SIST EN 16603-60-10:2014
(Main)Space engineering - Control performances
Space engineering - Control performances
EN 16603-60-10 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 standard defines a general framework for handling performance indicators, which applies to all disciplines involving control engineering, and which can be applied 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 - mainly stability and robustness. Rules are provided for combining different error sources in order to build up a performance error budget and use this to assess the compliance with a requirement. This standard may be tailored for the specific characteristic and constrains of a space project in conformance with ECSS-S-ST-00.
Raumfahrttechnik - Steuerungsleistung
Ingénierie spatiale - Performance de systèmes de contôle
Vesoljska tehnika - Zmogljivost krmiljenja
Standard EN 16603-60-10 zajema nadzorne sisteme, razvite kot del vesoljskega projekta. Uporablja se za vse elemente vesoljskega sistema, vključno z vesoljskim segmentom, zemeljskim segmentom in lansirnimi storitvami. Obravnava zmogljivost krmiljenja v smislu opredelitve, določanja, preverjanja in potrjevanja metod in postopkov. Standard določa splošen okvir za obravnavanje kazalnikov uspešnosti, ki se uporablja za vse discipline, povezane s krmilnim inženiringom, in ki ga je mogoče uporabiti na različnih ravneh, od opreme do sistemske ravni. Osredotoča se tudi na posebne kazalnike zmogljivosti, ki se uporabljajo v primeru krmilnih sistemov z zaprto zanko, predvsem pri stabilnosti in robustnosti. Pravila so na voljo za kombiniranje različnih virov napak, da bi se zgradil seznam zmogljivostnih napak in se nato uporabil za oceno skladnosti z zahtevo. Ta standard se lahko prilagodi posameznim lastnostim in omejitvam vesoljskega projekta v skladu s standardom ECSS-S-ST-00.
General Information
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Vesoljska tehnika - Zmogljivost krmiljenjaRaumfahrttechnik - SteuerungsleistungIngénierie spatiale - Performance de systèmes de contôleSpace engineering - Control performances49.140Vesoljski sistemi in operacijeSpace systems and operationsICS:Ta slovenski standard je istoveten z:EN 16603-60-10:2014SIST EN 16603-60-10:2014en,fr,de01-november-2014SIST EN 16603-60-10:2014SLOVENSKI
STANDARD
SIST EN 16603-60-10:2014
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 16603-60-10
September 2014 ICS 49.140
English version
Space engineering - Control performances
Ingénierie spatiale - Performance de systèmes de contrôle Raumfahrttechnik - Steuerungsleistung This European Standard was approved by CEN on 1 March 2014.
CEN and CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN and CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN and CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions.
CEN and CENELEC members are the national standards bodies and national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom.
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels © 2014 CEN/CENELEC All rights of exploitation in any form and by any means reserved worldwide for CEN national Members and for CENELEC Members. Ref. No. EN 16603-60-10:2014 E SIST EN 16603-60-10:2014
EN 16603-60-10:2014 (E) 2 Table of contents Foreword . 5 Introduction . 6 1 Scope . 7 2 Normative references . 8 3 Terms, definitions and abbreviated terms . 9 3.1 Terms from other standards . 9 3.2 Terms specific to the present standard . 9 3.3 Abbreviated terms. 14 4 Performance requirements and budgeting . 15 4.1 Specifying a performance requirement . 15 4.1.1 Overview . 15 4.1.2 Elements of a performance requirement . 16 4.1.3 Elements of a knowledge requirement . 16 4.1.4 Probabilities and statistical interpretations . 17 4.2 Use of error budgeting to assess compliance . 17 4.2.1 Scope and limitations . 17 4.2.2 Identification and characterisation of contributors . 18 4.2.3 Combination of contributors . 19 4.2.4 Comparison with requirement . 21 5 Stability and robustness specification and verification for linear systems . 23 5.1 Overview . 23 5.2 Stability and robustness specification . 24 5.2.1 Uncertainty domains . 24 5.2.2 Stability requirement . 26 5.2.3 Identification of checkpoints . 26 5.2.4 Selection and justification of stability margin indicators . 27 5.2.5 Stability margins requirements . 27 5.2.6 Verification of stability margins with a single uncertainty domain . 28 SIST EN 16603-60-10:2014
EN 16603-60-10:2014 (E) 3 5.2.7 Verification of stability margins with reduced and extended uncertainty domains . 28 Annex A (informative)
Use of performance error indices . 29 A.1 Formulating error requirements. 29 A.1.1 More about error indices . 29 A.1.2 Statistical interpretation of requirements . 30 A.1.3 Knowledge requirements. 32 A.1.4 Specifying the timescales for requirements . 32 A.2 More about performance error budgets . 34 A.2.1 When to use an error budget . 34 A.2.2 Identifying and quantifying the contributing errors . 35 A.2.3 Combining the errors . 36 A.2.4 Comparison with requirements . 38 Annex B (informative) Inputs to an error budget . 40 B.1 Overview . 40 B.2 Bias errors . 41 B.3 Random errors . 42 B.4 Periodic errors (short period) . 44 B.5 Periodic errors (long period) . 44 B.6 Distributions of ensemble parameters . 45 B.7 Using the mixed statistical distribution . 48 Annex C (informative) Worked example . 49 C.1 Scenario and requirements . 49 C.2 Assessing the contributing errors . 50 C.3 Compiling the pointing budgets . 52 Annex D (informative) Correspondence with the pointing error handbook . 54 References . 55 Bibliography . 56
Figures Figure A-1 : Example showing the APE, MPE and RPE error indices . 30 Figure A-2 : Example showing the PDE and PRE error indices . 30 Figure A-3 : Example of a statistical ensemble of errors. . 31 Figure A-4 : The different ways in which a requirement for P(|ε|<1º) > 0,9 can be met . 32 Figure A-5 : Illustration of how the statistics of the pointing errors differ depending on which statistical interpretation is used . 32 SIST EN 16603-60-10:2014
EN 16603-60-10:2014 (E) 4 Figure C-1 : Scenario example . 50
Tables Table B-1 : Parameters whose distributions are assessed for the different pointing error indices (knowledge error indices are similar) . 41 Table B-2 : Budget contributions from bias errors, where B represents the bias . 42 Table B-3 : Budget contributions from zero mean Gaussian random errors . 43 Table B-4 : Uniform Random Errors (range 0-C) . 43 Table B-5 : Budget contributions for periodic errors (low period sinusoidal) . 44 Table B-6 : Budget contributions for periodic errors (long period sinusoidal) . 45 Table B-7 : Some common distributions of ensemble parameters and their properties . 47 Table C-1 : Example of contributing errors, and their relevant properties . 51 Table C-2 : Example of distribution of the ensemble parameters . 52 Table C-3 : Example of pointing budget for the APE index . 53 Table C-4 : Example of pointing budget for the RPE index . 53 Table D-1 : Correspondence between Pointing error handbook and ECSS-E-ST-60-10 indicators . 54
SIST EN 16603-60-10:2014
EN 16603-60-10:2014 (E) 5 Foreword This document (EN 16603-60-10:2014) has been prepared by Technical Committee CEN/CLC/TC 5 “Space”, the secretariat of which is held by DIN. This standard (EN 16603-60-10:2014) originates from ECSS-E-ST-60-10C. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by March 2015, and conflicting national standards shall be withdrawn at the latest by March 2015. 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 EN covering the same scope but with a wider domain of applicability (e.g. : aerospace). According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. SIST EN 16603-60-10:2014
EN 16603-60-10:2014 (E) 6 Introduction This standard focuses on the specific issues raised by managing performance aspects of control systems in the frame of space projects. It provides a set of normative definitions, budget rules, and specification templates applicable when developing general control systems. The standard is split up in two main clauses, respectively dealing with: • Performance error indices and analysis methods. • Stability and robustness specification and verification for linear systems. This document constitutes the normative substance of the more general and informative handbook on control performance, issued in the frame of the E-60-10 ECSS working group. If clarifications are necessary (on the concepts, the technical background, the rationales for the rules for example) the readers should refer to the handbook. NOTE
It is not intended to substitute to textbook material on automatic control theory, neither in this standard nor in the associated handbook. The readers and the users are assumed to possess general knowledge of control system engineering and its applications to space missions. SIST EN 16603-60-10:2014
EN 16603-60-10:2014 (E) 7 1 Scope This standard 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 standard defines a general framework for handling performance indicators, which applies to all disciplines involving control engineering, and which can be applied 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 – mainly stability and robustness. Rules are provided for combining different error sources in order to build up a performance error budget and use this to assess the compliance with a requirement. NOTE 1 Although designed to be general, one of the major application field for this Standard is spacecraft pointing. This justifies why most of the examples and illustrations are related to AOCS problems.
NOTE 2 Indeed the definitions and the normative clauses of this Standard apply to pointing performance; nevertheless fully specific pointing issues are not addressed here in detail (spinning spacecraft cases for example). Complementary material for pointing error budgets can be found in ECSS-E-HB-60-10. NOTE 3 For their own specific purpose, each entity (ESA, national agencies, primes) can further elaborate internal documents, deriving appropriate guidelines and summation rules based on the top level clauses gathered in this ECSS-E-ST-60-10 standard. This standard may be tailored for the specific characteristic and constrains of a space project in conformance with ECSS-S-ST-00. SIST EN 16603-60-10:2014
EN 16603-60-10:2014 (E) 8 2 Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions of this ECSS Standard. For dated references, subsequent amendments to, or revision of any of these publications do not apply, However, parties to agreements based on this ECSS Standard are encouraged to investigate the possibility of applying the more recent editions of the normative documents indicated below. For undated references, the latest edition of the publication referred to applies.
EN reference Reference in text Title EN 16601-00-01 ECSS-S-ST-00-01 ECSS System – Glossary of terms
SIST EN 16603-60-10:2014
EN 16603-60-10:2014 (E) 9 3 Terms, definitions and abbreviated terms 3.1 Terms from other standards For the purpose of this Standard, the terms and definitions from ECSS-S-ST-00-01 apply, in particular for the following terms: error performance uncertainty 3.2 Terms specific to the present standard 1
3.2.1 absolute knowledge error (AKE) instantaneous value of the knowledge error at any given time NOTE 1 This is expressed by:
()()KAKEtet= NOTE 2 See annex A.1.3 for defining requirements on the knowledge error. 3.2.2 absolute performance error (APE) instantaneous value of the performance error at any given time NOTE
This is expressed by:
()()PAPEtet= 3.2.3 error index
parameter isolating a particular aspect of the time variation of a performance error or knowledge error NOTE 1 A performance error index is applied to the difference between the target (desired) output of the system and the actual system output.
1
As a preliminary note, the error signals introduced in clause 3.2 are very general. They represent any type of physical quantity (e.g. attitude, temperature, pressure, position). According to the situation and to the nature of the control system, they are scalar or multi-dimensional.
SIST EN 16603-60-10:2014
EN 16603-60-10:2014 (E) 10 NOTE 2 A knowledge error index is applied to the difference between the actual output of the system and the known (estimated) system output.
NOTE 3 The most commonly used indices are defined in this chapter (APE, RPE, AKE etc.). The list is not limitative. 3.2.4 individual error source
elementary physical characteristic or process originating from a well-defined source which contributes to a performance error or a performance knowledge error NOTE
For example sensor noise, sensor bias, actuator noise, actuator bias, disturbance forces and torques (e.g. microvibrations, manoeuvres, external or internal subsystem motions), friction forces and torques, misalignments, thermal distortions, assembly distortions, digital quantization, control law performance (steady state error), jitter, etc. 3.2.5 knowledge error difference between the known (estimated) output of the system and the actual achieved output NOTE 1 It is denoted by eK. NOTE 2 Usually this is time dependent. NOTE 3 Sometimes confusingly referred to as “measurement error”, though in fact the concept is more general than direct measurement. NOTE 4 Depending upon the system, different quantities can be relevant for parameterising the knowledge error, in the same way as for the performance error. A degree of judgement is used to decide which is most appropriate. NOTE 5 For example: the difference between the actual and the known orientation of a frame can be parameterised using the Euler angles for the frame transformation or the angle between the actual and known orientation of a particular vector within that frame. 3.2.6 mean knowledge error (MKE) mean value of the knowledge error over a specified time interval NOTE 1 This is expressed by:
()()1()KKtMKEtetetdtt∆∆=∆=∆∫
SIST EN 16603-60-10:2014
EN 16603-60-10:2014 (E) 11 NOTE 2 See annex A.1.4 for discussion of how to specify the interval ∆t, and annex A.1.3 for defining requirements on the knowledge error. 3.2.7 mean performance error (MPE) mean value of the performance error over a specified time interval NOTE 1 This is expressed by:
()()1()PPtMPEtetetdtt∆∆=∆=∆∫ NOTE 2 See annex A.1.4 for discussion of how to specify the interval t∆. 3.2.8 performance drift error (PDE) difference between the means of the performance error taken over two time intervals within a single observation period NOTE 1 This is expressed by:
21122121(,)()()11()()PPPPttPDEttetetetdtetdttt∆∆∆∆=∆−∆=−∆∆∫∫ NOTE 2 Where the time intervals ∆t1 and ∆t2 are separated by a non-zero time interval ∆tPDE.
NOTE 3 The durations of ∆t1 and ∆t2 are sufficiently long to average out short term contributions. Ideally they have the same duration. See annex A.1.4 for further discussion of the choice of ∆t1 , ∆t2, ∆tPDE. NOTE 4 The two intervals ∆t1 and ∆t2 are within a single observation period 3.2.9 performance error difference between the target (desired) output of the system and the actual achieved output NOTE 1 It is denoted by eP. NOTE 2 Usually this is time dependent. NOTE 3 Depending upon the system, different quantities can be relevant for parameterising the performance error. A degree of judgement is used to decide which is most appropriate. NOTE 4 For example: The difference between the target and actual orientation of a frame can be parameterised using the Euler angles for the frame transformation or the angle between the target and actual orientation of a particular vector within that frame. SIST EN 16603-60-10:2014
EN 16603-60-10:2014 (E) 12 3.2.10 performance reproducibility error (PRE) difference between the means of the performance error taken over two time intervals within different observation periods NOTE 1 This is expressed by:
21122121(,)()()11()()PPPPttPREttetetetdtetdttt∆∆∆∆=∆−∆=−∆∆∫∫ NOTE 2 Where the time intervals ∆t1 and ∆t2 are separated by a time interval ∆tPRE.
NOTE 3 The durations of ∆t1 and ∆t2 are sufficiently long to average out short term contributions. Ideally they have the same duration. See annex A.1.4 for further discussion of the choice of ∆t1, ∆t2, ∆tPRE. NOTE 4 The two intervals ∆t1 and ∆t2 are within different observation periods NOTE 5 The mathematical definitions of the PDE and PRE indices are identical. The difference is in the use: PDE is used to quantify the drift in the performance error during a long observation, while PRE is used to quantify the accuracy to which it is possible to repeat an observation at a later time. 3.2.11 relative knowledge error (RKE) difference between the instantaneous knowledge error at a given time, and its mean value over a time interval containing that time NOTE 1 This is expressed by:
(,)()()1()()KKKKtRKEttetetetetdtt∆∆=−∆=−∆∫
tt∈∆ NOTE 2 As stated here the exact relationship between t and ∆t is not well defined. Depending on the system it can be appropriate to specify it more precisely: e.g. t is randomly chosen within ∆t, or t is at the end of ∆t. See annex A.1.4 for discussion of how to specify the interval ∆t, and annex A.1.3 for defining requirements on the knowledge error. 3.2.12 relative performance error (RPE) difference between the instantaneous performance error at a given time, and its mean value over a time interval containing that time NOTE 1 This is expressed by:
(,)()()1()()PPPPtRPEttetetetetdtt∆∆=−∆=−∆∫
tt∈∆ SIST EN 16603-60-10:2014
EN 16603-60-10:2014 (E) 13 NOTE 2 As stated here the exact relationship between t and ∆t is not well defined. Depending on the system it can be appropriate to specify it more precisely: e.g. t is randomly chosen within ∆t, or t is at the end of ∆t. See annex A.1.4 for further discussion 3.2.13 robustness ability of a controlled system to maintain some performance or stability characteristics in the presence of plant, sensors, actuators and/or environmental uncertainties NOTE 1 Performance robustness is the ability to maintain performance in the presence of defined bounded uncertainties. NOTE 2 Stability robustness is the ability to maintain stability in the presence of defined bounded uncertainties. 3.2.14 stability ability of a system submitted to bounded external disturbances to remain indefinitely in a bounded domain around an equilibrium position or around an equilibrium trajectory 3.2.15 stability margin maximum excursion of some parameters describing a given control system for which the system remains stable NOTE
The most frequent stability margins defined in classical control design are the gain margin, the phase margin, the modulus margin, and – less frequently – the delay margins (see Clause 5 of this standard) 3.2.16 statistical ensemble set of all physically possible combinations of values of parameters which describe a control system NOTE
For example: Considering the attitude dynamics of a spacecraft, these parameters include the mass, inertias, modal coupling factors, eigenfrequencies and damping ratios of the appendage modes, the standard deviation of the sensor noises etc., that means all physical parameters that potentially have a significant on the performance of the system. SIST EN 16603-60-10:2014
EN 16603-60-10:2014 (E) 14 3.3 Abbreviated terms The following abbreviated terms are defined and used within this document:
Abbreviation Meaning AKE absolute knowledge error APE absolute performance error LTI linear time invariant MIMO multiple input – multiple output MKE mean knowledge error MPE mean performance error PDE performance drift error PDF probability density function PRE performance reproducibility error RKE relative knowledge error RMS root mean square RPE relative performance error RSS root sum of squares SISO single input – single output
SIST EN 16603-60-10:2014
EN 16603-60-10:2014 (E) 15 4 Performance requirements and budgeting 4.1 Specifying a performance requirement 4.1.1 Overview For the purposes of this standard, a performance requirement is a specification that the output of the system does not deviate by more than a given amount from the target output. For example, it can be requested that the boresight of a telescope payload does not deviate by more than a given angle from the target direction. In practice, such requirements are specified in terms of quantified probabilities.
Typical requirements seen in practice are for example: • “The instantaneous half cone angle between the actual and desired payload boresight directions shall be less than 1,0 arcmin for 95 % of the time” • “Over a 10 second integration time, the Euler angles for the transformation between the target and actual payload frames shall have an RPE less than 20 arcsec at 99 % confidence, using the mixed statistical interpretation.” • “APE(ε) < 2,5 arcmin (95 % confidence, ensemble interpretation), where
ε = arccos(xtarget.xactual)” Although given in different ways, these all have a common mathematical form: Ε)maxCprobXXP<≥ To put it into words, the physical quantity X to be constrained is defined and a maximum value maxX is specified, as well as the probability CP that the magnitude of X is smaller than maxX. Since there are different ways to interpret the probability, the applicable statistical interpretation is also given.
These concepts are discussed in Annex A. SIST EN 16603-60-10:2014
EN 16603-60-10:2014 (E) 16 4.1.2 Elements of a performance requirement a. The specification of a performance shall consist of: 1. The quantities to be constrained. NOTE 1 This is usually done specifying the appropriate indices (APE, MPE, RPE, PDE, PRE) as defined in 3.2. NOTE 2 All the elements needed to fully describe the constrained quantities are listed there; for example, the associated timescales for MPE or RPE. 2. The allowed range for each of these quantities. 3. The probability that each quantity lies within the specified range. NOTE
This is often called the confidence level. See 4.1.4; 4. The interpretation of this probability. NOTE 1 This is often referred to as the “statistical interpretation”. See annex A.1.2 NOTE 2 The way to specify the statistical interpretation is described in 4.1.4.2. 4.1.3 Elements of a knowledge requirement a. When specifying a requirement on the knowledge of the performance, the following elements shall be specified: 1. The quantities to be constrained. NOTE 1 This is usually done specifying the appropriate indices (AKE, MKE, RKE) as defined in 3.2. NOTE 2 All the elements needed to fully describe the constrained quantities are listed there; for example, the associated timescales for MKE or RKE. 2. The allowed range for each of these quantities. 3. The probability that each quantity lies within the specified range. NOTE
This is often called the confidence level. See 4.1.4; 4. The interpretation of this probability. NOTE 1 This is often referred to as the “statistical interpretation”. See annex A.1.2 NOTE 2 The way to specify the statistical interpretation is described in 4.1.4.2. 5. The conditions under which the requirement applies. NOTE
These conditions can be that the requirement refers to the state of knowledge on-board, on ground before post processing, or after post processing. This is explained further in annex A.1.3. SIST EN 16603-60-10:2014
EN 16603-60-10:2014 (E) 17 4.1.4 Probabilities and statistical interpretations 4.1.4.1 Specifying probabilities a. In the general case all probabilities shall be expressed as fractions or as percentages. b. Using the ‘nσ’ notation for expressing probabilities shall be restricted to cases where the hypothesis of Gaussian distribution holds. NOTE 1 For example: in the general case PC = 0,95 or PC = 95 % are both acceptable, but PC = 2σ is not. Indeed the ‘nσ’ format assumes a Gaussian distribution; using this notation for a general statistical distribution can cause wrong assumptions to be made. For a Gaussian the 95 % (2σ) bound is twice as far from the mean as the 68 % (1σ) bound, but this relation does not hold for a general distribution. NOTE 2 Upon certain conditions the assumption of Gaussian distribution is not to be excluded a priory. For example the central limit theorem states that the sum of a large number of independent and identically-distributed random variables is approximately normally distributed. 4.1.4.2 Specifying statistical interpretations a. When specifying the statistical interpretation (4.1.2a.4), it shall be stated which variables are varied across their possible ranges and which are set to worst case. NOTE
The most commonly used interpretations (temporal, ensemble, mixed) are extreme cases and can be inappropriate in some situations. Annex A.1.2 discusses this further. 4.2 Use of error budgeting to assess compliance 4.2.1 Scope and limitations A common way to assess compliance with a perform
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