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Comet Engineering Thermal Model I. Pelivan, E. Kührt

Comet Engineering Thermal Model I. Pelivan, E. Kührt. Reference: CSTM. Rosetta lander surface temperatures significantly depend on ambient temperatures -> comet surface temperatures needed as input to lander thermal mathematical model (TMM )

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Comet Engineering Thermal Model I. Pelivan, E. Kührt

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  1. Comet Engineering Thermal ModelI. Pelivan, E. Kührt MUPUS Team Meeting, Graz> I. Pelivan> Thermal Model > 24.10.2013

  2. Reference: CSTM • Rosetta landersurfacetemperaturessignificantlydepend on ambienttemperatures -> cometsurfacetemperaturesneededasinputtolander thermal mathematicalmodel (TMM) • Outdated CSTM restrictedtoequatorshallbereplacedbymoresuitablemodelpredictingthesurface temperature depending on time and location • Intended for operational use with the Philae TMM (planning and ground-testing operational sequences, NOT landing site selection) MUPUS Team Meeting, Graz> I. Pelivan> Thermal Model > 24.10.2013

  3. CSTM overview • Solve the 1D heat transport problem (ignore the lateral heat transfer) for a sphere • Include the time dependent (diurnal and seasonal) solar insolation at the surface boundary. • Assumes a no-heat transfer at the bottom boundary (adiabatic condition). • Set the simulation domain depth to 8 times the seasonal thermal penetration (necessary for high latitudes to achieve the required accuracy of the surface temperature) • One material component (no layering) was defined according to the parameters given in CSTM document • Energy consumption due to sublimation of water ice can be switched on and off • Sublimation is allowed only at surface. • The model was run for 3 orbital periods to ensure the convergence of the surface temperature (independent on initial conditions) • Approximations: • Heliocentric distance remains constant during one rotational period MUPUS Team Meeting, Graz> I. Pelivan> Thermal Model > 24.10.2013

  4. Model input parameters MUPUS Team Meeting, Graz> I. Pelivan> Thermal Model > 24.10.2013

  5. Model equations • Heatconduction: • Upperboundarycondition (conservationofenergy): • Lowerboundarycondition: • Initial condition: MUPUS Team Meeting, Graz> I. Pelivan> Thermal Model > 24.10.2013

  6. Case study For 15 latitudes (89N, 85N, 75N, 60N, 45 N, 30N, 15N, 0, 15S, 30S, 45S, 60S, 75S, 85S, 89S) • Surface temperature from 3.25AU to 1.25 AU heliocentric distance in (inbound orbit) in steps of 0.25 AU • Outputs were generated for each of 6 cases in steps of 5 deg in hour angle US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013

  7. Case study For 15 latitudes (89N, 85N, 75N, 60N, 45 N, 30N, 15N, 0, 15S, 30S, 45S, 60S, 75S, 85S, 89S) • Surface temperature from 3.25AU to 1.25 AU heliocentric distance in (inbound orbit) in steps of 0.25 AU • Outputs were generated for each of 6 cases in steps of 5 deg in hour angle US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013

  8. Model output parameters For 15 latitudes (89N, 85N, 75N, 60N, 45 N, 30N, 15N, 0, 15S, 30S, 45S, 60S, 75S, 85S, 89S) • Surface temperature from 3.25AU to 1.25 AU heliocentric distance in (inbound orbit) in steps of 0.25 AU • Outputs were generated for each of 6 cases in steps of 5 deg in hour angle US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013

  9. Someresults: active vs. inactivecomet • Sphere • Parameters used: recommended, with k = 0.1, 0.01, 0.001 W/m/K US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013

  10. Someresults: active vs. inactivecomet, k = 0.001 W/m/K active inactive US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013

  11. Someresults: comparisonwithdatafrom MIRO team ourmodel: red Miro: blue .. k1 - k01 -. k001 • min(ourmodel) = 28.0121 • max(ourmodel)= 359.0622 • min(MIRO) = 27.2600 • max(MIRO) = 360.6200 => 5 degshiftdetectedandcorrected in MIRO model US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013

  12. Sphereresultssummary • Changing the dust thermal conductivity from 0.1 to 0.001 can change the surface temperature by as much as 35K. • Sublimation has a max. 35K effect on the surface temperature at 3AU but can differ by more than 150K at 1.25 AU. • The sublimation effect is stronger for a smaller thermal conductivity. US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013

  13. Case study For 15 latitudes (89N, 85N, 75N, 60N, 45 N, 30N, 15N, 0, 15S, 30S, 45S, 60S, 75S, 85S, 89S) • Surface temperature from 3.25AU to 1.25 AU heliocentric distance in (inbound orbit) in steps of 0.25 AU • Outputs were generated for each of 6 cases in steps of 5 deg in hour angle US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013

  14. Shape model(s) • Inclusionofanyshapemodelwithtriangular (orquadrilateralelements) • Shape modelpreprocessingfinished (check of normal vectororientation, processingofelementdata) • Validation ofrevisedsourcecodeforshapemodelinclusionandotherapectswithdataforsphere Wrong normal vectororientation vs. corrected, validation example US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013

  15. Shape model(s) – cont‘d + some open points • New subroutines • calculationof solar incidence angle forshapeelements (boundarycondition) • Determination of Sun vectorandelement normal vector • Frame for NAIF SPICE ephemeridesasoptiontokepler(actualimplementationpending, seenextslide) • Open: • Model-specifictransformationroutines • Forarbitrarylocation on cometsurface: implementpoint-in-triangleroutine • NAIF SPICE interfaceforotherproducts? • Test implementations! US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013

  16. Some design decisions • C insteadofFortran: • Compiler difficulties (solved) btw. NAG FortranandFortran SPICE Toolkit, still existing: run time problems (segmentation fault @ inaccessible NAG routine (TO BE REPLACED?) • CSPICE vs. Fortran Toolkit: also implementedwith IDL andMatlab US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013

  17. Profile analysis – moreto do • Profiles: ____ k = constant - - - - k=c_k*T^3 • Temperaturedependanceof k leadstooveralltemperatureincrease • Surfacetemperaturepractically not depend on k US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013

  18. Thermal engineeringmodelsummaryandoutlook • Original Fortran code re-implemented in C – update for shape model to follow • Final ephemerides implementation (only tested with separate program so far) • Physics updates where required (TBD) • Test new implementations and changes US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013

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