Space product assurance - Worst case analysis

This handbook provides guidelines to perform the worst case analysis. It applies to all electrical and electronic equipment. This worst case analysis (WCA) method can also be applied at subsystem level to justify electrical interface specifications and design margins for equipment. It applies to all project phases where electrical interface requirements are established and circuit design is carried out.
The worst case analysis is generally carried out when designing the circuit. For selected circuitry, worst case analysis (WCA) can be used to validate a conceptual design approach.

RaumfahrtProduktsicherung - Worst-Case-Analysis

Assurance produit des projets spatiaux - Analyse pire cas

Zagotavljanje kakovosti proizvodov v vesoljski tehniki - Analiza najslabšega primera

V tem priročniku so podane smernice za izvedbo analize najslabšega primera. Uporablja se za vso električno in elektronsko opremo. To metodo analize najslabšega primera (WCA) je mogoče uporabiti tudi na ravni podsistema za utemeljevanje specifikacij električnih vmesnikov in mejnih vrednosti pri načrtovanju opreme. Metoda se uporablja za vse faze projekta, v katerih se določijo zahteve za električni vmesnik in izvede načrtovanje vezja.
Analiza najslabšega primera se običajno izvede med načrtovanjem vezja. Za izbrano vezje je mogoče analizo najslabšega primera uporabiti za potrjevanje pristopa konceptualnega načrtovanja.

General Information

Status
Published
Public Enquiry End Date
20-Oct-2021
Publication Date
19-Dec-2021
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
08-Dec-2021
Due Date
12-Feb-2022
Completion Date
20-Dec-2021

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SLOVENSKI STANDARD
SIST-TP CEN/TR 17602-30-01:2022
01-februar-2022
Zagotavljanje kakovosti proizvodov v vesoljski tehniki - Analiza najslabšega
primera
Space product assurance - Worst case analysis
RaumfahrtProduktsicherung - Worst-Case-Analysis
Assurance produit des projets spatiaux - Analyse pire cas
Ta slovenski standard je istoveten z: CEN/TR 17602-30-01:2021
ICS:
03.120.99 Drugi standardi v zvezi s Other standards related to
kakovostjo quality
49.140 Vesoljski sistemi in operacije Space systems and
operations
SIST-TP CEN/TR 17602-30-01:2022 en,fr,de

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

---------------------- Page: 1 ----------------------
SIST-TP CEN/TR 17602-30-01:2022
---------------------- Page: 2 ----------------------
SIST-TP CEN/TR 17602-30-01:2022
TECHNICAL REPORT CEN/TR 17602-30-01
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
December 2021
ICS 49.140
English version
Space product assurance - Worst case analysis

Assurance produit des projets spatiaux - Analyse pire RaumfahrtProduktsicherung - Worst-Case-Analysis

cas

This Technical Report was approved by CEN on 22 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

© 2021 CEN/CENELEC All rights of exploitation in any form and by any means Ref. No. CEN/TR 17602-30-01:2021 E

reserved worldwide for CEN national Members and for
CENELEC Members.
---------------------- Page: 3 ----------------------
SIST-TP CEN/TR 17602-30-01:2022
CEN/TR 17602-30-01:2021 (E)
Table of contents

European Foreword .......................................................................................... 4

1 Scope .............................................................................................................. 5

2 References ..................................................................................................... 6

3 Terms, definitions and abbreviated terms ................................................... 7

3.1 Terms from other documents ...........................................................................7

3.2 Terms specific to the present document ..........................................................7

3.2.1 ambient temperature ..........................................................................7

3.2.2 biased variation value ........................................................................7

3.2.3 component parameters ......................................................................7

3.2.4 component specification .....................................................................7

3.2.5 design lifetime ....................................................................................7

3.2.6 effective ageing data ..........................................................................7

3.2.7 lifetime assumed in database .............................................................7

3.2.8 radiation .............................................................................................7

3.2.9 random variation value .......................................................................8

3.2.10 reference condition.............................................................................8

3.2.11 temperature assumed in database .....................................................8

3.2.12 variation factors ..................................................................................8

3.2.13 worst case .......................................................................................... 8

3.2.14 worst case analysis (WCA) ................................................................8

3.2.15 functional block ..................................................................................8

3.3 Abbreviated terms............................................................................................ 8

4 General methodology .................................................................................. 10

4.1 Introduction ....................................................................................................10

4.2 Flow diagram of WCA ....................................................................................10

4.3 Identification of the critical aspects w.r.t. worst case performance ................. 12

4.4 Evaluation of worst case performance ........................................................... 12

4.5 Comparison of WCA with requirements .........................................................13

5 Analysis parameters and technical issues ................................................ 14

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CEN/TR 17602-30-01:2021 (E)

5.1 Definition of worst case parameters within parts database ............................. 14

5.1.1 Variation factors ...............................................................................14

5.1.2 Summary on deviations ....................................................................18

5.2 Phase and timing considerations within the WCA .......................................... 19

5.2.1 Introduction ......................................................................................19

5.2.2 Timing of transient pulses ................................................................19

5.3 Numerical analysis techniques.......................................................................19

5.3.1 Approach .........................................................................................19

5.3.2 Extreme value analysis ....................................................................20

5.3.3 Extreme value analysis combined approach .................................... 20

5.3.4 Root-sum-squared analysis ..............................................................20

5.3.5 Monte Carlo analysis ........................................................................20

6 WCA and project phases ............................................................................ 22

Figures

Figure 4-1: Flow diagram of WCA ...............................................................................11

Tables

Table 5-1: Deviations and attributes summary .............................................................18

Table 5-2: Numerical techniques and value summary ................................................. 21

---------------------- Page: 5 ----------------------
SIST-TP CEN/TR 17602-30-01:2022
CEN/TR 17602-30-01:2021 (E)
European Foreword

This document (CEN/TR 17602-30-01:2021) 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 EN 16602-30.

This Technical report (CEN/TR 17602-30-01:2021) originates from ECSS-Q-HB-30-01A.

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).

---------------------- Page: 6 ----------------------
SIST-TP CEN/TR 17602-30-01:2022
CEN/TR 17602-30-01:2021 (E)
Scope

This handbook provides guidelines to perform the worst case analysis. It applies to all electrical and

electronic equipment. This worst case analysis (WCA) method can also be applied at subsystem level to

justify electrical interface specifications and design margins for equipment. It applies to all project

phases where electrical interface requirements are established and circuit design is carried out.

The worst case analysis is generally carried out when designing the circuit. For selected circuitry, worst

case analysis (WCA) can be used to validate a conceptual design approach.
---------------------- Page: 7 ----------------------
SIST-TP CEN/TR 17602-30-01:2022
CEN/TR 17602-30-01:2021 (E)
References
EN Reference Reference in text Title
EN 16601-00-01 ECSS-ST-00-01 ECSS system - Glossary of terms
EN 16603-10-02 ECSS-E-ST-10-02 Space engineering -Verification
EN 16602-30 ECSS-Q-ST-30 Space product assurance - Dependability
EN 16602-30-11 ECSS-Q-ST-30-11 Space product assurance - Derating - EEE
components
- ECSS-Q-TM-30-12 Space product assurance – End-of-life parameters
drifts - EEE components

EN 16602-30-02 ECSS-Q-ST-30-02 Space product assurance - Failure modes, effects and

criticality analysis
EN 16602-40-02 ECSS-Q-ST-40-02 Space product assurance - Hazard analysis
- ECSS-Q-TM-40-04 Space product assurance - Sneak analysis
EN 16602-40-12 ECSS-Q-ST-40-12 Space product assurance - Fault tree analysis –
Adoption notice ECSS / IEC61025
CRTAWCCA Worst Case Circuit Analysis Application Guidelines,
1993 Reliability Analysis Center, Rome NY, U.S.A
JPL D-5703 Jet Propulsion Laboratory Reliability Analyses
Handbook
---------------------- Page: 8 ----------------------
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CEN/TR 17602-30-01:2021 (E)
Terms, definitions and abbreviated terms
3.1 Terms from other documents

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

specific to the present document.
3.2 Terms specific to the present document
3.2.1 ambient temperature
temperature of a medium surrounding the component
3.2.2 biased variation value

value with a deterministic direction or sign whose amplitude and direction of variation are known

3.2.3 component parameters
electrical performance parameters of EEE parts
3.2.4 component specification
specification of the EEE part used for procurement of the EEE part
3.2.5 design lifetime
duration for which the circuit is designed to work within a particular mission
3.2.6 effective ageing data

ageing data extrapolated from the lifetime assumed in database to the design lifetime

3.2.7 lifetime assumed in database

lifetime for which the parameter variation due to ageing and environmental effects is valid

3.2.8 radiation

phenomenon by which energy, in form of waves or particles, emanates from a source into space

Example Trapped electrons, trapped protons and solar protons.
---------------------- Page: 9 ----------------------
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CEN/TR 17602-30-01:2021 (E)
3.2.9 random variation value
value with no preferred direction or sign whose amplitude alone is known
3.2.10 reference condition
relative condition where the parameter variation is assumed to be zero
3.2.11 temperature assumed in database
temperature for which the parameter variation is given in the database
3.2.12 variation factors
factors which affect component parameters over its lifetime
NOTE For details see subclause 5.1.1.
3.2.13 worst case

highest or lowest boundary value of a given control parameter established in a validation or

qualification exercise
NOTE Failures or single event effects are not covered by
the worst case.
3.2.14 worst case analysis (WCA)
performance prediction of the circuit in the worst case condition
3.2.15 functional block
within a circuit, set of components which perform a specific function
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
critical design review
CDR
electrical, electronic, electromechanical
EEE
electromagnetic compatibility
EMC
end-of-life
EOL
extreme value analysis
EVA
activation energy
---------------------- Page: 10 ----------------------
SIST-TP CEN/TR 17602-30-01:2022
CEN/TR 17602-30-01:2021 (E)
Boltzmann constant
Monte-Carlo analysis
MCA
printed circuit board
PCB
probability density function
PDF
preliminary design review
PDR
radio frequency
root-sum-square
RSS
single event effect
SEE
junction temperature
worst case analysis
WCA
---------------------- Page: 11 ----------------------
SIST-TP CEN/TR 17602-30-01:2022
CEN/TR 17602-30-01:2021 (E)
General methodology
4.1 Introduction

The worst case analysis (WCA) is performed on electronic and electrical equipment to demonstrate that

it performs within specification despite particular variations in its constituent part parameters and the

imposed environment, at the end of overall lifetime (EOL).

A good survey of worst case circuit analysis can be found in CRTAWCCA “Worst Case Circuit Analysis

Application Guidelines, 1993 Reliability Analysis Center, Rome NY, U.S.A.”.
4.2 Flow diagram of WCA

The worst case analysis is used to demonstrate sufficient operating margins for all operating conditions

in electronic circuits.
A flow diagram of WCA is shown in Figure 4-1.
---------------------- Page: 12 ----------------------
SIST-TP CEN/TR 17602-30-01:2022
CEN/TR 17602-30-01:2021 (E)
Worst case analysis
- review of requirements
- review of parts database
- review of available analysis techniques
FMECA Identification of the critical aspects with
Sneak analys respect to worst case performance
Input
Fault tree analysis
Hazard analysis (Identification of critical functions where a
Radiation analysis WCA is performed)
Circuit partitioning
Redesign or
Critical circuit parameter selection optimization of the
analysis
Circuit models and equations
Results
Nonconformance not
acceptable
Conclusions
Yes or
nonconformance acceptable
End report
Figure 4-1: Flow diagram of WCA
---------------------- Page: 13 ----------------------
SIST-TP CEN/TR 17602-30-01:2022
CEN/TR 17602-30-01:2021 (E)
4.3 Identification of the critical aspects w.r.t. worst case
performance

The critical aspects with respect to worst case performance and the critical circuit parameters should be

identified. These critical aspects can be identified from results of other analyses:

• FMECA,
• sneak analysis,
• fault tree analysis,,
• hazard analysis,
• radiation analysis.
The sources of parameter variation are in general:
• initial tolerances,
• ageing,
• temperature,
• electrical interfaces,
• radiation, and
• EMC.
However, in some cases the effects of the above sources can be negligible.

To justify which effects influence the result and which can be neglected, a sensitivity analysis or

appropriate other method can be carried out.
4.4 Evaluation of worst case performance
The following basic tasks should be performed:

• partitioning of large circuits into smaller circuits which are better manageable (functional blocks);

• selection of critical circuit attributes;
• mathematical simulations of circuit behaviour;
• application of a worst case numerical analysis technique.

To facilitate the performance of the WCA, the analyst can reduce complex circuits into smaller

functional blocks. When a circuit is reduced to these functional blocks, performance requirements for

the inputs and outputs of each functional block can be established. These requirements serve as the

evaluation criteria for the WCA results for the functional blocks. If such criteria exists in another

document (e.g. design verification requirements document), reference to the source document should

be made. Some of the requirements for the functional blocks derive from higher level specification

requirements. In that case, the method of deriving these requirements should be clearly shown.

Non-linear effects: Within the process of splitting up the unit circuit into functional blocks the contractor

should consider non-linear effects resulting either from components intrinsic non-linearity (according

to the components specification), or effects resulting from reciprocal interaction of the functional blocks

(e.g. power supply variations induced by load changes, and load effects of the power supply drifts).

Otherwise the WCA should justify the absence of such effects, or should quantify such effects as

negligible, in comparison to other error sources.
---------------------- Page: 14 ----------------------
SIST-TP CEN/TR 17602-30-01:2022
CEN/TR 17602-30-01:2021 (E)

A combination of testing and analysis may be employed to obtain results through actual measurements.

4.5 Comparison of WCA with requirements

The WCA should conform to all requirements, both on the functional block level and at the circuit level.

Variations from these requirements should be noted explicitly and any proposed solutions outlined as

part of the report. Proof of conformance to certain less significant requirements may be omitted

provided that adequate justification for the specific omission is given in the WCA report. As a summary

the analysis results should be compared with the requirement specification.
---------------------- Page: 15 ----------------------
SIST-TP CEN/TR 17602-30-01:2022
CEN/TR 17602-30-01:2021 (E)
Analysis parameters and technical issues
5.1 Definition of worst case parameters within parts
database
5.1.1 Variation factors
5.1.1.1 General

For each physical parameter of the component affecting the worst case parameter analysed, the value

of the variation linked to each environment or interface stimulus should be determined. Sources of

variation include:
• the reference value (e.g. typical and adjusted),
• the initial tolerance,

• sensitivity to electrical interfaces (e.g. power supply, shared mode on inputs and output loads),

and

• sensitivity to ageing and environmental conditions (e.g. temperature, radiation and EMC).

5.1.1.2 Selection of reference condition

The variations of a component parameter due to radiation, ageing, temperature and tolerance are

applied to the reference condition. The reference condition should be chosen such that data is available.

This is usually room temperature (22±3) °C at beginning-of-life.
5.1.1.3 Compensation

If the circuit compensates initial tolerance or environmental variations (such as temperature) the

analysis report should include a justification for the residual variation.
5.1.1.4 Radiation
5.1.1.4.1 Radiation total dose effect

Under the influence of total dose radiation parametric degradations or variations can be expected in

particular for active electronic components. The electrical parametric changes can either be of a

permanent or temporary nature, depending upon the component technology. Radiation affects

parameter variations of active components only (those that have a semiconductor junction).

These parametric changes are related to the influence of the accum
...

SLOVENSKI STANDARD
kSIST-TP FprCEN/TR 17602-30-01:2021
01-oktober-2021
Zagotavljanje kakovosti proizvodov v vesoljski tehniki - Analiza najslabšega
primera
Space product assurance - Worst case analysis
RaumfahrtProduktsicherung - Worst-Case-Analysis
Assurance produit des projets spatiaux - Analyse pire cas
Ta slovenski standard je istoveten z: FprCEN/TR 17602-30-01
ICS:
03.120.99 Drugi standardi v zvezi s Other standards related to
kakovostjo quality
49.140 Vesoljski sistemi in operacije Space systems and
operations
kSIST-TP FprCEN/TR 17602-30-01:2021 en,fr,de

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

---------------------- Page: 1 ----------------------
kSIST-TP FprCEN/TR 17602-30-01:2021
---------------------- Page: 2 ----------------------
kSIST-TP FprCEN/TR 17602-30-01:2021
TECHNICAL REPORT
FINAL DRAFT
FprCEN/TR 17602-30-01
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
July 2021
ICS 49.140
English version
Space product assurance - Worst case analysis

Assurance produit des projets spatiaux - Analyse pire RaumfahrtProduktsicherung - Worst-Case-Analysis

cas

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 17602-30-01:2021 E

reserved worldwide for CEN national Members and for
CENELEC Members.
---------------------- Page: 3 ----------------------
kSIST-TP FprCEN/TR 17602-30-01:2021
FprCEN/TR 17602-30-01:2021 (E)
Table of contents

European Foreword .......................................................................................... 4

1 Scope .............................................................................................................. 5

2 References ..................................................................................................... 6

3 Terms, definitions and abbreviated terms ................................................... 7

3.1 Terms from other documents ...........................................................................7

3.2 Terms specific to the present document ..........................................................7

3.2.1 ambient temperature ..........................................................................7

3.2.2 biased variation value ........................................................................7

3.2.3 component parameters ......................................................................7

3.2.4 component specification .....................................................................7

3.2.5 design lifetime ....................................................................................7

3.2.6 effective ageing data ..........................................................................7

3.2.7 lifetime assumed in database .............................................................7

3.2.8 radiation .............................................................................................7

3.2.9 random variation value .......................................................................8

3.2.10 reference condition.............................................................................8

3.2.11 temperature assumed in database .....................................................8

3.2.12 variation factors ..................................................................................8

3.2.13 worst case .......................................................................................... 8

3.2.14 worst case analysis (WCA) ................................................................8

3.2.15 functional block ..................................................................................8

3.3 Abbreviated terms............................................................................................ 8

4 General methodology .................................................................................. 10

4.1 Introduction ....................................................................................................10

4.2 Flow diagram of WCA ....................................................................................10

4.3 Identification of the critical aspects w.r.t. worst case performance ................. 12

4.4 Evaluation of worst case performance ........................................................... 12

4.5 Comparison of WCA with requirements .........................................................13

5 Analysis parameters and technical issues ................................................ 14

---------------------- Page: 4 ----------------------
kSIST-TP FprCEN/TR 17602-30-01:2021
FprCEN/TR 17602-30-01:2021 (E)

5.1 Definition of worst case parameters within parts database ............................. 14

5.1.1 Variation factors ...............................................................................14

5.1.2 Summary on deviations ....................................................................18

5.2 Phase and timing considerations within the WCA .......................................... 19

5.2.1 Introduction ......................................................................................19

5.2.2 Timing of transient pulses ................................................................19

5.3 Numerical analysis techniques.......................................................................19

5.3.1 Approach .........................................................................................19

5.3.2 Extreme value analysis ....................................................................20

5.3.3 Extreme value analysis combined approach .................................... 20

5.3.4 Root-sum-squared analysis ..............................................................20

5.3.5 Monte Carlo analysis ........................................................................20

6 WCA and project phases ............................................................................ 22

Figures

Figure 4-1: Flow diagram of WCA ...............................................................................11

Tables

Table 5-1: Deviations and attributes summary .............................................................18

Table 5-2: Numerical techniques and value summary ................................................. 21

---------------------- Page: 5 ----------------------
kSIST-TP FprCEN/TR 17602-30-01:2021
FprCEN/TR 17602-30-01:2021 (E)
European Foreword

This document (FprCEN/TR 17602-30-01:2021) 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 EN 16602-30.

This Technical report (FprCEN/TR 17602-30-01:2021) originates from ECSS-Q-HB-30-01A.

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.
---------------------- Page: 6 ----------------------
kSIST-TP FprCEN/TR 17602-30-01:2021
FprCEN/TR 17602-30-01:2021 (E)
Scope

This handbook provides guidelines to perform the worst case analysis. It applies to all electrical and

electronic equipment. This worst case analysis (WCA) method can also be applied at subsystem level to

justify electrical interface specifications and design margins for equipment. It applies to all project

phases where electrical interface requirements are established and circuit design is carried out.

The worst case analysis is generally carried out when designing the circuit. For selected circuitry, worst

case analysis (WCA) can be used to validate a conceptual design approach.
---------------------- Page: 7 ----------------------
kSIST-TP FprCEN/TR 17602-30-01:2021
FprCEN/TR 17602-30-01:2021 (E)
References
EN Reference Reference in text Title
EN 16601-00-01 ECSS-ST-00-01 ECSS system - Glossary of terms
EN 16603-10-02 ECSS-E-ST-10-02 Space engineering -Verification
EN 16602-30 ECSS-Q-ST-30 Space product assurance - Dependability
EN 16602-30-11 ECSS-Q-ST-30-11 Space product assurance - Derating - EEE
components
- ECSS-Q-TM-30-12 Space product assurance – End-of-life parameters
drifts - EEE components

EN 16602-30-02 ECSS-Q-ST-30-02 Space product assurance - Failure modes, effects and

criticality analysis
EN 16602-40-02 ECSS-Q-ST-40-02 Space product assurance - Hazard analysis
- ECSS-Q-TM-40-04 Space product assurance - Sneak analysis
EN 16602-40-12 ECSS-Q-ST-40-12 Space product assurance - Fault tree analysis –
Adoption notice ECSS / IEC61025
CRTAWCCA Worst Case Circuit Analysis Application Guidelines,
1993 Reliability Analysis Center, Rome NY, U.S.A
JPL D-5703 Jet Propulsion Laboratory Reliability Analyses
Handbook
---------------------- Page: 8 ----------------------
kSIST-TP FprCEN/TR 17602-30-01:2021
FprCEN/TR 17602-30-01:2021 (E)
Terms, definitions and abbreviated terms
3.1 Terms from other documents

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

specific to the present document.
3.2 Terms specific to the present document
3.2.1 ambient temperature
temperature of a medium surrounding the component
3.2.2 biased variation value

value with a deterministic direction or sign whose amplitude and direction of variation are known

3.2.3 component parameters
electrical performance parameters of EEE parts
3.2.4 component specification
specification of the EEE part used for procurement of the EEE part
3.2.5 design lifetime
duration for which the circuit is designed to work within a particular mission
3.2.6 effective ageing data

ageing data extrapolated from the lifetime assumed in database to the design lifetime

3.2.7 lifetime assumed in database

lifetime for which the parameter variation due to ageing and environmental effects is valid

3.2.8 radiation

phenomenon by which energy, in form of waves or particles, emanates from a source into space

Example Trapped electrons, trapped protons and solar protons.
---------------------- Page: 9 ----------------------
kSIST-TP FprCEN/TR 17602-30-01:2021
FprCEN/TR 17602-30-01:2021 (E)
3.2.9 random variation value
value with no preferred direction or sign whose amplitude alone is known
3.2.10 reference condition
relative condition where the parameter variation is assumed to be zero
3.2.11 temperature assumed in database
temperature for which the parameter variation is given in the database
3.2.12 variation factors
factors which affect component parameters over its lifetime
NOTE For details see subclause 5.1.1.
3.2.13 worst case

highest or lowest boundary value of a given control parameter established in a validation or

qualification exercise
NOTE Failures or single event effects are not covered by
the worst case.
3.2.14 worst case analysis (WCA)
performance prediction of the circuit in the worst case condition
3.2.15 functional block
within a circuit, set of components which perform a specific function
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
critical design review
CDR
electrical, electronic, electromechanical
EEE
electromagnetic compatibility
EMC
end-of-life
EOL
extreme value analysis
EVA
activation energy
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Boltzmann constant
Monte-Carlo analysis
MCA
printed circuit board
PCB
probability density function
PDF
preliminary design review
PDR
radio frequency
root-sum-square
RSS
single event effect
SEE
junction temperature
worst case analysis
WCA
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General methodology
4.1 Introduction

The worst case analysis (WCA) is performed on electronic and electrical equipment to demonstrate that

it performs within specification despite particular variations in its constituent part parameters and the

imposed environment, at the end of overall lifetime (EOL).

A good survey of worst case circuit analysis can be found in CRTAWCCA “Worst Case Circuit Analysis

Application Guidelines, 1993 Reliability Analysis Center, Rome NY, U.S.A.”.
4.2 Flow diagram of WCA

The worst case analysis is used to demonstrate sufficient operating margins for all operating conditions

in electronic circuits.
A flow diagram of WCA is shown in Figure 4-1.
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Worst case analysis
- review of requirements
- review of parts database
- review of available analysis techniques
FMECA Identification of the critical aspects with
Sneak analys respect to worst case performance
Input
Fault tree analysis
Hazard analysis (Identification of critical functions where a
Radiation analysis WCA is performed)
Circuit partitioning
Redesign or
Critical circuit parameter selection optimization of the
analysis
Circuit models and equations
Results
Nonconformance not
acceptable
Conclusions
Yes or
nonconformance acceptable
End report
Figure 4-1: Flow diagram of WCA
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4.3 Identification of the critical aspects w.r.t. worst case
performance

The critical aspects with respect to worst case performance and the critical circuit parameters should be

identified. These critical aspects can be identified from results of other analyses:

• FMECA,
• sneak analysis,
• fault tree analysis,,
• hazard analysis,
• radiation analysis.
The sources of parameter variation are in general:
• initial tolerances,
• ageing,
• temperature,
• electrical interfaces,
• radiation, and
• EMC.
However, in some cases the effects of the above sources can be negligible.

To justify which effects influence the result and which can be neglected, a sensitivity analysis or

appropriate other method can be carried out.
4.4 Evaluation of worst case performance
The following basic tasks should be performed:

• partitioning of large circuits into smaller circuits which are better manageable (functional blocks);

• selection of critical circuit attributes;
• mathematical simulations of circuit behaviour;
• application of a worst case numerical analysis technique.

To facilitate the performance of the WCA, the analyst can reduce complex circuits into smaller

functional blocks. When a circuit is reduced to these functional blocks, performance requirements for

the inputs and outputs of each functional block can be established. These requirements serve as the

evaluation criteria for the WCA results for the functional blocks. If such criteria exists in another

document (e.g. design verification requirements document), reference to the source document should

be made. Some of the requirements for the functional blocks derive from higher level specification

requirements. In that case, the method of deriving these requirements should be clearly shown.

Non-linear effects: Within the process of splitting up the unit circuit into functional blocks the contractor

should consider non-linear effects resulting either from components intrinsic non-linearity (according

to the components specification), or effects resulting from reciprocal interaction of the functional blocks

(e.g. power supply variations induced by load changes, and load effects of the power supply drifts).

Otherwise the WCA should justify the absence of such effects, or should quantify such effects as

negligible, in comparison to other error sources.
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A combination of testing and analysis may be employed to obtain results through actual measurements.

4.5 Comparison of WCA with requirements

The WCA should conform to all requirements, both on the functional block level and at the circuit level.

Variations from these requirements should be noted explicitly and any proposed solutions outlined as

part of the report. Proof of conformance to certain less significant requirements may be omitted

provided that adequate justification for the specific omission is given in the WCA report. As a summary

the analysis results should be compared with the requirement specification.
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Analysis parameters and technical issues
5.1 Definition of worst case parameters within parts
database
5.1.1 Variation factors
5.1.1.1 General

For each physical parameter of the component affecting the worst case parameter analysed, the value

of the variation linked to each environment or interface stimulus should be determined. Sources of

variation include:
• the reference value (e.g. typical and adjusted),
• the initial tolerance,

• sensitivity to electrical interfaces (e.g. power supply, shared mode on inputs and output loads),

and

• sensitivity to ageing and environmental conditions (e.g. temperature, radiation and EMC).

5.1.1.2 Selection of reference condition

The variations of a component parameter due to radiation, ageing, temperature and tolerance are

applied to the reference condition. The reference condition should be chosen such that data is available.

This is usually room temperature (22±3) °C at beginning-of-life.
5.1.1.3 Compensation

If the circuit compensates initial tolerance or environmental variations (such as temperature) the

analysis report should include a justification for the residual variation.
5.1.1.4 Radiation
5.1.1.4.1 Radiation total dose effect

Under the influence of total dose radiation parametric degradations or variations can be expected in

particular for active electronic components. The electrical parametric changes can either be of a

...

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