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1
Integrated Modeling for the James Webb Space
Telescope (JWST) Project:
Structural Analysis Activities
Presented by: Mark McGinnis/Swales
John Johnston, Gary Mosier, Joe Howard,
Tupper Hyde, and Keith Parrish (NASA/GSFC)
Kong Ha (Jackson and Tull)
Frank Liu and Mark McGinnis (Swales Aerospace)
May 6, 2004
2
6/15/2004
Overview
l JWST Overview
l Observatory Structural Models
l Integrated Performance Analysis:
n Performance Budget
n Linear Optical Analysis
n Structural-Thermal-Optical
n Optical jitter dynamics
l Future Work and Challenges
3
6/15/2004
JWST Mission Concept
• Measure the luminosities, morphologies, and environments
of galaxies within the spectral band 0.6 – 10 µm
• Measure the spectra of 2500 galaxies over the redshift range
1 < z < 5
• Obtain a total observing time of at least 1.1x10
8
seconds.
JWST is designed for at least a 5-year lifetime.
Constraints
• Launch by 2011
• Cost capped
• Significant International Contributions
• Spacecraft from Prime Contractor (IRT Finding)
• Use existing Launch Vehicle Capabilities
Science Requirements
Key Mission Trades
• Orbit, Method to Orbit
• Launch Vehicle/Shroud
Configurations
• Filled vs Partially-Filled Apertures
• Thermal Management
• Instrument Packaging
• Sky Coverage
• Communications Strategy
• NIR Imaging Camera [NIRCam]
– 8 square arc minutes field of view
– Spectral resolution R (λ/∆λ) = 100
– Wavelength range 0.6-5 µm
• Multi-object spectrograph [NIRSpec]
– Observing > 100 objects/observatory pointing
– 9 square arc minutes field of view
– R ~1000 over wavelengths 1-5 µm
– R ~100 over wavelengths 0.6-5 µm
•MIR instrument [MIRI]
– Imaging and spectroscopy
– 2 square arcminutes field of view
– R ~1500 spectroscopy over wavelengths 5-28 µm.
Science Instruments
4
6/15/2004
Observatory Architecture
Optical Telescope Element
Integrated Science Instrument Module
(ISIM) Element
Spacecraft Element
Sunshield Spacecraft Bus
5
6/15/2004
Observatory Structural Model
6
6/15/2004
Integrated Performance Analysis
l Overview
n Multi-disciplinary analysis
• Thermal, Optical, GN&C, and Structural
• Tight requirements drive the project toward more integrated analysis
n Performance budget
• Northrup-Grumman Space Technology (NGST) has adopted a very
detailed optical performance budget allocating wavefront error
• Seek to place the project in a position to intelligently comment on this
budget as the contractors estimate the telescope’s performance
n Linear optical model
• MATLAB-based tool to allow non-optical engineers to estimate wavefront
error
l Baseline Analyses:
n STOP
n Jitter
7
6/15/2004
Performance Budget
l NGST allocates and tracks optical performance with a spreadsheet
l Rooted in project Strehl ratio and Encircled Energy requirements
n Calculations translate these into total allowable WFE
• Allocated into 3 spatial-frequency bands (cycles/aperture)
• Allocations for both beginning and end of life
l Two main branches divisions at top level
n Active control
n Stability
l Geometry errors of optics divided into “figure” and “alignment”
l Temporal performance is allocated to either “drift” or “vibrate”
l Lowest-level requirements often related to equivalent mechanical
requirements
8
6/15/2004
Conditions
NIRCam
instr'm'nt nm System Allocation 150 nm rms
wfe for Strehl =
0.80 at wavelength = 2.0
µ
m
temp (K) 40 rms tot lo mid hi 60 nm rms
mid & hi frequency rss set by EEF >
0.74 in 150 mas at
λ
=
1.0
µ
m
load (g) 0 Req 150 138 58 17
field (
µ
r)
0
EOL
150
138
58
17
nm Obs Allocated Reserve nm
OTE Alloc.
nm Obs Syst Perf Reserve nm ISIM Struct. Alloc. nm NIRCam Path Alloc
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
Req 43 41 10 5 Req 131 117 56 16 Req 95 94 13 5 Req 22 22 4 0 nm non-common path Req 56 55 8 2
EOL 43 41 10 5 EOL 131 117 56 16 EOL 95 94 13 5 EOL 22 22 4 0 rms tot lo mid hi EOL 56 55 8 2
Req 39 39 0 0
EOL 39 39 0 0
tot lo mid hi
48
27
38
12
nm OTE Reserve nm System Performance nm
ISIM Struct. Reserve
nm NIRCam path reserve
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
Req 76 75 7 2 Req 117 101 56 16 Req 16 16 3 0 Req 34 34 2 1
EOL
76
75
7
2
EOL
117
101
56
16
EOL
16
16
3
0
EOL
34
34
2
1
nm
OTE totals
nm
OTE with non-common
nm ISIM Struct. totals nm NIRCam path totals
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
Req 107 90 56 16 Req 114 98 56 16 Req 15 15 3 0 Req 44 43 8 1
EOL 107 90 56 16 EOL 114 98 56 16 EOL 15 15 3 0 EOL 44 43 8 1
nm Image Motion Equ. nm Image Motion Equ. nm Image Motion Equ.
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
Req 71 71 0 0 Req 11 11 0 0 Req 11 11 0 0
EOL 71 71 0 0 EOL 11 11 0 0 EOL 11 11 0 0
tot
lo
mid
hi
Req
IM
6.4
mas
im
Req
IM
1.0
mas
im
Req
IM
1.0
mas
im
40
9
38
12
EOL
IM
6.4
mas
im
EOL
IM
1.0
mas
im
EOL
IM
1.0
mas
im
nm OTE WFC Residual nm OTE Stability stab nm ISIM Struct WFC resid nm
ISIM Struct Stab
stab nm NIRCam WFC Resid nm
NIRCam Stability
stab
tot lo mid hi rms tot lo mid hi rms tot lo mid hi rms tot lo mid hi rms tot lo mid hi rms tot lo mid hi rms tot lo mid hi
81
18
75
23
Req
58
14
54
16
Req
54
53
12
0
Req
3
0
3
0
Req
10
10
0
0
Req
40
39
8
1
Req
14
14
0
0
EOL 58 14 54 16 EOL 54 53 12 0 EOL 3 0 3 0 EOL 10 10 0 0 EOL 40 39 8 1 EOL 14 14 0 0
Req
EOL
seg piston
5 nm
seg piston
5 nm nm
ISIM Struct align
isim
seg tilt
7
nr
seg tilt
7
nr
rms
tot
lo
mid
hi
nm
NIRCam WFE
NIRCam
seg decent
100
nm
seg decent
100
nm
Req
106
106
0
0
rms
tot
lo
mid
hi
seg clock
217
nr
seg clock
217
nr
EOL
106
106
0
0
Req
56
55
6
1
Seg Met.
10
nm
Seg Met.
10
nm
EOL
56
55
6
1
SM piston 100 nm SM piston 100 nm
SM tilt 2
µ
r SM tilt 2
µ
r nm Align to ISIMNIRCam
SM decent
2
µ
m
SM decent
2
µ
m rms tot lo mid hi
SM Met.
10
nm
SM Met.
10
nm
Req
7
7
0
0
EOL
7
7
0
0
nm
Config. OTE Residual
ote
rms tot lo mid hi
LEGEND
Req 93 75 52 16 unit System Allocations unit Active Control unit Stability
EOL
93
75
52
16
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
tot
lo
mid
hi
Req
tot
val
val
val
Req
tot
val
val
val
Req
tot
val
val
val
tot
val
val
val
EOL tot val val val EOL tot val val val EOL tot val val val
black font: calculated
unit Reserves unit Configured (static) Mechanicl Suballocation blue font: input
rms tot lo mid hi rms tot lo mid hi Req
value
unit(tot) red font: reference sheet
Req tot val val val Req tot val val val EOLvalue unit(tot)
EOL tot val val val EOL tot val val val lo frequency: sf <= 5 cycles/aperture
mid frequency: 5 c/a < sf <= 30 c/a
hi frequency: 30 c/a < sf
verification accuracy
DPI
EMA
NIRCam
SI System Verification
Performance Budget
nm
System Stability
rms tot lo mid hi nm Obs Syst Perf Reserve
Req 57 55 12 0 rms tot lo mid hi
EOL
57
55
12
0
Req
0
0
0
0
EOL 0 0 0 0
nm Stability Reserve nm OTE Stability nm ISIM Struct Stability nm NIRCam Stability nm System Performance
rms tot lo mid hi rms tot lo mid hi rms tot lo mid hi rms tot lo mid hi rms tot lo mid hi
Req 0 0 0 0 Req 54 53 12 0 Req 10 10 0 0 Req 14 14 0 0 Req 57 55 12 0
EOL
0
0
0
0
EOL
54
53
12
0
EOL
10
10
0
0
EOL
14
14
0
0
EOL
57
55
12
0
nm OTE Stability nm ISIM Struct Stability nm NIRCam Stability
rms tot lo mid hi rms tot lo mid hi rms tot lo mid hi
Req 54 53 12 0 Req 10 10 0 0 Req 14 14 0 0
EOL
54
53
12
0
EOL
10
10
0
0
EOL
14
14
0
0
nm Alignment Drift nm SI Despace nm WFE Stability
rms tot lo mid hi rms tot lo mid hi rms tot lo mid hi
Req 25 25 0 0 Req 5 5 0 0 Req 10 10 0 0
EOL
25
25
0
0
EOL
5
5
0
0
EOL
10
10
0
0
Req despace 40
µ
m
nm Alignment Vibrate EOL despace 40
µ
m nm Align to ISIM Stab.
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
Req 32 32 0 0 nm SI Tilt Req 10 10 0 0
EOL 32 32 0 0 rms tot lo mid hi EOL 10 10 0 0
Req
5
5
0
0
nm Figure Drift EOL 5 5 0 0
rms tot lo mid hi Req tilt 600
µ
r
Req
32
30
11
0
EOL
tilt
600
µr
EOL
32
30
11
0
nm SI Decenter
nm
Figure Vibrate
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
Req
5
5
0
0
Req 15 15 3 0 EOL 5 5 0 0
EOL
15
15
3
0
Req
decenter
2.0
mm
EOL
decenter
2.0
mm
nm FSM/LOS range
rms
tot
lo
mid
hi
nm
SI Clocking
Req
1
1
0
0
rms
tot
lo
mid
hi
EOL 1 1 0 0 Req 5 5 0 0
Req
IM range
100
µ
r
EOL
5
5
0
0
EOL
IM range
100
µr
Req
clocking
140
µr
EOL clocking 140
µ
r
Guidelines in lieu of integrated modeling
nm
Alignment Drift
rms tot lo mid hi
Req
25
25
0
0
EOL 25 25 0 0
nm
PM Global
nm
SM
nm
TM
nm
FSM
nm
SI Interface
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
Req 9 9 0 0 Req 23 23 0 0 Req 2 2 0 0 Req 1 1 0 0 Req 7 7 0 0
EOL
9
9
0
0
EOL
23
23
0
0
EOL
2
2
0
0
EOL
1
1
0
0
EOL
7
7
0
0
nm Despace nm Despace nm Despace nm Despace nm Despace
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
rms
tot
lo
mid
hi
Req
7
7
0
0
Req
21
21
0
0
Req
1
1
0
0
Req
1
1
0
0
Req
7
7
0
0
EOL 7 7 0 0 EOL 21 21 0 0 EOL 1 1 0 0 EOL 1 1 0 0 EOL 7 7 0 0
Req
0.1
µ
m
Req
0.8
µ
m
Req
0.2
µ
m
Req
0.2
µ
m
Req
51
µ
m
EOL 0.1 µm EOL 0.8 µ m EOL 0.2 µm EOL 0.2 µ m EOL 51 µm
Mirror Assembly Mirror Assembly Mirror Assembly Mirror Assembly Mirror Assembly
Req
0.1
µ
m
Req
0.1
µ
m
Req
0.1
µ
m
Req
0.1
µ
m
Req
10
µ
m
EOL
0.1
µ
m
EOL
0.1
µ
m
EOL
0.1
µ
m
EOL
0.1
µ
m
EOL
10
µ
m
BP Distortion SMSS Distortion Bench Distortion Bench Distortion Bench Distortion
Req
0.1
µ
m
Req
0.8
µ
m
Req
0.2
µ
m
Req
0.2
µ
m
Req
50
µ
m
EOL 0.1 µm EOL 0.8 µ m EOL 0.2 µm EOL 0.2 µ m EOL µm
nm
Decenter
nm
Decenter
nm
Decenter
nm
Decenter
nm
Decenter
rms tot lo mid hi rms tot lo mid hi rms tot lo mid hi rms tot lo mid hi rms tot lo mid hi
Req
4
4
0
0
Req
7
7
0
0
Req
0
0
0
0
Req
1
1
0
0
Req
0
0
0
0
EOL 4 4 0 0 EOL 7 7 0 0 EOL 0 0 0 0 EOL 1 1 0 0 EOL 0 0 0 0
Req
1.1
µ
m
Req
2.0
µ
m
Req
0.2
µ
m
Req
0.1
µ
m
Req
0.1
µ
m
EOL 1.1 µm EOL 2.0 µ m EOL 0.2 µm EOL 0.1 µ m EOL 0.1 µm
Mirror Assembly
Mirror Assembly
Mirror Assembly
Mirror Assembly
Mirror Assembly
Req 0.5
µ
m Req 0.1
µ
m Req 0.1
µ
m Req 0.1
µ
m Req 0.1
µ
m
EOL
0.5
µ
m
EOL
0.1
µ
m
EOL
0.1
µ
m
EOL
0.1
µ
m
EOL
0.1
µ
m
BP Distortion SMSS Distortion Bench Distortion Bench Distortion Bench Distortion
Req
1.0
µ
m
Req
2.0
µ
m
Req
0.2
µ
m
Req
0.1
µ
m
Req
0.1
µ
m
EOL 1.0 µm EOL 2.0 µ m EOL 0.2 µm EOL 0.1 µ m EOL 0.1 µm
nm
Tilt
nm
Tilt
nm
Tilt
nm
Tilt
nm
Tilt
rms tot lo mid hi rms tot lo mid hi rms tot lo mid hi rms tot lo mid hi rms tot lo mid hi
Req
4
4
0
0
Req
4
4
0
0
Req
1
1
0
0
Req
0
0
0
0
Req
0
0
0
0
EOL 4 4 0 0 EOL 4 4 0 0 EOL 1 1 0 0 EOL 0 0 0 0 EOL 0 0 0 0
Req
0.1
µ
r
Req
1.3
µ
r
Req
2.2
µ
r
Req
0.0
µ
r
Req
µ
r
EOL 0.1 µr EOL 1.3 µ r EOL 2.2 µr EOL 0.0 µ r EOL µr
Mirror Assembly
Mirror Assembly
Mirror Assembly
Mirror Assembly
Mirror Assembly
Req 0.1
µ
r Req 1.0
µ
r Req 1.0
µ
r Req 0.0
µ
r Req 1.0
µ
r
EOL
0.1
µ
r
EOL
1.0
µ
r
EOL
1.0
µ
r
EOL
0.0
µ
r
EOL
1.0
µ
r
BP Distortion SMSS Distortion Bench Distortion Bench Distortion Bench Distortion
Req
0.1
µ
r
Req
0.8
µ
r
Req
2.0
µ
r
Req
0.0
µ
r
Req
µ
r
EOL 0.1 µr EOL 0.8 µ r EOL 2.0 µr EOL 0.0 µ r EOL µr
nm
Clocking
nm
Clocking
nm
Clocking
nm
Clocking
nm
Clocking
rms tot lo mid hi rms tot lo mid hi rms tot lo mid hi rms tot lo mid hi rms tot lo mid hi
Req
0
0
0
0
Req
0
0
0
0
Req
0
0
0
0
Req
0
0
0
0
Req
0
0
0
0
EOL 0 0 0 0 EOL 0 0 0 0 EOL 0 0 0 0 EOL 0 0 0 0 EOL 0 0 0 0
Req
0.3
µ
r
Req
1.4
µ
r
Req
0.7
µ
r
Req
1.4
µ
r
Req
1.4
µ
r
EOL 0.3 µr EOL 1.4 µ r EOL 0.7 µr EOL 1.4 µ r EOL 1.4 µr
Mirror Assembly
Mirror Assembly
Mirror Assembly
Mirror Assembly
Mirror Assembly
Req 0.2
µ
r Req 1.0
µ
r Req 0.5
µ
r Req 1.0
µ
r Req 1.0
µ
r
EOL
0.2
µ
r
EOL
1.0
µ
r
EOL
0.5
µ
r
EOL
1.0
µ
r
EOL
1.0
µ
r
BP Distortion SMSS Distortion Bench Distortion Bench Distortion Bench Distortion
Req
0.2
µ
r
Req
1.0
µ
r
Req
0.5
µ
r
Req
1.0
µ
r
Req
1.0
µ
r
EOL 0.2 µr EOL 1.0 µ r EOL 0.5 µr EOL 1.0 µ r EOL 1.0 µr
30.0
50
30.0
30.0
30.0
9
6/15/2004
Linear Optical Analysis
l Provides accurate estimate of OPD wavefront error for
perturbed systems (within the limits of the model)
l Coefficients created by ray-tracing runs in OSLO
n 10nm (nrad) motion introduced in each of optical DOF
n 100x100 array showing OPD at exit pupil generated in
MATLAB for each optical perturbation
l Arrays scaled and summed in MATLAB based on actual
motion in each of the 132 DOF
n Displacements multiplied by appropriate array
n OPD maps summed
n FSM manipulated to minimize RMS wavefront error
n Results are reported as “Best Fit Plane” with global piston
offset removed
10
6/15/2004
Linear Model Accuracy
11
6/15/2004
Structural-Thermal-Optical (STOP) Analysis
OSLO
Observatory
Structural
Model
Observatory
Thermal
Models
TSS and SINDA,
or IDEAS/TMG
Thermal
Transient
Analysis
Temperature
vs Time
(thermal)
Generate
Interferograms
Map
Temperatures
to Structure
NASTRAN
SigFit
Temperature
vs Time
(structural)
Displacements
of optical
elements and
surfaces
Wavefront
Error
(OPD Map &
RMS value)
Static Loads
Analysis
Optics Model
Ray-Trace
Analysis
Linear Optical
Tool
MATLAB
Prelim.
Final
PATRAN
EXCEL
12
6/15/2004
STOP Analysis – WFE Predictions
l STOP analysis of slew maneuvers requires pairs of linear statics runs
n Calculate delta between displacements of two room to operational thermal-loaded runs
l Most STOP analyses use linear optical tool for WFE prediction
n Current generation thermal models rarely include PM segment details
n Beryllium PM segments not expected to develop substantial gradients
Best-fit Plane of Transient Case (All Optics)
RMS:17.6 nm P-V:111.9 nm
Global Piston Offset:58.7 nm
-0.03
-0.02
-0.01
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
13
6/15/2004
Optical Jitter Dynamics (Jitter) Analysis
Integrated
Jitter Model
Jitter Model
Validation
Eigenvectors
& Eigenvalues
from normal
modes analysis
Validation
Results &
Documents
Optical
Sensitivity
Matrix
from optical
systems analysis
Dynamic WFE
LOS Error
Disturbance
Models
FSM Model
ACS Model
FGS Model
from controls
model
Dynamics
Model
Reduction
14
6/15/2004
0 50 100 150 200 250 300 350 400 450
0
10
20
30
40
50
60
70
80
90
100
Frequency vs Mode Number
Mode Number
Frequency (Hz)
Jitter Analysis – Modal Analysis and Damping
l The structures discipline provides frequencies, mode shapes, and modal
damping values for use in integrated modeling (IM) and attitude control
system (ACS) studies:
n Mode shapes (mass normalized) are partitioned based on DOF
corresponding to predefined reference points (optics, RWAs, etc).
n Modal damping values are either:
• Uniform
• Variable (Based on group participation determined using modal strain energy
fractions)
0 50 100 150 200 250 300 350 400 450
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
Modal Strain Energy Fractions
Mode Number
SEF
Tower ISO
RWA ISO
SC+SC
OTE
ISIM
Frequency (Hz)
0
10
20
30
40
50
60
70
80
90
100
40 Modes in 0-100 Hz
Frequency Range
First flexible mode =
0.42 Hz
15
6/15/2004
Jitter Analysis: Mode Shapes
Secondary Mirror Support Structure
Bending Mode @ 8 Hz
Backplane Twisting Mode @ 12 Hz
16
6/15/2004
Jitter Analysis – LOS and WFE Predictions
l Reaction Wheel Assemblies (RWAs) are largest jitter disturbance
source:
n Harmonic disturbances
n Excite spacecraft and telescope structural modes when the RWA spin
speed or harmonics align with the lightly damped structural modes.
0 10 20 30 40 50 60 70 80 90 100
10
-7
10
-6
10
-5
10
-4
10
-3
10
-2
10
-1
V2-LOS Error (asec)
wheel speed (RPS)
LOS EQNS
Linear Optics
0 10 20 30 40 50 60 70 80 90 100
10
-10
10
-8
10
-6
10
-4
10
-2
10
0
RMS WFE Error (micron)
wheel speed (RPS)
linopt
trw
17
6/15/2004
Challenges and Future Work
l Future Work:
n Program plans on following a schedule of analysis cycles:
• STOP/Jitter/Launch analyses
• First such cycle is underway (6 month duration)
n Need to verify budget allocations by means of integrated modeling
n Government team performs independent modeling analysis to validate prime
contractor
• Performance predictions
• Requirements placed on subcontractors/partners
l Challenges:
n Constant pressure exists to create accurate, detailed models while keeping
run times tolerable:
• Need for high-fidelity (multi-million DOF solid element) structural model anticipated
for CDR distortion analysis.
• Superelement approaches under investigation
n Need to understand sensitivity of results to variations in material properties
n Need to expand linear optical tool to calculate WFE at multiple field points
and FOV locations