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Tether Laser A Contamination-Free Ultrahigh Precision Formation Flight Method Based on Intracavity Photon Thrusters and Tethers 2006 NIAC Fellow Meeting Presentation Young K. Bae, Ph.D. Bae Institute Tustin, California, USA www.baeinstitute.com Collaborators: C. W. Larson, Ph.D., AFRL T. Presilla, Ph.D., Northrop Grumman C. Phipps, Ph.D., Photonic Associates J. Carroll, Tether Applications, Inc.

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TetherLaser

A Contamination-Free Ultrahigh Precision Formation Flight Method

Based on Intracavity Photon Thrusters and Tethers

2006 NIAC Fellow Meeting Presentation

Young K. Bae, Ph.D.Bae Institute

Tustin, California, USAwww.baeinstitute.com

Collaborators:C. W. Larson, Ph.D., AFRLT. Presilla, Ph.D., Northrop GrummanC. Phipps, Ph.D., Photonic AssociatesJ. Carroll, Tether Applications, Inc.

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TetherLaser

Precision Formation Flying

TPF SI MissionMAXIM

LISA

SPECS

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Prior Propellant-Free Formation Flying Concepts

Tether Concepts• Spin-Stabilization

• Propulsive Conducting Tether

Electrodynamics Concepts• Microwave Scattering Concept -- M. R. LaPointe (NIAC)

• Coulomb Force Concept -- L. B. King et al. (NIAC)

• Magnetic Dipole Interaction Concept -- D. W. Miller (NIAC)

Present ConceptsTether + Electrodynamics → Ultrahigh Precision (nano-m accuracy) Baseline Distance Maintenance

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Proposed Formation Flying (FF) Method

Force Structure: Counter Balance of Two Forces:Contracting Force: Tether TensionExtending Force: Photon Thrust

- Intracavity Arrangement- Thrust Multiplied by Tens of Thousand Times by

Bouncing of Photons between Spacecraft

Geometrical Structure: Crystalline Structure

Interspacecraft Distance Accuracy: better than nm

Maximum Operation Range: Tens of km (Limited by Mirror Size)

Can be Used for both Static and Dynamic Applications

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Advantages of the Proposed FF Method

Propellantless-- System Mass Savings-- Contamination Free-- Long Operation Lifetime

Inherent Capability of Efficient Damping of Tether Vibration by Modulating Laser Thrust

Dual Usage of Photon Thruster Laser for Interferometric Ranging System

-- Simplified System Architecture and Control-- Low System Weight

Readily Downscalable to Nano- and Pico- Satellites Usage

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TetherLaser

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Satellite I Satellite II

Precision Laser Power Meter

HR Mirror HR Mirror

Laser Gain Media

Ultrahigh Precision CW Photon Thrust

TetherTension

Piezo-Translator Stepper Motor

Intracavity Laser Beam

TetherReel

Clamp

Lens

DiodePumpLaser

PumpLaser Beam

HR Mirror

HR MirrorPart al Mirrori

Photodetector

Part al Mirrori

Part al Mirrori

Tether System

Photon ThrusterSystem

InterferometricRanging System

Nano-Precision Formation Flying System Architecture

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Photon Thruster System: TRL 3

Satellite I Satellite II

Precision Laser Power Meter HR Mirror

HR Mirror

Laser Gain Media

Ultrahigh Precision CW Photon Thrust

Intracavity Laser BeamLens

DiodePumpLaser

PumpLaser Beam

Laser System-- Diode Pumped Intracavity Laser-- Lifetime of Diodes

1 Year for Continuous OperationPump Diode Carousel Design – Tens of Years

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TetherLaser

10 100 1000 10000 1000000.1

1

10

100

1000

1000010 W System

Intracavity Photon Thrust as a Function of the Mirror Reflectance (R)

Phot

on T

hrus

t (µN

)

11 - R

Off-the-ShelfSuper Mirror

Predicted Capability of the Proposed System

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Specific thrusts as functions of Isp of various conventional and photon thrusters.

Isp (sec)102 103 104 105 106 107 108

Spec

ific

Thr

ust (

mN

/W)

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

X 1,000

X 10,000

X 100

X 20,000

Electric Thrusters Photon Thrusters

Intracavity Multiplication Factors

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Intersatellite Distance (km)0.01 0.1 1 10 100

Mirr

or D

iam

ter (

cm)

1

10

Photon Thruster System: Mirror Diameter vs. Operation Distance

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TetherLaser

Interferometric Ranging System: TRL 5Satellite I Satellite II

Precision Laser Power Meter

HR Mirror HR Mirror

Laser Gain Media

Ultrahigh Precision CW Photon Thrust

Intracavity Laser BeamLens

DiodePumpLaser

PumpLaser Beam

HR Mirror

HR MirrorPart al Mirrori

Photodetector

Part al Mirrori

Part al Mirrori

Dual Usage of Photon Thruster Laser for Interferometric Ranging System Source Laser

-- System Architecture Simplification-- System Mass Reduction

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TetherLaser

Heterodyne Interferometric Ranging System Integrated with Photon Thruster System

Satellite I Satellite II

Precision Laser Power Meter

HR Mirror HR Mirror

Laser Gain Media

Ultrahigh Precision CW Photon Thrust

Intracavity Laser BeamLens

DiodePumpLaser

PumpLaser Beam

Part al Mirrori

Beam Splitter

MeasurementDetector Reference

Detector

AOM AOM

Retroreflector

Mirror

ODL

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Tether System: TRL 5

Satellite I Satellite II

Tether

ClampTetherReel Inchworm

Piezo-Translator

Electromechnical Damper

Coarse Control: Reel System-- mm Accuracy

Fine Control: Inchworm or Stepper Motor-- µm Accuracy

Ultrafine Control: Piezo-Translator (off-the-shelf) -- 0.1 nm Accuracy

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Method of Tether Vibration Suppression

• Longitudinal Tether Wave Damping• Tether Material Friction• Modulation of Photon Thruster Power

• Major Tether Vibrations will Result from Reorientation of the Whole Formation Structure, and other Sudden Environmental Perturbations, such as Meteoroid Impacts.

• Transverse Tether Wave Damping• Electromechanical Damper with Impedance Matching

Damping Applied

Electromechanical DampingSimulation by Lorenzini et al.For 1 km Baseline System

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Example of Formation Flying at L2

TetherLaser

1 km

Altitude: 1.5 x 106 km

Satellite Mass: 100 kg

Cross-sectional Area per Spacecraft: 1m2

Base Line Distance: 1 km

Tether Material: Kevlar

Tether Diameter: 4 mm(99.9 % survival at L2 for 5 years)

Not to Scale

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Exemplary System Design

Major Perturbation ForcesSolar Pressure Force Per Pair: < 20 µNOther Perturbations Including Gravitational Perturbations Per Pair: < 30 µNTotal Differential Force Per Pair : < 50 µN

The Tethers are extended with ~ 100 µN with Photon Thrust Per Pair-- 0.16 µm Extension

The Change in Tether Length due to the Perturbation:Countered with Length Adjustment with Piezo-Translator (sub nm Accuracy)

Laser Requirements with Off-the-Shelf Components:Power Requirement ~ 1 W with 0.99995 MirrorsWith 20 % Wall-Plug Efficiency: The Total Laser System Power ~ 5 WStability Requirement: ~10-3 (Lab Laser Stability ~ 10-5)Mirror Diameter: > 7 cm

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Application ExampleRequirements for New World Imager Freeway MissionBy Prof. W. Cash – 2005 NIAC Fellow Meeting

-- Searching for Advanced Civilization in Exo-Planets• 300 m resolution at 10 parsecs = 0.02 nano-arcseconds• 500,000 km based line distance between Collectors• Huge collecting area – one square kilometer

“Right now this is impossibly expensive, but not necessarily tomorrow,” by Prof. Cash 2005

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One-Year Later … “Km-Diameter Membrane Space TelescopeBased on Photon Thrusters and Tethers”

James WebbSpace Telescope

Membrane Mirror (NIAC)Image Processing With Real-TimeHolographic AberrationCorrection (NIAC)

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Roadmap

Optimized Photon Thruster Design and Development

Overall System Integration including the Interferometric RangingSystem and Tether System

Overall System Stability and Control including TetherVibration Related Issues

Development of Methods for Reorientation and Alignment of the Whole Formation Structure

Mission Specific Studies

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Technology Readiness Assessment Summary

Photon Thrusters: TRL 3

Interferometric Ranging System: TRL 5

Tether System: TRL 5

System Integration and Control: TRL 2

R&D3: II - III (moderate -high) (Degree of Difficulty)Requires to optimize photon thrust design based on the current laboratory system and system integration, and to develop control system.

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Phase I Study Accomplishment SummaryTheoretically proved that the proposed FF method is capable of maintaining the interspacecraft distance with accuracy of nm at the maximum baseline distance of tens of kms.

Successfully developed the engineering architecture of unification of photon thruster system with interferometric ranging system for simplified architecture control and system weight reduction.

Developed the method of controlling tether vibrations using electromechanical dampers and photon thruster power modulation.

Orbit specific mission applications have been identified and investigated.

Identified Phase II program topics and designed the Phase II experimental system.

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Phase II Proposed WorkProof-of-Concept Demonstration of Photon Thruster

Construction of a Thrust Stand with nN Accuracy

Overall System Stability and ControlTether Vibration DynamicsEnvironment Perturbation3-D Simulation

Design of Prototype Interferometric Ranging System

Design of Prototype Tether System

Detailed Study of Specific ApplicationsIn-Depth Revisits of Existing Concepts -- SPECS and MAXIMUltralarge Membrane Space TelescopesUltralarge Sparse Aperture Space TelescopesOthers

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Phase II Proposed WorkPhoton Thruster Development with Nano-Newton Accuracy Test Stand

Laser Power Meter

Concave HR Mirror

HR Mirror

Laser Media

Intracavity Laser Beam

TorsionFiber

CounterWeight

Vacuum Chamber

Interference Pattern

Low Power Laser

Corner Cube

Windows

Optical Fiber

Photo Detectorfor Fringe Counting

Pump Laser Diode

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Conclusions

The proposed system needs thorough study.

If successful, the proposed system will open new innovative (revolutionary) ways to implementing new and existing mission concepts.

Mission Specific Applications Simplifies the Architecture and Reduces the Weight in Distributed Interferometery Missions -- TPF, DARWIN, MAXIM, SPECS etc.Ultralarge Membrane Space Telescopes -- For New World Imager (300 m Resolution – Freeway Mission with km Mirror) and Earth Imaging/Monitoring/Surveillance (10 cm Resolution Monitoring at GEO with 200 m Mirror)Ultralarge Sparse Aperture Space Telescopes

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“I believe in intuitions and inspirations. I sometimes feel that I am right. I do not know that I am.”

by Albert Einstein

The Support by NIAC and NASA for this project is greatly appreciated.