NVM PFS

SADA PFS

ARM PFS

ST PFS

RWA PFSTAM PFS

IPCU PFS

TIB PFS cPCI PFS

SBEAS PFS

SBTBRFD PFS

APM PFS

ETR PFS

MMT PFS

S-BAND ANT PFS

Heat Pipes PFS

Solar Cell Pnl PFS

Ku Ant PFSKu XMTR PFS

Transfer Swtch PFS

PDU PFS

PRU PFSBattery PFS

OCXO SOW

GNC Design Doc

IMU SOWIMU SOW

CSS SOWCSS SOW

GPS SOWGPS SOW

PROP MOD SOWPROP MOD SOW

SSR PFSSSR PFS

PDE PFSPDE PFS

GPIO PFSGPIO PFS

LGIO PFSLGIO PFS

RAD750 CPU PFSRAD750 CPU PFS

SW Rqmts SpecSW Rqmts Spec

GDE PFSGDE PFS

PACI PFSPACI PFS

UDL PFSUDL PFS

NVM PFSNVM PFS

SADA PFSSADA PFS

ARM PFSARM PFS

ST PFSST PFS

RWA PFSRWA PFSTAM PFSTAM PFS

IPCU PFSIPCU PFS

TIB PFS cPCI PFScPCI PFS

SBEAS PFSSBEAS PFS

SBTBRFD PFSSBTBRFD PFS

APM PFSAPM PFS

ETR PFSETR PFS

MMT PFS

S-BAND ANT PFSS-BAND ANT PFS

Heat Pipes PFSHeat Pipes PFS

Solar Cell Pnl PFSSolar Cell Pnl PFS

Ku Ant PFSKu Ant PFSKu XMTR PFSKu XMTR PFS

Transfer Swtch PFSTransfer Swtch PFS

PDU PFSPDU PFS

PRU PFSPRU PFSBattery PFSBattery PFS

OCXO SOWOCXO SOW

GNC Design DocGNC Design Doc

OBS–SN ICD

OBS–GS ICD

MOC-USN ICD

FDF-MOC ICD

Ops Products ICD

MOC-BU GS ICD

GFEP-WSC ICD

GFEP-MOC ICD

PSS Rqmts Doc

GFEP Rqmts Doc

OBS–SN ICD

OBS–GS ICD

MOC-USN ICD

FDF-MOC ICD

Ops Products ICD

MOC-BU GS ICD

GFEP-WSC ICD

GFEP-MOC ICD

PSS Rqmts Doc

GFEP Rqmts Doc

GBM DPU Sys Spec

GBM-SPEC-1008

GBM Internal ICD

GBM-ICD-1009

GBM FSW Rqmts

GBM-REQ-1019

Detector Design

Description

TN-GBM-3200-DJO

GBM-PB Design

Description

TN-GBM-6200-AEO

GBM DPU Sys Spec

GBM-SPEC-1008

GBM DPU Sys Spec

GBM-SPEC-1008

GBM Internal ICD

GBM-ICD-1009

GBM Internal ICD

GBM-ICD-1009

GBM FSW Rqmts

GBM-REQ-1019

GBM FSW Rqmts

GBM-REQ-1019

Detector Design

Description

TN-GBM-3200-DJO

Detector Design

Description

TN-GBM-3200-DJO

GBM-PB Design

Description

TN-GBM-6200-AEO

GBM-PB Design

Description

TN-GBM-6200-AEO

Sim/Detector Resp

SW Funct Spec

GBM-SPEC-1026

Inst Ops & Data

Anal Funct Spec

GBM-SPEC-1031

Sim/Detector Resp

SW Funct Spec

GBM-SPEC-1026

Sim/Detector Resp

SW Funct Spec

GBM-SPEC-1026

Inst Ops & Data

Anal Funct Spec

GBM-SPEC-1031

Inst Ops & Data

Anal Funct Spec

GBM-SPEC-1031

Comp

Verif Spec

Comp

Verif Spec

GEVS-SE Rev AGEVS-SE Rev A

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Mission Verification Process

End-To-End Mission System Verification is the responsibility of the GLAST Project Officeand is led by Systems Engineering

Rigorous verification of engineering requirements is accomplished in the course of theintegration and verification program and reported on at formal Project life cycle reviews

– PER

– PSR

– ORR

– FRR

– LRR

Observatory Verification planning, execution, and coordination is contracted to GeneralDynamics

– Includes Observatory I&T and On-Orbit Checkout

The GLAST Systems Verification Plan (SVP) documents the methodology planned toverify system functionality and compliance with mission requirements

– 433-PLAN-0005

Acceptable verification methods used on GLAST

– Test, Analysis, Inspection, Demonstration

Verification Levels of Assembly

– Component, Subsystem, Spacecraft, Observatory, On orbit

Objective For This Presentation: Status on verification process for SRD table 3

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SRD Table 3 Requirements Summary

< 5 arcsec< 10 arcsec3.36 Pointing Knowledge 7Footnote 7: 1 sigma radius

< 0.5 degrees< 2 degrees3.35 Pointing Accuracy Absolute 7Footnote 7: 1 sigma radius.

< 4 sec< 7 sec3.34 GRB Notification Time to Ground by Spacecraft 6Footnote 6: Time from spacecraft receipt of GRB notification from GBM orLAT to delivery to the Gamma-ray Coordinates Network (GCN) computerfor 80% of all GRBs detected by the GBM or LAT.

< 5 min< 10 min3.33 Spacecraft Repointing Times for Autonomous Slews 5Footnote 5: Time for 75° slew, to be met 100% of the time under 4reaction wheel (RWA) control and 75% of the time under 3 RWA control(single RWA failure) accounting for slew constraints (e.g. yaw flip).

< 4 hours< 6 hours3.32 Time to Respond to TOO's on Ground 4Footnote 4: Response time for the SSC and MOC to plan and send aspacecraft repointing command after the decision is made to respond to aTarget of Opportunity (TOO).

> 2 kbps> 1 kbps3.31 Telemetry Uplink Realtime 3Footnote 3: Uplink telemetry rate for at least 80% of time outside of SAA

> 2 kbps> 1 kbps3.30 Telemetry Downlink Realtime 3Footnote 3: Uplink telemetry rate for at least 80% of time outside of SAA

> 1 Mbps> 300 kbps3.29 Telemetry Downlink Orbit Average

> 10 years> 5 years3.28 Mission Lifetime (<20% degradation) 2Footnote 2: 20% degradation = no more than 20% loss of LAT sciencereturn.

Goal RequirementTable 3. Science Requirements on the GLAST Mission

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SRD Table 3 Requirements SummaryContinued

- Rocking zenithpointing15

- Pointed mode8

3.37 Observing Modes

N/A> 30°

(adjustable)

3.45 Earth Avoidance 14Axis normal to LAT shall be capable of remaining at an angle greater thanthis above the Earth's horizon during normal operations, with the possibleexception of rapid slewing to acquire a GRB.

< 3 x 10-11

< 1 x 10-10

3.44 Data Corruption 13Footnote 13: Fraction of undetected corrupted events.

< 1%< 2 %3.43 Data Loss 12Footnote 12: Fraction of data taken by the instruments but not delivered tothe IOC. Not including SAA data loss. Not including instrument deadtime.

> 95%> 90 %3.42 Observing Efficiency 11Footnote 11: Fraction of time with data return, not including SAA effects.

< 1 km< 3.3 km3.41 Observatory Absolute Position Accuracy

< 3µsec< 10µsec3.40 Observatory Time Accuracy 10Footnote 10: Relative to Universal Time, 1 sigma r.m.s..

< ± 10%< ± 20%3.39 Uniformity of Sky Coverage during All-sky Survey 9Footnote 9: Sky coverage exposure uniformity integrating for 7 days, notincluding SAA effects

3.38 TargetingNo restrictions on Pointing 8 of axis normal to LATFootnote 8: Pointing of axis normal to LAT to within 30 degrees of source.(No science constraint on roll axis.).

Goal RequirementTable 3. Science Requirements on the GLAST Mission

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AgendaPresenter / SRD Requirements

Norman Rioux

– 3.28, 3.29, 3.30

– 3.31, 3.40, 3.42

– 3.34

– 3.43

– 3.44

Chris Connor

– 3.33, 3.35, 3.37

– 3.38, 3.41, 3.45

– 3.36

Julie McEnery

– 3.32

– 3.39

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SRD Table 3 Requirements3.28, 3.29, 3.30

Verified by test

Ground Selectable 1 k, 2 k, 4 k bps

Verified by CTV testing January 2007

Design provides commandable 8kbps data rate as a bonus if excess as-built margin permits

Final verification conducted in end to end testing with flight IEM and SSR

> 2kbps

> 1kbps

3.30 Telemetry DownlinkRealtime 3Footnote 3: Uplinktelemetry rate for at least80% of time outside of SAA

Verified by analysis and test

40 Mbps Ku band science downlink

80 minutes of TDRSS downlink time scheduled per day

Link verified in Compatibility Test Van (CTV) testing January 2007

Final verification conducted in end to end testing with flight IEM and SSRwith Ku downlinks schedule through the MOC

> 1Mbps

> 300kbps

3.29 Telemetry DownlinkOrbit Average

Mission design requirement verified by analysis

No consumables

Single fault tolerant redundant design meeting 85% 5 year reliabilityrequirement

Redundancy supporting graceful degradation in LAT Tracker, Calorimeterand ACD

> 10years

> 5years

3.28 Mission Lifetime(<20% degradation)

2

Footnote 2: 20%degradation = no more than20% loss of LAT sciencereturn.

Status

PerformanceGoal

PerformanceRequirement

3 Table 3. ScienceRequirements on theGLAST Mission

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Mission design requirement verified by analysis

Mission is designed to collect data at all times

Routine operations enable continuous science data collection and return

LAT resets under investigation

> 95%> 90 %3.42 Observing Efficiency11Footnote 11: Fraction oftime with data return, notincluding SAA effects.

To be verified at observatory level

GPS receivers have been verifed to provide timing accurate to 1.5 microseconds

C&DH pulse per second interface has been functionally verified at componentlevel of testing with EM IEM

End to End LAT to Spacecraft test will verify observatory timing using Muontelescope EGSE. Muon telescope timing provided by independent GPS receiver

< 3µsec< 10µ

sec3.40 Observatory TimeAccuracy 10Footnote 10: Relative toUniversal Time, 1 sigmar.m.s..

Verified by test

4 kbps

Verified by CTV testing January 2007

Final verification conducted in end to end testing with flight IEM and SSR

> 2kbps

> 1kbps

3.31 Telemetry UplinkRealtime 3Footnote 3: Uplinktelemetry rate for at least80% of time outside of SAA

Status

PerformanceGoal

PerformanceRequirement

3 Table 3. ScienceRequirements on theGLAST Mission

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SRD Requirement 3.34

3.34 GRB Notification Time to Ground by Spacecraft 6

< 7 sec

Footnote 6: Time from spacecraft receipt of GRB notification from GBM or LAT todelivery to the Gamma-ray Coordinates Network (GCN) computer for 80% ofall GRBs detected by the GBM or LAT.

To be verified during End to End Test

SC to MOC latency measured during Compatibility Test Van (CTV) testing forfour trials using a state of health message

– Averaging roughly 9 +/- 1 second SC to MOC

Contributing element: Lockup time of White Sands S-Band MA Demodulatorunit (DMU)

– Lockup time statistical in nature

– Code 450 (TDRSS Space Network) is developing improved FPGA algorithms for use in theWhite Sands DMU at 1Kbps

• May contribute reductions in latency on the order of 1 to 3 seconds

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SRD Requirement 3.34 (con’t)3.34 GRB Notification Time to Ground by Spacecraft 6

< 7 sec

Footnote 6: Time from spacecraft receipt of GRB notification from GBM or LAT to delivery to theGamma-ray Coordinates Network (GCN) computer for 80% of all GRBs detected by the GBM orLAT.

End to End Latency – GBM to GCN

-1.5-1.5-1.5Margin against GBM first message to SC requirement

57.512.9Potential End to End latency with DMU improvement

89.513.9Potential End to End latency without DMU improvement

9.51115.4Instrument to SC interface to GCN latency Total:

.512MOC ITOS to GCN

8910SC output to MOC ITOS

113.4Instrument to SC Interface to SC antenna output

OptimisticNominalEstimate

Pessimistic

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SRD Requirement 3.433.43 Data Loss 12

Requirement: < 2% Goal: <1%

Footnote 12: Fraction of data taken by the instruments but not delivered to theIOC. Not including SAA data loss. Not including instrument deadtime.

Verified via analysis

SC Data System is being thoroughly tested at Subsystem and ObservatoryLevels.

SC System designed to allow multiple retransmission of data

– SSR sized to provide 30 hours of science data and 36 hours of housekeeping data

• Analysis shows that 24 hrs of recorded HSK and Science data may be played back in~ 56 min at 40 Mbps.

• TDRSS Loading analysis determined that ~300 min/day of TDRSS SA contact timeavailable to support GLAST

• The FOT plans to schedule 80 to 90 minutes of contact time per day at 40 Mbps.

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SRD Requirement 3.43 (con’t)

FOT Data Retransmission Plan

– While MOC is staffed:

• FOT monitors frame statistics and will re-transmit to recover anylost frames

• All missing/corrupted data will be retransmitted.

– During off hours and weekends:

• FOT will be paged when automated monitoring at the MOCindicates frame loss above a settable threshold (currently 99%)

• ISOC monitors event loss, and can also page FOT to request are-transmit

– FOT will re-dump missing/corrupt data twice from the SSR to ensurecomplete data capture and lower any likelihood of error during re-dumps

13


Ground System redundancy implemented to prevent data loss

– Data captured on multiple Front-end Processors (GFEPs) at White SandsTDRSS ground terminal (WSC)

• HSK and Science Data maintained on GFEPs for 7 days

• GFEPs are redundant with hot backups

• Use high reliability network connections between ground stations andMOC for transfer of science data.

– Network availability is 99.50%

– Network outage restored within 4 hrs

– Data archived at MOC and backed-up on separate media

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3.44 Data Corruption 13

Footnote 13: Fraction of undetected corrupted events.

Requirement: < 1 x 10-10

Goal: < 3 x 10-11


Four categories of data coming out of the data channel:

1. Data is actually good and detected as good.

2. Data that is actually in error, detected as in error, and can be corrected based oncoding.

3. Data that is actually in error, detected as in error, but cannot be corrected with coding.

4. Data that is actually in error, but detected as being good.

This requirement is concerned with data in category 4.

Analysis of the science data return link performance including Reed Solomon coding andinterleaving shows that this requirement is easily met with margin.

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Two primary observing modes provided are sky survey(zenith pointing with rocking angle) and pointedobservation mode

3.37 Observing ModesObserving Modes- Rocking zenith pointing 15- Pointed mode 8Footnote 8: Pointing of axis normal to LATto within 30 degrees of source. (Noscience constraint on roll axis.).Footnote 15: The observatory shall becapable of scanning the LAT FOV (55°

half-angle) over >90% of the celestialsphere repetitively on selectabletimescales as short as every 2 orbits.


0.8 deg

Driven by environmental disturbances and commandlatency

< 0.5degrees

< 2degrees

3.35 Pointing Accuracy Absolute 7Footnote 7: 1 sigma radius.


4 RWAs: Maximum slew time is 9 min3 RWAs: 84% of 75 degree slews are within 10 min

RWA reliability information: Ps(15 yrs)=0.9555

< 5 min< 10 min3.33 Spacecraft Repointing Times forAutonomous Slews 5Footnote 5: Time for 75° slew, to be met100% of the time under 4 reaction wheel(RWA) control and 75% of the time under3 RWA control (single RWA failure)accounting for slew constraints (e.g. yawflip).

3 Table 3. Science Requirements onthe GLAST Mission

StatusPerformance Goal

Performance

Requirement

Science Requirements extracted fromSRD descriptive module

16



30 deg

Keep the earth out of the sweet spot. Will slew across earthif need be, taking into consideration the sun angle(maintain sun in X-Z plane).

N/A> 30°

(adjustable)

3.45 Earth Avoidance 14Axis normal to LAT shall be capable ofremaining at an angle greater than thisabove the Earth's horizon during normaloperations, with the possible exception ofrapid slewing to acquire a GRB.


0.2 Km

GPS design and supporting GNC software algorithms areheritage from previous GD programs.

< 1 km< 3.3 km3.41 Observatory Absolute PositionAccuracy


Physical Constraints: Default is 30 deg Earth Avoidance,as per 3.18.

30 deg half-angle is the "sweet" spot of the LAT (55 degFOV).

GD provides PAPA (predict ahead planning algorithm)which utilizes ephemerides and operational constraints tocompute slew profiles.

3.38 TargetingNo restrictions on Pointing

8 of axis

normal to LATFootnote 8: Pointing of axis normal to LATto within 30 degrees of source. (Noscience constraint on roll axis.).

3 Table 3. Science Requirements onthe GLAST Mission

StatusPerformance Goal

Performance

Requirement

Science Requirements extracted fromSRD descriptive module

17


Observatory Pointing Knowledge Performance (1-sigma, radial)

– All BOL Sky Survey Cases: CBE < 10 arcsec

– All BOL Cases (Sky Survey & Pointed Obs): CBE < 15 arcsec

– All Mission Cases (BOL & EOL): CBE < 30 arcsec

All analysis performed with integrated, observatory-level thermalmechanical distortion models (spacecraft + science instruments)

– Modeling uncertainty factors (MUFs) applied to distortion results

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Analysis efforts concentrated on identification of the primarydistortion terms & overall review of model fidelity

– Primary distortion sources are the optical bench skirt & star tracker to startracker distortion on the optical bench reference

– SC provider performed optical bench thermal test (Dec 2005) to help correlatemodels and refine predicted performance

LAT & SC thermal model correlation underway

– Observatory TVAC scheduled for Summer 2007

– Upon completion of these activities, we can reduce the MUFs

On-orbit GNC Kalman filter will help with some of the star tracker-to-star tracker distortion

– Cyclic thermal distortion due to day/night transitions each orbit

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RPS

Science Community

GSSCDutyScientist

Pager Tool

MOC

ProjectScientist

EvaluationTools

ToO Approver/RejectorToO Orderer

ToO Order

ToO StatusMessages

ToO StatusWeb Page

ToO StatusDatabase

As-Flown Timeline

Timeline Comparator

ToO Request

TimelineDifferences

ToOCommands

ToO Advice

ToO Decision

ToOQueries/Responses

ToO Request

Response time for the GSSC and MOC to plan and send a repointing comandafter the decision is made to respond to a ToO: 6 hours requirement, 4hours goal, 12 hours minimum.

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Target of Opportunity Handling

Upon receiving authorization to proceed with the ToO, the GSSC constructs the ToOOrder and forwards to the MOC

– GSSC checks for constraint violations, occultation, availability, etc.

– Approved ToO Order is sent to the MOC

MOC recognizes ToO Order and notifies appropriate FOT personnel for action

– FOT processes ToO Order and evaluates impact to current TDRSS contact schedule

– FOT schedules a forward link with TDRSS (if necessary)

– MOC transmits the ToO commands to the spacecraft as soon as the TDRSS forward link is available

Receipt of ToOs orders do not absolutely necessitate weekly ATS replans by the FOT

– Observatory autonomously returns to on-board observing schedule at completion of the ToO usingcheck-pointed commands from the ATS

– FOT will evaluate the affect of the ToO on scheduled TDRSS contacts and re-schedule additionalcontacts if necessary

GSSC will evaluate the affect of the ToO on current timeline and adjust accordingly witha re-planned timeline or adjust the upcoming planning week


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ToO Latency - Worst case scenario

221Total

5uplink command

30SN to prep for contact

30FOT to Schedule contact

90FOT to travel to MOC

5FOT to receive email

1MOC to send email

60GSSC duty scientist to perform evaluation and send mail

Time (min)Action

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Uniformity of sky coverage during all sky survey: +-20% (req), +-10%(goal) integrated for 7 days not including effects of the SAA.

Analysis:– Survey mode rocking 35 degrees north/south each orbit, orbit with 25.4 deg inclination.

– Convolve the pointing history with the LAT effective area as a function of inclination toobtain the exposure over the sky.

– The next two slides show the exposure from 100 MeV - 200 GeV for a 1 week and 55 daysurvey mode observation.

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Exposure Uniformity - 7 days

Colour scale is from maxto min pixel value (so it iseasy to see smallstructure)

Histogram of exposure inbins of equal angular areaon the sky.

rms/mean = 7.3%,however there are someoutliers.

1.6% (41) of the bins liefurther than 20% from themean.

24

Exposure Uniformity - 55 days

RMS/Mean = 2.3%, all bins liewithin 20% of the mean. Thelines +-20% of the mean lie offthe scale of this plot!

25

A caveat

The LAT Aeff vs inclination angle varies with energy, thus theexposure pattern on the sky also varies depending on the energyband being considered.

26

Exposure vs energy band

27

Effect of SAA - 1 week integration

The distribution ofexposure on the sky hasbecome significantly morenon-uniform.

rms/mean = 14%

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Effect of SAA - 55 day integration

On longer timescales, theeffect of SAA outages isto introduce a north/southasymmetry. However theoverall magnitude of thisis fairly small, all pointson the sky remain within20% of the mean.

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GLAST Mission Systems

USN(GN)

HEASARC

DELTA2920H-10

Commands 2 kbpsTelemetry 51 kbps

2.4 Mbps SSOH - RT

White Sands (SN)

TDRSS (SN)

LAT InstrumentOperations Center

GBM InstrumentOperations Center

GRBCoordinates Network

S-Band

Alerts

Data, Command Loads

Data, Command Loads

Schedules/CMDS

ArchiveMissionOperations Center

GSFC

ScienceSupport Center GSFC

GPS Signals Provide• Time 10 µsec• Position <3.3 km

• Ku-Band Downlink: 40 Mbps forStored Science, SSOH Data, Real-Time Data

• S-Band SA Downlink:1,2,4,8 kbps for RT Data

• S-Band MA Downlink: 1 kbps forAlerts (Burst, Safe Mode)

Commands 4 kbps (S-BandSA), 250 bps (S-Band MA)

= Ku-Band Downlink = S-Band Downlink = S-Band Uplink

Schedules/CMDS

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