Autonomous Recommendation of Fault Detection Algorithms for Spacecraft

Dear Editor, This letter deals with the problem of algorithm recommendation for online fault detection of spacecraft. By transforming the time series data into distributions and introducing a distribution-aware measure, a principal method is designed for quantifying the detectabilities of fault detection algorithms over special datasets.

Robust fault detection filter and its application in MEMS-based INS/GPS

Since any disturbance and fault may lead to significant performance degradation in practical dynamical systems,it is essential for a system to be robust to disturbances but sensitive to faults.For this purpose,this paper proposes a robust fault-detection filter for linear discrete time-varying systems.The algorithm uses H∞ estimator to minimize the worst possible amplification from disturbances to estimate errors,and H_ index to maximize the minimum effect of faults on the residual output of the filter.This approach is applied to the MEMS-based INS/GPS.And simulation results show that the new algorithm can reduce the effect of unknown disturbances and has a high sensitivity to faults.

An all-coefficient adaptive control method for a class of nonlinear time-varying systems

In this paper, the extension of the all-coefficient adaptive control method to nonlinear time-varying systems is studied. A novel discretizing method is first proposed to derive the discrete-time model for a class of nonlinear time-varying systems. The characteristics of the coefficients of the discrete-time model are derived by this method, based on which the all-coefficient adaptive control method is given for the class of nonlinear time-varying systems. Sufficient conditions on the closed-loop stability are given. Simulations show the purposed adaptive control method can achieve satisfying performance. Finally further discussion on applying low-order all-coefficient adaptive control method to high order nonlinear time-varying system is given.

Control capability analysis for complex spacecraft thruster configurations

The set of forces and moments that can be generated by thrusters of a spacecraft is called the"control capability"with respect to the thruster configuration.If the control capability of a thruster configuration is adequate to fulfill a given space mission,we say this configuration is a feasible one with respect to the task.This study proposed a new way to analyze the control capability of the complex thruster configuration.Precise mathematical definitions of feasibility were proposed,based on which a criterion to judge the feasibility of the thruster configuration was presented through calculating the shortest distance to the boundary of the controllable region as a function of the thruster configuration.Finally,control capability analysis for the complex thruster configuration based on its feasibility with respect to the space mission was given followed by a 2-D thruster configuration example to demonstrate its validity.

End-to-end Mars entry,descent,and landing modeling and simulations for Tianwen-1 guidance,navigation,and control system

On May 15,2021,the Tianwen-1 lander successfully touched down on the surface of Mars.To ensure the success of the landing mission,an end-to-end Mars entry,descent,and landing(EDL)simulator is developed to assess the guidance,navigation,and control(GNC)system performance,and determine the critical operation and lander parameters.The high-fidelity models of the Mars atmosphere,parachute,and lander system that are incorporated into the simulator are described.Using the developed simulator,simulations of the Tianwen-1 lander EDL are performed.The results indicate that the simulator is valid,and the GNC system of the Tianwen-1 lander exhibits excellent performance.

Powered-descent landing GNC system design and flight results for Tianwen-1 mission

The powered-descent landing(PDL)phase of the Tianwen-1 mission began with composite backshell–parachute(CBP)separation and ended with landing-rover touchdown.The main tasks of this phase were to reduce the velocity of the lander,perform the avoidance maneuver,and guarantee a soft touchdown.The PDL phase overcame many challenges:performing the divert maneuver to avoid collision with the CBP while simultaneously avoiding large-scale hazards;slowing the descent from approximately 95 to 0 m/s;performing the precise hazard-avoidance maneuver;and placing the lander gently and safely on the surface of Mars.The architecture and algorithms of the guidance,navigation,and control system for the PDL phase were designed;its execution resulted in Tianwen-1’s successful touchdown in the morning of 15 May 2021.Consequently,the Tianwen-1 mission achieved a historic autonomous landing with simultaneous hazard and CBP avoidance.

Entry vehicle control system design for the Tianwen-1 mission

The entry vehicle for the Tianwen-1 mission successfully landed on the surface of Mars at 7:18 AM BJT on May 15,2021.This successful landing made China the first country to orbit,land,and release a rover in their first attempt at the Mars exploration.The guidance,navigation,and control(GNC)system plays a crucial role in the entry,descent,and landing(EDL)phases.This study focused on the attitude control component of the GNC system design.The EDL phase can be divided into several sub-phases,namely the angle of attack control phase,lift control phase,parachute descent phase,and powered descent phase.Each sub-phase has unique attitude control requirements and challenges.This paper introduces the key aspects of designing attitude controllers for each phase.Furthermore,flight results are presented and analyzed.

Multiple Fading Factors Kalman Filter for SINS Static Alignment Application

To solve the problem that the standard Kalman filter cannot give the optimal solution when the system model and stochastic information are unknown accurately, single fading factor Kalman filter is suitable for simple systems. But for complex systems with multi-variable, it may not be sufficient to use single fading factor as a multiplier for the covariance matrices. In this paper, a new multiple fading factors Kalman filtering algorithm is presented. By calculating the unbiased estimate of the innovation sequence covariance using fenestration, the fading factor matrix is obtained. Adjusting the covariance matrix of prediction error Pk｜k-1 using fading factor matrix, the algorithm provides different rates of fading for different filter channels. The proposed algorithm is applied to strapdown inertial navigation system （SINS） initial alignment, and simulation and experimental results demonstrate that, the alignment accuracy can be upgraded dramatically when the actual system noise characteristics are different from the pre-set values. The new algorithm is less sensitive to uncertainty noise and has better estimation effect of the parameters. Therefore, it is of significant value in practical applications.

Adaptive entry guidance for the Tianwen-1 mission

To meet the requirements of the Tianwen-1 mission,adaptive entry guidance for entry vehicles,with low lift-to-drag ratios,limited control authority,and large initial state bias,was presented.Typically,the entry guidance law is divided into four distinct phases:trim angle-of-attack phase,range control phase,heading alignment phase,and trim-wing deployment phase.In the range control phase,the predictor–corrector guidance algorithm is improved by planning an on-board trajectory based on the Mars Science Laboratory(MSL)entry guidance algorithm.The nominal trajectory was designed and described using a combination of the downrange value and other states,such as drag acceleration and altitude rate.For a large initial state bias,the nominal downrange value was modified onboard by weighing the landing accuracy,control authority,and parachute deployment altitude.The biggest advantage of this approach is that it allows the successful correction of altitude errors and the avoidance of control saturation.An overview of the optimal trajectory design process,including a discussion of the design of the initial flight path angle,relevant event trigger,and transition conditions between the four phases,was also presented.Finally,telemetry data analysis and post-flight assessment results were used to illustrate the adaptive guidance law,create good conditions for subsequent parachute reduction and power reduction processes,and gauge the success of the mission.