Core Points - The Shenzhou-20 crew successfully completed a 204-day mission in space, setting a new record for the longest duration for a single crew in China's space history [1] - Astronaut Chen Dong became the first Chinese astronaut to spend over 400 days in space and holds the record for the most extravehicular activities [1] - The Shenzhou-20 mission involved significant scientific experiments across various fields, including microgravity physics and space medicine [1] Summary by Sections Mission Duration and Achievements - The Shenzhou-20 crew spent 204 days in orbit, completing four extravehicular activities and multiple cargo operations [1] - The mission contributed to extensive research in microgravity basic physics, space materials science, space life science, aerospace medicine, and aerospace technology [1] Return Mission and Safety Concerns - The Shenzhou-20 crew will return aboard the Shenzhou-21 spacecraft due to concerns over potential damage from space debris [1][2] - The Shenzhou-20 return capsule was found to have minor cracks in the window glass, likely caused by external impacts from space debris, which do not meet safety conditions for a manned return [2] - An emergency backup mission with the Shenzhou-22 spacecraft is planned to ensure safe return for the crew, with the launch timing dependent on the space station's operational status [2]

Core Viewpoint - The Shenzhou-20 manned spacecraft has been delayed due to a suspected impact from space debris, prompting an analysis of the risks and potential preventive measures [1] Group 1: Sources of Space Debris - Space debris primarily originates from human space activities, with over 40% coming from defunct spacecraft and related components, including retired satellites and rocket remnants [2] - Operational waste generated during space missions also contributes significantly to space debris, including intentionally or unintentionally discarded items [2] - Secondary debris from collisions and explosions of spacecraft is a key factor in the increasing amount of space debris [3] Group 2: Dangers of Space Debris - Even small debris, less than 1 centimeter in diameter, can cause fatal damage to spacecraft due to its high velocity, typically ranging from 7 to 10 kilometers per second [4] - Millimeter-sized debris can scratch spacecraft windows and solar panels, while centimeter-sized debris can penetrate the spacecraft's shell, potentially causing fuel leaks or explosions [4] - A critical density of debris in low Earth orbit can lead to a "domino effect," creating a debris cloud that could severely hinder future space activities [4] - Astronauts have minimal protection against space debris, with even 0.1 millimeter fragments posing a risk of injury [4] Group 3: Technologies to Mitigate Impact Risks - Current methods for predicting space debris impact risks rely on monitoring technologies and data analysis models, employing a combination of active avoidance, passive protection, and debris removal strategies [5] - Optical observation techniques utilize telescopes and cameras to detect debris, while radar monitoring provides all-weather, long-range detection capabilities [5][6] - New technologies, such as laser radar and multi-sensor fusion, enhance debris tracking accuracy and real-time updates on debris locations [6] - For larger debris over 10 centimeters, spacecraft typically perform orbital maneuvers to avoid collisions, while smaller debris is managed through passive protective measures [6]

Mission Update - Shenzhou-20 manned spacecraft return mission is postponed due to suspected impact from space debris [1] - The China Manned Space Engineering Office is conducting impact analysis and risk assessment [1] Safety Concerns - The decision to postpone is to ensure the health and safety of astronauts and the success of the mission [1]