Eng, Ron

NASA Technical Reports Server

Large space telescope development programs
Ron Eng
Optics and Imaging Branch
NASA Marshall Space Flight Center
1st Silicon Carbide International workshop
https://ntrs.nasa.gov/search.jsp?R=20180007892 2019-08-31T17:12:23+00:00Z
NASA Marshall Space Flight Center
Oct 29, 2018 1st SiC international workshop 2
Marshall Space Flight Center
Space Transportation, Propulsion Systems, Space Systems, and Science
Huntsville, Alabama
Oct 29, 2018 1st SiC international workshop 3
Space Transportation, Propulsion Systems
Oct 29, 2018 1st SiC international workshop 4
Space Systems and Science
High Energy Astronomy 
Observatories (1977-1981)
International Space Station (1998-present)
Hubble Space Telescope (1990-present)
Imaging X-ray Polarimetry Explorer (IXPE)
Under development
Chandra X-Ray Observatory
(1999-present)
Oct 29, 2018 1st SiC international workshop 5
Current and planned astrophysics missions
Chandra
7/23/1999
Kepler
3/7/2009
TESS
4/18/2018
JWST
2021
WFIRST
Mid 2020s
Oct 29, 2018 1st SiC international workshop 6
4/24/1990
7/23/1999
Launch 2003
2021 Mid 2020s
Oct 29, 2018 1st SiC international workshop 7
Detecting exoplanet
Image Credit: NASA/JPL Cassini wide-angle camera
Earth
Imaging exoplanet (a planet orbiting a sun-like star) is a tremendous 
technological challenge, since the Earth is 10 billion times fainter than the sun. 
The Cassini wide-angle camera used Saturn as an external occulter to block the 
sun.
Oct 29, 2018 1st SiC international workshop 8
Direct imaging technique with external starshade
Star
Exoplanet Starshade
62m
80,000 km
> 4 m
Telescope
Oct 29, 2018 1st SiC international workshop 9
Chandra X-Ray Observatory
Oct 29, 2018 1st SiC international workshop 10
X-ray & Cryogenic facility (XRCF)
Large test chamber:
• 7.3 x 22.9 m (O.D. x L) horizontal 
cylinder
• 6 x 18.3 m (I.D. x L)  test volume
• 4.25 x 9.4 m (I.D. x L) Helium shroud
• < 22.5 m ROC without modification 
• Up to 30 m ROC with modifications
Cryo shroud enclosure: 320º to 20º K
Refrigeration system: 2 gaseous helium 
refrigerators; each capable of ~1 kW at 20K.
Vacuum systems: 10-8 Torr
X-ray source: 527 m guide tube
History
Testing grazing-incidence x-ray telescopes (Chandra, Solar X-ray Imager, Solar B) since 1992.  
Cryogenic optical testing of normal incidence, visible & IR optics (JWST) since 1999.
Oct 29, 2018 1st SiC international workshop 11
JWST PMSA test configuration
7.3 x 22.9 m vacuum chamber
6 x 18.3 m test volume
5 m dia. gaseous helium-cooled shroud
16 m ROC; ~4 m dia. (JWST 6 PMSA) 
2 closed-loop helium cryogenic refrigeration systems <20 deg. K (2 KW capacity)
Existing structure prevents testing mirrors with ROC < 3.5 meters
A pressure tight enclosure (PTE) configuration to test mirror with short ROC < 3.5 meter
Oct 29, 2018 1st SiC international workshop 12
XRCF class 2K clean room
Oct 29, 2018 1st SiC international workshop 13
James Webb Space Telescope (JWST)
NASA, ESA, and CSA
Planned launch date 3/30/2021
0.6 – 30 microns (visible to mid IR)
4 scientific instruments
6.5m primary mirror
L2 orbit, 1,500,000 km
Science objectives: first light, formation of galaxies, birth of stars and planets, and 
origin of life.
Technical challenges: deployable segmented telescope and structure, lightweight yet 
stable optics at 40 degrees Kelvin operational temperature.
Oct 29, 2018 1st SiC international workshop 14
James Webb Space Telescope (JWST)
Oct 29, 2018 1st SiC international workshop 15
JWST orbit
•~1,500,000 km from earth vs ~650 km for Hubble
•30 to 60 deg. K operational temperature
Oct 29, 2018 1st SiC international workshop 16
HST & JWST primary mirror comparison
2.4 m dia.
3.6 m2
6.5 m (18 mirror segments)
25 m2
Oct 29, 2018 1st SiC international workshop 17
6 of 18 mirror segments cryo test at MSFC
Oct 29, 2018 1st SiC international workshop 18
OTE deployment test at GSFC
Oct 29, 2018 1st SiC international workshop 19
OTE cryo test at JSC
Oct 29, 2018 1st SiC international workshop 20
JWST mirror optical test instrument
Oct 29, 2018 1st SiC international workshop 21
Test configuration for < 0.8 m dia. mirror
Oct 29, 2018 1st SiC international workshop 22
Motivation for SiC testing
• Silicon Carbide for mirror substrate and structural support material
• Low density and CTE, high modulus or stiffness and thermal 
conductivity
• Can be polished to < 10Å rms
• More than a dozen SiC mirror substrate manufacturers in US 
• Over 70 types of SiC: converted SiC, C-SiC, CVC SiC, CVD SiC, CVD 
SiC on structural graphite core, hot pressed SiC, monolithic CVD-SiC, 
reaction bonded SiC, siliconized Carbon, sintered SiC, etc.
• Need for independent material properties database
Oct 29, 2018 1st SiC international workshop 23
Approach
• OBJECTIVE
– provide test data on materials using consistent test methods
– vendor independent test data
– characterize vendor’s process and lot uniformity
• APPROACH
– phase I : samples from 2 or more lots from each participating 
vendors
– phase 2 : samples from 3 additional processing lots
– final report and material properties database
Oct 29, 2018 1st SiC international workshop 24
Test plan
• Phase 1
– incoming surface roughness evaluation; polish if needed
– cryogenic strain tests (from room temperature down to 30° K)
– metallographic analysis/chemical analysis
– microstructure analysis/X-Ray diffraction
– density/porosity measurements
• Phase 2
– CTE
– thermal conductivity
– tensile strength and elastic modulus
– 4-point bending tests
– fracture toughness
– Analysis: metallographic, chemical, microstructure, X-Ray diffraction
– density/porosity measurements
Oct 29, 2018 1st SiC international workshop 25
Cryogenic strain test plan
• Sample Description: 125 mm plano disk, P-V and 100Å rms or best 
effort. Vendor supply 1 unclad + 1 cladded sample from 2 lots/batches. 
If unclad sample is not polish-able, then supply 2 cladded samples 
from 2 batches
• Objective: measures optical figure changes from room temperature 
to 30° K. The data output will be figure map, rms value, and power as 
a function of temperature
• Test Method: interferometric test will be performed under vacuum at 
room temperature 290°, 200°, 100°, 70°, 50°, 30°, and 290° Kelvin
Oct 29, 2018 1st SiC international workshop 26
Cryo strain SiC sample geometry
Oct 29, 2018 1st SiC international workshop 27
Participating SiC vendors
• Phase 1: tested 46 samples for cryogenic optical strain
– Boostec S.A.
– CoorsTek
– GE Power Systems Composites, LLC / ECM
– M-Cubed Technologies, Inc.
– Poco Graphite, Inc.
– SSG Precision Optronics, Inc.
– Trex Enterprises Corp.
• Phase 2:
– CoorsTek
– Poco Graphite, Inc.
– SSG Precision Optronics, Inc.
– Trex Enterprises Corp.
Oct 29, 2018 1st SiC international workshop 28
1 x 2 m cryo test chamber for mirror characterization
Oct 29, 2018 1st SiC international workshop 29
Cryo test of 12 SiC mirrors (~150 mm dia. each)
Oct 29, 2018 1st SiC international workshop 30
Cryo strain test setup
Oct 29, 2018 1st SiC international workshop 31
Observations
• large variance among each vendor’s samples
• SiC cryo strain caused by materials and more importantly,
residual stress from polishing
• Test results along with vendor part # will be given to each
perspective vendor
Oct 29, 2018 1st SiC international workshop 32
Advanced Mirror Technology Development (AMTD)
• Develop enabling technology for 4 meters or larger monolithic 
or segmented, UV, optical, and IR space telescope primary 
mirror assemblies for general astrophysics, and ultra-high-
contrast observations of exoplanet missions
• Large UV optical IR (LUVOIR) surveyor mission concept
• HabEx mission concept
• Mission concepts for the 2020 Decadal Survey
Oct 29, 2018 1st SiC international workshop 33
Pressure tight enclosure in large chamber 
Existing structure prevents testing mirrors in this configuration with ROC < 3.5 meters
A pressure tight enclosure (PTE) configuration to test mirror with ROC < 3.5 meter
Oct 29, 2018 1st SiC international workshop 34
Test configuration for < 3.5 m radius of curvature mirror 
Oct 29, 2018 1st SiC international workshop 35
Test configuration for < 3.5 m radius of curvature mirror 
Oct 29, 2018 1st SiC international workshop 36
Test envelop for large and small chambers
Chamber Max Diameter Max radius of curvature
Large 4.25 m 22.5 m
Small 0.8 m 2.5 m
Oct 29, 2018 1st SiC international workshop 37
Optical test equipment inside pressure tight enclosure (PTE)
1. alignment CCD
2. alignment pinhole
3. interferometer
4. ADM
5. IR camera stage
6. hexapod
Oct 29, 2018 1st SiC international workshop 38
Cryo optical test with PTE
Oct 29, 2018 1st SiC international workshop 39
Thermal optical test surface figure error
- =
Predicted SFE uses:
• as-built CTE distribution
• as-built shape from X-ray CT
• includes prying (due to aluminum frame) and all possible forces 
reacting between mount and bond pad
Residual SFE could be CTE inhomogeneity
Gravity sag (predicted vs measured)
Oct 29, 2018 1st SiC international workshop 40
Predicted 
580 nm rms
Measured
582.5 nm rms
Oct 29, 2018 1st SiC international workshop 41
Vertical optical test configuration
Thermal gradient test
Oct 29, 2018 1st SiC international workshop 42
Oct 29, 2018 1st SiC international workshop 43
Mirror assembly modal test
Mirror assembly suspended with bungees to simulate free-free condition
• Tapped at 42 locations with an instrumented 
modal test hammer
• Each location was tapped 5x and averaged
Oct 29, 2018 1st SiC international workshop 44
X-Ray computed tomography
Future test plans
Oct 29, 2018 1st SiC international workshop 45
Current test facility modifications 
• Predictive thermal control
• Passive thermal
• Active thermal control
• Low CTE glass-ceramic mirrors
• Low CTE ceramic mirrors
• Low CTE metal mirrors
• Additive manufactured mirrors
Oct 29, 2018 1st SiC international workshop 46
Acknowledgments
Phil Stahl: PI
Michael Effinger: program manager
Mark Baker, Bill Hogue, Jeffrey Kegley, Richard Siler, John Tucker, Ernest Wright: XRCF 
thermal-vac test support team
Thomas Brooks: thermal-mechanical analysis
Brent Knight, Frank Tsai: modal analysis
Alex McCool, Russel Parks: modal test
Ron Beshears, Dave Myers: X-ray computed tomography
Darrell Gaddy: thermal IR video
Brian Odom: MSFC historical photos
Oct 29, 2018 1st SiC international workshop 47
Thank you
Dr. Jeong-Yeol Han
Ron Eng
ron.eng@nasa.gov
https://optics.nasa.gov
Oct 29, 2018 1st SiC international workshop 48
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Large Space Telescope Development Programs

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