Behind the hole that left the Chinese crew stranded in space

The incident on the Shenzhou-20 spacecraft forced the crew to stay in space for three more days. Photo: Space .

A small crack in a spacecraft window forced China to trigger an emergency launch procedure for the first time in the history of its manned space program. The incident occurred on November 5, when the Shenzhou-20 crew was conducting a routine check before returning to Earth. They discovered an abnormality on the edge of the cabin window and immediately sent images back to the ground.

Jia Shijin, chief designer of the manned spacecraft system at the Fifth Academy of Aerospace Science and Technology, said in a CCTV program that the first image was not clear enough to be conclusive. Only after the astronaut took additional photos from multiple angles and the controller used a robotic arm camera to capture the outer surface did experts determine it was a “penetrating crack,” extending from the inner layer to the outer layer of the glass.

The spacecraft window consists of three layers, the outermost of which is a heat shield that can withstand friction of over 1,000 degrees Celsius when re-entering the atmosphere. The crack means that an important link in the protection system has been damaged. Less than 12 hours later, the command decided to postpone the Shenzhou-20's return plan.

Ji Qiming, assistant director and spokesman of the China Manned Space Engineering Office, said safety was the top priority, adding that the delay was necessary when the risk level was uncertain.

In the following days, the team reviewed the entire process of developing and testing the spacecraft window, and simulated and conducted wind tunnel tests to determine the worst-case scenario. According to the analysis, if the crack spreads, the glass could detach, causing the cabin to suddenly depressurize during re-entry. Although this possibility is “very small,” the team of engineers affirmed that it cannot be ruled out.

On November 8, a special meeting concluded that Shenzhou-20 no longer met the safety conditions for a manned reentry mission. From here, the emergency launch plan was activated. In the “one for one, rotating backup” strategy applied since Shenzhou-12, each launched spacecraft has a backup spacecraft on the ground. At this time, Shenzhou-22 is on standby.

China has always maintained a special contingency strategy for emergency incidents on spacecraft. Photo: THX .

In the end, two options were presented: returning Shenzhou-20 using Shenzhou-21 or Shenzhou-22. The command chose Shenzhou-21 because its configuration was closest to the failed spacecraft, while Shenzhou-22 had many improvements. They also decided to return Shenzhou-20 first before launching Shenzhou-22, avoiding having to move the docked spacecraft and prolonging the crew's waiting time.

While engineers were calculating each option, the three Shenzhou-20 astronauts extended their stay in orbit for another three days. This was also the first time that six people were on the Chinese space station at the same time.

During the 20 days, evaluation, simulation and decision-making were carried out continuously, according to Mr. Ji Qiming. Despite the great pressure, the implementation process was maintained thanks to the backup plans that had been prepared in advance.

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