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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 • • • • • • 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 -M s m et e wh eets ole ctio en thr cul n ae esh ar b Do ros ol p a ols d re cks pler no qu catt Lid t p ire er ar res me en nts t r Lida pler tter p o tD ca erenosol backsds when Coh r in s ae cy w -Use accura ent h s -Hig sols pre aero Nadir Telescope Modules (4) GWOS Payload Data • • • • • 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 -- 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: – – – – – – 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 – – – – – – 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 • Theoretical Performance of Reflective Coating • 1 Reflectivity 0.8 0.6 355 nm coating 0.4 2054 nm coating • 0.2 0 200 700 1200 1700 Wavelength (nm) 2200 • • • 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 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