Presented by: Allison Barto

1. 1
Innovative, Non-Classical Optical performance
Verification Methodology:
Applied to the 6.6m James Webb Space Telescope
Allison Barto
November 8, 2012

2. 2
Fluctuations
condense into first
stars and proto-
galaxies
A Brief History of TimeA Brief History of Time
Big
Bang
Particle
Physics
Today
Atoms &
Radiation
First
Galaxies
Galaxies
Evolve
Planets, Life &
Intelligence
3
minutes
1 Gyr
Z ~ 5 14 Gyrs
Z ~ 0
400 Myr
Z ~ 12
Cosmic
Dark
Zone
Cosmic
Dark
Zone
Fluctuations in
microwave
background
300,000 yr
Z ~ 5000
The JWST mission
 JWST will be a space
based astronomical
observatory that explores
the gap between the distant
microwave background
and the nearer universe
observed by today’s
observatories.
 JWST will be able to “see
through the dust” to probe
galaxy and planet
formation
 The four science themes
are:
– First light and re-ionization
– Assembly of galaxies
– Birth of stars and
protoplanetary systems
– Planetary systems and
origins of life
Adapted from: H. S. Stockman, ed. “the Next Generation Space Telescope, “Visiting a Time When Galaxies were
Young”, Space Telescope Science Institute, (June 1997.)

3. 3
JWST: Large, Cold and Deployable
 Science objectives require observations of very faint
objects in NIR and MIR
– 0.6 mm to 27 mm wavelengths
– Diffraction limited performance at 2 mm wavelengths and longer
– Collecting aperture > 25 m2
 Warrants large aperture telescope operating at cryogenic
temperatures 32K to 59K
 Large size requires telescope be stowed for launch in
folded configuration, then deployed on orbit

4. 4
OTE Architecture Overview
SM Support Structure (SMSS)
• Deployable four-bar linkage strut assembly
• Secondary Mirror Mount (SMM)
Thermal Management Subsystem (TMS)
• Panel Roof Radiators
• Panel +/- V2 Radiators
• ISIM Enclosure (MLI)
• Parasitic Tray Radiator
Aft Optics Subsystem (AOS)
• Fixed tertiary mirror
• Fine steering mirror
• Baffle and pupil mask
SM Assembly (SMA)
• Low mass Beryllium mirror
• 6 DoF pose control
PM Segment Assembly (PMSA)
• 18 low mass Beryllium mirrors
• 6 DoF pose control
• Radius of curvature control
PM Backplane Assembly (PMBA)
• Fixed Center Section supports 12 segments
• Two deployable wings support 3 segments each
Deployable Tower Assembly
• Deployable telescoping tube
• Two deployable harness trays
• Cryocooler line accommodation
Isolator Assembly
• 1-Hz passive isolators
• Tower support
TMS (continued)
• Deployable “bat wings”
• Fixed diagonal shield
• Deployable stray light “bib”

5. 5
JWST is BIG!

6. 6
Optical Verification Methodology
 Key Features of the JWST architecture make a traditional “test as you fly” ground test
challenging from both a technical and cost perspective:
– 6.5 meter aperture
– Passively cooled to cryogenic temperatures (~40 K)
– Thermal Stability effects on Optical Performance (requirements allow DT ~ 0.15 K)
– Final flight configuration cannot be tested on the ground (alignment is not deterministic)
 Test program has been designed to support a final performance prediction via analysis
– High fidelity verification at lower levels of assembly
– Focus system-level testing on measuring data that cannot be obtained at a lower level
- Alignment between major components
– “Crosscheck” tests at the integrated system level to confirm lower-level test data can be relied upon
– Extensive model validation program
- Supported by crosscheck testing and independent modeling efforts
– Alignment range on-orbit
- Because system is aligned in flight, margin in actuator range gives added confidence to ability to
achieve aligned and phased state on orbit.

7. 7
Optical Verification Overview
 In order to verify Observatory optical performance on-orbit, there are four main aspects
of the system that need to be understood:
1. Optical performance of each optical component
2. Alignment between the optics
3. Adjustability of the PMSAs and SMA
4. Performance of the WFS&C Algorithms
 Each of these pieces of data is then used by the Integrated Telescope Model (ITM) to
analytically align the telescope and predict final performance
StrehlStrehl
WFE stabilityWFE stability EE StabilityEE Stability
Initial AlignmentInitial Alignment
Image MotionImage Motion
Thermal distortionThermal distortion
FGS-FSM-ACS loopFGS-FSM-ACS loop
Disturbance
Response
Disturbance
Response
Component WFE
(PM, SM, TM, FM, SI)
Component WFE
(PM, SM, TM, FM, SI)
WFSC
algorithms
WFSC
algorithms
Ground to flight effectsGround to flight effects
Test Uncertainties
(Alignment & WFE)
Test Uncertainties
(Alignment & WFE)
STOP Analysis Using As-Built Models
Encircled
Energy
Encircled
Energy
(Used for Sensitivity
Calculation)
Monte Carlo As-
Built In-Flight
Telescope/SIs
WFS&C
Commissioning
Simulations
ITM

8. 8
Relationship Between Test Performance
and Final Verification Uncertainty
Fixed
Alignment
Errors
AOS
TM
FSM
ISIM to AOS
Compensation
by PMSA
actuation
Compensation
by SMA
actuation
Compensation
by SMA
actuation
Residual WFE
after SMA
compensation
Adjustable
Alignment
Errors
(incl PM
Prescrip
& all
uncert)
PMSA level &
PM figure
Alignment
SMA level &
SM to AOS
Alignment
OTE
Optic
Figure
Optic Figure
Science Inst.
Non-Common
Path Uncert
Prescription
(SM/TM/FSM) Figure/
WFE
Alignment
Legend
Residual WFE
after all
compensation
Other Error Introduced
by WFS&C
•Sensing Error
•Control Error
•Field Dependent Error
Compensation by
SMA actuation
PM to AOS
Alignment
Errors
Compensation
by PMSA
actuation
Mid/High Frequency Errors not compensatable
Final uncertainty after
PMSA/SMA compensation
through WFS&C:
 Therefore, the verification program must:
– Show verification uncertainties of alignment and
low frequency figure errors are within the capture
range of the adjustable optics
– Show the remaining uncertainties are sufficiently
bound to ensure Image Quality reqs are met
- Mid/High frequency optic figure
- Actuator Control
- Sensing
 During WFS&C commissioning, low frequency errors are compensated by the PM & SM
– Fixed alignment errors
– Low frequency mirror figure errors

9. 9
Actuator Range Verification
 Optical performance budgets are based on the assumption that we have enough
actuator range to reach an aligned configuration on orbit
 Test and analysis uncertainties combine to impact total range needed on orbit and
magnitude of error that needs to be corrected using WFS&C
 Actuator Range is verified through a combination of:
– Ground alignment during Observatory testing in JSC Chamber-A
– Careful tracking of uncertainties of each constituent of the range budget
– Analysis of ground to orbit alignment and figure changes
Nominal
Deployed
Position
Actuator
Range for
Alignment
Tolerance
(OTE-252)
50% Actuator
Range Margin
(OTE-258)
50% Actuator
Range Margin
(OTE-258)
Ground
Measured
Range
Extrapolated
to FlightPredicted
“Ground
Nominal”
Position
Ground
measured
Range
Example
Acceptable
Actuator
Position
Deployed
Flight
Position
Algorithm
Capture Range
(OTE-254)
Req & Budget Range
Allocations
JSC Actuator Range Test
Extrapolate Test
Results to Flight
On-Orbit
Deployment
Nominal
Deployed
Position
Actuator
Range for
Alignment
Tolerance
(OTE-252)
50% Actuator
Range Margin
(OTE-258)
50% Actuator
Range Margin
(OTE-258)
Ground
Measured
Range
Extrapolated
to FlightPredicted
“Ground
Nominal”
Position
Ground
measured
Range
Example
Acceptable
Actuator
Position
Deployed
Flight
Position
Algorithm
Capture Range
(OTE-254)
Req & Budget Range
Allocations
JSC Actuator Range Test
Extrapolate Test
Results to Flight
On-Orbit
Deployment

10. 10
Optical Performance of Each Optical Component
Tests highlighted with a green box supply
data input directly into the ITM model and
are considered verification tests
Tests not highlighted with a green box are
crosscheck are model validation tests of
optical performance
PMSA Optical
Testing
SMA Optical
Testing
TMA Optical
Testing
FSM Optical
Testing
Individual SI
Optical Testing
COCI Testing of
Integrated PM at JSC
AOS Optical Test using
AOS Source Plate during
Pathfinder Testing at JSC
Integrated ISIM
Optical Testing with
OSIM at GSFC
AOS/ISIM Optical
Test using AOS
Source Plate Inward
Sources at JSC
Pass-and-a-Half Observatory
Optical Test using AOS Source
Plate Outward Sources at JSC
PMSA Optical
Testing
SMA Optical
Testing
TMA Optical
Testing
FSM Optical
Testing
Individual SI
Optical Testing
COCI Testing of
Integrated PM at JSC
AOS Optical Test using
AOS Source Plate during
Pathfinder Testing at JSC
Integrated ISIM
Optical Testing with
OSIM at GSFC
AOS/ISIM Optical
Test using AOS
Source Plate Inward
Sources at JSC
Pass-and-a-Half Observatory
Optical Test using AOS Source
Plate Outward Sources at JSC

11. 11
Installation Align (to AOS)
Actuator Range & Stow/Deploy
Pre/Post Vibe Mechanical Gaps
Alignment to AOS
Actuator Performance
Actuator Range
Ambient Tests
Cryogenic Tests
Simplified PMSA Optical Test Flow
Other Test Data
Mirror Fab (CGH-T)
(in process figure
measurements)
BOTS
(CGH-B1)
Prescription
Alignment
XRCF 1 (CGH-B2)
Cryo Hit Map
Early Fig & Prescrip
Actuators
Prescrip Align
Tinsley Final
(CGH-T)
Figure & Prescrip
XRCF 2 (CGH-B2)
Final Figure
BOTS
(CGH-B1)
Prescription
Alignment
Prescription
Alignment
Actuator range/resolution
Prescrip Align
Ambient Tests
Cryogenic Tests
Integrated PM Optical Test Flow
Other Test Data
SSDIF
Pre/Post Vibe PMSA figure
(optical testing under review)
JSC Ambient
(Null Lens)
PMSA figure
including Astig
JSC Cryo (Null Lens)
Final RoC & Low freq figure
Alignment to AOS
Gaps (optical)
 In addition to the system-level optical crosschecks, several independent
measurements of mirror prescriptions are made at the subsystem level
 The figure below shows a simplified test flow for the PMSAs as an example of all
the in-process measurements that are made
– Individual optics are tested both at ambient and cryogenic temperatures
– Testing before and after repeated mounting verifies mount distortion
– Testing before and after environmental testing verifies allocation for launch induced changes
Repeated Optical Testing Builds
Confidence & Crosschecks Performance

12. 12
Alignment Verification Between
Each Optical Component
ISIM
Verification
Data
OTE
Verification
Data
ISIM
Crosscheck
Data
OTE
Crosscheck
Data
Legend
OTE / ISIM
Verification
Data
OTE / ISIM
Crosscheck
Data
Element I&T Observatory I&T
SMSS alignment
PMBSS
cryo shift
PMBSS
1-g/0-g release
PMBSS
shape
SI internal
alignment
AOS internal
alignment
PMSA-PMSA
Alignment
SMSS
Deployment
ISIM to AOS
alignment
PM to AOS alignment
& PMSA Ground Test
Actuator Range
SM to AOS
alignment & SMA
Ground Test
Actuator Range
Fixed
Alignments
Adjustable
Alignments PMBA Wing
Deployment
Subsystem Test
AOS internal
alignment
ISIM to AOS
alignment
SI to ISIM
alignment
Fixed
Alignments
 Alignment between major optical components is the primary system-level cryo test
output for optical verification
– Understanding alignment of the optics is critical to verifying actuator range requirements are met
– Uncertainty in alignment testing is one of the primary contributors to the capture range needed by
WFS&C
 System cryo testing is the only opportunity to obtain many alignments
 Critical fixed alignments that cannot be measured directly are obtained
in lower-level tests

13. 13
OTE Cassegrain
Focal Surface –
downward
pointing IR
sources.
Images at AOS
focal point (up
to 3000 nm rms
WFE)
AOS
TM
FSM
Backplane
I/F
(3 places)
Alignment Verification During System Cryogenic Test
 Alignment between major optical components is verified at cryogenic temperatures using
photogrammetry and the inward sources on the AOS Source Plate
– Photogrammetry measures alignment to 100 micrometer / 150 micron levels
– ASPA measures alignment of the AOS to the ISIM to approximately
1.0 mm despace, 0.5 mm decenter, 0.25 mrad tip/tilt, 1.2 mrad clocking
 The system-level “Pass-and-a-Half” optical test described earlier serves as a crosscheck
to the alignments measured through the verification tests.
Photogrammetry Measures alignment of:
- PM to AOS
- SM to AOS
COCI measures PMSA to
PMSA alignment
(Photogrammetry is
crosscheck for outer
12 PMSAs)
AOS Source Plate inward facing
sources are used during the
Field Alignment Test to measure
ISIM to AOS Alignment
WFE retrieved by SI WFS;
wavefront power extracted to
determine defocus
Targets
Photogrammetry AOS Source Plate
PG Cameras on
four windmills

14. 14
Adjustability Verification of the PMSAs and SMA
PMSA/SMA Adjustability Verification
 PMSA/SMA Adjustability is dominated by actuator performance. Therefore, the test program
focuses on detailed verification at the actuator level
– Each actuator is tested to the sub-nanometer level for resolution and accuracy at both ambient and
cryogenic temperatures (requirements are 10 nm step size with 3 nm accuracy)
 Adjustability of the fully-integrated PMSAs and SMA are further tested during component
cryogenic testing. During these tests, actuator performance is verified to the 2-4 step level
– Also compared to hexapod models developed using actuator-level test data
 Total actuator range is verified at all the test points above
 During the system-level cryogenic testing, adjustability is crosschecked when mirrors are
exercised during PM alignment and when aligning the SMA for the Pass-and-a-Half test.
– PMSA motions can be measured to the 2-4 step level through the COCI.
Wavefront Sensing Verification
 Performance of the algorithms is verified using the Integrated Telescope Model
– Both individual algorithm performance and full end-to-end commissioning simulation is performed
 Performance of WFS&C components and Science Instrument detectors is verified at the
component and instrument level

15. 15
Communication
 This all sounds pretty complicated
– How do you communicate such an idea?
– How do you show nothing has been missed?
1. Graphically explain the big picture – keep it to one page!
– Because the key JWST optical verification is building a representative model of the as-built
hardware, we developed a “Verification Roadmap” to show the top-level data flow (NOT event
flow (i.e. not from a schedule). Address how test uncertainty is handled
– The roadmap delineates key concepts to understand how the pieces fit together:
- At what level of integration is the data collected? (component, system)
- Are there key differences between how the data is collected and how it
must be used? (temperature, gravity orientation)
- What is the fidelity of the test (verification test, model validation test)
- Identify system cross check tests – what pieces of data do they crosscheck?
2. Catalog the piece parts to show all are accounted for
– We developed a “Crosscheck Matrix”
- each row represents a critical parameter (figure of an optic, alignment between optics)
- columns represent all major test events (component, assembly, system)
- Data within each cell shows the requirement we are trying to measure and the uncertainty of that test

16. 16
Summary
 JWST Optical Performance Verification program has been developed to balance technical
challenges with the desire to “test-as-you-fly”
 Data for each component of the system is verified at the component level and input directly
into the as-built Observatory model
– I&T Workmanship concerns, actuator range, and combined uncertainties have been considered
 Flight alignment process/algorithms applied directly to the as-built model
 This approach gives an accurate prediction of final performance
– Use of analysis minimizes the technical difficulties of verification of system performance to requirement-
level through an end-to-end test
– Allows a more accurate verification and understanding of the effect of test uncertainties on the final in-
flight alignment and optical performance of JWST
 Non-classical approaches to verification programs can be successfully
implemented and may be both more technically accurate and more cost effective
than traditional approaches
 Clear communication, careful tracking, and model validation help ensure success
Work was supported in part by Ball Aerospace & Technologies Corp subcontract with Northrop Grumman Aerospace Systems (NGAS)
under the JWST contract NAS5-02200 with NASA GSFC. The JWST system is a collaborative effort involving NASA, ESA, CSA, the
astronomy community, and numerous principal investigators