We have been concerned about when the Shenzhou 20 crew will return. Finally, the China Manned Space Engineering Office has released information: the return mission of the Shenzhou 20 crew is being steadily advanced, and results are expected soon.

Currently, the six astronauts from Shenzhou 20 and Shenzhou 21 have been stationed in the space station for more than 12 days, setting a new record for the continuous stay of six astronauts in the space station. This presents an unprecedented test of the entire system's environmental control and life support capabilities.

In the microgravity environment of space, long-term stay cannot rely solely on oxygen and water carried from Earth; it must depend on regenerative environmental control and life support systems. This system not only recycles oxygen but also removes and restores carbon dioxide in real time, eliminating various trace harmful gases to maintain a safe and livable atmosphere inside the cabin.

Astronauts' breathing continuously consumes oxygen and produces carbon dioxide. If the concentration of carbon dioxide in the cabin becomes too high, it may cause headaches, drowsiness, or even breathing difficulties, and in severe cases, could lead to poisoning or suffocation.

Additionally, up to 72 types of trace harmful gases have been detected in the space station, including alcohols, aldehydes, ketones, and alkanes. These originate from human metabolism, equipment volatilization, and scientific experiments. Although the concentration of each gas is extremely low, their long-term coexistence and accumulation can still pose potential threats to astronauts' respiratory systems, nervous systems, or organ functions. Therefore, they must be effectively filtered and removed through specialized equipment.

Notably, carbon dioxide in the space station is not just a waste product; it also has significant resource value. Through catalytic reactions, captured carbon dioxide can react with hydrogen to produce water and methane.

Water can then be reprocessed into oxygen and hydrogen through electrolysis, thus achieving a partial closed-loop cycle of oxygen and water. Calculating at the minimum daily drinking requirement of 3 liters per astronaut, the total water needed over 12 days would be at least 216 liters.

Currently, the astronauts' water supply mainly comes from two sources: flexible water bags transported by cargo spacecraft and the station's wastewater regeneration system. The latter consists of three subsystems: condensate collection, urine processing, and water purification, basically achieving complete recycling of the station's water resources.

Among these, urine processing is one of the most technically challenging aspects of the environmental control and life support system. Urine contains over 100 types of organic and inorganic substances, and under microgravity conditions, the absence of fluid static pressure makes liquid directional flow and phase separation extremely complex.

China's space station adopts the most advanced vapor compression distillation technology to process urine. This technology was developed by the 206th Institute of the China Aerospace Science and Technology Corporation since 2012. After ten years of research, the team successfully overcame more than ten key technologies, including low-pressure rotating distillation, gas-liquid two-phase flow delivery and separation, non-lubricated rotating dynamic sealing, calcium crystallization and precipitation in urine, and exhaust treatment, achieving breakthroughs in water recovery from urine and filling multiple domestic technical gaps.

Specifically, the urine processing subsystem in the Tianhe core module first performs rotating distillation on pre-treated urine, collects the generated water vapor, condenses it into distilled water, and transports it to the water processing subsystem for deep purification, thereby extracting usable water from the urine. This system can extract 5 liters of distilled water from 6 liters of urine, with a maximum water production rate of 2.5 liters per hour, effectively ensuring the astronauts' daily water needs while significantly reducing the payload burden of cargo spacecraft and lowering the long-term operating costs of the space station.

Although it may not feel very comfortable psychologically, the water processed by this system is actually purer than most drinking water on Earth.

From an economic perspective, this technology is even more important: as early as 2015, the cost of launching 0.5 kilograms of water to the International Space Station was approximately $25,000. Based on the daily water consumption of six astronauts, without a regeneration system, the launch cost required for daily water supply alone would reach about $425,000, and the annual total could exceed $155 million. Water recycling technology fundamentally alleviates this economic and transportation pressure.

Regarding the current situation of six people simultaneously in orbit, the regenerative environmental control and life support system of China's space station has two operating modes: three-person mode and six-person mode.

The system is currently operating in the high-load six-person mode, which can meet the operational requirements under maximum metabolic load. In addition, the space station always maintains a high level of emergency preparedness, with the ability to quickly troubleshoot equipment failures and switch redundancies. It has established a comprehensive medical intervention and ground-to-space evacuation plan, and through uninterrupted space-ground communication links, it realizes real-time interconnection of command transmission and status monitoring.

This long-term joint stay of six people is not only a comprehensive test of the environmental control and life support system's ability to support human metabolic limits, but also a key test to verify the overall system's performance under the maximum configuration of three modules and three spacecraft.

Whether it is the return of the Shenzhou 20 crew or the emergency launch of the Shenzhou 22 crew to pick up the astronauts, the return time of the Shenzhou 20 crew will not be far away. Regardless of the method used, we always prioritize the safety of the astronauts.

Original article: https://www.toutiao.com/article/7571876514048885286/

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