7.5 Typical Technology
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site could be reset and landing maneuvers could be achieved within a certain range
to complete rough obstacle avoidance.
4. Guidance Law for Hovering
The main purpose of the hovering was to use the 3-D Imaging Sensor to perform
fine hazard detection on the landing area, and to provide the position information of
the safe landing point relative to the lunar lander bottom point at the imaging time.
The initial navigation altitude of the hovering was used as the guidance target of
the suspending altitude, and the gravity of the lunar lander was compensated by the
throttling engine to ensure that the lunar lander was in a suspending status with zero
speed and stable attitude. The guidance goal of the hovering was: the altitude was the
initial navigation altitude of the hovering, the target velocity in the three directions
was 0 m/s, and the acceleration in the direction of the altitude was 0 m/s
2 . In order
to ensure the adaptability and robustness of the guidance logic for the hovering and
subsequent mission phase, the guidance law of hovering and subsequent mission
phase was based on the combination of outer loop guidance (PID) and inner loop
guidance (phase plane control using position and velocity). Outer loop control was
achieved by the main engine and attitude maneuvers; inner loop control was achieved
by horizontal thrusters.
5. Guidance Law for Hazard Avoidance
The main task of the hazard avoidance was to accurately avoid obstacles and descent.
According to the relative position information of the safe landing point given by the
hovering, the lunar lander would horizontally maneuver above the selected safe
landing point and the horizontal velocity at terminal of the horizontal maneuver was
around 0 m/s; then the lunar lander descended to about 30 m above the landing
point, and the terminal descent velocity relative to lunar surface was −1.5 m/s. The
obstacle avoidance guidance law was similar to the guidance law of the hovering.
The horizontal channel controlled the velocity and position, and the vertical channel
controlled the altitude, velocity and acceleration. At the beginning of the obstacle
avoidance, the time-based altitude, velocity, and acceleration to track target trajectory
was designed in the vertical direction, and the target trajectory was tracked in real
time in the obstacle avoidance descent phase, so that the terminal status of the obstacle
avoidance could be better controlled.
6. Guidance Law for Slow Descending
The safety of landing was considered in the slow descending. To ensure the accuracy
of the control of the speed and attitude for landing to lunar surface, the vertical
descent should be made at a uniform speed with a low preset speed to eliminate the
horizontal speed and acceleration until the shutdown sensor signals were received.
The descent speed of −2 m/s was chosen when the propellant consumption and
navigation position drift were considered. The guidance law during slow descending
was the same as the guidance law during the hovering, besides that the guidance
parameters were different. The target velocity in the horizontal direction was 0 m/s,
and the position control target was the position of the lunar lander at the beginning
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site could be reset and landing maneuvers could be achieved within a certain range
to complete rough obstacle avoidance.
4. Guidance Law for Hovering
The main purpose of the hovering was to use the 3-D Imaging Sensor to perform
fine hazard detection on the landing area, and to provide the position information of
the safe landing point relative to the lunar lander bottom point at the imaging time.
The initial navigation altitude of the hovering was used as the guidance target of
the suspending altitude, and the gravity of the lunar lander was compensated by the
throttling engine to ensure that the lunar lander was in a suspending status with zero
speed and stable attitude. The guidance goal of the hovering was: the altitude was the
initial navigation altitude of the hovering, the target velocity in the three directions
was 0 m/s, and the acceleration in the direction of the altitude was 0 m/s
2 . In order
to ensure the adaptability and robustness of the guidance logic for the hovering and
subsequent mission phase, the guidance law of hovering and subsequent mission
phase was based on the combination of outer loop guidance (PID) and inner loop
guidance (phase plane control using position and velocity). Outer loop control was
achieved by the main engine and attitude maneuvers; inner loop control was achieved
by horizontal thrusters.
5. Guidance Law for Hazard Avoidance
The main task of the hazard avoidance was to accurately avoid obstacles and descent.
According to the relative position information of the safe landing point given by the
hovering, the lunar lander would horizontally maneuver above the selected safe
landing point and the horizontal velocity at terminal of the horizontal maneuver was
around 0 m/s; then the lunar lander descended to about 30 m above the landing
point, and the terminal descent velocity relative to lunar surface was −1.5 m/s. The
obstacle avoidance guidance law was similar to the guidance law of the hovering.
The horizontal channel controlled the velocity and position, and the vertical channel
controlled the altitude, velocity and acceleration. At the beginning of the obstacle
avoidance, the time-based altitude, velocity, and acceleration to track target trajectory
was designed in the vertical direction, and the target trajectory was tracked in real
time in the obstacle avoidance descent phase, so that the terminal status of the obstacle
avoidance could be better controlled.
6. Guidance Law for Slow Descending
The safety of landing was considered in the slow descending. To ensure the accuracy
of the control of the speed and attitude for landing to lunar surface, the vertical
descent should be made at a uniform speed with a low preset speed to eliminate the
horizontal speed and acceleration until the shutdown sensor signals were received.
The descent speed of −2 m/s was chosen when the propellant consumption and
navigation position drift were considered. The guidance law during slow descending
was the same as the guidance law during the hovering, besides that the guidance
parameters were different. The target velocity in the horizontal direction was 0 m/s,
and the position control target was the position of the lunar lander at the beginning