This Standard defines the dependability assurance programme and the dependability requirements for space systems. Dependability assurance is a continuous and iterative process throughout the project life cycle. The ECSS dependability policy for space projects is applied by implementing a dependability assurance programme@ which comprises: ? identification of all technical risks with respect to functional needs which can lead to non-compliance with dependability requirements@ ? application of analysis and design methods to ensure that dependability targets are met@ ? optimization of the overall cost and schedule by making sure that: ?? design rules@ dependability analyses and risk reducing actions are tailored with respect to an appropriate severity categorisation@ ?? risks reducing actions are implemented continuously since the early phase of a project and especially during the design phase. ? inputs to serial production activities. The dependability requirements for functions implemented in software@ and the interaction between hardware and software@ are identified in this Standard. NOTE 1 The requirements for the product assurance of software are defined in ECSS-Q-ST-80. NOTE 2 The dependability assurance programme supports the project risk management process as described in ECSS-M-ST-80 This Standard applies to all European space projects. The provisions of this document apply to all project phases. Depending of the product category@ the application of this standard needs to be checked and if needed tailored. The pre-tailoring table in clause 8 contains the applicability of the requirements of this document and its annexes according to product type. This standard may be tailored for the specific characteristics and constraints of a space project in conformance with ECSS-S-ST-00.