460
13 Metrology Technology of Lunar Lander
propellant is filled; and (4) According to test data after propellant filling and mission
requirement, the best mass center could be achieved by fine-tuning of ballast.
3. Practical Application
Here is an example of the process and result of integrated ballast and propellant
correction in the Chang’E-3 lunar lander. The dry mass of the lunar lander was
adjusted by ballast. The Y c is −8.53 mm before ballast was installed. After ballast
was installed, the Y c is −0.10 mm. By correction of the lunar lander mass center with
conventional ballast, the risk beyond the mass center limit of propellant correction
method was eliminated and it was prepared for propellant correction. The filling
process of methyl hydrazine was as follows: (1) Each tank was filled in 425 kg. The
Y c was −0.27 mm; (2) The R1 was filled in 436.5 kg and 433.5 kg for R2. The Y c
was 1.53 mm, which meant that the mass center was changed significantly and the
mass center correction by propellant instead of ballast was achieved. For the filling
of oxidizer, it was filled uniformly. The test result of mass center did not change
significantly. The Y c is 0.5 mm. After propellant was loaded, the mass center of the
lunar lander was corrected by traditional ballast again. The Y c was 0.00 mm before
ballast was installed, and Y c was −0.61 mm after ballast was installed, which was
optimal by design.
13.5 Summary
During development of the Chang’E-3 lunar lander, some professional metrology
technologies were developed, which improved the accuracy, reliability and safety
of metrology. For the alignment metrology, laser tracker, laser radar and theodolite
integrated measurement technology were applied. The fusion of laser tracker and
theodolite coordinate system was implemented by common point transformation,
which was applied in normal direction measurement of RVS antenna end surface
by laser tracker in the lunar lander coordinate system. At the same time, scanning
measurement technology with laser radar and theodolite based on generalized USMN
adjustment were applied in 3-D shape measurement of the interface ring in the lunar
lander coordinate system to verify the stability of the interface ring under load. In
the system leak test, the automated leak test technology and the flexible helium
hood technology for quick leak positioning were applied. By application of highly
accurate automatic leak test technology, automatic gas fill and vent, automatic leakage
rate test, automatic comparison measurement with standard container and automatic
sampling were implemented, which improved the efficiency and reliability of pipeline
sealing performance test. At the same time, the quick leak positioning technology
by flexible helium hood was applied to improve the accuracy of total leak test and
the efficiency of quick leak positioning in complex conditions were realized, which
gave a solution to the issue of leak positioning in complex system which could not
apply bubble method. In the mass property test, technologies were applied including
mass property test based on multiple DOF transformation, test data correction for
13 Metrology Technology of Lunar Lander
propellant is filled; and (4) According to test data after propellant filling and mission
requirement, the best mass center could be achieved by fine-tuning of ballast.
3. Practical Application
Here is an example of the process and result of integrated ballast and propellant
correction in the Chang’E-3 lunar lander. The dry mass of the lunar lander was
adjusted by ballast. The Y c is −8.53 mm before ballast was installed. After ballast
was installed, the Y c is −0.10 mm. By correction of the lunar lander mass center with
conventional ballast, the risk beyond the mass center limit of propellant correction
method was eliminated and it was prepared for propellant correction. The filling
process of methyl hydrazine was as follows: (1) Each tank was filled in 425 kg. The
Y c was −0.27 mm; (2) The R1 was filled in 436.5 kg and 433.5 kg for R2. The Y c
was 1.53 mm, which meant that the mass center was changed significantly and the
mass center correction by propellant instead of ballast was achieved. For the filling
of oxidizer, it was filled uniformly. The test result of mass center did not change
significantly. The Y c is 0.5 mm. After propellant was loaded, the mass center of the
lunar lander was corrected by traditional ballast again. The Y c was 0.00 mm before
ballast was installed, and Y c was −0.61 mm after ballast was installed, which was
optimal by design.
13.5 Summary
During development of the Chang’E-3 lunar lander, some professional metrology
technologies were developed, which improved the accuracy, reliability and safety
of metrology. For the alignment metrology, laser tracker, laser radar and theodolite
integrated measurement technology were applied. The fusion of laser tracker and
theodolite coordinate system was implemented by common point transformation,
which was applied in normal direction measurement of RVS antenna end surface
by laser tracker in the lunar lander coordinate system. At the same time, scanning
measurement technology with laser radar and theodolite based on generalized USMN
adjustment were applied in 3-D shape measurement of the interface ring in the lunar
lander coordinate system to verify the stability of the interface ring under load. In
the system leak test, the automated leak test technology and the flexible helium
hood technology for quick leak positioning were applied. By application of highly
accurate automatic leak test technology, automatic gas fill and vent, automatic leakage
rate test, automatic comparison measurement with standard container and automatic
sampling were implemented, which improved the efficiency and reliability of pipeline
sealing performance test. At the same time, the quick leak positioning technology
by flexible helium hood was applied to improve the accuracy of total leak test and
the efficiency of quick leak positioning in complex conditions were realized, which
gave a solution to the issue of leak positioning in complex system which could not
apply bubble method. In the mass property test, technologies were applied including
mass property test based on multiple DOF transformation, test data correction for