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7 Guidance, Navigation and Control Technology …
When both the Laser Rangefinder and the MRVS provided valid signal outputs,
a fusion weighed correction method was used: the respective altitude corrections
calculated by the two sensors were weighed and averaged, and then used for position
correction. The weighing coefficients were calculated based on the traces of the
Kalman filter variance matrix of the two modification system.
3. Velocity Correction and Multi-Beam Combination
The velocity of the Chang’E-3 lunar lander was corrected by the data of the velocity
measuring beams in the MRVS. The sensor could provide three independent velocity
measuring beams and a beam with both range and velocity measurement functions.
In addition, the altitude estimation algorithm could also provide an estimate of
the vertical velocity, which could also be introduced as a “beam” in one direction
into the velocity correction. Due to the existence of multiple beams, the number
of beams measurement information obtained at each time was not necessarily the
same. Therefore, in the velocity correction strategy, a single beam calculation error
and multi-beam combination correction method was used.
1) Calculation of single beam error
The kinematics equation of the lunar lander and the microwave velocity measurement
equation were established. The Kalman filter method was used to calculate the gain
matrix. Similar to the range correction, the steady-state gains of different velocity
measuring beams were firstly obtained, and then they were fitted with the heightdependent curve function, and the preset parameters of the gain matrix was finally
obtained.
2) Multi-beam combination correction.
According to different flight conditions, the number of available effective beams in
each measurement period is different. Each error is calculated separately for each
effective beam, and they were combined to calculate the velocity correction error
vector, then the velocity of the lander was corrected. Obviously, if there were 3
or more effective beams in one measurement period, a complete three-dimensional
velocity error correction could be obtained. When the number of effective beams was
reduced to less than 3, only the dimensionality reduction velocity correction could
be obtained. When two beams were effective, two-dimensional (in-plane) velocity
correction could be obtained; when one beam was effective, only one-dimensional
(single direction) velocity correction could be obtained.
7.5.4 Guidance Law Design of Powered Descent Process
In each phase of powered descent, different guidance laws should be designed
according to the requirements. The main task of the main deceleration was deceleration; The major concern of propellant consumption optimization should be considered when the guidance law was designed. The main task of the hazard avoidance was
7 Guidance, Navigation and Control Technology …
When both the Laser Rangefinder and the MRVS provided valid signal outputs,
a fusion weighed correction method was used: the respective altitude corrections
calculated by the two sensors were weighed and averaged, and then used for position
correction. The weighing coefficients were calculated based on the traces of the
Kalman filter variance matrix of the two modification system.
3. Velocity Correction and Multi-Beam Combination
The velocity of the Chang’E-3 lunar lander was corrected by the data of the velocity
measuring beams in the MRVS. The sensor could provide three independent velocity
measuring beams and a beam with both range and velocity measurement functions.
In addition, the altitude estimation algorithm could also provide an estimate of
the vertical velocity, which could also be introduced as a “beam” in one direction
into the velocity correction. Due to the existence of multiple beams, the number
of beams measurement information obtained at each time was not necessarily the
same. Therefore, in the velocity correction strategy, a single beam calculation error
and multi-beam combination correction method was used.
1) Calculation of single beam error
The kinematics equation of the lunar lander and the microwave velocity measurement
equation were established. The Kalman filter method was used to calculate the gain
matrix. Similar to the range correction, the steady-state gains of different velocity
measuring beams were firstly obtained, and then they were fitted with the heightdependent curve function, and the preset parameters of the gain matrix was finally
obtained.
2) Multi-beam combination correction.
According to different flight conditions, the number of available effective beams in
each measurement period is different. Each error is calculated separately for each
effective beam, and they were combined to calculate the velocity correction error
vector, then the velocity of the lander was corrected. Obviously, if there were 3
or more effective beams in one measurement period, a complete three-dimensional
velocity error correction could be obtained. When the number of effective beams was
reduced to less than 3, only the dimensionality reduction velocity correction could
be obtained. When two beams were effective, two-dimensional (in-plane) velocity
correction could be obtained; when one beam was effective, only one-dimensional
(single direction) velocity correction could be obtained.
7.5.4 Guidance Law Design of Powered Descent Process
In each phase of powered descent, different guidance laws should be designed
according to the requirements. The main task of the main deceleration was deceleration; The major concern of propellant consumption optimization should be considered when the guidance law was designed. The main task of the hazard avoidance was