Research On Autonomous Navigation Method For Automated Transfer Vehicle

The purpose of this research is to investigate proper navigation methods for different missions of Automated Transfer Vehicle(ATV).Autonomous navigation method is presented to meet the navigation precision of low earth orbit ATV. Coupled GNSS/SINS navigation systems are hired to compensate the lack of one single system. In a tightly coupled system, GNSS pseudorange and deltarange measurements are processed by the data fusion algorithm to calibrate the IMU, which allows for a limited aiming of the SINS in situations with less than four satellites in view, where the GNSS receiver cannot provide postion and velocity information anymore in a loosely coupled system. The system dynamic model and GNSS mesasurement models are discussed which are the key to the development of GNSS/SINS data fusion algorithms. To improve the navigation precision, the guidance instrumentation error coefficients are modeled as augmented states and the leverarm effect is also considered. SINS errors are modeled as Markov processes to reduce the order of the system. Simulation results indicate that two different coupled systems have similar results in accuracy and the Markov process model can spend less time to accomplish the filter and achieve the similar navigation precision.For high orbit ATV, the usable conditions of GNSS are analyzed by estimating the carrier to noise spectral density which includes the received power plus constant assumptions regarding the noise figure of the receiver and antennas, the system noise tempreture, and the implementation losses in the receiver. A star sensor is utilized to correct the ATV attitude when a ATV moving occurs. Strong tracking EKF and UKF are derived to avoid the steady bias in identifying the parameter bias fault of nonlinear system and restrain the influence of modeling errors. Quaternion and Rodrigues parameters are expressed to describe ATV attitudes. Simulation results show that even GNSS satellite visibility is not good, it is feasible to use GNSS for ATV navigaton.Differential GNSS methods are developed when ATV approaches a cooperative target. Raw GNSS data are first processed through time synchronizing and cycle detection. Coordinate diffential navigation is used during the far-distance rendezvous mission planning. In the course of automatic homing, the method of double-differential carrier phase smoothing is applied. When the two spacecrafts are close, the float solustion is very efficient. A method is presented to resolve the integer ambiguity when using single frequency receiver. Firstly, the differential technique for carrier phase smoothing pseudorange is used in relative positioning to estimate the floate numbers of integer ambiguities. Secondly, the LAMBDA searching method is utilized to achieve the solution of integer ambiguity. After the integer ambiguity acquision, the integer solution can have a very high precision.Time differenced carrier phase(TDCP) measurements without the need of ambiguity resolution techniques are developed to acquire high precision of ATV. Absolute dynamic functions and relative dynamic functions are built to compare the navigation results using two different navigation algorithms. Simulation results indicate that TDCP method can obtain centimeter precision and absolute navigation algorithm is better than C-W algorithm.