7.2 Development of GNC Technology
227
astronauts after finding obstacles before landing. Lunar soft-landing mission in the
twenty-first century, such as SELENE-2 mission of Japan, is not only equipped
with advanced microwave range and velocity sensors to improve range and velocity
accuracies, but also equipped with a Laser Scanning Sensor and optical sensors
specifically for lunar surface recognition to improve landing safety, and also Camera
System for navigation, and etc.
For landing guidance, the gravity-turn guidance law was applied in the Surveyor
missions, while the nominal trajectory guidance law was applied in the Luna missions
and the fourth-order polynomial guidance law was adopted in the Apollo missions.
In strategic plan of CLEP, there were three phases including orbiting, landing,
and sample return, which would be implemented step by step. In 2007 and 2010,
the Chang’E-1 and the Chang’E-2 probes achieved the target of the “orbiting” phase
and verified the guidance navigation and control technology in LTO and circumlunar
orbit. The Chang’E-3 the lunar lander achieved the target of the “landing” phase and
verified the guidance navigation and control technology of lunar soft-landing [4].
7.3 Analysis of Technical Characteristics
During lunar soft-landing, the task and work conditions of the lunar lander GNC
subsystem were very different from those of satellites and spacecraft developed in
the past. The duration of lunar soft-landing process was short (about 10 min). At the
same time, the Moon was a non-cooperative target. Therefore, it was necessary to
design a highly autonomous and real-time GNC system. The soft-landing process was
achieved by active deceleration and the propellant consumption was large (about 2/3
of the lunar lander mass at beginning of powered descent phase). The optimization
of the propellant consumption was necessary when the guidance law was designed.
The high safety should be ensured for soft-landing mission, which needed rigorous
requirements for navigation, hazard detection, and obstacle avoidance guidance for
the landing process. High-precision tracking of the guided target attitude should be
achieved, while the engine disturbance torque should be compensated at the same
time in attitude control. In addition, the effect of lunar surface dust and the engine
plume on performance of the sensors and the system during the landing process
should be considered [5].
227
astronauts after finding obstacles before landing. Lunar soft-landing mission in the
twenty-first century, such as SELENE-2 mission of Japan, is not only equipped
with advanced microwave range and velocity sensors to improve range and velocity
accuracies, but also equipped with a Laser Scanning Sensor and optical sensors
specifically for lunar surface recognition to improve landing safety, and also Camera
System for navigation, and etc.
For landing guidance, the gravity-turn guidance law was applied in the Surveyor
missions, while the nominal trajectory guidance law was applied in the Luna missions
and the fourth-order polynomial guidance law was adopted in the Apollo missions.
In strategic plan of CLEP, there were three phases including orbiting, landing,
and sample return, which would be implemented step by step. In 2007 and 2010,
the Chang’E-1 and the Chang’E-2 probes achieved the target of the “orbiting” phase
and verified the guidance navigation and control technology in LTO and circumlunar
orbit. The Chang’E-3 the lunar lander achieved the target of the “landing” phase and
verified the guidance navigation and control technology of lunar soft-landing [4].
7.3 Analysis of Technical Characteristics
During lunar soft-landing, the task and work conditions of the lunar lander GNC
subsystem were very different from those of satellites and spacecraft developed in
the past. The duration of lunar soft-landing process was short (about 10 min). At the
same time, the Moon was a non-cooperative target. Therefore, it was necessary to
design a highly autonomous and real-time GNC system. The soft-landing process was
achieved by active deceleration and the propellant consumption was large (about 2/3
of the lunar lander mass at beginning of powered descent phase). The optimization
of the propellant consumption was necessary when the guidance law was designed.
The high safety should be ensured for soft-landing mission, which needed rigorous
requirements for navigation, hazard detection, and obstacle avoidance guidance for
the landing process. High-precision tracking of the guided target attitude should be
achieved, while the engine disturbance torque should be compensated at the same
time in attitude control. In addition, the effect of lunar surface dust and the engine
plume on performance of the sensors and the system during the landing process
should be considered [5].