Eng, Ron

NASA Technical Reports Server

Future space telescope development at NASA
Ron Eng
Optics and Imaging Branch
NASA Marshall Space Flight Center
Korean Space Science Society (KSSS) 2018 fall conference
https://ntrs.nasa.gov/search.jsp?R=20180007890 2019-08-31T17:13:53+00:00Z
NASA Marshall Space Flight Center
Oct 24-26, 2018 KSSS 2018 fall conference 2
Marshall Space Flight Center
Space Transportation, Propulsion Systems, Space Systems, and Science
Huntsville, Alabama
Oct 24-26, 2018 KSSS 2018 fall conference 3
Space Transportation, Propulsion Systems
Oct 24-26, 2018 KSSS 2018 fall conference 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 24-26, 2018 KSSS 2018 fall conference 5
Current and planned astrophysics missions
Chandra
7/23/1999
Kepler
3/7/2009
TESS
4/18/2018
JWST
2021
WFIRST
Mid 2020s
Oct 24-26, 2018 KSSS 2018 fall conference 6
4/24/1990
7/23/1999
Launch 2003
2021 Mid 2020s
Oct 24-26, 2018 KSSS 2018 fall conference 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 24-26, 2018 KSSS 2018 fall conference 8
Direct imaging technique with external starshade
Star
Exoplanet Starshade
62m
80,000 km
> 4 m
Telescope
Oct 24-26, 2018 KSSS 2018 fall conference 9
Chandra X-Ray Observatory
Oct 24-26, 2018 KSSS 2018 fall conference 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 24-26, 2018 KSSS 2018 fall conference 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 24-26, 2018 KSSS 2018 fall conference 12
XRCF class 2K clean room
Oct 24-26, 2018 KSSS 2018 fall conference 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 24-26, 2018 KSSS 2018 fall conference 14
James Webb Space Telescope (JWST)
Oct 24-26, 2018 KSSS 2018 fall conference 15
JWST orbit
•~1,500,000 km from earth vs ~650 km for Hubble
•30 to 60 deg. K operational temperature
Oct 24-26, 2018 KSSS 2018 fall conference 16
HST & JWST primary mirror comparison
2.4 m dia.
3.6 m2
6.5 m (18 mirror segments)
25 m2
Oct 24-26, 2018 KSSS 2018 fall conference 17
6 of 18 mirror segments cryo test at MSFC
Oct 24-26, 2018 KSSS 2018 fall conference 18
OTE deployment test at GSFC
Oct 24-26, 2018 KSSS 2018 fall conference 19
OTE cryo test at JSC
Oct 24-26, 2018 KSSS 2018 fall conference 20
JWST mirror optical test instrument
Oct 24-26, 2018 KSSS 2018 fall conference 21
Simultaneous phase shifting interferometer
Micro-polarizer array camera 
sensor
Spatial phase shifting overcomes 
previous single frame or temporal 
phase shifting interferometer 
technique
Overcomes vibration and air 
turbulence in long optical path test 
setup found in astronomical 
telescope metrology in vacuum 
test chamber
Oct 24-26, 2018 KSSS 2018 fall conference 22
1 x 2 m cryo test chamber for mirror characterization
Oct 24-26, 2018 KSSS 2018 fall conference 23
Test configuration for < 0.8 m dia. mirror
Oct 24-26, 2018 KSSS 2018 fall conference 24
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 24-26, 2018 KSSS 2018 fall conference 25
Six enabling technologies
1. Large-aperture, low-areal density, high-stiffness mirror 
2. Mirror support system
3. Integrated model validation
4. Mid & high spatial frequency figure error
5. Segment edges 
6. Segment to segment gap phasing
Oct 24-26, 2018 KSSS 2018 fall conference 26
Approach
• Develop structural, thermal and optical performance (STOP) models of 
candidate mirror assembly
• Models are validated by testing of subscale mirror assembly in relevant 
thermo-vacuum environments
• Develop & improve test methods to characterize mirror performance
• Using same test setup, facility to characterize competing mirror 
architecture
• Utilize and add capabilities to existing test facilities
• Gain valuable testing experience for personnel
Oct 24-26, 2018 KSSS 2018 fall conference 27
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 24-26, 2018 KSSS 2018 fall conference 28
Test configuration for < 3.5 m radius of curvature mirror 
Oct 24-26, 2018 KSSS 2018 fall conference 29
Test configuration for < 3.5 m radius of curvature mirror 
Oct 24-26, 2018 KSSS 2018 fall conference 30
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 24-26, 2018 KSSS 2018 fall conference 31
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 24-26, 2018 KSSS 2018 fall conference 32
Cryo optical test with PTE
Oct 24-26, 2018 KSSS 2018 fall conference 33
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 24-26, 2018 KSSS 2018 fall conference 34
Predicted 
580 nm rms
Measured
582.5 nm rms
Oct 24-26, 2018 KSSS 2018 fall conference 35
Vertical optical test configuration
Thermal gradient test
Oct 24-26, 2018 KSSS 2018 fall conference 36
Oct 24-26, 2018 KSSS 2018 fall conference 37
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 24-26, 2018 KSSS 2018 fall conference 38
X-Ray computed tomography
Future test plans
Oct 24-26, 2018 KSSS 2018 fall conference 39
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 24-26, 2018 KSSS 2018 fall conference 40
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 24-26, 2018 KSSS 2018 fall conference 41
Thank you
Dr. Jeong-Yeol Han
Ron Eng
ron.eng@nasa.gov
https://optics.nasa.gov


Future Space Telescope Development at NASA

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