ESP Model for Solar Particle Risk Assessment

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ESP Model for Solar Particle Risk Assessment

• Mike Xapsos
• NASA/GSFC, Code 561
• Greenbelt, MD 20771

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ACKNOWLEDGMENTS

• Co-Investigators
• Janet Barth and E.G. Stassinopoulos, Code 561
• Robert McGuire, Code 632
• Craig Stauffer and George Gee, SGT Inc.
• Ed Burke, Consultant
• Sponsors
• MSFC Space Environments and Effects Program
• GSFC RTD

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OUTLINE

• Introduction
• Data Base
• Initial Distribution of Solar Proton Event (SPE)
  Magnitudes
• Worst Case Event Distributions
• Cumulative Fluence Distributions
• Ongoing Work

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INTRODUCTION

• Long-term models of solar particle radiation
  exposure are useful for spacecraft subsystem and
  instrument design
• especially critical for missions to the moon or
  Mars
• The Emission of Solar Protons (ESP) model
  predicts for user specified confidence level and
  mission time period
• omnidirectional fluences and fluxes at 1 AU
• gt1 to gt300 MeV protons
• Model based on advanced statistical methods
• Maximum Entropy Theory
• Extreme Value Theory
• Compound Poisson Process Theory

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DATA BASE

• Our model is based primarily on the IMP-8 Goddard
  Medium Energy (GME) Instrument data
• Nearly continuous coverage since 1973
• IMP-8 near circular orbit at 35 Earth radii
  suitable for determining fluxes at 1 AU
• 30 energy bins of proton differential flux
  ranging from 0.88 to 485 MeV.
• Main problem occasional detector saturation
  observed during largest events and occasional
  gaps in data
• Supplement GME data with
• IMP-8 CPME data
• GOES SEM data

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October November 1989 Episode
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INITIAL DISTRIBUTION OF SOLAR PARTICLE EVENT
MAGNITUDES

• Determine probability distributions using maximum
  entropy theory
• Method for determining probability distribution
  when data are incomplete
• Maximize the distributions entropy (uncertainty)
  subject to known constraints
• Results in least biased distribution in the face
  of missing information
• Distribution turns out to be truncated power law
  in event magnitude (fluence or flux).

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ESP MODEL INITIAL DISTRIBUTIONSMaximum Entropy
Approach
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WORST CASE EVENT DISTRIBUTIONS

• Determine probability distributions using
• extreme value statistics
• Well established for modeling environmental
  phenomena such as earthquakes, floods, etc.
• In contrast to central value statistics, extreme
  value theory focuses on the distribution of
  largest (or smallest) values
• Results for worst case events are obtained from
  initial distribution as function of confidence
  level and mission duration.

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ESP MODEL WORST CASE DISTRIBUTIONSExtreme Value
Theory Approach
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CUMULATIVE FLUENCE DISTRIBUTIONS

• Determine probability distributions using
• maximum entropy and compound Poisson process
  theory
• Maximum entropy approach indicates cumulative
  distribution is lognormal and has time dependent
  parameters.
• Compound Poisson process theory predicts
  evolution of lognormal parameters over time.
• Results are consistent with Monte Carlo type
  simulations using initial distribution of SPE
  fluences.

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ESP MODEL CUMULATIVE DISTRIBUTIONMaximum
Entropy Approach
.50
.80
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Cumulative Fluences for Solar Max and Solar Min
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ONGOING WORK

• Apply what we have learned about solar proton
  event models to construct models of solar heavy
  ion exposures.
• Currently funded by MSFC to add IMP-8 GME heavy
  ion data to existing models (long-term, mainly
  low energy data)
• Will require support to expand efforts to include
  higher energy data obtained with more modern
  instrumentation
• Also need to integrate abundance model to be used
  with ion species present in small amounts.
• Incorporate Langley HZETRN code for shielding.