Space engineering

Mechanisms

Foreword

This Standard is one of the series of ECSS Standards intended to be applied together for the management, engineering and product assurance in space projects and applications. 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. Requirements in this Standard 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.

This Standard has been prepared by the ECSS-E-ST-33-01C Rev.1 Working Group, reviewed by the ECSS Executive Secretariat and approved by the ECSS Technical Authority.

Disclaimer

ECSS does not provide any warranty whatsoever, whether expressed, implied, or statutory, including, but not limited to, any warranty of merchantability or fitness for a particular purpose or any warranty that the contents of the item are error-free. In no respect shall ECSS incur any liability for any damages, including, but not limited to, direct, indirect, special, or consequential damages arising out of, resulting from, or in any way connected to the use of this Standard, whether or not based upon warranty, business agreement, tort, or otherwise; whether or not injury was sustained by persons or property or otherwise; and whether or not loss was sustained from, or arose out of, the results of, the item, or any services that may be provided by ECSS.

Published by:     ESA Requirements and Standards Division
    ESTEC, P.O. Box 299,
    2200 AG Noordwijk
    The Netherlands
Copyright:     2017 © by the European Space Agency for the members of ECSS

Change log

ECSS-E-30 Part 3A	First issue
ECSS-E-ST-33-01B	Never issued
ECSS-E-ST-33-01C 6 March 2009	Second issue The following is a summary of changes between ECSS-E-30 Part 3A and the present issue: Complete review, restructuring and rewording of standard to be in line with ECSS drafting rules and formatting Addition of DRDs Deletion of the Tailoring information formerly contained in Annex A Harmonization of the standard with other ECSS standards Review and update of cross-references to other ECSS standards
ECSS-E-ST-33-01C Rev.1 15 February 2017	Second issue, Revision 1 Major changes of this version with regard to the previous version are: Implementation of Change Requests Addition of two new DRDs for "Safety critical mechanisms verification plan (MSVP) and "Safety critical mechanisms verification report (MSVR)" Implementation of editorial corrections to align this standard to the ECSS drafting rules Added requirements: 4.7.5.2.3b, 4.7.5.2.6f-i, 4.7.5.3.2i, 4.7.5.3.3a-b and Table 4-3, 4.7.5.4.2c-d, 4.7.5.4.5i, 4.7.5.4.6d, 4.7.5.4.10d, 4.7.7.2c-d, 4.7.8.5d-l, 4.8.3.3.5c, 4.8.3.3.9e, 4.8.3.3.14f, Table 4-6, Table 4-7, 4.8.3.4.3b-d (moved from clauses 4.7.8.6-4.7.8.11), 4.10d, Annex F.2.1<1>to <5> (added DRD), Annex G.2.1<1> to <5> (added DRD). Modified requirements: 4.2.4.2c NOTE, 4.2.5.1a, b and e, 4.2.5.2f, 4.4.2b NOTE added, 4.5.2.3 NOTE deleted, 4.5.2.7a, 4.5.3e, 4.7.3.4.1a, 4.7.3.4.2e-f, 4.7.4.2c, 4.7.4.3a, 4.7.5.2.3a, 4.7.5.2.6b, 4.7.5.3.1a-f, Table 4-2, 4.7.5.3.2b-e and h, 4.7.5.4.4f, 4.7.5.4.5g, 4.7.5.4.6a, 4.7.5.4.7a, 4.7.5.4.8a, 4.7.5.4.10c NOTE added, 4.7.7.2a, 4.7.7.7a, 4.7.8.2a-b, 4.8.1a NOTE2, 4.8.2.1c (embedded NOTES moved at the end of requirement), 4.8.2.4 NOTE2, 4.8.2.5a, 4.8.2.6.1a, 4.8.2.6.3a and d, 4.8.2.7a-b, 4.8.2.8a NOTE, 4.8.2.12a, 4.8.2.15a-b, 4.8.3.2.2a, 4.8.3.3.6a, 4.8.3.3.8a, 4.8.3.3.9a, 4.8.3.3.9c, 4.8.3.3.11 NOTE2 added, 4.8.3.3.11b, 4.8.3.3.14a, e NOTE, 4.8.3.3.16a, 4.8.3.3.17a, 4.8.3.4.1a, 4.8.3.4.3a, 4.10c NOTE2 deleted, A.2.1<5>a (embedded NOTE moved to end of requirement, A.2.1<6>a, A.2.1<7>b, C.2.1<1>b (embedded NOTE moved to end of requirement, D.2.1<5>a (hyphen added)D.2.1<7>a (brackets removed), D.2.1<8>a (hyphen added). Deleted requirements: 4.7.3.3.2b, Table 4-1, 4.7.5.2.5d-g, 4.7.5.3.2a, 4.7.5.4.5g (changed to new recommendation 4.7.5.4.5h), 4.7.7.3a-b, 4.7.8.4a, 4.7.8.6a (moved to 4.7.8.5d with informative change), 4.7.8.6b (moved unchanged to 4.7.8.5e), 4.7.8.7a (moved unchanged to 4.7.8.5f), 4.7.8.8a-b (moved unchanged to 4.7.8.5g-h), 4.7.8.9a-b (moved unchanged to 4.7.8.5i-j), 4.7.8.10a (moved modified to 4.7.8.5k), 4.7.8.11a, 4.8.2.14c, 4.8.3.3.9b and d. Editorial corrections: Clause 2 and 3 updated and Nomenclature added, 4.5.1, 4.6.1. Titles modified of clauses 4.7.3.4, 4.7.5.3, 4.7.5.3.2, 4.7.7.2, 4.8.3.3.9, 4.8.3.4.3. Titles added for all sub-clauses of 4.7.8. Table E-1 updated. Bibliography updated.

Introduction

This document has been established to provide mechanism engineering teams with a set of requirements, design rules and guidelines based on the state of the art knowledge and experience in the field of space mechanisms.

The use of this document helps mechanisms developers to establish generic mechanisms designs and to derive application specific requirements.

The main objectives are to achieve reliable operation of space mechanisms in orbit and to prevent anomalies during the development phase influencing schedule and cost efficiency of space programmes.

Scope

This Standard specifies the requirements applicable to the concept definition, design, analysis, development, production, test verification and in­orbit operation of space mechanisms on spacecraft and payloads in order to meet the mission performance requirements.

This version of the standard has not been produced with the objective to cover also the requirements for mechanisms on launchers. Applicability of the requirements contained in this current version of the standard to launcher mechanisms is a decision left to the individual launcher project.

Requirements in this Standard are defined in terms of what shall be accomplished, rather than in terms of how to organise 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. Complementary non-ECSS handbooks and guidelines exist to support mechanism design.

This standard may be tailored for the specific characteristic and constrains of a space project in conformance with ECSS-S-ST-00.

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.

ECSS-S-ST-00-01	ECSS system — Glossary of terms
ECSS-E-ST-10-02	Space engineering – Verification
ECSS-E-ST-20	Space engineering – Electrical and electronic
ECSS-E-ST-20-06	Space engineering – Spacecraft charging
ECSS-E-ST-20-07	Space engineering – Electromagnetic compatibility
ECSS-E-ST-31	Space engineering – Thermal control general requirements
ECSS-E-ST-32	Space engineering – Structural
ECSS-E-ST-32-01	Space engineering – Fracture control
ECSS-E-ST-32-10	Space engineering – Structural factors of safety for spaceflight hardware
ECSS-E-ST-33-11	Space engineering – Explosive systems and devices
ECSS-Q-ST-30	Space product assurance Dependability
ECSS-Q-ST-40	Space product assurance – Safety
ECSS-Q-ST-70	Space product assurance – material, mechanical part and process
ECSS-Q-ST-70-36	Space product assurance – Material selection for controlling stress corrosion cracking
ECSS-Q-ST-70-37	Space product assurance – Determination of the susceptibility of metals to stress corrosion cracking
ECSS-Q-ST-70-71	Space product assurance – Data for selection of space materials and processes
ISO 76 (2006)	Rolling bearings – Static load rating
ISO 128 (1996)	Technical drawings
ISO 677 (1976)	Straight bevel gears for general engineering and for heavy engineering – Basic rack
ISO 678 (1976)	Straight bevel gears for general engineering and for heavy engineering – Modules and diametral pitches
ISO 6336-1 (2006)	Calculation of the load capacity of spur and helical gears — Part 1: Basic principles, introduction and general influence factors
ISO 6336-2 (2006)	Calculation of the load capacity of spur and helical gears — Part 2: Calculation of surface durability (pitting)
ISO 6336-3 (2006)	Calculation of the load capacity of spur and helical gears — Part 3: Calculation of tooth bending strength

Terms, definitions and abbreviated terms

Terms from other standards

For the purpose of this Standard, the term and definition from ECSS-S-ST-00-01 apply, and in particular the following:
cleanliness
component
interface
product
For the purpose of this Standard, the term and definition from ECSS-S-ST-32-10 apply, and in particular the following:
fail-safe
model factor (KM)
project factor (KP)

Terms specific to the present standard

actuator
component that performs the moving function of a mechanism

• 1    An actuator can be either an electric motor, or any other mechanical (e.g. spring) or electric component or part providing the torque or force for the motion of the mechanism.
• 2    This term is defined in the present standard with a different meaning than in ECSS-S-ST-00-01. The term with the meaning defined herein is applicable only to the present standard.
  control system
  system (open or closed loop) which controls the relative motion of the mechanism

deliverable output torque (TL )
torque at the mechanism or actuator output

• 1    The deliverable output torque or force can be specified by the customer for an undefined purpose and not affect the actual performance of the mechanism.
• 2    For example: A theoretical torque or force of a robotic mechanism (service tool) for which no specific function except torque or force provision can be specified at an early stage in the project development.
  deliverable output force (FL)
  force at the mechanism or actuator output

elementary function
lowest level function

For example: One degree of freedom (rotation and translation), torque or force generation, sensing.

inertial resistance force (FD)
force to accelerate the mass

inertial resistance torque(TD)
torque to accelerate the inertia

fastener
item used to provide attachment of two or more separate parts, components or assemblies

For example: Fasteners have the function of locking the parts together and providing the structural load path between the parts or, if used as a securing part, to ensure proper locating of the parts to be secured.

flushing or purging
control of the mechanism environment by enclosing the mechanism in specific gaseous or fluid media which are surrounding, passing over or through the mechanism

latching or locking
intentional constraining of one or more previously unconstrained degrees of freedom which cannot be released without specific action

lubrication
use of specific material surface properties or an applied material between two contacting or moving surfaces in order to reduce friction, wear or adhesion

mechanism
assembly of parts that are linked together to enable a relative motion

off-loading
complete or partial unloading of a part or assembly from an initial pre-load

Off-loading is usually employed so as not to expose a mechanisms part or assembly to launch loads or other induced loads.

phase margin
indicator for the stability of dynamic control systems

positively locked
form-locked into a defined position from which release can only be obtained by application of a specific actuation force

positive indication of status
direct monitoring of the state of the primary function at the output level of the mechanism

primary function
high level function

For example: To hold, to release, to deploy, to track, and to point.

safety critical mechanism
mechanical product having a critical or catastrophic hazard potential

threaded fastener
fastener with a threaded portion

For example: Screws, bolts and studs.

tribology
discipline that deals with the design, friction, wear and lubrication of interacting surfaces in relative motion to each other

venting
compensation of the internal mechanism pressure environment with its surrounding pressure environment

For example: Use of dedicated venting holes or passages

Abbreviated terms

For the purpose of this Standard, the abbreviated terms from ECSS-S-ST-00-01 and the following apply:

Abbreviation	Meaning
A/D	analogue to digital
AC	alternating current
COG	centre of gravity
CVCM	collected volatile condensable material
D/A	digital to analogue
DC	direct current
DFMR	design for minimum risk
DLL	design limits loads
EMC	electromagnetic compatibility
ESD	electrostatic discharge
F	actuation force
FD	inertial resistance force
FL	deliverable output force
FMECA	failure mode effects and criticality analysis
Fmin	minimum actuator force required
FOS	factor of safety
FR	friction torque or force
GSE	ground support equipment
HA	harness and other torque or force resistances
HD	adhesion torque or force
HV	hardness Vickers
HY	hysteresis torque or force
I	inertia resistance (linear or angular)
I/F	Interface
LEO	low Earth orbit
M	mass
MAV	mechanism analytical verification
MDD	mechanism design description
MUM	mechanism user manual
MLI	multi­layer insulation
MOI	moment of inertia
MOS	margin of safety
MS	strength safety margin
MSVP	safety critical mechanisms verification plan
MSVR	safety critical mechanisms verification report
n.a.	not applicable
SMS	specific mechanism specification
RML	recovered mass loss
S	spring force
SI	international system of units
S/C	spacecraft
SMS	specific mechanism specification
T	actuation torque
TD	inertial resistance torque
TL	deliverable output torque
Tmin	minimum actuator torque required
TML	total mass loss
UV	ultraviolet
VCD	verification control document

Nomenclature

The following nomenclature applies throughout this document:

The word “shall” is used in this Standard to express requirements. All the requirements are expressed with the word “shall”.
The word “should” is used in this Standard to express recommendations. All the recommendations are expressed with the word “should”.

It is expected that, during tailoring, recommendations in this document are either converted into requirements or tailored out.

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”.
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.

In ECSS “may” and “can” have completely different meanings: “may” is normative (permission), and “can” is descriptive.

The present and past tenses are used in this Standard to express statements of fact, and therefore they imply descriptive text.

Requirements

Overview

This Standard addresses the requirements related to the generic aspects of the engineering steps for the various engineering disciplines involved in the achievement of the specified space mechanism performance.

The following requirements are identified considering interfaces and interactions of mechanisms with those disciplines: thermal control, structures, functional operations, materials and parts, pyrotechnics, propulsion, electrical and electronics, and servo­control interactions. Where interactions with other European space regulation are identified, reference is made to the related regulation.

General requirements

Overview

Requirements of clause 4.2 cover the interaction of mechanisms engineering with project management, processes, parts and components, product assurance, and the related requirements affecting the conceptual definition, design, sizing, analysis, development, and hardware production of mechanisms.

In view of the criticality of space mechanisms, which are often potential mission critical single point failures, particular attention is placed upon the reliability and redundancy of space mechanisms (see clause 4.2.5).

Mission specific requirements

A dedicated specific mechanism specification (SMS) shall be established in conformance with Annex A for each individual mechanism in a project, and agreed by the customer.

The SMS specification identifies all specific requirements for a specific mechanism in a project, that are not covered by the present standard.

Units

SI-units and associated symbols system shall be used.

Product characteristics

Marking and labelling

Specific identification

The identification of delivered pieces of hardware, parts, components, sub­assemblies and assemblies shall carry at least the equipment title.

• 1    For the identification of pieces of hardware, parts, components, sub­assemblies, and assemblies of the mechanism, see clause 5.3.1.5 of ECSS-M-ST-40.
• 2    The identification can be removable.
• 3    The identification number and the equipment title can be defined by the contracting authority.

Marking

Marking shall be applied on non-functional surfaces.
Bearings shall not be marked by the use of vibro­etch marks on the lateral faces of the bearing races.

Etched marks on the lateral faces of the bearing races affect the mounting tolerances of the bearing in the housing and the bearing’s tribological performance characteristics.

Parts and components

Existing parts and components used in mechanisms shall have been previously qualified for the intended application according to a qualification procedure approved by the customer.

Existing parts and components relate to parts and components that were not specifically developed for this specific application and cover commercially available and off-the-shelf hardware.

Existing parts and components used in mechanisms should have been previously qualified at part or component level.
Flight proven parts and components should be used.

For the selection of not-flight proven parts and components, see ECSS-Q-ST-60 for EEE components and ECSS-Q-ST-70 for materials and parts.

Interchangeability

All items having the same identification number shall be functionally and dimensionally interchangeable.

Maintainability

The mechanism should be designed to be maintenance free during storage and ground life.
If the design is not maintenance free, the maintenance requirements shall be documented in the SMS, justified, agreed by the customer.
If ground maintenance during storage or ground operation is not avoided, the maintenance procedures shall be provided.

Reliability and redundancy

Reliability

For all mechanisms, which are critical to mission success, conformance to the specified reliability figure shall be demonstrated according to the following methods:

• electronic components: by parts count as a minimum or other methods approved by the customer;
• mechanical parts: by stress analysis or other methods approved by the customer;
• mechanical limited­life: by life test approved by the customer. For non­critical mechanisms, conformance to the reliability figure shall be demonstrated by simplified methods or other methods accepted by the customer.
• 1    The methods to achieve by design, derive by analysis, and demonstrate by test the specified reliability figures are presented in ECSS-Q-ST-30.
• 2    An example of a simplified method is parts count.
  Failure of one part or element shall not result in consequential damage to the equipment or other spacecraft components.
  For structural reliability aspects ECSS-E-ST-32 shall apply.
  For safety critical mechanisms in a crewed space mission where structural failure can cause a catastrophic hazardous event, fasteners and load carrying paths within mechanisms shall be designed in conformance with fracture control requirements from ECSS-E-ST-32-01.

Definitions of catastrophic and critical hazardous events are provided in ECSS-Q-ST-40. Fracture control requirements are provided in ECSS-E-ST-32-01.

Redundancy

During the design of the mechanism, all single point failure modes shall be identified.
All single points of failure should be eliminated by redundant components.
If single points of failure cannot be avoided, they shall be justified by the supplier and approved by the customer.
Redundancy concepts shall be agreed by the customer.

Redundancy concepts are selected to minimize the number of single points of failure and to conform to the reliability requirements.

Where a single point failure mode is identified and redundancy is not provided, compliance with the reliability, availability and maintainability requirements specified in ECSS-Q-ST-30 shall be demonstrated.
Unless redundancy is achieved by the provision of a complete redundant mechanism, active parts of mechanisms, such as sensors, motor windings, brushes, actuators, switches and electronics, shall be redundant.
Failure of one element or part shall not prevent the other redundant element or part from performing its intended function, nor the mechanism from meeting its performance requirements specified in the specific mechanism specification.

High-reliability of a mechanism can be incorporated in a design by including component redundancy or high design margins. The aim is to deliver a design which is single failure tolerant.

Flushing and purging

If operating the mechanism in air is detrimental to the performance of the mechanism over its complete mission, means for flushing the critical parts with an inert clean dry gas shall be provided.

Example of detrimental cause to operate the mechanism in air is the presence of moisture or other deleterious contamination.

Only lubricants qualified in respect to the residual humidity of the dry gas shall be used.

Mission and environments

The mechanism engineering shall consider every mission phase identified for the specific space programme and conform to the related mission requirements and environmental constraints.

The mission starts with on­ground life of the mechanisms after assembly and is completed at the end of operational life of the space system.

Functional

System performance

The mechanism functional performance shall conform to the system performance requirements.

Mechanism function

The kinematic requirements applicable to each position change shall be specified.

For example, position over time, velocity and acceleration.

Mechanical interface, position accuracy or velocity tolerances shall be specified and verified that they conform to the functional needs.

Mechanical interfaces include assembly and test rigging and other installation and integration conditions.

The envelope of movement for each moving part shall be defined.
The movement of each part shall ensure that there is no mechanical interference with any other part of the mechanism, the spacecraft, the payload or the launcher.

Constraints

Overview

Requirements of clause 4.5 cover the constraints to which mechanisms are designed, manufactured and operated.

For the physical constraints, it is important to ensure that the requirements for climatic protection and for sterilization are defined in the SMS, as identified in A.2.1<4>.

Materials

Material selection

Materials shall be selected in conformance with ECSS-Q-ST-70 clause 5, or be verified that they conform to requirements, approved by the customer.

• 1    For general requirements on materials used for space mechanisms, see ECSS-E-ST-32-08. The material requirements in 4.5.2.2 to 4.5.2.7 are specific to mechanisms.
• 2    For selection of materials, see ECSS-Q-ST-70-71.
• 3    For additional requirements relating to tribology, see clause 4.7.3.

Corrosion

For corrosion, ECSS-Q-ST-70-71 clause “Chemical (corrosion)” shall apply.

Dissimilar metals

For dissimilar metals, ECSS-Q-ST-70 clause 5.1.12 “Galvanic compatibility” shall apply.
Materials treatments to prevent galvanic and electrolytic corrosion shall be approved by the customer.

Stress corrosion cracking

Materials shall be selected as specified in ECSS-Q-ST-70-36.
Materials with unknown characteristics shall be tested in conformance with ECSS-Q-ST-70-37.
ECSS-Q-ST-70-71 clause “Stress corrosion resistance” shall apply.

Fungus protection

For fungus protection, ECSS-Q-ST-70-71 clause “Bacterial and fungus growth” shall apply.

Flammable, toxic and unstable materials

For flammable materials, ECSS-Q-ST-70-71 clause “Flammability” shall apply.
For toxic materials, ECSS-Q-ST-70-71 clause “Offgassing and toxicity” shall apply.
In manned space systems, flammable, toxic and unstable materials shall not be used.

Induced emissions (stray light protection)

Materials and their coatings shall be selected to conform to the requirements of induced emissions.

An example of induced emission is stray light.

Radiation

The exposure to radiation shall not degrade the functional performance of the mechanism below the minimum functional performances specified in the SMS, over the complete mission.
ECSS-Q-ST-70-71 clause “Radiation” shall apply.

Atomic oxygen

The exposure to atomic oxygen shall not degrade the functional performance of the mechanism below the minimum functional performances specified in the SMS, over the complete mission.
ECSS-Q-ST-70-71 clause “Atomic oxygen” shall apply.

Fluid compatibility

For fluid compatibility, ECSS-Q-ST-70-71 clause “Fluid compatibility” shall apply.

Operational constraints

The mechanism should not impose any operational constraints on the spacecraft and mission.
If operational constraints are imposed by the mechanism, they shall be identified, justified and approved by the customer.
All operational constraints shall be documented in the mechanism user manual.

For the contents of the user manual, see Annex D.

Mechanisms moving with limited oscillatory travel shall be identified.
All oscillatory rolling parts should be exercised over a complete revolution at regular intervals, according to an operational procedure agreed by the customer.

Examples of oscillatory rolling parts are: ball bearing and nuts.

Operational procedures to exercise the mechanism beyond the oscillatory travel range shall be defined.

Interfaces

Overview

Requirements of clause 4.6 cover the interfaces of mechanisms on spacecraft and payload. Most of the interfaces requirements are application specific, and therefore are covered by the SMS, as identified in A.2.1<5>.

Thermo-mechanical interfaces

Thermo­mechanical interfaces shall be designed to take into account the stresses induced by the structure between the mechanism and its I/F attachment points.

Design requirements

Overview

This clause covers general design, tribology, thermal control, mechanical design and sizing, pyrotechnics, electric and electronics, and control engineering.

The requirements for tribology (see clause 4.7.3) cover the tribological related issues of mechanisms on the spacecraft and payload. The tribology of surfaces that separate or move relative to one another play a key function in the conceptual definition, design, analysis, test verification, launch, and in-orbit performance of the mechanisms.

The thermal requirements (see clause 4.7.4) cover the interaction of mechanisms engineering with thermal control and its related requirements affecting mechanisms engineering. General thermal control requirements are covered in ECSS-E-ST-31.

The requirements for mechanical design and sizing (see clause 4.7.5) cover the overall conceptual design, the mechanical sizing of parts, components and assemblies, and the detailed design definition of mechanisms. General structural requirements, including design loads (for example, pyrotechnical shock), are covered in ECSS-E-ST-32.

The requirements for electrical and electronics (see clause 4.7.7) cover the interaction of mechanisms engineering with electrical and electronic engineering and its related requirements affecting mechanisms engineering. General requirements for electrical and electronic are covered in ECSS-E-ST-20. If no electrical or electronic provisions are applied on the mechanism, the applicability of ECSS-E-ST-20 is limited to the potential compatibility requirements of mechanical systems with electrical and electronic systems.

General design

The mechanism design shall be compatible with operation on ground in ambient and thermal vacuum conditions.

Tribology

General

Mechanisms shall be designed with a lubrication function between surfaces in relative motion in order to ensure they conform to the mechanism performance requirements specified in the specific mechanism specification, throughout the specified lifetime.

The lubrication function aims to provide the motorization margins and minimize wear.

Mechanisms shall use only lubricants or lubricating surfaces qualified for the mission.

• 1    For example, environment, lifetime, contact pressure, temperature, number of cycles, minimum and maximum velocity of surfaces in relative motion.
• 2    For space environment, see ECSS-E-ST-10-04.
• 3    Vacuum is one of the main concerns regarding lubrication.
  It shall be verified that the degradation of the lubricant in the on-ground and in-orbit environments does not lead to a mechanism performance degradation below the limits specified in the SMS.

Examples of such degradation are friction, wear and lubricant performance variability.

The use of sliding surfaces shall be avoided.
If requirement 4.7.3.1d cannot be met, sliding surfaces are used one of the surfaces shall be hard and the other shall be lubricated or shall be composed of a self-lubricating material.

Example of self-lubricating material: polyimide resins.

Metal to metal tribological contacts should be composed of dissimilar materials, in conformance with 4.5.2.3.
Metal to metal tribological sliding contacts shall be composed of dissimilar materials in conformance with 4.5.2.3.
Prior to the application of lubricant and in order to facilitate adhesion or wetting of lubricant on the substrate surface, the surfaces shall be cleaned in conformance with a procedure approved by the customer.
The cleaning of the surfaces prior to lubricant application shall not degrade the lubricating action.
The lubricant shall conform to the molecular and particulate contamination requirements specified for the entire mission.

For molecular and particulate contamination, see ECSS-Q-ST-70-01.

Dry lubrication

During the lubrication of mechanism tribological surfaces, samples of representative material, surface roughness, surface cleanliness and surface orientation shall be co­deposited in each process run with the flight components so that verification checks can be performed.
The thickness and adhesion of the lubricant on samples defined in requirement 4.7.3.2a shall be verified.
The dry lubricant application process shall be verified with respect to lubricant performance and repeatability.

Fluid lubrication

Amount of fluid lubricant

The quantity of lubricant used shall be determined.

This determination allows quantifying a surplus of lubricant at the end of the total lifetime of the mechanism.

The quantity of lubricant shall take into account outgassing, creep and other sources of absorption or degradation.
The effect of exposure to on­ground storage and related gravity effects, and other ground or in­orbit accelerations on lubricant distribution shall be validated.

Outgassing

The outgassing rate of fluid lubricants shall be measured by a screening test approved by the customer.

See ECSS-Q-ST-70-02.

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Anti­creep barriers

Anti­creep barriers shall be used to avoid migration of fluid lubricants to the external sensitive equipment agreed by the customer.

It is also important to use the anti-creep barriers for sensitive equipment within the mechanism.

Anti-creep barriers shall be used when migration of fluids lubricants causes a change of the lubricant amount on the parts to be lubricated resulting in mechanism performance degradation below the limits specified in the SMS.
The integrity of the anti­creep barrier shall be verifiable by indicators.

For example, UV­detectable.

Tribological contacts

Life

The life of tribological contacts shall be verified under worst case ground and flight conditions.

Bearing pre­loading

Ball bearings shall be pre­loaded with a load calculated in order to withstand the mechanical environment during launch and throughout the mission.
The calculation specified in requirement 4.7.3.4.2a shall be made available to the customer.
Pre­loading should be applied by solid pre­load or flexible pre-load produced by loading techniques without sliding at the bearing mounting interfaces.
If pre­loading is not applied by 4.7.3.4.2c solutions, sliding shall be facilitated by a lubricated sliding sleeve, bush or dedicated tribological coating.
If bearing gapping occurs during vibration, adequacy of lubricant and potential consequential mechanisms damage or degradation due to the relative motion of the bearing parts shall be demonstrated to conform to the specified functional performance and lifetime.
Any set pre­load at sub-assembly level shall be measured.
Bearing preload should be measured after final mechanism assembly.
If bearing preload is not measured after final mechanism assembly, it shall be assessed by means of measurements approved by the customer.
If bearing preload can be affected by the running­in process, the preload shall be confirmed after running­in.

Mechanical cables

Mechanical cables under friction used on moving parts or assemblies shall be lubricated in conformance with 4.7.3.1, 4.7.3.2 and 4.7.3.3.

Thermal control

Thermal engineering

The mechanism engineering shall conform to the thermal engineering requirements specified by the customer.

For thermal control, see ECSS-E-ST-31.

Mechanisms thermal design and sizing

The thermal design of the mechanism shall ensure that all components are maintained within their qualification temperature range under all specified ground, test, launch and in­orbit conditions throughout the lifetime of the mechanism.
The mechanism shall be compatible with on­ground thermal vacuum testing representative of in­orbit thermal conditions.
The temperature margins defined in ECSS-E-ST-31 clause 3.2 shall be applied.
Unless the use of active thermal control is previously agreed with the customer, thermal control shall be passive.
The mechanism design shall take into account the worst-case combinations (including uncertainties) of:

• extremes of operational and survival steady­state,
• transient temperatures,
• mechanism heat dissipation, and
• the temperature gradients across the mechanism.

Failure to consider the effects of differential expansion can lead to a catastrophic failure.

Multi­layer insulation (MLI)

When using MLI, supported at discrete positions at the distance of not more than 100 mm, the following shall be provided:

• between any mechanisms parts and MLI hardware a minimum clearance of 20 mm in out­of­plane direction to the MLI,
• between MLI protected moving parts and other MLI hardware a minimum clearance of 35 mm in out­of­plane direction to the MLI.

Clearance is relative to moving parts of mechanisms or on spacecraft structure close to its moving paths.

For other design solutions, it shall be verified that clearances with margins, agreed by the customer, are maintained throughout the mission.

Example of such design solutions are MLI not supported at discrete positions or MLI supported at discrete positions which are more than 100 mm apart.

The MLI clearance assessment shall take into account the dynamic envelopes of the MLI during vibration exposure and venting or purging or in orbit environment.

For example, spin.

Mechanical design and sizing

General

Mechanisms shall be designed to meet the mechanical performance requirements and to withstand the specified environment during handling, transportation, testing, storage, launch and operation in orbit for the specified lifetime.

Structural dimensioning

General

Mechanisms in their different configurations shall conform to the specified stiffness, strength and safety requirements derived from the launcher and the spacecraft structural requirements.

Loads

The load general requirements of ECSS-E-ST-32, shall apply in­orbit loads.
The operational loads shall be added to the in­orbit loads.

Operational loads are the loads generated by the mechanism during operation, including thermoelastic effects.

The operational loads of the mechanisms shall be derived according to the functional dimensioning requirements based on dynamic performance analyses or test measurements in worst-case conditions.
For the derivation of the operational loads, the related induced reaction of the spacecraft shall be taken into account.

Limit loads

The worst-case condition requirements of ECSS-E-ST-32 clause 4.2.7 shall apply with the modifications as per requirement 4.7.5.2.3b to 4.7.5.2.6.
For cases where a statistical distribution of the loads cannot be demonstrated, the limit loads shall be defined based on the worst-case conditions.

Examples of cases where a statistical distribution of the loads cannot be demonstrated are mechanisms operating loads.

Material allowables

For the allowable A-values of materials, to be used for structural sizing, see ECSS-E-ST-32, clause 4.5.

For metallic materials, A-values data can be found in the latest version of the document: Metallic Material Properties Development and Standardisation (MMPDS).

Margin of safety (MOS)

For structural margin of safety requirements, ECSS-E-ST-32 shall apply.
Mechanisms shall be designed with a positive margin of safety against yielding and against ultimate under all environmental and operational load conditions.
The actual stress or load shall be considered at their worst case qualification level.
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Factors of safety (FOS)

For the structural factors of safety, requirements of ECSS-E-ST-32-10 shall apply.
In the computation of safety margins the following minimum factors of safety shall be used for standard metallic materials:

• buckling factor of safety:                2 Fatigue verification shall take into account thermoelastic cycles over all lifetime.
  Factors of safety for other materials shall be approved by the customer on a case by case basis.
  The following specific factors of safety shall apply:
• For cables, stress factor of safety against rupture:         3
• For stops, shaft shoulders and recesses, against yield:        2 In the mechanism requirement specification the Design Limit Loads (DLL) shall be specified.
• 1    It is good practice to clarify with the customer that the Project factor (KP) and the Model factor (KM) are already included, to avoid duplication of factors.
• 2    DLL are intended to be environmental loads.
  In case the verification of fatigue by test is needed, the factor 4 shall apply to the quantity of fatigue cycle on the mechanism part that is susceptible to fatigue.
• 1    Mechanism parts are considered susceptible to fatigue if it cannot be demonstrated infinite life by analysis.
• 2    No fatigue test is needed if the analysis demonstrate the factor minimum of 8.
  For safety critical mechanisms in crewed space missions, the factors of safety shall apply for all loading conditions, including those after credible mechanism failures.
  For safety critical mechanisms in crewed space missions, verification by an analysis-only approach shall be approved by the safety approval authority.

Functional dimensioning

Motorization factors

Actuators shall be sized to provide throughout the operational lifetime and over the full range of travel actuation torques or forces in conformance with 4.7.5.3.1d or 4.7.5.3.1e.

• 1    Example of actuators are electrical, mechanical and thermal.
• 2    Torque or force contributors providing helping torques or forces are treated as motorization.
  To derive the factored worst-case resistive torques or forces, each contributors, considering all mission phases worst-case conditions , shall be multiplied by the applicable minimum uncertainty factor specified in Table 42.
• 1    Example of such environmental effects over the life are vacuum, temperature, and zero G.
• 2    The resistive contributors due to Magnetic effects are all but those coming from the internal design of an electrical motor (e.g. motor detent torque).
• 3    Increased factors are typically applied to take into account effects that cannot be measured by test.
  TableTable 42: Minimum uncertainty factors for actuation function

Resistive torque or force contributors	Symbol	Theoretical Factor	Measured Factor
Inertia	I	1,1	1,1
Spring	S	1,2	1,1
Magnetic effects	HM	1,5	1,1
Friction	FR	3	1,5
Hysteresis	HY	3	1,5
Others (e.g. Harness)	HA	3	1,5
Adhesion	HD	3	3

The theoretical uncertainty factors in Table 42 may be reduced to the measured factors, provided that the worst-case resistive contributors are based on measurements, according to a test procedure approved by the customer.
The minimum actuation torque (Tmin) shall be derived by the equation:
where:

I is the resistive inertial torque applied to a mechanism subjected to acceleration in an inertial frame of reference (e.g. spinning spacecraft, payload or other).

TD is the inertial resistance torque caused by the worst-case acceleration function specified by the customer at the mechanism level.

TL is the deliverable output torque, when specified by the customer.

The minimum actuation force (Fmin) shall be derived by the equation:
where:

I is the resistive inertial force applied to a mechanism subjected to acceleration in an inertial frame of reference (e.g. spinning spacecraft, payload or other).

FD is the inertial resistance force caused by the worst-case acceleration function specified by the customer at the mechanism level.

FL is the deliverable output force, when specified by the customer.

• 1    Margins against any dynamic coupling between the mechanism and its payload are not covered by the above formulae, and they are addressed on a case by case basis when appropriate.
• 2    The inertial resistance torque (TD) or force (FD)apply to mechanisms which have a specified acceleration requirement or for which an indirect acceleration requirement can be deduced from speed, time or other (dynamic) requirements.
• 3    When a function of the mechanism is to deliver output torques (TL) or forces (FL) for further actuation at higher level, the output torque or force is derived by the customer according to the torque or force requirements specified in 4.7.5.3.1d and 4.7.5.3.1e., taking into account the specified uncertainty factors on the individual resistive contributors and applying a motorization factor of two as presented as :
  where all resistive contributors in the two equations above are related to the customer specific actuation application.

The kinetic energy of the mechanism moving parts, and its effects, shall not be taken into account to meet the specified motorization factor.

Such effects are acceleration and deceleration force and torque of moving parts.

Actuation torque or force dimensioning (motorization)

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Torque T or force F shall be greater or equal than Tmin or Fmin respectively as calculated in the clause 4.7.5.3.1.
When the actuation torque or force is supplied by an electrically controlled device, the actuation torque or force supplied by this device shall be derived considering worst-case conditions.

• 1    Examples of such electrical devices are electromagnetic motor, piezo actuator, pneumatic, or smart materials.
• 2    Example of such worst case conditions are supplied voltage, current, and frequency.
  When the actuation torque or force is provided by inertia means, the actuation torque or force supplied by the inertia shall:
• be derived considering worst-case conditions defined and agreed by the customer.
• be multiplied by the maximum uncertainty factor of 0,9 and then comply with the equations in clause 4.7.5.3.1.
• 1    Inertia is calculated in the appropriate reference frame and according to the type of movement.
• 2    An example of inertia actuating torques or forces is deployment from a spinning spacecraft.
  When the actuation torque or force is supplied by a spring actuator, the actuation torque or force supplied by the spring, shall be:
• derived considering worst-case conditions,
• multiplied by the maximum uncertainty factor of 0,8 when ageing measurement are not available, and
• agreed with the customer when ageing measurement are performed. Spring actuators shall be redundant unless it is
• agreed by the customer,
• verified by analysis and test that the spring sizing and functional performance characteristics meet the specified reliability of the mission, and
• verified that a spring failure can not cause any catastrophic, critical or major hazardous event in conformance with ECSS-Q-ST-40, clause 6.4. Actuating torques or forces based on hysteresis, harness generated, or any item whose primary function is not to provide torques or forces, should not be used as a motorization source.
  If torques or forces are based on hysteresis, harness generated, or any item whose primary function is not to provide torques or forces are used as motorization sources, their use shall be:
• justified,
• agreed by the customer, and
• subject to the verification by analysis and test of the adequacy of the uncertainty factor with respect to the dispersion of the actuation torque or force. When the actuation torque or force is supplied by an electric motor the worst case torque or force generated by the motor shall be based on:
• measurement at operating conditions, or
• agreement with the customer if a measurement is not available.

Operating conditions include speed and duty cycle.

Holding torque or force dimensioning

For safety critical mechanisms in crewed space missions, the holding torque or force shall be sized to provide 2 times the torques or forces applied by operational or environmental design limit loads under worst case conditions and throughout the operational lifetime.

The holding function prevents motion and inadvertent operation of a mechanism by providing torque or force using powered or unpowered means.

For safety critical mechanisms in crewed space missions, minimum uncertainty factors for torque or force shall be applied in conformance with Table 43 according to the following rules:

• for torque or force contributors that help the holding function, divide the worst case value by the uncertainty factor;
• for torque of force contributors that prevents the holding function, multiply the worst case value by the uncertainty factor. TableTable 43:Minimum uncertainty factors for holding function

Torque of Force contributors	Theoretical Factor	Measured Factor
Inertia	1,1	1,1
Spring	1,2	1,1
Magnetic effects	1,5	1,1
Friction	3	1,5
Hysteresis	3	1,5
Others (Harness)	3	1,5
Adhesion	3	3

Other mechanical design and sizing requirements

Replaceable elements

Where parts or components are intended for possible replacement or re-installation, they shall be designed to ensure they can only be installed in the correct orientation and position.
Mechanisms using deformable elements shall be designed to ensure they can only be installed in the correct orientation and position.

Examples of such mechanisms are crush dampers.

The design of replaceable items shall inhibit the reuse in the mechanism or spacecraft in the un­refurbished state.

Status monitoring

Unless monitored at spacecraft system level, the design of mechanisms shall include means to monitor the execution of its main functions.
Mission critical mechanisms shall be designed in such way that monitoring information of its critical functions is accessible to the spacecraft telemetry.

For telemetry requirements, see ECSS-E-ST-70-11, clause 5.9.5

For crewed space missions, safety critical mechanisms shall provide positive indication of status.
For crewed space missions, electrical status indicators shall be failure tolerant.

Latching or locking

Latching mechanisms used to assure positive locking shall be designed to avoid inadvertent opening by vibration or shock occurring during the mission.
Unless agreed by the customer, locking or latching mechanisms shall provide an indication of whether the latch or lock is open or closed.
Electrically actuated deployable items shall use positive latching or locking.
The latch capture range shall ensure capture of the mechanism over the complete range of temperatures or temperature gradients and manufacturing and assembly tolerances.
The design shall not prevent subsequent successful latching if latching is not achieved on the initial completion of motion.
Latches shall be self locking.
Latches shall be resettable for ground testing.
Off-load mechanisms shall be capable of being operated manually.
Shock loads for latches and locks shall be derived by analysis or test, and specified in the mechanism requirements specification.

End stops

Mechanisms with restricted travel or rotation shall be provided with regular or emergency mechanical end stops to limit their motion and travel extremes to the maximum position specified in the SMS.
End stops shall be provided to prevent interference with interfacing equipment.

Regular end stops are provided for proper functioning of the actuated item.

The mechanical end stops and arresting mechanisms shall be designed to withstand without damage the maximum shock loads with the structural margins defined in clause 4.7.5.4.5.
The end stop sizing shall conform to the separable contact surfaces requirements specified in 4.7.5.4.5.
The end stop sizing shall take into account the worst-case loads, including the shock loads.
Contact with an end stop shall not result in a non­recoverable situation; nor performance or life degradation of the mechanism.

In case of specific application where this requirement is a main design driver, an alternative solution for emergency end stop can be adopted if agreed by the customer.

Electrical deployment indicators shall not be used as mechanical end stops.

Example of electrical deployment indicators are micro-switches.

The mating surfaces used in separable end stops shall be Ra <0,4 m.

Separable contact surfaces (other than gears, balls and journal bearings)

Except for gears and ball or journal bearings, separable contact surfaces shall be designed to maintain adhesion forces below the specified limits.
Except for gears and ball or journal bearings, the contact between the mating surfaces shall be characterized.

Characterisation includes surfaces roughness, hardness, material properties, and contact geometry.

Except for gears and ball or journal bearings, the repeatability of the contact between the mating surfaces shall be verified and agreed by the customer.

Repeatability includes contact loads, contact area, contact stress, and alignment.

Except for gears and ball or journal bearings, the peak hertzian contact stress shall be verified to be below 93 % of the yield limit of the weakest material.
Except for gears and ball or journal bearings, sliding at the separable contact surfaces before separation shall be prevented, in order to avoid potential contact surface property changes.
Except for gears and ball or journal bearings, the functional dimensioning of the actuator which separates the contact surfaces shall be

• sized in conformance with clause 4.7.5.3, and
• verified by test under representative environmental conditions to conform to clause 4.7.5.3. <<deleted>>
  Except for gears and ball or journal bearings, and unless one surface is a self­lubricating material, when metallic material mating or separating surfaces subject to relative motion are used, they should
• have a minimum hardness of 500 HV, and
• either:
  • be composed of dissimilar material, or
  • at least one of the two surfaces have a dissimilar coating.
• 1    Example of self-lubricating material is bronze.
• 2    Examples of dissimilar coatings are nitride, carbide or oxide.
• 3    The use of bonded or sputtered MoS2 or polymeric materials is not excluded.
• 4    The use of any dissimilar materials with a minimum hardness of 500 HV is often not sufficient to prevent cold welding.
  In case recommendation 4.7.5.4.5h is not met, justification shall be provided and approved by the customer.

Ball bearings

Ball bearings made of hardened steel shall be sized with respect to the maximum allowable peak hertzian contact stress.

Commonly used values for allowable peak hertzian contact stress can be found in ISO 76.

The sizing of ball bearings made of materials other than hardened steel shall be agreed by the customer.
Ball bearings should be shielded.
For the evaluation of the peak hertzian contact stress, a minimum factor of 1,45 shall be applied to the design limit load.

The design limit load is derived in compliance with requirements of clause 4.2 of ECSS-E-ST-32-10.

Gears

Dimensioning and sizing of gears shall be performed in conformance with, ISO 6336-1, ISO 6336-2, ISO 6336-3, ISO 677, and ISO 678.

Mechanical clearances

When designing and locating mechanisms, clearance shall be provided to prevent movable and actuating elements from:

• interfering, including collision, with the structure,
• contacting with electrical wiring and components, thermal insulation, or other subsystem components,
• puncturing of fluid lines, valves and tanks,
• blocking optical paths. Clearances shall be verified by analysis using worst-case tolerance budgets including thermoelastic effects and operational loads.
  Clearances shall be verified by inspection.
  Clearances should be at least 3 times its associated tolerance.

MLI clearance

For MLI clearance, clause 4.7.4.3 shall apply.

Threaded parts or locating devices

Threaded parts and locating devices shall use secondary, positive locking.
Threaded fasteners shall be made from materials, which are not susceptible to stress corrosion cracking.

• 1    For materials preferred list, see ECSS-Q-ST-70-36. For other materials validation, see ECSS-Q-ST-70-37.
• 2    For manufacturing of threaded fasteners see ECSS-Q-ST-70-46.
  Threaded fasteners shall be designed to be fail­safe.

It is important to pay special additional attention for all fasteners for which failure or particle release endangers operation of a mechanism.

The tightening preload shall be justified taking into account the scattering of all parameters impacting the preload.

Scattering parameters, for example, are related to manufacturing, lubrication and tightening.

Venting

Unless the mechanism is hermetically sealed or sized in all its functions and performances for internal pressure build­up, all closed cavities shall be provided with a venting hole sized according to the launch ascent depressurisation profile.
The method and design of venting shall prevent particles contamination of bearings, optics and external sensitive components agreed by the customer.

• 1    It is important to prevent also particles contamination of the sensitive components within the mechanism.
• 2    Filters with mesh size of 1 to 2 microns placed in the venting path are means to prevent particles contamination.
  If venting to the outside of a lubricated enclosure is implemented, compatibility of the lubricant with the other spacecraft materials used and with contamination requirements specified in the specific mechanism specification shall be verified.

Release and locking devices with pyrotechnics or other actuators

Pyrotechnic and other release and locking device actuators should be redundant.

Example of such actuators are thermal knives, memory metal and paraffin actuators.

Where no actuator redundancy is provided, redundancy shall be provided by duplicating up to and including the level of the initiators, heating element or equivalent for non­pyrotechnic devices, and its power supply.
The conformity of the design, material and manufacture of elements to be cut used in release and locking devices to the reliability requirements specified in the SMS shall be verified by test.

Example of such elements are bolts, rods and cables.

The operation of release devices shall be compatible with the cleanliness requirements.
All debris shall be contained.
If critical, contamination shall be measured.
Shock loads for release and locking devices shall be derived by analysis or test, and specified in the mechanism requirements specification.

Pyrotechnics

Pyrotechnic actuators shall be designed in conformance with ECSS-E-ST-33-11.

Electrical and electronic

Electrical design

General

Mechanisms shall be designed to meet all the requirements regarding electrical interfaces and performances.
Mechanisms shall exhibit stable electrical characteristics and electromechanical transfer functions throughout their specified period of life.
Electrical power consumption, generation and thermal dissipation shall be quantified by design.
Fault propagation shall be prevented.
Generated electrical disturbances shall conform to the project specific EMC requirements.
If brush motors are used, it shall be verified under representative environment and over specified lifetime that debris generation does not result in contamination.
If brush motors are used, it shall be verified under representative environment and over specified lifetime that debris generation does not result in electrical failure.

For example, short circuit of commutators.

If brush motors are used, it shall be verified under representative environment and over specified lifetime that brush wear does not result in functional performance degradation.
If brush motors are used, it shall be verified under representative environment and over specified lifetime that long storage period does not result in functional performance degradation.

Electrical Insulation resistance

Electrical wires shall be insulated from the structure and from each other by not less than 100 M measured with a DC voltage of 500 V applied.
Electric motor windings shall be insulated from the structure and from each other by not less than 100 M measured with a DC voltage five times the worst-case flight operating voltage.
The measurement DC voltage of requirement 4.7.7.2b shall not exceed 500 V, under any circumstances.
For AC applications, insulation requirements 4.7.7.2a and 4.7.7.2b shall apply for both polarities, considering the worst-case flight operating voltage being the peak voltage.

For application voltage over 250 V, recommendations are provided inside ECSS-E-HB-20-05.

Dielectric

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Grounding

Each mechanism shall be electrically bonded to the spacecraft structure or its carrying equipment.
If electronic or electrical components are mounted internally to or externally on the mechanism a ground bonding strap shall be used between the mechanism housing and the mounting ground plane.
If electronic or electrical components are mounted internally to or externally on the mechanism, the length­to­width ratio of the bonding strap should be smaller than four.
If electronic or electrical components are mounted internally to or externally on the mechanism, the DC resistance, between the mechanism bonding reference point and the mounting ground plane or carrying equipment ground plane in both polarities, shall be less than 10 m.
If electronic or electrical components are mounted internally to or externally on the mechanism, the DC resistance, between any point on the mechanism housing and the bonding point reference of the mechanism, shall be less than 5 m.
Where the grounding is to provide protection against electrostatic discharge only and the mechanism contains no electronics, the DC resistance shall be less than 0,1 .

Electrical connectors

With the exception of the bonding strap for grounding, all electrical connections to the mechanism shall be made through electrical connectors of a type qualified for the intended application.
Flying leads should be avoided.
Connector types and configurations shall be selected to preclude damage or inadvertent operation resulting from mis­mating.

For example, for the number of pins.

Electrical connectors shall be redundant.

Over current protection

Mechanisms containing electrical parts and circuitry shall be protected against overcurrent due to abnormal applied voltage or internal conditions in conformance with ECSS-E-ST-20, clause 5.8.1.

The current protection can be provided externally.

The mechanism shall be protected against the generation of over voltage in conformance with ECSS-E-ST-20, clause 5.8.1.

Strain on wires

Routing shall be designed to be reproducible.
Implementation shall be verified.
Resistive torques or forces shall be measured under worst-case conditions.
The relative position of cables within the harness shall not change during motion.

The four previous requirements are introduced in order to achieve reproducible resistive torques or forces of moving cable harness.

Connections shall be protected from harness induced loads.

Magnetic cleanliness and ESD or EMC protection

Mechanisms shall conform to the spacecraft system requirements on magnetic cleanliness in conformance with ECSS-E-ST-20-07, and conductivity of surfaces for electrostatic discharge (ESD) protection in conformance with ECSS-E-ST-20-06.

Open-loop and closed-loop control system for mechanisms

Gain margin

The gain margin shall be higher than a factor of two (2) throughout the operational lifetime for linear or quasi­linear control systems, including A/D and D/A conversions effects.
Non­linear control systems stability margin value and assessment method shall be agreed by the customer.

Phase margin

The phase margin shall be higher than 30 degrees throughout the operational lifetime of the equipment and under worst-case combination of parameters, including A/D and D/A conversions effects.

The worst-case combination of parameters includes drift and temperature effects.

Bandwidth

The bandwidth of the control system shall be designed to achieve the commanded action within the specified response time.

Damping ratio

The damping ratio of the control system shall be agreed with the customer.

Additional control system design requirements

The control system shall not excite mechanism eigenmodes.
The control system shall take into account aliasing effects.
The control system shall not excite structural resonances of the spacecraft as specified by the customer.
The control system should be decoupled between the six directions of movement.

The six directions of movement are three translations and three rotations.

If requirement 4.7.8.5d is not met, then coupling effects shall be characterized.

Multidimensional methods provide the best results.

The control system shall be compatible with the specified maximum angular and linear rates and accelerations of the spacecraft.
To prevent excessive amplification of the noise, transfer functions of the controller should not contain pure derivative terms.
The ratio between the derivative time constant and the time constant limiting the high frequency gain should not exceed 20.
Harnesses and cables to moving parts shall be characterized in terms of hysteresis and stiffness in representative configuration over the full range of displacement and over the specified qualification levels in terms of temperature range, lifetime, speed effects.
Harnesses and cables to moving parts shall be taken into account in the control system design.
If the sampling frequency results in aliasing of the sampled data, an anti­aliasing filter to reduce the bandwidth of the analogue signal shall be used.
The resolution of sensors used in the control system to feedback information should be at least a factor of 5 (five) better than the specified resolution of the complete system.

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Verification

General

Development of space mechanisms shall include a verification process in conformance with ECSS-E-ST-10-02.

• 1    The mechanisms verification requirements are subdivided into analytical and test verification requirements.
• 2    The model definition is provided in ECSS-E-HB-10-02.
  A verification matrix shall be established by the supplier and provided to the customer for agreement.

Verification by analysis

General

The mechanisms parts, components and assembly analytical verification shall include the analysis specified in 4.8.2.2 to 4.8.2.19.
If any of the analysis specified in requirement 4.8.2.1a is not performed, justification shall be provided and agreed by the customer.
The analyses specified in requirement 4.8.2.1a shall cover

• the combinations of range of extreme conditions for the flight system and which do not necessarily all occur during qualification testing
• the effect of on-ground environmental conditions
• the worst or extreme case conditions.
• 1    to item 1: For example, worst-case friction levels.
• 2    to item 2: For example, air pressure, gravity effects, and test rigs perturbations.

Worst-cases identification

The worst-case operational and non­operational sizing of a mechanism shall be identified according to the environmental, load and functional performance characteristics for the particular spacecraft and mechanism.

Thermal analysis

For the derivation of margins of safety clause 4.7.4.1 shall apply.

See ECSS-E-ST-31 for thermal analysis of mechanisms.

Structural analysis

For the derivation of margins of safety clause 4.7.5.2 shall apply.

• 1    Structural analysis includes stiffness, stress or strength, thermo-mechanical effects, fatigue and fracture control. See ECSS-E-ST-32 for structural analysis of mechanisms.
• 2    The objective is to demonstrate adequate sizing of the part and the overall assembly for all sizing cases.

Pre­load and tolerance budget analysis

Mechanisms pre­load and tolerance budget analysis shall take into account the relevant combination of the worst-cases environmental, functional, residual loads and manufacturing tolerances.

The worst-cases environmental, functional, residual loads include external and induced loads, and thermo-mechanical effects.

Mechanisms pre­load and tolerance budget analysis shall verify the adequacy of mechanical plays in the worst-case conditions.

Functional performance analysis

General

Functional performance analysis shall be performed for worst case environmental and operational conditions.

Operational conditions are based on worst-case identification.

Functional model requirements

The analysis shall be based on an analytical or numerical model, which represents the flight hardware mechanisms and its components, including interface conditions and overall spacecraft characteristics, with respect to

• mass,
• inertia,
• location of the centre of mass,
• structural stiffness,
• actuation forces or torques, and
• resistances for conditions specified in clause 4.7.5.3. The model specified in requirement 4.8.2.6.2a shall be such that the following can be performed:
• a parametric study of all the mechanical variables, and
• an update of input parameters during the design and test phase.

Analysis requirements

It shall be demonstrated by analysis that the mechanism conforms to

• the specific mechanism specification (SMS), and
• the mechanical design and sizing requirements under worst-case parameter combinations.

For mechanical design and sizing see clause 4.7.5.

Failure cases shall be analysed and, where identified, contingency scenarios shall be established and validated by analysis.
An integrity check of the results of the analysis shall be performed.

For example, energy or momentum balance.

A sensitivity analysis covering the uncertainty of parameters shall be carried out.

The sensitivity analysis is based on parameter variation.

If test results do not match predictions, the reason of the disagreement shall be found, and the analysis shall be updated accordingly.
Remaining deviations between test results and analyses shall be justified with respect to performance acceptability.

Hertzian contact and contact stress

An analysis shall be provided of the predicted hertzian contact or yield or bending stresses of moving surfaces in contact under worst-case conditions to verify the compliance with the material allowables of the chosen material couple, lubricant and other coating used.

Surfaces in contact encompass separable and sliding contacts, and bearings.

An analysis shall be provided to verify sizing of ball bearings in conformance with the allowable peak hertzian contact stress.

Functional dimensioning analysis

Conformance of mechanisms to specified requirements on functional dimensioning shall be verified by analysis.

Examples of such requirements are torque, force, and kinematics.

Reliability analysis, FMECA

The reliability of a mechanism shall be determined.

For reliability, see ECSS-Q-ST-30. For FMECA, see ECSS-Q-ST-30-02.

Gear analysis

An analytical verification of the conformity of dimensioning and sizing of gears shall be performed.

For gear dimensioning and sizing see ISO 6336.

Shock generation and susceptibility

The conformity of the mechanism to the requirements for shock generation and susceptibility specified in the SMS shall be verified by analysis.
Dimensioning and sizing methods shall be agreed by the customer.

Disturbance generation (emission) and susceptibility

The mechanism operation shall be verified by analysis using parameters representative of the flight configuration, including electronics, to comply with the specified requirements for induced loads.

For example, micro­vibrations.

The moving parts of the mechanism should be balanced to conform to the specified requirements on disturbances.

Analysis of control systems

A mathematical model or computer simulation describing the dynamic behaviour of the mechanism and its associated control system shall be established to perform verification by analysis.
The functional performance of the control system shall be analysed for

• stability,
• bandwidth,
• dynamic and static accuracy,
• resolution, and
• generation of and susceptibility to disturbances at the interfaces of the mechanism. All non­linearities shall be analysed.
  Non­linearities such as backlash, dead zones, friction, saturation of drive electronics shall be characterized and taken into account in the control system analysis.
  Characterization of non­linearities shall take place over the full range of displacements and over the full specified qualification temperature range.
  The worst-case combinations of parameters occurring during the operational lifetime of the equipment shall be taken into account in the analysis of the non­linearities.
  The robustness of the control against variations in the environment, between models and over the operational lifetime shall be verified by analysis.

Lubrication analysis

An analysis of the choice of lubrication system and its dimensioning for the proposed application and lifetime shall be provided.
The analysis specified in requirement 4.8.2.14a shall be based on similarity to a qualified application with regards to the following parameters:

• worst case peak contact hertzian stress;
• worst case operational contact hertzian stress;
• number and range of cycles;
• worst case environmental conditions. <<deleted>>

Lifetime analysis

Limited­life items shall be identified.
Conformance of limited­life items to the lifetime requirements specified in the specific mechanism specification shall be verified by analysis, using as a minimum the lifetime factors specified in clause 4.8.3.3.14 in addition to the fatigue factor specified in clause 4.7.5.2.

Hygroscopic effect analysis

The design compatibility with the hygroscopic environment during the complete lifetime shall be verified by analysis.

The hygroscopic environment is mainly relevant on-ground.

Magnetic and electromagnetic analysis

The sizing of magnetic or electromagnetic components shall be verified by analysis.

Radiation analysis

Conformity of the components susceptible to radiation to the (lifetime) performance requirements shall be verified by analysis.

Electrical analysis

Electrical parts stress analysis shall be performed to demonstrate that the electrical parts conform to the derating requirements.

For derating see ECSS-Q-ST-30-11.

Verification by test

General

The tests to be performed to verify that the mechanism fulfils the requirements for use as space hardware shall be:

• defined in a test plan, and
• agreed by the customer.

The aim of testing can be either characterization, development, qualification or acceptance.

The permissible operations and the constraints for the operations on ground shall be defined by the supplier and agreed by the customer.
The mechanisms test programme shall include the verification that the hardware conforms to the requirements on design specified in clause 4.7, on construction specified in clause 4.9, and on performance specified in the specific mechanism specification.
The tests shall verify that the mechanism conforms to the functional dimensioning requirements specified in clause 4.7.5.3.
Tests shall be performed to check mechanism performance in both launch and operational configurations.
The mechanism shall be subjected to a thermal verification.
The mechanism shall be subjected to a structural verification.

For structural requirements, see ECSS-E-ST-32.

Non-linearities shall be measured in order to characterize the dynamic behaviour of the mechanism.

Examples of non-linearities are hysteresis and backlash.

Characterization or development testing

Model requirements

Development tests shall be carried-out on the bread-board models to test the specific aspect agreed by the customer.

The objective is to use bread­board models of varying levels of sophistication to test specific aspects or assumptions of a design on which the outcome of the design depends.

Test

Except in the case specified in requirement 4.8.3.2.2b, the following verification tests on development model mechanisms shall be performed during phases A or B of the project:

• functional performance tests in ground ambient environment.
• vibration and thermal tests.
• tribological lifetime test on life critical items. Verification test specified in requirement 4.8.3.2.2a need not be performed if the customer agrees that the test available data from previous space application can be used instead.

Qualification testing

General

All mechanisms shall be qualified by test for the application in which they are used.
The qualification tests shall be performed in a representative sequence and in a representative environment, agreed by the customer.

Structural qualification testing

The mechanisms structure shall be qualified by testing.

Thermal vacuum qualification testing

A thermal qualification of the mechanism shall be performed.
Operation of the mechanism in a representative environment under worst-case temperature gradients shall be verified by test at a level agreed by the customer.

Functional qualification testing

Settling and thermal stabilization shall be performed prior to functional performance testing.
The conformance of the mechanism to the performance requirements following exposure to environmental conditions (loads, thermal) at qualification level and mechanism qualification duration shall be verified by test.

Energy or shock

Mechanisms shall be verified by test to withstand release and end shocks caused by the motion of the mechanism.
Latching shock emissions shall be measured.
When relevant, micro-vibration emissions due to mechanism operation shall be tested in a representative configuration.

Solid lubricated ball bearing verification

Solid lubricated ball bearing cage material, design and performance shall be verified by testing.
The environment for the lubricant life test demonstration shall be agreed by the customer.

Fluid lubricated ball bearing verification

Ball bearing cage material, design, impregnation procedures for cages and reservoirs, and performance shall be verified by testing.
Lubricant quantity shall be verified by tests.
The compatibility of the fluid lubricant with the mechanism materials and other lubricants used within the mechanism shall be verified.

EMC or ESD qualification testing

The EMC performance of mechanisms shall be verified by testing when:

• EMC sensitive components are used on the mechanism, or
• spacecraft specific EMC requirements are applicable to the mechanism.

EMC comprises susceptibility and emissivity.

ESD testing shall be performed on a complete mechanism including all electrical components and thermal hardware.

For EMC and ESD see ECSS-E-ST-20.

Electrical insulation resistance qualification testing

Electrical wires and connectors shall be tested to verify their insulation from the structure and from each other by not less than 100 M with a DC voltage of 500 V applied for a duration of 1 minute or until a steady state resistance value is measured.
<<deleted>>
Motor windings shall be tested to verify their insulation from the structure and from each other by not less than 100 M with a DC voltage of at least five times the worst-case flight operating voltage applied for a duration of 2 minutes or until a steady state resistance value is measured.
<<deleted>>
For AC applications, insulation test requirement 4.8.3.3.9a and 4.8.3.3.9c shall apply for both polarities, considering the worst-case flight operating voltage being the peak voltage.

For application voltage over 250 V, recommendations are provided inside ECSS-E-HB-20-05.

Control system qualification testing

The mathematical model used to analyse the dynamic behaviour of the control system shall be correlated with measurements performed on representative hardware agreed by the customer.
The verification of control system performance by test should be performed using independent measurement devices.
The control system transducer shall not be used as a reference during the tests unless the transducer has been calibrated previously in a representative environment.

Lifetime qualification testing

The mechanism design, lubricant lifetime and performance shall be verified by test on a flight representative life test model in the specified environment after exposure to flight representative environmental tests.

• 1    For example, worst-case loads and accumulated vibration durations.
• 2    FMs are excluded from life testing.
  Exposure of lifetime model to vibrations prior to life test shall include:
• exposure to accumulated durations of acceptance tests at acceptance load level and additional accumulated durations corresponding to the number of vibrations tests expected by the flight hardware, including sub-system and system tests, and
• one time exposure to qualification load level and duration of vibration, which covers the flight. The environment for the verification of the lifetime of a lubricant shall be agreed by the customer.

Life test model requirements

The model and lifetime testing shall be representative with respect to the following parameters:

• Thermal conditions, loading conditions, contact stress, motion profile and speed during testing, representative of the operational conditions.
• Lubrication regime representative of worst-cases expected operational conditions, and for durations factored as agreed by the customer.

The duration factors are defined in clause 4.8.3.3.14.

Extended life durations to be agreed by the customer shall be implemented for the simulation of realistic conditions during accelerated tests.

These parameters can influence the life of the mechanism.

Life test profile

The profile and sequence of a life test shall be defined and agreed by the customer.

Life test duration

The lifetime qualification shall be verified using the factored sum of the predicted nominal ground test cycles, including run-in, acceptance testing and the in­orbit operation cycles.
For the test verification, the number of expected cycles shall be multiplied by the factors in Table 44.
TableTable 44: Life test duration factors

Type	Number of expected cycles	Factor
Ground testing (minimum 10 cycles to be tested)	1 to 1 000 cycles	4
	1 001 to 100 000 cycles	2
	> 100 000 cycles	1,25
In­orbit	1 to 10 cycles	10
	11 to 1 000 cycles	4
	1 001 to 100 000 cycles	2
	> 100 000 cycles	1,25

The cycle definition shall be agreed by the customer and take into account at least.

• the number of motions over the same location, and
• motion amplitude and number of reversals. In order to determine the lifetime to be demonstrated by test, an accumulation of cycles multiplied by their individual factors shall be used.

Table 45 presents two case examples to calculate the number of cycles to be used in the test.

TableTable 45: Examples of lifetime to be demonstrated by test

Example	Data	Calculations
Example 1	Expected ground test cycles: 15	15×4 = 60
	Expected in-orbit cycles: 100
	First 10 cycles	10×10 = 100
	Remaining 90 cycles	90×4 = 360
	Total life test number	520
Example 2	Expected ground test cycles: 2	2×4 = 8
	But minimum is 10	10
	Expected in-orbit cycles: 1	1×10 = 10
	Total life test number	20

Any element in a chain of actuation shall conform to the maximum number of cycles applicable to any of the other elements in the chain.

Examples of such elements are motors, bearings, and gears.

For crewed space missions, safety critical mechanisms using “design for minimum risk” to control hazards, the following minimum factors shall be applied for both ground and in-orbit cycles when the result of calculation using the Table 44Table 4-4 is lower than:

• an overall factor of 2 for critical hazard potential, and
• an overall factor of 4 for catastrophic hazard potential.

Table 46 and Table 47 present two case examples to calculate the number of cycles to be used in the test for safety critical mechanisms.

TableTable 46: Example of lifetime to be demonstrated by test for safety critical mechanisms having critical hazard potential

	Calculations
Expected ground test cycles: 50	50×4 = 200	50×2 = 100
Expected in-orbit cycles: 3000		3000×2 = 6000
First 10 cycles	10×10 = 100
11- 1000 cycles	990×4 = 3960
1001-3000 cycles	2000×2 = 4000
Calculated life test number	8260	6100
Required life test number	8260

TableTable 47: Example of lifetime to be demonstrated by test for safety critical mechanisms having catastrophic hazard potential

	Calculations
Expected ground test cycles: 50	50×4 = 200	50×4 = 200
Expected in-orbit cycles: 3000		3000×4 = 12000
First 10 cycles	10×10 = 100
11- 1000 cycles	990×4 = 3960
1001-3000 cycles	2000×2 = 4000
Calculated life test number	8260	12200
Required life test number	12200

Accelerated lifetime testing

If accelerated lifetime testing is employed to verify the lifetime performance of the mechanism, the model used for accelerated lifetime testing shall be representative of the worst-case environmental conditions with respect to degradation.

Post­test inspection

After completion of the life test, the mechanisms shall be disassembled into its tribological parts and the status of the parts verified with respect to the life test success criteria identified in clause 4.8.3.3.17.

Qualification testing success criteria

Qualification testing of the mechanism or of mechanical subsystem shall be considered successful when all the following criteria are demonstrated at the end of the test:

• No direct contact between metallic parts in relative motion identified in the interface of solid lubricated contact surfaces;
• Surface properties of contact surfaces not modified beyond the specified limits of their performance properties;
• No chemical deterioration beyond the specified limits of fluid lubricants is found, and anti-creep barrier, when present, are still operational;
• The amount and size of wear products conforms to contamination and overall mechanism performance requirements specified in the specific mechanism specification (SMS);
• Worst-case variation or degradation peak torque or force overall throughout qualification, including life, testing is compatible with the functional dimensioning requirements specified in clause 4.7.5.3;
• Deterioration torque or force performance is less than or equal to 50 % of the values measured at the beginning of qualification tests;
• Other degradation factors agreed on a case by case basis with the customer are within the specified limits;
• All measured performances conform to the requirement of the specific mechanism specification.

Acceptance testing

Mechanical settling and thermal stabilization

As a part of manufacturing and assembly processes, mechanical settling, run-in and thermal stabilization shall be performed prior to acceptance testing.

Acceptance tests

New builds of qualified designs shall be acceptance tested to verify that the actual manufactured hardware is free from manufacturing defects.
The acceptance test sequence shall be agreed by the customer.
The acceptance level testing shall be carried out at levels, which are higher than expected in flight but less than the qualification levels.
After acceptance testing, refurbishment should not be performed.

This is for the test levels experienced to be at a level, which is not detrimental to the health of the hardware.

Insulation resistance appetence test

Electrical wires shall be tested to verify their insulation from the structure and from each other by not less than 100 M with a DC voltage of 500 V applied until a steady state resistance value is measured with a minimum duration of 1s.
For AC applications, insulation test requirement 4.8.3.4.3a shall apply for both polarities, considering the worst-case flight operating voltage being the peak voltage.
Motor windings shall be tested to verify their insulation from the structure and from each other by not less than 100 M with a DC voltage of at least five times the worst-case flight operating voltage never exceeding 500 V, applied until a steady state resistance value is measured with a minimum duration of 1 s.
For AC applications, insulation test requirement 4.8.3.4.3c. shall apply for both polarities, considering the worst-case flight operating voltage being the peak voltage.

For application voltage over 250 V, recommendations are provided inside ECSS-E-HB-20-05.

Acceptance tests criteria

Acceptance testing shall be considered successful when all the following criteria are met:

• The peak torque or force, resulting from the summation of the following, comply with the functional dimensioning requirements specified in clause 4.7.5.3:
  • the worst-case variation or degradation of the peak torque or force measured on the qualification model overall throughout life testing, and
  • the worst case force or torque measured on the flight unit.
• Deterioration torque or force performance throughout acceptance tests is less than the values measured on the qualification model.
• All measured performances conform to the specific mechanism specification (SMS).

Production and manufacturing

Manufacturing process

All processes used in the manufacture of space mechanisms hardware shall be

• approved by the customer, and
• part of the overall product assurance system.

This approval is normally based on their repeatability and proven capability of achieving the specified levels of safety and reliability.

Manufacturing drawings

Manufacturing drawings shall be established in conformance with ISO 128.

Assembly

The assembly of mechanisms shall be performed in a clean environment specified by the customer.

Deliverables

The supplier shall provide the mechanisms design description in conformance with the DRD in Annex B.
The supplier shall provide the mechanisms analytical verification (MAV) in conformance with the DRD in Annex C.
The supplier shall provide the mechanism user manual (MUM) in conformance with the DRD in Annex D.

In accordance with requirement 4.2.2a, a specific mechanism specification is also delivered by the supplier for customer approval.

For safety critical mechanisms in crewed space missions the supplier shall provide:

• a safety critical mechanisms verification plan (MSVP) in conformance with the DRD in Annex F.
• a safety critical mechanisms verification report (MSVR) in conformance with the DRD in Annex G.

Table E-1 in Annex E provides a list of the mechanism documentation technical items and the ECSS document where they are covered.

ANNEX(normative)Specific mechanism specification (SMS) - DRD

DRD identification

Requirement identification and source document

This DRD is called from ECSS-E-ST-33-01, requirement 4.2.2a.

Purpose and objective

The purpose of the specific mechanism specification (SMS) is to specify the mechanism requirements specific to the particular application. It is expected that a SMS is developed for each individual mechanism in a project.

The SMS is developed by the supplier, and propose to the customer for approval.

Expected response

Scope and content

Introduction, references and terminology

The SMS shall contain a description of the purpose, objective, content and the reason prompting its preparation.

For example: “This document describes the application specific requirements of the <name> mechanism for the <name> project”.

The SMS shall list any applicable and reference documents to support the generation of the document.
The SMS shall include any additional definition, abbreviation or symbol used.
Customer specific requirements

The SMS shall include all the specific requirements expressed by the customer.
General requirements

The SMS shall specify or refer to the qualification procedure for parts and components.

See 4.2.4.2a.

If the mechanism is not maintenance free during storage and ground life, the SMS shall list the maintenance requirements, including for each of them:

• number of operations,
• frequency of operations,
• special tooling and test equipment,
• calibration and adjustments,
• fault identification and repair, and
• environment for maintainability operation.

See 4.2.4.4b.

The SMS shall include or refer to the method to demonstrate the mechanism reliability compliance.

See 4.2.5.1.

The SMS shall describe the redundancy concepts for the mechanism.

See 4.2.5.2d.

The SMS shall include the cleanliness requirements of the inert dry for flushing the critical parts of the mechanisms.

See 4.2.6a.

The SMS shall include the minimum functional performances to be conformed to, over the complete mission (including on-ground).

This minimum functional performance is used to ensure that the mechanism is not degraded over the mission. In particular, it is used to ensure that there is not unacceptable degradation due to:

• Radiation (see 4.5.2.8);
• Atomic oxygen (see 4.5.2.9);
• Degradation of the lubricant in the on­ground and in­orbit environments (see 4.7.3.1c);
• Migration of fluid lubricants that can cause a change of the lubricant amount on the parts to be lubricated. In this case, anti­creep barriers can be used (see 4.7.3.3.3c).
  Constraints

The SMS shall include the specific climatic protection and environmental requirements.
The SMS shall include the sterilization requirements and the sterilization test procedure requirements.
The SMS shall include the stray light and emission requirements.

These requirements are used to select the materials and coatings (see 4.5.2.7).

Interfaces requirements

The SMS shall list the following interface definitions and requirements:

• Structural
• Thermal
• Thermo-mechanical
• Electrical
• Data
• Physical
• Optical
• Alignment
• Access and stay-out zones
• GSE

Examples of physical interfaces are: mass, geometry, MOI, COG, and I/F pattern.

Design requirements

The SMS shall list the handling, storage and operational requirements for all lubricated parts.
The SMS shall include the limits for outgassing, creeping and potential sources of contamination.

• 1    This limits have a strong impact on the design of the fluid lubricated system.
• 2    For generic requirements on outgassing limits, see requirement 4.7.3.3.2.b.
  The SMS shall define the specific requirements for mission involving advanced optical instruments.
  The SMS shall include the qualification temperature range under all ground, test, launch and in­orbit conditions.

This is used for the mechanism thermal design and sizing (see 4.7.4.2a).

The SMS shall list the shock load requirements for latches and locks.

For the derivation of such requirements, see 4.7.5.4.3i.

The SMS shall include the specified maximum positions of the mechanism.

These maximum positions are provided to design end stops in accordance with 4.7.5.4.4a.

The SMS shall specify the reliability requirements, to verify the conformity of the design, material and manufacture of elements to be cut used in release and locking.

See 4.7.5.4.12c.

The SMS shall specify the shock loads for release and locking devices.

For the derivation of such requirements, see 4.7.5.4.12g.

Verification requirements

The SMS shall list the requirements for shock generation and susceptibility.

See 4.8.2.11a.

The SMS shall list the limited­life items lifetime requirements.

See 4.8.2.15b.

Special remarks

None.

ANNEX(normative)Mechanism design description (MDD) - DRD

DRD identification

Requirement identification and source document

This DRD is called from ECSS-E-ST-33-01, requirement 4.10a.

Purpose and objective

The purpose of the mechanism design description (MDD) is to provide the customer with a comprehensive understanding of the mechanism design and functionality.

Expected response

Scope and content

Introduction, references and terminology

The MDD shall contain a description of the purpose, objective, content and the reason prompting its preparation.

For example: “This document describes the functionality and design of the <name> mechanism for the <name> project.

The MDD shall list:

• the model standard of the mechanism being described;

Examples are DM, EM, QM, and FM for which the definition is provided in ECSS-E-HB-10-02.

• the list of documents providing additional subsystem design description;
• any other applicable and reference documents to support the generation of the document. The MDD shall include any additional definition, abbreviation or symbol used.
  Mission and mechanism main functions

The MDD shall describe the mission and the role of the mechanism in achieving the mission.
The primary functions of the mechanism shall be described.
Key requirements

The MDD shall include the requirements that drive the selected mechanism concept.

Examples of such requirements are functional, operational, and imposed design solutions.

Functional principle

The MDD shall describe how the mechanism primary functions are broken down into their elementary functions.

For example, use functional tree.

Schematic functional elements should be added to the tree.
Detailed description of the mechanism

The MDD shall describe the mechanism detailed design, including the following:

• product tree (sub assembly break down);
• physical design of the mechanism in all configurations;
• how each function is achieved;
• protection and redundancy implementation;
• general assembly drawings with cross sections or equivalent;
• interface descriptions (mechanical, thermal and electrical);
• static and dynamic envelopes. Performance and budgets

The MDD shall provide informative data with regard to performance, mass and power budgets.

This is provided for information only. The contractual values are provided in the verification files.

Special remarks

None.

ANNEX(normative)Mechanism analytical verification (MAV) - DRD

DRD identification

Requirement identification and source document

This DRD is called from ECSS-ST-E-33-01, requirement 4.10b.

Purpose and objective

The purpose of the mechanism analytical verification (MAV) is to provide the customer with a comprehensive functional and performance analysis of the mechanism.

Expected response

Scope and content

Introduction, references and terminology

The MAV shall contain a description of the purpose, objective, content and the reason prompting its preparation.

For example: This document provides all functional and performances analyses of the “name” mechanism for the “name” project. This document is part of the verification files and ensures that the mechanism is sized to meet the related requirements.

The MAV shall list:

• all the applicable documents regarding requirements related to design and performance;
• the design definition file reference of the mechanism being analysed;
• the list of documents providing inputs to analyses presented in this document;
• any other applicable and reference documents to support the generation of the document.
• 1     to item 3: For example, thermal analysis, structural analysis, and test reports.
• 2    to item 3: Subsystems and parts data to be included.
  The MAV shall include any additional definition, abbreviation or symbol used.
  Mission and mechanism main functions

The MAV shall describe the mission and the role of the mechanism in achieving the mission.
The primary functions of the mechanism shall be described.
Analytical verification

The MAV shall provide all analyses regarding analytical verification as defined in 4.8.2
For each of the analyses of C.2.1<3>a, the results shall be summarized in a table and compared to the requirements.

Each specific analysis can be provided in a separate document or grouped together.

Special remarks

None.

ANNEX(normative) Mechanism user manual (MUM) - DRD

DRD identification

Requirement identification and source document

This DRD is called from ECSS-E-ST-33-01, requirement 4.10c.

Purpose and objective

The purpose of the mechanism user manual (MUM) is to provide the customer with a comprehensive set of information and instructions for storage, transportation, handling, integration at subsystem or system level, and on ground and in-orbit operation of the mechanism.

Operational information and instructions provided by the mechanism supplier are limited to mechanism level.

Expected response

Scope and content

Introduction, references and terminology

The user manual shall contain a description of the scope and applicability of the document.

For example: This document provides all information and instructions for storage, transportation, handling, integration at subsystem or system level, and on ground and in-orbit operation of the “name” mechanism for the “name” project.

The user manual shall include:

• the mechanism requirement specification;
• the delivered mechanism applicable CIDL;
• the list of consumables and spares;
• the list of GSE and special tools;
• the list of user manuals for GSE and special tools;
• the calibration data. The user manual shall include any additional definitions, abbreviations or symbols used.
  Mission and mechanism main functions

The user manual shall describe the mission and the role of the mechanism in achieving the mission.
The primary functions of the mechanism shall be described.
Safety instructions

The user manual shall present all aspects with regard to personnel safety and shall detail all necessary safety precautions.
Traceability requirements

The user manual shall define the information to be recorded after delivery.

For example: Number of limited operations.

Delivery configuration

The user manual shall present the following information regarding the mechanism delivery configuration:

• short description of the mechanism and all self-standing subassemblies;
• short description of GSE and special tools, including drawings or pictures. The description specified in D.2.1<5>a shall include drawings or pictures.
  Storage, transportation and handling

The user manual shall describe the following topics:

• mechanism configuration for storage, transportation and handling;
• container characteristics and operation instructions;
• packing, and transportation instructions;
• unpacking and incoming inspections;
• handling and storage instructions;
• environmental conditions for the in D.2.1<6>a.1.to D.2.1<6>a.5. defined phases.

Examples of such environmental conditions are mechanical, thermal, hygrometry, and pressure, cleanliness.

Interfaces definition

The user manual shall provide the following information with regards to interfaces definition:

• description of mechanical and thermal interfaces, including the list of applicable mechanical and thermal ICD;
• description of electrical interfaces, including the list of applicable electrical ICD;
• description of optical interfaces, including the list of applicable optical ICD.

In case the ICDs are provided in a specific chapter of the EIDP, the list of applicable ICDs can be limited to the EIDP chapter reference.

Integration instructions

The user manual shall provide the following information with regards to integration instructions:

• integration sequence;
• preparation prior to integration, including
  • mechanism and self-standing subassemblies configuration;
  • GSE and special tools to be used;
  • items to be removed;
  • specific precautions and safety instructions;
  • cleaning instructions;
  • environmental conditions for integration;
  • detailed handling instructions for integration.
• step by step mounting instructions including torque on threaded fasteners, alignment provisions, shims, electrical connections, intermediate inspections and checks;
• final inspections.

For example, visual, electrical checks, clearances, and health checks.

Onground operation instructions

The user manual shall describe all activities to operate the mechanism on ground, including:

• Preparation for start up:
  • operational configuration;
  • GSE and special tools to be used;
  • items to be removed;
  • specific precautions and safety instructions including limitations in terms of operation and performances;
  • cleaning instructions;
  • environmental conditions for operation.
• Step by step Start up operation instructions.
• For each operational mode
  • operational configuration;
  • GSE and special tools to be used;
  • specific precautions and safety instructions including limitations in terms of operation and performances;
  • environmental conditions for operation;
  • step by step operation instructions;
  • telemetry requirements and health monitoring;
  • recovery contingencies.

Example of such operational modes are release, calibration, deployment, and pointing, scanning.

Maintenance operations

The user manual shall describe all maintenance operations.

For example:

• Time limited consumables replacement
• Cycles limited consumables replacement
• Periodic health check
• Periodic operations
  In-orbit operation instructions

The user manual shall describe all activities to operate the mechanism in-orbit.
For each operational mode the following topics shall be described:

• operational configuration;
• specific precautions including limitations in terms of operation;
• operation sequence;
• telemetry requirements and health monitoring;
• recovery contingencies.

Examples of such operational modes are release, calibration, deployment, pointing, and scanning.

Special remarks

None.

ANNEX(informative)Documentation technical items

Table E-1 includes the mechanism documentation technical items, and the ECSS documents where they are covered.

Table: Documentation technical items

Document	ECSS reference
Configuration item data	ECSS-M-ST-40
Critical items	ECSS-Q-ST-10-04
Declared components	ECSS-Q-ST-60
Declared materials, parts and processes	ECSS-Q-ST-70
Design description	ECSS-E-ST-33-01 Annex B
Design, development and verification approach	ECSS-E-ST-10-02
Failure modes and effects criticality analysis (FMECA)	ECSS-Q-ST-30-02
Fracture control	ECSS-E-ST-32-01
Analytical verification	ECSS-E-ST-33-01 Annex C
Hazard and safety analysis	ECSS-Q-ST-40-02
Interface control	ECSS-E-ST-10
Manufacturing file	-
Manufacturing, assembly, integration and test approach (including Zero G rigs)	ECSS-E-ST-10-02
Mechanism user manual	ECSS-E-ST-33-01 Annex D
Qualification status	ECSS-Q-ST-10
Requirements compliance	ECSS-E-ST-10-02
Thermal analysis	ECSS-E-ST-31
Structural analysis	ECSS-E-ST-32
Safety critical mechanisms verification plan (MSVP)	ECSS-E-ST-33-01 Annex F.
Safety critical mechanisms verification report (MSVR)	ECSS-E-ST-33-01 Annex G.

ANNEX(normative)Safety critical mechanisms verification plan (MSVP) - DRD

DRD identification

Requirement identification and source document

This DRD is called from ECSS‐E‐ST‐33‐01, requirement 4.10d.1.

Purpose and objective

The purpose of the Safety Critical Mechanisms Verification Plan (MSVP) is to provide the customer with a comprehensive set of information for the design and verification of safety critical mechanisms, including:

Description of the mechanisms in a payload including the specifications and performance requirements

Identification of safety critical functions

Performance of a fault tolerance analysis of the mechanisms in the system

Demonstration of a compliance to the requirements in ECSS-E-ST-33-01

Determination of necessary controls depending on the severity level of the hazard

Hazard control verification methods list

Detailed description of the design and verification approach for safety critical mechanisms, including test conditions, test duration, loads, pass/fail criteria. This includes compliance to the requirements specific to the DFMR approach, if applicable.

Expected response

Scope and content

Introduction, references and terminology

The MSVP shall contain a description of the scope and applicability of the document.

For example: This document provides information on the design and verification approach of the “name” mechanism for the “name” project.

The MSVP shall list:

• the development phase of the mechanism being described;
• the list of documents providing additional subsystem design description;
• any other applicable and reference documents to support the generation of the document. The MSVP shall include any additional definition, abbreviation or symbol used.
  Mission and mechanism main functions

The MSVP shall describe the mission and the role of the mechanism in achieving the mission.
The MSVP shall describe the primary functions of the mechanism.
Detailed description of the mechanism

The MSVP shall describe the mechanism detailed design, including the following:

• product tree down to sub assembly break down;
• physical design of the mechanism in all configurations;
• how each function is achieved;
• protection and redundancy implementation;
• general assembly drawings with cross sections or equivalent;
• interface descriptions, comprising mechanical, thermal and electrical;
• static and dynamic envelopes. The MSVP shall identify safety critical mechanisms and determine the severity level of the hazard.
  Fault tolerance analysis

The MSVP shall include a fault-tolerance analysis for the safety-critical mechanisms.
The fault-tolerance analysis of F.2.1<4>a shall outline the hazard controls planned to meet fault-tolerance requirements.
Justification, in case DFMR is used as hazard control, shall be described in the MSVP.
The MSVP shall describe the fracture control approach.
Design justification and verification approach

The MSVP shall provide a description of the approach to achieve compliance to the requirements for safety critical mechanisms.
The MSVP shall include any required or supporting analysis.
The MSVP shall describe the verification approach for each critical mechanism operation or feature, including

• operating and holding force or torque margin;
• derived factors for design life testing;
• structural verification, comprising supporting analysis and safety factors used;
• qualification tests;
• acceptance tests;
• testing approaches for proto-flight hardware;
• life testing;
• run-in test;
• the environment, loads and test durations for all tests;
• the pass/fail criteria for each test.

Special remarks

None.

ANNEX(normative)Safety critical mechanisms verification report (MSVR) - DRD

DRD identification

Requirement identification and source document

This DRD is called from ECSS‐E‐ST‐33‐01, requirement 4.10d.2.

Purpose and objective

The purpose of the Safety Critical Mechanisms Verification Report (MSVR) is to provide the customer with a comprehensive set of information of the results of the verification of safety critical mechanisms.

Expected response

Scope and content

Introduction, references and terminology

The MSVR shall contain a description of the scope and applicability of the document.

For example: This document provides information on the design and verification approach of the “name” mechanism for the “name” project.

The MSVR shall list:

• the development phase of the mechanism being described;
• the list of documents providing additional verification description;
• any other applicable and reference documents to support the generation of the document. The MSVR shall include any additional definition, abbreviation or symbol used.
  Test objectives and test description

The MSVR shall describe the objectives of the verification process.
The MSVR shall include a comprehensive list of the test conditions.
Test results

The MSVR shall contain the test results with supporting data.

This includes the test execution dates, the as-run procedure, and the test facility results.

The MSVR shall contain the analysis of test data and the relevant assessment.
The MSVR shall provide a synthesis of the test results.
Anomalies

The MSVR shall include the list of deviations to the test procedure, the nonconformances and failures.
Conclusions

The MSVR shall summarize:

• the test results, including:
  • the list of the requirements to be verified in correlation with the VCD,
  • traceability to used documentation,
  • conformance or deviation including references and signature and date,
• the comparison with the requirements, and
• the verification close‐out judgment. The MSVR shall state and describe any open issues.
  The MSVR shall cross-reference any separate test analyses.

Special remarks

None.

Bibliography

ECSS-S-ST-00	ECSS system – Description, implementation and general requirements
ECSS-E-ST-10	Space engineering – System engineering general requirements
ECSS-E-HB-10-02	Space engineering – Verification handbook
ECSS-E-HB-20-05	Space engineering – High voltage engineering and design handbook
ECSS-E-ST-10-04	Space engineering – Space environment
ECSS-E-ST-32-01	Space engineering – Fracture control
ECSS-E-ST-10-04	Space engineering – Space environment
ECSS-E-ST-70-11	Space engineering – Space segment operability
ECSS-M-ST-40	Space project management – Configuration and information management
ECSS-Q-ST-10	Space engineering – Product assurance management
ECSS-Q-ST-10-04	Space product assurance – Critical-item control
ECSS-Q-ST-20	Space product assurance – Quality assurance
ECSS-Q-ST-30-02	Space product assurance – Failure modes, effects (and criticality) analysis (FMEA/FMECA)
ECSS-Q-ST-30-11	Space product assurance – Derating – EEE components
ECSS-Q-ST-40-02	Space product assurance – Hazard analysis
ECSS-Q-ST-60	Space product assurance – Electrical, electronic and electromechanical (EEE) components
ECSS-Q-ST-70-01	Space product assurance – Contamination and cleanliness control
ECSS-Q-ST-70-02	Space product assurance – Thermal vacuum outgassing test for the screening of space materials
ECSS-Q-ST-70-46	Space product assurance – Requirements for manufacturing and procurement of threaded fasteners