Space engineering - Control performance guidelines

This Handbook deals with control systems developed as part of a space project. It is applicable to all the elements of a space system, including the space segment, the ground segment and the launch service segment. It addresses the issue of control performance, in terms of definition, specification, verification and validation methods and processes. The handbook establishes a general framework for handling performance indicators, which applies to all disciplines involving control engineering, and which can be declined as well at different levels ranging from equipment to system level. It also focuses on the specific performance indicators applicable to the case of closed-loop control systems. Rules and guidelines are provided allowing to combine different error sources in order to build up a performance budget and to assess the compliance with a requirement. This version of the handbook does not cover control performance issues in the frame of launch systems.

Raumfahrttechnik - Richtlinien für Leistung von Regelung/Steuerung

Ingénierie spatiale - Lignes directrices des performances du contrôle

Vesoljska tehnika - Smernice za nadzor delovanja

Ta priročnik zajema nadzorne sisteme, razvite kot del vesoljskega projekta. Uporablja se za vse elemente vesoljskega sistema, vključno z vesoljskim delom, zemeljskim delom in lansirnimi storitvami. Obravnava nadzor delovanja v smislu opredelitve, določanja, preverjanja ter potrjevanja metod in postopkov. Priročnik vzpostavlja splošen okvir za obravnavanje kazalnikov uspešnosti, ki se uporablja za vse discipline, povezane s krmilnim inženiringom, in ki ga je mogoče zavrniti na različnih ravneh, od opreme do sistemov. Osredotoča se tudi na posebne kazalnike zmogljivosti, ki se uporabljajo v primeru krmilnih sistemov z zaprto zanko. Pravila in smernice so na voljo za kombiniranje različnih virov napak za namene priprave proračuna uspešnosti in ocenjevanja skladnosti z zahtevo. Ta različica priročnika ne zajema vprašanj nadzora delovanja v okviru sistemov za zagon.

General Information

Status
Published
Public Enquiry End Date
27-Oct-2021
Publication Date
01-Feb-2022
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
31-Jan-2022
Due Date
07-Apr-2022
Completion Date
02-Feb-2022

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SLOVENSKI STANDARD
SIST-TP CEN/TR 17603-60-10:2022
01-marec-2022
Vesoljska tehnika - Smernice za nadzor delovanja
Space engineering - Control performance guidelines
Raumfahrttechnik - Richtlinien für Leistung von Regelung/Steuerung
Ingénierie spatiale - Lignes directrices des performances du contrôle
Ta slovenski standard je istoveten z: CEN/TR 17603-60-10:2022
ICS:
49.140 Vesoljski sistemi in operacije Space systems and
operations
SIST-TP CEN/TR 17603-60-10:2022 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 17603-60-10:2022
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SIST-TP CEN/TR 17603-60-10:2022
TECHNICAL REPORT CEN/TR 17603-60-10
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
January 2022
ICS 49.140
English version
Space engineering - Control performance guidelines

Ingénierie spatiale - Lignes directrices des Raumfahrttechnik - Richtlinien für Leistung von

performances du contrôle Regelung/Steuerung

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 17603-60-10:2022 E
reserved worldwide for CEN national Members and for
CENELEC Members.
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CEN/TR 17603-60-10:2022 (E)
Table of contents

European Foreword ................................................................................................... 7

Introduction ................................................................................................................ 8

1 Scope ..................................................................................................................... 10

2 References ............................................................................................................ 11

3 Terms, definitions and abbreviated terms .......................................................... 12

3.1 Terms from other documents .................................................................................. 12

3.2 Terms specific to the present handbook ................................................................. 12

3.3 Abbreviated terms................................................................................................... 16

4 General outline for control performance process ............................................. 18

4.1 The general control structure .................................................................................. 18

4.1.1 Description of the general control structure – Extension to system

level .......................................................................................................... 18

4.1.2 General performance definitions ............................................................... 19

4.1.3 Example – Earth observation satellite ....................................................... 20

4.2 Review of generic performance specification elements ........................................... 21

4.2.1 General ..................................................................................................... 21

4.2.2 Preliminary remark on intrinsic and extrinsic performance properties ........ 21

4.2.3 Examples of high-level performance requirements .................................... 23

4.2.4 Formalising requirements through performance indicators ........................ 25

4.3 Overview on performance specification and verification process ............................ 27

4.3.1 Introduction ............................................................................................... 27

4.3.2 Requirements capture & dissemination ..................................................... 28

4.3.3 Performance verification............................................................................ 29

4.3.4 Control performance engineering tasks during development phases ........ 31

5 Extrinsic performance – error indices and analysis methods .......................... 38

5.1 Introduction ............................................................................................................. 38

5.2 Performance and measurement error indices ......................................................... 38

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5.2.1 Definition of error function ......................................................................... 38

5.2.2 Definition of error indices........................................................................... 39

5.2.3 Common performance error indices .......................................................... 39

5.2.4 Common knowledge error indices ............................................................. 41

5.3 Formulation of performance requirements using error indices................................. 42

5.3.1 Structure of a requirement ......................................................................... 42

5.3.2 Choice of error function ............................................................................. 42

5.3.3 Use of error indices ................................................................................... 43

5.3.4 Statistical interpretation of a requirement .................................................. 43

5.3.5 Formulation of Knowledge Requirements .................................................. 46

5.4 Assessing compliance with a performance requirement ......................................... 46

5.4.1 Overview ................................................................................................... 46

5.4.2 Experimental approach ............................................................................. 47

5.4.3 Numerical simulations ............................................................................... 47

5.4.4 Use of an error budget .............................................................................. 49

5.5 Performance error budgeting .................................................................................. 50

5.5.1 Overview ................................................................................................... 50

5.5.2 Identifying errors ....................................................................................... 50

5.5.3 Statistics of contributing terms .................................................................. 51

5.5.4 Combination of error terms ........................................................................ 52

5.5.5 Comparison with requirements .................................................................. 53

5.5.6 Practical use of a budget (Synthesis) ........................................................ 53

6 Intrinsic performance indicators for closed-loop controlled systems............. 56

6.1 Overview ................................................................................................................ 56

6.2 Closed-loop controlled systems .............................................................................. 57

6.2.1 General closed-loop structure ................................................................... 57

6.2.2 General definitions for closed-loop controlled systems .............................. 57

6.3 Stability of a closed-loop controlled system............................................................. 59

6.4 Stability margins ..................................................................................................... 60

6.4.2 Stability margins for SISO LTI systems ..................................................... 60

6.4.3 Stability margins for MIMO LTI system – S and T criteria .......................... 62

6.4.4 Why specifying stability margins? .............................................................. 64

6.5 Level of robustness of a closed-loop controlled system .......................................... 65

6.6 Time & Frequency domain behaviour of a closed-loop controlled system ............... 65

6.6.1 Overview ................................................................................................... 65

6.6.2 Time domain indicators (transient) ............................................................ 65

6.6.3 Frequency domain performance indicators ............................................... 67

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6.7 Formulation of performance requirements for closed-loop controlled systems ........ 70

6.7.1 General ..................................................................................................... 70

6.7.2 Structure of a requirement ......................................................................... 70

6.7.3 Specification for general systems (possibly MIMO, coupled or nested

loops) ........................................................................................................ 71

6.7.4 Example of stability margins requirement .................................................. 71

6.8 Assessing compliance with performance requirements ........................................... 72

6.8.1 Guidelines for stability and stability margins verification ............................ 72

6.8.2 Methods for (systematic) robustness assessment ..................................... 73

7 Hierarchy of control performance requirements ............................................... 74

7.1 Overview ................................................................................................................ 74

7.2 From top level requirements down to design rules .................................................. 74

7.2.1 General ..................................................................................................... 74

7.2.2 Top level requirements .............................................................................. 74

7.2.3 Intermediate level requirements ................................................................ 75

7.2.4 Lower level requirements – Design rules ................................................... 75

7.3 The risks of counterproductive requirements .......................................................... 76

7.3.1 An example of counterproductive requirement .......................................... 76

7.3.2 How to avoid counterproductive control performance requirements? ........ 76

Annex A LTI systems .............................................................................................. 77

A.1 Overview ................................................................................................................ 77

A.2 General properties of LTI systems .......................................................................... 77

A.2.1 Simplified structure of a closed-loop controlled system ............................. 77

A.2.2 Representation of LTI systems .................................................................. 78

A.3 On stability margins of SISO and MIMO LTI systems ............................................. 80

A.3.1 Interpretation of stability margins ............................................................... 80

A.3.2 Analysis of stability margins – some illustrations ....................................... 82

Annex B Appendices to clause 5: Guidelines and mathematical elements ....... 84

B.1 Error Indices with domains other than time ............................................................. 84

B.2 Considerations regarding time intervals .................................................................. 85

B.3 Relationship between error indices and physical quantities .................................... 85

B.4 Statistics for Monte Carlo Minimum Number of Runs .............................................. 87

B.5 Determining the error PDFs .................................................................................... 88

B.5.1 Overview ................................................................................................... 88

B.5.2 White noise ............................................................................................... 88

B.5.3 Biases ....................................................................................................... 89

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B.5.4 Uniform random errors .............................................................................. 90

B.5.5 Harmonic errors ........................................................................................ 90

B.5.6 Drift Errors ................................................................................................ 91

B.5.7 Transient Errors ........................................................................................ 92

B.5.8 Others (General Analysis Methods) .......................................................... 93

B.5.9 Distributions of Ensemble Parameters ...................................................... 94

B.6 Mathematics of an Error Budget ............................................................................. 95

B.6.1 Probability distributions and the statistical interpretation ........................... 95

B.6.2 Exact error combination methods .............................................................. 96

B.6.3 Alternative approximation formulae ........................................................... 97

Annex C Satellite AOCS case study ...................................................................... 98

C.1 Introduction ............................................................................................................. 98

C.2 Satellite AOCS architecture .................................................................................... 98

C.3 From Image quality to AOCS requirements............................................................. 98

C.4 Formulation of the requirements C.3a1 to C.3a4 using error indices ..................... 101

C.4.1 General ................................................................................................... 101

C.4.2 Choice of signal error function ................................................................. 102

C.4.3 Choice of error indices and maximum values .......................................... 102

C.4.4 Assigning a probability density function (PDF) ........................................ 102

C.4.5 Choice of statistical interpretation (temporal, ensemble, mixed…) .......... 103

C.4.6 Requirements formulation ....................................................................... 103

C.5 Formulation of requirements C.3b1 and C.3b2 ..................................................... 104

C.6 Control Performance verification principles ........................................................... 104

C.6.1 Choice of verification method .................................................................. 104

C.6.2 Compiling the error budget (requirements C.3a1 to C.3a4) ..................... 105

C.6.3 Assessing compliance to control loop requirements C.3b1 and C.3b2 .... 110

C.7 Performance budget examples ............................................................................. 111

C.7.1 Overview ................................................................................................. 111

C.7.2 Pointing Knowledge Budget .................................................................... 111

C.7.3 Pointing budget ....................................................................................... 114

C.7.4 Pointing stability Budget (Requirements C.3a3 and C.3a4) ..................... 116

Figures

Figure 4-1 General control structure, ECSS-E-HB-60A ....................................................... 18

Figure 4-2 General control structure extended up to system level ....................................... 19

Figure 4-3 Example of requirements capture and dissemination for a typical AOCS

case ................................................................................................................... 30

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Figure 4-4 Example of pointing performance verification, for a typical mission profile.......... 30

Figure 5-1 Illustration of the different ways of meeting a requirement. ................................. 44

Figure 5-2 Statistics for the different statistical interpretations. L-R: temporal

interpretation, ensemble interpretation, mixed interpretation .............................. 44

Figure 6-1 Simplified scheme for a closed-loop controlled system ....................................... 57

Figure 6-2 Example of gain and phase margins identification .............................................. 62

Figure 6-3 Illustration of the transient response indicators ................................................... 66

Figure 6-4 Bandwidth, cut-off frequency and rejection of resonances .................................. 69

Tables

Table 3-1: Relationships of the definitions of the different kinds of performance,

performance knowledge and their corresponding errors ..................................... 16

Table 4-1 Example of a control structure breakdown for an Earth observation satellite ...... 21

Table 4-2 Example of AOCS extrinsic and intrinsic specifiable performances .................... 22

Table 4-3 General template for building extrinsic performance indicators ........................... 26

Table 4-4 Summary of control performance engineering tasks ........................................... 28

Table 4-5 Summary of the control performance management activities during the

phases of mission development (guidelines only) ............................................... 31

Table 4-6 Control performance engineering inputs, tasks and outputs, Phase 0/A ............. 32

Table 4-7 Control performance engineering inputs, tasks and outputs, Phase B ................ 34

Table 4-8 Control performance engineering inputs, tasks and outputs, Phase C/D ............ 36

Table 4-9 Control performance engineering inputs, tasks and outputs, Phase E/F ............. 37

Table 5-1 Minimum number of simulation runs required to verify a requirement at

confidence level Pc to a verification confidence of 95 % .................................... 49

Table 5-2 Example of a table used for a performance budget (APE for Euler angles) ........ 55

Table 6-1 Formulas for the usual SISO stability margins .................................................... 61

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European Foreword
This document (CEN/TR 17603-60-10:2022) 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 EN 16603-

60.

This Technical report (CEN/TR 17603-60-10:2022) originates from ECSS-E-HB-60-10A.

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).

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Introduction

This document focuses on the specific issues raised by managing all performance aspects of control

systems in the frame of space projects. It provides a set of practical definitions, engineering rules,

recommendations and guidelines to be used when specifying or verifying the performance of a

general control system; attention was paid by the authors to keep the application field as open as

possible, and not to restrict to a specific domain – such as spacecraft attitude control for example.

It is not intended to substitute to textbook material on automatic control theory. The readers and the

users are assumed to possess general knowledge of control system engineering and its applications to

space missions. Nevertheless when required – to avoid any risks of ambiguity for example, or for the

clearness of the presentation – some basic definitions and rules are provided in dedicated annexes.

This document was originally intended to focus on the specific case of pointing systems and AOCS,

starting from an existing ESA handbook [Pointing Error Handbook, ESA-NCR-502], to be updated,

completed, and extended to be built up as an applicable ECSS document. But after reviewing the

scope, this approach appeared somewhat restrictive:

• restricting performance concepts to “pointing” does not allow to deal with problems such as

thermal control, position control (robotics), or more generally any other type of control systems,

even though these problems share the same theoretical framework;

• AOCS is one major contributor to the overall system pointing performance, yet not the only

one: misalignments, thermoelastic effects, payload behaviour, etc. all contribute to the final

performance. This remark can be extended to general systems, considering that the controlled

part is but one of the contributors.

Accounting for these remarks led to extending the initial scope of this document. The upgraded

objective is to set up a generalised framework introducing performance definitions, performance

indices and budget calculations. “Generalised” is understood here in two directions:

• transversally, so as to be applicable independently on the physical nature of the control system

(not only pointing),

• and vertically, in the sense that in many practical situations the proposed definitions and

techniques can also apply to any part of the system (basically to the controlled part, but not

restrictively). This should assure consistency between the performances indices (error budgets)

of the complete system and of the controlled system part. Motivation is also that dedicated but

generic methods for budget breakdown can be applied on different levels i.e. on system level

and on controlled system level.
NOTE 1 The idea of defining a general framework applying from
equipment level to system level is driven by a concern for technical
and conceptual consistency. In a later phase, relevant system
aspects can be transferred or copied to the appropriate System
Engineering standard – if found more convenient.
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NOTE 2 The general control structure from the Control Engineering
handbook [ECSS-E-HB-60A, Figure 4-1] has been extended in
support, showing also the system performance in the output
(Figure 4-2 of this handbook)
NOTE 3 The objective of this document is not to cover the high level system
or mission performance aspects, which clearly belong to a different
category.

In addition to this will for general and generic concepts, a clause of this document covers the

performance issues which are more specific for the controlled systems themselves (mainly involving

feedback loops in practice) or which are based on well-known control methods. The need for this

clause arises as such systems call for particular technical know-how and feature specific performance

indicators that require additional insight. For example: stability and robustness properties, transient

responses (settling time, response time etc.) and frequency domain indicators.

Although this document is designed to be as general as possible, clearly in practice pointing and

AOCS issues are the most demanding space engineering disciplines in terms of control systems. They

are covered by an informative annex of the document which declines the general concepts and

illustrates how pointing issues can be managed as a special case of vector-type data on a high

resolution Earth observation mission.

Driven by a similar concern for illustration on space engineering applications of practical interest,

another annex of the document shows how to decline the general concepts to deal with the control

performance issue arisen by robotics applications.
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Scope

This Handbook deals with control systems developed as part of a space project. It is applicable to all

the elements of a space system, including the space segment, the ground segment and the launch

service segment.

It addresses the issue of control performance, in terms of definition, specification, verification and

validation methods and processes.

The handbook establishes a general framework for handling performance indicators, which applies to

all disciplines involving control engineering, and which can be declined as well at different levels

ranging from equipment to system level. It also focuses on the specific performance indicators

applicable to the case of closed-loop control systems.

Rules and guidelines are provided allowing to combine different error sources in order to build up a

performance budget and to assess the compliance with a requirement.

This version of the handbook does not cover control performance issues in the frame of launch

systems.
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References
EN Reference Reference in text Title
EN 16601-00-01 ECSS-S-ST-00-01 ECSS System - Glossary of terms
EN 16603-10 ECSS-E-ST-10 Space engineering – System engineering general
requirements
EN 16603-60-10 ECSS-E-ST-60-10 Space engineering – Control performance
EN 16603-60-20 ECSS-E-ST-60-20 Space engineering – Stars sensors terminology and
performance specifications
TR 16703-60 ECSS-E-HB-60 Space engineering – Control engineering handbook
EN 16601-40 ECSS-M-ST-40 Space project management – Configuration and
information management
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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.

3.2 Terms specific to the present handbook
3.2.1 control performance (state)
quantified output of a controlled system
NOTE 1 Depending on the context, the control performance is realised
either as signal performance or as control loop performance.
NOTE 2 Can also be applied to a control system.
3.2.2 control (performance) knowledge (state)
estimated control performance after measurement and processing, if any
NOTE The control performance knowledge is not necessarily the best
available knowledge of the control performance. The achieved
accuracy and the allowed deviation (control performance
knowledge error) depends on the application.
3.2.3 control reference (state)

ideal reference input, desired state or reference state of controlled part of the plant

3.2.4 domain variable

independent variable which can be used to put some dependent quantity into a certain order

NOTE This comprises continuous time, discrete time, N-dimensional
space, etc.
3.2.5 ergodicity

property of a stochastic process such that its ensemble and time statistical properties are identical.

Ergodicity allows to transfer the statistical results of a single realisation of a stochastic process to the

whole ensemble
NOTE (Weak) stationarity is prerequisite for (weak) ergodicity.
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3.2.6 error index

parameter isolating a particular aspect of the time variation of a performance error or knowledge error

3.2.7 extrinsic performance

element of performance related to the response of the system to its interaction with the outer world

(control reference signal, error sources and other disturbances)
NOTE 1 for example the pointing error of a satellite is relevant to this
category of extrinsic performance (it depends on the disturbing
torques and on the measurement noises)
NOTE 2 can also be defined in opposition to intrinsic performance
3.2.8 intrinsic performance

element of performance related to the intrinsic properties of the system, independently on its

interaction with the outer world (control reference, the nature and the amplitude of the error sources

and other disturbances)
NOTE 1 for example the stabili
...

SLOVENSKI STANDARD
kSIST-TP FprCEN/TR 17603-60-10:2021
01-oktober-2021
Vesoljska tehnika - Smernice za nadzor delovanja
Space engineering - Control performance guidelines
Raumfahrttechnik - Richtlinien für Leistung von Regelung/Steuerung
Ingénierie spatiale - Lignes directrices des performances du contrôle
Ta slovenski standard je istoveten z: FprCEN/TR 17603-60-10
ICS:
49.140 Vesoljski sistemi in operacije Space systems and
operations
kSIST-TP FprCEN/TR 17603-60-10:2021 en,fr,de

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

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kSIST-TP FprCEN/TR 17603-60-10:2021
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kSIST-TP FprCEN/TR 17603-60-10:2021
TECHNICAL REPORT
FINAL DRAFT
FprCEN/TR 17603-60-10
RAPPORT TECHNIQUE
TECHNISCHER BERICHT
August 2021
ICS 49.140
English version
Space engineering - Control performance guidelines

Ingénierie spatiale - Lignes directrices des Raumfahrttechnik - Richtlinien für Leistung von

performances du contrôle Regelung/Steuerung

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 17603-60-10:2021 E

reserved worldwide for CEN national Members and for
CENELEC Members.
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FprCEN/TR 17603-60-10:2021 (E)
Table of contents

European Foreword ................................................................................................... 7

Introduction ................................................................................................................ 8

1 Scope ..................................................................................................................... 10

2 References ............................................................................................................ 11

3 Terms, definitions and abbreviated terms .......................................................... 12

3.1 Terms from other documents .................................................................................. 12

3.2 Terms specific to the present handbook ................................................................. 12

3.3 Abbreviated terms................................................................................................... 16

4 General outline for control performance process ............................................. 18

4.1 The general control structure .................................................................................. 18

4.1.1 Description of the general control structure – Extension to system

level .......................................................................................................... 18

4.1.2 General performance definitions ............................................................... 19

4.1.3 Example – Earth observation satellite ....................................................... 20

4.2 Review of generic performance specification elements ........................................... 21

4.2.1 General ..................................................................................................... 21

4.2.2 Preliminary remark on intrinsic and extrinsic performance properties ........ 22

4.2.3 Examples of high-level performance requirements .................................... 23

4.2.4 Formalising requirements through performance indicators ........................ 25

4.3 Overview on performance specification and verification process ............................ 27

4.3.1 Introduction ............................................................................................... 27

4.3.2 Requirements capture & dissemination ..................................................... 28

4.3.3 Performance verification............................................................................ 29

4.3.4 Control performance engineering tasks during development phases ........ 31

5 Extrinsic performance – error indices and analysis methods .......................... 38

5.1 Introduction ............................................................................................................. 38

5.2 Performance and measurement error indices ......................................................... 38

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5.2.1 Definition of error function ......................................................................... 38

5.2.2 Definition of error indices........................................................................... 39

5.2.3 Common performance error indices .......................................................... 39

5.2.4 Common knowledge error indices ............................................................. 41

5.3 Formulation of performance requirements using error indices................................. 42

5.3.1 Structure of a requirement ......................................................................... 42

5.3.2 Choice of error function ............................................................................. 42

5.3.3 Use of error indices ................................................................................... 43

5.3.4 Statistical interpretation of a requirement .................................................. 43

5.3.5 Formulation of Knowledge Requirements .................................................. 46

5.4 Assessing compliance with a performance requirement ......................................... 46

5.4.1 Overview ................................................................................................... 46

5.4.2 Experimental approach ............................................................................. 47

5.4.3 Numerical simulations ............................................................................... 47

5.4.4 Use of an error budget .............................................................................. 49

5.5 Performance error budgeting .................................................................................. 50

5.5.1 Overview ................................................................................................... 50

5.5.2 Identifying errors ....................................................................................... 50

5.5.3 Statistics of contributing terms .................................................................. 51

5.5.4 Combination of error terms ........................................................................ 52

5.5.5 Comparison with requirements .................................................................. 53

5.5.6 Practical use of a budget (Synthesis) ........................................................ 53

6 Intrinsic performance indicators for closed-loop controlled systems............. 56

6.1 Overview ................................................................................................................ 56

6.2 Closed-loop controlled systems .............................................................................. 57

6.2.1 General closed-loop structure ................................................................... 57

6.2.2 General definitions for closed-loop controlled systems .............................. 57

6.3 Stability of a closed-loop controlled system............................................................. 59

6.4 Stability margins ..................................................................................................... 60

6.4.2 Stability margins for SISO LTI systems ..................................................... 60

6.4.3 Stability margins for MIMO LTI system – S and T criteria .......................... 63

6.4.4 Why specifying stability margins? .............................................................. 64

6.5 Level of robustness of a closed-loop controlled system .......................................... 65

6.6 Time & Frequency domain behaviour of a closed-loop controlled system ............... 65

6.6.1 Overview ................................................................................................... 65

6.6.2 Time domain indicators (transient) ............................................................ 66

6.6.3 Frequency domain performance indicators ............................................... 67

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6.7 Formulation of performance requirements for closed-loop controlled systems ........ 70

6.7.1 General ..................................................................................................... 70

6.7.2 Structure of a requirement ......................................................................... 70

6.7.3 Specification for general systems (possibly MIMO, coupled or nested

loops) ........................................................................................................ 71

6.7.4 Example of stability margins requirement .................................................. 71

6.8 Assessing compliance with performance requirements ........................................... 72

6.8.1 Guidelines for stability and stability margins verification ............................ 72

6.8.2 Methods for (systematic) robustness assessment ..................................... 73

7 Hierarchy of control performance requirements ............................................... 74

7.1 Overview ................................................................................................................ 74

7.2 From top level requirements down to design rules .................................................. 74

7.2.1 General ..................................................................................................... 74

7.2.2 Top level requirements .............................................................................. 74

7.2.3 Intermediate level requirements ................................................................ 75

7.2.4 Lower level requirements – Design rules ................................................... 75

7.3 The risks of counterproductive requirements .......................................................... 76

7.3.1 An example of counterproductive requirement .......................................... 76

7.3.2 How to avoid counterproductive control performance requirements? ........ 76

Annex A LTI systems .............................................................................................. 77

A.1 Overview ................................................................................................................ 77

A.2 General properties of LTI systems .......................................................................... 77

A.2.1 Simplified structure of a closed-loop controlled system ............................. 77

A.2.2 Representation of LTI systems .................................................................. 78

A.3 On stability margins of SISO and MIMO LTI systems ............................................. 80

A.3.1 Interpretation of stability margins ............................................................... 80

A.3.2 Analysis of stability margins – some illustrations ....................................... 82

Annex B Appendices to clause 5: Guidelines and mathematical elements ....... 84

B.1 Error Indices with domains other than time ............................................................. 84

B.2 Considerations regarding time intervals .................................................................. 85

B.3 Relationship between error indices and physical quantities .................................... 85

B.4 Statistics for Monte Carlo Minimum Number of Runs .............................................. 87

B.5 Determining the error PDFs .................................................................................... 88

B.5.1 Overview ................................................................................................... 88

B.5.2 White noise ............................................................................................... 88

B.5.3 Biases ....................................................................................................... 89

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B.5.4 Uniform random errors .............................................................................. 90

B.5.5 Harmonic errors ........................................................................................ 90

B.5.6 Drift Errors ................................................................................................ 91

B.5.7 Transient Errors ........................................................................................ 92

B.5.8 Others (General Analysis Methods) .......................................................... 93

B.5.9 Distributions of Ensemble Parameters ...................................................... 94

B.6 Mathematics of an Error Budget ............................................................................. 95

B.6.1 Probability distributions and the statistical interpretation ........................... 95

B.6.2 Exact error combination methods .............................................................. 96

B.6.3 Alternative approximation formulae ........................................................... 97

Annex C Satellite AOCS case study ...................................................................... 98

C.1 Introduction ............................................................................................................. 98

C.2 Satellite AOCS architecture .................................................................................... 98

C.3 From Image quality to AOCS requirements............................................................. 98

C.4 Formulation of the requirements C.3a1 to C.3a4 using error indices ..................... 101

C.4.1 General ................................................................................................... 101

C.4.2 Choice of signal error function ................................................................. 102

C.4.3 Choice of error indices and maximum values .......................................... 102

C.4.4 Assigning a probability density function (PDF) ........................................ 102

C.4.5 Choice of statistical interpretation (temporal, ensemble, mixed…) .......... 103

C.4.6 Requirements formulation ....................................................................... 103

C.5 Formulation of requirements C.3b1 and C.3b2 ..................................................... 104

C.6 Control Performance verification principles ........................................................... 104

C.6.1 Choice of verification method .................................................................. 104

C.6.2 Compiling the error budget (requirements C.3a1 to C.3a4) ..................... 105

C.6.3 Assessing compliance to control loop requirements C.3b1 and C.3b2 .... 110

C.7 Performance budget examples ............................................................................. 111

C.7.1 Overview ................................................................................................. 111

C.7.2 Pointing Knowledge Budget .................................................................... 111

C.7.3 Pointing budget ....................................................................................... 114

C.7.4 Pointing stability Budget (Requirements C.3a3 and C.3a4) ..................... 116

Figures

Figure 4-1 General control structure, ECSS-E-HB-60A ....................................................... 18

Figure 4-2 General control structure extended up to system level ....................................... 19

Figure 4-3 Example of requirements capture and dissemination for a typical AOCS

case ................................................................................................................... 30

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Figure 4-4 Example of pointing performance verification, for a typical mission profile.......... 30

Figure 5-1 Illustration of the different ways of meeting a requirement. ................................. 44

Figure 5-2 Statistics for the different statistical interpretations. L-R: temporal

interpretation, ensemble interpretation, mixed interpretation .............................. 44

Figure 6-1 Simplified scheme for a closed-loop controlled system ....................................... 57

Figure 6-2 Example of gain and phase margins identification .............................................. 62

Figure 6-3 Illustration of the transient response indicators ................................................... 67

Figure 6-4 Bandwidth, cut-off frequency and rejection of resonances .................................. 69

Tables

Table 3-1: Relationships of the definitions of the different kinds of performance,

performance knowledge and their corresponding errors ..................................... 16

Table 4-1 Example of a control structure breakdown for an Earth observation satellite ...... 21

Table 4-2 Example of AOCS extrinsic and intrinsic specifiable performances .................... 22

Table 4-3 General template for building extrinsic performance indicators ........................... 26

Table 4-4 Summary of control performance engineering tasks ........................................... 28

Table 4-5 Summary of the control performance management activities during the

phases of mission development (guidelines only) ............................................... 31

Table 4-6 Control performance engineering inputs, tasks and outputs, Phase 0/A ............. 32

Table 4-7 Control performance engineering inputs, tasks and outputs, Phase B ................ 34

Table 4-8 Control performance engineering inputs, tasks and outputs, Phase C/D ............ 36

Table 4-9 Control performance engineering inputs, tasks and outputs, Phase E/F ............. 37

Table 5-1 Minimum number of simulation runs required to verify a requirement at

confidence level Pc to a verification confidence of 95 % .................................... 49

Table 5-2 Example of a table used for a performance budget (APE for Euler angles) ........ 55

Table 6-1 Formulas for the usual SISO stability margins .................................................... 62

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European Foreword

This document (FprCEN/TR 17603-60-10:2021) 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 16603-

60.

This Technical report (FprCEN/TR 17603-60-10:2021) originates from ECSS-E-HB-60-10A.

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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Introduction

This document focuses on the specific issues raised by managing all performance aspects of control

systems in the frame of space projects. It provides a set of practical definitions, engineering rules,

recommendations and guidelines to be used when specifying or verifying the performance of a

general control system; attention was paid by the authors to keep the application field as open as

possible, and not to restrict to a specific domain – such as spacecraft attitude control for example.

It is not intended to substitute to textbook material on automatic control theory. The readers and the

users are assumed to possess general knowledge of control system engineering and its applications to

space missions. Nevertheless when required – to avoid any risks of ambiguity for example, or for the

clearness of the presentation – some basic definitions and rules are provided in dedicated annexes.

This document was originally intended to focus on the specific case of pointing systems and AOCS,

starting from an existing ESA handbook [Pointing Error Handbook, ESA-NCR-502], to be updated,

completed, and extended to be built up as an applicable ECSS document. But after reviewing the

scope, this approach appeared somewhat restrictive:

 restricting performance concepts to “pointing” does not allow to deal with problems such as

thermal control, position control (robotics), or more generally any other type of control systems,

even though these problems share the same theoretical framework;

 AOCS is one major contributor to the overall system pointing performance, yet not the only

one: misalignments, thermoelastic effects, payload behaviour, etc. all contribute to the final

performance. This remark can be extended to general systems, considering that the controlled

part is but one of the contributors.

Accounting for these remarks led to extending the initial scope of this document. The upgraded

objective is to set up a generalised framework introducing performance definitions, performance

indices and budget calculations. “Generalised” is understood here in two directions:

 transversally, so as to be applicable independently on the physical nature of the control system

(not only pointing),

 and vertically, in the sense that in many practical situations the proposed definitions and

techniques can also apply to any part of the system (basically to the controlled part, but not

restrictively). This should assure consistency between the performances indices (error budgets)

of the complete system and of the controlled system part. Motivation is also that dedicated but

generic methods for budget breakdown can be applied on different levels i.e. on system level

and on controlled system level.
NOTE 1 The idea of defining a general framework applying from
equipment level to system level is driven by a concern for technical
and conceptual consistency. In a later phase, relevant system
aspects can be transferred or copied to the appropriate System
Engineering standard – if found more convenient.
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NOTE 2 The general control structure from the Control Engineering
handbook [ECSS-E-HB-60A, Figure 4-1] has been extended in
support, showing also the system performance in the output
(Figure 4-2 of this handbook)
NOTE 3 The objective of this document is not to cover the high level system
or mission performance aspects, which clearly belong to a different
category.

In addition to this will for general and generic concepts, a clause of this document covers the

performance issues which are more specific for the controlled systems themselves (mainly involving

feedback loops in practice) or which are based on well-known control methods. The need for this

clause arises as such systems call for particular technical know-how and feature specific performance

indicators that require additional insight. For example: stability and robustness properties, transient

responses (settling time, response time etc.) and frequency domain indicators.

Although this document is designed to be as general as possible, clearly in practice pointing and

AOCS issues are the most demanding space engineering disciplines in terms of control systems. They

are covered by an informative annex of the document which declines the general concepts and

illustrates how pointing issues can be managed as a special case of vector-type data on a high

resolution Earth observation mission.

Driven by a similar concern for illustration on space engineering applications of practical interest,

another annex of the document shows how to decline the general concepts to deal with the control

performance issue arisen by robotics applications.
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Scope

This Handbook deals with control systems developed as part of a space project. It is applicable to all

the elements of a space system, including the space segment, the ground segment and the launch

service segment.

It addresses the issue of control performance, in terms of definition, specification, verification and

validation methods and processes.

The handbook establishes a general framework for handling performance indicators, which applies to

all disciplines involving control engineering, and which can be declined as well at different levels

ranging from equipment to system level. It also focuses on the specific performance indicators

applicable to the case of closed-loop control systems.

Rules and guidelines are provided allowing to combine different error sources in order to build up a

performance budget and to assess the compliance with a requirement.

This version of the handbook does not cover control performance issues in the frame of launch

systems.
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References
EN Reference Reference in text Title
EN 16601-00-01 ECSS-S-ST-00-01 ECSS System - Glossary of terms
EN 16603-10 ECSS-E-ST-10 Space engineering – System engineering general
requirements
EN 16603-60-10 ECSS-E-ST-60-10 Space engineering – Control performance
EN 16603-60-20 ECSS-E-ST-60-20 Space engineering – Stars sensors terminology and
performance specifications
TR 16703-60 ECSS-E-HB-60 Space engineering – Control engineering handbook
EN 16601-40 ECSS-M-ST-40 Space project management – Configuration and
information management
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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.

3.2 Terms specific to the present handbook
3.2.1 control performance (state)
quantified output of a controlled system
NOTE 1 Depending on the context, the control performance is realised
either as signal performance or as control loop performance.
NOTE 2 Can also be applied to a control system.
3.2.2 control (performance) knowledge (state)
estimated control performance after measurement and processing, if any
NOTE The control performance knowledge is not necessarily the best
available knowledge of the control performance. The achieved
accuracy and the allowed deviation (control performance
knowledge error) depends on the application.
3.2.3 control reference (state)

ideal reference input, desired state or reference state of controlled part of the plant

3.2.4 domain variable

independent variable which can be used to put some dependent quantity into a certain order

NOTE This comprises continuous time, discrete time, N-dimensional
space, etc.
3.2.5 ergodicity

property of a stochastic process such that its ensemble and time statistical properties are identical.

Ergodicity allows to transfer the statistical results of a single realisation of a stochastic process to the

whole ensemble
NOTE (Weak) stationarity is prerequisite for (weak) ergodicity.
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3.2.6 error index

parameter isolating a particular aspect of the time variation of a performance error or knowledge error

3.2.7 extrinsic performance

element of performance related to the response of the system to its interaction with the outer world

(control reference signa
...

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