Space radiation measured during first-ever commercial suborbital mission on Virgin Galactic SpaceShipTwo Unity on 29 June 2023

The paper presents the variations of space radiation (primary and secondary galactic cosmic rays (GCR) absorbed dose rate in silicon and flux) measured during the first-ever commercial suborbital flight of the Virgin Galactic (VG) SpaceShipTwo Unity on 29 June 2023. A Portable Dosimeter-Spectrometer Liulin-CNR-VG is used. It is developed in the Space Research and Technology Institute, Bulgarian Academy of Sciences (SRTI-BAS) under a scientific contract with National Research Council of Italy (CNR), Italy. Liulin-CNR-VG size is 63х54 × 23 mm. Its weight is 0.092 kg. During the first part of the SpaceShipTwo flight, up to 14.4 km, the dose rate rises from 0.058 μGy h^-1 up to 2.5 μGy h^-1. Above the altitude of 30 km, the dose rate falls to 2.2 μGy h^-1, while the dose to flux ratio increases to values about 1.0 nGy cm² particle^-1. The latter confirms the outcomes of previous balloon experiments, i.e. the change of the composition of the radiation field of the GCR and secondary radiation source from predominantly light particles as electrons, pions and muons towards heavier particles as protons and neutrons. On the descending part of the flight, one maximum in the flux and dose rate curves is obtained as Regener-Pfotzer maximum (R-PM). The flux calculated by the moving avervage is equal to 1.2 cm^-2 s^-1 and the dose rate is equal to 2.9 μGy h^-1 at an altitude of 13 km. These values are well in line with those expected in conditions of relatively high solar activity, such as during the flight. The dose rates measured by Liulin-CNR-VG are in good agreement with other Liulin data, such as those recorded during balloon flights in 2005 and 2015 and civil aviation flights. The calculated total equivalent dose rate during the VG SpaceShipTwo flight is 7.46 μSv for 1.22 h. This reveals that there is a very small radiation risk for the pilots and astronauts flying at the VG SpaceShipTwo up to 85.1 1 km altitude.