Core Viewpoint - The successful landing of the Shenzhou-21 manned spacecraft marks a significant advancement in China's re-entry and return technology, achieving a new level of system reliability with a reduced return time of over 3 hours compared to previous missions [1] Group 1: Re-entry Control - The re-entry control of the spacecraft is managed by the Guidance, Navigation, and Control (GNC) system, which acts as the "intelligent driver" for the spacecraft, overseeing the entire flight control process from launch to return [2] - The re-entry control involves two main aspects: orbital departure control and atmospheric re-entry control, with the latter focusing on lift control within the atmosphere [2] Group 2: Transition from 5 Orbits to 3 Orbits - The transition from a 5-orbit to a 3-orbit return strategy was designed to enhance the efficiency and emergency response capabilities of the Shenzhou spacecraft, with the key change being the shift from ground-based to onboard computer calculations for departure control parameters [3] - Multiple rounds of verification and recalculation were conducted to ensure the accuracy of the onboard calculations, confirming the feasibility of the new return strategy [3] Group 3: Significance of 3-Orbit Autonomous Quick Return - The implementation of the 3-orbit autonomous quick return significantly improves the spacecraft's ability to handle major faults during autonomous flight and docking phases, demonstrating the stability and reliability of China's re-entry technology [4] - The evolution of re-entry technology from the standard ballistic adaptive guidance of Shenzhou-1 to the adaptive predictive guidance of Shenzhou-12, culminating in the 3-orbit quick return of Shenzhou-21, showcases over 30 years of unique development in this field [4]

Core Points - The Shenzhou-21 manned spacecraft successfully completed its return mission, marking a breakthrough in China's re-entry and return technology with enhanced system reliability [1] - The re-entry and return process involves the spacecraft leaving orbit, entering the Earth's atmosphere, and landing safely, with the GNC system being crucial for flight control [1] - The Shenzhou program has evolved through two generations of re-entry technology, with the latest Shenzhou-21 utilizing a new three-orbit autonomous quick return strategy [2] Group 1 - The Shenzhou-21 spacecraft implemented a three-orbit autonomous quick return, improving upon the previous five-orbit method, which reduces the return time by over three hours [2] - The transition from ground-based to onboard computation for deorbit control parameters represents a significant advancement in the spacecraft's autonomous capabilities [2] - The GNC system, developed by the 502nd Institute, plays a critical role in ensuring the accuracy and reliability of the spacecraft's return process [1][2] Group 2 - The development of re-entry technology in China's manned space program has progressed from standard ballistic adaptive guidance to adaptive predictive guidance, culminating in the current autonomous quick return method [3] - The ongoing efforts by the 502nd Institute aim to strengthen key core technologies and achieve new heights in manned spaceflight technology [3]