New celestial assisted INS initial alignment method for lunar explorer

In the future lunar exploration programs of China, soft landing, sampling and returning will be realized. For lunar explorers such as Rovers, Landers and Ascenders, the inertial navigation system （INS） will be used to obtain high-precision navigation information. INS propagates position, velocity and attitude by integration of sensed accelerations, so initial alignment is needed before INS can work properly. However, traditional ground-based initial alignment methods cannot work well on the lunar surface because of its low rotation rate （0.55°/h）. For solving this problem, a new autonomous INS initial alignment method assisted by celestial observations is proposed, which uses star observations to help INS estimate its attitude, gyroscopes drifts and accelerometer biases. Simulations show that this new method can not only speed up alignment, but also improve the alignment accuracy. Furthermore, the impact factors such as initial conditions, accuracy of INS sensors, and accuracy of star sensor on alignment accuracy are analyzed in details, which provide guidance for the engineering applications of this method. This method could be a promising and attractive solution for lunar explorer＇s initial alignment.

基于TOA和TDTOA的增广状态脉冲星组合导航误差抑制方法

脉冲星导航是一种极具潜力的深空自主导航技术,通常采用脉冲到达时间(time of arrival,TOA)作为量测信息.但脉冲星星历误差和星载原子钟误差等系统误差对导航性能有显著影响.为了解决上述问题,提出了一种基于TOA和时间差分TOA(TDTOA)的增广状态脉冲星组合导航误差抑制方法,通过将每个脉冲星的星历误差和时钟误差增加到状态向量,并利用TOA和TDTOA量测值对其进行估计和校正.仿真结果表明,该方法提高了脉冲星星历误差和时钟误差的可观测性,有效地消除了这些系统误差的影响,导航精度相比传统脉冲星导航提高了29%.

Modeling and analysis of solar Doppler difference bias with arbitrary rotation axis

The solar rotation causes the solar Doppler difference bias,which leads to the decline of the velocity measurement accuracy.Modeling and compensation are an effective solution.The limited model with specific geometric direction,where the solar rotation axis is perpendicular to the plane through the Sun,the Earth and Mars,was established.However,in fact,the geometric relationship among the Sun,Mars and the spacecraft is not fully in line with the hypothesis of the model due to the spacecraft orbital angle and the solar rotation axis drift.Thus,this model is not consistent with the fact.In order to solve this problem,a universal solar Doppler difference bias model,which provides the expression with arbitrary rotation axis,is established in this paper.In this method,for any point at the solar surface,four variables including the direction of the solar rotation linear velocity at this point,the distance from this point to the rotation axis,the vector from this point to Mars,and the vector from this point to the spacecraft are calculated.Based on these four variables,the solar Doppler difference bias corresponding to this point is obtained.The theoretical analysis and simulation results demonstrate that the solar Doppler difference bias model with the actual rotation axis is different from that with one of the specific rotation axes.Therefore,it is indispensable to build the proposed model for compensation.Besides,the direction of the solar rotation axis,the spacecraft-Mars-Sun angle and the spacecraft-to-Mars distance are important impact factors for the proposed model.

Accelerometer Bias and Star Sensor Installation Error Joint Calibration for the SINS/CNS Integrated Navigation System Using Attitude Maneuver

The integrated strap-down inertial nav igation system/olelestial navigation system(SINS/CNS)i an important autonomous navigation method with efective concealment and high predision.Both accelerometer biss and star ensor installation error ame important factors that aflect the performanoe of this mavigation system,which needl to be calibratexd and compensatedl.A new acelerometer bias and star sensor installation error joint calibration method for the SINS/CNS integrated navigation system i propoeed.In this newly propoeed method,the installation error of star sensor is augmented to the state vector,and the star vector,nadir angle,horkzontal poeition error and velbcity error ame ueed a8 measurementa to calbrate the two errors mentioned above.Simulations show that both accelerometer bias and star sensor installation enror an be calibratedl efectively.