Source: Science and Technology Daily
Before the re-entry module of Shenzhou 14 manned spacecraft successfully returns to the ground, it will go through five stages: separation, braking, re-entry, deceleration and landing buffer.
Separation and braking phase
The "fast return plan" is still adopted for this return, that is, the Shenzhou XIV will start to return to the ground after 5 circles after separating from the space station assembly; Then, the orbital module in the front section is separated from the return module in the middle section; The combination of the return module and the propulsion module can change the orbit from a circular orbit of nearly 400km to an elliptical orbit of less than 100km at the perigee by braking; Then, the propulsion module and the re-entry module are separated, and the re-entry module enters the earth's atmosphere at an accurately calculated reentry angle, and the propulsion module is burned when crossing the atmosphere.
Reentry stage
The shape of the Shenzhou XIV re-entry capsule is like a big clock, which is narrow at the top and wide at the bottom. Before reentry, the engine on the capsule will adjust the re-entry capsule to a trim state with the big bottom facing forward, and reentry by means of lift control. During re-entry, the re-entry capsule and atmospheric air rub violently, forming a plasma zone that encloses the re-entry capsule, causing signal interruption between the ground and the cabin. This period of time is called the "black barrier area". During this process, the ground cannot control the spacecraft through any remote control method, and it relies on the aircraft for full automatic processing.
Deceleration phase
At a distance of about 40 kilometers from the ground, the spacecraft has basically left the "black barrier area". A static pressure altitude controller is installed on the return cabin to determine the altitude by measuring the atmospheric pressure. When the return capsule is about 10km from the ground, the static pressure altitude controller will give a signal, and the pilot parachute, deceleration parachute and main parachute will open successively. The area of the three umbrellas has increased from a few square meters to dozens of square meters and then to more than 1000 square meters. By opening the umbrellas step by step, the overload can be reduced and the astronauts can be protected. In addition, in order to prevent the force borne by the deceleration parachute and the main parachute from being too large at the moment of opening, the parachute will be in the closing and half opening state when opening, and will be fully opened after working for a few seconds. At the same time, in order to ensure the life safety of astronauts and improve the reliability and safety of the recovery landing system, the return capsule is also equipped with a backup parachute. Once the spacecraft detects a fault, it will switch to the working state of the backup parachute according to the scheduled procedure.
Landing buffer phase
The heat proof bottom is the "armor" of the spacecraft after entering the atmosphere. Soon after the main parachute is fully opened, the re-entry module will throw off the "armor", and the gamma height control device will start to work. The height above the ground will be measured in real time by emitting gamma rays. When the return capsule drops to a height of 1 m from the ground, the gamma source at the bottom sends out an ignition signal, and the four reverse thrust engines on the capsule ignite, generating an upward impulse, which further reduces the landing speed of the return capsule to 3 m/s. At the same time, the astronaut seat installed with the buffer device will start to rise before landing, so that the impact energy can be absorbed by buffering, fully ensuring the comfort of the astronaut landing, reflecting the concept of "people-oriented" spacecraft design.
After the re-entry capsule landed safely, in order to ensure that the ground search and rescue system could find the re-entry capsule in time, in addition to deploying a certain number of radars to track and measure the orbit of the re-entry capsule and predict the landing position, the re-entry capsule was also equipped with an autonomous calibration device to tell the search and rescue personnel that "I am here".
The smooth progress of the whole return process is inseparable from the participation of all subsystems of the Fifth Academy of Aerospace Science and Technology Group. GNC (guidance, navigation and control) subsystem is responsible for attitude control of spacecraft during braking and entering the atmosphere; The thermal protection materials, thermal protection coatings and buffer devices on the external surface of the thermal control subsystem and the structural mechanism subsystem ensure the life safety of astronauts throughout the whole process; The recovery and landing subsystem lands stably with the help of the landing buffer engine through the precise braking of the parachute; The measurement and control subsystem, the digital tube subsystem, and the overall circuit subsystem play the roles of "voice transmission from heaven to earth" and "intelligent network", providing energy, collecting and sorting data, and transmitting signals to ensure zero error throughout the process.
