1 Pre-decisional NASA Internal Use Only Curved Extendable/Retractable Boom-Deployed Bag Asteroid...

1Pre-decisional • NASA Internal Use Only

Curved Extendable/Retractable Boom-Deployed Bag Asteroid Capture System Concept

Scott Belbin, Mechanical Systems Branch

NASA Langley Research Center

(757) 864-8452

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

Stowed Deploy bag then match spin for capture Cinched up and retracted,Booms kink and conform to shape of the asteroid, ready to de-spin asteroid


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

7) 3rd section taut, pulls last8) Booms stop at their limits

9) System ready for spin-up


ConOps

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

Add cinch motorsAdd multiple pics of sequences

Bag mounted winches drive cinching cables in batten pockets

Single drive in stowed position

500 mm

15 meters

20 meter booms


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

Preliminary Sizing Results


Current Best Estimate of Mass

Total Boom System Mass 124.87kg

Enclosure System Mass 69.42kg

Structure Mass 27.00kg

Attachments and Cabling 10.00kg

Capture System Avionics 20.00kg

Micro Meteorite and Thermal Shielding 30.00kg

CBE 281.29kg

Contingency Percentage 30%Contingency Mass 84.39kg

CBE + Contingency 365.68kg

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


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-upMedium to High TRLsReliable mechanical drivesLeverages abundant electrical power to reduce mass; no gas systemCan demonstrate in 1G environmentCBE Mass meets LV criteriaImproved Crew Access

Scott Belbin, Mechanical Systems BranchNASA Langley Research Center, Hampton [email protected](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

Tubular shape collapses and spools without permanent deformation. Section shape is restored

when spooled out

Variations of the STEMboom concept [Source: NASA]

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


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

Preliminary Lenticular Boom Sizing

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 DataSF, ultimate 1.40SF, yield 1.25Force at half Ø contact pts, total 7500NNo. of Booms 6

Beam GeometryBeam Length 20.50mBeam Length to half Ø contact pts. 10mEnd Force, Tangential 1250NNeutral axis dist., strong axis, c 0.1625mMOI, strong axis 3.18E+06mm^4

Beam CalcsMax Moment, M 12500NmMax Stress, δ 639.55MPa

Ti-6Al-4V, .020" thkYoung's Mod, E 113.8GPaFtu 951.48Mpa

Fty 882.53MpaMS, Ftu 0.059

MS, Fty 0.094

Beam mass/length 1.756kg/m

Beam mass (1) 36.00kg Max Displacement, w 1153mm

T500 12k/976 unidirectional tape, Mil 17, V2, Pg 4-4. 0.020"thk layupTensile Mod, E 141.34GPa

Ftu 1771.96Mpa

MS, Ftu 0.495

Beam mass/length 0.464kg/m

Beam mass (1) 9.51kg Max Displacement, w 928mm

Flattened Width =390mmI=3176049 mm^4

Flattened Width =280mmI=1396924 mm^4

Solving for minimum composite cross section = 250mm width


Conical Instrumentation Volume provides unobstructed forward view

Boom Mechanism

Volume

Capture Bag Stow

Volume

Volume trades allowed as design matures

Atlas V Medium Fairing Payload Volume

Packaging


Design Details

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

Cinch Cables


Internal View

Bag Dimensions 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

1 Pre-decisional NASA Internal Use Only Curved Extendable/Retractable Boom-Deployed Bag Asteroid...

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