This paper addresses the first results of the application of a generic methodology developed to assess the risk of space missions due to the threat of space debris. This work is performed as part of the 30 months P²-ROTECT project (Prediction, Protection & Reduction of OrbiTal Exposure to Collision Threats) that was initiated in March 2011 within the EU seventh framework programme. The method is briefly presented through the vulnerability assessment of the mission of a "SENTINEL-1 type" sub system. Different mitigation scenarios are considered and their efficiencies quantified using the risk-oriented criteria. Numerical results are presented and analysed to illustrate the proposed approach.