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Global Tropospheric Winds Sounder(GTWS)

Reference Designs

Ken Miller, Mitretek SystemsJanuary 24, 2002

15-Jan-02

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Agenda

• GTWS Mission Objective• Purpose• Draft Wind Data Product Requirements• Rapid Design• Reference Instruments• Reference Missions• Direct Mission• Conclusions• Acknowledgments

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Purpose

• Mission Objective is to acquire global wind velocity profiles per NASA/NOAA requirements

• Purpose of Briefing is to discuss Government Reference Designs for• Direct and Coherent Instruments • Direct Mission• Coherent Mission design scheduled Feb 2002

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Purpose of Reference Designs

• To establish instrument and mission architectures for reference purposes• Identify tall poles (technology readiness and risk)• Provide information to support a basis for

government cost estimate• Provide sanity check information for assessing

future concepts

• It is not assumed that future implementations will physically match study results

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Draft Wind Data ProductRequirements

• Threshold and Desired requirements prepared by the GTWS Science Definition Team (SDT)• Reconciled between NASA and NOAA users• Threshold requirements were minimum for useful

impact on models

• Posted for comment Oct 16, 2001http://nais.msfc.nasa.gov/cgi-bin/EPS/sol.cgi?acqid=99220#Draft

Document

• See Yoe/Atlas presentation

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Rapid Design Environmentsat NASA GSFC

• ISAL• Instrument Synthesis and Analysis Laboratory • Rapid instrument design and concepts for remote

sensing• 2 week GTWS studies

• IMDC• Integrated Mission Development Center• Rapid mission engineering analyses and services • Concepts, trades, technology and risk assessment• 1 week GTWS studies

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Rapid Design Areas

ISAL IMDC

Systems

Electro-mechanical

Mechanical/Structural

Thermal

Optical

Laser

Electrical

Integration & Test

Detectors

Costing

Systems

Mission Design

Attitude Control System

Propulsion

Mechanical

Thermal

Power

Command & DH

Communications

Flight Dynamics

Flight Software

Reliability

Integration and Test Spacecraft bus

Launch Vehicle

Ground Systems

Data Processing

Mission Operations

End of Life Disposal

Costing

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Reference Instruments

• Direct and Coherent lidars• Meet threshold data requirements, including

• 0 to 20 km altitude• Target Sample Volume (TSV)

• Maximum volume for averaging laser shots• 2 perspectives per TSV

• Reference atmosphere including cloud coverage and shear

• 2 year mission life

• Exceptions• Single laser designs may not meet lifetime

requirement• Single satellite did not meet temporal resolution

requirement

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Reference Instruments (cont’d)

• Do not provide • Implementation recommendations or preferences• Exhaustive technology trades• Basis to compare direct and coherent approaches

• General limitations• Based on first-cut point designs, not optimized• Numerous assumptions need verification• Low TRL components• May not meet all requirements• Requirements refined during design period• Some details are competition sensitive

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Reference Instruments-Design

• GTWS Team guidance on point designs• Direct– Bruce Gentry (NASA GSFC), Sept 2001• Coherent– Michael Kavaya (NASA LaRC), Dec 2001

• Parameters• 400 km circular orbit, 97o inclination, sun

synchronous, dawn/dusk• 100% duty cycle• Nadir angle 45 o

• Scan discrete azimuth angles• Point (~ 1 s) and Stare (~ 5 s)• 4 cross-track soundings, 4 positions fore, 4 aft

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Measurement Concept

7.7 km/s

400 km

585 km

414 km

290 km

290 km

45°

45°

7.2 km/s

HorizontalTSV

• Vertical resolution range gates• 45 o nadir angle• Scan through 8 azimuth angles• Fore and aft perspectives in TSV• Move scan position ~ 1 sec• No. shots averaged ~ 5 sec * prf

Aft perspective

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Reference Instruments -Concepts

Telescope with Sunshade

Radiator (Solar Array not shown)

Rotating Deck

Coherent

Direct

Belt Drive

Solar Array (Radiator not shown)

Component Housing

Component Boxes

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• IMDC • Direct - October 2001• Coherent - February 2002

• Large, heavy spacecraft with high power requirements

• 400 km orbit is challenging• Altitude tradeoff between lidar SNR and orbit

maintenance• Solar array & radiator in orbital plane to reduce drag• Battery power during eclipse (max 25 min/day)

• Delta 2920-10L, long fairing option • Current technology spacecraft• Conventional hydrazine propulsion

Direct MissionHighlights

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Direct MissionHighlights (concluded)

• TDRSS Demand Access Downlink• Controlled disposal at end-of-life• COTS-based Mission Operations Center, 8x5

operations • Data System

• Internal computer• 70 Gbits storage for 3 days

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Direct MissionLaunch Configuration

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Direct Mission - Deployed Configuration Concept

TDRS

Antenna

SC Bus

Solar

Array

Instrument

Radiator

Belt Drive

Rotating

Mechanism

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Direct MissionTechnology Readiness Level

(TRL)• Low instrument TRL: development, test, and

demonstration are needed• Spacecraft Overall TRL: 6• Definitions

• TRL 6: System/subsystem model or prototype demonstration in a relevant environment (ground or space)

• TRL 7: System prototype demonstration in a space environment

• TRL 8: Actual system completed and "flight qualified" through flight test demonstration (ground or space)

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Conclusions

• Mass, size, and power are very large • Need to increase instrument TRL

• Assumed lasers are well beyond current on-orbit laser power, efficiency, and lifetime

• Desirable laser improvements• Increase optical output to reduce telescope size and

mass • Increase efficiency to reduce power and heat• Increase life expectancy

• Increase DWL experience across range of atmospheric conditions

• Reduce risk:• Scanner• Momentum compensation• Lag angle compensation• Other areas

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Conclusions (cont’d)

• Still a lot to learn and assess - including• Fundamental differences between data products

from direct and coherent lidars• Global cloud and aerosol distributions • Data product impacts from

• Clouds• Aerosol distribution• Wind shear• Solar backscatter • Spacecraft pointing and jitter

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NASAFarzin Amzajerdian, Coherent Lidar Engineer, f.amzeajerdian@larc.nasa.govRobert Atlas, Science Definition Team Lead, robert.m.atlas.1@gsfc.nasa.govJames Barnes, GTWS Program Executive, j.c.barnes@larc.nasa.govJennifer Bracken, ISAL Team Lead, jennifer.bracken@gsfc.nasa.govDave Emmitt, Senior Scientist, gde@swa.comBruce Gentry, Direct Lidar Principal Investigator, bruce.m.gentry.1@gsfc.nasa.govGabe Karpati, IMDC Systems Engineer, gkarpati@pop700.gsfc.nasa.gov Michael Kavaya, Coherent Lidar Principal Investigator, m.j.kavaya@larc.nasa.govJohn Martin, IMDC Team Lead, jmartin@pop400.gsfc.nasa.govKen Miller, Systems Engineer, kenm@mitretek.orgMike Roberto, ISAL Systems Engineer, mroberto@pop700.gsfc.nasa.govGTWS TeamIMDC TeamsISAL Team

NOAAJohn Pereira, Program Manager, john.pereira@noaa.govJames Yoe, Science Definition Team Lead, james.g.yoe@noaa.gov

Acknowledgments