Scientists propose safety design for the China space station

Firstly, the author provides a summary of the safety design process for the space station. The process begins by establishing safety target for the space station design, crew member safety, station safety, and mission safety. Hazard identification is then conducted, followed by the formulation of safety control measures, ultimately leading to the safety design. In terms of astronaut safety, emphasis is placed on ensuring the comprehensive safety of astronauts during their residence on the space station, including environmental control and hazard management. Station safety necessitates ensuring the availability of the space station's functional systems during orbital operation through system reconfiguration and safety modes, thus avoiding catastrophic consequences resulting from failures. Hazard identification involves recognizing potential general hazards and failure risks through hazard identification and analysis. Safety control measures encompass design measures, safety protection equipment, alarm equipment, and operational regulations. The safety design adheres to the principle of 'one fault at work, two faults safely,' ensuring that after a single fault, platform functions and critical tasks can operate normally. In the event of a second fault, emergency resources are provided to prevent potential catastrophic consequences. The safety design system of the CSS is illustrated in Fig. 1.

Secondly, the author elaborates on the safety design for general hazards, fault hazards, dangerous events, and critical missions. For general hazard events, safety measures encompass intrinsic hazard materials, environmental risks, propellants, pressure vessels, and more. As shown in Table 1, the safety design for propellants emphasizes structural strength and material compatibility to prevent leaks. Pressure vessels are designed with a 'leak without explosion' principle, ensuring that faults only result in limited gas leakage. High-pressure equipment adopts multiple safety measures, including baffles, insulating materials, and cable isolation. Radiation risks are reduced through path planning and adjustments to equipment usage patterns, while harmful gases are controlled within acceptable limits through adsorption and catalytic oxidation. Pyrotechnic equipment employs multiple measures to prevent misoperations, and high-temperature equipment ensures astronaut safety through temperature monitoring and thermal insulation design. Excess materials and microorganisms are controlled to meet targets through filtration and purifiers. Dew protection design prevents electronic equipment from short circuits. Protection against space debris includes a dual-layer filled protection structure and a real-time monitoring system. These comprehensive measures effectively address potential hazards, ensuring the safe execution of missions. For the safety design of failure hazards on the space station, particular emphasis is placed on system functional failures and key functions in mission planning. reliability design and the principle of ensuring operability under the first failure and safety under the second failure are applied to cabin structure, rendezvous and docking control equipment, energy management equipment, and others. In the event of equipment failure, redundancy measures are employed to isolate the fault, reduce the impact of faulty equipment, and ensure equipment status recovery through on-orbit repairs.

In the safety design against hazardous events, particular attention is given to scenarios involving fire in sealed modules and depressurization in sealed modules. For fire in sealed modules, safety control measures are designed in four main aspects. Firstly, fire-resistant materials with flame retardancy and combustion product testing are selected to ensure non-propagation in the event of a fire. Secondly, smoke and temperature detectors are installed in critical areas to monitor fire situations in real-time. The inclusion of carbon dioxide fire extinguishers, fire extinguishing wipes, and emergency response measures, such as astronauts wearing emergency breathing apparatus, is implemented. Emergency operation drills have been conducted to verify the operational procedures for astronauts to collaboratively extinguish fires in orbit. Strategy for emergency disposal of fire in a sealed module is illustrated in Figure 2. Regarding depressurization in sealed modules, a multi-layered structure is employed for structural protection to prevent damage caused by space debris or micrometeoroids to the sealed compartment. Leak detection and positioning systems, as well as emergency pressure supply systems, are installed. Emergency pressure disposal measures for astronauts in orbit are designed, and specific emergency response strategies are formulated based on the total pressure maintenance time. The priority is given to in-orbit repair of the leak fault to ensure astronaut safety.

Additionally, the safety design for critical tasks on the space station primarily involves proximity operations, docking, and extravehicular activities. The focus is on the following aspects: Firstly, for proximity operations, both active and passive safety modes are employed, with a defined boundary of 5 kilometers as the separation line between active and passive safety zones. Within the active safety zone, safety retreat is implemented in the event of anomalies in visiting spacecraft to ensure no collisions with the space station occur. Within the safety corridor, real-time position and velocity assessments are used for emergency avoidance. Secondly, during extravehicular activities, path planning is employed to avoid equipment that may harm astronauts or impact space station operations. Emergency return paths are established to ensure astronauts can independently return in case of accidents. Thirdly, the decompression and recompression system for tasks involving astronaut extravehicular activities incorporates redundant measures controlled both electrically and manually to ensure astronaut safety. Lastly, the space station utilizes an active potential control system, measuring and controlling structural potential to ensure it stays within a safe range during astronaut extravehicular activities, preventing any adverse effects on astronauts and equipment.

Furthermore, the author provides examples illustrating how the space station autonomously handles severe malfunction issues. Different state transitions of space station are depicted in Figure 4. The space station can actively monitor and assess potential malfunctions in real-time through the main controller and parameter acquisition devices, initiating in-orbit autonomous responses within predefined threshold ranges. Measures are taken to address excessive battery discharge depth by the energy management computer, which monitors and autonomously sends device management commands in real-time. The main controller monitors the power status of devices under two buses, enabling autonomous responses in the event of power faults to prevent interruptions. For attitude deviations, the control computer monitors attitude angles and angular velocities in real-time, autonomously sending commands to switch the space station to sun-oriented mode, ensuring the establishment of a normal Earth-space communication link. Alerts and warning signs are utilized to notify astronaut crews of potential risks.

Finally, the author concludes the paper. This article systematically summarizes the safety design objectives and principles of the Chinese space station. The comprehensive safety design of the space station considers various risks, analyzing each type of risk to identify key links in safety control. It achieves effective hazard control with minimal resource costs, ensuring the overall safety of astronauts, the platform, and critical tasks during orbital operations. All safety measures described in the paper have been implemented on the space station and validated through on-orbit flights, demonstrating their effectiveness. Looking ahead, the safety design of the space station will be improved based on actual working conditions and system safety control. This indicates that space station safety design is a dynamic process that needs to continuously adapt to changes in orbital operation states to ensure the ongoing safety of the entire system. In summary, this paper provides comprehensive and in-depth guidance for the safety design of the space station, laying a solid foundation for the safety of future space missions.