神二十飞船舷窗裂纹维修，细节披露

Core Viewpoint - The Shenzhou 20 spacecraft experienced a delay in its return due to a crack in the window caused by suspected impact from small space debris, leading to a series of tests in orbit before its eventual return in an unmanned state [1][2]. Group 1: Unmanned Return vs. Manned Return - The Shenzhou 20 spacecraft's return was conducted in an unmanned mode, relying entirely on ground commands, unlike previous manned returns which involved astronaut manual operations [3]. - The Beijing Aerospace Flight Control Center re-evaluated all flight control plans for the unmanned return, ensuring the spacecraft's stability and conducting thorough inspections before the return [3]. Group 2: Window Repair Process - The window of the Shenzhou spacecraft consists of a three-layer composite glass structure, with the outer layer designed to withstand temperatures exceeding 1000 degrees Celsius during re-entry [5]. - After discovering a penetrating crack in the outer layer, the crew switched to Shenzhou 21 for return, and an internal reinforcement plan was implemented to enhance safety [5]. - The Shenzhou 22 spacecraft delivered a specialized device to the space station to improve the thermal and sealing capabilities of the Shenzhou 20 return capsule, which successfully landed with its exterior intact and cargo undamaged [5]. Group 3: Importance of Windows - The windows on the spacecraft serve critical functions beyond observation, including ensuring astronaut safety during emergencies and acting as a backup for attitude determination in case of system failures [6][10]. Group 4: Returned Cargo - The Shenzhou 20 spacecraft returned with a record amount of cargo due to the absence of three astronauts, including an over-aged extravehicular spacesuit and several large items from the space application system [9]. - The extravehicular suit, which has been used by 11 astronauts across 8 missions, is expected to contribute to lunar suit research and may be publicly displayed after fulfilling its scientific mission [9].