JWST FGS SRR
April 7, 2004
Ed Nelan
TIPS
May 20, 2004
FGS SRR 7-April-04
02-1
System Requirements Review: Objectives
The FGS SRR will be a joint CSA/NASA review.
•
The System Requirements Review (SRR) assesses the
completeness of the baseline System and Instrument
requirements for the FGS and identifies any potential
performance non-compliance’s or marginal design aspects.
•
A successful SRR demonstrates that the Instrument conceptual
design is ready to proceed into preliminary design.
•
Flow-down of requirements will be emphasized.
FGS SRR 7-April-04
02-2
System Requirements Review: Process
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Requirements Overview:
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JWST System & Requirements Flow
FGS Requirements Flow
Trace of all FGS Requirements from ISIM Requirements
Classification of FGS Requirements
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FGS-Guider
FGS-TF
FGS Assemblies:
• Optical Assembly (Structure, Optics, Detectors, Mechanisms)
• FPE/ICE Assemblies (FPE, ICE, TCE)
• C&DH Assembly (SBC, Memory, Interfaces, Software)
SRR Process
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For each class of requirements those which are design
drivers are identified and will be presented in more detail.
FGS SRR 7-April-04
02-3
JWST Observatory Architecture
Optical Telescope Element (OTE)
Primary Mirror (PM)
• 18 (1.315 m) hex segments
• Semi-rigid WFS&C for phasing
• Deployable chord fold
ISIM
• NIRCam, NIRSpec, MIRI & FGS
Secondary Mirror (SM)
Sunshield
• Passive cooling of ISIM/OTE to
<40K
Spacecraft Bus
FGS SRR 7-April-04
Tower
02-4
FGS Requirements Flow & Status
System
JWST Mission
Requirements
JWST-RQMT-000634 MRD
JWST Science
Requirements Document
JWST-RQMT-002558
JWST Observatory
Specification
OBS
JWST-SPEC-002020
OBS
Baselined
In CM Review
Drafts Available
Allocation Documents
Phase B Documents
JWST Mission Operations
Concept Document
JWST-OPS-002018
Segment
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
All FGS rqmts flow from ISIM
FGS Science
Rational & Analysis Document
Subsystem
Mission Assurance Requirements
For the JWST Instruments
JWST-RQMT-002363
MAR
IOSC
FGS IRD
JWST-IRD-000783
IF
FGS to ISIM ICD
JWST-ICD-000727
CSA Performance Assurance
Requirements
IFC
FGS Instrument Performance
and Functional Requirements
JWST-SPEC-002069
FGS
FGS Guider
Operations Concept
FGS Tunable Filter
Operations Concept
FGS Optical Assembly
Requirements
FGS SRR 7-April-04
CSA FGS Specification
FGS FPE/ICE/TCE
Requirements
FGS C&DH Requirements
FGS Flight
Software Requirements
02-5
FGS Future Requirements Flow
Phase A Documents
CSA Performance Assurance
Requirements
FGS Tunable Filter
Operations Concept
FGS Instrument Performance
and Functional Requirements
JWST-SPEC-002069 FGS
FGS Interface
Requirements
JWST-IRD-000783 IF
FGS Science
Rationale &
Analysis
Document
FGS Guider
Operations Concept
Phase B Documents
LY
N
O
PT
E
C
CON
FGS Optical Assembly
Requirements
FGS Specification
IFC
FGS FPE/ICE/TCE
Requirements
TMA (Optics)
Specification
OA Structure
Requirements
Filter Wheel & Drive
Specification
Blocking Filter
Requirements
FPE Requirements
Focus Mechanism &
Drive Specification
Tunable Filter
Requirements
ICE Requirements
Detector Specification
Coronagraphic Mask
Requirements
FGS SRR 7-April-04
FGS Interface Control
Document
JWST-ICD-000727
C&DH Specification
Flight Software Requirements
FPE/ICE/TCE Power
Supply Specification
Baselined
In CM Review
Drafts Available
Allocation Documents
Phase B Documents
02-6
FGS Requirements Flow (1 of 6)
FGS SRR 7-April-04
02-7
FGS Requirements Flow
•One ISIM requirement can spawn several FGS requirements,
but each FGS requirement must have just one ISIM “parent”.
•An ISIM requirement can be flowed to FGS from higher level
(i.e., 95% guide star availability is a mission level requirement
that must be met by the FGS.)
FGS SRR 7-April-04
02-8
New ISIM Requirements
Number
Status
Requirement
Comment
ISIM-xxx
TBD
FGS Optical Distortion
ISIM-xxx
TBD
FGS-TF Optical Distortion
(Astrometric Calibration)
Initial flowdown of OBS-93 (SI+OTE field distortion correction)
was removed, although this is partly a ground allocation, there
should be a requirement for the SI ‘s and FGS-Guider to collect
data to support the ground calibration.
Note that in the case of the FGS-Guider there is a related
requirement ISIM-589 Pointing Accuracy but its purpose is
different.
ISIM-xxx
TBD
FGS-Guider Acquisition Performance
during Large (<20”) Slews
ISIM-xxx
TBR
FGS-Guider Acquisition Performance
during Small (<1”) Slews
ISIM-xxx
Moving Target
The Observatory will slew to a target during Acquisition or Fine
Guiding, and a performance should be specified during the
slew. Also there is the potential Observatory The slew
parameters will be described in the FGS IRD Section 3.8.
A moving target requirement has been discussed and is
assumed to imply 30 mas / s rates where the FGS-Guider NEA
can relax to >4.3 mas
Key
Requirements change requests in process for
Mission / Observatory Requirements
FGS SRR 7-April-04
Requirements change requests in process
for ISIM Requirements
02-9
FGS (IPFR) TBD/TBR Requirements
Number
Status
Requirement
Comment
FGS-104
TBD
Operating Modes, Updates
Define which parameters can be updated “on the fly” (while guiding), and which
should be restricted to updating on subsequent command: For ISIM Requirements
FGS-117
TBD
Identification Image Collection
IRD needs to specify maximum allowable motion rate (low slew rate mode) for
entry into Identification Mode. Estimated to be ~1”/50 s.
FGS-124
TBD
Acquisition Mode Entry
IRD needs to specify maximum allowable motion rate (low slew rate mode) for
entry into Acquisition Mode. Estimated to be 0.5”/s.
FGS-231
TBR
Identification Mode, Sensitivity
Derive dimmest identifiable star (min Jab).
FGS–239
TBR
Identification Mode, Pattern Recognition
Derive max. # of objects to be processed by recognition algorithm.
FGS–242
TBD
Identification Mode, Single Stars
Specify min. angular separation of binary star systems that need to be resolvable.
FGS–262
TBD
Acquisition Mode, Single Stars
Specify min. angular separation of binary star systems that need to be resolvable.
FGS–268
TBR
Image Motion Rate, Large Angle Slews
Specify max. motion rate for Acquisition Mode. (See “New ISIM Reqs.”)
FGS–270
TBR
Image Motion Rate, Small Angle Slews
Specify max. motion rate for Acquisition Mode. (See “New ISIM Reqs.”)
FGS-277
TBR
NEA Magnitude Limit
ISIM Spec TBR dim magnitude limit.
FGS–393
TBD
TF Wavefront Error, Long Term Stability
ISIM / IRD needs to specify allowable I/F temp. rate of change.
FGS–403
TBD
TF PSF Anisotropy
ISIM Spec TBR low order asymmetric wave front error.
FGS–405
TBD
TF PSF Anisotropy Stability
Specify low order asymmetric wave front error variation.
FGS–436
TBR
Power-Up Duration
ISIM Spec TBR power-up duration.
FGS–567
TBD
Guider Temporal Efficiency
ISIM Spec TBD Guider efficiency.
FGS–569
TBR
TF Temporal Efficiency
ISIM Spec TBR TF efficiency.
Requirements change requests in
process for ISIM Requirements
FGS SRR 7-April-04
Requirements change requests in
process for IRD Requirements
FGS to determine requirements
via analysis (operations input)
02-10
FGS-Guider Operations Concept
Requirements Driving the Design and Operation of the FGS-Guider
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ISIM-264 (MR-171) Guide Star Availability
• 95% guide star availability (with both FGS channels)
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ISIM-265 (MR-365) FGS Single-Point Failure
• 90% guide star availability (single channel)
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ISIM-591 (OBS-1677) FGS Noise Equivalent Angle
• 3.5 mas/axis RMS
determines sensitivity & total FOV for guide function, limiting
magnitude of candidate guide stars, catalog performance
FGS SRR 7-April-04
02-11
Current JWST FOV Layout
Coronagraphic Spot Location
20”
80”
1
FGS SRR 7-April-04
2
02-12
JWST FOV Layout
Coronagraphic Spot Location
20”
80”
1
FGS SRR 7-April-04
2
02-13
JWST FOV Layout
Coronagraphic Spot Location
20”
80”
?
FGS SRR 7-April-04
1
2
02-14
Loss of a Single Channel (FOV) in FGS
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ISIM-265 requires 90% probability of a guide star being available
following the loss of 1 FGS FOV.
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trade off between instrument sensitivity & remaining FOV that can
be used to access guide stars (is FGS-TF available for guiding?).
CSA has proposed sensitivity to access guide stars with JAB<19.
Nelan & Kriss (STScI-JWST-TM-2004-0008) show that using GSC-2,
ISIM-265 is not achieved for JAB<19 unless FGS-TF can be used
as a guider.*
We registered our concern that FGS-TF is not required to be
capable of guide function. We also tried unsuccessfully to
add a requirement that GSC-2 be the JWST GSC.
*On going study of GSC-2 suggests with JAB<19.5 FGS will meet ISIM-265
w/o FGS-TF
FGS SRR 7-April-04
02-15
Guide Star Identification Issues
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During SRR there was an extended discussion about
the guide star identification process as this drive cost
for FSW and the FGS C&DH.
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FGS-Guider OCD points out that FGS will be
confronted with both sparse and crowded fields.
Same guide star identification should be applied in
both cases.
FGS SRR 7-April-04
02-16
Guide Star Recognition
FGS images the sky,
FGS SRR 7-April-04
02-17
Guide Star Recognition
overlays a “catalog segment”,
FGS SRR 7-April-04
02-18
Guide Star Recognition
performs a pattern match,
FGS SRR 7-April-04
02-19
Guide Star Recognition
locates guide star.
FGS SRR 7-April-04
02-20
Guide Stars in Crowded Fields
HST/ACS image of Galactic bulge region from Kailash Sahu @ STScI
FGS SRR 7-April-04
02-21
FGS SRR, FGS-TF
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Most significant FGS-TF issue is the size of the FGS
partition on the solid state recorder.
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FGS-TF data will not be stored on same partition as
other SIs (NIRCam, NIRSpec, MIRI).
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Vicki’s day-in-the-life assessment of FGS-TF data
volume suggests that it will fill its partition in ~1/2 day!
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Changing partition size on orbit requires complete
erase of SSR -> not going to happen. We do not
expect FGS-TF observing “campaigns”.
FGS SRR 7-April-04
02-22
Spectral/Spatial Variation of TF:
Data Volume
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Central wavelength of pass band will vary across the FGS-TF
FOV for a given etalon setting (Fabry-Perot design).
λ
∆λ
FOV
FGS SRR 7-April-04
02-23
Spectral/Spatial Variation of TF:
Data Volume
•
•
Central wavelength of pass band will vary across the FGS-TF
FOV for a given etalon setting (Fabry-Perot design).
This will not be an issue for observations of compact objects (or
blind surveys for emission lines sources).
Compact object
λ
∆λ
FOV
FGS SRR 7-April-04
02-24
Spectral/Spatial Variation of TF:
Data Volume
•
•
Central wavelength of pass band will vary across the FGS-TF
FOV for a given etalon setting (Fabry-Perot design).
To sample the entire field at a given wavelength, multiple
exposures at different etalon settings will be necessary.
(Nsettings = R ∆λ/λ)
5
4
3
2
λ
1
∆λ
FOV
FGS SRR 7-April-04
02-25
JWST FGS SRR Summary:
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CSA gave the SRR a passing grade.
We (STScI, GSFC) do not know what RFAs were
submitted, or how they were addressed.
The RFA list and CSA’s SRR assessment are to be
made available (don’t know when).
Other news:
FGS RFP submission deadline was 5/19/04. CSA
expects to chose a vendor by mid-June.
We are curious to see how/if the FGS-TF survives
descope (if any).
FGS SRR 7-April-04
02-26