folie 1 mupus team meeting, graz> i. pelivan> thermal model > 24.10.2013 comet engineering...
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Folie 1MUPUS Team Meeting, Graz> I. Pelivan> Thermal Model > 24.10.2013
Comet Engineering Thermal Model
I. Pelivan, E. Kührt
Folie 2MUPUS Team Meeting, Graz> I. Pelivan> Thermal Model > 24.10.2013
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Outdated CSTM restricted to equator shall be replaced by more suitable model predicting the surface temperature depending on time and location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)
Folie 3MUPUS Team Meeting, Graz> I. Pelivan> Thermal Model > 24.10.2013
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
Folie 4MUPUS Team Meeting, Graz> I. Pelivan> Thermal Model > 24.10.2013
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
Folie 7US 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
Folie 8US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013
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
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
US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013
active
inactive
Folie 11
Some results: comparison with data from MIRO team
US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013
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
US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013
• 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.
Folie 13US 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
Folie 14
Shape model(s)
US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013
• 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
US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013
• 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
US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013
• 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
US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013
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
US Rosetta Co-I Workshop> I. Pelivan> Thermal Model > 07.02.2013
• 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