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