Curved Extendable/Retractable Boom-Deployed Bag Asteroid Capture System Concept Scott Belbin, Mechanical Systems Branch NASA Langley Research Center (757) 864-8452

RFI Concept Criteria Capture an asteroid of unknown composition (possible dust/rubble pile) – Encapsulation bag required Atlas V Medium Payload Fairing Asteroid Mass ≤1000 metric tons Accommodate different asteroid shapes 17.8m x 8.8m x 8.8m prolate spheroid 14m x 14m x7m oblate spheroid

Design Drivers Short development time: Launch in 2018 Need High TRL approach with minimal complexity Deploy, close and retract bag without robot arms Electrically driven system only to reduce mass (abundant S/C bus capacity) Need to be able to reliably model Rigid structures are readily modeled and simulated Rigid structures to enhance dynamic stability while spinning up to match asteroid Extendables are predictable and functionally reliable Need to be able to test Test in 1G Vacuum chamber not required for testing (no inflatables), only still air needed Need to provide crew access Non-inflatable capture bag – single ply easy for crew to cut through Non-inflatables allow access panels to be easily incorporated

Concept Overview Proposed system uses extendable booms to deploy a non-inflatable bag to capture and control an asteroid Cinched up and retracted, Booms kink and conform to shape of the asteroid, ready to de-spin asteroid Stowed Deploy bag then match spin for capture

Deployment Storyboard 1) Booms in initial position 2) Bag ready to deploy 3) Booms deploy, pulling bag 4) 1st section taut, pulls next 5) 2nd section taut, pulls next 6) Curved booms minimizes material 8) Booms stop at their limits 7) 3rd section taut, pulls last 9) System ready for spin-up

Single drive in stowed position ConOps Bag mounted winches drive cinching cables in batten pockets Booms deploy single-ply Vectran bag Circumferential cinch cables close bag, pulling in the booms which kink and conform to the asteroid’s shape Booms retract to draw asteroid against spacecraft Independent boom drives allow for CG adjustment of asteroid 15 meters Add cinch motors Add multiple pics of sequences 500 mm 20 meter booms Single drive in stowed position

Preliminary Sizing Results Lenticular cross section chosen due to favorable buckling characteristics wrt conforming to the asteroid’s shape Conducted trades for materials and minimum cross sections Results: Titanium: 325mm width, 390mm flattened MS = 0.059 1756 g/m 36.00 kg per boom Composite: 250 mm width, 280mm flattened MS = 0.012 464 g/m 9.51 kg per boom Composite booms selected for mass estimate

Current Best Estimate of Mass Used Vectran areal density as reference for bag mass calcs Incorporated catalog selections for space-rated drive motors and gearing Based on preliminary Pro-E models; included large margins of uncertainty typical of concept level design Total Boom System Mass 124.87 kg Enclosure System Mass 69.42 Structure Mass 27.00 Attachments and Cabling 10.00 Capture System Avionics 20.00 Micro Meteorite and Thermal Shielding 30.00 CBE 281.29 Contingency Percentage 30% Contingency Mass 84.39 CBE + Contingency 365.68

Cursory Schedule in RFI Submittal Timeline: 10/2013 -01/2018 Concurrent design and development testing Includes boom tooling design and procurement Incorporates Ground Test Article build and test

Potential Next Steps Boom cross section design and analysis Boom section property demonstration (bending, torsion, buckling) Boom to drive buckling limit demonstration Bag material demonstration for abrasion and puncture resistance Cinch cable drive design and testing Boom tooling design and semi-section bonding demonstration Boom extension and retraction demonstration

Conclusion Dynamically stable in spin-up Medium to High TRLs Reliable mechanical drives Leverages abundant electrical power to reduce mass; no gas system Can demonstrate in 1G environment CBE Mass meets LV criteria Improved Crew Access Scott Belbin, Mechanical Systems Branch NASA Langley Research Center, Hampton VA scott.p.belbin@nasa.gov (757) 864-8452

Design Details Backup

Boom Type Trade 1: STEM Boom Storable Tubular Extendable Member Extensive flight heritage; TRL 9 Formable as a curved boom Exerts force during extension for capture bag unfurl Exerts retraction force to bring asteroid to bear against spacecraft Drives mount on torsion spring bases to accommodate flexure during capture Good Bending and torsional capability Poor Buckling/Crippling characteristics wrt conforming to asteroid; possible reduction in tensile capability; no recovery from buckling/crippling for retraction into spool Variations of the STEMboom concept [Source: NASA] Tubular shape collapses and spools without permanent deformation. Section shape is restored when spooled out STEM TIP Drum antenna boom, self deploying [Source: Northrop Grumman]

Boom Type Trade 2: Lenticular Section TRL 5 – tested in zero-G Formable as a curved boom (two halves construction, continuous length members) Exerts force during extension for capture bag unfurl Exerts retraction force to bring asteroid to bear against spacecraft Drives mount on torsion spring bases to accommodate flexure during capture Good Bending and torsional capability Good Buckling/Crippling characteristics wrt conforming to asteroid; no appreciable tensile capability reduction; recoverable from buckling/crippling for re-spool Lenticular shape readily collapses and spools without permanent deformation. Section shape restores when spooled out

Preliminary Lenticular Boom Sizing Examined load case from de-spin of asteroid Used loads for JPL2 case (worst case) 7500N tangential de-spin load (6 booms, 1250N per boom) Assumed contact at half-diameter (10 meters) but more likely ~6 meters (at second cinch cable); conservative Analyzed for simple cantilever load case in strong axis Safety Factors used: 1.4 on ultimate and 1.25 on yield Three materials analyzed: AL 6061 T6, Ti-Al6-4V, Carbon Composite (T500 12k/976) Geometry optimized until MS=>0.0 to determine minimum section size Results: Aluminum min. section too large to fit volumetric constraints; Titanium and Composite are viable candidates FT

Preliminary Lenticular Boom Sizing, Min. Cross Section Examined for lateral loads in strong axis direction Safety Factors applied Beam section properties from Pro-E Composite properties from Mil-Hbk-17 Case shown here for T1-6Al-4V, 325mm section width Design Data SF, ultimate 1.40 SF, yield 1.25 Force at half Ø contact pts, total 7500 N No. of Booms 6 Beam Geometry Beam Length 20.50 m Beam Length to half Ø contact pts. 10 End Force, Tangential 1250 Neutral axis dist., strong axis, c 0.1625 MOI, strong axis 3.18E+06 mm^4 Beam Calcs Max Moment, M 12500 Nm Max Stress, δ 639.55 MPa Ti-6Al-4V, .020" thk Young's Mod, E 113.8 GPa Ftu 951.48 Mpa Fty 882.53 MS, Ftu 0.059   MS, Fty 0.094 Beam mass/length 1.756 kg/m Beam mass (1) 36.00 kg Max Displacement, w 1153 mm T500 12k/976 unidirectional tape, Mil 17, V2, Pg 4-4. 0.020"thk layup Tensile Mod, E 141.34 1771.96 0.495 0.464 9.51 928 Flattened Width =390mm I=3176049 mm^4 Solving for minimum composite cross section = 250mm width Flattened Width =280mm I=1396924 mm^4

Packaging Atlas V Medium Fairing Payload Volume Conical Instrumentation Volume provides unobstructed forward view Capture Bag Stow Volume Boom Mechanism Volume Volume trades allowed as design matures

Design Details Cinch Cables Bag made of six 4-panel gores with Velcro deployment staging (can deploy well in advance of asteroid encounter) Bag-mounted winches driving cinch cables in batten pockets close the bag in sequence around the asteroid, pulling the booms inward Booms buckle/cripple by design as they contact the asteroid and conform to asteroid’s shape without losing tensile capability Booms make a rigid connection for de-spin Booms retract to draw asteroid against spacecraft Independent boom drives allow for CG adjustment of asteroid

Internal View Bag Dimensions Instrumentation Volume Bag Volume 15 meters across flats at mouth, 18 meters across apices 20 meter booms Thin Vectran construction w/reinforcement doubling in critical areas Instrumentation Volume Unobstructed view for asteroid characterization and bag deployment Provides rigid coupling to captured asteroid while protecting boom drives Bag Volume Facilitates bag packaging and unfurling by mimicking bag shape Boom Drive Volume Allows for boom drive flexure motion Provides volume for electrical harnesses and system to bus attachments

Boom Drive and Bag Attachments Bag Extraction Attach Point attaches to mouth of bag Cable Rings attach to bag via straps Boom unfurls first segment Subsequent segments Velcro retained Booms slide through rings; bag segments become taut then pulls subsequent segments Drive with Torsion Spring Base Decreases risk of local boom buckling at boom exit point Internal guides and compliant members further decrease local crippling risk