The Moon will be a primary target for human space exploration in the near future. A limiting factor for a crewed mission to the Moon is the radiation dose during their stay on the lunar surface. While the total dose is expected to be dominated by the galactic cosmic radiation, the potential occurrence of large solar energetic particle events may lead to severe short-term effects and endanger the success of the mission. This work investigated the expected dose rates for maximum galactic cosmic radiation intensity and the total dose from several historical solar energetic particle events, including the NASA reference event, through the application of numerical simulations with the Geant4 Monte-Carlo framework. An evaluation of the shielding effect of lunar regolith was carried out. For the solar particle events a shielding of more than 4 g/cm2 of regolith would reduce the expected dose to below the current 30-day limits and a shielding of more than 10 g/cm2 would result in a safety margin factor of two. For galactic cosmic radiation adding additional mass shielding did not reduce the absorbed dose significantly. The estimated total dose equivalent received utilizing around 180 g/cm2 of regolith amounted to 200 mSv/year, which is only about 25% below the corresponding estimates for an unshielded environment. The comparison to model and experimental data from literature showed reasonable agreement to measurements but the analysis of various earlier model results revealed, that substantial differences between the models exist, despite all improvements that have been achieved in recent years.

Remarkably, we know more about the radiation environment onboard the International Space Station than we do about radiation values at altitudes between 30-40 km in the middle stratosphere. Within this work, we provide data about the radiation dose measured during two consecutive balloon flights flown within a 4-month timeframe over New Mexico and Antarctica Data were measured with the M-42 radiation detector. On each flight, the M-42 was installed as part of a larger research payload: MARSBOx (New Mexico, 23 September 2019); and E-MIST (Antarctica, 15 December 2019-12 January 2020). The temporal proximity of the flights provided similar prevailing space weather conditions and solar activity (minimal during each mission). Against that common backdrop, the main differences between flights, including mission duration and geomagnetic shielding could be readily compared. Near identical space weather conditions provided a window of opportunity for studying the influence of altitude and geomagnetic shielding on dose and fluence rate of galactic cosmic radiation under maximum intensity conditions. Herein, we report relevant count- and dose rates for the missions, alongside Geant4 Monte Carlo calculations; this included crossings of the Regener maximum during the ascent and descent flights over New Mexico and the absence of a distinct maximum in dose rates at zero geomagnetic shielding for the polar flight. While dose rates in silicon at float altitudes (≈35 km-39 km) were a maximum of 2.5 +/- 0.4 microGy/h over New Mexico, we reached values of up to 8.4 +/- 0.3 microGy/h over Antarctica, thereby approaching dose rates similar to the surface of Mars.