January 16, 2012

Specification of Requirement - E-2

Express needs in terms of requirements and technical constraints for the recommended concept

A. Scope

The Technical Need Specification is a contractual document established by the caller of a product for the designer, through which he expresses his need (or the need he has been assigned to express) in terms of technical requirements.

The Technical Need Specification must be sufficient for a designer to be able to develop a design of the product that unambiguously meets it.

Along with the Definition File (see E 4) and the Design Justification File (see E 7), it constitutes a set of documents intended as the basis of a document system for any hardware or software product.

This document is based on the CNES Standards Reference (RNC) document "RNC-CNES-E-HB-10-504 Contenu typique de la Spécification Technique de Besoin (STB)".

B. Fundamentals

Feasibility phase (phase A)

The preliminary Technical Need Specification expresses the need in precise technical terms that are directly usable by the designer.

Definition phase (phase B)

The preliminary Technical Need Specification has been progressively completed for the points that have required more detailed analyses concerning the environmental conditions, the interface requirements, the qualification requirements, etc. It is frozen at the end of this phase.

This final issue of the Technical Need Specification becomes contractual for development work (phase C).

This Technical Need Specification is a part of the Technical Clauses of the development contract.

C. Typical content

1. Scope

This section shall contain the general information defining the scope and coverage of the specification.

Example

"This specification defines the requirements concerning the performance, the design and the qualification of the R2D2 spectrometer. It is applicable to the flight model ...".

2. Documentation

2.1 Applicable documents

These are all the documents whose applicability is mandatory for the definition of the product.

These documents are usually issued as a part of the system, by CNES or by the satellite customer (ESA, NASA, etc.).

Example

EIDA Interface Experiment Document / ESA.
Product Assurance Plan.

2.2 Reference documents

These constitute the bibliography that is necessary in order to prepare the Technical Need Specification .

2.3 Glossary

The terminology and acronyms used in the document shall be explained in this paragraph.

3. Product overview

3.1 The product and its design

This paragraph synthesises the information provided in the Functional Performance Specification of the product and describes the concept selected.

Example

Product: the spectrometer shall transform the characteristics of the photons received from a local source, in a given visual field, into digital data.

The characterisation concerns:

  • the energy of the photon,
  • the position of the source in the field of view,
  • the photon detection time.

 

 

Concept: the radiation is intercepted by a passive mask, made up of hexagonal pixels, which either blocks the gamma rays or allows them to pass ...

3.2 Life profile

This sub-paragraph shall describe the utilisation, the missions and the situations of the product life profile, including a brief characterisation of them.

3.3 Main components

Here, the product tree shall be broken down into the main components.

4. Requirements

4.1 Functional requirements

These are directly determined by the service expected of the product.

These are the performances and functional characteristics required of the product over its entire life profile, with the required minimum durations and the associated event conditions.

  • Functional requirements

    They correspond to the specific value criteria of the service functions identified in the Functional Performance Specifications. They result from each of the functions that the product must fulfil and are independent of the adopted technical solution.

    The functional requirements shall be verifiable:

    • by using metrics at the end of the manufacturing phase, or during manufacture if the corresponding measurement is no longer available at the final stage,
    • by demonstration of conformity or compatibility,

 

  • Technical requirements

    They result from the technical solution adopted:

    • reference axes system,
    • alignment constraints,
    • field of view,
    • dimensions,
    • centre of gravity / weight / inertia,
    • stiffness,
    • dynamic disturbance produced by the product,
    • power consumption,
    • EMC disturbance produced by the product,

 

  • Environment requirements

    Requirements concerning the resistance to the different aspects of the environment (climatic, mechanical, etc.) and to the various aggressions that the product is liable to encounter during its life profile.

 

4.2 Operational requirements

These concern the operational aspects identified as follows:

  • Dependability
    • availability,
    • reliability,
    • maintainability,
    • safety,
    • usability,
    • human factor.
  • Lifetime

    This part contains the lifetimes of the product in storage, in integrated condition and in operation.

  • Operating modes

    Each operating mode corresponds to a phase of the product mission profile.

    All the operating modes shall be described here, along with their specific characteristics.

    The sequencing of the modes shall also be specified.

  • Logistics
    • Constraints connected with maintenance: periodicity, duration, tools, etc.
    • Requirements concerning packaging, transport, handling and storage.

 

Example

  1. Initiation mode: this mode corresponds to the launcher thrust phase; the instrument is not energised.
  2. Operational mode: the spectrometer is active; telemetry and telecommand are active.
  • Telemetry

    This paragraph shall state:

    • the nature of the scientific data to be supplied by the product;

 

Example

  • temperature measurement,
  • power consumption,
  • ...

 

  • Telecommands

    This section shall include the telecommands required for the operation of the product.

 

Example

The following parameters shall be controllable by means of telecommands:

  • sensor detection threshold,
  • ...

 

4.3 Interface requirements

These list all the product's interface constraints with respect to the outside elements already identified in the Functional Performance Specifications.

These requirements shall be coherent with respect to the interface documents issued by the higher level.

They concern the following fields:

  • mechanical,
  • thermal,
  • electrical,
  • optical,
  • software,
  • test equipment.

 

N.B. : in the case where there is an existing interface document that states the requirements of the higher level, this document must be mentioned here as an applicable document.

Example

EIDA for ESA.

4.4 Design requirements and mandatory solutions

This paragraph of the Technical Need Specification should cover the regulation-based requirements, the applicable standards and the customer's requirements (mandatory or prohibited solutions, development facilities to be used, etc.).

These requirements concern:

  • Main design constraints
  • Specifications - Norms and standards
  • Materials - Processes - Components
  • Protection - Preservation of the product

 

4.5 Design and manufacturing requirements

  • Design requirements

    These correspond to the requirements that have been imposed by the customer to the designer (in other words, these are design solution elements that have been imposed in the definition of the product).

 

Example

The detection surface is defined by 19 hexagonal germanium sensors, with a height of 7 cm.

  • Design rules

    This paragraph lists the general rules (norms or standards) or specific rules applicable to the definition of the product.

  • Manufacturing requirements

    These are the requirements connected with the accessibility, dismountability and testability of the product.

 

4.6 Environment requirements

These concern the resistance to the different aspects of the environment and the various aggressions that the product is liable to encounter throughout its mission profile.

  • Natural environment

    This part specifies the natural environment to which the product is subjected in all the phases of its life.

    • vacuum,
    • climatic environment (temperature / pressure / humidity),
    • cleanliness,
    • radiation.
  • Environment in service

    This part is used to specify the general stresses, the local stresses, the kinetic fluxes, the temperature domains, the mechanical environments, the dynamic environments, etc., that the product shall withstand during its normal mission, without compromising the specified reliability objectives, both its own and those of the other products.

    • mechanical environment: vibration levels, shocks, dynamic disturbance (micro-vibrations), quasi-static loads, acoustics, etc.;
    • thermal environment: solar fluxes, albedo, etc.;
    • EMC environment.

 

Risks

RisksNeeds and solutions do not match
 RecommandationsDETERMINE THE EXACT FUNCTIONAL NEED
Tender Specification (CDCF)
CLEARLY EXPRESS THE TECHNICAL REQUIREMENTS AND CONSTRAINTS
Technical Specification (STB)

 

Activities / documentation

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