China to Return Damaged Shenzhou 20 Without Crew After Window Crack

A cracked window changes the journey home

China will bring Shenzhou 20 back to Earth without astronauts after a crack in a return capsule window forced the first decision during a mission in the country's human spaceflight program to cancel a planned crewed return. The spacecraft remains docked to the Tiangong space station, awaiting a flight that will let engineers inspect the damage and measure how the window responds to reentry.

The problem was discovered on November 5 during routine checks before undocking. Astronauts noticed a small flaw near the edge of a window. Images taken from several angles, including views from an external camera on Tiangong, showed that it was a real crack rather than residue on the surface.

Chen Dong, Chen Zhongrui and Wang Jie had completed a six month assignment aboard Tiangong and were preparing to leave. Their departure was delayed by nine days. They eventually returned aboard Shenzhou 21, landing at the Dongfeng site in Inner Mongolia after a little over 200 days in orbit, the longest continuous stay by a Chinese crew to that point.

Taking Shenzhou 21 home left the incoming crew without an immediate, usable escape spacecraft. China responded by launching the uncrewed Shenzhou 22 on November 25, restoring a lifeboat for the three astronauts still aboard the station and delivering supplies and tools.

As of December 2, 2025, the next step is to return the damaged Shenzhou 20 without people aboard. Ji Qiming, spokesperson for the China Manned Space Agency, said that flight would provide valuable measurements that could not be obtained any other way. Engineers want to see what happens to the crack under the heat and stress of an actual descent.

What engineers found in the glass

Jia Shijin, chief designer for China's crewed spacecraft system at the China Academy of Space Technology, said specialists in glass materials examined photographs and video taken inside the cabin and by a camera on Tiangong's robotic arm. Their assessment led to the decision to abandon the original return plan.

The spacecraft design team described a crack extending through the thickness of a window pane, from its inner surface to its outer surface. It was visible near the edge of the viewport. Program officials believe a tiny fragment of space debris was the likely cause.

Jia explained the preliminary assessment and why a close inspection would have to wait until the spacecraft reached Earth.

Our preliminary judgment is that the piece of space debris was smaller than 1 millimeter, but it was traveling incredibly fast. The resulting crack extends over a centimeter. We cannot examine it directly in orbit, so we will study it closely when Shenzhou 20 returns.

Shenzhou windows have a structure made of three layers. Window assemblies on crewed vehicles generally use multiple panes and redundant barriers, so that safety does not depend on a single piece of glass. An outer thermal protection element on Shenzhou must withstand the extreme heat of reentry, when temperatures can exceed 1,000 degrees Celsius.

A crack running through a pane reduces the safety margin built into that arrangement. Ground teams modeled a worst case in which the fracture grew during descent, the cabin lost pressure and gases moving at high speed entered the spacecraft. Life support could be overwhelmed within seconds in that scenario.

Shenzhou 20 could likely have survived the stresses of a normal return, but engineers had no way to confirm that while it remained in orbit. A small chance of the crack growing into a fatal failure was enough to make a return with astronauts unacceptable.

Nine extra days and an emergency launch

Mission control postponed the Shenzhou 20 return and moved to contingency procedures within 12 hours of confirming the crack. The astronauts stayed aboard Tiangong while teams arranged a safe journey home.

Shenzhou 21 had brought the next rotation to the station. The outgoing crew used that fresh spacecraft for their return, making this the first time in China's station program that astronauts came home in a ship different from the one they had launched aboard.

The swap solved the immediate problem for Chen Dong, Chen Zhongrui and Wang Jie, but left the incoming team without a sound return vehicle ready for an emergency. China's standby launch system was then called into action.

The sequence stretched across several November milestones:

• November 5: A flaw was found during checks before Shenzhou 20's planned departure. Images confirmed a crack, and the return was postponed.
• After a delay of nine days: The Shenzhou 20 crew returned aboard Shenzhou 21, landing at Dongfeng after a little over 200 days in orbit.
• November 25: A Long March 2F rocket launched Shenzhou 22 without a crew, twenty days after the delay was announced.
• A few hours after launch: Shenzhou 22 completed an automated rendezvous and docking with Tiangong, restoring an escape option for the remaining crew.

Shenzhou 22 also carried extra supplies and specialized tools for work on the damaged viewport as Shenzhou 20 is prepared for departure. The launch therefore addressed both the need for a lifeboat and the practical work required to send the damaged vehicle home.

Why a fragment smaller than a millimeter matters

Objects in low Earth orbit travel at roughly 7 to 8 kilometers per second. When their paths meet at different angles, the speed at which they approach one another can be even higher. A fragment smaller than a grain of sand can therefore deliver a powerful impact.

The energy released in such a collision can chip or crack glass and metals. Particles smaller than a millimeter can pit metal, damage thermal blankets or fracture a window, even though they are too small for ground tracking systems to follow.

Spacecraft have suffered other forms of debris damage in the past. Confirmed strikes by larger fragments have scarred solar arrays and punctured radiator coolant loops. Windows have also been sandblasted by impacts. Each type of damage affects a different part of the equipment that keeps a spacecraft working.

Engineers protect many spacecraft surfaces with layered bumpers known as Whipple shields. These are designed to break up small particles before they reach the pressure hull, the structure holding the air inside the cabin.

Windows present a harder design problem because astronauts need to see through them for docking and awareness of their surroundings. Dense shielding would block that view. Designers instead use thick panes arranged in multiple layers, toughened materials and protective covers when visibility is unnecessary. They also limit the number and size of windows.

Those protections reduce the risk, but a particle approaching at an unlucky angle or an extremely high speed can still cause damage. The suspected Shenzhou 20 impact illustrates how a very small object can disrupt an entire crew rotation.

The debris that spacecraft cannot dodge

Tracking networks monitor more than thirty thousand objects large enough to catalog. Millions of smaller fragments are too small to track but remain large enough to cause harm. A spacecraft can change course to avoid a known object; shielding must carry much of the burden when an approaching fragment cannot be detected.

Spent rocket stages, old satellites and fragments from collisions contribute to the debris environment. Tiny natural micrometeoroids also present an impact threat. Together, these objects create risks for stations and spacecraft traveling through heavily used orbital lanes.

The United Nations and national space agencies encourage measures to reduce debris, including passivation, controlled reentry at the end of a mission and the use of responsible disposal orbits. Passivation makes equipment left in space less likely to break apart by removing remaining sources of stored energy. Disposal measures move retired spacecraft out of the way or bring them back into the atmosphere.

The density of objects in popular orbital lanes continues to rise despite those practices. Stations and visiting spacecraft regularly adjust their orbits to avoid tracked debris. During risky close approaches, crews may shelter in their return capsules so they are ready to leave if necessary.

Calls for better coordination of space traffic and shared tracking data have grown in recent years. China has promoted joint debris observation projects with partners and is investing in technologies including deorbit sails and precision tracking. Deorbit sails help a spacecraft leave orbit, while better tracking gives controllers more information about potential collisions.

Why the crew waited rather than taking the risk

China's decision rested on both the likelihood of a failure and the severity of its consequences. Even if the probability of the crack growing catastrophically was low, the possible outcome was the loss of the crew. Waiting for a sound spacecraft removed that danger from their journey home.

Chen Dong, the mission commander, addressed the episode after landing. He described the difficulties that accompany human exploration of space.

The path of human exploration of space is not smooth and is full of difficulties and challenges.

The additional nine days extended an already lengthy mission and produced a new national duration record. The response also tested emergency launch and landing procedures that will become part of the operating plans for future crews.

China's human spaceflight program has experienced relatively few failures during flight, making this episode unusual. The response combined a delay for safety, a change of return vehicle and a rapid launch to restore protection for those still in orbit.

What the uncrewed return will test

Flight controllers will carry out standard checks on Shenzhou 20, close its hatches and command it to undock from Tiangong. The spacecraft will then perform a deorbit burn, using its propulsion system to leave orbit and enter the atmosphere along a designated corridor.

Recovery teams at the Dongfeng landing area in the Gobi Desert will secure the return capsule after it descends under parachute. The return is expected in the coming days or weeks, but no precise date had been given as of December 2.

Engineers want to recover more than the damaged glass. They aim to gather realistic measurements of how the crack responds to reentry. Temperature, pressure and vibration sensors can record its behavior as heat builds up and the capsule experiences air loads and acoustic stress.

Ji Qiming said the uncrewed return would yield the most authentic experimental data. Measurements from the flight can be compared with computer models and ground tests, helping engineers judge how accurately those methods represent conditions during a real descent.

Laboratory examination will allow specialists to measure the shape of the crack, analyze any residue at the suspected impact site and check whether the fracture grew during the return. Investigators will also review manufacturing records and the installation of the window assembly to rule out hidden defects unrelated to orbital debris.

The results can strengthen future designs and improve the rules used to decide whether a spacecraft is fit to carry people home after an unusual problem. Shenzhou 20's descent will provide a test under actual flight conditions without exposing astronauts to the damaged window.

Why Tiangong needs a ready lifeboat

Shenzhou 22 now gives the current Tiangong crew an escape option in the event of a medical problem or another emergency. A return capsule docked to a station serves several purposes: it carries astronauts between Earth and orbit, provides shelter during some hazards and waits ready to take them home.

Tiangong can accommodate six astronauts during crew changeovers, while its life support system is tuned for three people during extended stays. A healthy return spacecraft is central to that arrangement, because the resident crew needs a way to leave even between scheduled rotations.

China keeps both a Shenzhou spacecraft and a Long March 2F rocket in a standby configuration for rapid use. Russia and the United States similarly maintain Soyuz and other crew vehicles for contingencies. The accelerated Shenzhou 22 mission demonstrated China's readiness system in practice.

The mission also supplied tools, spare parts and experiments to keep work aboard the station moving. Restoring an emergency ride and delivering equipment allowed station operations to continue while preparations for Shenzhou 20's return proceeded.

Other crews have needed a different ride home

A Russian Soyuz docked at the International Space Station suffered damage in 2022 when a micrometeoroid punctured a coolant line. The astronauts assigned to return aboard it stayed in orbit until a replacement Soyuz arrived without a crew.

NASA astronaut Frank Rubio and two cosmonauts eventually returned safely after their extended mission. Their experience provides a parallel to the Shenzhou 20 response: when a spacecraft waiting at a station develops a serious problem, a replacement can become necessary before the crew can leave.

An American crew capsule on a separate test flight experienced thruster and propulsion problems that kept two astronauts at the International Space Station far longer than planned. They joined the resident crew's work while ground teams arranged a safe return.

In both cases, caution and backup options took priority over the original schedule. The same reasoning guided the decision to send the Shenzhou 20 astronauts home aboard another spacecraft and reserve the damaged vehicle's return for an uncrewed flight.

The next milestones for China's station program

Shenzhou 20's return and the inspection after landing are the next major steps. Meanwhile, Shenzhou 22 will serve as Tiangong's lifeboat as the station continues its science and maintenance schedule.

The rotation that launched aboard Shenzhou 21 includes the youngest Chinese astronaut to date. One member is expected to spend more than one year in space as part of a study of long duration biology and human factors. Restoring an emergency return vehicle allows those plans to proceed.

Investigators will use the recovered capsule and its flight measurements to better understand the window damage. The findings are likely to inform window design, impact shielding and rules for returning spacecraft to service after problems, including work relevant to China's planned lunar landing attempt later in the decade.

The episode has already demonstrated the value of maintaining a spacecraft and rocket ready for an emergency launch. The remaining task is to recover Shenzhou 20 and turn the damage into information that helps protect future crews.

Key Points

• Shenzhou 20 will return without astronauts after a cracked window halted its planned crewed descent.
• Chen Dong, Chen Zhongrui and Wang Jie returned aboard Shenzhou 21 after a delay of nine days and a little over 200 days in orbit.
• Engineers suspect debris smaller than 1 millimeter caused a crack extending through a window pane and measuring more than a centimeter.
• Shenzhou 22 launched without a crew on November 25 and docked a few hours later, restoring Tiangong's emergency ride.
• The replacement spacecraft also delivered supplies and specialized tools for preparing the damaged vehicle to leave.
• Shenzhou 20's return will provide flight measurements before engineers inspect the capsule at Dongfeng and in a laboratory.
• No precise return date had been announced as of December 2, 2025.