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Lunar radiation environment specification and analysis

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The last years have seen a renewed interest in the exploration of the Moon and the possibility for commercial exploitation of its resources. The modelling of the lunar radiation environment and its effects is an important element for designing and protecting lunar-based assets. We have used ESA’s SPace ENvironment Information System (SPENVIS) developed at BIRA-IASB, to support the design of a miniature X-Ray Fluorescence (XRF) spectrometer for a future ESA mission to the Moon.
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SPENVIS is providing interfaces to various models and tools that can be utilised for scientific and engineering studies related to the characterisation of the space environment and its effects.

In particular, SPENVIS users can employ these tools to:

  • verify instrument and detector responses
  • optimise space radiation shielding
  • investigate radiation-induced effects on spacecraft components

Lunar radiation environment specification and analysis

In order to support the development of a miniature X-Ray Fluorescence (XRF) spectrometer for a future ESA mission to the Moon we have used SPENVIS to perform a lunar radiation environment specification and analysis. We know that the primary radiation environment is due to Galactic Cosmic Rays (GCR) and Solar Energetic Particles (SEP) reaching the surface of the Moon.

However, it is important to look also at the lunar albedo particles such as neutrons, protons and electrons. These secondary particles are the result of the interaction of the incident high-energy particles with the lunar soil. We have computed the spectra of these albedo particles by modelling the lunar surface (composition and geometry) and performing Monte Carlo Geant4 simulations using the tools that are available in SPENVIS.

Potential effects for a one-year mission on the surface of the Moon

Finally, we looked at potential effects of the estimated lunar radiation environment for a one-year mission on the surface of the Moon. More specifically, we calculated the GCR and SEP linear energy transfer (LET) spectra that are necessary for estimating the rates of single event effects due to direct ionisation and the annual total ionising doses (TID) in a silicon device as a function of aluminium shielding.

The results are important inputs for evaluating the degradation of instruments/detectors and their operational lifetime on the lunar surface.

 

Reference:

De Donder, E., and Messios,N. Preparation of Enabling Space Technologies and Building Blocks: Lunar XRF Spectrometer. Lunar-XRF-WP13_RP, Issue 1.0, May 2020.

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Figure 2 caption (legend)
Plot showing the annual total ionizing dose (TID) from primary GCR and SEP event protons and secondary backscattered particles generated in the lunar soil from De Donder and Messios (2020) projected over an image of the Moon (Credit: NASA).
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Figure 3 caption (legend)
SPENVIS Geant4 simulation of the interaction of GCR protons with the Moon where the lunar soil was modelled as five regolith layers with different thicknesses and densities.