Radiation environment for future human exploration on the surface of Mars: the current understanding based on MSL/RAD dose measurements

Abstract

Potential deleterious health effects to astronauts induced by space radiation is one of the most important long-term risks for human space missions, especially future planetary missions to Mars which require a return-trip duration of about 3 years with current propulsion technology. In preparation for future human exploration, the Radiation Assessment Detector (RAD) was designed to detect and analyze the most biologically hazardous energetic particle radiation on the Martian surface as part of the Mars Science Laboratory (MSL) mission. RAD has measured the deep space radiation field within the spacecraft during the cruise to Mars and the cosmic ray induced energetic particle radiation on Mars since Curiosity’s landing in August 2012. These first-ever surface radiation data have been continuously providing a unique and direct assessment of the radiation environment on Mars. We analyze the temporal variation of the Galactic Cosmic Ray (GCR) radiation and the observed Solar Energetic Particle (SEP) events measured by RAD from the launch of MSL until December 2020, i.e., from the pre-maximum of solar cycle 24 throughout its solar minimum until the initial year of Cycle 25. Over the long term, the Mars’s surface GCR radiation increased by about 50% due to the declining solar activity and the weakening heliospheric magnetic field. At different time scales in a shorter term, RAD also detected dynamic variations in the radiation field on Mars. We present and quantify the temporal changes of the radiation field which are mainly caused by: (a) heliospheric influences which include both temporary impacts by solar transients and the long-term solar cycle evolution, (b) atmospheric changes which include the Martian daily thermal tide and seasonal CO$$_2$$ 2 cycle as well as the altitude change of the rover, (c) topographical changes along the rover path-way causing addition structural shielding and finally (d) solar particle events which occur sporadically and may significantly enhance the radiation within a short time period. Quantification of the variation allows the estimation of the accumulated radiation for a return trip to the surface of Mars under various conditions. The accumulated GCR dose equivalent, via a Hohmann transfer, is about $$0.65 \pm 0.24$$ 0.65 ± 0.24 sievert and $$1.59 \pm 0.12$$ 1.59 ± 0.12 sievert during solar maximum and minimum periods, respectively. The shielding of the GCR radiation by heliospheric magnetic fields during solar maximum periods is rather efficient in reducing the total GCR-induced radiation for a Mars mission, by more than 50%. However, further contributions by SEPs must also be taken into account. In the future, with advanced nuclear thrusters via a fast transfer, we estimate that the total GCR dose equivalent can be reduced to about 0.2 sievert and 0.5 sievert during solar maximum and minimum periods respectively. In addition, we also examined factors which may further reduce the radiation dose in space and on Mars and discuss the many uncertainties in the interpreting the biological effect based on the current measurement.

Mission Overview and Scientific Contributions from the Mars Science Laboratory Curiosity Rover After Eight Years of Surface Operations

“…Furthermore, knowledge of the radiation environment is necessary to quantify the health risk to crewed missions and to inform mitigation strategies (Guo et al. 2021 ). Through Sol 2844 the RAD investigation was conducted jointly by NASA’s Science Mission Directorate and Human Exploration and Operations Mission Directorate.…”

Protons Interaction with Nomex Target: Secondary Radiation from a Monte Carlo Simulation with Geant4

“…The dominant radiation with a very wide spectrum in energy, up to about 0.1 TeV, is constituted by the Galactic Cosmic Rays (GCR). The GCR [2] are composed of protons (87%), alpha particles (12%), and a relatively small amount of heavier nuclei (~1%) arriving from outside the heliosphere [3][4][5][6][7][8]. These particles continuously enter the solar cavity and are isotropically distributed.…”

From the Top of Martian Olympus to Deep Craters and Beneath: Mars Radiation Environment Under Different Atmospheric and Regolith Depths

“…We note that the neutron contribution to the total effective dose is around 50% while the MSL/RAD measures about 5% contribution by neutrons to the total dose rate in the plastic detector (Guo et al, 2021). To understand this discrepancy, we need to keep in mind that dose and effective dose are defined and derived differently.…”

“…Since the landing, the Radiation Assessment Detector (RAD) (Hassler et al., 2012) carried by the rover has been measuring the Mars surface radiation field and its characteristics. The RAD measurements have been providing a direct reference of the radiation environment at Gale crater (e.g., Ehresmann et al., 2014; Guo et al., 2015; Hassler et al., 2014; Wimmer‐Schweingruber et al., 2015), improving our understanding of the associated radiation risks for a manned Mars mission (Guo et al., 2021; Zeitlin et al., 2019), and serving to benchmark radiation transport models (e.g., Guo, Banjac, et al., 2019; Matthiä et al., 2016, 2017).…”