SIST EN ISO 21351:2005

SLOVENSKI STANDARD
SIST EN ISO 21351:2005
01-september-2005
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Space systems - Functional and technical specifications (ISO 21351:2005)
Raumfahrtsysteme - Funktionale und technische Spezifikationen (ISO 21351:2005)
Systemes spatiaux - Cahier des charges fonctionnel et spécification technique de besoin
(ISO 21351:2005)
Ta slovenski standard je istoveten z: EN ISO 21351:2005
ICS:
49.140 Vesoljski sistemi in operacije Space systems and
operations
SIST EN ISO 21351:2005 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 21351:2005

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SIST EN ISO 21351:2005
EUROPEAN STANDARD
EN ISO 21351
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2005
ICS 49.140
English version
Space systems - Functional and technical specifications (ISO
21351:2005)
Systèmes spatiaux - Cahier des charges fonctionnel et Raumfahrtsysteme - Funktionelle und technische
spécification technique de besoin (ISO 21351:2005) Spezifikationen (ISO 21351:2005)
This European Standard was approved by CEN on 28 February 2005.
CEN 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 Central Secretariat or to any CEN 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 member into its own language and notified to the Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 21351:2005: E
worldwide for CEN national Members.

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SIST EN ISO 21351:2005
EN ISO 21351:2005 (E)
Contents
Page
Foreword.4
Introduction .5
1 Scope .6
2 Normative references .6
3 Terms, definitions and abbreviations.6
3.1 Terms and definitions .6
3.2 Abbreviated terms .8
4 Functional specification and technical specification purpose and description .8
4.1 Functional specification purpose and description .8
4.2 Technical specification purpose and description.8
4.3 FS and TS content .8
5 Process for establishing a functional specification and a technical specification .9
5.1 General.9
5.2 Process for establishing a functional specification.11
5.3 Process for establishing a technical specification .12
6 Technical requirements description.13
6.1 General description .13
6.2 Identification of attributes assigned to technical requirements.13
6.2.1 Introduction.13
6.2.2 Functional requirements description .14
6.2.3 Mission requirements description .14
6.2.4 Interface requirements description.14
6.2.5 Environmental requirements description .14
6.2.6 Physical requirements description.14
6.2.7 Operational requirements description.15
6.2.8 Human factor requirements description .15
6.2.9 (Integrated) logistics support requirements description .15
6.2.10 Product assurance (PA) requirements description.15
6.2.11 Configuration requirements description.16
6.2.12 Design requirements description.16
7 Requirements and recommendations for functional specifications and technical
specifications.16
7.1 Requirements and recommendations common to FS and TS .16
7.1.1 General.16
7.1.2 Responsibility .16
7.1.3 Technical requirements organisation.16
7.1.4 Unique technical reference.17
7.1.5 Configuration management.17
7.1.6 Format.17
7.1.7 Supplementary information.17
7.1.8 Restrictions .17
7.1.9 Severity classification .17
7.2 Requirement specific to the functional specification .17
8 Requirements and recommendations for characterizing the technical requirements.17
8.1 Requirements and recommendations for the characteristics of a technical requirement
common to FS and TS.17
8.1.1 Performance .17
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8.1.2 Justification .18
8.1.3 Configuration management and traceability .18
8.1.4 Ambiguity .18
8.1.5 Uniqueness .18
8.1.6 Identifiability .18
8.1.7 Singularity .18
8.1.8 Completeness .19
8.1.9 Prioritization.19
8.2 Requirements and recommendations for the characteristics of a technical requirement in
the FS.19
8.2.1 Flexibility .19
8.2.2 Severity.19
8.2.3 Maturity.19
8.3 Requirements and recommendations for the characteristics of a technical requirement in
the TS.19
8.3.1 Verification .19
8.3.2 Attainability .20
8.3.3 Tolerance.20
8.3.4 Risk .20
8.4 Requirements and recommendations for the wording.20
8.4.1 General format .20
8.4.2 Required verbal form .20
8.4.3 Format restrictions.20
Bibliography.22

Figures
Figure 1  Model presentations .9
Figure 2  Relationship between the FS and the TS.10
Figure 3  Process to establish the first issue of the FS .11
Figure 4  Process to establish the final issue of the FS.12
Figure 5  Process to establish the TS.13

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SIST EN ISO 21351:2005
EN ISO 21351:2005 (E)
Foreword
This document (EN ISO 21351:2005) has been prepared by European Cooperation for Space Standardization
(ECSS), the secretariat of which is held by CMC, in collaboration with Technical Committee ISO/TC 20
“Aircraft and space vehicles”.
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 November 2005, and conflicting national standards shall be withdrawn
at the latest by November 2005.
1)
It is based on a previous version originally prepared by the ECSS Functional and Technical Specification
Working Group, reviewed by the ECSS Engineering Panel and approved by the ECSS Steering Board. The
ECSS is a cooperative effort of the European Space Agency, national space agencies and European industry
associations for the purpose of developing and maintaining common standards.
This European Standard is one of the series of space standards intended to be applied together for the
management, engineering and product assurance in space projects and applications.
Requirements in this document are defined in terms of what shall be accomplished, rather than in terms of
how to organize and perform the necessary work. This allows existing organizational structures and methods
to be applied where they are effective, and for the structures and methods to evolve as necessary without
rewriting the standards.
The formulation of this document takes into account the existing EN ISO 9000 family of documents.
This document includes a Bibliography.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland
and United Kingdom.

1) ECSS-E-10 Part 6.
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Introduction
This document introduces the strategy of establishing and positioning the Functional Specification (FS) and
the Technical Specification (TS) in a project process to improve the effectiveness of its management in terms
of performance, cost, schedule and risk.
These two specifications are recommended in ISO 14300-1 in order to focus to customer (or user) needs and
to allocate proper time and resources for investigating and comparing a sensible range of candidate concepts,
and selecting a preferred solution to be developed or to be purchased.
The FS is the baseline for investigating and comparing candidate concepts, while the TS is the baseline of the
business agreement to develop or purchase the selected solution.
NOTE Functional Specification is also referred as “Functional Performance Specification (FPS)” in EN 1325-1.
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1 Scope
This document provides an overview of the respective purposes and positions of functional and technical
specifications, their required contents, and the process for developing these documents.
This document is applicable to all types of space systems, all product elements, and projects.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
EN 13701:2001, Space systems — Glossary of terms.
EN ISO 17666:2003, Space systems — Risk management (ISO 17666:2003).
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 13701:2001 and the following apply.
3.1.1
constraint
characteristic, result or design feature which is made compulsory or has been prohibited for any reason
NOTE 1 Constraints are generally restrictions on the choice of solutions in a system.
NOTE 2 Two kinds of constraints are considered, those which concern solutions, and those which concern the use of
the system.
NOTE 3 For example constraints can come from environmental and operational conditions, law, standards, market
demand, investments and means availability, or the organization’s policy.
NOTE 4 Adapted from EN 1325-1.
3.1.2
environment, noun
natural conditions (such as weather, climate, ocean conditions, terrain, vegetation, dust, light and
radiation) and induced conditions (such as electromagnetic interference, heat, vibration, pollution and
contamination) that constrain the design definitions for end products and their enabling products
3.1.3
environment, noun
external factors affecting an enterprise or project
3.1.4
environment, noun
external factors affecting development tools, methods, or processes
3.1.5
function
intended effect of a system, subsystem, product or part
NOTE 1 Adapted from EN 1325-1.
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NOTE 2 Functions should have a single definite purpose. Function names should have a declarative structure
(e.g. “Validate Telecommands”), and say “what” is to be done rather than “how”. Good naming allows design components
with strong cohesion to be easily derived.
3.1.6
functional analysis
technique of identifying and describing all functions of a system
NOTE Adapted from EN 1325-1.
3.1.7
functional specification
document by which the customer establishes the intended purpose of a product, its associated constraints
and environment, the operational and performances features, and the permissible flexibility
NOTE 1 This document contains a complete set of provisional technical requirements for a product.
NOTE 2 This term is equivalent to "functional performance specification” as defined in EN 1325-1.
3.1.8
life cycle
time interval between the conceptual exploration of the product introduction to its withdrawal from service
3.1.9
need
what is necessary for, or desired by, the user
NOTE 1 A need can be declared or undeclared; it can be an existing or a potential one.
NOTE 2 The user is a person or an organization for which the product is designed and which exploits at least one of its
functions at any time during its life cycle.
NOTE 3 For the space community, the needs are often called mission statement.
NOTE 4 Adapted from EN 1325-1.
3.1.10
specification
document stating requirements
NOTE 1 A specification can be related to activities (e.g. procedure document, process specification and test
specification), or products (e.g. functional specification, technical specification)
NOTE 2 Adapted from ISO 9000:2000.
3.1.11
technical specification
specification expressing technical requirements for designing and developing the solution to be implemented
NOTE The technical specification evolves from the functional specification and defines the technical requirements for
the selected solution as part of a business agreement.
3.1.12
verification matrix
matrix that defines the verification strategy for each product technical requirement in terms of methods, level
and stages
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3.2 Abbreviated terms
The following abbreviated terms are defined and used within this document:
Abbreviation Meaning
IEC International Electrotechnical Commission
FS functional specification
PA product assurance
TS technical specification
4 Functional specification and technical specification purpose and description
4.1 Functional specification purpose and description
A functional specification is a document through which a customer expresses his needs (or those that he is
responsible for expressing) and the related environment and constraints in terms of technical requirements.
The FS is used for searching for possible concepts, evaluating them and selecting a preferred solution.
The technical requirements contained in the FS provide flexibility to:
• allow potential suppliers to propose the best technical and programmatic solutions;
• facilitate the adjustment among the need or mission statement, the context (e.g. programmatic elements
and environmental constraints) and possible solutions.
NOTE The intention of the functional specification is not to assume or refer to specific solutions.
4.2 Technical specification purpose and description
The technical specification evolves from the functional specification and defines the technical performances
for the proposed solution as part of a business agreement.
The TS is the technical reference for the acceptance of the definition and for the acceptance of the end
product.
In that scope, the technical requirements contained in the TS have no flexibility. They are attainable and
verifiable, and for each technical requirement, the method of verification (e.g. by test, by analysis) is specified.
4.3 FS and TS content
A specification (FS or TS) is typically composed of three major sets of information:
• General information related to the context of the document (e.g. administrative information, normative
documents and informative documents);
• General information related to the context of the project, the product or system;
• Technical requirements (described in Clauses 6 and 8).
The specification provides the general information related to its context:
• Administrative information: to provide all the information regarding, for example, the owner, status,
identification, distribution list, and management rule;
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• Scope: to define without ambiguity the subject of the FS and TS and aspects covered, thereby indicating
limits of applicability;
• References: to list all the normative (applicable) documents and standards, with titles, issue revision, and
dates that are referred to in the FS;
• Terms, definitions and abbreviated terms: to list the specific terms and abbreviated terms used in the FS.
It also provides general information related to the context of the project, product or system:
• to provide a clear and rapid understanding of the project and the main needs or mission statements;
• to give indications of the market as additional information, as well as information about the context of the
project and the objectives (situation of the project in a larger programme, further developments);
• to provide information on the environment and its constraints;
• to detail the different situations of the product or system life cycle.
5 Process for establishing a functional specification and a technical specification
5.1 General
The management of a programme necessitates the establishment of a set of successive states of a product
and a network of customer and supplier relationships. At any intermediate level, the supplier of an item acts as
customer in specifying components towards its suppliers.
The two first states - the functional state and the specified state - are expressed in a FS and in a TS.
The procurement of products is governed by business agreements constituting the contract between two
parties - the customer and the supplier.
A business agreement results from a negotiation process between a customer with a problem to solve, and a
supplier with potential solutions. This results in a set of requirements that engages both parties. The list of
requirements constitutes an important part of the business agreement and is adapted to the nature of the
expected outcome.
Figures through 2 to 5 are provided to help supporting the understanding of a process for establishing a
functional specification and a technical specification. The model used for these figures is presented in Figure 1.

Figure 1  Model presentations
Where:
• The box represents the task to be performed;
• The left– and top–side arrows represent the necessary inputs to the task;
• An arrow on the right–side represents the output produced by the task;
• An arrow coming from below represent the actor involved in performing the task.

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Figure 2 presents the macro-process that generates the functional and technical specifications.
This principle can be used at different system levels.


Figure 2  Relationship between the FS and the TS
Where:
• F1 task: the customer expresses the need in a FS (see 4.2);
• F2 task: each bidder analyses this FS and establishes one or more proposals. This task is presented
to ensure a consistent approach between the bidders and the customer;
• F3 task: the customer select the supplier/solution and releases the TS (see 4.3).
As part of a business agreement, the customer establishes his needs for the development of a product or a
system in a technical specification.
The FS clarifies the global needs (mission statement) and is the technical reference for invitations to tender
and consultations.
An FS is also used when a design–to–cost process applies to help in defining the best compromized solution.
Moreover, it facilitates the selection of “off–the–shelf” items because it forces to define the needs and
constraints even if solutions are preselected.
The technical specification derives from the FS and is compatible with the proposed baseline solution. It is the
result of the business negotiation process. It is the baseline for the product or system development.
A TS defines the related set of technical requirements established and used to develop or procure a product
or a system as part of the business agreement.
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The TS is the technical reference for the design definition and the end product acceptance.
The technical requirements are usually negotiated with the customer and take into account the technical
feasibility, availability and cost of the proposed solution.
5.2 Process for establishing a functional specification
For space projects, this process can be divided into two steps:
• establishment of the first issue of the FS;
• identification, evaluation of the different possible concepts to establish the final issue of the FS.
The first step consists of an initial assessment of the project and results in the first issue of the FS, as
illustrated in Figure 3. The purpose of this first issue of the FS is to express the customer’s need, mission
statement, associated environmental constraint and programmatic element in terms of technical requirements
(i.e. the problem to solve). This document serves as a basis to initiate the next step.
NOTE A functional analysis can be performed to capture the FS requirements (see EN 12973).

Figure 3  Process to establish the first issue of the FS

Where:
• The F1.1 task: The customer identifies and captures the user’s needs or mission statements,
associated environments and constraints. He expresses these in terms of technical requirements;
• The F1.2 task: The customer structures, classifies and justifies (see 8.1.1) individual technical
requirements;
• The F1.3 task: The customer assesses the entire set of technical requirements for correctness,
consistency and suitability for the intended use;
• The F1.4 task: The customer establishes the first issue of the FS and releases it.
The second step consists of the exploration among the different possible concepts ensuring the conformity to
the defined needs, then the selection of one concept and results in the final issue of the FS. This final version
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