13.3 Technical Characteristics Analysis of Metrology Technology
437
13.3 Technical Characteristics Analysis of Metrology
Technology
The Chang’E-3 was the first lunar lander of China, which had new requirements for
measurement of alignment accuracy, system seal performance and mass property.
In order to implement autonomous navigation and control during powered descent
of the lunar lander, it was necessary for GNC instruments to measure the velocity,
position and attitude of the lunar lander relative to lunar surface in real time. Therefore, when the lunar lander was assembled, on the one hand, the measurement accuracy of alignment of GNC instruments to main structure of the lunar lander should
be improved; on the other hand, there were new requirements such as measurement
of new GNC instruments like ranging and speedometer antennas and the structural
stability of the lunar lander. Because there were a lot of new measurement systems
introduced, it was difficult to unify the measurement data in different coordinate
systems. For example, the laser tracker was applied in measurement of the new
ranging and speedometer antennas, and the laser radar was applied in measurement
of structural stability of the lunar lander, while the reference coordinate system of
the lunar lander was established by traditional theodolite network. Therefore, it was
difficult to transfer the measurement data of different systems and unify several
measurement coordinate systems for measurement of alignment accuracy in system
assembly [4].
The measurement of seal performance for the lunar lander was to test seal of the
propulsion subsystem. The propulsion subsystem was an important subsystem which
was crucial for successful soft-landing and key for the mission success. It would
provide not only Delta-V for trajectory maneuver corrections in LTO and LOI, but
also enough force during powered descent, as well as torque for attitude control. In
order to implement above tasks, the propulsion subsystem was complex with large
volume of propellant and gas tanks, high pressure of gas tanks, high pressure during
leak test, high precision for control of gas fill and vent, lots of engines/thrusters and
valves. There were a lot of seal in propulsion subsystem. So, the requirements for
seal performance of propulsion subsystem were more stringent.
The characteristics of mass properties of the lunar lander were variable during
the mission profile. After the lunar lander was separated with the launch vehicle,
the mass property would change after the antenna, solar panel, landing legs and
other mechanisms were deployed. With consuming of propellant in LTO, LOI and
powered descent, the mass property was changing. In order to ensure the control
during all flight phases, the changes of mass property caused by status changes
should be simulated and tested on the ground, so as to acquire the change pattern of
the mass property parameters and formulate detailed flight control strategy to ensure
the mission success. The loading of propellant was the reverse process of propellant
consumption. By measuring the dynamic change of the propellant during loading,
the change pattern of the mass property during propellant consumption could also
be acquired. In order to ensure the measurement accuracy of the mass property
437
13.3 Technical Characteristics Analysis of Metrology
Technology
The Chang’E-3 was the first lunar lander of China, which had new requirements for
measurement of alignment accuracy, system seal performance and mass property.
In order to implement autonomous navigation and control during powered descent
of the lunar lander, it was necessary for GNC instruments to measure the velocity,
position and attitude of the lunar lander relative to lunar surface in real time. Therefore, when the lunar lander was assembled, on the one hand, the measurement accuracy of alignment of GNC instruments to main structure of the lunar lander should
be improved; on the other hand, there were new requirements such as measurement
of new GNC instruments like ranging and speedometer antennas and the structural
stability of the lunar lander. Because there were a lot of new measurement systems
introduced, it was difficult to unify the measurement data in different coordinate
systems. For example, the laser tracker was applied in measurement of the new
ranging and speedometer antennas, and the laser radar was applied in measurement
of structural stability of the lunar lander, while the reference coordinate system of
the lunar lander was established by traditional theodolite network. Therefore, it was
difficult to transfer the measurement data of different systems and unify several
measurement coordinate systems for measurement of alignment accuracy in system
assembly [4].
The measurement of seal performance for the lunar lander was to test seal of the
propulsion subsystem. The propulsion subsystem was an important subsystem which
was crucial for successful soft-landing and key for the mission success. It would
provide not only Delta-V for trajectory maneuver corrections in LTO and LOI, but
also enough force during powered descent, as well as torque for attitude control. In
order to implement above tasks, the propulsion subsystem was complex with large
volume of propellant and gas tanks, high pressure of gas tanks, high pressure during
leak test, high precision for control of gas fill and vent, lots of engines/thrusters and
valves. There were a lot of seal in propulsion subsystem. So, the requirements for
seal performance of propulsion subsystem were more stringent.
The characteristics of mass properties of the lunar lander were variable during
the mission profile. After the lunar lander was separated with the launch vehicle,
the mass property would change after the antenna, solar panel, landing legs and
other mechanisms were deployed. With consuming of propellant in LTO, LOI and
powered descent, the mass property was changing. In order to ensure the control
during all flight phases, the changes of mass property caused by status changes
should be simulated and tested on the ground, so as to acquire the change pattern of
the mass property parameters and formulate detailed flight control strategy to ensure
the mission success. The loading of propellant was the reverse process of propellant
consumption. By measuring the dynamic change of the propellant during loading,
the change pattern of the mass property during propellant consumption could also
be acquired. In order to ensure the measurement accuracy of the mass property