Zhou Jianping, Chief Designer of China's Manned Space Program: On November 4th, during a porthole inspection, astronauts discovered a localized anomaly on the porthole edge. Initial photos were taken with a camera, but the astronauts then used a 40x microscope on the space station to photograph the defect from different angles. We consulted glass experts who confirmed a small triangular area with a crack.
The area suspected to have been impacted by space debris was the outermost layer of heat-insulating glass in the porthole. During reentry, the spacecraft will experience intense friction with the atmosphere, generating temperatures exceeding 1000 degrees Celsius. If the glass's heat-insulating effect is compromised, the astronauts' safety may be compromised. Simulation analysis, testing, and safety assessment of the Shenzhou-20 manned spacecraft were rapidly initiated.
Zheng Wei, China Aerospace Science and Technology Corporation: Because it is heat-insulating glass, the focus is mainly on its heat-insulating performance and whether it can withstand the ablation process during reentry. Based on simulations, we used the porthole of the return capsule to simulate the damage state and conducted wind tunnel ablation tests. The test results show that the crack will still propagate further.
Zhou Jianping: We convened a review meeting, and everyone agreed that given the damaged glass, ensuring the safe return of the astronauts posed a significant risk. Therefore, the General Command decided that the Shenzhou-20 spacecraft would no longer be used for the Shenzhou-20 astronaut crew's return.
Zhou Jianping: We had two emergency launch plans, one for 8.5 days and the other for 16 days. The 8.5-day plan was for situations where an emergency occurred in space requiring the astronauts to be brought back as quickly as possible. Currently, the space station is in excellent condition, and the astronauts are residing there, ensuring a very high level of safety. Therefore, we decided to adopt the 16-day emergency plan. Next, the Shenzhou-21 astronauts will conduct an extravehicular activity (EVA) to inspect the Shenzhou-20 spacecraft's windows from outside the spacecraft. Afterwards, the Shenzhou-20 spacecraft will be systematically re-entered Earth with cargo to conduct a more detailed study and analysis of the damaged area.
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Zheng Wei: Actually, when we originally designed the emergency plan, there was no payload loading component; it was omitted to save time and launch quickly. This time, because of the 16-day timeframe, we had time to prepare the payloads, and we worked overtime to load them. The amount of supplies and payloads [600kg] sent this time was more than before.
