Spacecraft returning technique's Guidance Technology

The return trajectory of spacecraft during ballistic reentry is determined by the off-orbit conditions, which can not be corrected midway, so the return control is mainly the control of braking direction and the control of ignition time of thrust rocket. The braking direction directly determines the reentry angle, thus affecting the reentry braking overload and aerodynamic heating. The braking direction is controlled by the spacecraft attitude control system. The ignition time of the reverse rocket directly affects the landing position of the return capsule. For example, the ignition time difference of a low-earth orbit thrust reverser rocket is 1 s, which will make the landing position of the return capsule differ by about 9 kilometers. The ignition of the thrust rocket is controlled directly by the ground monitoring station or by the pre-injection program. For manned spacecraft, the manual control of astronauts can be used as the preparation or main control mode of return control. When a spacecraft performs lift re-entry, it is necessary to control the lift in the atmosphere in addition to orbit control. Semi-ballistic reentry spacecraft flies at a certain angle of attack, the center of gravity shifts, and the lift direction is changed by rolling control, which has certain maneuverability. After the space shuttle re-enters the atmosphere, the attitude control system controls the pitch and roll to generate lift and change the direction of lift, so it has strong maneuverability, and can maneuver over thousands of kilometers to choose the best re-entry route. When the space shuttle descends below the altitude of 25 kilometers, the attitude control system stops working completely, and the parameters such as altitude, speed, flight route, heading and lateral distance continue to be controlled by pneumatic control, so that the space shuttle can land horizontally at the predetermined location. When the spacecraft returns from the moon, in addition to the orbit control, it must make several orbit corrections on the way back, so as to break into the reentry corridor, and then return along the gliding orbit or jumping orbit through lift control.