13.4 Application of Special Measurement Technology
457
a small percent of total accuracy; the other one was the positioning accuracy of the
lunar lander on the test bed. Because the lunar lander was docked with the test bed at
first, the lunar lander to be tested was changed to a complex of the lunar lander and the
docking bracket, which was 1700 mm in height. As analysis of three-coordinate test
principle, mechanical structural parameters of the docking bracket, such as flatness,
parallelism and coaxiality could directly affect the mass center test accuracy.
2. Technical Design and Principle
There was no direct solution for positioning of the lunar lander on the mass center
bad. It could only be achieved by correction of test data. The principle of such method
was to establish the transformation matrix of the measurement coordinate system of
mass center bed through reference transfer technology of accuracy test, and then test
the mass center of the lunar lander in test bed coordinate system during propellant
filling in real time, so as to calculate the mass center in real time by transfer matrix.
The process is as follows.
(1) Before the lunar lander was docked with the mass center bed, a transitional
cubic prism was fixed in the appropriate location in facility. The theodolite
was applied to establish the angle and position relationship between transitional cubic prism and the coordinate system of the mass center bed. During
measurement, the position of the transitional cubic prism should be stable.
(2) After the lunar lander was docked with the mass center bed, the angle and
position relationship between the mechanical coordinate system of the lunar
lander and the transitional cube prism was precisely measured. The relationship between the mechanical coordinate system of the lunar lander and the
coordinate system of the mass center bed was calculated, including the angles
between the coordinate axis of the lunar lander coordinate system and the
coordinate axis, as well as the coordinates of the origin of the lunar lander
coordinate system in the mass center bed coordinate system. The results of
accuracy measurement are listed in Table 13.4.
If the coordinates of the lunar lander mass center in the coordinate system of mass
test bed was (X 1
, Y 1
, Z 1
) and the coordinates in the lunar lander coordinate system
is (X 1 , Y 1 , Z 1 ), then
Table 13.4 Accuracy test results
Test reference
Test item and status
Coordinate system of mass
center bed
X
Y
Z
Mechanical coordinate system of the
lunar lander
X
0.0499° 89.961° 89.9689°
Y
90.0388° 0.1845° 90.1804°
Z
90.0289° 89.8414° 0.1612°
Coordinates of center X 1
Y 1
Z 1
457
a small percent of total accuracy; the other one was the positioning accuracy of the
lunar lander on the test bed. Because the lunar lander was docked with the test bed at
first, the lunar lander to be tested was changed to a complex of the lunar lander and the
docking bracket, which was 1700 mm in height. As analysis of three-coordinate test
principle, mechanical structural parameters of the docking bracket, such as flatness,
parallelism and coaxiality could directly affect the mass center test accuracy.
2. Technical Design and Principle
There was no direct solution for positioning of the lunar lander on the mass center
bad. It could only be achieved by correction of test data. The principle of such method
was to establish the transformation matrix of the measurement coordinate system of
mass center bed through reference transfer technology of accuracy test, and then test
the mass center of the lunar lander in test bed coordinate system during propellant
filling in real time, so as to calculate the mass center in real time by transfer matrix.
The process is as follows.
(1) Before the lunar lander was docked with the mass center bed, a transitional
cubic prism was fixed in the appropriate location in facility. The theodolite
was applied to establish the angle and position relationship between transitional cubic prism and the coordinate system of the mass center bed. During
measurement, the position of the transitional cubic prism should be stable.
(2) After the lunar lander was docked with the mass center bed, the angle and
position relationship between the mechanical coordinate system of the lunar
lander and the transitional cube prism was precisely measured. The relationship between the mechanical coordinate system of the lunar lander and the
coordinate system of the mass center bed was calculated, including the angles
between the coordinate axis of the lunar lander coordinate system and the
coordinate axis, as well as the coordinates of the origin of the lunar lander
coordinate system in the mass center bed coordinate system. The results of
accuracy measurement are listed in Table 13.4.
If the coordinates of the lunar lander mass center in the coordinate system of mass
test bed was (X 1
, Y 1
, Z 1
) and the coordinates in the lunar lander coordinate system
is (X 1 , Y 1 , Z 1 ), then
Table 13.4 Accuracy test results
Test reference
Test item and status
Coordinate system of mass
center bed
X
Y
Z
Mechanical coordinate system of the
lunar lander
X
0.0499° 89.961° 89.9689°
Y
90.0388° 0.1845° 90.1804°
Z
90.0289° 89.8414° 0.1612°
Coordinates of center X 1
Y 1
Z 1