Over the last ten years the number of satellites on orbit has grown significantly to more than 1000. We also depend on satellites more than ever for applications such as TV, internet, mobile phones, navigation, banking and finance. All these satellites must be designed to withstand the harsh radiation in space for up to 15 years or more. Space weather events can increase radiation levels by five orders of magnitude in the Earth’s radiation belts and trigger bursts of high energy particles which can disrupt satellite operations and sometimes cause a complete satellite loss. Europe is investing heavily in space with the Galileo radio-navigation system and developing a competitive space industry. It is therefore important that we assess and mitigate the impact of space weather, particularly extreme events. This proposal brings together scientists and engineers from across Europe with commercial stakeholders to assess the impact of space weather and develop mitigation strategies. We will undertake studies of past space weather events using state-of-the-art computer models and data analysis techniques. We will reconstruct 30 years of the radiation environment for medium Earth orbit for Galileo, and for geostationary orbit. We will use data, models, and plasma theory to define the radiation environment for extreme space weather events, and conduct simulations and experiments to determine the impact on systems and components. We will assess the risk and develop new mitigation guidelines. We will perform experiments on new materials and techniques to reduce surface charging on solar arrays, and develop better physical models to forecast the radiation belts to provide warnings and alerts. We will develop a stakeholder community and deliver the results in a form accessible to the public. The project will deliver data, mitigation guidelines and experimental results that will continue long after the project and which will improve the design of future satellites.