This Standard specifies the requirements for the development of the endtoend data communications system for spacecraft. Specifically, this standard specifies: ·ð The terminology to be used for space communication systems engineering. ·ð The activities to be performed as part of the space communication system engineering process, in accordance with the ECSS-E-ST-10 standard. ·ð Specific requirements on space communication systems in respect of functionality and performance. The communications links covered by this Standard are the space-ground (i.e. spacetoground and ground-to-space) and spacetospace links used during spacecraft operations, and the communications links to the spacecraft used during the assembly, integration and test, and operational phases. Spacecraft endtoend communication systems comprise components in three distinct domains, namely the ground network, the space link, and the space network. This Standard covers the components of the space link and space network in detail. However, this Standard only covers those aspects of the ground network that are necessary for the provision of the endtoend communication services. NOTE Other aspects of the ground network are covered in ECSS-E-ST-70. This Standard may be tailored for the specific characteristics and constraints of a space project in conformance with ECSS-S-ST-00.