SpaceSpace TethersTethers andand SmallSmall Satellites:Satellites: FormationFormation FlightFlight andand PropulsionPropulsion ApplicationsApplications

NestorNestor VoronkaVoronka

TTETHERSETHERS UUNLIMITED,NLIMITED, IINC.NC. 11711 N. Creek Pkwy S., Suite D-113 Bothell, WA 98011 (425) 486-0100x678 Fax: (425) 482-9670 [email protected] SpaceSpace TetherTether ApplicationsApplications && BenefitsBenefits

– EnableEnable highhigh ∆∆VV missionsmissions byby usingusing mechanicalmechanical oror electrodynamicelectrodynamic propulsionpropulsion andand motionmotion controlcontrol

– ReduceReduce systemsystem massmass byby eliminatingeliminating complexcomplex subsystemssubsystems

– MinimizeMinimize formationformation flyingflying systemsystem complexitycomplexity andand risksrisks

– EnableEnable newnew missionsmissions byby nonnon-- KeplerianKeplerian motionmotion ofof tetheredtethered satellitessatellites

Provide new and improved system capabilities by exploiting unique motion of tethered satellite system Orbit-Raising and Repositioning Launch-Assist & of LEO Spacecraft Space Tethers LEO to GTO Payload Transfer for Propellantless Propulsion

Propellantless propulsion enables large ∆V missions with low mass impact

Drag-Makeup Stationkeeping Capture & Deorbit of Space Debris for LEO Assets Formation Flying for Long-Baseline SAR & Interferometry PastPast TetherTether FlightFlight ExperimentsExperiments

– ≥≥ 1717 tethertether experimentsexperiments flown,flown, startingstarting withwith GeminiGemini capsulecapsule tethertether – SmallSmall ExpendableExpendable DeployerDeployer SystemSystem (SEDS)(SEDS) • SEDS 1&2: successfully deployed 20km tethers • PMG: 500m conducting tether – 7 hour lifetime, currents up to 300mA observed – ShuttleShuttle TetheredTethered SatelliteSatellite SystemSystem (TSS)(TSS) • 20 km insulated conducting electrodynamic tether • TSS-1: 200m deployed, demostrated stable dynamics – Bolt that was too long caused deployer jam (engineering process failure) •• TSSTSS--1R:1R: 19.9km19.9km deployed,deployed, >5>5 hourshours ofof excellexcellentent datadata validatingvalidating EDED tethertether physicsphysics – Arc caused tether to fail (tether fabrication/design/handling flaw) – TiPSTiPS – 4km non-conducting tether – On orbit since June 1996 IntroIntro toto GravityGravity GradientGradient TetherTether SystemSystem

– TheThe gravitygravity gradientgradient andand centrifugalcentrifugal forceforce differencedifference createscreates tensiontension inin thethe tethertether whichwhich resultsresults inin aa netnet locallocal verticalvertical restoringrestoring forceforce

Fc-g Fnet Center of Gravity Ft Local Vertical

– TheThe tensiontension causedcaused byby thethe physicalphysical connectionconnection couplescouples thethe motionmotion ofof twotwo satellitessatellites atat differentdifferent altitudes,altitudes, speedingspeeding upup thethe higherhigher massmass andand slowingslowing Ft downdown thethe lowerlower massmass

Fnet – BothBoth satellitessatellites traveltravel atat thethe orbitalorbital velocityvelocity ofof thethe Fc-g systemsystem’’ss centercenter ofof gravitygravity NanosatellitesNanosatellites && SpaceSpace Tethers?Tethers?

– FormationFormation FlightFlight withoutwithout expendingexpending propellantpropellant •• TwoTwo freeflyersfreeflyers separatedseparated byby 100100 verticalvertical metersmeters @@ 700km700km wouldwould requirerequire ∆∆VV≈≈3232 m/secm/sec PERPER DAYDAY forfor stationkeepingstationkeeping

– NanosatellitesNanosatellites cancan easilyeasily havehave orbitalorbital lifetimeslifetimes exceedingexceeding 2525 yearsyears •• CommonlyCommonly launchedlaunched asas secondarysecondary payloadspayloads =>=> littlelittle controlcontrol overover insertioninsertion orbitorbit ElectrodynamicElectrodynamic TethersTethers

Drag/Power Generation Mode Propulsive Mode • Motion-induced electric field drives current up the tether • Apply voltage to overcome motion-induced electric field • Current flowing across magnetic field induces drag force and drive current across magnetic field • Tether voltage & current can be used to provide peak • Current flowing down tether produces thrust force power to spacecraft • Plasma waves close the electrical circuit • Orbital energy converted to electrical energy PropellantlessPropellantless EDED TetherTether PropulsionPropulsion

Propulsion for Microsatellites Deorbit of LEO Space Debris - Large total ∆V with very low mass requirements - Autonomous assured disposal at end-of- mission with low mass penalty (~1-2% of s/c) - 5 kg to boost 100 kg s/c from 350->1500 km

Orbital Tug for Satellite Stationkeeping for LEO Assets Deployment & Repositioning - >$1B cost savings possible for ISS reboost Propellant Launch Costs ($M) - Fly assets at lower altitudes 0 20 40 60 80 100 120 140 160

Star 48V PAM-D (DeltaIII) MR-502 Resistojet IUS (Titan IV) Hybrid J2 Centaur Avanced Cryo Ammonia Arcjet Solar Thermal Derated Ion (1500 s) SPT Thruster Ion (3800 s) Tether 5,000 kg spacecraft w/ 100 m2 drag area 0 1000 2000 3000 4000 5000 6000 7000 8000

Propellant Mass (kg)

Propellant mass and propellant launch costs for reusable upper stages based on various chemical and advanced propulsion technologies. Mission analyzed is to boost ten 3000Źkg satellites from a 300 km holding orbit to a 1400 kg operational orbit. IsIs OrbitalOrbital DebrisDebris aa Problem?Problem?

– MostMost LethalLethal population:population: objectsobjects 11--10cm(!)10cm(!) inin sizesize NanosatelliteNanosatellite OrbitalOrbital LifetimeLifetime

100

10

1

Equatorial Inc lination=28.5

Orbital LifetimeOrbital (years) 0.1 Inc lination=51.6 Sun-Synchronous Years 25

0.01 300 350 400 450 500 550 600 650 700 Circular Orbit Altitude (km)

– OrbitalOrbital LifetimeLifetime simulationsimulation forfor aa CubeSatCubeSat withoutwithout deployablesdeployables •• SingleSingle (1U)(1U) CubeSatCubeSat hashas 1kg1kg mass,mass, 0.01m0.01m2 crosscross sectionalsectional area,area, ballisticballistic coefficientcoefficient ≈≈ 4545 kg/mkg/m2 TUITUI’’ss Solution:Solution: nanoTerminatornanoTerminator™™

– AA completelycompletely passivepassive deorbitdeorbit systemsystem •• NoNo avionics,avionics, nono commandcommand andand controlcontrol capabilitiescapabilities – LowLow mass,mass, volume,volume, andand powerpower deorbitdeorbit systemsystem thatthat simplysimply meetsmeets 2525 yearyear lifetimelifetime requirement/requirement/ recommendationrecommendation forfor orbitalorbital debrisdebris mitigationmitigation nanoTerminatornanoTerminator™™ ModuleModule

– Design targeted for single (1U) CubeSat (1kg, 100x100x100mm) and RocketPod CubeSat Plus (2kg, 100x100x164mm) – nanoTerminator™ envelope: 54.5 x 38 mm diameter, mass: 56g • Equivalent volume of a D-cell alkaline battery – Consists of tether (nominally 100 meters), spindle & shroud, spring ejection deployer & mount LongLong--LifeLife MultiMulti--strandstrand HoytetherHoytether™™

1.00

0.90 nanoTerm tether 0.80

0.70 96.7% at 25 years 0.60

0.50

0.40 99.8% at 10 years 0.30

0.20 Tether Survival Probability Survival Tether Single-Line Tether 0.10

0.00 0 60 120 180 240 300 360 Time (months)

– Multi-strand braided tether construction • 2 primary lines nominally spaced 25mm apart, with one secondary • Secondary line providing redundant load paths every 0.5 meters • Dupont’s Aracon™ used for the conductive element – copper and nickel clad Kevlar™ (9180Ω/km) • Fine denier DSM Dyneema™ used to complete tether structure nanoTerminatornanoTerminator™™ OperationOperation

– AtAt endend ofof nominalnominal missionmission operations,operations, tethertether deploymentdeployment initiatedinitiated •• SatelliteSatellite operatoroperator commandcommand •• WatchdogWatchdog timertimer expirationexpiration

– RestraintsRestraints released,released, andand integralintegral deployerdeployer springspring ejectsejects spoolspool

– SpringSpring ejectionejection velocityvelocity tunedtuned forfor fullfull tethertether deploymentdeployment

– CombinationCombination ofof electrodynamicelectrodynamic andand aerodynamicaerodynamic dragdrag changechange deorbitdeorbit nanoTerminatornanoTerminator™™ DeorbitDeorbit TimesTimes

100

10

1

Equatorial 0.1 Inclination=28.5 Inclination=51.6 Orbital Lifetime (years) Sun-Synchronous 0.01 Years 25 Single CubeSat with nanoTerminator

0.001 300 400 500 600 700 800 900 1000 Circular Orbit Altitude (km)

– OrbitalOrbital LifetimeLifetime simulationsimulation forfor aa CubeSatCubeSat withwith nanoTerminatornanoTerminator™™ • Single (1U) CubeSat has 1kg mass, 0.06m2 area, and ED tether! MASTMAST ExperimentExperiment

– MMultiulti--AApplicationpplication SSurvivableurvivable TTetherether – PRIMARYPRIMARY MissionMission ObjectiveObjective •• DeployDeploy multimulti--strandstrand spacespace tethertether •• InspectInspect multimulti--strandstrand forfor micrometeoritemicrometeorite impactimpact damagedamage – Image tether which is a multi-strand 1 kilometer Hoytether™ – SECONDARYSECONDARY MissionMission ObjectiveObjective •• CollectCollect datadata onon passivepassive tethertether dynamicsdynamics forfor studystudy ofof formationformation dynamicsdynamics andand validationvalidation ofof tethertether dynamicsdynamics modelsmodels – Measure relative position of tether endpoints, and crawling body MASTMAST OperationsOperations

– InspectorInspector crawlscrawls alongalong tethertether takingtaking imagesimages • 45,500 images per 1km of tether! • Expect to see 3.3 to 9.3 cuts/month!

– AllAll satellitessatellites gathergather dynamicsdynamics datadata • GPS Position, Ambient Magnetic Field, Coarse Sun Sensing

– DownlinkDownlink ImagesImages andand TelemetryTelemetry DataData usingusing 2.4GHz2.4GHz downlinkdownlink (20kbps)(20kbps) OtherOther TUITUI nanosatnanosat TechnologiesTechnologies

– nanosatnanosat IMUIMU •• 6DOF6DOF withwith integratedintegrated 33--axisaxis magnetometermagnetometer •• VERYVERY compact:compact: 38.138.1 xx 50.850.8 xx 15.215.2 mm,mm, 3434 gramsgrams – nanosatnanosat ReleaseRelease MechanismMechanism •• UsedUsed toto initiateinitiate mechanismmechanism releaserelease •• CutsCuts SpectraSpectra® looploop withwith NiCrNiCr wirewire •• IntegratedIntegrated WatchdogWatchdog TimerTimer •• VERYVERY compact:compact: 34.434.4 xx 20.220.2 xx 7.37.3 mm,mm, 55 gramsgrams SpaceSpace PropulsionPropulsion LandscapeLandscape

10,000 sec

2,000 sec

Isp

Courtesy Gallimore, A., UMich EDED PropulsionPropulsion ExperimentExperiment

– PrimaryPrimary ExperimentExperiment ObjectivesObjectives •• GenerateGenerate directlydirectly detectabledetectable torquetorque •• GenerateGenerate directlydirectly measurablemeasurable thrustthrust

– SecondarySecondary ExperimentExperiment ObjectivesObjectives •• ValidateValidate performanceperformance ofof FieldField EmissiveEmissive ElectronElectron device(s)device(s) •• ValidateValidate performanceperformance ofof lightweightlightweight electronelectron collectorscollectors

– GOALGOAL:: DriveDrive 11 AmpereAmpere ofof currentcurrent throughthrough lightweightlightweight deployable,deployable, conductiveconductive 1010--2020 metermeter boomsbooms •• 0.20.2--1.01.0 secondsecond impulsesimpulses >> 0.50.5 mNmN ExperimentExperiment ConopsConops

– Converted Solar Energy is stored onboard in capacitor bank • Allow for thrust pulse every 4-6 orbits

– At desired B-field alignment, discharge capacitor to generate 1 Ampere pulse

– Measure Thrust with onboard accelerometers

– Measure Torque with body attitude rate change SummarySummary

– TethersTethers inin SpaceSpace areare anan enablingenabling technologytechnology –– eveneven forfor nanosatellites!nanosatellites! – TethersTethers enableenable persistentpersistent formationformation flightflight withoutwithout anyany expendituexpenditurere ofof propellantpropellant – EDED TethersTethers areare suitablesuitable forfor lowlow--mass,mass, lowlow--volume,volume, deorbitdeorbit systemsystem wherewhere deorbitdeorbit timetime requirementsrequirements areare simplysimply 2525 yearsyears ((nanoTerminatornanoTerminator™™)) • Can expand the altitude ceiling for a single CubeSat/RocketPod class satellite from 620-680 km to almost 1000km • Help control the growth of the orbital debris population