ISO 21494:2019

Space systems — Magnetic testing

ISO 21494:2019 specifies magnetic test methods including magnetic field test methods, magnetic moment test methods, magnetization and demagnetization test methods and magnetic compensation test methods. This document is applicable to magnetic tests on several levels: spacecraft-level, subsystem-level and unit-level. ISO 21494:2019 gives guidelines for conducting magnetic tests both in zero-magnetic field environment provided by magnetic test facilities and in the presence of the geomagnetic field environment.

Systèmes spatiaux — Essais magnétiques

General Information

• Status: Published
• Publication Date: 21-Feb-2019
• ICS: 49.140 - Space systems and operations
• Technical Committee: ISO/TC 20/SC 14 - Space systems and operations
• Drafting Committee: ISO/TC 20/SC 14/WG 2 - System requirements, verification and validation, interfaces, integration, and test
• Current Stage: 6060 - International Standard published
• Start Date: 22-Feb-2019
• Completion Date: 22-Feb-2019

RELATIONS

• Consolidated By: ISO/TS 23758:2021 - Guidelines for the validation of qualitative screening methods for the detection of residues of veterinary drugs in milk and milk products
• Effective Date: 06-Jun-2022

Standards Content (sample)

INTERNATIONAL ISO
STANDARD 21494
First edition
2019-02
Space systems — Magnetic testing
Systèmes spatiaux — Essais magnétiques
Reference number
ISO 21494:2019(E)
ISO 2019
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ISO 21494:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2019

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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ISO 21494:2019(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Abbreviated terms .............................................................................................................................................................................................. 3

5 Requirements .......................................................................................................................................................................................................... 3

5.1 EUT requirements ................................................................................................................................................................................ 3

5.2 Test requirements ................................................................................................................................................................................ 4

6 Test items ..................................................................................................................................................................................................................... 4

7 Test room environments .............................................................................................................................................................................. 5

8 Magnetic field test methods ...................................................................................................................................................................... 5

8.1 Test purpose .............................................................................................................................................................................................. 5

8.2 Test facilities.............................................................................................................................................................................................. 5

8.3 Procedures for magnetic field test ......................................................................................................................................... 6

9 Magnetic moment test methods ........................................................................................................................................................... 6

9.1 Test purpose .............................................................................................................................................................................................. 6

9.2 Test facilities.............................................................................................................................................................................................. 6

9.3 Procedures and calculating formulas for magnetic moment test ............................................................... 7

9.4 Magnetic moment test in the geomagnetic field ........................................................................................................ 7

10 Magnetization and demagnetization test methods .......................................................................................................... 7

10.1 Test purpose .............................................................................................................................................................................................. 7

10.2 Test facilities.............................................................................................................................................................................................. 7

10.3 Procedures for magnetization and demagnetization test .................................................................................. 8

11 Magnetic compensation test method .............................................................................................................................................. 8

11.1 Test purpose .............................................................................................................................................................................................. 8

11.2 Procedures for magnetic compensation test ................................................................................................................ 9

12 Test report ................................................................................................................................................................................................................... 9

Annex A (informative) Procedures for a magnetic field test ....................................................................................................10

Annex B (informative) Procedures and calculating formulas for a magnetic moment test .....................13

Annex C (informative) Procedures for a magnetization and demagnetization test .........................................24

Annex D (informative) Procedures for a magnetic compensation test ..........................................................................26

Bibliography .............................................................................................................................................................................................................................27

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ISO 21494:2019(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

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/patents).

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constitute an endorsement.

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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 vehicles,

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 21494:2019(E)
Introduction

The magnetic torque, which is created by the interaction between a geomagnetic field and the remnant

magnetic moment of the spacecraft, has considerable disturbance on the flight attitude of the spacecraft.

The magnetic field of the spacecraft itself will affect a magnetometer scientific payload sensitive to

spacecraft-induced magnetic fields. Thus, magnetic tests on Earth-orbiting or interplanetary spacecraft

missions with very stringent requirements on magnetic cleanliness are needed in order to ensure that

the spacecraft’s inherent magnetic properties meet the design goals.

This document provides magnetic test requirements and methods for measuring and evaluating

magnetic properties of the spacecraft. The magnetic test methods outlined in this requirements

document are effective enough to verify the compliance of magnetic requirements imposed on the

spacecraft and to ensure the success of spacecraft flight missions free of magnetic interference and

magnetic contamination due to magnetic materials and induced current-generated magnetic fields of

the spacecraft.
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INTERNATIONAL STANDARD ISO 21494:2019(E)
Space systems — Magnetic testing
1 Scope

This document specifies magnetic test methods including magnetic field test methods, magnetic

moment test methods, magnetization and demagnetization test methods and magnetic compensation

test methods. This document is applicable to magnetic tests on several levels: spacecraft-level,

subsystem-level and unit-level.

This document gives guidelines for conducting magnetic tests both in zero-magnetic field environment

provided by magnetic test facilities and in the presence of the geomagnetic field environment.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes 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 14644-1, Cleanrooms and associated controlled environments — Part 1: Classification of air cleanliness

by particle concentration
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:

— IEC Electropedia: available at https: //www .electropedia .org/
— ISO Online browsing platform: available at https: //www .iso .org/obp
3.1
equipment under test
EUT
object under the magnetic test on system, subsystem or unit level generally
3.2
remnant magnetic moment

magnetic moment of the EUT in a zero-magnetic field environment when the EUT is not in a powered on

operational mode, that is mostly due to the residual magnetic fields from spacecraft materials

3.3
stray magnetic moment

magnetic moment of the EUT in zero-magnetic field environment when the EUT is in a powered on

operational mode
3.4
induced magnetic moment

additional magnetic moment of the EUT generated in an external magnetic field environment when the

EUT is not in a powered on operational mode, that is mostly due to soft magnetic materials that easily

magnetize in an external magnetic field
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ISO 21494:2019(E)
3.5
remnant magnetic field

magnetic field produced by the remnant magnetic moment of the EUT as measured at a distance from

the magnetic moment location and falls off as the inverse cube of the distance from the magnetic

moment location
3.6
stray magnetic field

magnetic field produced by the stray magnetic moment of the EUT in a powered on operational mode

3.7
induced magnetic field

magnetic field produced by the induced magnetic moment of the EUT and mostly due to soft magnetic

materials that easily magnetize in an external magnetic field
3.8
zero-magnetic field

magnetic field within a certain volume reduced to very low levels when the geomagnetic field is

compensated by a cancelling magnetic field provided by a typical main coil system such as a Helmholtz

coil or Braunbeck coil system
3.9
controllable magnetic field

magnitude of magnetic field within a certain volume that is controlled by adjusting electric current of a

typical main coil system such as a Helmholtz coil or Braunbeck coil system
3.10
magnetization field

magnetic field used for magnetization tests of the EUT when exposed to a uniform and steady magnetic

field for a certain period of time and provided by a magnetization and demagnetization coil system

3.11
demagnetization field

magnetic field used for demagnetization tests of the EUT by exposing them in an alternating sinusoidal

magnetic field with a continuously attenuated amplitude and provided by a magnetization and

demagnetization coil system
3.12
main coil system

coil system, usually composed of Helmholtz or Braunbeck coils and energized by power supplies, that

can provide a zero-magnetic field environment within a given volume of the coil system or that can

generate a controllable magnetic field environment by applying the system with calibrated electric

current levels
3.13
magnetization and demagnetization coil system

coil system, usually composed of a Helmholtz coil and energized by power supplies, that can provide

magnetization and demagnetization fields by applying the system with electric current

3.14
magnetic field stability
variation of the magnetic field at the same location during a certain period
3.15
magnetic field homogeneity

ratio (given in %) of the maximum magnetic field deviation in the volume divided by the magnetic field

at the centre of the volume, or the range (given in ± values) of the maximum magnetic field deviation in

the volume
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ISO 21494:2019(E)
3.16
homogeneous volume of magnetic field
spatial volume that satisfies the requirement of magnetic field homogeneity
3.17
soft magnetic material

ferromagnetic material with low field strength (coercivity) that can be magnetized and

demagnetized easily
EXAMPLE Invar and Kovar materials.
3.18
hard magnetic material

ferromagnetic material with high field strength (coercivity) that cannot be demagnetized easily

EXAMPLE Permanent magnets.
3.19
compensation magnet
permanent magnet used for magnetic compensation
4 Abbreviated terms
EUT Equipment Under Test
IMF Initial Magnetic Field
RMF Remnant Magnetic Field
SMF Stray Magnetic Field
IDMF Induced Magnetic Field
IMDM Initial Magnetic Dipole Moment
RMDM Remnant Magnetic Dipole Moment
SMDM Stray Magnetic Dipole Moment
IDMDM Induced Magnetic Dipole Moment
MFAM Magnetic Field After Magnetization
MFAD Magnetic Field After Demagnetization
MDMAM Magnetic Dipole Moment After Magnetization
MDMAD Magnetic Dipole Moment After Demagnetization
5 Requirements
5.1 EUT requirements

When a spacecraft requires the protection of a magnetic sensitive payload such as a magnetometer

sensor or plasma search coil and the control of magnetic torque for attitude control, a magnetic

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ISO 21494:2019(E)

cleanliness control plan shall be instituted based on properties and constraints, which are related to

mission objectives. This plan should:

a) Prepare magnetic control guidelines, outlining examples on how to control magnetic materials,

what materials are acceptable, how to perform tests and to model the overall spacecraft based on

magnetic moment results.

b) Establish a magnetic moment budget or allocation list for parts, units, subsystems and spacecraft

in the actual magnetic field environment on the orbit, such as the magnetic moment or field of the

EUT at low levels of magnetic field and the delta of magnetic moment or field between unpowered

and powered mode.

c) Include the steps for reducing magnetic sources. Outline of detailed proven methods for the

reduction and cancellation of magnetic fields, elimination of magnetic materials replaced with non-

magnetic materials etc.

d) Define magnetic test methods and requirements for parts, units, subsystems and spacecraft.

The steps for reducing magnetic sources include avoiding hard magnetic materials, limiting the use

of soft magnetic materials, applying self-compensating configuration of magnetic sources, designing

all current carrying and electrical grounding elements to minimize stray magnetic field and stray

magnetic moment by self-cancelling methods including solar array backwiring.
5.2 Test requirements

In order to check and control the magnetic properties of the EUT, the magnetic test should be conducted.

An example of magnetic test flow is:
a) IMF and IMDM measurement.
b) Magnetization test.
c) MFAM and MDMAM measurement.
d) Demagnetization test.
e) MFAD and MDMAD measurement.
f) Magnetic compensation test.
g) RMF, SMF, RMDM and SMDM measurement after magnetic compensation.
h) IDMF and IDMDM measurement.
References [1]–[5] recommend the magnetic test requirements.
6 Test items

Magnetic test items described in this document refer to magnetic field test, magnetic moment test,

magnetization test, demagnetization test and magnetic compensation test.

Magnetic test items are tailored based upon magnetic test requirements for each unique mission or

plan. The logic flow of test items is defined according to magnetic requirements imposed for each

specific spacecraft.

The magnetic field of the spacecraft will affect precision measurements of magnetic sensitive payload

such as magnetometers or plasma wave search coils. Therefore, the spacecraft has requirements

on magnetic cleanliness imposed by the sensitivity of the scientific payloads requiring low levels of

magnetic fields. According to the requirements, the magnetic field test shall be conducted to predict

magnetic cleanliness level of the spacecraft with the goal of meeting the reduced magnetic field levels

needed by the sensitive payloads.
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ISO 21494:2019(E)

The magnetic disturbance torque acting on the spacecraft is equal to the cross-product of the

remnant magnetic moment of the spacecraft and the ambient magnetic flux density. If required, the

magnetic moment test shall be conducted to predict the flight attitude changes caused by the magnetic

disturbance torque of the spacecraft.

Magnetization and demagnetization tests shall be conducted if the spacecraft is easily influenced by

the external magnetic fields while on the orbit. Demagnetization tests shall be conducted as a final

step in the magnetic testing process well before its launching if the spacecraft may have inadvertently

become magnetized after the magnetic tests.

Magnetic compensation tests shall be conducted if the magnetic properties of the spacecraft do not

satisfy the overall magnetic cleanliness requirements.

The spacecraft-level magnetic tests for qualification and acceptance are recommended to be conducted

after the vibration test. This provides an opportunity to eliminate or reduce any magnetization of

the flight hardware caused by the magnetic fields associated with the vibration shaker test facilities,

especially for a spacecraft with magnetically sensitive payloads.

References [6]–[7] provide examples of actual implementation of the approach in recent missions

requiring magnetic cleanliness.
7 Test room environments
The requirements of test room environments are as follows:
a) Temperature, cleanliness and humidity shall meet customer’s requirements.
b) The air cleanliness in test room shall comply with ISO 14644-1.
8 Magnetic field test methods
8.1 Test purpose

The purpose of magnetic field test is to measure and evaluate magnetic field of the EUT and verify

whether it conforms to magnetic field requirements of the EUT.

Magnetic field test methods include RMF, SMF and IDMF measurements of the locations sensitive to

magnetic field on the EUT and RMF, SMF and IDMF distribution measurements on a sphere around

the EUT.

RMF is mainly generated by magnets, electro-magnets in off-state or residual perm-up (or

magnetization) due to hysteresis of soft magnetic materials in the EUT. SMF is generated by electric

current flowing within the EUT when in a powered on operational mode. RMF and SMF are independent

of the environmental magnetic field. RMF and SMF tests should be conducted in zero-magnetic field.

IDMF is mainly generated by the soft magnetic materials in the EUT. If an external magnetic field is

applied to the EUT, the magnetic field measurement result of the EUT may be different in zero-magnetic

field. This difference is called IDMF. IDMF disappears when the external field is ceased. IDMF test should

be conducted in the controllable magnetic field.
8.2 Test facilities

The test facilities are mainly composed of the main coil system, turntable, fixtures/brackets and

magnetic field measuring instruments or test magnetometer sensors. The main coil system shall be

able to provide the zero-magnetic field or controllable magnetic field within a given volume where the

EUT will be located in the centre of the turntable. The controllable magnetic field also can be provided

by the additional coil system. The main coil system access opening shall be large enough to allow the

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ISO 21494:2019(E)

transit of the EUT and its non-magnetic fixture and/or holding brackets into the zero-magnetic field

volume. The magnitude, homogeneity and stability of the zero-magnetic field and the controllable

magnetic field shall satisfy test requirements.

The turntable shall be rotated from 0° to 360° along the vertical axis, with all angles easily identifiable.

The ball bearing capacity of the turntable shall be more than the total weights of the EUT and its fixed

bearing. Proof loading of the turntable shall be conducted prior to the test to ensure proper rotation

without galling the bearings. The turntable is not required for the magnetic field measurement of

locations sensitive to magnetic field on the EUT. The turntable shall be required for the magnetic field

distribution measurement on a sphere around the EUT.

The test facilities shall be made of non-magnetic materials. Copper, aluminium, titanium, brass, treated

wood and other non-metallic materials are recommended.

The fluxgate magnetometers are recommended for measuring the magnetic field of the EUT. The

measurement range and resolution of the magnetometers should be adapted to the required results

and accuracy of the magnetic test.

The test facilities and measurement instruments shall be calibrated periodically or in advance of testing

and used during its useful-life.
8.3 Procedures for magnetic field test

Two procedures for magnetic field test methods in Annex A are provided as examples: (1) test

procedure for locations sensitive to magnetic field on the EUT and (2) test procedure for magnetic field

distribution measurement on a sphere around the EUT. The procedures for the magnetic field test shall

be selected according to magnetic test requirements.
9 Magnetic moment test methods
9.1 Test purpose

The purposes of magnetic moment tests are to measure and evaluate magnetic moments of the EUT and

verify whether it conforms to magnetic moment requirements of the EUT.

The magnetic dipole moment is the major part of the magnetic moment of the EUT, so magnetic moment

test methods include RMDM, SMDM and IDMDM measurements of magnetic dipole method, near-field

method and multiple magnetic dipole method.

RMDM is generated by magnets, electro-magnets in off-state or residual perm-up (or magnetization)

due to hysteresis of soft magnetic materials in the EUT. SMDM is generated by electric current flowing

within the EUT. RMDM and SMDM are independent of the environmental magnetic field. RMDM and

SMDM tests are conducted in the zero-magnetic field or geomagnetic field.

IDMDM is the induced magnetic dipole moment in soft magnetic materials caused by an external

magnetic field. This magnetic moment contribution changes instantaneously with the magnitude and

the direction of the external magnetic field. IDMDM test is conducted in the controllable magnetic field.

9.2 Test facilities

The test facilities and measurement instruments for the magnetic moment test in zero-magnetic field

shall be the same as those described in 8.2 for the magnetic field test.

The turntable is not required for the magnetic moment measurement of the magnetic dipole method.

The turntable shall be required for the magnetic moment measurement with the near-field method and

multiple magnetic dipole modelling method.

The main coil system shall be unnecessary for the magnetic moment test in the geomagnetic field. The

turntable, fixture/bracket and measurement instruments shall be the same as those described in 8.2.

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ISO 21494:2019(E)
9.3 Procedures and calculating formulas for magnetic moment test

The procedures and calculating formulas for three magnetic moment test methods (magnetic dipole

method, near-field method and multiple magnetic dipole modelling method) shown in Annex B may be

used as examples.

The magnetic dipole method is usually used to obtain a rough magnetic moment of the EUT. The near-

field method is one of spherical harmonics analysis methods and shall test magnetic dipole moment

of the EUT more precisely. The multiple magnetic dipole modelling method is a precise method too.

Procedures and calculating formulas for magnetic moment tests shall be selected according to magnetic

test requirements.

The magnetic dipole method is commonly used for RMDM, SMDM and IMDM measurements of the EUT.

The near-field method and multiple magnetic dipole modelling method are commonly used for RMDM

and SMDM measurement of the EUT.
9.4 Magnetic moment test in the geomagnetic field

Magnetic moment test for RMDM and SMDM measurements may be conducted in the geomagnetic field.

Magnetic moment test methods in the geomagnetic field may be used for the EUT where the precision

requirement of the measuring result is not high.

The magnetic field induced may be generated by soft magnetic materials of the EUT in the geomagnetic

field. When the magnetic moment test is conducted in the geomagnetic field, the magnetic fields

induced in the geomagnetic field will have some effect on the measuring results. Magnetic moment test

may be conducted in the geomagnetic field for the EUT, under the condition that the EUT contains a

sufficiently small amount of soft magnetic material and other magnetic material is hard enough such

that only negligible small changes of the remnant magnetization occur in the environmental field. If the

magnetic field induced in the geomagnetic field is larger than remnant magnetic field of the EUT, it is

better that the measurement method needs to be adapted to eliminate the magnetic field induced in the

geomagnetic field from the calculation for the magnetic moment of the EUT.

The magnetic moment test conducted in the geomagnetic field may be influenced by environmental

magnetic field perturbations. During magnetic tests, no other magnetic sources are allowed to be close

to the fluxgate sensors on the magnetic test site. Environmental magnetic field perturbations may be

monitored and eliminated from the calculation for the magnetic moment of the EUT.

10 Magnetization and demagnetization test methods
10.1 Test purpose

The EUT is magnetized for determining the EUT history of magnetic field exposures. The EUT is

demagnetized for the removal of the effects of any previous exposures in environmental magnetic field.

The magnetization and demagnetization test is critical for some scientific payloads such as

...