A review on the interfaces of orbital replacement unit: Great efforts for modular spacecraft

Over the past decades, the development of single spacecraft for outer space exploration requires more complicated design and higher investment. From the modular design ideas of the International Space Station on-orbit service, an interface design for orbital replacement unit (ORU) provides a path to develop modular spacecraft with reduction of design period and cost for satellites. A review on the ORU interfaces has been made in order to summarize the development of grabbing interfaces, mechanical docking interfaces, and multifunctional docking interfaces of ORUs in the recent 30 years. The interface parameters for both grabbing and mechanical docking processes have been summarized and compared based on the design features of ORUs. The characteristics of mechanical, power, data, thermal flow, and fluid interfaces of the ORUs are discussed as well. The future direction, challenges, and applications of the ORU interfaces have been investigated, and advanced technologies such as target recognition and precise measurement and control are suggested for the development of autonomous and intelligent interfaces. This work provides fundamental knowledge and guidelines for the development of ORU interfaces.