1 Scope
The purpose of this Standard is to define the Factors Of Safety (FOS), Design Factor and additional factors to be used for the dimensioning
and design verification of spaceflight hardware including qualification and acceptance
tests.
This standard is not self standing and is used in conjunction with the ECSS-E-ST-32,
ECSS-E-ST-32-02 and ECSS-E-ST-33-01 documents.
Following assumptions are made in the document:
-
• that recognized methodologies are used for the determination of the limit loads, including
their scatter, that are applied to the hardware and for the stress analyses;
-
• that the structural and mechanical system design is amenable to engineering analyses
by current state-of-the-art methods and is conforming to standard aerospace industry
practices.
Factors of safety are defined to cover chosen load level probability, assumed uncertainty
in mechanical properties and manufacturing but not a lack of engineering effort.
The choice of a factor of safety for a program is directly linked to the rationale
retained for designing, dimensioning and testing within the program. Therefore, as
the development logic and the associated reliability objectives are different for:
-
• unmanned scientific or commercial satellite,
-
• expendable launch vehicles,
-
• man-rated spacecraft, and
-
• any other unmanned space vehicle (e.g. transfer vehicle, planetary probe) specific
values are presented for each of them.
Factors of safety for re-usable launch vehicles and man-rated commercial spacecraft
are not addressed in this document.
For all of these space products, factors of safety are defined hereafter in the document
whatever the adopted qualification logic: proto-flight or prototype model.
For pressurized hardware, factors of safety for all loads except internal pressure
loads are defined in this standard. Concerning the internal pressure, the factors
of safety for pressurised hardware can be found in ECSS-E-ST-32-02. For loads combination
refer to ECSS-E-ST-32-02.
For mechanisms, specific factors of safety associated with yield and ultimate of metallic
materials, cable rupture factors of safety, stops/shaft shoulders/recess yield factors
of safety and limits for peak Hertzian contact stress are specified in ECSS-E-ST-33-01.
Alternate approach
The factors of safety specified hereafter are applied using a deterministic approach
i.e. as generally applied in the Space Industry to achieve the structures standard
reliability objectives. Structural safety based on a probabilistic analysis could
be an alternate approach but it has to be demonstrated this process achieves the reliability
objective specified to the structure. The procedure is approved by the customer.
This standard may be tailored for the specific characteristics and constraints of
a space project in conformance with ECSS-S-ST-00.