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

Folie 1MUPUS Team Meeting, Graz> I. Pelivan> Thermal Model > 24.10.2013

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)

Outdated CSTM restricted to equator shall be replaced by more suitable model predicting the surface temperature depending on time and location

Intended for operational use with the Philae TMM (planning and ground-testing operational sequences, NOT landing site selection)


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


Model input parameters

Symbol Parameter Value (or range), unit

ε IR Emissivity (hemispherical) 0.9

k Thermal conductivity, effective 0.001…0.1 W/m/K, temperature

independent

ρ Density of surface material Nominal 370 (range 100‐1000) kg/m³

AB Bond Albedo 0.01 (geometric albedo 0.053, phase

integral

~0.2 by analogy with Tempel‐1, Borrelly,

Wild‐2)

S Solar constant (TSI) 1 AU 1366.1 W/m² [ASTM 2000]

All other parameters (e.g., Specific heat capacity at

constant pressure)

Agreed upon between teams (“best

estimate”)

Folie 5

Model equations

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

),(),(

txTt

txTcp

- Heat conduction:

- Upper boundary condition (conservation of energy):

- Lower boundary condition:

- Initial condition:

0T

0)0,( TxT

)()(

)(cos)1( 42

TQTTtr

tAF

H

S

Folie 6US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013

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


Case study





Model output parameters




Case

Dust Thermal Conductivity (W/K m)

Sublimation

1 0.1 Off

2 0.01 Off

3 0.001 Off

4 0.1 On

5 0.01 On

6 0.001 On

Folie 9

Some results: active vs. inactive comet

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

Folie 10

Some results: active vs. inactive comet, k = 0.001 W/m/K


active

inactive

Folie 11

Some results: comparison with data from MIRO team


min(our model) = 28.0121

max(our model)= 359.0622

min(MIRO) = 27.2600

max(MIRO) = 360.6200

-200 -100 0 100 20080

100

120

140

160

180

200

220

240

H (deg)

T (

K)

3 AU, active, k001, 0° latitude: Miro vs. Berlin

our model: redMiro: blue

.. k1- k01-. k001

=> 5 deg shift detected and corrected in MIRO model

Folie 12

Sphere results summary


• 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.


Case study




Folie 14

Shape model(s)


• Inclusion of any shape model with triangular (or quadrilateral elements)

• Shape model preprocessing finished (check of normal vector orientation, processing of element data)

• Validation of revised source code for shape model inclusion and other apects with data for sphere

Wrong normal vector orientation vs. corrected, validation example

Folie 15

Shape model(s) – cont‘d + some open points


• New subroutines- calculation of solar incidence angle for shape elements (boundary condition)- Determination of Sun vector and element normal vector- Frame for NAIF SPICE ephemerides as option to kepler (actual

implementation pending, see next slide)

• Open:- Model-specific transformation routines- For arbitrary location on comet surface:

implement point-in-triangle routine- NAIF SPICE interface for other products?

- Test implementations!

Folie 16

Some design decisions


• C instead of Fortran:

- Compiler difficulties (solved) btw. NAG Fortran and Fortran SPICE Toolkit, still existing: run time problems (segmentation fault @ inaccessible NAG routine (TO BE REPLACED?)

- CSPICE vs. Fortran Toolkit: also implemented with IDL and Matlab

Folie 17

Profile analysis – more to do


Profiles:

____ k = constant

- - - - k=c_k*T^3

Temperature dependance of k leads to overall temperature increase

Surface temperature practically not depend on k

Folie 18

Thermal engineering model summary and outlook


• 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

Documents

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