Architecture Alternatives for the DWL Space Demonstration

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Architecture Alternatives for the DWL Space
Demonstration

• Ken Miller
• Mitretek Systems
• June 28, 2006

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Background Objective

• Space demonstration mission
• Multiagency support
• Significant science products
• Instrument
• Hybrid
• Biperspective
• Adaptive targeting for Direct Detection
• Purpose Discuss some important architecture
  trades

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Relaxed Requirements Reduce Risk and Timeline

• Reduced risk and timeline
• Resolution
• Temporal
• Vertical and horizontal
• Number of ground tracks
• Cross-track width of regard and spacing
• Location accuracy
• Horizontal separation of wind pair
• Horizontal extent of each measurement
• Max wind speed
• Orbit latitude coverage
• Product latency

(Kavaya et al, ESTO Laser-Lidar-WG.pdf)
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Major Roadmap Steps

• Hybrid ground demonstration
• Hybrid aircraft demonstration
• NASA IIPs at GSFC and LaRC
• Space-like geometry and scanning
• Space demonstration
• NPOESS, STP, or other
• Space operational mission, threshold requirements

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Mission Phases

• Conceptual Design
• Hybrid Ground Demo
• Standalone Aircraft Demos
• Hybrid Aircraft Demo
• Space Demo
• Instrument
• Spacecraft Integration
• Launch
• Operations
• Data Simulation, Processing, and Assimilation

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Top Level Alternatives

• Approach to acquire and organize multiagency
  support?
• Platform and Orbit
• NPOESS P3I
• AF STP
• ESA ADM follow-on (no response yet)
• Japanese ISS demo (not explored yet)

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Multiagency Support Scenarios

• How to share responsibilities?
• 3 alternative scenarios to start discussions
• NPOESS P3I mission
• AF STP
• International
• Looked at traditional agency roles in each phase

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Example Organizational Roles In Demo Mission
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NPOESS P3I Alternative

• NPOESS
• Supported past and current work
• Funded by NOAA DOD
• Preplanned Product Improvement (P3I)
• Provides launch and operations for selected
  demonstrations
• Shared platform and onboard services
• Delayed by reorganization
• 833 km orbit
• Tight mass, power, and integration constraints

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STP Alternative

• Possibly earlier opportunity than NPOESS
• 400 km orbit reduces technical risk and
  challenges
• STP can support
• Planning and support activities
• Acquisition of a dedicated satellite
• Launch vehicle and integration hardware
• Integration onto satellite, launch vehicle, NASA
  shuttle and/or the International Space Station
• Readiness reviews, launch support
• Approximately one year of on-orbit operations
• Could support US Government missions on cost
  reimbursable basis

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International Alternative

• Could include
• Direct detection subsystem or components derived
  from ADM
• Shared launch or platform
• Other
• No responses yet

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Example Support Scenarios
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Platform and Orbit

• NPOESS 833 km shared platform and launch
• Reduces some costs for spacecraft, launch, power,
  thermal, communications, etc.
• Constrains
• Power, mass, volume
• Field of view (maybe not per Wang, Kavaya)
• Vibration
• Orbit depending on which NPOESS spacecraft
• STP 400 km dedicated spacecraft
• Increases some costs
• Improves power, mass, volume budgets
• Lower orbit increases signal by 13 db
• Can chose orbit crossing time, terminator or
  other
• Eliminates interoperability concerns with other
  instruments

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Some Implementation Trades

• Instrument power, mass, volume budget
• Orbit
• Altitude
• Time of day
• Terminator
• Telescope
• Aperture
• Conventional vs. holographic optics
• Scanner
• Rotate telescope as in GTWS Coherent Reference
  Design
• Holographic Optical Element (HOE) as in GTWS
  Direct Detection Reference Design
• Shared Aperture Diffractive Optical Element
  (ShADOE)
• Laser power (J/shot)
• More power can reduce instrument mass, power,
  rotational momentum
• Increased laser wallplug efficiency
• Pulse rate and integration time
• Increased optical and detector efficiencies
  reduce mass, power, rotational momentum
• Component sharing between direct and coherent
  subsystems
• Direct Detection duty cycle

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Power, Mass, Volume

• Critical challenges in
• GTWS single-wavelength reference designs
• NPOESS budgets (see LaRC accommodation study)
• Advances that reduce power, mass, volume
• Hybrid concept
• Laser wallplug efficiency
• Adaptive targeting
• Holographic Optical Element (HOE) scanner
• Lower (terminator) orbit
• Direct Detection (DD) subsystem contributes most
  to power, mass, volume

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NPOESS P3I Mass Power Budgets for Direct
Detection
Aperture Effects
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Orbit Altitudes NPOESS DD with 400 km Overlay
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Lower Orbit, Reduce Aperture

• 400 km vs. 833 km
• Primary impact signal strength up 13 db
• Reduces
• Some combination of aperture, power, mass, volume
• Scanner momentum compensation
• Pulse round trip time (pointing)
• Smaller aperture reduces all challenges except
  laser power

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(No Transcript)
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Volume vs. Aperture
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Instrument Diagram
Instrument Diagram
GTWS Direct Detection Instrument Diagram
1.5 m Ø
Belt and Drive Motor
Holographic Optical Element
Hexagonal Support Structure
Laser
3 m
Laser Power Box
Main Electronics Box
Baseplate and Receiver
GSFC ISAL 2001
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Direct Detection Telescope Volume vs. Aperture
1.5m Telescope (GTWS, ADM)
50 cm Telescope
Receiver (GTWS)
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GTWS DD Ref. Design
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Conventional vs. Holographic Optics

• Conventional optics currently favored for
  coherent
• Better wavefront quality
• Smaller coherent aperture makes it less critical
• Efficiency
• HOE currently favored for direct detection
• Larger direct detection aperture makes it
  critical
• Lighter rotating mass
• Rotationally balanced for simpler momentum
  compensation
• Less scanner power
• Improvements in wavefront quality could enable
  use for coherent
• Shared Aperture Diffractive Optical Element
  (ShADOE)
• Eliminates rotation of large optics
• Less critical as aperture decreases

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Optical Designs Considered
GTWS- Direct Lidar (ISAL 2001)
From Dennis Evans
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Holographic Optical Telescope

• Small HOEs have flown in star trackers
• 40-cm HOEs being used, ground airborne
• Meter class HOEs are being processed
• Expansion to 1.5 meter class requires only larger
  processing tanks

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HOE in GTWS Direct ISAL 2001

• Belt Drive Rotating Mechanism
• Point and stare
• HARLIE system used in aircraft experiment (0.4
  meter diameter HOE)
• Needs scaled up for GTWS (1.5 meter)
• Needs space qualified

From Cooper, Bolognese, Brannen, Correia
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GTWS- Direct Lidar (ISAL 2001)
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GTWS- Direct Lidar (ISAL 2001)
Holographic Optical Element (Telescope and Beam
Director)
From Dennis Evans Briefing
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Ray Tracings for a ShADOE
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Nadir Angle

• Smaller angle improves signal strength
• Relates to
• Geometry of biperspective looks
• Distance between ground tracks

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Laser Power, PRF, Integration Time

• More laser power (J/shot)
• For same performance, can reduce instrument mass,
  volume, rotational momentum
• Challenges
• Wallplug efficiency
• Reliability
• Increase product of PRF Integration Time
• For same performance, reduces mass, volume,
  rotational momentum

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Scan and Settle vs. Integration Time

• Observation time
• Fixed by along track resolution requirement
• Divided between scan and settle vs. integration
• More scan settle time
• Helps
• Scanner power
• Vibration
• Hurts integration time

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Laser Wallplug Efficiency

• Consensus from laser engineers at GSFC
• 1.9 GLAS and CALIPSO experience
• gt 5 now
• 80 DC to DC conversion
• 45 diode
• 15 optical to optical
• gt 8 in 5 years
• 80 DC to DC
• 55 diode
• 20 optical to optical
• Need to look at model output for mass power vs.
  efficiency

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GTWS DD Instrument
Deployable Radiator Panels
Telescope Aperture
Mirror Drive Radiator
Fixed Radiator
Laser , Instrument Boxes, Heat Pipe Controller
Spacecraft Bus
Solar Arrays
GSFC ISAL 2001
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Direct Detection NPOESS Point DesignEfficiencies
Parameters
Emmitt Demo Point Design
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Component Sharing Needs Study

• Bus Resources
• Bus Structure
• Attitude Control
• Command and Data Handling
• Electrical Power
• Thermal
• Bus Harness
• RF Communications
• Propulsion
• Instrument Components
• Telescope and Scanner?
• Pointing
• ?

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Direct Detection Duty Cycle

• Adaptive targeting can acquire most information
  with as little as 10 duty cycle
• Standby power lt active power
• Need to see average power vs. duty cycle curves
• Thermal cycling of laser under study
• Higher laser wallplug efficiency
• Reduce power, mass, volume, radiator, solar
  panels
• Allows higher duty cycle for same energy

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Conclusions

• Identify multiagency support scenario
• Major advances since GTWS reference designs
• Benefits
• Feasibility
• Timeline
• Risk
• Key trades
• Platform orbit
• DD aperture vs. laser power and efficiency
• Hybrid component sharing
• Need laser improvements, e.g. NASA LRRP