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

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.

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

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  1. 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

  2. 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.

  3. Hybrid Doppler Wind LidarMeasurement Geometry: 400 km 350 km/217 mi 53 sec Along-Track Repeat “Horiz. Resolution” 586 km/363 mi

  4. Star Tracker GPS Nadir Telescope Modules (4) GWOS IDL Instrument Hybrid DWL Technology Solution GWOS Payload Data 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

  5. NWOS System Configurations(Courtesy M.Clark and D.Palace) Configuration 3 (ShADOE) Configuration 1 and 2 (Inverted GWOS) Return

  6. Objective Approach Key Milestones Hybrid Doppler Wind Lidar (HDWL) Transceiver PI: Cathy Marx, GSFC • 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 • Define science requirements and interfaces for 7/09 • the 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 CoIs/Partners: Bruce Gentry, GSFC; Patrick Jordan, GSFC; Michael Kavaya, LaRC TRLin = 2 1/09

  7. Requirements * NASA research aircraft, e.g. DC8 and WB57, are target platforms for design. ACT demonstration will be on ground.

  8. Functional Block Diagram

  9. Optics

  10. Telescope Design Outgoing laser Incoming return Primary • 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. Secondary Outgoing laser Incoming return Window 4 Primaries

  11. Telescope Packaging Window Top View Side View

  12. 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.

  13. 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

  14. 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.

  15. Error Budget • 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.

  16. Mechanical

  17. 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

  18. Design of Telescope Structure Latest layout of ACT Structural Design

  19. Ray Trace Layout Secondary mirror Risely optics Indexing mirror Primary mirror Folding Mirror Indexing mechanism

  20. Telescope Volume 18.48 inches Top View 19.30 inches 27.66 inches

  21. Composite Structure One Piece Frame Design

  22. 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.

  23. 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. Technical Risks/Concerns

  24. 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

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