DOSIS and DOSIS 3D – data from the DOSTEL instruments focusing on 2024 – 2025 with special emphasis on SPEs measured inside the ISS

Abstract

The radiation level in space far exceeds the ones present on Earth and therefore can pose a significant health risk for astronautical space missions. Inside the International Space Station (ISS), the total radiation exposure is often divided into contributions from a) Galactic Cosmic Rays (GCR), b) trapped particles in the inner radiation belt, c) sporadically occurring Solar Particle Events (SPEs) and seldom, but seen d) contributions from trapped particles from the outer radiation belt. With the 11-year solar cycle, the proportions of these contributions to the total exposure changes. Since the ISS is located within the Earth's magnetosphere, GCR and SPE are partially shielded by its magnetic field. This shielding is particularly weak at the Earth's magnetic poles. If the Earth is hit by a strong geomagnetic storm, the Earth's magnetic field is briefly disturbed. This can result in the creation of a third but unstable radiation belt. Within the DOSIS and DOSIS 3D project the two DOSTEL instruments measures the relevant count- and doserate with a time resolution of 20 or 60 seconds. They also provide relevant energy deposition and linear energy transfer (LET) spectra within certain time intervals. This makes it possible to separate the contributions from a) GCR, b) radiation belt particles, and c) SPEs to the total exposure, because SPEs, for example, are much less shielded in the polar region. The analysis of the DOSTEL data for recent solar maximum conditions in 2024 and 2025 led to the identification of seven SPEs measured inside the ISS which is the highest number of SPEs ever seen since the start of the experiment. In addition, time periods exhibiting signatures of an unstable radiation belt within the ISS could be observed. These results will be presented here, especially with regard to their contribution to the total radiation exposure.