Modelling the irradiation experiments of microbic films within the BOREALIS payload

BOREALIS (Biofilm Onboard Radiation Exposure Assessment Lab In Space) is one of the missions within the Italian Space Agency's ALCOR space program, based on using CubeSats satellites. The mission objective is to investigate the combined effect of microgravity, ionising radiation, and radiation protection strategies on biofilms of microbic populations at different orbital altitudes. The project foresees that, after a first set of experiments at a lower orbital altitude (700- 1250 km), BOREALIS will be transferred with a low-thrust manoeuvre to an altitude greater or equal to 2000 km for a second set of experiments. According to the method developed for the ABCS mission [5], we have defined the contribution of TP, GCR and SEP sources for a set of orbital conditions between 700 and 2000 km of altitude. Using the FLUKA MC code, we simulated the radiation transport and the interaction of each orbital source with a simplified conceptual model of the BOREALIS satellite. The payload model was implemented to have two zones with different shielding degrees hosting two sets of similar microbial film plates, each coupled with a RadFET dosimeter whose scope is to estimate the physical dose delivered near the bio-materials. During the simulation, the dose directly delivered to the bio-materials, which can not be measured experimentally, was also estimated and compared with the simulated dosimeter estimation, obtaining a good correlation between the two responses. Depending on the considered orbit, the adopted shielding solution differentiates the 28-41 per cent dose uptake between films in homologous shielded and non-shielded payload irradiation positions. The dose responses collected in the simulations executed at 700, 900, 1150 and 2000 km of altitude and three orbital inclinations (51°, 70° and 98°) also allow considerations on the radio exposition of the satellite system and the optimal choice of the initial and final irradiation orbits and the transfer manoeuvre.