In deep space, astronauts will be exposed to galactic cosmic rays, whose high-energy heavy ions - minority elements - are highly toxic to cells. The consequences for the body of this chronic, low-dose exposure are still poorly understood, due to a lack of human data. In order to assess the impact of a prolonged stay in space on male fertility, this project proposes to study the effects of irradiation by a 56Fe ion beam on mouse spermatogonial stem cells (SSCs). In adults, the continuous production of spermatozoa relies on a stock of SSCs maintained by self-renewal. The integrity of the activity of irradiated CSS will be tested in vivo using transplantation tests. Various parameters of irradiated CSS will be analysed (DNA lesions, mortality, cell cycle, etc.). A transcriptional signature and markers of exposure to heavy ions will be sought in undifferentiated spermatogonia (single cell - RNA seq), and the gene networks involved in stress responses will be studied in particular. All of this data could serve as a basis for studying the hereditary and epigenetic risk associated with space flights, as well as for improving protective measures.