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Nestor Voronka, Robert Hoyt, Nestor Voronka, Robert Hoyt, Brian Gilchrist, Keith Brian Gilchrist, Keith Fuhrhop Fuhrhop T T ETHERS ETHERS U U NLIMITED, NLIMITED, I I NC. NC. 11711 N. Creek Pkwy S., Suite D 11711 N. Creek Pkwy S., Suite D - - 113 113 Bothell, WA 98011 Bothell, WA 98011 (425) 486 (425) 486 - - 0100 Fax: (425) 482 0100 Fax: (425) 482 - - 9670 9670 [email protected] [email protected] An Architecture of Modular Spacecraft An Architecture of Modular Spacecraft with Integrated Structural with Integrated Structural Electrodynamic Propulsion (ISEP) Electrodynamic Propulsion (ISEP) NIAC 7 NIAC 7 th th Annual Meeting Annual Meeting Tucson, Arizona Tucson, Arizona October 18 October 18 th th , 2006 , 2006

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Page 1: 1386 voronka[1]

Nestor Voronka, Robert Hoyt,Nestor Voronka, Robert Hoyt,Brian Gilchrist, Keith Brian Gilchrist, Keith FuhrhopFuhrhop

TTETHERS ETHERS UUNLIMITED, NLIMITED, IINC.NC.11711 N. Creek Pkwy S., Suite D11711 N. Creek Pkwy S., Suite D--113113

Bothell, WA 98011Bothell, WA 98011(425) 486(425) 486--0100 Fax: (425) 4820100 Fax: (425) 482--9670 9670 [email protected]@tethers.com

An Architecture of Modular Spacecraft An Architecture of Modular Spacecraft with Integrated Structural with Integrated Structural

Electrodynamic Propulsion (ISEP)Electrodynamic Propulsion (ISEP)

NIAC 7NIAC 7thth Annual MeetingAnnual MeetingTucson, ArizonaTucson, ArizonaOctober 18October 18thth, 2006, 2006

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MotivationMotivation–– Traditional propulsion uses propellant as reaction massTraditional propulsion uses propellant as reaction mass–– Advantages (of reaction mass propulsion)Advantages (of reaction mass propulsion)

•• Can move spacecraft center of mass, onCan move spacecraft center of mass, on--demand, and demand, and relatively quicklyrelatively quickly

•• Multiple thrusters offer independent and complete control of Multiple thrusters offer independent and complete control of spacecraft (6DOF)spacecraft (6DOF)

–– DisadvantagesDisadvantages•• Propellant is a finite and mission limiting resourcePropellant is a finite and mission limiting resource•• Propellant mass requirements increases exponentially with Propellant mass requirements increases exponentially with

mission mission ∆∆V requirementsV requirements•• Propellant may be a source of contamination for optics and Propellant may be a source of contamination for optics and

solar panelssolar panels–– Current Architectures of NASACurrent Architectures of NASA’’s Vision of Exploration s Vision of Exploration

require launching and transporting large massesrequire launching and transporting large masses–– Are there innovative alternatives?Are there innovative alternatives?

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Space Propulsion LandscapeSpace Propulsion Landscape10,000 sec

2,000 sec

Courtesy Gallimore, A., UMich

Isp

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Electrodynamic Space Tether PropulsionElectrodynamic Space Tether Propulsion–– InIn--space propulsion systemspace propulsion system–– PROS:PROS:

•• Converts electrical energy into Converts electrical energy into thrust/orbital energythrust/orbital energy

•• Little or no consumables are requiredLittle or no consumables are required

–– CONS:CONS:•• Long (1Long (1--100km) flexible structures 100km) flexible structures

exhibit complex dynamics, especially in exhibit complex dynamics, especially in higher current/thrust caseshigher current/thrust cases

•• Gravity gradient tethers have constrained Gravity gradient tethers have constrained thrust vectorthrust vector

•• Relies on ambient plasma to close Relies on ambient plasma to close current loop current loop Given a fixed amount of power available Given a fixed amount of power available

and fixed conductor mass, thrust and fixed conductor mass, thrust efficiency is independent of the length efficiency is independent of the length

of the conductorof the conductor

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Proposed SolutionProposed Solution–– MultifunctionalMultifunctional propulsionpropulsion--andand--structure structure

system that utilizes system that utilizes LorentzLorentz forces (forces (F = F = iLiL x Bx B) generated by current carrying ) generated by current carrying booms to generate thrust with little or booms to generate thrust with little or no propellant expenditureno propellant expenditure

•• Utilizes same principles as electrodynamic Utilizes same principles as electrodynamic tether propulsiontether propulsion

–– Utilize relatively short (Utilize relatively short (≈≈100 meter), 100 meter), rigid booms with integrated conductors rigid booms with integrated conductors capable of carrying large currents, that capable of carrying large currents, that have plasma contactors at the endshave plasma contactors at the ends•• Space Tether Electrodynamic PropulsionSpace Tether Electrodynamic Propulsion

–– Ex: 10km conductor, 1Ampere in LEOEx: 10km conductor, 1Ampere in LEO•• Thrust |Thrust |iLxBiLxB| | ≈≈ 0.3 Newtons0.3 Newtons

–– Proposed Integrated Structural Proposed Integrated Structural PropulsionPropulsion•• Ex: 100m conductor, 100 Ampere (!) in Ex: 100m conductor, 100 Ampere (!) in

LEOLEO–– Thrust |Thrust |iLxBiLxB| | ≈≈ 0.3 Newtons0.3 Newtons–– Torque Torque ≈≈ 750 N750 N·· mm

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Single Boom Concept of OperationSingle Boom Concept of Operation– Apply potential to overcome motion-induced electric field and drive

current across magnetic field– Current flowing down boom produces thrust force– Plasma waves close the electrical circuit

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‘‘StructuralStructural’’ ED PropulsionED Propulsion–– By connecting six booms to a spacecraft along By connecting six booms to a spacecraft along

orthogonal axes, 4DOF of motion can be orthogonal axes, 4DOF of motion can be controlled (translational and rotational)controlled (translational and rotational)

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ISEP BoomsISEP Booms–– Cold biased, lowCold biased, low--resistance resistance

element to maximize propulsive element to maximize propulsive performanceperformance•• Copper Clad Aluminum (CCA) Copper Clad Aluminum (CCA)

offers low specific offers low specific resistivityresistivity, yes , yes remains easy to work withremains easy to work with

–– Ex. 0.01Ex. 0.01ΩΩ/50 meter boom has a 0.44 /50 meter boom has a 0.44 kg/m densitykg/m density

–– Stiffness dictated by applicationStiffness dictated by application–– Boom ends contain plasma Boom ends contain plasma

contactors & docking sensorscontactors & docking sensors–– HemaphroditicHemaphroditic highhigh--current current

capacity docking mechanismcapacity docking mechanism

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100 Ampere Contactors for ISEP100 Ampere Contactors for ISEPEmission Device Power Notes

TC + Electron Gun 2.1 MW 18 emitters, < 1.25 V for SCL FEA 5860 W 10 emitters, < 0.4 V for SCL Electron

Emission HC 1250 W to 10 kW Flow Rates & Ion Type

9 sccm to 40 sccm Xe

Passive Sphere a 4.7 MW 1 m radius, 6.6E-3 N Drag 90% Porous – 6.6E-4 N

Passive Sphere b 1 MW 2.29 m radius, 3.46E-2 N Drag 90% Porous – 3.46E-3 N

Passive Plate a 61.3 MW 5 m2 – 5.26E-5 N Drag Passive Plate b 1 MW 54.52 m2 – 5.73E-4 N Drag

Electron Collection

HC 6150 W + 330 W (20 A ion prod.)

280 sccm fuel 27.35 mg/s Xe+ or 0.21 mg/s H+

Ion Emission + Ion Gun

1 MW + 1650 W (100 A ion prod.) 83,334 emitters needed

Ion Emission

HC 1000 W + 1650 W (100 A ion prod.)

1400 sccm fuel 27.35 mg/s Xe+ or 0.21mg/s H+

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ISEP NodesISEP Nodes–– Node geometryNode geometry

•• Simplest has 6 orthogonal Simplest has 6 orthogonal mating surfacesmating surfaces

•• Can also utilize polyhedrons Can also utilize polyhedrons with mating surfaces spaced with mating surfaces spaced 4545°° along the circumferencealong the circumference

–– Node componentsNode components•• Energy storage (flywheels @ Energy storage (flywheels @

75 W75 W--hr/kg)hr/kg)•• System & Navigation System & Navigation

ControllersControllers

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Modular SpacecraftModular Spacecraft–– By making booms and spacecraft modules By making booms and spacecraft modules

modular and modular and interconnectableinterconnectable, we create self, we create self--assembling assembling TinkertoyTinkertoy®® like components for like components for space structures and systemsspace structures and systems

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ISEP ApplicationsISEP Applications–– SelfSelf--Assembling Modular Spacecraft (SAMS)Assembling Modular Spacecraft (SAMS)–– SelfSelf--Assembling Structure for Refueling StationAssembling Structure for Refueling Station

•• Integral rail gun for commodity deliveryIntegral rail gun for commodity delivery

–– SelfSelf--Assembling Space TugAssembling Space Tug–– SelfSelf--Assembling Structure for Large Mirror Assembling Structure for Large Mirror

or Antenna Arraysor Antenna Arrays–– Formation Flying Space Systems Formation Flying Space Systems

•• Terrestrial Planet Finder (TPF)Terrestrial Planet Finder (TPF)

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0

5000

10000

15000

20000

25000

30000

35000

40000

200.0 400.0 600.0 800.0 1000.0 1200.0Circular Orbit Altitude (km)

Del

ta-V

(m/s

e

Inclination = 0.0ºInclination = 28.5ºInclination = 51.6ºInclination = 90.0ºInclination = 97.0º

ISEP Performance AnalysisISEP Performance Analysis–– Six 50m orthogonal booms in 300Six 50m orthogonal booms in 300--1100km, 01100km, 0--9797°°

inclination orbitsinclination orbits–– FEAsFEAs for electron emission, for electron emission, HCsHCs for ion emissionfor ion emission–– Total system mass Total system mass –– 1000kg with 20kg H consumable 1000kg with 20kg H consumable

(approx 3 years full time operation)(approx 3 years full time operation)–– Current commanded to 100A continuous for 30 daysCurrent commanded to 100A continuous for 30 days

•• System Input power System Input power -- 6500 Watts6500 Watts–– Performance metrics tabulated & averagedPerformance metrics tabulated & averaged

0

5000

10000

15000

20000

25000

30000

35000

40000

200.0 400.0 600.0 800.0 1000.0 1200.0Circular Orbit Altitude (km)

Del

ta-V

(m/s

e

Inclination = 0.0ºInclination = 28.5ºInclination = 51.6ºInclination = 90.0ºInclination = 97.0º

0

5000

10000

15000

20000

25000

30000

35000

40000

200.0 400.0 600.0 800.0 1000.0 1200.0Circular Orbit Altitude (km)

Del

ta-V

(m/s

e

Inclination = 0.0ºInclination = 28.5ºInclination = 51.6ºInclination = 90.0ºInclination = 97 0º

Along-track Total ∆V Cross-track Total ∆V Radial Total∆V

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ISEP Performance (cont.)ISEP Performance (cont.)–– Thrust magnitude and efficiency Thrust magnitude and efficiency

highly dependent on alignment highly dependent on alignment of of boom(sboom(s) with magnetic field) with magnetic field

–– Torques in the 1Torques in the 1--10 N10 N--m range m range as compared to disturbances in as compared to disturbances in the 10the 10--88 to 10to 10--11 rangerange

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

200.0 400.0 600.0 800.0 1000.0 1200.0

Circular Orbit Altitude (km)

Thru

st s

t (

Inclination = 0.0ºInclination = 28.5ºInclination = 51.6ºInclination = 90.0ºInclination = 97.0º

Average Along-track Thrust (N)

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

200000

200.0 400.0 600.0 800.0 1000.0 1200.0

Circular Orbit Altitude (km)

Spec

ific

Impu

lse

(se

Inclination = 0.0ºInclination = 28.5ºInclination = 51.6ºInclination = 90.0ºInclination = 97.0º

Average Specific Impulse (Isp) Isp vs. Thrust to Power (uN/w)

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

200000

0 5 10 15 20 25 30 35

Thrust to Power Ratio (µN/W)

Spec

ific

Impu

lse

(s

Inclination = 0.0ºInclination = 28.5ºInclination = 51.6ºInclination = 90.0ºInclination = 97.0º

0

1

2

3

4

5

6

7

8

9

10

200 400 600 800 1000 1200

Circular Orbit Altitude (km)

ISEP

boo

m T

orqu

e (N

Inclination = 0.0ºInclination = 28.5ºInclination = 51.6ºInclination = 90.0ºInclination = 97.0º

Along-track current torque (N-m)

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ISEP PerformanceISEP Performance–– ISEP is competitive with other EP technologiesISEP is competitive with other EP technologies–– In systems where collinear booms are assembled, performance In systems where collinear booms are assembled, performance

improvesimproves–– For missions where structural elements are required, For missions where structural elements are required, ISEPISEP’’ss dual use dual use

(propulsive/structural) has significant advantages(propulsive/structural) has significant advantages

–– KEY TECHNOLOGY CHALLENGE: PowerKEY TECHNOLOGY CHALLENGE: Power-- and Massand Mass-- Efficient Efficient collection and emission of electrons from/to the ambient plasmacollection and emission of electrons from/to the ambient plasma

1

10

100

1000

10000

100000

1000000

0.001 0.01 0.1 1

Thrust-to Power (N/kW)

Spec

ific

Impu

lse

(se

ResistojetArcjetPulsed Plasma ThrusterHall Effect ThrusterIon ThrusterIntegrated Structural EP

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Technology Demonstration ExperimentTechnology Demonstration Experiment–– Primary Experiment ObjectivesPrimary Experiment Objectives

•• Generate directly detectable torqueGenerate directly detectable torque•• Generate directly measurable thrustGenerate directly measurable thrust

–– Secondary Experiment ObjectivesSecondary Experiment Objectives•• Validate performance of Field Emissive Validate performance of Field Emissive

Electron Electron device(sdevice(s))•• Validate performance of lightweight Validate performance of lightweight

electron collectorselectron collectors

–– GOALGOAL: Drive 1 Ampere of current : Drive 1 Ampere of current through lightweight deployable, through lightweight deployable, conductive 10conductive 10--20 meter booms20 meter booms•• 0.20.2--1.0 second impulses > 0.5 1.0 second impulses > 0.5 mNmN

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Experimental MethodExperimental Method–– PicosatellitePicosatellite launched as a secondary launched as a secondary

payloadpayload–– Target platform Target platform –– CubeSatCubeSat

•• 1kg 1kg –– 10x10x10 cm envelope10x10x10 cm envelope•• Standard initially designed for University class Standard initially designed for University class

experiments and educational purposesexperiments and educational purposes•• Typically 1Typically 1--2 launch opportunities a year2 launch opportunities a year•• Launch costs $40Launch costs $40--120K for a 1U CubeSat120K for a 1U CubeSat•• Ideal for simple experiments andIdeal for simple experiments and

technology demonstrationstechnology demonstrations

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PicosatPicosat Experiment ContactorsExperiment Contactors–– Field Emissive CathodesField Emissive Cathodes

•• MicrofabricatedMicrofabricated Emitter tips rely on sharp emitter Emitter tips rely on sharp emitter tips, and close nontips, and close non--intercepting electrodes to intercepting electrodes to generate high field required to enable electrons to generate high field required to enable electrons to quantum tunnel out of the material into spacequantum tunnel out of the material into space

•• High current densities (5000A/cmHigh current densities (5000A/cm22) have been ) have been demonstrateddemonstrated

•• Development undergoing to increase total current Development undergoing to increase total current output and reduce environmental constraintsoutput and reduce environmental constraints

–– Passive Electron Collector (Passive Electron Collector (‘‘HedgehogHedgehog’’))•• Bundle of conductive yarnsBundle of conductive yarns•• Yarns tied together at root, and when charged will Yarns tied together at root, and when charged will

form approximately a form approximately a ‘‘KooshKoosh--ballball’’ like spherical like spherical structure due to electrostatic repulsive forcesstructure due to electrostatic repulsive forces

•• 2 meter diameter structure with yarns every 402 meter diameter structure with yarns every 40°°, , and filament every 1and filament every 1°° can weigh 10 grams(!)can weigh 10 grams(!)

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Experiment Experiment ConopsConops–– Converted Solar Energy is stored onboard in capacitor bankConverted Solar Energy is stored onboard in capacitor bank

•• Allow for thrust pulse every 4Allow for thrust pulse every 4--6 orbits6 orbits

–– At desired BAt desired B--field alignment, discharge capacitor to generate 1Ampere pulsefield alignment, discharge capacitor to generate 1Ampere pulse–– Measure Thrust with onboard accelerometersMeasure Thrust with onboard accelerometers–– Measure Torque with body attitude rate changeMeasure Torque with body attitude rate change

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SummarySummary–– Proposed Concept IS feasibleProposed Concept IS feasible

•• Requires small amount of consumables for ion sourceRequires small amount of consumables for ion source•• 4DOF4DOF propulsionpropulsion–– no thrust in Bno thrust in B--field directionfield direction•• Competitive with tradition Electric Propulsion with added benefiCompetitive with tradition Electric Propulsion with added benefit of structural t of structural

elementselements

–– Technology ChallengesTechnology Challenges•• High Current Plasma ContactorsHigh Current Plasma Contactors

–– Devices exist Devices exist –– robust units with higher efficiencies neededrobust units with higher efficiencies needed

•• Plasma Contactor Space Charge LimitingPlasma Contactor Space Charge Limiting–– High current densities may be environmentally limitedHigh current densities may be environmentally limited

•• Collision proof coordinated control laws for formation flight, aCollision proof coordinated control laws for formation flight, and selfnd self--assembly assembly –– Additional constraints imposed on lowAdditional constraints imposed on low--thrust control lawsthrust control laws

–– Experiment in Phase II will demonstrate system feasibility and vExperiment in Phase II will demonstrate system feasibility and validate alidate component technologiescomponent technologies

–– Potential ApplicationsPotential Applications•• Space Tug and Commodity Depot (with integral rail gun?)Space Tug and Commodity Depot (with integral rail gun?)•• Structure for Beamed Power Solar Array/Antenna FieldsStructure for Beamed Power Solar Array/Antenna Fields•• Structure for Space Habitats with Integral Drag MakeupStructure for Space Habitats with Integral Drag Makeup