ISO 12208:2015

INTERNATIONAL ISO
STANDARD 12208
First edition
2015-10-01
Space systems — Space environment
(natural and artificial) — Observed
proton fluences over long duration at
GEO and guidelines for selection of
confidence level in statistical model of
solar proton fluences
Systèmes spatiaux — Environnement spatial (naturel et artificiel) —
Fluences de protons observées sur une longue durée au GEO et lignes
directrices pour la sélection du niveau de confiance dans le modèle
statistique des fluences de protons solaires
Reference number
©
ISO 2015
© ISO 2015, Published in Switzerland
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ii © ISO 2015 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Terms and definitions . 1
3 Symbols and abbreviated terms . 2
4 Principles of the method (see Reference [3]) . 2
4.1 Cumulative fluence . 2
4.2 Confidence level . 3
4.3 Archives of observed energetic protons in GEO . 3
4.4 Remarks . 3
5 Guidelines for selection of a confidence level in a statistical model of solar
proton fluences . 4
Annex A (informative) Example of estimation and selection . 5
Bibliography . 9
Foreword
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The committee responsible for this document is ISO/TC 20, Aircraft and space vehicles, Subcommittee
SC 14, Space systems and operations.
This first edition of ISO 12208 cancels and replaces ISO/TS 12208:2011.
iv © ISO 2015 – All rights reserved

Introduction
This International Standard is intended for use in the engineering community.
It is well known that solar energetic protons (SEPs) damage spacecraft systems, i.e. electronics and
solar cells, through ionization and/or atomic displacement processes. This results in single-event
upsets and latch-ups in electronics, and output degradation of solar cells.
Solar cells of spacecraft are obviously one of the key components of spacecraft systems. Degradation of
solar cells by energetic protons is unavoidable and causes power loss in spacecraft systems. Estimation
of cell degradation is crucial to the spacecraft’s long mission life in geosynchronous earth orbit (GEO).
Therefore, an estimation of SEP fluences in GEO is needed when designing solar cell panels.
Solar cell engineers use a statistical model, the jet propulsion laboratory (JPL) fluence model for
example, for estimating solar cell degradation. However, with regard to solar cell degradation, a
statistical model predicts higher SEP fluences than the values actually experienced by spacecraft in
GEO, especially seven years after the launch. Nowadays, spacecraft manufacturers are very conscious
of minimum cost design of spacecraft because the lifetime of spacecraft is becoming longer (15 years
to 18 years) and the cost of manufacturing spacecraft is increasing. Therefore, the aerospace industry
requires a more accurate SEP fluence model for a more realistic design of solar cells.
INTERNATIONAL STANDARD ISO 12208:2015(E)
Space systems — Space environment (natural and
artificial) — Observed proton fluences over long duration
at GEO and guidelines for selection of confidence level in
statistical model of solar proton fluences
1 Scope
This International Standard describes a method to estimate energetic proton fluences in geosynchronous
earth orbit (GEO) over a long duration (beyond the 11-year solar cycle), and presents guidelines for the
selection of a confidence level in a model of solar proton fluences to estimate solar cell degradation.
Many of the proton data observed in GEO are archived, for example from GMS (Japan), METEOSAT (ESA)
and GOES (USA). This method is a direct integration of these fluence data (or the observed data over
11 years is used periodically).
As a result, the confidence level can be selected from a model of solar proton fluences.
This International Standard is an engineering-oriented method used for specific purposes such as
estimating solar panel degradation.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
confidence level
level used to indicate the reliability of a cumulative fluence estimation
2.2
extremely rare event
solar energetic proton (SEP) event that occurs about once in a solar cycle and whose fluence dominates
that for the entire cycle
Note 1 to entry: Examples are those which took place in August 1972, October 1989 and July 2000.
2.3
flux
number of particles passing through a specific unit area per unit time
2.4
fluence
time-integrated flux
2.5
n-year fluence
fluence during a mission of n years duration
3 Symbols and abbreviated terms
EOL end of life
ESA European Space Agency
JPL Jet Propulsion Laboratory
METEOSAT Meteorological Satellite
GEO Geosynchronous Earth Orbit
GMS Geosynchronous Meteorological Satellite
GOES Geostationary Operational Environmental Satellite
RDC relative damage coefficients
SEP solar energetic proton
SSN sun spot number
4 Principles of the method (see Reference [3])
4.1 Cumulative fluence
The n-year fluence for a given mission life of n-years is shown in Figure 1 and estimated as follows.
a) The n-year fluence is calculated by integrating observed daily fluences for n-years from archives.
st
The start day for integration is January 1 in the first year (defined as A). The integration windows
nd
are shifted each day from January 2 in the first year to December 31 in n-years later (defined as
B, C . Z). These are possible fluences that a spacecraft might experience during its mission life (see
A, B, C … Z in Figure 1).
b) The maximum of the n-year fluences, F (t), for the n-year mission life i
...