1 Architecture Alternatives for the DWL Space Demonstration Ken Miller Mitretek Systems June 28, 2006

2 Background & Objective Space demonstration mission –Multiagency support –Significant science products –Instrument Hybrid Biperspective Adaptive targeting for Direct Detection Purpose: Discuss some important architecture trades

3 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)

4 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

5 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

6 Top Level Alternatives Approach to acquire and organize multiagency support? Platform and Orbit –NPOESS P 3 I –AF STP –ESA ADM follow-on (no response yet) –Japanese ISS demo (not explored yet)

7 Multiagency Support Scenarios How to share responsibilities? 3 alternative scenarios to start discussions –NPOESS P 3 I mission –AF STP –International Looked at traditional agency roles in each phase

8 Example Organizational Roles In Demo Mission NASANOAADOD- non STP IPOSTPInter- natio nal 1. Hybrid Ground Demo XX XX 2. Conceptual Design X XX X 3. Standalone a/c Demos XXXX 4. Hybrid a/c Demo Mission XX X X 5. Space Demo Mission 5.1 Instrument XXX X X 5.2 S/C Integration XX 5.3 Demo Launch XX 5.4 Demo Ops XX 5.5 Data Simulation, Processing, Assimilation X

9 NPOESS P 3 I Alternative NPOESS –Supported past and current work –Funded by NOAA & DOD Preplanned Product Improvement (P 3 I) –Provides launch and operations for selected demonstrations –Shared platform and onboard services –Delayed by reorganization –833 km orbit –Tight mass, power, and integration constraints

10 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

11 International Alternative Could include –Direct detection subsystem or components derived from ADM –Shared launch or platform –Other No responses yet

12 Example Support Scenarios

13 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

14 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

15 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

16 NPOESS P 3 I Mass & Power Budgets for Direct Detection Aperture Effects

17 Orbit Altitudes: NPOESS DD with 400 km Overlay

18 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

19

20 Volume vs. Aperture

21 Instrument Diagram ~ 3 m ~ 1.5 m Ø Holographic Optical Element Belt and Drive Motor Hexagonal Support Structure Baseplate and Receiver Laser Laser Power Box Main Electronics Box GTWS Direct Detection Instrument Diagram GSFC ISAL 2001

22 Direct Detection Telescope Volume vs. Aperture 1.5m Telescope (GTWS, ADM) 50 cm Telescope Receiver (GTWS)

23 GTWS DD Ref. Design

24 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

25 Optical Designs Considered Design Type Rotating Mass (kg) Comment Holographic Optical Element 1 41 (71)HOE,(rotating assembly) Fresnel Mirror (mirror only)91 (70)SiC (Composite Optics) Fresnel Lens (glass only) h x 5t cm prisms Rotating Telescope (optical structure only) Scaled from Be SIRTF Scaled, Composite Optics Flat Mirror (optical element only) 294 (or more) Scaled from 2.2 kg GOES-like SiC Scanning Spacecraftn/aProblems with ACS, Arrays, Antenna GTWS- Direct Lidar (ISAL 2001) From Dennis Evans

26 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

27 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 HOE in GTWS Direct– ISAL 2001 From Cooper, Bolognese, Brannen, Correia

28 Sample 45-degree Reflective Holographic Optical Element (400 mm diameter) Dennis Evans brief HOE courtesy of Gary Schwemmer GTWS- Direct Lidar (ISAL 2001)

29 Holographic Optical Element (Telescope and Beam Director) GTWS- Direct Lidar (ISAL 2001) From Dennis Evans Briefing

30 Six holographic exposures on single plate Each directs collimated portion toward rotating scan mirror Mirror sequentially addresses each FOV Directs light to a single optical fiber Ray Tracings for a ShADOE

31 Nadir Angle Smaller angle improves signal strength Relates to –Geometry of biperspective looks –Distance between ground tracks

32 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

33 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

34 Laser Wallplug Efficiency Consensus from laser engineers at GSFC ~ 1.9% GLAS and CALIPSO experience > 5% now 80% DC to DC conversion 45% diode 15% optical to optical > 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

35 Deployable Radiator Panels Fixed Radiator Solar Arrays Spacecraft Bus Laser, Instrument Boxes, Heat Pipe Controller Telescope Aperture Mirror Drive Radiator GTWS DD Instrument GSFC ISAL 2001

36 Direct Detection NPOESS Point Design Efficiencies & Parameters Energy per 1.06 microns0.75 J PRF100 Hz Laser Conversion Efficiency0.45 Laser Wallplug0.042 Transmit/Receive Optical0.36 Detector Quantum Efficiency0.6 Beam Split Fraction0.4 Filter Throughput0.17 Edge Sensitivity Telescope Diameter0.75 m Integration Time12 sec Emmitt: Demo Point Design

37 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 ?

38 Direct Detection Duty Cycle Adaptive targeting can acquire most information with as little as 10% duty cycle Standby power < 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

39 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