Benvenuto, R.

Lavagna, M.

BENVENUTO, RICCARDO

LAVAGNA, MICHÈLE

Archivio istituzionale della ricerca - Politecnico di Milano

- R. Benvenuto, S. Salvi and M. Lavagna, “Dynamics Analysis and GNC design of flexible systems for space debris active removal”. Acta Astronautica, 2015.- R. Benvenuto and M. Lavagna, “Towing tethers to control debris removal dynamics”, 65th International Astronautical Congress, IAC-14-C1.6.09, Toronto, Canada, 2014.- R. Benvenuto, M. Lavagna, A. Cingoli, C. Yabar and M. Casasco, “MUST: multibody dynamics simulation tool to support the GNC design for active debris removal with flexible elements”, 9th InternationalESA Conference on Guidance, Navigation & Control Systems, Porto, Portugal, 2014.- K. Wormnes, J.H. de Jong, H. Krag and G. Visentin, “Throw-nets and tethers for robust space debris capture”. 64th International Astronautical Congress, IAC-13,A6.5,2x16445, Beijing, China, 2013.- H. P. Menard, “Dynamic Mechanical Analysis – A practical introduction”. 2nd Edition, CRC Press, Taylor & Francis Group, 2008.- H. A. McKenna, J.W.S. Hearle and N. O’Hear, “Handbook of fibers rope technology”. The Textile Institute, Woodhead Publishing Limited, Cambridge, England, 2004.Towing TethersTether DesignSubset of related referencesMission OverviewTETHER DESIGN FOR SPACE DEBRIS TOWINGR. Benvenuto, M. LavagnaDepartment of Aerospace Science and Technology (DAER), Politecnico di Milano - ItaliaTowing Tethers’ Dynamics and Control SimulationsDesign Drivers and Requirements Thermal AnalysisMechanical Properties of Candidate MaterialsTether support systemTether TestingConclusions and RoadmapMaterial Mechanical and Dynamical TestsGAS PLUME IMPINGEMENT ON THE TETHER: • Thrusters’ exhaust plume impingement during disposal burns      (limited time)• Aramid fibers high retention of strength at high temperatures (depending on burning time)• Thermal analysis have demonstrated that insulation is necessary for         the first 5 to 10 meters of the tether• Chemical resistance to plume impingement is also a requirementFunctions:• Storing, releasing, holding• Winding/unwinding • Depend on control strategiesACTIVE REEL• If variable length tether control• Critical system, more complex• Actively controlledPASSIVE SPOOL• If fixed length tether control• Simpler system, more reliable• Passive releasing system• Decoupled from chaser dynamics to limit interactionsMaterialBreaking strength[GPa]Young’s modulus [GPa]Density [Kg/m3]Melting/decomposing temperature [°C]FunctionDyneema 3.7 116 970 150MechanicalKevlar 3.6 130 1440 500Technora 3.4 73 1390 500Sylramic(Silicon carbide fibre)2.6 350 3000 Over 1400Thermal insulationNextel (alumina fibre) 2 190 3050 1800• Dynamics/Thermal simulations allow to set mechanical/thermal design drivers• Synthetic fibers as Aramid/HPME identified as candidate materials• high tensile strength, high breaking tenacity• high impact strength• low density (lightweight)• fatigue resistance, creep and shrinkage resistance• dimensional stability• heat resistance• chemical resistance• Other material requirements:• Stiffness (dynamic behavior): to be correctly tuned depending on expected dynamic behavior and control bandwidth• Foldable, spoolable • Stress relaxationFiber mechanical properties are weakened by:• Braiding, weaving, twining• Knotting, looping, splicingMaterial testing:• to characterize real parameters for design technological solutions• to reduce the number of uncertain parameters in flexible dynamics model validation processMaterial test campaign on 547 tex Technora braids and knotted braids:• Tensile tests • Dynamical-mechanical testingDesign and testing:• Detailed design and testing of support system/connections/insulation• Tests to Validate dynamics models• Tests to characterize real parameters and verify functional requirements • Performances quantification, requirements verification in relevant environmentProposed qualification roadmap:• Friction-less table or underwater scaled dynamics + DMA• Microgravity testing  + thermo-vacuum• Sub-orbital flight or I.O.D. • MITIGATION: tethered devices installed on-board (drag augmentation, EDTs)• REMEDIATION: elastic connection established in-orbit by means of different capture strategies: nets, harpoons, tentacles, grasper, etc.Debris Tethered-Disposal OptionsTOWING TETHERS: • Non-conductive• Exploiting chaser thrusters to de/re-orbit systemELECTRO-DYNAMICS TETHERS: • Conductive• Exploiting Lorentz Force through interaction with magnetic field and ionosphereCapture net and towing tether de-orbiting conceptTethers’ exploitation for space debris mitigation/remediation• TETHER: long thin cable – mechanical connection – not withstanding compressive loadsBenefits of Tethers for Active Debris Removal:• Safety distance• Lightweight payload• Centre of mass alignment with thrust axis not a constraintCriticalities:• System flexibility effects on the connected system (tether oscillations, entanglement and breakage)• Whiplash effect (pre-tensioning)• Post-burn bounce-back• Atmospheric re-entry – differential drag• Tail-wagging – tumbling target• Gas plume impingement on tetherCASEStiffness [N/m]Damping [Ns/m]PROS CONSStiff 1.57e30.3• Stronger control authority on stack pose• Pre-tensioning needed• Harder post-burn controlNon-stiff 1.57e1• Easier post-burn control• Limited whiplash effect • Greater tail-wagging effect (strongly dependent onconnections)Fundamental influence of tether elasticity on dynamics behaviorTail-wagging = target angular momentum build-up, may lead to entanglementRelative distance during pulling and post-burn phases (non-controlled post-burn)StiffNon-stiffNon-stiffDifferential drag effectsRequirements on re-entry flight angle Relative distance during pulling and post-burn phasesTether tensionSTIFF TETHER CASEMass [kg]Chaser = 1300Target = 5000Tether = 0.58Initial orbit altitude [km]600Thrust [N]Main = 800RCS = 25ΔV [m/s]160Flight angle at 120km [deg]-1.6Operations sequence for high-thrust controlled re-entry• Stabilization/Pre-tensioning• Dragging• Post-burn control• Tether cut and CAM (if needed)GNC• Closed-loop GNC with feedback on tether tension and relative distance• RCS (PWM) for relative maneuvering• No control on tether length (fixed-lengthMODEL• 6 DOF end-bodies with flexible appendages• Discretized viscoelastic model for flexible tether• Perturbations: air drag, solar pressure, gravityClosed loop GNC & thermal control have proved to be necessary and effectiveTRL 4/5TRL 5/6TRL 7Axial damping ratio [-]0.106Torsional damping ratio [-]0.079Bending ratio [-] 0.014Braid Young’s modulus [GPa] 25Braid Shear Modulus [GPa] 0.118Braid Breaking Stress [GPa] 1.6Knot Breaking Stress [GPa] 0.5Black TechnoraTorsional rehometerDMA test machineSplicing/LoopingTechnora braids damping characteristicsTechnora braids mechanical characteristicsTensile testsTechnora braids experimental results obtained within the ESA-sponsored ESA- PATENDER Study, in consortium with GMV Spain, Prodintec,Spain34% of nominal fiber47% of nominal fiberActive reel mechanical designInsulation’s options:• First part of the tether in Sylramic• Good mechanical properties at high temperatures• Heavier solution• Link Aramid/Sylramic TBD• Nextel insulation sheath• Lightweight solution• Limited burning time –cold down phase necessaryTechnora heat resistance: retention of strengthThermal analysis: tether temperature during burnsThermal model to analyze impingementTwisted yarn geometry: directly related to braid retention of strengthModern rope types (different strand #, braiding technique and covers/jackets, influencing thread final properties)

Tether Design for Space Debris Towing

http://robotics.estec.esa.int/ASTRA/Astra2015/Posters/P02_Benvenuto.pdf

Tether Design for Space Debris Towing

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