prEN 16603-35-06

Space engineering - Cleanliness requirements for spacecraft propulsion hardware

EN 16603-35-06 (equivalent of ECSS-E-ST-35-06) belongs to the Propulsion field of the mechanical discipline, and concerns itself with the cleanliness of propulsion components, sub-systems and systems
The standard
- defines design requirements which allow for cleaning of propulsion components sub-systems and systems and which avoid generation or unwanted collection of contamination,
- identifies cleanliness requirements (e.g. which particle / impurity / wetness level can be tolerated),
- defines requirements on cleaning to comply with the cleanliness level requirements, and the requirements on verification,
- identifies the cleanliness approach, cleaning requirements, (e.g. what needs to be done to ensure the tolerable level is not exceeded, compatibility requirements),
- identifies, specifies and defines the requirements regarding conditions under which cleaning or cleanliness verification takes place (e.g. compatibility, check after environmental test).
The standard is applicable to the most commonly used propulsion systems and their related storable propellant combinations: Hydrazine (N2H4), Mono Methyl Hydrazine (CH3N2H3), MON (Mixed Oxides of Nitrogen), Nitrogen (N2), Helium (He), Propane (C3H8), Butane (C4H10) and Xenon (Xe).
This standard is the basis for the European spacecraft and spacecraft propulsion industry to define, achieve and verify the required cleanliness levels in spacecraft propulsion systems.
This standard is particularly applicable to spacecraft propulsion as used for satellites and (manned) spacecraft and any of such projects including its ground support equipment.
External cleanliness requirements, e.g. outside of tanks, piping and aspects such as fungus and outgassing are covered by ECSS-Q-ST-70-01.
This standard may be tailored for the specific characteristic and constraints of a space project in conformance with ECSS-S-ST-00.

Raumfahrttechnik - Sauberkeitsanforderungen für die Antriebstechnik von Raumfahrzeugen

EN 16603-35-06 (equivalent of ECSS-E-ST-35-06) belongs to the Propulsion field of the mechanical discipline, and concerns itself with the cleanliness of propulsion components, sub-systems and systems The standard
• defines design requirements which allow for cleaning of propulsion components sub-systems and systems and which avoid generation or unwanted collection of contamination,
• identifies cleanliness requirements (e.g. which particle / impurity / wetness level can be tolerated),
• defines requirements on cleaning to comply with the cleanliness level requirements, and the requirements on verification,
• identifies the cleanliness approach, cleaning requirements, (e.g. what needs to be done to ensure the tolerable level is not exceeded, compatibility requirements),
• identifies, specifies and defines the requirements regarding conditions under which cleaning or cleanliness verification takes place (e.g. compatibility, check after environmental test).
The standard is applicable to the most commonly used propulsion systems and their related storable propellant combinations: Hydrazine (N2H4), Mono Methyl Hydrazine (CH3N2H3), MON (Mixed Oxides of Nitrogen), Nitrogen (N2), Helium (He), Propane (C3H8), Butane (C4H10) and Xenon (Xe).
This standard is the basis for the European spacecraft and spacecraft propulsion industry to define, achieve and verify the required cleanliness levels in spacecraft propulsion systems.
This standard is particularly applicable to spacecraft propulsion as used for satellites and (manned) spacecraft and any of such projects including its ground support equipment.
External cleanliness requirements, e.g. outside of tanks, piping and aspects such as fungus and outgassing are covered by ECSS-Q-ST-70-01.
This standard may be tailored for the specific characteristic and constraints of a space project in conformance with ECSS-S-ST-00.

Ingénierie spatiale - Exigences de propreté des éléments de propulsion des véhicules spatiaux

Vesoljska tehnika - Zahteve za čistočo pogonske tehnike vesoljskih plovil

General Information

• Status: Not Published
• ICS: 49.140 - Space systems and operations
• Technical Committee: CEN/CLC/TC 5 - Space
• Drafting Committee: CEN/CLC/TC 5/WG 6 - Upstream standards
• Current Stage: 4060 - Closure of enquiry - Enquiry
• Due Date: 09-Sep-2021
• Completion Date: 09-Sep-2021
• Mandate: M/496 - Mandate addressed to CEN, CENELEC and ETSI to develop standardisation regarding space industry (Phase 3 of the process)
• Ref Project: oSIST prEN 16603-35-06:2021 - Space engineering - Cleanliness requirements for spacecraft propulsion hardware

RELATIONS

• Revised: EN 16603-35-06:2014 - Space engineering - Cleanliness requirements for spacecraft propulsion hardware
• Effective Date: 02-Dec-2020

Standards Content (sample)

SLOVENSKI STANDARD
oSIST prEN 16603-35-06:2021
01-september-2021
Vesoljska tehnika - Zahteve za čistočo pogonske tehnike vesoljskih plovil
Space engineering - Cleanliness requirements for spacecraft propulsion hardware
Raumfahrttechnik - Sauberkeitsanforderungen für die Antriebstechnik von
Raumfahrzeugen

Ingénierie spatiale - Exigences de propreté des éléments de propulsion des véhicules

spatiaux
Ta slovenski standard je istoveten z: prEN 16603-35-06
ICS:
49.140 Vesoljski sistemi in operacije Space systems and
operations
oSIST prEN 16603-35-06:2021 en,fr,de

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

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oSIST prEN 16603-35-06:2021
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oSIST prEN 16603-35-06:2021
EUROPEAN STANDARD
DRAFT
prEN 16603-35-06
NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2021
ICS 49.140
Will supersede EN 16603-35-06:2014
English version
Space engineering - Cleanliness requirements for
spacecraft propulsion hardware

Ingénierie spatiale - Exigences de propreté des Raumfahrttechnik - Sauberkeitsanforderungen für die

éléments de propulsion des véhicules spatiaux Antriebstechnik von Raumfahrzeugen

This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee

CEN/CLC/JTC 5.

If this draft becomes a European Standard, 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.

This draft European Standard was established by CEN and CENELEC 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, 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.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 European Standard. It is distributed for review and comments. It is subject to change without

notice and shall not be referred to as a European Standard.
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. prEN 16603-35-06:2021 E

reserved worldwide for CEN national Members and for
CENELEC Members.
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oSIST prEN 16603-35-06:2021
prEN 16603-35-06:2021 (E)
Table of contents

European Foreword .......................................................................................... 6

1 Scope .............................................................................................................. 7

2 Normative references .................................................................................... 8

3 Terms, definitions and abbreviated terms ................................................. 10

3.1 Terms from other standards ........................................................................... 10

3.2 Terms specific to the present standard .......................................................... 10

3.3 Abbreviated terms.......................................................................................... 12

3.4 Symbols ......................................................................................................... 13

3.5 Nomenclature ................................................................................................ 13

4 Cleanliness requirements ........................................................................... 14

4.1 General .......................................................................................................... 14

4.2 Design requirements ...................................................................................... 15

4.2.1 General ............................................................................................ 15

4.2.2 Components..................................................................................... 15

4.2.3 System ............................................................................................. 17

4.2.4 Ground support equipment (GSE) .................................................... 17

4.3 Manufacturing ................................................................................................ 18

4.3.1 General ............................................................................................ 18

4.3.2 Manufacturing processes ................................................................. 18

4.3.3 Machined parts ................................................................................ 18

4.3.4 Tubing and manifolds ....................................................................... 18

4.3.5 Components..................................................................................... 19

4.3.6 Subsystems and systems................................................................. 21

4.3.7 Final rinsing solutions ....................................................................... 21

4.4 Cleanliness classes definition ........................................................................ 21

4.4.1 Particulate ........................................................................................ 21

4.4.2 Non-volatile residues (NVR) ............................................................. 25

4.4.3 Dryness and liquid residuals ............................................................ 25

4.4.4 Requirements on process fluids to meet cleanliness classes ........... 26
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4.5 Test methods ................................................................................................. 27

4.6 Code usage ................................................................................................... 27

5 Cleaning techniques ................................................................................... 28

5.1 General .......................................................................................................... 28

5.2 Environment, health and safety...................................................................... 29

5.2.1 General ............................................................................................ 29

5.2.2 Hardware configuration requirements............................................... 29

5.2.3 Cleaning process approval ............................................................... 30

5.3 Pre-cleaning .................................................................................................. 30

5.3.1 General ............................................................................................ 30

5.3.2 Mechanical pre-cleaning .................................................................. 30

5.3.3 Chemical pre-cleaning ..................................................................... 31

5.4 Precision cleaning.......................................................................................... 32

5.4.1 General ............................................................................................ 32

5.4.2 Re-cleaning operational systems ..................................................... 32

5.5 Drying methods ............................................................................................. 33

5.5.1 General ............................................................................................ 33

5.5.2 Gaseous purge-drying ...................................................................... 33

5.5.3 Drying sample .................................................................................. 34

5.5.4 Flow rates during purging ................................................................. 35

5.5.5 Vacuum drying procedure ................................................................ 35

5.6 Excepted components, subsystems and systems .......................................... 36

6 Cleanliness verification requirements ....................................................... 37

6.1 Surface .......................................................................................................... 37

6.1.1 Visual and UV inspection ................................................................. 37

6.1.2 pH-test ............................................................................................. 37

6.2 Acceptance inspection of items cleaned in a controlled environment ............. 38

6.2.1 General ............................................................................................ 38

6.2.2 Test fluids ........................................................................................ 38

6.2.3 Test fluid volume for analysis ........................................................... 38

6.2.4 Analysis of test fluid-flush sample (solvent) ...................................... 39

6.2.5 Analysis of aqueous-based, liquid-flush sample ............................... 40

6.2.6 Drying .............................................................................................. 41

6.2.7 Vacuum drying ................................................................................. 41

6.3 Maintaining cleanliness .................................................................................. 42

6.3.1 Pressurant gas purge ....................................................................... 42

6.3.2 Installation and marking of temporary hardware ............................... 42

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6.3.3 Temporary hardware replacement ................................................... 42

6.3.4 Component replacement .................................................................. 43

6.4 Dryness verification ....................................................................................... 43

6.4.1 General ............................................................................................ 43

6.4.2 Purge dryness .................................................................................. 43

6.4.3 Vacuum dryness .............................................................................. 43

6.4.4 Sample test and qualified procedure ................................................ 44

7 Acceptance inspection of packaging materials ........................................ 45

7.1 Environmental control .................................................................................... 45

7.2 Sampling ....................................................................................................... 45

7.3 Thickness of packaging film ........................................................................... 45

7.4 Static electricity .............................................................................................. 46

7.5 Verification of cleanliness level ...................................................................... 46

7.5.1 General ............................................................................................ 46

7.5.2 Minimum surface area for test .......................................................... 46

7.5.3 Sample preparation .......................................................................... 46

7.5.4 Rinsing procedures .......................................................................... 47

8 Packaging and protection ........................................................................... 48

8.1 Approved coverings ....................................................................................... 48

8.2 Packaging operations .................................................................................... 48

8.3 Certification labels ......................................................................................... 48

9 Deliverables ................................................................................................. 50

10 Test procedures ......................................................................................... 51

10.1 Test liquid-flush procedure (solvent) .............................................................. 51

10.2 Gas flow test procedure ................................................................................. 51

11 Sampling and analytical practices ........................................................... 52

11.1 Cleanliness level test methods....................................................................... 52

11.1.1 General ............................................................................................ 52

11.1.2 Method I “Liquid Flush Test” ............................................................. 52

11.1.3 Method II “Liquid Flow Test” ............................................................. 53

11.1.4 Method III “Gas Flow Test” ............................................................... 53

11.1.5 Method IV “Liquid flow test under operating conditions” ................... 53

12 Determination of particle population and NVR analysis ........................ 55

12.1 Microscopic particle population ...................................................................... 55

12.2 Gravimetric NVR analysis method ................................................................. 56

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Annex A (normative) Cleanliness Requirements Analysis (CRA) for
spacecraft propulsion components, subsystems and systems - DRD . 57
Annex B (normative) Cleaning Technique Selection (CTS) for spacecraft
propulsion components, subsystems and systems - DRD .................... 59
Annex C (normative) Cleanliness Certificate (CC) for spacecraft
propulsion components, subsystems and systems - DRD .................... 61

Annex D (normative) Typical test and cleaning liquids............................... 64

Annex E (informative) Pre-cleaning sequences ........................................... 67

Annex F (informative) Cleanliness certificate .............................................. 69

Bibliography .................................................................................................... 71

Figures

Figure F-1 : Example of a cleanliness certificate.......................................................... 70

Tables

Table 4-1: Cleanliness classes .................................................................................... 24

Table 4-2: NVR contamination levels ........................................................................... 25

Table 4-3: Visible contamination levels ........................................................................ 27

Table 7-1: Packaging materials ................................................................................... 46

Table D-1 : Typical test and cleaning fluids ................................................................. 64

Table E-1 : Typical pre-cleaning sequence for common materials ............................... 67

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oSIST prEN 16603-35-06:2021
prEN 16603-35-06:2021 (E)
European Foreword
This document (prEN 16603-35-06:2021) has been prepared by Technical
Committee CEN/CLC/TC 5 “Space”, the secretariat of which is held by DIN
(Germany).
This document (prEN 16603-35-06:2021) originates from ECSS-E-ST-35-06C
Rev.2.
This document is currently submitted to the ENQUIRY.
This document will supersede EN 16603-35-06:2014.
The main changes with respect to EN 16603-35-06:2014 are listed below:
• Implementation of Change Requests received to the ECSS equivalent standard
• Addition of the Nomenclature in clause 3.5
• Definition of “accuracy” deleted in 3.2 and reference to ECSS-S-ST-00-01 made
in 3.1
• Definition “condensable hydrocarbon” and “dewar” deleted in clause 3.2 as
they were not used in the standard
• Added requirements 6.4.3d; 12.1b; 12.1c.
• Modifed requirements: 4.1h Note 2 (reference to Figure of other ECSS

Standard corrected); 6.2.6.2a; 6.4.3a; 6.4.3c; 12.1a; 12.2c Note to item 10 moved

to the end of the requirement.
• Interleaved Notes in requirement 12.1a move to the end of the requirement
• Cross-reference in Annex B.1.1 to added requirement 6.4.3d created
• Caption of Table in Annex D corrected from “Table A-1” to “Table D-1”.
This document has been developed to cover specifically space systems and will
therefore have precedence over any EN covering the same scope but with a wider
do-main of applicability (e.g. : aerospace).
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oSIST prEN 16603-35-06:2021
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Scope

ECSS-E-ST-35-06 belongs to the Propulsion field of the mechanical discipline, and

concerns itself with the cleanliness of propulsion components, sub-systems and
systems
The standard
 defines design requirements which allow for cleaning of propulsion
components sub-systems and systems and which avoid generation or
unwanted collection of contamination,
 identifies cleanliness requirements (e.g. which particle / impurity / wetness
level can be tolerated),
 defines requirements on cleaning to comply with the cleanliness level
requirements, and the requirements on verification,
 identifies the cleanliness approach, cleaning requirements, (e.g. what
needs to be done to ensure the tolerable level is not exceeded, compatibility
requirements),
 identifies, specifies and defines the requirements regarding conditions
under which cleaning or cleanliness verification takes place (e.g.
compatibility, check after environmental test).
The standard is applicable to the most commonly used propulsion systems and
their related storable propellant combinations: Hydrazine (N2H4), Mono Methyl
Hydrazine (CH3N2H3), MON (Mixed Oxides of Nitrogen), Nitrogen (N2), Helium
(He), Propane (C3H8), Butane (C4H10) and Xenon (Xe).
This standard is the basis for the European spacecraft and spacecraft propulsion

industry to define, achieve and verify the required cleanliness levels in spacecraft

propulsion systems.
This standard is particularly applicable to spacecraft propulsion as used for
satellites and (manned) spacecraft and any of such projects including its ground
support equipment.

External cleanliness requirements, e.g. outside of tanks, piping and aspects such

as fungus and outgassing are covered by ECSS-Q-ST-70-01.

This standard may be tailored for the specific characteristic and constraints of a

space project in conformance with ECSS-S-ST-00.
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oSIST prEN 16603-35-06:2021
prEN 16603-35-06:2021 (E)
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 revisions 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 most 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 ECSS-S-ST-00-01 ECSS system — Glossary of terms
EN 16603-35 ECSS-E-ST-35 Space engineering — Propulsion general
requirements
EN 16602-40 ECSS-Q-ST-40 Space product assurance — Safety
EN 16602-70-01 ECSS-Q-ST-70-01 Space product assurance — Cleanliness and
contamination control.
EN 16602-70 ECSS-Q-ST-70 Space product assurance — Materials, mechanical
parts and processes
ISO 2210:1972 Liquid halogenated hydrocarbons for industrial use-
Determination of residue on evaporation
ISO 5789:1979 Fluorinated hydrocarbons for industrial use —
Determination of non-volatile residue
ISO 5884:1978 Aerospace — Fluid systems and components —
Methods for system sampling and measuring the
solid particle contamination of hydraulic fluids
ISO 14951-3:2000 Space systems —Fluid characteristics —Part 3:
Nitrogen
ISO 14951-4:2000 Space systems — Fluid characteristics —Part 4:
Helium
ISO 14951-10:2000 Space systems — Fluid characteristics —Part 10:
Water
ISO 14952-3:2003 Space systems — Surface cleanliness of fluid systems
— Part 3: Analytical procedures for the
determination of non-volatile residues and
particulate contamination
ASTM D257(99) 2005 Standard Test Method for DC Resistance or
Conductance of Insulating Materials
ASTM D329 10 Dec Standard specification for Acetone
2002
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EN reference Reference in text Title
ASTM D740 Standard specification for Methyl Ethyl Ketone
15 May 2005
ASTM D770-05 Standard specification for Isopropyl Alcohol
15 May 2005
ASTM D1152 Standard specification for Methanol (Methyl
1 Apr 2006 Alcohol)
ASTM D1293 10 Dec Standard test methods for pH of water
1999
ASTM D4376 Standard specification for vapor-degreasing grade
Perchloroethylene
MIL-PRF-27415B Performance specification, propellant pressurizing
8 Feb 2007 agent, Argon
O-E-760D Federal specification
28 May 1987
SEMI C47-0699 Guideline for Trans 1,2 Dichloroethylene
May 1999
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oSIST prEN 16603-35-06:2021
prEN 16603-35-06:2021 (E)
Terms, definitions and abbreviated terms
3.1 Terms from other standards
a. For the purpose of this Standard, the terms and definitions from ECSS-S-
ST-00-01 apply, in particular for the following term:
1. accuracy
b. For the purpose of this Standard, the terms and definitions from ECSS-E-
ST-35 apply.
3.2 Terms specific to the present standard
3.2.1 blank

result for an analytical sample of the virgin test fluid prior to use in performing

a cleanliness verification test
3.2.2 cleanliness verification

activity intended to verify that the actual cleanliness conditions of an item are in

conformance with the applicable specification
3.2.3 crazing
creating microvoids in glassy thermoplastic polymers preceding the formation of
cracks
3.2.4 critical surface
any surface of an item that contacts the service medium
NOTE Examples of service media are propellants and
pressurants.
3.2.5 dew point
temperature at which condensation of water vapour takes place at prevailing
pressure
NOTE The prevailing pressure is usually atmospheric
pressure.
3.2.6 fibre
flexible structure having a length-to-width ratio of 10 to 1 or greater
NOTE 1 A fibre is considered to be a particle, see clause
3.2.11.
NOTE 2 The size of a fibre is its maximum length.
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3.2.7 field cleaning
processes of pre-cleaning and precision cleaning of components, subsystems and
systems which cannot be processed in a controlled environment such as a clean
room
3.2.8 generally clean
free from manufacturing residue, dirt, oil, grease, processing debris, or other
extraneous contamination based on visual examination
3.2.9 high-efficiency particulate air filter
filter that is at least 99,97 % efficient by volume on 0,3 μm particles
3.2.10 non-volatile residue
soluble or suspended material and insoluble particulate matter remaining after
temperature-controlled evaporation of a volatile liquid
NOTE See also clause 6.2.4.3
3.2.11 particle
unit of solid matter with observable size
NOTE 1 Various methods for defining its size may be
used and are dependant upon the measurement
technique.
NOTE 2 For the manual method the apparent maximum
linear dimension of a particle in the plane of
observation as observed with instruments such
as optical, electron, or atomic force microscopes
is the particle size.
NOTE 3 For the automatic method, the equivalent
diameter of a particle detected by automatic
instrumentation is the particle size.
NOTE 4 The equivalent diameter is the diameter of a
reference sphere having known properties and
producing the same response in the sensing
instrument as the particle being measured.
NOTE 5 A fibre is considered a particle, see clause 3.2.6.
3.2.12 passivation
process by which a corrosion-resistant layer is formed on a metal surface by
submersing the surface in an acid solution
3.2.13 pickling
chemical or electrochemical process by which surface oxides are removed from
metals
3.2.14 precision cleaning
cleaning process used to achieve cleanliness levels more stringent than visibly
clean
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3.2.15 pre-cleaning
cleaning process normally used to achieve the visibly clean cleanliness level
3.2.16 reversion
decrease in viscosity, strength, or in rubber modulus due to heating or
overworking, resulting in a tacky and soft material
3.2.17 silting
accumulation of particles of sufficient quantity to cause a haze or obscuring of
any portion of a filter membrane when viewed visually or under 40-power
maximum magnification
3.2.18 test fluid
specified fluid that is utilized to determine the fluid system wetted-surface
cleanliness level
3.2.19 threshold limit value
maximum average daily dosage, based on an 8-h day, 5-day week, to which an
average worker may be exposed to hazardous chemicals without harmful effect
NOTE 1 The TLV is a time-weighted average
concentration.
NOTE 2 The TLV is normally expressed in parts of the
gas or vapour in micro litres per litre.
3.2.20 visibly clean
absence of surface contamination when examined with a specific light source,
angle of incidence, and viewing distance using normal or magnified vision up to
×20
3.2.21 visibly clean plus ultraviolet

cleaning level that is visibly clean and also meets the requirements for inspection

with the aid of an ultraviolet light of wavelength 250 nm to 395 nm
3.2.22 volatile hydrocarbon
hydrocarbon capable of going from liquid or solid to a gaseous state at ambient
temperature and pressure
3.3 Abbreviated terms
For the purpose of this Standard, the abbreviated terms from ECSS-S-ST-00-01
and the following apply:
Abbreviation Meaning
CC cleanliness certificate
CRA cleaning requirement analysis
CTS cleaning technique selection
GC generally clean
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HEPA high-efficiency particulate air filter
HFE hydro fluor ether (Per fluoro-n-butyl methyl ether)
IPA isopropanol
MAIT manufacturing, assembly, integration and test
MEK methyl ethyl keton
MS mass spectroscopy
NVR non-volatile residue
ppmv parts per million, volumetric
TLV threshold limit value
US ultra sonic
VC visibly clean
VC + UV visibly clean plus ultraviolet
3.4 Symbols
Symbol
Meaning
dp mean pore diameter of a filter
3.5 Nomenclature
The following nomenclature applies throughout this document:
c. The word “shall” is used in this Standard to express requirements. All the
requirements are expressed with the word “shall”.
d. The word “should” is used in this Standard to express recommendations.
All the recommendations are expressed with the word “should”.
NOTE It is expected that, during tailoring,
recommendations in this document are either
converted into requirements or tailored out.
e. The words “may” and “need not” are used in this Standard to express
positive and negative permissions, respectively. All the positive
permissions are expressed with the word “may”. All the negative
permissions are expressed with the words “need not”.
f. The word “can” is used in this Standard to express capabilities or
possibilities, and therefore, if not accompanied by one of the previous
words, it implies descriptive text.
NOTE In ECSS “may” and “can” have completely
different meanings: “may” is normative
(permission), and “can” is descriptive.
g. The present and past tenses are used in this Standard to express statements
of fact, and therefore they imply descriptive text.
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Cleanliness requirements
4.1 General
a. This standard shall only apply to propulsion systems using Hydrazines,
MON, Propane, Butane, Nitrogen, Helium, Xenon as propellants.
b. Cleanliness assurance precautions and features shall be specified and
incorporated in the hardware at the design phase.
NOTE In propulsion systems cleanliness is a major
requirement to avoid loss of function and
performance.
c. Cleanliness verification shall be applied at progressive MAIT stages
...