ISO 23670:2021

INTERNATIONAL ISO
STANDARD 23670
First edition
2021-09
Space systems — Vibration testing
Systèmes spatiaux — Essais de vibration
Reference number
ISO 23670:2021(E)
©
ISO 2021

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ISO 23670:2021(E)

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© ISO 2021
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ISO 23670:2021(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Abbreviated terms . 2
5 General . 2
6 Test technical requirements . 3
6.1 Test specification . 3
6.2 Tolerances . 3
6.3 Test control . . 3
6.3.1 Control strategy . 3
6.3.2 Control point . 4
6.4 Specimen configuration requirements . 5
6.5 Response measurement point . 5
6.6 Test success criteria . 5
7 Test system . 5
7.1 Test facility requirements . 5
7.2 Equipment requirements . 6
7.2.1 Shaker . 6
7.2.2 Fixture . 7
7.2.3 Force measurement device (FMD) . 7
7.2.4 Vibration control system . 9
7.2.5 Measurement system .10
8 Test procedure .11
8.1 Test preparation .11
8.1.1 Preparation of the test documents .11
8.1.2 Check of test equipment and test specimen .11
8.1.3 Safety check .12
8.2 Test implementation .12
8.2.1 General.12
8.2.2 Before test .12
8.2.3 During test .12
8.2.4 After test . .13
9 Test interruption and handling .13
9.1 Test interruption .13
9.2 Interruption handling .13
10 Test data and result evaluation .13
10.1 Test data .13
10.2 Result evaluation .14
11 Test reports .14
Annex A (Informative) A method for random vibration and acoustic test tailoring.15
Annex B (Informative) An example of notching principles and calculation method for
notching control .18
Annex C (informative) Force limit determination .20
Bibliography .28
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ISO 23670:2021(E)

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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
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on the ISO list of patent declarations received (see www .iso .org/ patents).
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expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www .iso .org/
iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicle,
Subcommittee SC 14, Space systems and operations.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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ISO 23670:2021(E)

Introduction
Vibration testing is one of the most important test items of space systems. The primary goals of
vibration testing are to verify the design and to detect manufacturing issues of spacecraft, subsystems
and units that could result in in-flight failures. In design, material selection, manufacture, assembly and
integration phase, the test aims on exposing defects and non-conformances existing and eliminating
potential quality problems. With regard to the launch phase, it also serves to prevent structural failure
of a space system, loosening of fasteners and connectors, failure of electronic components, leakage of
sealing elements or malfunction of mechanical system.
During vibration testing, over-testing can result in unnecessary destruction of the test specimen. In
the 1990s, at the Jet Propulsion Laboratory, Mr. Terry Scharton elaborated the methodology of force
notching for qualification of satellites and spacecraft to mitigate unnecessary over-testing. Since then,
several attempts have been made to establish this methodology for a broader range of application. This
document includes the methodology of force-based testing.
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INTERNATIONAL STANDARD ISO 23670:2021(E)
Space systems — Vibration testing
IMPORTANT — The electronic file of this document contains colours which are considered to be
useful for the correct understanding of the document. Users should therefore consider printing
this document using a colour printer.
1 Scope
This document provides guidance and requirements for test providers and interested parties to
implement vibration testing.
This document specifies methods, including the force limiting approach, to mitigate unnecessary over-
testing of spacecraft, subsystems and units for space application.
The technical requirements in this document can be tailored to meet the actual test objectives.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitute requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 15864:2021, Space systems — General test methods for space craft, subsystems and units
ISO 19924:2017, Space systems — Acoustic testing
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
notching
reduction of the input level or spectrum in a vibration testing to limit structural responses at resonant
frequencies according to qualification or acceptance loads to avoid over-testing.
3.2
response limited vibration testing
reduction of input acceleration in a vibration testing to maintain the measured response at or below a
specified value
3.3
force limited vibration testing
reduction of reaction force in a vibration testing to specified values, which are usually the interface
forces predicted for flight, plus a desired margin.
3.4
statistical DOF
number of independent variables in a statistical estimate of a probability
Note 1 to entry: The number of degrees of freedom determines the statistical accuracy of an estimate.
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[SOURCE: ISO 2041:2018, 3.5.16, modified — The term has been changed from "statistical degrees of
freedom" to "statistical DOF".]
4 Abbreviated terms
For the purposes of this document, the abbreviated terms described in Table 1 apply.
Table 1 — Abbreviated terms
DOF degree of freedom
FEA finite element analysis
FLV force limited vibration
FLVT force limited vibration test
FMD force measurement device
FRF frequency response function
POGO propulsion generated oscillations
PSD power spectral density
RMS root mean square
TDFS two-degree of freedom system
5 General
Vibration testing is distinguished between sinusoidal vibration testing and random vibration testing.
Sinusoidal vibration testing is intended to simulate the vibration environment produce by unstable
combustion, by coupling of structural resonant frequencies (POGO), by imbalances in rotating
equipment. Sinusoidal vibration testing is also to simulate ground transportation and handling, due to
resonant responses of tires and suspension systems of the transporters.
Random vibrations are generated by the launcher engines and by acoustic and aerodynamic excitation
of the launch vehicle and spacecraft fairing. During flight or ground transportation and handling, broad
band vibration environment is imposed on the spacecraft. ISO 15864 recommends either vibration or
acoustic testing, whichever is more appropriate, with the other one left optional. Generally, if acoustic
testing is performed, random vibration may be skipped. For a small compact spacecraft, acoustic testing
does not provide adequate environmental simulation, and random vibration may replace the acoustic
test. To take this decision it is important to consider:
— vibration testing do not reach high frequency contents;
— whether the structure is sensitive to acoustic loads;
— whether the structure is sensitive to acoustic loads where the units are mounted.
Information for random vibration and acoustic test tailoring is provided in Annex A.
Conventional acceleration control during vibration testing may lead to the so-called over-testing
problem due to the difference of the interface impedance of the mounting structure and the shaker.
In order to overcome this problem, the force limited vibration (FLV) testing technique was developed.
In the FLV testing, in addition to the acceleration specification, the specification of the reaction force
between fixture and test specimen shall be defined. Using the FLV technique, both the acceleration
and force at the interface of test specimen and fixture are limited so that the vibration environment
characterizes the real situation more precisely.
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ISO 23670:2021(E)

6 Test technical requirements
6.1 Test specification
The test specification shall meet the requirements of the respective launch vehicle user manual.
The test specification generally includes testing level, frequency range, test direction and test duration.
The duration of sinusoidal vibration testing is determined by the sweep rate and frequency range. The
duration of random vibration testing is expressed in seconds or minutes. The test directions usually
correspond with the three orthogonal axes, one of which is in accordance with the launch direction.
If FLVT will be applied, the test specifications shall be extended with the FLVT requirements.
When needed to re-check workmanship by dynamic mechanical environmental test for flight units that
have undergone rework and that required random vibration testing at acceptance test, the minimum
retesting shall be random vibration testing at workmanship screening level to be agreed with the
customer. However, if the most effective single axis of workmanship screening re-test for all the
reworked areas is determined, re-test excitation can be based just on that axis.
6.2 Tolerances
The tolerances shall be determined based on the design standard. If not specified otherwise, the
following test level tolerances can be used.
a) Sinusoidal vibration
Frequency: −2 % to +2 % (or −1 Hz to +1 Hz, whichever is greater)
Acceleration amplitude: −10 % to +10 %
b) Random vibration
Acceleration spectral density (frequency resolution better than 10 Hz)
10 Hz to 100 Hz (analysis bandwidth 10 Hz or narrower): −3 dB to +3 dB
100 Hz to 1 000 Hz (analysis bandwidth is 10 % or narrower of the central frequency): −3 dB to +3 dB
1 000 Hz to 2 000 Hz (analysis bandwidth 100 Hz or narrower): −3 dB to +3 dB
Statistical DOF: not less than 100
Overall grms.: −10 % to +10 %
Test duration: −0 % to +10 %
6.3 Test control
6.3.1 Control strategy
6.3.1.1 General
The control strategy shall provide the required vibration at the required locations in or on the test
specimen. This depends on the kind of vibration to be generated and on the test specimen/shaker
interaction. Generally, a single strategy is appropriate (e.g. only acceleration input control strategy
is used). There are cases where multiple strategies are used simultaneously (e.g. acceleration input
control strategy and force limited vibration testing strategy are used simultaneously).
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ISO 23670:2021(E)

6.3.1.2 Acceleration input control
Acceleration input control is the basic method of vibration testing. The control accelerometers shall
be mounted on the fixture at the test specimen mounting points. Shaker motion shall be controlled
with feedback from the control accelerometer(s) to provide defined vibration levels at the fixture/ test
specimen interface.
6.3.1.3 Notching
Notching is a general accepted practice in full-level vibration testing to avoid over-testing.
Implementation of notching shall be subject to customer approval and relevant to Launcher authority
approval. Refer to Annex B for an example of the notching calculate method. The following requirements
apply.
a) The force on the main structure shall not be higher than the design value of quasi-static load plus a
desired margin.
b) The vibration level shall not be less than the level of coupling analysis result for the interface
between spacecraft and launcher, unless agreed by the launcher authority.
c) The response of key equipment fixed position shall not be higher than the equipment vibration
testing level.
6.3.1.4 Force limited vibration testing
For force limited vibration testing, the vibration level is defined by acceleration. In addition, the
reaction force between fixture and test specimen shall be measured and limited. Dynamic force gauges
are mounted between the fixture and the test specimen. If the force achieves the limited value, the
exciter motion shall be controlled with feedback from the force gages.
Force limiting is most useful for test specimens that exhibit distinct, lightly damped resonances on the
shaker. The amount of relief available from force limiting is greatest when the structural impedance
of the test specimen is equal to, or greater than that of the mounting structure in the actual mounting
situation.
The force limit value shall be slightly larger than the real reaction force of the interface during launch,
plus the desired margin. Force limits value can be determined in several ways including simple and
complex TDFS Method, semi-empirical method, FEA method, quasi-static-load method, apparent
masses envelope method and design/flight loads method. A non-exhaustive list of force limit method is
specified in Annex C.
6.3.1.5 Response limited vibration testing
For response limited vibration testing, the vibration level is defined by acceleration. In addition,
vibration response limits at specific points on the test specimen shall be defined. Monitoring
accelerometers shall be located at these points. The test specimen shall be excited using control point
accelerometer signals to control the exciters. The control inputs shall be automatically modified as
needed to limit responses at the monitoring accelerometers to the predefined limits. This strategy is
used to avoid damage to the specific equipment or lower level assembly.
6.3.2 Control point
The control accelerometer(s) shall be mounted on the test fixture near the specimen attachment points.
For multiple-point control, an even distribution should be adopted. In case specific requirements
exist, the positions of the control points shall be determined accordingly. If more than one control
accelerometer is used, the test levels may be controlled by a control scheme either based on the
average response or on the response extremes. The control scheme shall be consistent with the test
requirement.
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ISO 23670:2021(E)

6.4 Specimen configuration requirements
The specimen configuration shall be as described in ISO 15864:2021, 7.13.3 and 7.14.3.
6.5 Response measurement point
The test requirements shall specify the number, installation position and orientation, type and
measurement range of test sensors, as well as the processing modes and requirements for data
measurement. See more detailed requirements in 7.2.5.
6.6 Test success criteria
It is presupposed that an accomplished test is formally compliant with the contract requirements.
For the test provider, if not specified otherwise, the following requirements shall apply.
— All vibration testing shall be applied at the right test level.
— The acquisition of test specimen vibration response data shall be complete and valid.
For the specimen provider, if not specified otherwise, the following requirements shall apply.
— The intended test purposes shall be achieved.
— There shall be no visual damage to the test specimen.
— The characteristic response curve (which includes the resonance frequencies and the amplification
ratio) shall be the same before and after each full level vibration testing (see 8.2.3 a)) under
consideration of the specified tolerance bands.
— The test specimen performance after the test shall be specified by the customer.
7 Test system
7.1 Test facility requirements
A vibration testing facility includes a vibration excitation system, a vibration control system, a
measuring system and auxiliary equipment. An example of a vibration testing facility is shown in
Figure 1.
For FLVT, dynamic force gauges are mounted between the shaker/fixture and the test specimen. The
force at the interface is measured by the force gauges and is fed back to the control system to implement
response limiting.
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ISO 23670:2021(E)

Key
1 accelerance signal conditioner 7 shaker
2 test specimen 8 data storage and processing system
3 force signal conditioner 9 data acquisition system
4 vibration controller 10 measurement system
5 power amplifier 11 accelerometer
6 force measurement device (for FLV) 12 force gauge
Figure 1 — Illustration of a force limited testing system
The test facility, including all auxiliary equipment,
— shall provide the specified vibration environments,
— shall implement the required control strategies, and
— shall meet the specified tolerances.
Measurement transducers, data recording and data reduction equipment capable of measuring,
recording, analysing, and displaying data shall be sufficient to document the test and to acquire any
additional data required.
The facility shall be maintained in regular intervals and shall be checked before test campaign.
7.2 Equipment requirements
7.2.1 Shaker
The requirements of the shaker are as follows.
a) The shaker test facility shall fulfil the requirements of the test concerning power, dimension,
applicable forces and moments with a margin. The test requirements shall not be limited by the
shaker performance.
b) The static load capacity shall be greater than the sum of mass of the test specimen, moving part of
the shaker and the fixture. Flexible supports are necessary if this requirement cannot be met. The
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ISO 23670:2021(E)

natural frequency of this supporting system shall be less than the lowest test frequency, and the
allowed displacement shall be no less than the required displacement.
c) The maximum displacement of shaker shall be greater than that required by the test conditions.
d) The shaker frequency range shall allow reaching the upper and lower limit frequencies specified in
the test conditions.
7.2.2 Fixture
The requirements for the test fixture are as follows.
a) The fixture stiffness-and-mass ratio shall be as large as possible.
b) The fixture shall mate with the test specimen in the same way as the flight interface does, so that
the interface load distribution is similar to that in flight.
c) The acceleration response of the interface between fixture and test specimen shall be uniform in
the test frequency range.
d) The first natural frequency of the fixture shall be higher than the higher frequency of the vibration
testing. When this requirement cannot be met, the first natural frequency of the fixture is a number
of times “N” of the first natural frequency of the test specimen. The number of times “N” shall be
greater than 3 and agreed with the customer. Any additional notching or input level reduction
cause by the fixture shall comply with requirements of 6.3.
e) S force measurement device is used as test fixture in FLVT, requirements for a force measurement
device are specified in 7.2.3.
f) The vibration fixture configuration, and its interfaces to the test specimen / vibration source /
other ground support equipment, shall be defined, inspected, fit checked and proof tested well
before the vibration testing is carried out.
7.2.3 Force measurement device (FMD)
7.2.3.1 General
...