ISO/TS 21979:2018

Space environment (natural and artificial) — Procedure for obtaining worst case and confidence level of fluence using the quasi-dynamic model of earth's radiation belts

This document, by using a model that reproduces the fluctuations of radiation belts, defines the calculation method (orbit, operation period) of the radiation fluence received by a satellite. The quasi-dynamic model of Earth's radiation belts adopts input parameters (index values) to predict variation. The input parameters are selected from those that are easy to obtain data and have high correlation with the variation in Earth's radiation belts. NOTE This method is an engineering method used for satellite design and similar purposes.

Environnement spatial (naturel et artificiel) — Mode opératoire pour obtenir le cas le plus défavorable et le niveau de confiance de la fluence en utilisant le modèle quasi-dynamique des ceintures de radiation terrestres

General Information

• Status: Published
• Publication Date: 23-Aug-2018
• 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 4 - Space environment (natural and artificial)
• Current Stage: 9093 - International Standard confirmed
• Completion Date: 09-Dec-2021

Standards Content (Sample)

TECHNICAL ISO/TS
SPECIFICATION 21979
First edition
2018-09
Space environment (natural and
artificial) — Procedure for obtaining
worst case and confidence level of
fluence using the quasi-dynamic
model of earth's radiation belts
Environnement spatial (naturel et artificiel) — Mode opératoire
pour obtenir le cas le plus défavorable et le niveau de confiance de
la fluence en utilisant le modèle quasi-dynamique des ceintures de
radiation terrestres
Reference number
ISO/TS 21979:2018(E)
©
ISO 2018

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ISO/TS 21979:2018(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2018
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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ii © ISO 2018 – All rights reserved

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ISO/TS 21979:2018(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2  Normative references . 1
3  Terms and definitions . 1
4  Radiation belts model . 2
5  Principles of the method . 3
5.1 Cumulative fluence . 3
5.2 Confidence level . 3
5.3 Quasi-dynamic model of Earth’s radiation belts . 3
5.3.1 Overview . 3
5.3.2 Available models . 3
5.4 Remarks . 3
Annex A (informative) . 4
Annex B (informative) CRRESELE Model . 7
Annex C (informative) MDS-1 Radiation Belt Model . 8
Bibliography .18
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ISO/TS 21979:2018(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
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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).
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.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.
iv © ISO 2018 – All rights reserved

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ISO/TS 21979:2018(E)

Introduction
The space environment changes greatly due to solar activity, magnetic storms, etc. Therefore, the
radiation fluence environment received by a satellite varies depending on its launch date, orbit, and
operation period.
What is important for satellite design is the worst condition and confidence level of fluence. Optimum
design can be done by knowing these conditions. Although the radiation belts model so far can be
distinguished between the solar activity maximum and the minimum, it was difficult to deal with short-
term and long-term fluctuations. The procedure for obtaining the worst condition and confidence level
of fluence is defined using the quasi-dynamic model of Earth’s radiation belts.
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TECHNICAL SPECIFICATION  ISO/TS 21979:2018(E)
Space environment (natural and artificial) — Procedure
for obtaining worst case and confidence level of fluence
using the quasi-dynamic model of earth's radiation belts
1 Scope
This document, by using a model that reproduces the fluctuations of radiation belts, defines the
calculation method (orbit, operation period) of the radiation fluence received by a satellite. The quasi-
dynamic model of Earth’s radiation belts adopts input parameters (index values) to predict variation.
The input parameters are selected from those that are easy to obtain data and have high correlation
with the variation in Earth’s radiation belts.
NOTE This method is an engineering method used for satellite design and similar purposes.
2  Normative references
There are no normative references in this document.
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 http: //www .electropedia .org/
3.1
L-value
distance to a point where the magnetic lines of force intersect with the equatorial plane of the
geomagnetic field from Earth’s core, with Re (radius of Earth) used as the unit
3.2
B/B0
value normalized to the minimum value of the field line in the magnetic equator
3.3
Kp and ap
planetary indices that are based on 3-hour measurements from 13 ground stations
Note 1 to entry: Values of ap range from 0 to 400 and are expressed in units of 2 nT. Kp is essentially the logarithm
of ap, with its scale of 0 to 9 being expressed in thirds of a unit (e.g., 5− = 4 2/3, 5o = 5, 5+ = 5 1/3). A daily index
(Ap) is obtained by averaging the eight values of ap for each day and the index Ap can have values intermediate to
those of ap
3.4
solar wind speed
outward flux of solar particles and magnetic fields from the Sun used in external magnetic field model
computation
Note 1 to entry: Typically, solar wind velocities are around 350 km/s−1.
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ISO/TS 21979:2018(E)

3.5
F10.7
F10
traditional solar energy proxy that is used on atmosphere models
Note 1 to entry: Measure of the solar radio flux at a wavelength of 10,7 cm at Earth’s orbit, given in units of
10−22 W·m−2.
3.6
Sunspot number
R
Ri
Rz
daily index of sunspot activity, defined as R=k (10g + s) where s is the number of individual spots, g the
number of sunspot groups, and k is an observatory factor
[SOURCE: ISO 16457:2014, modified — synonymous terms editorially revised for alignment with ISO/
IEC Directives Part 2]
3.7
Dst
Disturbance storm time
geomagnetic index used in external magnetic field model computation that describes variations in
the equatorial ring current and is derived from hourly scalings of low-latitude horizontal magnetic
variation
Note 1 to entry: Dst is expressed in nT.
3.8
IMF
Interplanetary Magnetic Field
geomagnetic index used in external magnetic field model computation that corresponds to the part of
the Sun’s magnetic field that is carried into interplanetary space by solar wind
Note 1 to entry: The three orthogonal components of the IMF are Bx, By, and Bz. Bx and By are oriented parallel
to the ecliptic.
Note 2 to entry: The IMF is a weak field, varying in strength near Earth from 1 to 37 nT, with an average of
about 6 nT.
4  Radiation belts model
The magnetically trapped radiation around Earth is known as the Van Allen belts. The belts consist of
energetic electrons from ~100 keV to 10 s of MeV and protons from ~100 keV up to around 1 GeV. The
belts are organized into an inner zone and an outer zone separated by a slot region. Below 100 keV, a
plasma population, known as the ring current, is also magnetically confined in this region.
Currently, many of the models used in satellite design are what we call a static model to predict the
average particle distribution. However, the actual environment from various observation data fluctuates
much more complexly than the static environment described by their models. In particular, spatial
and especially temporal variations in satellite design are becoming more important than previously
believed. When designing a satellite, the uncertainty of these models is dealt with by taking a design
margin. Currently, physics-based models that enable an understanding and prediction of the dynamics
of Earth’s radiation belts are now available, but are complicated models that require a lot of parameter
data. However, there is also a simple quasi-dynamic model of Earth's belts that predicts variations in
the radiation belts with several input parameters (highly available, long-term accumulated index). This
document specifies the worst case and confidence level calculation method using the latter model.
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ISO/TS 21979:2018(E)

5  Principles of the method
5.1  Cumulative fluence
See ISO 12208:2015, 4.1.
5.2  Confidence level
See ISO 12208:2015, 4.2.
5.3  Quasi-dynamic model of Earth’s radiation belts
5.3.1 Overview
The variations in radiation belt particles greatly depending on the solar cycle effect, secular changes
in the geomagnetic field, the anisotropy of trapping, and the geomagnetic state. The variations of the
radiation belts can be predicted quasi-empirically by using the activity level of the Sun and disturbance
of the geomagnetic field. Most activity indices are given for short periods and as long duration averages.
By statistically analysing the variations of these indices and radiation belts, it is possible to predict
variations of radiation belts quasi-empirically. The input parameters are selected from those that are
easy to obtain data and have high correlation with Earth’s radiation belt variations.
The solar activity indices include Sunspot number (R), F10.7, solar wind speed, and so on. Also, Kp and
ap, Dst and IMF are examples of geomagnetic activity indices.
Annex A shows the procedure for calculating the worst case and reliability level using the quasi-
dynamic model.
5.3.2  Available models
a) CRRESSELE model in Annex B.
b) MDS-1 Radiation belt model in Annex C.
5.4  Remarks
a) The worst case and confidence level of fluence can be easily obtained by using the radiation belts
variation parameter SW, AP, and F10.7 index.
b) This technique is applicable when there are at least ten years’ worth of parameters used to predict
radiatio
...