Transcript Status of the Hybrid Doppler Wind Lidar (HDWL) Transceiver ACT

Status of the Hybrid Doppler Wind
Lidar (HDWL) Transceiver ACT
Project
Cathy Marx (NASA/GSFC), Principal Investigator
Bruce Gentry (NASA/GSFC), Michael Kavaya
(NASA/LaRC), Patrick Jordan (NASA/GSFC)
Co-Investigators
Ed Faust (SGT), Lead Designer
Space-Based Lidar Winds Working Group
August 24-26, 2010
Bar Harbor, Maine
Outline
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Space-based Design Background
Objectives
Requirements
Optical Design
Mechanical Design
Risks/Concerns
Acknowledgements:
Support for development of the HDWLT provided by the NASA
ESTO ACT program.
Hybrid Doppler Wind Lidar
Measurement Geometry: 400 km
350 km/217 mi
53 sec
Along-Track Repeat
“Horiz. Resolution”
586 km/363 mi
GWOS IDL Instrument
GPS
Star Tracker
Hybrid DWL Technology Solution
Altitude Coverage
Dir
-U ect
se
D
Overlap allows:
- Cross calibration
- Best measurements
selected
in assimilation process
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Telescope
Modules (4)
GWOS Payload Data
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Dimensions
1.5m x 2m x 1.8m
Mass
567 Kg
Power
1,500 W
Data Rate
4 Mbps
Orbit: 400 km, circ, sun-sync, 6am – 6pm
Selectively Redundant Design
+/- 16 arcsec pointing knowledge (post-processed)
X-band data downlink (150 Mbps); S-band TT&C
Total Daily Data Volume517 Gbits
Velocity Estimation Error
GWOS in Delta 2320-10 Fairing
Dimensions (mm)
NWOS System Configurations
(Courtesy M.Clark and D.Palace)
Configuration 1 and 2
(Inverted GWOS)
Configuration 3
(ShADOE)
Return
Hybrid Doppler Wind Lidar (HDWL) Transceiver
PI: Cathy Marx, GSFC
Objective
• Build a compact, light weight, four field-of-view
(4-FOV) transceiver, including a reliable FOV
select mechanism, in support of the Global
Tropospheric 3D Winds mission
• Integrate the hybrid transceiver with ground
based 355nm and 2um lasers and receivers
Approach
• Us e compact mechanical packaging to achieve a 4-FOV
hybrid transceiver
• Designed for efficient operation in the UV and IR
• Design long life mechanisms to select operational FOV
• Conduct ground based tests by integrating HDWL with
the Goddard Lidar Observatory for Winds (GLOW) and
LaRc Validar systems
• Leverage prior NASA investments in coherent and direct
detection lidar instrument technologies
CoIs/Partners:
Bruce Gentry, GSFC; Patrick Jordan, GSFC; Michael Kavaya,
LaRC
1/09
Key Milestones
• Define science requirements and interfaces for
the 355nm and 2um systems
• Complete telescope optical design
• Complete mechanical design of select mechanism
• Complete opto-mechanics of telescope mirrors
• Complete assembly and performance testing of
select mechanism
• Assemble transceiver
• Integrate transceiver with 355nm and 2um
lasers and receivers
• Conduct hybrid system validation
TRLin = 2
7/09
12/09
2/10
8/10
3/11
7/11
10/11
1/12
Requirements
Platform Altitude*
Telescope collecting
aperture
ACT
ACT
Space Demo
Space Demo
355 nm
12 to 20 km
2 um
12 to 20 km
355 nm
400 km
2 um
400 km
8" (0.2 m)
8" (0.2 m)
0.5 m
0.5 m
4
45 deg above horizon,
equally spaced in
azimuth
4
45 deg above horizon,
equally spaced in
azimuth
4
45 deg above horizon,
equally spaced in
azimuth
10
TBD
TBD
unobscured telescope
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unobscured telescope
>90%
diffraction limited at 2um
>90%
95% in 100 urad blur
(TBR)
>90%
diffraction limited at 2um
Number of look angles
4
45 deg above horizon,
equally spaced in
Telescope view angle
azimuth
Telescope
magnification
10
Telescope
configuration
-Throughput
requirements
>90%
Telescope image
95% in 100 urad blur
quality
(TBR)
Field of view
100 urad
Diffraction limited
* NASA research aircraft, e.g. DC8 and WB57, are target platforms for
design. ACT demonstration will be on ground.
Functional Block Diagram
Optics
Telescope Design
Outgoing laser
Incoming return
Primary
Secondary
Outgoing laser
Incoming return
Window
4 Primaries
• Key parameters
– 4 identical telescopes
– 8” collecting aperture
– Demagnification of 10
– Afocal system
– Primary and secondary are
both off-axis parabolas
• Iterated packaging to continue to
make compact
• Added the window up front to
ensure compatibility with aircraft
version.
Telescope Packaging
Window
Top View
Side View
Telescope Mirrors
• Primary mirror specifications:
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Clear Aperture: 200 mm
Off-axis distance: 150mm
Focal Length: 500mm
Surface accuracy: 1/10 wave PV at 633nm
Surface Quality: 40-20
Fiducials indicating off-axis distance, direction to parent vertex, clocking
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Clear Aperture: 18 mm
Off-axis distance: 13.5mm
Focal Length: 45mm
Surface accuracy: 1/10 wave PV at 633nm
Surface Quality: 40-20
Fiducials indicating off-axis distance, direction to parent vertex, clocking
• Secondary mirror specifications:
• Current baseline is to use light-weighted, low CTE mirrors
– Requested quotes from several vendors.
Light Weight Mirrors Option
Lightweight Zerodur substrates reduce
the mass of each 8 in mirror in half (From
8.5 lbs To 4.25 lbs).
Fabrication Process:
-Grind & polish solid blank using
conventional techniques
-Lightweight using machining per drawing
-Cut 4 mirrors from single blank
Multi-layer Dielectric Mirror Coating Design
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Theoretical Performance of Reflective
Coating
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Reflectivity
0.8
0.6
355 nm coating
0.4
2054 nm coating
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0.2
0
200
700
1200
1700
Wavelength (nm)
2200
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Current design is two multi-layer
designs. Coating optimized for
2.054um on substrate. Coating
optimized for 355 nm on top.
7 pairs optimized for performance at
354.7 nm and 7 pairs optimized for
performance at 2 um.
Predicted reflectivity of greater than
98% at 355 nm and 98% at 2 μm.
<1.5% difference in Rs and Rp at 355
nm. <0.4% difference in Rs and Rp
at 2054 nm.
Test windows have been ordered.
Preparing to test coatings with high
powered lasers.
Error Budget
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tip/tilt of secondary
1
arcmin
clocking of secondary
15
arcmin
decenter of secondary
25
microns
focus of secondary
5
microns
tip/tilt of primary
20
arcsec
clocking of primary
2
arcmin
decenter of primary
25
microns
focus of primary
5
microns
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Optical performance driven by
requirement for diffraction limited
performance at 2um.
Alignment and fabrication requirements
are tight.
Flats and beamsplitters cause beam
displacement. Also causes wavefront
error if, when tracing transmit beam, the
beam is not parallel to the telescope
optical axis.
Using alignment plan to aid in error
allocations.
Using this analysis to help determine
adjustment range and step size.
Mechanical
Mechanical Design
- Design of Telescope
Light Weight Structure (Material Selection)
Light Weight 8 in Mirrors Design
Select Mechanism
Release Optic ICD drawings (In Process)
Interface with optics designs (In Process)
Analysis (In Process)
- Assembly
Assy Plan
Location
GSE
- Package Lasers / Receiver and interface with
telescope
Design of Telescope
Structure
Latest layout of ACT Structural Design
Ray Trace Layout
Secondary mirror
Indexing mirror
Risely optics
Primary mirror
Folding Mirror
Indexing mechanism
Telescope Volume
18.48
inches
Top View
19.30
inches
27.66 inches
Composite Structure
One Piece Frame Design
Select Mechanism Reqts
Purpose:
• Sends outgoing laser light to correct telescope
Requirements (derived from GWOS study for demo mission):
• Four position mechanism where each position is separated by 90 deg
• Make as redundant as possible
• No preferred state if mechanism fails (because if it fails the mission is over….)
• Duty Cycle is 9*106 moves for 3-year mission
• 1 move every 11 seconds (10 sec for stare, 1 sec for move)
• Will always move in same direction
• First move is 90 deg, next move is 180 deg, next move is 270 deg and last move
is 180 deg
• Operation speed is 1 sec for movement and stabilization
Working with Pure Precision for a Precision Rotary Table
that will meet our requirements.
Technical Risks/Concerns
• Precision of optics required for coherent
system.
• Maintaining precision when thermal
environment is changing.
• Laser damage of mirror coatings.
• Maintaining manpower due to other
commitments.
Summary
• Telescope optical design and alignment
tolerancing complete
• Primary and secondary mirrors ordered (20 wk
delivery)
• COTS Select Mechanism identified
• Mechanical design ~85% complete.
– Working on mirror mounting details
– Iterating design with GSFC composites group to
optimize fabrication/cost