The trend towards Operationally Responsive Space, where spacecraft can be rapidly assembled, configured and deployed, to meet specific mission needs, e.g. disaster support, requires flexible on board communication networks with plug-and-play capability. The growing autonomy of scientific missions to remote planets requires networks that are robust and durable, able to recover from transitory errors and faults automatically. The importance of spacecraft mass reduction motivates the sharing of networks for payload data-handling and avionics. Avionics and robotics impose requirements on network responsiveness and determinism. Increasing international collaboration on scientific and Earth observation spacecraft requires standard network technology where a component developed by one nation will interoperate effectively with equipment developed by another. SpaceWire-RT aims to fulfil these demanding requirements with a flexible, robust, responsive, deterministic and durable standard network technology that is able to support both avionics and payload data-handling applications. SpaceWire is a very successful first step in this direction, providing networking technology for payload data-handling on over 30 major space missions. It falls short, however, of the requirements for avionics systems. A quality of service (QoS) layer is needed for SpaceWire to support mixed avionics and data-handling applications. SpaceWire-RT will: use virtual channels to provide a variety of QoS; provide broadcast and multicast capability; support extremely low latency time and out-of band signalling; and incorporate novel fault detection, isolation and recovery methods. The network will be fully responsible for information transfer, decoupling application and data transfer. Creation of this technology will substantially strengthen collaborative bonds between the Russian and European organisations involved in the research, and lead to technology of vital importance for future space mission.