On-orbit space technology experiment and verification project outlook of China’s Tiangong Space Station

China's Tiangong Space Station was completed in 2022, featuring large payload capacity, long on-orbit operational periods, support for Earth-space transportation, global tracking and communication, astronaut care, and replaceable and upgradeable experimental equipment. These characteristics provide excellent conditions for on-orbit experiments in space technology. The space station offers unprecedented opportunities for the development of China's space technology. By fully utilizing the unique experimental resources of the space station, conducting on-orbit experiments, and addressing the issues hindering high-level space technology development, a series of influential technological research results can be achieved. This will promote the innovation and development of space technology, laying a foundation for mastering new space technologies and key core technologies, achieving leapfrog development, and providing strong technical support for building a strong space nation. This will also drive high-quality innovation and development of economic and social benefits through space technology, contributing "China's strength" to the advancement of human scientific knowledge. In a newly published opinion article in Space: Science & Technology, experts from the Beijing Institute of Spacecraft System Engineering proposed a top-level plan for space technology development, addressing the needs of China's space industry and the frontiers of space technology.

The article first introduces the mission objectives of space technology experiments on China's Tiangong Space Station. The mission objectives are divided into three dimensions: foundational space technology, advanced equipment or subsystems, and advanced space mission systems. 
1. Strengthening the foundation of space technology to enhance the basic level of space technology. This includes promoting the large-scale application of domestically produced core components, basic materials, processes, and precision components to achieve independent and controllable foundational space technology and continuous improvement.
2. Evaluating and validating the application of core components and advanced equipment. This involves developing and mastering a series of new space core technologies, accumulating technological reserves, and achieving leapfrog development in space technology.
3. Promoting new space systems or space applications. This aims to form stronger capabilities to handle complex space missions, accelerate the construction of more complete space systems and facilities, master more comprehensive management methods and technologies for complex space mission systems, and promote the substantial application and benefits of new space systems or innovative space applications (Figure 1).

Figure 1 Mission Objectives System

Next, the authors outline the conditions for conducting space technology experiments on the Tiangong Space Station (Figure 2). 
1. Support capabilities within the space station modules. The basic space experiment cabinet can serve as a general support system, providing standard interfaces for mechanical, thermal control, power supply, information, and vacuum for experimental devices, ensuring the smooth implementation of on-orbit experimental projects.
2. Support capabilities outside the space station modules. The open experimental platform provides mechanical installation interfaces for external payloads through payload adapters and offers interface support for power supply, information, and thermal control for the payloads.
3. Support capabilities of cargo spacecraft. The cargo spacecraft utilizes the remaining resources from cargo transportation to establish a regular payload experiment support platform, supporting various types of payload and experimental tasks.
4. Downlink capabilities of manned spacecraft. Currently, some experimental payloads requiring downlink can be transported to the ground through the return capsule of the Shenzhou manned spacecraft. Overall, human participation in space technology experiments on the space station offers better experimental conditions, richer experimental resources, more diverse experimental methods, more flexible and controllable experimental processes, and more reliable experimental results. The space station engineering space technology experiments can cover all fields of space technology experiments, offering unparalleled advantages compared to other spacecraft.

Figure 2 Logical Relationship of Space Technology Experiment Conditions on Tiangong Space Station

The authors then provide a systematic layout for space technology experiment missions on the Tiangong Space Station. Based on the direction of space technology, five research themes are planned (Figure 3).
1. Developing robotic and autonomous system technologies to enhance the ability to handle complex space missions and accelerate the construction of more complete space system facilities, including human-machine collaborative on-orbit operation technology and space debris capture and removal technology.
2. Developing space on-orbit assembly and construction technologies to meet the needs of future manned deep space exploration missions and on-orbit service missions, including large space facility on-orbit assembly and manufacturing technology, on-orbit additive manufacturing technology, and on-orbit deployable structure and mechanism technology.
3. New energy and propulsion technologies primarily focused on new-generation high-efficiency power sources and high-performance propulsion technologies, including new energy system technologies and propulsion system technologies.
4. Environmental Control and Life Support System (ECLSS) technologies mainly targeting longer-duration and farther-distance manned space exploration missions, including highly closed controlled ecological life support systems, long-term space environment microbial prevention technology, and extraterrestrial resource utilization technology.
5. Common new spacecraft technologies, including space thermal management technology, new technologies in components, raw materials, and processes, new measurement technologies, advanced navigation information and control technologies, on-orbit satellite deployment technologies, and on-orbit maintenance technologies.

Figure 3 Layout of On-orbit Technology Experiment and Verification Missions on Tiangong Space Station

Finally, the authors propose suggestions for the development of China's space technology. The development strategy for on-orbit experiments and verification projects of space technology on the China Space Station can be summarized as follows:
1. Adhering to the primary goal of achieving significant benefits in science and applications.
2. Top-level planning and overall layout.
3. Systematic planning and categorized implementation. Based on the five research themes planned earlier, the authors make the following recommendations for future on-orbit experiments and verification projects of space technology on the Tiangong Space Station:
   - In the aspect of robotic and autonomous system technologies, it is recommended to conduct phased verifications of key on-orbit technologies such as human-machine collaboration and multi-machine collaboration, focusing on enhancing the operational capability of the space station platform, improving astronauts' on-orbit operation capability, and the capabilities of the robotic arm system.
   - In the aspect of on-orbit assembly and construction technologies, it is recommended to conduct phased verifications of key technologies such as large optical telescopes, large truss structures, and space welding.
   - In the aspect of new energy and propulsion technologies, it is recommended to conduct verification of new-generation energy system technologies, such as high-efficiency solar cells and high specific energy batteries.
   - In the aspect of ECLSS technologies, it is recommended to verify the on-orbit integration of core functional modules of highly closed life support systems, expand existing ECLSS functions, build typical controlled ecological systems in stages, and directly apply them to space station missions.
   - In the aspect of common new spacecraft technologies, it is recommended to develop key technologies for space liquid metal thermal management and conduct technical experiments on the impact of the space environment on domestically produced components and raw materials. As the demands for future space missions continue to evolve, the development of space technology will also undergo rapid changes. Accordingly, on-orbit space technology experiments and verification projects should be dynamically adjusted to meet the overall mission layout and dynamically match the long-term planning for space technology development.