Thales Alenia Space has recently widely deployed user centered design process in their software product conception. This standard breaks today technology and data centric approach by integrating end-users all along the iterative design stages: context and usage understanding, end-user need specification, quick mockups and end-user validation. This paper is a return on experience. It describes and investigates a dirty UCD methodology relevance based on prototyping and user testing only (skipping user research first activities). This process is made to fit project which needs front-end requirements at day one.