ISO 21648:2008
(Main)Space systems — Flywheel module design and testing
Space systems — Flywheel module design and testing
ISO 21648:2008 establishes the design, analysis, material selection and characterization, fabrication, test and inspection of the flywheel module (FM) in a flywheel used for energy storage in space systems. These requirements, when implemented on a flywheel module, will ensure a high level of confidence in achieving safe operation and mission success. With appropriate modifications, ISO 21648:2008 can also be applied to similar devices, such as momentum and reaction wheels and control-moment gyroscopes. The requirements set forth in ISO 21648:2008 are the minimum requirements for flywheel modules in flywheels used in space flight applications. They are specifically applicable to the parts in the flywheel rotor assembly (FRA), including rim, hub and/or shaft and other associated rotating parts, such as the bearings and the motor generator rotor. The requirements are also relevant to the non-rotating parts, such as module housing, main suspension assembly (magnetic or rolling element bearings, superconductor bearings, etc.), motor stator, caging mechanism and sensors within the module housing, and backup bearings, if applicable. However, control and interface electronics are not covered in ISO 21648:2008.
Systèmes spatiaux — Conception et essai du module de volant moteur
General Information
Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 21648
First edition
2008-12-01
Space systems — Flywheel module
design and testing
Systèmes spatiaux — Conception et essai du module de volant moteur
Reference number
©
ISO 2008
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ii © ISO 2008 – All rights reserved
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Terms, definitions, symbols and abbreviated terms. 1
2.1 Terms and definitions. 1
2.2 Symbols . 5
2.3 Abbreviated terms . 6
3 Requirements . 6
3.1 General requirements. 6
3.2 Design requirements . 7
3.3 Requirements for materials . 11
3.4 Fabrication and process control. 14
3.5 Quality assurance. 15
3.6 Repair and refurbishment . 16
3.7 Storage requirements. 16
3.8 Transportation requirements. 16
4 Verification requirements . 17
4.1 Design requirements verification. 17
4.2 Qualification tests. 20
4.3 Acceptance tests . 24
Bibliography . 28
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 21648 was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles, Subcommittee
SC 14, Space systems and operations.
iv © ISO 2008 – All rights reserved
Introduction
Flywheels are mechanical devices that store kinetic energy in a rotating mass. A simple example is the
potter’s wheel, which was widely used by people in ancient times. The first use of such devices dates from
between 3500 and 3000 BC. According to archaeological evidence, these early flywheels were built from
wood, stone and clay. One type of potter’s wheel was a rim made from a unidirectional material (bamboo),
wound in the hoop direction and embedded in a matrix (clay). This design option is clearly a foreshadowing of
the later use of composites for their inherent strength and lightweight nature.
It is, however, only since the 1970s that the use of flywheels as energy storage systems has become the
focus of serious attention from energy researchers due to the constant threat of a shortage of fossil fuel
supplies. Today, a typical flywheel energy system consists of a flywheel rotor, a supporting device (magnetic
bearing ball bearings, superconductor bearings or other types of bearings), a charge/discharge device
(motor/generator) and a safety containment (housing). For space applications, due to weight constraints, the
use of a bulky safety containment system is not necessarily a desirable design. Thus, from a safety point of
view, the design of flywheel energy systems needs to concentrate on reliability and longevity.
Current flywheel energy storage technology is made possible by the use of high-strength, carbon-fibre-based
composite materials in the rotor. Flywheel energy storage systems are designed to both control spacecraft
attitude and to store energy — functions which have historically been performed by two separate systems.
The stored energy is needed for the dark portions of the orbit when the Earth’s shadow makes solar power
unavailable for spacecraft. For many spacecraft, flywheels offer the potential to significantly reduce weight and
extend service life. However, the use of composite materials, coupled with variations in design approaches
and demanding operating conditions, combine to present certification challenges for the rotor assemblies.
This International Standard establishes the design, analysis, material selection and characterization,
fabrication, test and inspection of the flywheel module in a flywheel. Many requirements set forth in this
International Standard can also be adapted by similar types of rotating machineries, but for different usage.
The momentum wheels and momentum gyroscopes are typical examples. The implementation of these
requirements will ensure a high level of confidence in achieving safe operation and mission success for these
critical hardware items.
INTERNATIONAL STANDARD ISO 21648:2008(E)
Space systems — Flywheel module design and testing
1 Scope
This International Standard establishes the design, analysis, material selection and characterization,
fabrication, test and inspection of the flywheel module (FM) in a flywheel used for energy storage in space
systems. These requirements, when implemented on a flywheel module, will ensure a high level of confidence
in achieving safe operation and mission success. With appropriate modifications, this International Standard
can also be applied to similar devices, such as momentum and reaction wheels and control-moment
gyroscopes.
The requirements set forth in this International Standard are the minimum requirements for flywheel modules
in flywheels used in space flight applications. They are specifically applicable to the parts in the flywheel rotor
assembly (FRA), including rim, hub and/or shaft and other associated rotating parts, such as the bearings and
the motor generator rotor. The requirements are also relevant to the non-rotating parts, such as module
housing, main suspension assembly (magnetic or rolling element bearings, superconductor bearings, etc.),
motor stator, caging mechanism and sensors within the module housing, and backup bearings, if applicable.
However, control and interface electronics are not covered in this International Standard.
2 Terms, definitions, symbols and abbreviated terms
2.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1.1
A-basis allowable
mechanical strength value above which at least 99 % of the population of values is expected to fall, with a
confidence level of 95 %
NOTE See also B-basis allowable (2.1.4).
2.1.2
acceptance tests
required formal tests conducted on hardware items to ascertain that the materials, manufacturing processes
and workmanship meet specifications
2.1.3
allowable load
allowable stress
allowable strain
maximum load that can be accommodated by a structure/material without rupture, collapse or detrimental
deformation in a given environment
NOTE Allowable loads commonly correspond to the statistically-based minimum ultimate strength, buckling strength
and yield strength, as applicable.
2.1.4
B-basis allowable
mechanical strength value above which at least 90 % of the population of values is expected to fall, with a
confidence level of 95 %
NOTE See also A-basis allowable (2.1.1).
2.1.5
catastrophic failure
structural failure event due to the rotor separation, or the rupture or collapse, of other flywheel rotor assembly
components or assembly
2.1.6
composite material
combination of materials which differ in composition or form on a macro-scale
NOTE The constituents retain their identities in the composite, i.e. they do not dissolve or otherwise merge
completely into each other, although they act in concert. Normally, the composites can be physically identified and exhibit
an interface between one another.
2.1.7
damage tolerance
ability of structure/material to resist failure due to the presence of flaws for a specified period of unrepaired
usage
2.1.8
damage tolerance life
required period during which a part of a flywheel module, even containing a large undetected crack, is shown
by analysis or testing not to fail catastrophically in the expected service load and environment
2.1.9
damage tolerance analysis
damage tolerance testing
analysis/testing that is used to demonstrate damage tolerance life
NOTE For metallic parts, this type of analysis is also referred to as safe-life analysis.
2.1.10
design safety factor
multiplying factor to be applied to the limit load and/or maximum expected operating speed
2.1.11
fatigue life
number of load cycles experienced in service that a defect-free part in a flywheel module can sustain before
failure of a specified nature could occur
NOTE The number of load cycles experienced in service can be flight loads, ground test loads and charge/discharge
cycles.
2.1.12
flaw
local discontinuity in a structural material
EXAMPLE Crack, delamination, void.
2.1.13
flight-like test article
test article that is built in accordance with a fabrication process identical to the flight hardware
2 © ISO 2008 – All rights reserved
2.1.14
flywheel module
FM
assembly of mechanical parts which support and spin the flywheel rotor assembly and which house the
appropriate sensors, rotor support systems and motor, which with the appropriate avionics suite and software
can act as a stand-alone functional flywheel unit
NOTE A flywheel module typically includes the housing, main suspension system (magnetic or rolling element
bearing, superconductor bearings), motor stator, caging mechanism, sensors and backup bearings, if applicable.
2.1.15
flywheel rotor assembly
FRA
assembly in a flywheel which consists of rim, shaft and/or hub, bearings, motor generator rotor and other
associated parts that rotate under normal operation
2.1.16
fracture critical part
classification of a part for manned space systems, which assumes that fracture or failure of that part resulting
from occurrence of a crack-like defect would create a catastrophic hazard
NOTE Such classification is required on components u
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