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Summary of the JWST Mission and Observatory
Systems Requirements Reviews,
and
Micro-Shutter Array (MSA) Confirmation Review
Jerry Kriss
01/15/2004
TIPS/JIM
SRR Objectives
 Confirm that mission-level and observatory
requirements meet the project objectives
 Confirm observatory-level specifications are
sufficient to meet the project objectives
 Validate that the mission architecture concept
can support the functional, operational,
interface and performance requirements
 Show that the requirements have been flowed
down and are understood at the next level.
01/15/2004
TIPS/JIM
SRR Review Team
Dennis Dillman, Chair
Steve Graham
Alain Berinstain
Ted Harper
Jacques Louet
Colin Jones
Steve Scott
Alexander Krimchansky
Gene Waluschka
Sachi Babu
Tom McCarthy
Mark Fontaine
Joe Schepis
Peiman Maghami
Minh Phan
Dr. Mal Niedner
01/15/2004
GSFC System Review Office
GSFC Project Management
CSA
CSA
ESA
ESA
GSFC Chief Engineer
GSFC
GSFC Optics
GSFC Detectors
GSFC Thermal
GSFC
GSFC Electromechanical
GSFC
GSFC
GSFC Space Sciences
TIPS/JIM
JWST Requirements Tree
JWST Program Plan
JWST-PLAN-000633 L1
Program
Baselined
In CM Review
Drafts Available
Allocation Documents
System
FGS SRD
JWST Science
Requirements Document
JWST-RQMT-002558SR
NIRCam SRD
NIRSpec SRD
JWST Mission
Requirements
JWST-RQMT-000634 MR
JWST Performance
Assurance Requirements
JWST-RQMT-000650 PA
JWST Mission Operations
Concept Document
JWST-OPS-002018 MOC
FGS OCD
MIRI SRD
Budgets
WFE Rev Q 03-JWST-0405
Efficiency
Pointing
WFS&C Requirements
Allocation Document
JWST-RQMT-002017 WFS
NIRCam OCD
EMC Control Plan
JWST-PLAN-002449
NIRSpec OCD
EMC
Performance Quality
Assurance Plan
JWST-PLAN-002412
Contamination Control
Plan
JWST-PLAN-002028
CCP
PQ
MIRI OCD
Segment
Flight Observatory to
Ground Segment IRD
JWST-IRD-000696 FG
Ground Segment
Requirements
JWST-RQMT-001056
GS
JWST Observatory
Specification
JWST-SPEC-002020
RD
Launch Segment
Specification
JWST-SPEC-001999
OL
OBS
JWST-ICD-001998 FGC
Radiation Requirements
Allocation Specification
JWST-SPEC-000871
Observatory to Launch
Segment IRD
JWST-IRD-002000
JWST System
Verification Plan
JWST-PLAN-002027
LS
JWST-ICD-002001
OLC
Environmental Req’s
for the JWST Observatory
JWST-SPEC-003149 EV
Observatory I&T Plan
JWST-PLAN-002030
Observatory to
GSE IRD
D36127 OG
D36128 OGC
Fault Protection
Requirements Document
JWST-RQMT-002450
FP
Element
ISIM Requirements
Document
JWST-RQMT-000835
ISIM
ISIM to OTE and
Spacecraft IRD
JWST-IRD-000640
ISIM to OTE and IOS-IR
JWST-ICD-001831
01/15/2004
SC Requirements Document
JWST-RQMT-002039
SC
IOSC
TIPS/JIM
Spacecraft to OTE
ICD
D35231 SOIC
OTE Specification
JWST-RQMT-002021
OTE
JWST Science Requirements
(John Mather presenting)
 Four themes:
•
•
•
•
First Light
Assembly of Galaxies
Birth of Star and Planetary Systems
Planetary Systems and the Origins of Life
 Level 1 Mission Success Criteria:
•
•
•
•
•
•
•
•
Density of galaxies
Spectra of galaxies
Physical and Chemical properties of young stellar objects
Observing time---5 yr mission, 1.1e9 s on target
Telescope > 25 m2
Strehl ratio > 0.8 at 2 m
Encircled energy > 0.74 within 0.15 arc sec at 1 m, stable for > 24 hrs.
Thermal environment zodi limited 0.6 -- 10 m
 Example of how Level 1 requirements flow down: 1st-light objects are rare
(<1 arcmin-2) ==> large, unvignetted FOV with low distortion.
01/15/2004
TIPS/JIM
Requirement Changes Since
the Delta-MDR
 Redesigned sun shield---smaller, better
clearances, simpler deployment – but, it could
make mission planning more difficult.
 Upgrade the power system to accommodate
ISIM power needs.
01/15/2004
TIPS/JIM
Requirements Still in Work
 Moving targets. Quantitative requirements are TBD,
depending on cost.
 Sensitivity. New numbers developed, but CCB on hold
pending NGST replan contract change.
 Mass allocations are TBD pending resolution of the ISIM
Electronics Compartment (IEC) study.
 Ariane 5 change not yet flowed down (no expected impact).
 FOV offsets not yet flowed done (no expected impact).
 Reliability. Recent MRD change says goal is 92% for
Spacecraft+OTE. Goal for whole observatory is pending.
 OTE to ISIM structural interface definition.
 X vs. Ka-band study. [Should finish soon in favor of Ka.]
01/15/2004
TIPS/JIM
Key Issues
 Concept for locating ISIM electronics in Region 2 is not viable.
• FPEs must be within 6m of focal planes, in Region 2
• Adding ICE boxes advantageous
• "Saddle-bag" configuration won't work. (Too massive; thermal
problems.) Further work underway. (IEC trade study. Will take FPE
rqmnts into account.)
 Mass Allocations
• Current mass reserves are at 21%. Would like to be at 25%. Biggest
problem areas are the IEC accommodation, and the sun shield
containment system.
• Spacecraft is 250 kg over its allocation
• OTE is 405 kg over its allocation
• MIRI dewar is 20 kg over its allocation; NIRCam is 7 kg too heavy.
01/15/2004
TIPS/JIM
(ISIM Region 1)
(ISIM Region 2)
(ISIM Region 3)
01/15/2004
TIPS/JIM
SRR Summary Results
 The board thought that the review was excellent.
 ~60 Requests for Action (RFAs) generated.
 Major issues in the RFAs:
• Request for an Observatory-level TV test.
• Request for deployment tests in TV.
• Desire to make several of the Mission/Obs rqmnts less
vague and more verifiable (e.g., those related to eventdrive ops).
• Need to do a better flow down of the efficiency rqmnt and
tie it in to data quality and reliability in a more
comprehensive way.
• Fault handling requires more development.
01/15/2004
TIPS/JIM
Micro-Shutter Array (MSA)
Confirmation Review
 Held 12/18/03 at GSFC to assess whether the MEMS microshutter array should be the slit-defining mechanism for
NIRSpec.
 Successes:
• Fabricated 128 x 64 arrays (flight will be 384 x 175)
• Demonstrated 2-D addressing
• Implemented light shields
• Performed cryogenic life tests
• Measured pixel failure rate at end-of-life
• Measured open/closed shutter contrast ratio [2,00010,000 warm; ~200 cold (due to shutter curvature)]
• Performed an acoustic test
01/15/2004
TIPS/JIM
100 m
20 m
01/15/2004
Magnetic Stripes on MSA Frontside
MSA Light Shields
100 m
TIPS/JIM
MSA Backside
Micro-Shutter Array (MSA)
Confirmation Review
 Concerns:
•
•
•
•
Yield is still low
Light shields frequently break off
Shutters curve and bend when cooled
Life testing does not meet <10% of rows with a failedopen shutter
• Crude acoustic/shake tests increase rate of failed-opens
 Further development needed, but optimism prevails.
 The MSA remains the preferred approach, and the European
selection is proceeding on this basis.
01/15/2004
TIPS/JIM