Could a fragment no larger than a coin stop a spacecraft from making its way home? For China’s Shenzhou-20 crew, that unsettling possibility turned real when their return capsule was hit by suspected orbital debris just hours before their scheduled departure from the Tiangong space station. The incident has forced Wang Jie, Chen Zhongrui, and mission commander Chen Dong to stay in orbit while engineers conduct a detailed impact analysis and risk assessment.
The Shenzhou-20 has been docked since April, with three detachable sections: a power and propulsion module, crew living quarters, and a parachute-assisted return module. Any compromise to any of these systems may make reentry unsafe. So, if the capsule is unfit according to standard procedure under the China Manned Space Agency, it will be sent back unmanned, and the crew returns aboard the capsule of Shenzhou-21. A backup Shenzhou spacecraft, together with a Long March-2F rocket, is kept on standby at the Jiuquan Satellite Launch Centre in preparation for this possibility.
The delay lifted Chen Dong’s accumulated time in space above 400 days, increasing the national record. His case is not an exception: last year, the return of NASA astronaut Frank Rubio from the International Space Station was postponed for several months after a meteoroid disabled his Soyuz capsule. Other crews faced similar delays, including Boeing Starliner’s nine-month delay for the flight of Wilmore and Williams due to technical malfunctions.
Space debris collisions are not new to Tiangong. In 2023, a hit against its solar panels caused partial power loss, and CMSA installed additional shielding during spacewalks. These form part of a broader strategy of mitigating debris, including improved orbit forecasting and collision avoidance procedures that have cut false alarms by 30%. High-definition cameras mounted on the robotic arm of Tiangong now monitor vulnerable external structures while crews reinforce critical piping and cables during extravehicular activities.
This threat is magnified by the sheer velocity of orbital debris. At velocities above 7 km/s, even a 1-cm fragment can deliver kinetic energy equivalent to a hand grenade. NORAD currently tracks over 43,000 objects in orbit; more than 14,000 satellites and an estimated 120 million debris fragments inhabit low Earth orbit. The proliferation of large constellations SpaceX’s Starlink alone exceeds 7,000 satellites has focused concerns on so-called Kessler Syndrome, a cascading chain reaction of collisions, possibly rendering low Earth orbit unusable.
Both the Tiangong and the ISS perform avoidance manoeuvres whenever debris enters a predefined “pizza box” safety zone. The really dangerous fragments, however, are the ones too small to be tracked. Those can pierce through shielding and render vital systems useless with little to no warning. The Canadarm2 robotic arm of the ISS once suffered punctures from such hits.
Agencies and companies around the world are now racing to develop mitigation technologies. Concepts vary from robotic arm retrieval systems by Astroscale and ClearSpace, TransAstra’s “Capture Bag” for recycling in space, and laser ablation to nudge debris into safer orbits. The CMSA has invested in deorbiting sails to accelerate the atmospheric burn-up of defunct spacecraft like Tiangong to reduce long-term debris risks.
International cooperation is essential but highly politically complex. The UN Office for Outer Space Affairs calls for harmonised regulations, but there is irregular adherence to the guidelines already in place-only about 50% of satellites are deorbited to date. China has called for joint debris observation centres with other nations and also pointed out the hazards from debris created by anti-satellite weapon tests, which have generated thousands of trackable fragments.
For now, the crew of Shenzhou-20 waits for their fate based on results from CMSA. The incident underlines the fragility of human spaceflight when it comes to even minor orbital risks and the dire need for substantial engineering solutions and coordinated international action to protect low Earth orbit for future missions.
