450
13 Metrology Technology of Lunar Lander
temperature, the container should be able to adapt to the pressure difference between
the internal and external of the container, which was −2–5 kPa. The inside of the
reference container should be clean and smooth, and there should not be material
which could adsorb helium.
The automatic sampling and calibration system was applied to implement the
calibration of the leak test system. Generally, the standard leak hole is applied for
sampling calibration of the leak test system. When the standard leak hole was applied,
the sampling status should be exactly same as the measuring status. However, because
of the long sampling period and the uncertainty of the standard leak hole itself
(The uncertainty of constant pressure method was still 5%. Because of the lack of
constant pressure method, the uncertainty was usually about 18% in China), the
uncertainty of test result was big. In the leak test of the Chang’E-3 lunar lander,
the standard gas volume was used, whose uncertainty was less than 1%. When the
standard gas volume was measured, the helium was slowly filled into the collecting
chamber, while the helium was instantaneously filled into the collecting container
when the sample was used. Because of the difference between the measurement
statuses, the adsorption of helium on the surface material of collection chamber
and the lunar lander was different, which would theoretically cause error in leak
test result. The relevant analysis and experimental results showed that adsorption of
helium on the surface material of collecting chamber and the lunar lander would not
affect the leak test result. A new automatic sampling system was developed for the
Chang’E-3 lunar lander. The sampling process of conventional mode depended on
experience of operator, equipment, environment and tool preparation, which could
possibly lead to failure of sampling. Compared with sampling system in traditional
mode, the technical process of newly developed calibration system for sampling was
greatly simplified, the accuracy of sampling was raised to 0.5% FS of the regulation
pressure, the sampling time was shortened to 5 min, and the efficiency of sampling
was increased by more than 2 times. Meanwhile, the requirements for environment
and personnel operation experience were reduced. The automatic control could be
implemented by program. In the technical process of total leak test for the lunar
lander container, which was based on operation mode of automatic sampling control
system, there were equipment and tool preparation, logon and system parameter
setup, automatic program control sampling, leakage rate test and vent.
3. Analysis of Accuracy
The application of automated leak test technology of propulsion subsystem greatly
improved the automation level of leak test for the Chang’E-3 lunar lander, so as to
improve the sensitivity, accuracy, safety and reliability of leak test.
In the implementation of automated leak test, the uncertainty of the leak test
system was evaluated [12]. Through analysis, the factors on the uncertainty of nonvacuum accumulation leak test method by helium Mass Spectrometer are shown in
Fig. 13.13.
After analysis and experiment of all factors, the uncertainty of general spacecraft
leakage caused by system effect and random effect was analyzed. The uncertainty
of synthetic standard of the leak test system was determined (Seen in Table 13.1).
13 Metrology Technology of Lunar Lander
temperature, the container should be able to adapt to the pressure difference between
the internal and external of the container, which was −2–5 kPa. The inside of the
reference container should be clean and smooth, and there should not be material
which could adsorb helium.
The automatic sampling and calibration system was applied to implement the
calibration of the leak test system. Generally, the standard leak hole is applied for
sampling calibration of the leak test system. When the standard leak hole was applied,
the sampling status should be exactly same as the measuring status. However, because
of the long sampling period and the uncertainty of the standard leak hole itself
(The uncertainty of constant pressure method was still 5%. Because of the lack of
constant pressure method, the uncertainty was usually about 18% in China), the
uncertainty of test result was big. In the leak test of the Chang’E-3 lunar lander,
the standard gas volume was used, whose uncertainty was less than 1%. When the
standard gas volume was measured, the helium was slowly filled into the collecting
chamber, while the helium was instantaneously filled into the collecting container
when the sample was used. Because of the difference between the measurement
statuses, the adsorption of helium on the surface material of collection chamber
and the lunar lander was different, which would theoretically cause error in leak
test result. The relevant analysis and experimental results showed that adsorption of
helium on the surface material of collecting chamber and the lunar lander would not
affect the leak test result. A new automatic sampling system was developed for the
Chang’E-3 lunar lander. The sampling process of conventional mode depended on
experience of operator, equipment, environment and tool preparation, which could
possibly lead to failure of sampling. Compared with sampling system in traditional
mode, the technical process of newly developed calibration system for sampling was
greatly simplified, the accuracy of sampling was raised to 0.5% FS of the regulation
pressure, the sampling time was shortened to 5 min, and the efficiency of sampling
was increased by more than 2 times. Meanwhile, the requirements for environment
and personnel operation experience were reduced. The automatic control could be
implemented by program. In the technical process of total leak test for the lunar
lander container, which was based on operation mode of automatic sampling control
system, there were equipment and tool preparation, logon and system parameter
setup, automatic program control sampling, leakage rate test and vent.
3. Analysis of Accuracy
The application of automated leak test technology of propulsion subsystem greatly
improved the automation level of leak test for the Chang’E-3 lunar lander, so as to
improve the sensitivity, accuracy, safety and reliability of leak test.
In the implementation of automated leak test, the uncertainty of the leak test
system was evaluated [12]. Through analysis, the factors on the uncertainty of nonvacuum accumulation leak test method by helium Mass Spectrometer are shown in
Fig. 13.13.
After analysis and experiment of all factors, the uncertainty of general spacecraft
leakage caused by system effect and random effect was analyzed. The uncertainty
of synthetic standard of the leak test system was determined (Seen in Table 13.1).