15.7 Test of Engine Thrust Pulsation Effect on GNC Sensors
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a spring-mass oscillator model with a certain natural frequency. The key of gravity
compensation by spring in pulsation tests was that the spring should meet the load
capacity and have a low enough natural frequency.
The gravity compensation subsystem of near zero stiffness spring was applied to
simulate the free boundary conditions of the lunar lander when it was excited by
pulsation thrust on orbit. As long as the support stiffness was low enough, the natural
oscillation caused by elastic recovery in the test had negligible influence on the test
system.
3. Pulsation Thrust Exciter and Input Control System
In the test of dynamic response of pulsation excitation to the lunar lander and the
test of transfer path, it was necessary to use the pulsation source of the lunar lander
as the excitation source. However, in order to determine the response and transfer
characteristics of the lunar lander structure, it was inconvenient to install the pulsation
excitation source on the structure and simulate by firing of engine. It was necessary
to use external excitation to simulate the pulsation excitation. In the ground test, the
exciter was a good choice. The amplitude and frequency range of the pulsation load
should be considered when the exciter was selected.
4. Measurement Subsystem
The measurement subsystem was composed of acceleration measurement system,
angle measurement system and GNC sensors ground test system. The acceleration
measurement system and the angle measurement system were applied to measure the
acceleration response and angle response at the installation interface of the sensor and
critical position of the lunar lander. Because the pulsation load was in small amplitude
and wide frequency range, generally sensors with low-range, high-sensitivity and
wide frequency bandwidth were preferred. In the test, the interested GNC landing
navigation sensors should be powered on and its performance should be monitored,
so as to analyze the influence of pulsation load.
15.7.4 Test Example
During development of the Chang’E-3 lunar lander, the test system for 7500 N engine
thrust pulsation effect on GNC sensors were designed and developed. The pulsation
thrust test was conducted, as shown in Fig. 15.16.
509
a spring-mass oscillator model with a certain natural frequency. The key of gravity
compensation by spring in pulsation tests was that the spring should meet the load
capacity and have a low enough natural frequency.
The gravity compensation subsystem of near zero stiffness spring was applied to
simulate the free boundary conditions of the lunar lander when it was excited by
pulsation thrust on orbit. As long as the support stiffness was low enough, the natural
oscillation caused by elastic recovery in the test had negligible influence on the test
system.
3. Pulsation Thrust Exciter and Input Control System
In the test of dynamic response of pulsation excitation to the lunar lander and the
test of transfer path, it was necessary to use the pulsation source of the lunar lander
as the excitation source. However, in order to determine the response and transfer
characteristics of the lunar lander structure, it was inconvenient to install the pulsation
excitation source on the structure and simulate by firing of engine. It was necessary
to use external excitation to simulate the pulsation excitation. In the ground test, the
exciter was a good choice. The amplitude and frequency range of the pulsation load
should be considered when the exciter was selected.
4. Measurement Subsystem
The measurement subsystem was composed of acceleration measurement system,
angle measurement system and GNC sensors ground test system. The acceleration
measurement system and the angle measurement system were applied to measure the
acceleration response and angle response at the installation interface of the sensor and
critical position of the lunar lander. Because the pulsation load was in small amplitude
and wide frequency range, generally sensors with low-range, high-sensitivity and
wide frequency bandwidth were preferred. In the test, the interested GNC landing
navigation sensors should be powered on and its performance should be monitored,
so as to analyze the influence of pulsation load.
15.7.4 Test Example
During development of the Chang’E-3 lunar lander, the test system for 7500 N engine
thrust pulsation effect on GNC sensors were designed and developed. The pulsation
thrust test was conducted, as shown in Fig. 15.16.