Pulsed Plasma Thrusters (Total 8 Kg, 32 W) Roll Stabilizer Bar Secondary ACS for Backup Mode

PreliminaryPreliminary DevelopmentDevelopment ofof anan ExperimentalExperimental LightweightLightweight PulsedPulsed PlasmaPlasma ThrusterThruster forfor SolarSolar SailSail AttitudeAttitude ControlControl

KevinKevin Pryor,Pryor, BongBong Wie,Wie, andand PavlosPavlos MikellidesMikellides ArizonaArizona StateState UniversityUniversity

18th Annual AIAA/USU Conference on Small Satellites SSC04-XI-4 OutlineOutline

¾¾ AttitudeAttitude ControlControl needsneeds ofof aa solarsolar sailsail ¾¾ BaselineBaseline attitudeattitude controlcontrol systemssystems ¾¾ PulsedPulsed plasmaplasma thrustersthrusters basics,basics, benefits,benefits, andand designdesign ¾¾ PrototypePrototype detailsdetails AttitudeAttitude ControlControl RequirementsRequirements

¾¾ SmallSmall solarsolar disturbancedisturbance torquetorque mustmust bebe counteractedcounteracted ¾¾ ManyMany possiblepossible methodsmethods

Roll Sun Line α = Sun Angle α ψ = Yaw Angle = −π/2 + α Solar Thrust Yaw Control Thrust F Control Mass m

M ε c.p. Pitch l y(t) AttitudeAttitude ControlControl SystemSystem

Inertial Stellar Compass (ISC) Attitude Determination System Sail Attitude Control System 2.5 kg, 3.5 W, 0.1 deg (1σ), 5 Ηz (SACS)

¾¾ BriefBrief ACSACS Active-Pixel Attitude 3-axis Attitude Star Camera Determination Stabilization & Algorithm Thrust Vector overviewoverview MicroGyros (Quaternions) Control Logic

yaw pitch Control Ballast Primary ACS for Normal Flight Mode Propellantless 3-axis Trim and Control Mechanisms (total 5 kg, 10 W)

Pulsed Plasma Thrusters (total 8 kg, 32 W) Roll Stabilizer Bar Secondary ACS for Backup Mode

Sail Carrier Spacecraft ADCS: reaction wheels, thrusters, magnetic torquers, sensors, (total 20 kg, 50 W) Sailcraft attitude stabilization prior to sail deployment, during post-deployment checkout, and for pre-flight standby mode MainMain ControlControl SystemSystem

¾¾ PropellantlessPropellantless PrimaryPrimary ACSACS Pitch j Roll y x i Ballast mass for cm/cp trim balance

Orbital Flight Path

Yaw

k z r

θ Micro-PPT module (conceptual drawing)

Perigee Earth

BackupBackup System:System: PulsedPulsed PlasmaPlasma ThrustersThrusters ¾¾ FlightFlight provenproven technologytechnology

z DecadesDecades ofof flightflight experienceexperience ¾¾ MoreMore RobustRobust andand ManeuverableManeuverable

z NotNot dependentdependent onon sunsun angleangle ¾¾ MomentMoment armarm proportionalproportional toto sailsail sizesize PPTPPT BasicsBasics

¾ ElectromagneticElectromagnetic ThrusterThruster ¾ PowerPower ProcessingProcessing UnitUnit convertsconverts voltagevoltage ¾ CapacitorCapacitor chargescharges overover ~1~1 secsec

z Releases in µs ¾ SolidSolid TeflonTeflonÆÆPlasmaPlasma ¾ LorentzLorentz (jxB)(jxB) forceforce acceleratesaccelerates plasmaplasma PPTPPT BenefitsBenefits

¾ High Specific Impulse (Isp)

z Typically from 300-1400 s ¾ Solid Fuel = Low Volume ¾ Simplicity of device leads to more reliability and lower cost

PPT vs Cold Gas: Comparison

Cold Gas Thruster Pulsed Plasma Thruster

1 0.9 0.8 I = 700 s 0.7 sp 0.6

0.5 0.4 0.3 Isp = 100 s 0.2 0.1 0 0 1000 2000 3000 4000 5000 6000 ∆V (m/s) DesignDesign RequirementsRequirements

¾ ControlControl requirementsrequirements basedbased offoff ofof predictedpredicted cmcm-- cpcp offsetoffset

Sail Size 40 80 m Mast length 28 56 m cm-cp offset* 0.1 0.2 m Solar disturbance torque* 0.001 0.008 N-m Control torque† 0.004 0.0084‡ N-m Total impulse (required) 1126 4505 N-s Total pulses (required) 7.5 30 million

* the normally worst case for untrimmed sailcraft † using one thruster ‡ this torque can be doubled using a pair of thrusters PreviousPrevious PPTsPPTs

AFRL’s micro-PPT

University of Washington Dawgstar’s PPT

GRC’s EO-1 PPT DesignDesign ApproachApproach

¾ ComparisonComparison ofof previousprevious PPTsPPTs toto choosechoose baselinebaseline designdesign

z EO-1, LES 8/9, TIP-II NOVA, and Dawgstar • LES 8/9 was fully flight qualified, but was never flown, though its predecessor LES-6 operated successfully for 10 years. • EO-1’s PPT acquired 33 hours of in flight use in 2002 ¾ SelectionSelection——DesignDesign reusereuse ofof EOEO--11 PPTPPT

z Lowest dry mass of many recent PPTs • Due mostly to advances in electronics ¾ DecreasedDecreased massmass throughthrough electronicselectronics changeschanges

z Lower power levels allow smaller electronics SpecificSpecific ComponentsComponents

¾ PowerPower ProcessingProcessing UnitUnit • 94 x 38.1 x 19.6 mm • Off the shelf from UltraVolt • Available up to 30W and 6,000 V at same dimensions and weight ¾ CapacitorCapacitor • Sample from Dearborn Electronics • 50 µF, 1000 V only 2” diam, 4.5” long and 250 grams ¾ SparkSpark PlugPlug • 1000 V rated from Unison ¾ OtherOther • Assembly made from Ultem 2300® Prototype:Prototype: PPT150PPT150 Discharge Thruster Circuit *, Assembly, 0.375 kg, ¾ PicturePicture ofof PPT150PPT150 0.706 kg, 25% prototypeprototype andand weightweight 48% breakdownbreakdown PPU, 0.142 kg, 10% Capacitor, 0.250 kg, 17%

Optimized Prototype ITEM Mass (kg) Mass (kg) Three Thruster Assembly 0.706 1.15 Capacitor 0.250 0.250 PPU 0.142 0.284 Discharge Circuit * 0.375 0.375 Misc --- 0.391

Total 1.473 2.45 InitialInitial VacuumVacuum TestingTesting

¾¾ PreliminaryPreliminary VacuumVacuum TestingTesting shownshown successsuccess ¾¾ PicturePicture showsshows plasmaplasma dischargedischarge inin vacuumvacuum

z UtilizedUtilized acrylicacrylic housinghousing forfor visualizationvisualization ConclusionConclusion

¾¾ LightweightLightweight andand reliablereliable pulsedpulsed plasmaplasma thrustersthrusters cancan performperform attitudeattitude controlcontrol ofof solarsolar sailssails ¾¾ TheThe simplicitysimplicity ofof thethe devicesdevices operationoperation createscreates anan excellentexcellent backupbackup systemsystem ¾¾ TheThe higherhigher efficiencyefficiency ofof propellantpropellant andand higherhigher reliabilityreliability leadsleads toto aa betterbetter overalloverall systemsystem