# SIST-TP CEN/TR 17603-31-17:2022

(Main)## Space engineering - Thermal analysis handbook

## Space engineering - Thermal analysis handbook

This handbook is dedicated to the subject of thermal analysis for space applications. Thermal analysis is an important method of verification during the development of space systems. The purpose of this handbook is to provide thermal analysts with practical guidelines which support efficient and high quality thermal modelling and analysis.

Specifically, the handbook aims to improve:

1.the general comprehension of the context, drivers and constraints for thermal analysis campaigns;

2.the general quality of thermal models through the use of a consistent process for thermal modelling;

3.the credibility of thermal model predictions by rigorous verification of model results and outputs;

4.long term maintainability of thermal models via better model management, administration and documentation;

5.the efficiency of inter-organisation collaboration by setting out best practice for model transfer and conversion.

The intended users of the document are people, working in the domain of space systems, who use thermal analysis as part of their work. These users can be in industry, in (inter)national agencies, or in academia. Moreover, the guidelines are designed to be useful to users working on products at every level of a space project - that is to say at system level, sub-system level, unit level etc.

In some cases a guideline could not be globally applicable (for example not relevant for very high temperature applications). In these cases the limitations are explicitly given in the text of the handbook.

## Raumfahrttechnik - Handbuch für thermische Analyse

## Ingénierie spatiale - Manuel d'analyse thermique

## Vesoljska tehnika - Priročnik o toplotni analizi

Ta priročnik je posvečen toplotni analizi za vesoljske tehnike. Toplotna analiza je pomembna metoda preverjanja pri razvoju vesoljskih sistemov. Namen tega priročnika je analitikom toplote zagotoviti praktične smernice, ki podpirajo učinkovito in visokokakovostno toplotno modeliranje oziroma analizo.

Natančneje, namen priročnika je izboljšati:

1. splošno razumevanje konteksta, ključnih dejavnikov in omejitev za izvedbo toplotne analize;

2. splošno kakovost toplotnih modelov z uporabo doslednega procesa toplotnega modeliranja;

3. verodostojnost napovedi toplotnega modela s strogim preverjanjem rezultatov in izhodnih podatkov modela;

4. dolgoročno vzdržljivost toplotnih modelov z boljšim upravljanjem, administracijo in dokumentacijo modelov;

5. učinkovitost medorganizacijskega sodelovanja z določitvijo dobre prakse za prenos in pretvorbo modelov.

Predvideni uporabniki dokumenta so osebe, ki delajo na področju vesoljskih sistemov in pri svojem delu uporabljajo toplotno analizo. To so lahko uporabniki v industriji, v (med)nacionalnih agencijah ali v akademskih krogih. Poleg tega so smernice zasnovane tako, da jih lahko uporabljajo tudi tisti, ki delajo na vseh ravneh vesoljskega projekta – to je na ravni sistema, ravni podsistema, ravni enote itd.

V nekaterih primerih smernice ni mogoče uporabiti globalno (na primer ni pomembna za uporabo pri zelo visokih temperaturah). V teh primerih so omejitve izrecno navedene v besedilu priročnika.

### General Information

### Standards Content (Sample)

SLOVENSKI STANDARD

SIST-TP CEN/TR 17603-31-17:2022

01-marec-2022

Vesoljska tehnika - Priročnik o toplotni analizi

Space engineering - Thermal analysis handbook

Raumfahrttechnik - Handbuch für thermische Analyse

Ingénierie spatiale - Manuel d'analyse thermique

Ta slovenski standard je istoveten z: CEN/TR 17603-31-17:2022

ICS:

49.140 Vesoljski sistemi in operacije Space systems and

operations

SIST-TP CEN/TR 17603-31-17:2022 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST-TP CEN/TR 17603-31-17:2022

TECHNICAL REPORT CEN/TR 17603-31-17

RAPPORT TECHNIQUE

TECHNISCHER BERICHT

January 2022

ICS 49.140

English version

Space engineering - Thermal analysis handbook

Ingénierie spatiale - Manuel d'analyse thermique Raumfahrttechnik - Handbuch für thermische Analyse

This Technical Report was approved by CEN on 29 November 2021. It has been drawn up by the Technical Committee

CEN/CLC/JTC 5.

CEN and CENELEC members are the national standards bodies and national electrotechnical committees of Austria, Belgium,

Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy,

Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia,

Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom.

CEN-CENELEC Management Centre:

Rue de la Science 23, B-1040 Brussels

© 2022 CEN/CENELEC All rights of exploitation in any form and by any means

Ref. No. CEN/TR 17603-31-17:2022 E

reserved worldwide for CEN national Members and for

CENELEC Members.

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Table of contents

European Foreword . 6

1 Scope . 7

1.1 Objectives and intended audience . 7

1.2 Context .7

2 References . 9

3 Terms, definitions and abbreviated terms . 11

3.1 Terms from other documents . 11

3.2 Terms specific to the present document . 12

3.3 Abbreviated terms. 13

4 Modelling guidelines . 16

4.1 Model management . 16

4.2 Model configuration and version control . 17

4.3 Modelling process . 17

4.4 Modularity and decomposition approach . 19

4.5 Discretisation . 19

4.5.1 Overview . 19

4.5.2 Spatial discretisation and mesh independence . 20

4.5.3 Observability . 20

4.5.4 Time discretisation . 21

4.5.5 Input parameters . 22

4.6 Transient analysis cases. 23

4.7 Modelling thermal radiation . 23

4.7.1 Introduction to thermal radiation . 23

4.7.2 Radiative environment . 24

4.7.3 Thermo-optical properties . 25

4.7.4 Transparency and optical elements . 26

4.7.5 Spectral dependency . 26

4.7.6 Radiative cavities . 27

4.7.7 Geometrical modelling . 28

2

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4.8 Considerations for non-vacuum environments . 29

4.8.1 General . 29

4.8.2 Specific regimes . 29

4.8.3 Conduction or convection . 29

4.8.4 Heat transfer coefficient correlation . 30

4.8.5 Charge/discharge of gas inside pressurised systems . 30

5 Model verification . 31

5.1 Introduction to model verification . 31

5.2 Topology checks . 31

5.3 Steady state analysis . 32

5.4 Finite element models . 33

5.5 Verification of radiative computations. 34

6 Uncertainty analysis . 35

6.1 Uncertainty philosophy . 35

6.2 Sources of uncertainties . 36

6.2.1 General . 36

6.2.2 Environmental parameters . 36

6.2.3 Physical parameters . 37

6.2.4 Modelling parameters . 37

6.2.5 Test facility parameters . 37

6.3 Classical uncertainty analysis . 38

6.4 Stochastic uncertainty analysis . 39

6.5 Typical parameter inaccuracies . 39

6.6 Uncertainty analysis for heater controlled items . 41

7 Model transfer, conversion and reduction . 42

7.1 Model transfer . 42

7.1.1 Introduction to model transfer . 42

7.1.2 Analysis files and reference results . 42

7.1.3 Documentation . 44

7.1.4 Portability of thermal models . 44

7.2 Model conversion. 45

7.2.1 Introduction to model conversion . 45

7.2.2 Management of thermal model conversions . 46

7.2.3 Model conversion workflow . 47

7.2.4 Verification of radiative model conversions . 50

7.2.5 Verification of thermal model (TMM) conversions . 52

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7.3 Model reduction . 52

7.3.1 Introduction to model reduction . 52

7.3.2 Management . 53

7.3.3 Model reduction guidelines . 53

7.3.4 Model reduction correlation success criteria . 54

7.3.5 Model reduction approaches . 55

Annex A Specific guidelines . 57

A.1 Multilayer insulation . 57

A.1.1 Introduction . 57

A.1.2 Modelling principles . 57

A.1.3 Modelling patterns . 58

A.2 Heat pipes . 58

A.2.1 Introduction . 58

A.2.2 Modelling principles . 59

A.2.3 Modelling patterns . 59

A.2.4 Design verification . 59

A.2.5 Model verification . 60

A.3 Layered materials . 60

A.3.1 Modelling principles . 60

A.3.2 Modelling patterns . 60

A.4 Electronic units . 63

A.4.1 Introduction . 63

A.4.2 Physical data and modelling advice . 64

Figures

Figure 1-1: Thermal analysis in the context of a space project . 8

Figure 4-1: Modelling process . 18

Figure 4-2: Examples of cavities: top showing two completely closed cavities, bottom

showing two almost separated cavities with a small opening . 27

Figure 7-1: Diagram for the ideal model conversion workflow . 47

Figure 7-2: Activity diagram for conversion workflow - Conversion done by developer. . 48

Figure 7-3: Activity diagram for conversion workflow - Conversion done by recipient. . 48

Figure 7-4: Comparison of converted GMM radiative couplings . 51

: Typical heat pipe nodal topology . 59

: Example of verifying heat pipe heat transport capability . 60

: Typical electronic unit thermal network . 63

4

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Tables

Table 6-1: Typical parameter inaccuracies (pre-phase A and phase B) . 39

Table 6-2: Typical parameter inaccuracies (phase B and phase C/D) . 40

Table 7-1: Model reduction methods . 55

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European Foreword

This document (CEN/TR 17603-31-17:2022) has been prepared by Technical Committee

CEN/CLC/JTC 5 “Space”, the secretariat of which is held by DIN.

It is highlighted that this technical report does not contain any requirement but only collection of data

or descriptions and guidelines about how to organize and perform the work in support of EN16603-

31.

This Technical report (CEN/TR 17603-31-17:2022) originates from ECSS-E-HB-31-03A.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

This document has been prepared under a mandate given to CEN by the European Commission and

the European Free Trade Association.

This document has been developed to cover specifically space systems and has therefore precedence

over any TR covering the same scope but with a wider domain of applicability (e.g.: aerospace).

6

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1

Scope

1.1 Objectives and intended audience

This handbook is dedicated to the subject of thermal analysis for space applications. Thermal analysis

is an important method of verification during the development of space systems. The purpose of this

handbook is to provide thermal analysts with practical guidelines which support efficient and high

quality thermal modelling and analysis.

Specifically, the handbook aims to improve:

a. the general comprehension of the context, drivers and constraints for thermal analysis

campaigns;

b. the general quality of thermal models through the use of a consistent process for thermal

modelling;

c. the credibility of thermal model predictions by rigorous verification of model results and

outputs;

d. long term maintainability of thermal models via better model management, administration and

documentation;

e. the efficiency of inter-organisation collaboration by setting out best practice for model transfer

and conversion.

The intended users of the document are people, working in the domain of space systems, who use

thermal analysis as part of their work. These users can be in industry, in (inter)national agencies, or in

academia. Moreover, the guidelines are designed to be useful to users working on products at every

level of a space project – that is to say at system level, sub-system level, unit level etc.

In some cases a guideline could not be globally applicable (for example not relevant for very high

temperature applications). In these cases the limitations are explicitly given in the text of the

handbook.

1.2 Context

The use of computational analysis to support the development of products is standard in modern

industry. Figure 1-1 illustrates the typical thermal modelling and analysis activities to be performed at

each phase of the development of a space system.

NOTE More information about the project lifecycle can be found in ECSS-

M-ST-10 [RD5].

7

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• Adapt thermal models for mission

• Analyse requirements

• Define final design of TCS • Perform mission predictions

• Define TCS concept

• Update thermal models (ground & flight)

• Perform trade-off

• Perform calculations covering all • Perform flight correlation

• Assess TRL of TCS

mission cases • Perform analysis in support of

products

operations

Phase B Phase C Phase D

Phase A Phase E

Preliminary Detailed Qualification

Feasibility Utilization

definition Definition production

PRR PDR CDR QR

• Adapt thermal models for test configuration

• Define preliminary design of TCS • Perform test prediction

• Develop thermal models • Perform test correlation

• Perform calculation for worst hot/cold • Update flight thermal models with outcomes

cases of test correlation

• Perform and correlate development tests • Perform analysis in support of production

activities

Figure 1-1: Thermal analysis in the context of a space project

It can be seen that thermal models are used during all phases of the space system development to

support a large number of activities, ranging from conceptual design right through to final in-flight

predictions.

Indeed, in some cases, thermal analysis is the only way that certain thermal requirements can be

verified; as physical tests are either too expensive or unrealisable. It is therefore vital for the credibility

of the predictions made that the quality of the models is as high as possible.

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2

References

RD # EN Reference Reference in text Title

[RD1] E N 16603-31 ECSS-E-ST-31, Space engineering - Thermal control general

requirements

[RD2] E N 16603-32-03 ECSS-E-ST-32-03 Space engineering - Structural finite element

models

[RD3] E N 16603-31-02 ECSS-E-ST-31-02 Space engineering - Two-phase heat transport

equipment

[RD4] T R 16603-31-01 ECSS-E-HB-31-01 Space engineering - Thermal design handbook

[RD5] E N-16601-10 ECSS-M-ST-10 Space project management - Project planning and

implementation

[RD6] E N 16601-00-01 ECSS-S-ST-00-01 ECSS system – Glossary of terms

[RD7] Gilmore, D., G., “Spacecraft Thermal Control

Handbook – Volume 1: Fundamental

Technologies”, 2002

[RD8] Anderson, B. J. and Smith, R. E. “Natural Orbital

Environment Guidelines for Use in Aerospace

Vehicle Development”, NASA Technical

Memorandum 4527, June 1994

[RD9] Anderson, B. J., Justus, C. G., and Batts, G. W.

“Guidelines for the Selection of Near-Earth

Thermal Environmental Parameters for Spacecraft

Design”, NASA Technical Memorandum 2001-

211221, October 2001

[RD10] Anderson, B. J., James, B. F., Justus, C. G., Batts

“Simple Thermal Environment Model (STEM)

User’s Guide, NASA Technical Memorandum

2001-211222, October 2001

[RD11] Sauer, A. “Implementation of the Equation of

Time in Sun Synchronous Orbit Modelling and

ESARAD Planet Temperature Mapping Error at

the Poles “, 22nd European Workshop on Thermal

and ECLS Software. October 2008.

https://exchange.esa.int/thermal-

workshop/attachments/workshop2008/

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RD # EN Reference Reference in text Title

[RD12] “Feasibility of Using a Stochastic Approach for

Space Thermal Analysis”, Blue Engineering &

Alenia Spazio, 2004,

https://exchange.esa.int/stochastic/

[RD13] “Guide for Verification and Validation in

Computational Solid Mechanics,” The American

Society of Mechanical Engineers, Revised Draft:

2006

[RD14] Remaury, S., Nabarra, P., Bellouard, E.,

d’Escrivan, S., “In-Flight Thermal Coatings

Ageing on the THERME Experiment” CNES,

Proceedings of the 9th International Symposium

on Materials in a Space Environment, 2003

Noordwijk, The Netherlands

[RD15] M. Molina & C. Clemente, “Thermal Model

Automatic Reduction: Algorithm and Validation

Techniques”, ICES 2006.

[RD16] F. Jouffroy, D. Charvet, M. Jacquiau and A.

Capitaine, “Automated Thermal Model Reduction

for Telecom S/C Walls”, 18th European Workshop

on Thermal and ECLS Software, 6–7 October 2004

[RD17] Gorlani M., Rossi M., “Thermal Model Reduction

with Stochastic Optimization”, 2007-01-3119, 37th

ICES Conference, 2007, Chicago

[RD18] M. Bernard, T. Basset, S. Leroy, F. Brunetti and J.

Etchells, “TMRT, a thermal model reduction tool”,

23rd European Workshop on Thermal and ECLS

Software, 6–7 October 2009

[RD19] STEP-TAS Technical Details

http://www.esa.int/TEC/Thermal_control/SEME7

NN0LYE_0.html

[RD20] CRTech, “How to Model a Heat Pipe”,

http://www.crtech.com/docs/papers/HowToMode

lHeatpipe.pdf

[RD21] Juhasz, A., “An Analysis and Procedure for

Determining Space Environmental Sink

Temperatures with Selected Computational

Results”, NASA Technical Memorandum 2001-

210063

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3

Terms, definitions and abbreviated terms

3.1 Terms from other documents

a. For the purpose of this document, the terms and definitions from ECSS-ST-00-01 [RD6] apply,

in particular for the following terms:

1. validation

NOTE Validation is the process of determining the degree to which a

computational model is an accurate representation of the real

world from the perspective of the intended uses of the model.

2. verification

NOTE 1 Verification is the process of determining that a computational

model accurately represents the underlying mathematical model

and its solution

NOTE 2 The topic of V&V is well known in the context of quality assurance

and systems engineering (including software systems). There has

also been some work in other domains such as Computational

Fluid Dynamics (CFD) and structural mechanics to develop

processes for V&V of simulation models. In the particular context

of computational analysis the formal definitions usually apply

[RD13].

NOTE 3 More informally the following questions are often used to explain

V&V in the context of computational analysis:

• Verification “did we solve the equations correctly?”

• Validation “did we solve the correct equations?”

b. For the purpose of this document, the terms and definitions from ECSS-E-ST-31 apply, in

particular for the following terms:

1. geometrical mathematical model

mathematical model in which an item and its surroundings are represented by radiation

exchanging surfaces characterised by their thermo-optical properties

2. thermal mathematical model

numerical representation of an item and its surroundings represented by concentrated

thermal capacitance nodes or elements, coupled by a network made of thermal

conductors (radiative, conductive and convective)

NOTE The current trend is towards integrated thermal modelling tools, in

which case the distinction between Geometrical Mathematical

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Model (GMM) and Thermal Mathematical Model (TMM) becomes

ill-defined. Nonetheless the terms GMM and TMM are still used in

the everyday language of thermal engineers and so the terms are

retained in this document.

3. thermal node

representation of a specific volume of an item with a representative temperature,

representative material properties and representative pressure (diffusion node) used in a

mathematical lumped parameter approach

NOTE The current document is written to be, as far as possible, tool and

method independent. It is therefore useful to generalise the

concept of thermal node to cover other numerical methods (e.g. the

finite element method). Mathematically speaking a thermal node

represents a “degree of freedom” in the equation system. More

practically, the purpose of a thermal node is to provide a

temperature evaluation (and output) at a selected location.

4. uncertainties

inaccuracies in temperature calculations due to inaccurate physical, environmental and

modelling parameters

NOTE This definition of uncertainty refers specifically to temperature

calculations. In the context of this document this is widened to

calculations of other key model outputs such as heater power or

duty cycle.

3.2 Terms specific to the present document

3.2.1 accuracy

degree of conformance between an output of a thermal analysis and the true value

NOTE The true value is usually a measurement from a physical test, for

example a thermal balance test. The purpose of the verification and

validation effort is thus to improve and quantify modelling

accuracy.

3.2.2 arithmetic thermal node

thermal node with zero thermal capacitance

NOTE 1 Arithmetic nodes are normally treated specially by thermal solvers

and a quasi-steady state solution is obtained for them during

transient runs. This is useful to avoid excessively small time steps

when lightweight items need to be represented in large models.

NOTE 2 Additionally arithmetic nodes are often used to represent thermal

interfaces or the edges of region

3.2.3 computational model

numerical implementation of a mathematical model

NOTE 1 This is usually comprises numerical discretisation, solution

algorithm, and convergence criteria.

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NOTE 2 This definition is taken from RD11, where a more detailed

discussion of the relationship between mathematical and

computation models can be found.

3.2.4 CSG

ratio of capacitance to sum of connected conductances for a thermal node

NOTE No specific acronym is available for CSG, most likely the C

represents capacitance, the S represents the sum, and the G

represents the conductors.

3.2.5 error

difference between an output of a thermal analysis and the true value

NOTE 1 High accuracy analyses therefore produce outputs with small

associated errors.

NOTE 2 This is a typical dictionary definition of error and generic. More

specific and formal definitions occur in a number of other sources,

for example ASME [RD13].

3.2.6 key model output(s)

output(s) from the thermal model having high level of importance

NOTE Examples of key model outputs are TRP temperatures, heater duty

cycles, and any other output form the model with special

significance for the verification of the TCS.

3.2.7 radiative cavity

collection of radiative surfaces of the thermal-radiative model, having the property that its surfaces

cannot exchange heat through thermal radiation with the surfaces belonging to another cavity

NOTE This term is synonymous with “radiative enclosure”.

3.2.8 radiative enclosure

See “radiative cavity”.

3.3 Abbreviated terms

For the purpose of this document, the abbreviated terms from ECSS-S-ST-00-01 and the following

apply:

Abbreviation Meaning

BOL beginning-of-life

CCHP constant conductance heat pipe

CFD computational fluid dynamics

CLA

coupled launcher analysis

CNES Centre National d'Etudes Spatiales

COTS commercial off-the-shelf

DGMM detailed geometrical mathematical model

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Abbreviation Meaning

DRD document requirements definition

DTMM detailed thermal mathematical model

EEE electrical, electronic and electromechanical

EOL

end-of-life

ESATAN

thermal/fluid analyser from ITP Engines

FEM finite element method

GMM geometrical mathematical model

HP heat pipe

HTC heat transfer coefficient

I/O

input / output

ICD

interface control document

ICES International Conference on Environmental Systems

IR infrared

KMO key model output(s)

LHP loop heat pipe

LP lumped parameter

MCRT

Monte Carlo ray tracing

MLI multi-layer insulation

OS open source

PCB printed circuit board

PID proportional integral derivative

PLM product lifecycle management

REF

radiation exchange factor

RGMM reduced geometrical mathematical model

RTMM reduced thermal mathematical model

S/C spacecraft

SDM simulation data management

SINDA thermal/fluid analyser from C&R technologies

SVD

singular value decomposition

TB

thermal balance

TCS thermal control system

TMG thermal/fluid analyser from MAYA HTT Engineering Software Solutions

TMM thermal mathematical model

TMRT thermal model reduction tool

TRL

technology readiness level

TRP

temperature reference point

14

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**...**

SLOVENSKI STANDARD

kSIST-TP FprCEN/TR 17603-31-17:2021

01-oktober-2021

Vesoljska tehnika - Priročnik o toplotni analizi

Space engineering - Thermal analysis handbook

Raumfahrttechnik - Handbuch für thermische Analyse

Ingénierie spatiale - Manuel d'analyse thermique

Ta slovenski standard je istoveten z: FprCEN/TR 17603-31-17

ICS:

49.140 Vesoljski sistemi in operacije Space systems and

operations

kSIST-TP FprCEN/TR 17603-31-17:2021 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------

kSIST-TP FprCEN/TR 17603-31-17:2021

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kSIST-TP FprCEN/TR 17603-31-17:2021

TECHNICAL REPORT

FINAL DRAFT

FprCEN/TR 17603-31-17

RAPPORT TECHNIQUE

TECHNISCHER BERICHT

August 2021

ICS 49.140

English version

Space engineering - Thermal analysis handbook

Ingénierie spatiale - Manuel d'analyse thermique Raumfahrttechnik - Handbuch für thermische Analyse

This draft Technical Report is submitted to CEN members for Vote. It has been drawn up by the Technical Committee

CEN/CLC/JTC 5.

CEN and CENELEC members are the national standards bodies and national electrotechnical committees of Austria, Belgium,

Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy,

Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia,

Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom.

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are

aware and to provide supporting documentation.

Warning : This document is not a Technical Report. It is distributed for review and comments. It is subject to change without

notice and shall not be referred to as a Technical Report.

CEN-CENELEC Management Centre:

Rue de la Science 23, B-1040 Brussels

© 2021 CEN/CENELEC All rights of exploitation in any form and by any means Ref. No. FprCEN/TR 17603-31-17:2021 E

reserved worldwide for CEN national Members and for

CENELEC Members.

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Table of contents

European Foreword . 6

1 Scope . 7

1.1 Objectives and intended audience . 7

1.2 Context . 8

2 References . 9

3 Terms, definitions and abbreviated terms . 11

3.1 Terms from other documents . 11

3.2 Terms specific to the present document . 12

3.3 Abbreviated terms. 13

4 Modelling guidelines . 15

4.1 Model management . 15

4.2 Model configuration and version control . 16

4.3 Modelling process . 16

4.4 Modularity and decomposition approach . 18

4.5 Discretisation . 18

4.5.1 Overview . 18

4.5.2 Spatial discretisation and mesh independence . 19

4.5.3 Observability . 19

4.5.4 Time discretisation . 20

4.5.5 Input parameters . 21

4.6 Transient analysis cases. 22

4.7 Modelling thermal radiation . 22

4.7.1 Introduction to thermal radiation . 22

4.7.2 Radiative environment . 23

4.7.3 Thermo-optical properties . 24

4.7.4 Transparency and optical elements . 25

4.7.5 Spectral dependency . 25

4.7.6 Radiative cavities . 26

4.7.7 Geometrical modelling . 27

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4.8 Considerations for non-vacuum environments . 28

4.8.1 General . 28

4.8.2 Specific regimes . 28

4.8.3 Conduction or convection . 28

4.8.4 Heat transfer coefficient correlation . 29

4.8.5 Charge/discharge of gas inside pressurised systems . 29

5 Model verification . 30

5.1 Introduction to model verification . 30

5.2 Topology checks . 30

5.3 Steady state analysis . 31

5.4 Finite element models . 32

5.5 Verification of radiative computations. 33

6 Uncertainty analysis . 34

6.1 Uncertainty philosophy . 34

6.2 Sources of uncertainties . 35

6.2.1 General . 35

6.2.2 Environmental parameters . 35

6.2.3 Physical parameters . 36

6.2.4 Modelling parameters . 36

6.2.5 Test facility parameters . 36

6.3 Classical uncertainty analysis . 37

6.4 Stochastic uncertainty analysis . 38

6.5 Typical parameter inaccuracies . 38

6.6 Uncertainty analysis for heater controlled items . 40

7 Model transfer, conversion and reduction . 41

7.1 Model transfer . 41

7.1.1 Introduction to model transfer . 41

7.1.2 Analysis files and reference results . 41

7.1.3 Documentation . 43

7.1.4 Portability of thermal models . 43

7.2 Model conversion. 44

7.2.1 Introduction to model conversion . 44

7.2.2 Management of thermal model conversions . 45

7.2.3 Model conversion workflow . 46

7.2.4 Verification of radiative model conversions . 49

7.2.5 Verification of thermal model (TMM) conversions . 51

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7.3 Model reduction . 51

7.3.1 Introduction to model reduction . 51

7.3.2 Management . 52

7.3.3 Model reduction guidelines . 52

7.3.4 Model reduction correlation success criteria . 53

7.3.5 Model reduction approaches . 54

Annex A Specific guidelines . 56

A.1 Multilayer insulation . 56

A.1.1 Introduction . 56

A.1.2 Modelling principles . 56

A.1.3 Modelling patterns . 57

A.2 Heat pipes . 57

A.2.1 Introduction . 57

A.2.2 Modelling principles . 58

A.2.3 Modelling patterns . 58

A.2.4 Design verification . 58

A.2.5 Model verification . 59

A.3 Layered materials . 59

A.3.1 Modelling principles . 59

A.3.2 Modelling patterns . 59

A.4 Electronic units . 62

A.4.1 Introduction . 62

A.4.2 Physical data and modelling advice . 63

Figures

Figure 1-1: Thermal analysis in the context of a space project . 8

Figure 4-1: Modelling process . 17

Figure 4-2: Examples of cavities: top showing two completely closed cavities, bottom

showing two almost separated cavities with a small opening . 26

Figure 7-1: Diagram for the ideal model conversion workflow . 46

Figure 7-2: Activity diagram for conversion workflow - Conversion done by developer. . 47

Figure 7-3: Activity diagram for conversion workflow - Conversion done by recipient. . 47

Figure 7-4: Comparison of converted GMM radiative couplings . 50

Figure A-1 : Typical heat pipe nodal topology . 58

Figure A-2 : Example of verifying heat pipe heat transport capability . 59

Figure A-3 : Typical electronic unit thermal network . 62

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Tables

Table 6-1: Typical parameter inaccuracies (pre-phase A and phase B) . 38

Table 6-2: Typical parameter inaccuracies (phase B and phase C/D) . 39

Table 7-1: Model reduction methods . 54

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European Foreword

This document (FprCEN/TR 17603-31-17:2021) has been prepared by Technical Committee

CEN/CLC/JTC 5 “Space”, the secretariat of which is held by DIN.

It is highlighted that this technical report does not contain any requirement but only collection of data

or descriptions and guidelines about how to organize and perform the work in support of EN16603-

31.

This Technical report (FprCEN/TR 17603-31-17:2021) originates from ECSS-E-HB-31-03A.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such

patent rights.

This document has been prepared under a mandate given to CEN by the European Commission and

the European Free Trade Association.

This document has been developed to cover specifically space systems and has therefore precedence

over any TR covering the same scope but with a wider domain of applicability (e.g.: aerospace).

This document is currently submitted to the CEN CONSULTATION.

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1

Scope

1.1 Objectives and intended audience

This handbook is dedicated to the subject of thermal analysis for space applications. Thermal analysis

is an important method of verification during the development of space systems. The purpose of this

handbook is to provide thermal analysts with practical guidelines which support efficient and high

quality thermal modelling and analysis.

Specifically, the handbook aims to improve:

a. the general comprehension of the context, drivers and constraints for thermal analysis

campaigns;

b. the general quality of thermal models through the use of a consistent process for thermal

modelling;

c. the credibility of thermal model predictions by rigorous verification of model results and

outputs;

d. long term maintainability of thermal models via better model management, administration and

documentation;

e. the efficiency of inter-organisation collaboration by setting out best practice for model transfer

and conversion.

The intended users of the document are people, working in the domain of space systems, who use

thermal analysis as part of their work. These users can be in industry, in (inter)national agencies, or in

academia. Moreover, the guidelines are designed to be useful to users working on products at every

level of a space project – that is to say at system level, sub-system level, unit level etc.

In some cases a guideline could not be globally applicable (for example not relevant for very high

temperature applications). In these cases the limitations are explicitly given in the text of the

handbook.

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1.2 Context

The use of computational analysis to support the development of products is standard in modern

industry. Figure 1-1 illustrates the typical thermal modelling and analysis activities to be performed at

each phase of the development of a space system.

NOTE More information about the project lifecycle can be found in ECSS‐

M‐ST‐10 [RD5].

· Adapt thermal models for mission

· Analyse requirements

· Define final design of TCS · Perform mission predictions

· Define TCS concept

· Update thermal models (ground & flight)

· Perform trade-off

· Perform calculations covering all · Perform flight correlation

· Assess TRL of TCS

mission cases · Perform analysis in support of

products

operations

Phase B Phase C Phase D

Phase A Phase E

Preliminary Detailed Qualification

Feasibility Utilization

definition Definition production

PRR PDR CDR QR

· Adapt thermal models for test configuration

· Define preliminary design of TCS · Perform test prediction

· Develop thermal models · Perform test correlation

· Perform calculation for worst hot/cold · Update flight thermal models with outcomes

cases of test correlation

· Perform and correlate development tests · Perform analysis in support of production

activities

Figure 1-1: Thermal analysis in the context of a space project

It can be seen that thermal models are used during all phases of the space system development to

support a large number of activities, ranging from conceptual design right through to final in-flight

predictions.

Indeed, in some cases, thermal analysis is the only way that certain thermal requirements can be

verified; as physical tests are either too expensive or unrealisable. It is therefore vital for the credibility

of the predictions made that the quality of the models is as high as possible.

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2

References

RD # EN Reference Reference in text Title

[RD1] E N 16603-31 ECSS-E-ST-31, Space engineering - Thermal control general

requirements

[RD2] E N 16603-32-03 ECSS-E-ST-32-03 Space engineering - Structural finite element

models

[RD3] E N 16603-31-02 ECSS-E-ST-31-02 Space engineering - Two-phase heat transport

equipment

[RD4] TR 16603-31-01 ECSS-E-HB-31-01 Space engineering - Thermal design handbook

[RD5] EN -16601-10 ECSS-M-ST-10 Space project management - Project planning and

implementation

[RD6] E N 16601-00-01 ECSS-S-ST-00-01 ECSS system – Glossary of terms

[RD7] Gilmore, D., G., “Spacecraft Thermal Control

Handbook – Volume 1: Fundamental

Technologies”, 2002

[RD8] Anderson, B. J. and Smith, R. E. “Natural Orbital

Environment Guidelines for Use in Aerospace

Vehicle Development”, NASA Technical

Memorandum 4527, June 1994

[RD9] Anderson, B. J., Justus, C. G., and Batts, G. W.

“Guidelines for the Selection of Near-Earth

Thermal Environmental Parameters for Spacecraft

Design”, NASA Technical Memorandum 2001-

211221, October 2001

[RD10] Anderson, B. J., James, B. F., Justus, C. G., Batts

“Simple Thermal Environment Model (STEM)

User’s Guide, NASA Technical Memorandum

2001-211222, October 2001

[RD11] Sauer, A. “Implementation of the Equation of

Time in Sun Synchronous Orbit Modelling and

ESARAD Planet Temperature Mapping Error at

the Poles “, 22nd European Workshop on Thermal

and ECLS Software. October 2008.

https://exchange.esa.int/thermal-

workshop/attachments/workshop2008/

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RD # EN Reference Reference in text Title

[RD12] “Feasibility of Using a Stochastic Approach for

Space Thermal Analysis”, Blue Engineering &

Alenia Spazio, 2004,

https://exchange.esa.int/stochastic/

[RD13] “Guide for Verification and Validation in

Computational Solid Mechanics,” The American

Society of Mechanical Engineers, Revised Draft:

2006

[RD14] Remaury, S., Nabarra, P., Bellouard, E.,

d’Escrivan, S., “In-Flight Thermal Coatings

Ageing on the THERME Experiment” CNES,

Proceedings of the 9th International Symposium

on Materials in a Space Environment, 2003

Noordwijk, The Netherlands

[RD15] M. Molina & C. Clemente, “Thermal Model

Automatic Reduction: Algorithm and Validation

Techniques”, ICES 2006.

[RD16] F. Jouffroy, D. Charvet, M. Jacquiau and A.

Capitaine, “Automated Thermal Model Reduction

for Telecom S/C Walls”, 18th European Workshop

on Thermal and ECLS Software, 6–7 October 2004

[RD17] Gorlani M., Rossi M., “Thermal Model Reduction

with Stochastic Optimization”, 2007-01-3119, 37th

ICES Conference, 2007, Chicago

[RD18] M. Bernard, T. Basset, S. Leroy, F. Brunetti and J.

Etchells, “TMRT, a thermal model reduction tool”,

23rd European Workshop on Thermal and ECLS

Software, 6–7 October 2009

[RD19] STEP-TAS Technical Details

http://www.esa.int/TEC/Thermal_control/SEME7

NN0LYE_0.html

[RD20] CRTech, “How to Model a Heat Pipe”,

http://www.crtech.com/docs/papers/HowToMode

lHeatpipe.pdf

[RD21] Juhasz, A., “An Analysis and Procedure for

Determining Space Environmental Sink

Temperatures with Selected Computational

Results”, NASA Technical Memorandum 2001-

210063

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3

Terms, definitions and abbreviated terms

3.1 Terms from other documents

a. For the purpose of this document, the terms and definitions from ECSS‐ST‐00‐01 [RD6] apply,

in particular for the following terms:

1. validation

NOTE Validation is the process of determining the degree to which a

computational model is an accurate representation of the real

world from the perspective of the intended uses of the model.

2. verification

NOTE 1 Verification is the process of determining that a computational

model accurately represents the underlying mathematical model

and its solution

NOTE 2 The topic of V&V is well known in the context of quality assurance

and systems engineering (including software systems). There has

also been some work in other domains such as Computational

Fluid Dynamics (CFD) and structural mechanics to develop

processes for V&V of simulation models. In the particular context

of computational analysis the formal definitions usually apply

[RD13].

NOTE 3 More informally the following questions are often used to explain

V&V in the context of computational analysis:

· Verification “did we solve the equations correctly?”

· Validation “did we solve the correct equations?”

b. For the purpose of this document, the terms and definitions from ECSS‐E‐ST‐31 apply, in

particular for the following terms:

1. geometrical mathematical model

mathematical model in which an item and its surroundings are represented by radiation

exchanging surfaces characterised by their thermo‐optical properties

2. thermal mathematical model

numerical representation of an item and its surroundings represented by concentrated

thermal capacitance nodes or elements, coupled by a network made of thermal

conductors (radiative, conductive and convective)

NOTE The current trend is towards integrated thermal modelling tools, in

which case the distinction between Geometrical Mathematical

Model (GMM) and Thermal Mathematical Model (TMM) becomes

ill-defined. Nonetheless the terms GMM and TMM are still used in

the everyday language of thermal engineers and so the terms are

retained in this document.

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3. thermal node

representation of a specific volume of an item with a representative temperature,

representative material properties and representative pressure (diffusion node) used in a

mathematical lumped parameter approach

NOTE The current document is written to be, as far as possible, tool and

method independent. It is therefore useful to generalise the

concept of thermal node to cover other numerical methods (e.g. the

finite element method). Mathematically speaking a thermal node

represents a “degree of freedom” in the equation system. More

practically, the purpose of a thermal node is to provide a

temperature evaluation (and output) at a selected location.

4. uncertainties

inaccuracies in temperature calculations due to inaccurate physical, environmental and

modelling parameters

NOTE This definition of uncertainty refers specifically to temperature

calculations. In the context of this document this is widened to

calculations of other key model outputs such as heater power or

duty cycle.

3.2 Terms specific to the present document

3.2.1 accuracy

degree of conformance between an output of a thermal analysis and the true value

NOTE The true value is usually a measurement from a physical test, for

example a thermal balance test. The purpose of the verification and

validation effort is thus to improve and quantify modelling

accuracy.

3.2.2 arithmetic thermal node

thermal node with zero thermal capacitance

NOTE 1 Arithmetic nodes are normally treated specially by thermal solvers

and a quasi-steady state solution is obtained for them during

transient runs. This is useful to avoid excessively small time steps

when lightweight items need to be represented in large models.

NOTE 2 Additionally arithmetic nodes are often used to represent thermal

interfaces or the edges of region

3.2.3 computational model

numerical implementation of a mathematical model

NOTE 1 This is usually comprises numerical discretisation, solution

algorithm, and convergence criteria.

NOTE 2 This definition is taken from RD11, where a more detailed

discussion of the relationship between mathematical and

computation models can be found.

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3.2.4 CSG

ratio of capacitance to sum of connected conductances for a thermal node

NOTE No specific acronym is available for CSG, most likely the C

represents capacitance, the S represents the sum, and the G

represents the conductors.

3.2.5 error

difference between an output of a thermal analysis and the true value

NOTE 1 High accuracy analyses therefore produce outputs with small

associated errors.

NOTE 2 This is a typical dictionary definition of error and generic. More

specific and formal definitions occur in a number of other sources,

for example ASME [RD13].

3.2.6 key model output(s)

output(s) from the thermal model having high level of importance

NOTE Examples of key model outputs are TRP temperatures, heater duty

cycles, and any other output form the model with special

significance for the verification of the TCS.

3.2.7 radiative cavity

collection of radiative surfaces of the thermal-radiative model, having the property that its surfaces

cannot exchange heat through thermal radiation with the surfaces belonging to another cavity

NOTE This term is synonymous with “radiative enclosure”.

3.2.8 radiative enclosure

See “radiative cavity”.

3.3 Abbreviated terms

For the purpose of this document, the abbreviated terms from ECSS-S-ST-00-01 and the following

apply:

Abbreviation Meaning

BOL beginning-of-life

CCHP

constant conductance heat pipe

CFD computational fluid dynamics

CLA coupled launcher analysis

CNES Centre National d'Etudes Spatiales

COTS commercial off-the-shelf

DGMM detailed geometrical mathematical model

DRD

document requirements definition

DTMM detailed thermal mathematical model

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Abbreviation Meaning

EEE electrical, electronic and electromechanical

EOL end-of-life

ESATAN thermal/fluid analyser from ITP Engines

FEM

finite element method

GMM

geometrical mathematical model

HP heat pipe

HTC heat transfer coefficient

I/O input / output

ICD interface control document

ICES International Conference on Environmental Systems

IR

infrared

KMO key model output(s)

LHP loop heat pipe

LP lumped parameter

MCRT Monte Carlo ray tracing

MLI multi-layer insulation

OS

open source

PCB

printed circuit board

PID proportional integral der

**...**

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