The National Institute for Aerospace Studies (ONE) is a public, scientific and technical establishment with industrial and commercial responsibilities. ONE reports to the French Ministry of Defence and enjoys financial independence. The expertise of ONE covers all the scientific disciplines involved in aircraft, spacecraft and missile design. Its Space Environment Department (DESP) aims at evaluating the environmental conditions of space missions and preventing the damage they may cause. The DESP studies the different components of the space mission environment and evaluates the associated risks through modelling ground and in-flight experiments, in particular in the fields of planetary radiation belts and spacecraft charging.