Abstract: Upper stage is an indispensable vehicle in the space transportation system. For its role in multi-satellite transportation area in China, the development of the Yuanzheng 3 upper stage was approved. The article introduces in detail the Yuanzheng 3 upper stage development requirements, task definition and systems as well as main features and performance including payload capacity and insertion accuracy for typical orbits, interfaces with satellites. The article also presents the development cycle of Yuanzheng 3 upper stage, which is divided into 3 stages including concept demonstration stage, prototype stage and flight proof stage. The Yuanzheng 3 upper stage, which will make its maiden flight in 2018, is capable of restarting more than 20 times, and operating for more than 48 hours. It is equivalent to mainstream upper stages in the world in terms of performance, such as restart times, in-orbit operation time, independent digital control system, and adaptable behavior for various tasks. Technologies tackled and accumulated in the development of the Yuanzheng 3 upper stage will lay a solid foundation for the development of future space transportation vehicles.

Key words: Yuanzheng 3 upper stage, System composition, Payload performance