Mars Radiation Environment Characterization Results, previous and ongoing activities



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Mars Radiation Environment Characterization

  • Results, previous and ongoing activities

  • Ana Keating

  • Ali Mohammadzadeh

  • Petteri Nieminen

  • Mario Pimenta

  • Eamonn Daly


Outline

  • MarsREC model description

  • Radiation Environment at the surface

    • Fluences
    • Doses
    • Dose Equivalents
  • Variability of the Radiation Environment

    • Dependence on Time of the day
    • Dependence on Solar Longitude
    • Dependence on Landing Location
  • MarsREM ongoing activities

    • Dependence on soil density
    • Dependence on subsoil composition
  • Conclusions



MarsREC

  • LIP & ESA

  • ESA 18121/04/NL/CH

  • Ana Keating

  • keating@lip.pt



Abstract

  • MarsREC :

  • Integrated simulation tool for Mars Radiation Environment and Radiation induced Effect in EEE Components.

    • landing locations, time and season of the Martian year.
  • MarsREC consists of two Modules:

    • Radiation Environment Characterization Module
    • Radiation Effects Module.
  • Models features include

    • input solar cycle modulated GCR and SEP spectra, both based on CREME-96,
    • transport thru the Martian atmosphere and regolith,
    • creation of secondary radiation, using the Geant4 Monte-Carlo toolkit
    • atmosphere MCD
    • Seasonal and diurnal variations are considered for different location.
    • Surface topology (MOLA)
  • Outputs:

    • Energetic particle transport histories, maps of radiation fluxes, doses dose equivalents and SEU rate predictions.


Atmospheric Database

  • European Martian Climate Database (MCD)

    • Temperature, wind, density, pressure, radiative fluxes, etc
    • Stored on a 5ºx5 º, longitude-latitude grid from the surface to 120km
    • Height of each atmospheric layer
    • Fields (wind, temperature, pressure...) are averaged and stored 12 times a day (Mars Universal Time at longitude 0o),
    • for 12 Martian “seasons”
    • Each season covers 30º in solar longitude (Ls)


MACLIDIG4



Topology

  • Radiation Environment mapping

  • Mars Orbiter Laser Altimeter (MOLA) on board NASA's Mars Global Surveyor (MGS) spacecraft. Data converted into a 5ºx5º Grid



Atmosphere and Geology

  • The Martian atmospheric density being very low (in the order of magnitude of 10-2 Kg m-3), works as a soft attenuator for incoming radiation.

  • Important contribution from secondary particles generated and backscattered at the surface of Mars.

  • Mars soil is about 3.75 g cm-3 and the mantle and crust bulk composition consist mainly of SiO2 and FexOy.

  • The impact of different dust scenarios is not expected to be very significant!

  • Dust density is typically less than 10-3 g/cm2 (= 0.5x10-3% of the atmospheric density).



Simulation Setup

  • The geometry implemented in Geant4 program takes into account:

  • The pixel size given by the 5ºx5º accuracy of MCD, for each (long, latitude) location

  • Average composition of the soil of 30% Fe2O3 and 70% of SiO2, and density of 3.75 g/cm3;

  • The thickness of the 32 atmospheric layers given by the sigma levels of MCD;

  • A fix atmospheric composition consisting of:

    • 95% CO2
    • 2.5% N2
    • 1.25% Ar
    • 1.15% O2
    • 0.07% CO
    • 0.03% H2O
  • The atmospheric density, temperature and pressure are given by the 32 layers of the atmospheric table computed from MCD.

  • Different times of the Martian Day correspond to different geometry set-ups



Radiation inputs

  • CREME96 for near-Earth interplanetary.

  • Galactic cosmic rays (GCR)

    • Solar-quiet proton flux in the solar maximum
    • Simulated as isotropic momentum distribution: 105protons
  • Particle events (SPE)

    • Energetic protons : “worst week” model
    • Simulated perpendicularly to the surface : 105protons
  • Models are based on measurements at Earth (1AU)

  • The phasing in the solar cycle : foreseen for ExoMars.



Analysed Locations

  • 6 different Locations

  • North and South, East& West

  • Solar Longitude 180º-210º



Fluxes of Particles



Fluences and Doses



Ambient Dose Equivalent

  • MarsREC post-processing module

  • Uses the FLUKA fluence-to-ambient dose equivalent conversion coefficients,

  • For each kind of particles

  • Convoluted by the MarsREC

  • fluence as function of particle

  • energy



Transfer Functions

  • Fluence at the surface varies with the atmospheric pressure at the surface



Dependence with Solar Longitude



Day and Night Variations



Low Energy Neutrons Variation

  • Neutrons E< 30MeV

  • Mars Univarsal Time

  • Martian Longitude 0º:

    • 22h : 191K
    • 02h : 208K
    • 12h : 248K
  • Fluences Per year

  • ~ 5x108n/cm2

  • Temperature changes

  • -> 1%



Dependence on landing site



MarsREM

  • Preliminar results, ongoing

  • A. Keating

  • M. Pimenta

  • L. Desorgher

  • F. Lei

  • P. Truscott

  • B. Quaghebeur

  • P.Nieminen 19770/06/NL/JD



Aim

  • Merge and extending MarsREC & Mars-Planetocosmic models for the Mars, Phobos and Deimos, including treatment of surface topology and composition, subsurface, atmospheric composition and density (including diurnal and annual variations), and local magnetic fields.

  • Create a user-friendly engineering tool (QARM)

  • Interface with SPENVIS

  • New ion physics



Dependence on soil:  & Composition



Conclusions

  • MarsREC framework is capable of:

  • Predicting RE at the surface (locations, solar longitudes, Time)

  • Tracking all primary and secondary particles (backscattering)

  • Predicting RE variation with climate changes along the Martian year.

  • Evaluating Dose Equivalents and Dose depositions at the surface of Mars

  • Calculating the energy spectra and particle species, radiation fluxes at component level, energy depositions and doses

  • Computing SEU rates in specific components.

  • Results show:

  • TID at the surface of Mars is of lesser concern to EEE components,

  • Dose Equivalents are of major concern for manned missions

  • Relative abundance of protons and neutrons may result in important DD and SEE effects.

  • Results show good agreement with experimental data and other software predictions.

  • MarsREM

  • Activities will improve and merge de existent models for Mars and Moons

  • Results expected to improve with description of new ion physics, soil information ...



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