Status of the Hybrid Doppler Wind Lidar (HDWL) Transceiver ACT
ProjectCathy 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• 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 LidarMeasurement Geometry: 400 km
350 km/217 mi53 secAlong-Track Repeat“Horiz. Resolution”
586 km/363 mi
GWOS IDL Instrument
GWOS Payload Data
Telescope Modules (4)
GPS
Nadir
Star Tracker
Dimensions 1.5m x 2m x 1.8m
Mass 567 Kg
Power 1,500 W
Data Rate 4 Mbps
GWOS in Delta 2320-10 Fairing
Dimensions (mm)
• 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 Volume 517 Gbits
Hybrid DWL Technology Solution
Velocity Estimation Error
Direct Detection Doppler Lidar
-Uses molecular backscatter
-Meets threshold requirements
when aerosols not present
Coherent Doppler Lidar
-Uses aerosol backscatter
-High accuracy winds when
aerosols present
Alti
tud
e C
ove
rage
Overlap allows:- Cross calibration- Best measurements
selected in assimilation process
Velocity Estimation Error
Direct Detection Doppler Lidar
-Uses molecular backscatter
-Meets threshold requirements
when aerosols not present
Coherent Doppler Lidar
-Uses aerosol backscatter
-High accuracy winds when
aerosols present
Alti
tud
e C
ove
rage
Overlap allows:- Cross calibration- Best measurements
selected in assimilation process
NWOS System Configurations(Courtesy M.Clark and D.Palace)
Configuration 1 and 2(Inverted GWOS)
Configuration 3(ShADOE)
Return
• Define science requirements and interfaces for 7/09the 355nm and 2um systems
• Complete telescope optical design 12/09• Complete mechanical design of select mechanism 2/10• Complete opto-mechanics of telescope mirrors 8/10• Complete assembly and performance testing of 3/11
select mechanism• Assemble transceiver 7/11• Integrate transceiver with 355nm and 2um 10/11
lasers and receivers• Conduct hybrid system validation 1/12
Hybrid Doppler Wind Lidar (HDWL) Transceiver
PI: Cathy Marx, GSFC
CoIs/Partners:Bruce Gentry, GSFC; Patrick Jordan, GSFC; Michael Kavaya, LaRC
•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
• 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
TRLin = 2
1/09
Objective
Key Milestones
Approach
Requirements
ACT ACT Space Demo Space Demo
355 nm 2 um 355 nm 2 umPlatform Altitude* 12 to 20 km 12 to 20 km 400 km 400 km
Telescope collecting aperture 8" (0.2 m) 8" (0.2 m) 0.5 m 0.5 mNumber of look angles 4 4 4 4
Telescope view angle
45 deg above horizon, equally spaced in
azimuth
45 deg above horizon, equally spaced in
azimuth
45 deg above horizon, equally spaced in
azimuth
45 deg above horizon, equally spaced in
azimuth
Telescope magnification 10 10 TBD TBDTelescope configuration -- unobscured telescope -- unobscured telescope
Throughput requirements >90% >90% >90% >90%
Telescope image quality
95% in 100 urad blur (TBR)
diffraction limited at 2-um
95% in 100 urad blur (TBR)
diffraction limited at 2-um
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• 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.
Outgoing laser
Incoming return Primary
Secondary
Window
4 Primaries
Outgoing laser
Incoming return
Telescope Packaging
Window
Top View Side View
Telescope Mirrors• Primary mirror specifications:
– 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
• Secondary mirror specifications:– 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
• Current baseline is to use light-weighted, low CTE mirrors– Requested quotes from several vendors.
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
Light Weight Mirrors Option
Multi-layer Dielectric Mirror Coating Design
• 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
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
• 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 DesignSelect Mechanism Release Optic ICD drawings (In Process)Interface with optics designs (In Process)Analysis (In Process)
- AssemblyAssy PlanLocationGSE
- Package Lasers / Receiver and interface with telescope
Design of Telescope
Structure
Latest layout of ACT Structural Design
Ray Trace Layout
Risely optics
Primary mirror
Secondary mirror
Folding Mirror
Indexing mirror
Indexing mechanism
Telescope Volume
27.66 inches
19.30inches
18.48 inches
Top View
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