Photoflexibility Modeling for Design, Operations, and Post ...
Transcript of Photoflexibility Modeling for Design, Operations, and Post ...
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
ACS & Structure Sizings Affect Mass, So Predict Shape for External Moments & Internal Loads
• Sailscanbemadepassivelystableintwoaxes• Solarmomentsrestorea5tudetosunline-normal• Causedbyeffec:veshu<lecock,cantedvanes,and/orcenterofmass
• Greatforsafety,butthesailmustbeheldoff-normalforforwardthrust,formonths• Themorestable,thegreaterthecontroleffectormass,thelowerperformance
• Needtoknowthesurfaceshapetoknowitscontribu:ontorestoringmoments
• Shapealsoaffectsinternalloadsonthegossamerstructure,thereforeitsmass• ThesailmustbillowoutofplanetotransferpropulsiveloadstothecentralS/C&P/L
• Thecloserthesolarapproach,thehighertheinternalloads(doublesatVenus)
ACS & Structure Sizings Affect Mass, So Predict Shape for External Moments & Internal Loads
• Sailscanbemadepassivelystableintwoaxes• Solarmomentsrestorea5tudetosunline-normal• Causedbyeffec:veshu<lecock,cantedvanes,and/orcenterofmass
• Greatforsafety,butthesailmustbeheldoff-normalforforwardthrust,formonths• Themorestable,thegreaterthecontroleffectormass,thelowerperformance
• Needtoknowthesurfaceshapetoknowitscontribu:ontorestoringmoments
• Shapealsoaffectsinternalloadsonthegossamerstructure,thereforeitsmass• ThesailmustbillowoutofplanetotransferpropulsiveloadstothecentralS/C&P/L
• Thecloserthesolarapproach,thehighertheinternalloads(doublesatVenus)
• SurfaceQUALITYaffectsneithersignificantly• But,a<emptstoimproveitbyenforcingstressgreatlyincreasestructuralmass
• Thesea<emptsareunnecessary–“PropulsiveReflec:vity”isgoodatzerostress• Stress-enforcedandnon-spokeddesignswerenotanalyzed,butcanbe
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Factors Affecting Shape
“Photoflexibility:”• Thesunline-normalshapeofsailbillowisnotthecirculararcofaninflatable,
nottheparabolaofasuspensionbridge,notthegravitycatenaryofasurveyor’stape.• Solarforceshapesthemembrane,soshapeisdependentonreflec:vity,etc.• Atoff-normala5tudes,theshapebecomesasymmetric.
• Difficulttoanalyzebecausethedirec:onofsolarforcechangesalongthebillowarc
EXPANDEDVERTICALSCALE
Factors Affecting Shape
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.
Factors Affecting Shape
• Thehigh-CTEmembranewillcontractrela:vetothelow-CTEboomsatoff-normala5tude• Drama:callydecreasesmembranedepth–atleast4.4%depth/chordisneeded• Somethermalcompliancemechanismisrequired,suchas“stripenet”suspension
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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
Photoflexible Numerical Model, and Results for a Trough
• Thesailisactuallyphotoflexible,theshapechangingwitha5tude• Previousa<emptstouseFEAhavefailedtoconverged• “Ribbon”modelusesnumericalshoo:ngmethod:
Thetroughisunstable
Theinternalloadsoftheribbonontherodsbecomeasymmetricata5tude:
Thisraisesaconcernofspiralmodefailure:
10%depth/chord
Results for a Trough
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
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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
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“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)