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13 Metrology Technology of Lunar Lander
metrology methodology and practical application in system integration of the lunar
lander are described.
13.2 Development Status of Metrology Technology
Along with development of aerospace technology, new metrology-based technologies and instruments for advanced manufacture and test had been emerged. In global
aerospace manufacture industry, there were geometry metrology technologies in
assembly including theodolite metrology, laser tracker metrology and laser radar
metrology, and etc. The theodolite metrology had been widely applied in spacecraft
assembly process all over the world. In order to determine the relative alignment
between spacecraft components, a measurement network of theodolites was usually
built up. Because the operator was necessary to observe the target in measurement
process, the accuracy was affected by environment and personal skill. Generally, the
positioning accuracy could be as less than 0.2 mm and the angle accuracy could be
a dozen of arc-seconds. The accuracy of laser tracker metrology could be within
10 ppm, which had been applied in Boeing and NASA. But it could only be applied
to measure point. It cannot be applied to measure a normal direction of small mirror
surface. Laser radar metrology was a three-dimensional metrology to scan object
surface. Now many companies such as Metric Vision, Cyra in USA and Mensi in
France had introduced different types of laser scanner systems, in which the largest
measuring range was 60 m and the minimums distance was 2 m and the highest
accuracy could be as higher as 0.05 mm, which could be applied to measure the
surface of structural component [2].
Up to date, there were two measures to test seal performance of spacecraft, nonvacuum accumulation leak test technology and vacuum leak test technology. The
features of non-vacuum accumulation leak test technology were low cost, no requirement for large vacuum vessel and vacuum system, but low sensitivity. The features
of vacuum leak test technology were relatively high sensitivity and expensive. The
non-vacuum accumulation leak test method by helium Mass Spectrometer had been
widely applied in powered descent of the United States, ESA, France and Italy. For
the British SB4000 satellite platform, accumulation leak test method was defined for
system leakage rate in its leak test requirement. The test accuracy was about 50%.
Such method was also applied for some satellite in France about 50% test accuracy.
In aerospace industry, three-point weighing method with centroid bed was applied
for measurement of mass and center of gravity. The torsion pendulum method with
torsion pendulum bed was applied for measurement of inertia. Along with continuous
development of metrology technology, the traditional methods and equipment had
gradually become inadequate in terms of efficiency and accuracy. The integrated test
system was developed for measurement of mass, center of gravity and inertia, which
had been applied in NASA, ESA and JAXA [3].
13 Metrology Technology of Lunar Lander
metrology methodology and practical application in system integration of the lunar
lander are described.
13.2 Development Status of Metrology Technology
Along with development of aerospace technology, new metrology-based technologies and instruments for advanced manufacture and test had been emerged. In global
aerospace manufacture industry, there were geometry metrology technologies in
assembly including theodolite metrology, laser tracker metrology and laser radar
metrology, and etc. The theodolite metrology had been widely applied in spacecraft
assembly process all over the world. In order to determine the relative alignment
between spacecraft components, a measurement network of theodolites was usually
built up. Because the operator was necessary to observe the target in measurement
process, the accuracy was affected by environment and personal skill. Generally, the
positioning accuracy could be as less than 0.2 mm and the angle accuracy could be
a dozen of arc-seconds. The accuracy of laser tracker metrology could be within
10 ppm, which had been applied in Boeing and NASA. But it could only be applied
to measure point. It cannot be applied to measure a normal direction of small mirror
surface. Laser radar metrology was a three-dimensional metrology to scan object
surface. Now many companies such as Metric Vision, Cyra in USA and Mensi in
France had introduced different types of laser scanner systems, in which the largest
measuring range was 60 m and the minimums distance was 2 m and the highest
accuracy could be as higher as 0.05 mm, which could be applied to measure the
surface of structural component [2].
Up to date, there were two measures to test seal performance of spacecraft, nonvacuum accumulation leak test technology and vacuum leak test technology. The
features of non-vacuum accumulation leak test technology were low cost, no requirement for large vacuum vessel and vacuum system, but low sensitivity. The features
of vacuum leak test technology were relatively high sensitivity and expensive. The
non-vacuum accumulation leak test method by helium Mass Spectrometer had been
widely applied in powered descent of the United States, ESA, France and Italy. For
the British SB4000 satellite platform, accumulation leak test method was defined for
system leakage rate in its leak test requirement. The test accuracy was about 50%.
Such method was also applied for some satellite in France about 50% test accuracy.
In aerospace industry, three-point weighing method with centroid bed was applied
for measurement of mass and center of gravity. The torsion pendulum method with
torsion pendulum bed was applied for measurement of inertia. Along with continuous
development of metrology technology, the traditional methods and equipment had
gradually become inadequate in terms of efficiency and accuracy. The integrated test
system was developed for measurement of mass, center of gravity and inertia, which
had been applied in NASA, ESA and JAXA [3].