photoflexibility modeling for design, operations, and …. william... · photoflexibility modeling...

Photoflexibility Modeling for Design, Operations, and

Post-Flight Improvements Billy Derbes

www.BCDAerospace.com Healdsburg, California

Fourth International Symposium on Solar Sailing

Kyoto, Japan, January 19, 2017

If these fibers were spaced 12 cm apart, without the droplets, the weight of the web would just match the photonic force on a solar sail at 1 AU.

ACS & Structure Sizings Affect Mass, So Predict Shape for External Moments & Internal Loads

•  Sailscanbemadepassivelystableintwoaxes•  Solarmomentsrestorea5tudetosunline-normal•  Causedbyeffec:veshu<lecock,cantedvanes,and/orcenterofmass

Shu<lecock

VaneCant

CM-CPOffset

•  Greatforsafety,butthesailmustbeheldoff-normalforforwardthrust,formonths•  Themorestable,thegreaterthecontroleffectormass,thelowerperformance

•  Needtoknowthesurfaceshapetoknowitscontribu:ontorestoringmoments





•  Shapealsoaffectsinternalloadsonthegossamerstructure,thereforeitsmass•  ThesailmustbillowoutofplanetotransferpropulsiveloadstothecentralS/C&P/L

•  Thecloserthesolarapproach,thehighertheinternalloads(doublesatVenus)





•  Shapealsoaffectsinternalloadsonthegossamerstructure,thereforeitsmass•  ThesailmustbillowoutofplanetotransferpropulsiveloadstothecentralS/C&P/L

•  Thecloserthesolarapproach,thehighertheinternalloads(doublesatVenus)

•  SurfaceQUALITYaffectsneithersignificantly•  But,a<emptstoimproveitbyenforcingstressgreatlyincreasestructuralmass

•  Thesea<emptsareunnecessary–“PropulsiveReflec:vity”isgoodatzerostress•  Stress-enforcedandnon-spokeddesignswerenotanalyzed,butcanbe

L’Garde,Inc.

Factors Affecting Shape

“Photoflexibility:”•  Thesunline-normalshapeofsailbillowisnotthecirculararcofaninflatable,

nottheparabolaofasuspensionbridge,notthegravitycatenaryofasurveyor’stape.•  Solarforceshapesthemembrane,soshapeisdependentonreflec:vity,etc.•  Atoff-normala5tudes,theshapebecomesasymmetric.

•  Difficulttoanalyzebecausethedirec:onofsolarforcechangesalongthebillowarc

EXPANDEDVERTICALSCALE


Iner:aleffectsonsailshape:•  ∑Fext≠0Thevehicleisaccelera:ngduetosolarpressure,inadirec:onwhichdoes

notlineupwiththedirec:onofsolarforceoneachindividualsquareofsailmaterial•  Ifclosetoalargebody,gravitygradientalsocanchangeshape•  Rota:onalaccelera:onsduetomaneuversorspinning

Beambend,sway,andtwistundersolarandactuatorloadswillalsochangesailshape:

“Photoflexibility:”•  Thesunline-normalshapeofsailbillowisnotthecirculararcofaninflatable,

nottheparabolaofasuspensionbridge,notthegravitycatenaryofasurveyor’stape.•  Solarforceshapesthemembrane,soitisdependentonreflec:vity,etc.•  Atoff-normala5tudes,theshapebecomesasymmetric.

Greschik,G.


•  Thehigh-CTEmembranewillcontractrela:vetothelow-CTEboomsatoff-normala5tude•  Drama:callydecreasesmembranedepth–atleast4.4%depth/chordisneeded•  Somethermalcompliancemechanismisrequired,suchas“stripenet”suspension

L’Garde,Inc.

Numerical Models

•  “Trough”solarsailusedtoquan:zeexternalsolarmomentsandinternalstructuralloads.•  Ribbonofsailmaterialdividedintoflatrectanglesortriangles

•  Elementalsolarforcemodelusesvectorreduc:onofBDRdataonwrinkledMylar•  Loadsoftheribbonendsontherodsdirectlyoutput

•  Toillustratedynamicstability,troughdisturbed5°off-normal,allowedtofreelyrotateina6DOFsimula:on:

Prac:calmodelofaba<en–ba<en

segmentofaheliogyro7g/mrod 1µmribbon

7g/mrod

Results for a Trough

Themostsimplemodelofbillowisachevron:

10%depth/chord

Thetroughisunstable


Astepupisasta:ccirculararc:

Thetroughisunstable

10%depth/chord

Photoflexible Numerical Model, and Results for a Trough

•  Thesailisactuallyphotoflexible,theshapechangingwitha5tude•  Previousa<emptstouseFEAhavefailedtoconverged•  “Ribbon”modelusesnumericalshoo:ngmethod:

Thetroughisunstable

Theinternalloadsoftheribbonontherodsbecomeasymmetricata5tude:

Thisraisesaconcernofspiralmodefailure:

10%depth/chord


Iner:alrelief(∑Fext≠0)hasasmalleffectondynamics;alargeeffectonloads:

Thetroughisunstable

Distributedmasseffect:

10%depth/chord

Thermal Compliance Numerical Model, and Results for a Trough

Toinves:gatethermaleffects,a“string”modelisintegratedwithribbonmodels:

Codecanalsooutputillumina:onvs.viewingangle

Thetroughisunstable

string

ribbons

rod

Structuralloadsareslightlylower,duetodecreasedthrust

10%depth/chord

Billow is Dynamically Unstable, Even with More Realistic Booms

•  Billowisdestabilizing,evenwhenmorerealis:cboommassdrivestheCMclosertotheboomplane:

ThetroughisSTILLunstable

Billow Instability is Less if Shallow, but That Would Increase Internal Loads

•  Reducingbillowdepthreducesinstability,BUT•  Shallowsailshavehigherinternalloads,requiringheavierstructures:

Thisisbecauseofthemechanicaladvantagesolarpressurehaswithshallowangles:

•  Billowisdestabilizing,evenwhenbusmassdrivestheCMclosertotheboomplane

Thetroughisunstable

How DO We Get Positive Passive Stability for Vehicle Safety?

•  Howtogetposi:vepassivestabilityforvehiclesafety?•  Placingthecmsunwardofthesailwouldstabilizeit,

•  Billowisdestabilizing,evenwhenbusmassdrivestheCMclosertotheboomplane

•  BUTwouldpreventflippingthesail,whichisdesirableforcommunica:ons,andtorecoverfromanya5tudeaqerdeployment:

•  Reducingbillowdepthreducesinstability,BUT•  Shallowsailshavehigherinternalloads,requiringheavierstructures:

Spoked Sails are Stabilized by Shuttlecock

Inasquaresail,assuminganobliqueconicsailquadrantshape,theforeandaqquadrantsappearshu<lecockedwhenviewedfromtheside:

Portandstarboardquadrantsares:llunstablelikethetrough,buttheneteffectisstable:

Thedeeperthesail,thegreaterthestability(andthelowertheinternalloads)Stabilitycanbeenhancedwithvanecant,butatacostinmass:

Shuttlecock Stability is Excessive if Deep, Setting up a Basic Trade

Somestabilityisdesirableforvehiclesafety,butthesailmustbeheldoff-normalforforwardthrust,formonthsata:me

Themorestable,thegreaterthecontroleffectormass,thelowerperformance

Thereisabasictradetoperformindesign,op:mizingperformance:deepsail=biggervanes,smallerbooms

vs. shallowsail=smallervanes,biggerbooms

vs.

Notethatbillowdepthalsotakesawayfromthrustsomewhat.Thrust,andtheuseofvanecant,arepartofageneraltrade,aswellasthepropulsiveareaofthevanes(ifused).

1.  Knowinginternalloadsandrestoringmomentsallowsatleastanadequatestructureanda5tudecontroleffectors,withoutthemmakingthedesignheavy.(Don’tneedstressforthrust,soit’spossibletodesigntoloadandbetrulygossamer)

2.  Thedesigncanbeop:mizedforperformance,tradingvs.billowdepth,andtheanalysisisthebasisforthattrade.

3.  Itisimpossibletotestforeitherdesignoras-builtopera:onalshapein1-G.Analysiscanuncoverunknowns,suchasasymmetricinternalloadsorlowerlufflimits,In-flightphotogrammetry(therelevantenvironment)mightthenbecorrelatedwithanalysistomakepost-flightimprovementsindesignorfabrica:on.

4.  Evenifnoneoftheabovearedone,thebe<erthetransferfunc:onofthesailisknown,themoreflightreadythefeedbackcontroloftrim,maneuvers,andtrajectory.

5.  Thisanalysiswasappliedtospokedsailswithperiodica<achmentofthesailtothebeams,buttheasymmetriceffectsofphotoflexibility,etc.existfor5-pointsquaresails,spinners,andheliogyros.Theanalysiscanbeappliedtothemawell.

Conclusions on Usefulness of Shape Modeling

Improvements and Future Work: Shoelace Sail Suspension

•  Instripe-netsailsuspension,thelinesareparallel•  Tobeartransversein-planeloads,thelineshavetomoveandcurve,affec:ngsag

•  “Shoelace”improvementallowsloadstobetransferredatcross-:es,limitsvariability

L’Garde,Inc.

Improvements and Future Work: Elliptical Billow Profile

Obliqueconicbillowprofile

Ellip:calbillowprofile

Shu<lecockoutboardtouselongermomentarm

Fla<erinboardforbe<erpropulsiveefficiency

Future Work: Structural Deflections & CSI

•  Vacuumtes:nghasshownsignifica:onvibra:oncanoccurasaresultofvaneactua:on,

•  Maynotbeanissuefora5tudecontrol,butwhataboutpoin:nghighgain,narrowbeamwidthantennasfromdeepspacetowardEarth?

•  1.Modeldeflec:on,shape,andcontrol-structureinterac:on.

•  2.Useas:ffstructure:

Target Application: Tri-Spoke Sail with Integral Control Tabs

forespoke

portaqspoke

centermast

gaff

“groundup”redesigntoload,stability,andfitPackagingin6Uor12Ugivesbestshotatalaunchfromacostandescapeavailability(SLS)standpoint,buts:llneedsperformancetocompeteforaprac:calapplica:on.

Goals(@0.9µm):6U:280m2,26.5g/m2,0.33mm/s2(2XGeostormwarning;asteroidhopping)12U:1000m2,8.8g/m2,1mm/s2(allapplica:ons)

gaff

stbdaqspoke

6U

170m2(parametric)

photoflexibility modeling for design, operations, and …. william... · photoflexibility modeling...

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