A Study On Measurement-updated IMU Based Autonomous Navigation For Lunar Soft Landing
- Paper number
IAC-07-C1.I.11
- Author
Dr. Dayi Wang, Beijing Institute of Control Engineering, China
- Coauthor
Dr. Xiangyu Huang, Beijing Institute of Control Engineering, China
- Coauthor
Dr. yifeng Guan, Beijing Institute of Control Engineering, China
- Year
2007
- Abstract
A lunar landing spacecraft plans to be sent into an earth-moon transfer orbit to perform lunar soft landing mission and shall be carried on a LM-x platform. After several complicated orbit maneuvers, the spacecraft will arrive in lunar circular orbit. Once the landing area has been selected and it is time to de-orbit for landing, a ΔV burn is performed to establish an elliptical orbit. At perilune, the landing jets are ignited, and a propulsive landing is performed to make the horizontal velocity relative to the lunar surface nearly zero. Then a vertical landing is taken by control of thrusters at the final phase. In order to send as many scientific payloads as possible to a specified zone on the lunar surface safely and accurately, Guidance, navigation and control (GNC) is the key technique for achieving lunar soft landing. The baseline is a 3-axis stabilized system during all the phases of the mission. Attitude control is performed by bi-propellant thrusters. Orbit maneuver is achieved by assembled constant thrust engines or a throttleable thrust engine. The orbit determination for Earth-Moon transfer and lunar circular orbit phases is performed by ground deep space networks. Orbit determination and lunar surface terrain identification during landing phase are performed by IMU (Inertial Measurement Unit), altimeter, velometer and lunar surface imaging sensor. In order to meet the requirements of high-accuracy orbit determination and prediction to achieve safe and accurate lunar soft landing, this paper presents an autonomous navigation method based on velocity & distance measurement updated IMU. To continuously measure thrust acceleration and attitude angular velocity during the key propulsive descent phase of lunar soft landing, IMU is the critical navigation sensor applied for lunar soft landing. Since the accumulation of initial navigation error and IMU measurement error will cause the gradual increase in navigation error, external measurement information must be used to correct the navigation results of IMU to ensure accuracy. In order to remove the initial navigation error and IMU measurement error, the IMU navigation method making use of velocity & distance measurement update is proposed. First, the state and observation equations are linearized by making use of the reference trajectory provided by inertial navigation. Then, according to the linearization models and the property of observation variables, the observability of velocity or distance measurement updated IMU navigation system is analyzed. Finally, the analysis conclusions on the feasibility and observability of autonomous navigation are validated by carrying out mathematical simulation.
- Abstract document