Table of Contents ECSS Model Page
Background Information Radiation sources and effects
Mars Energetic Radiation Environment Models (MEREM)

The interplanetary radiation environment and its effects on systems and crews of long-duration space missions is becoming an increasing concern as a result of the growing interest in the operation of equipment on Mars, potentially leading to manned missions to Mars on the thirty-year timescale. Much of the current experience of manned space-flight results from operation in missions in low-Earth orbit, where there is significant benefit from geomagnetic shielding against some of the principal radiation sources, and the possibility of rapid return to Earth in the event of an emergency, such as very intense solar energetic particle events. The assessment of the interplanetary radiation threat, and the performance of mitigation measures, therefore requires careful and accurate assessment.

The MarsREM study (ESA Contract 19770/06/NL/JD, 2007) addressed part of this problem by developing the Mars Energetic Radiation Environment Model (MEREM) framework, which has been integrated into SPENVIS. MEREM allows the user to input mission-related information such as mission epoch (defining solar cycle and Martian season), duration, Mars orbit, coordinates of lander/habitat and local soil conditions. MEREM produces a variety of output quantities: particle flux or fluence spectra as a function of species, absorbed dose, effective dose, etc.

MEREM uses the following radiation environment models:

MEREM model selection

Two MEREM applications were developed: dMEREM runs a full Geant4 Monte Carlo simulation for each specified location, taking into account the detailed soil and atmosphere composition. In contrast, eMEREM uses a set of response matrices for energetic radiation incidence at the top of the Martian atmosphere, pre-calculated with FLUKA using a simple fixed layered atmosphere model and a selection of four ground materials (global average, equatorial composition, water ice and dry ice) [Lei, 2008].

Coordinate input

Four types of coordinate input are available:
  1. single location: for eMEREM and dMEREM,
  2. elevation profile: for eMEREM and dMEREM (10 pre-set elevations),
  3. Mars orbit (calculated with the orbit generator): for eMEREM only,
  4. moon surface: for dMEREM only.

Soil and atmosphere composition

A pre-processor tool was developed to characterize the atmospheric and surface specifications for Mars and Moons geology description. It extracts data from the Mars Climate Database and MOLA and the Gamma Ray Spectrometer on board of Mars Odyssey, using MACLIDI and SOILCOMPI.

eMEREM only uses the atmosphere composition for single locations and eleveation profiles. The pre-processor is used to determine the amount of air above and the total atmosphere thickness at a given location. The radiation at this location in the atmosphere is calculated using the response function corresponding to the same air depth. For the orbital runs, the trajectory locations are considered to be above the top of the atmosphere (elevation 50 km). For orbital runs, only the soil composition of the polar cap (water ice or dry ice) can be specified.

By default, dMEREM uses the soil composition generated by the pre-processor, both for the surface of Mars and for the moons.

Advanced users have the option (for dMEREM) to specify a custom soil (for Martian or moon surface) composition by entering the mass fractions for a set of 14 minerals plus water and dry ice, and the total density. For guidance, the table below lists a number of compositions based on different studies (Keating and Valente, 2007).

General compositions (% mass fraction) of important minerals and soil samples of Mars
Composition Basalt Andesite Basalt-Andesite Olivine Pyroxenes Viking 1 Sojourner
(generic) (generic) (generic)   LCP HCP   (PF)
SiO2 50.2 59.7 53.9 39.2 53.0 45.1 56.4 55.3
Fe2O3 6.0 8.3 8.6 18.8 18.8 10.1 20.4 17.8
Al2O3 17.0 17.2 17.1 0.0 0.8 6.5 8.2 8.8
MgO 10.6 3.9 7.2 42.1 24.0 12.5 6.9 7.7
MnO 0.0 0.0 0.0 0.0 0.3 0.4 0.0 0.0
CaO 14.7 5.8 9.6 0.0 2.0 19.9 6.6 6.4
Na2O 1.5 3.5 2.7 0.0 0.0 0.0 0.0 2.3
K2O 0.0 1.6 1.0 0.0 0.0 0.0 0.8 0.5
TiO2 0.0 0.0 0.0 0.0 0.7 5.3 0.7 1.3
Cr2O3 0.0 0.0 0.0 0.0 0.4 0.3 0.0 0.0
FeS 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
CoO 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
NiO 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
P2O3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

Default custom composition (% mass fraction) used for Phobos and Deimos
Composition Phobos & Deimos
SiO2 38.7
Fe2O3 23.2
Al2O3 2.0
MgO 24.4
MnO 0.3
CaO 1.8
Na2O 0.9
K2O 0.1
TiO2 0.1
Cr2O3 0.5
FeS 6.3
CoO 0.1
NiO 1.2
P2O3 0.3

Total 100.0

Results

The pre-processor, dMEREM and eMEREM produce the files listed in the tables below. A description of the format of the files can be brought up by clicking on their description in the table.

Output files generated by the pre-processor, dMEREM and eMEREM
File name Description
spenvis_mpc.txt Pre-processor command file
spenvis_mpl.txt Pre-processor log file
spenvis_atmo.txt Atmosphere file generated by the pre-processor
spenvis_soil.txt Soil file generated by the pre-processor
spenvis_mes.txt Incident radiation spectrum
spenvis_mer.g4mac Geant4 macro file for dMEREM
spenvis_mer.g4log dMEREM log file
spenvis_dmo.txt dMEREM output file
spenvis_emr.html eMEREM report file
spenvis_emd.txt eMEREM single position dose and total flux/fluence
spenvis_ems.txt eMEREM single position spectra
spenvis_eme.hbook eMEREM single position spectra
spenvis_emp.txt eMEREM profile output file
spenvis_emo.txt eMEREM orbital output file

To generate plots, select the plot type(s), options and graphics format, and click the button. The current page will be updated with the newly generated plot files.

References

Keating, A., and S. Valente, MarsREM Technical Note 3, ESA Contract 19770/06/NL/JD, 2007.

Lei, F., Mars Energetic Radiation Environment Models (MEREM)—eMEREM Software Design & Justification Document, QINETIQ/IS/AERO/SDD0800770, 2008.


Last update: Mon, 12 Mar 2018