Yidi Wang

X-Ray Pulsar Profile Recovery Based on Tracking-Differentiator

The profile recovery is an important work in X-ray pulsar-based navigation. It is a key step for the analysis on the pulsar signal’s characteristic and the computing of time of arrival (TOA). This paper makes an argument for an algorithm based on the tracking-differentiator (TD) to recover the profile from the low Signal-to-Noise Ratio (SNR) signals. In the method, a TD filter with cascade structure is designed which has very low phase delay and amplitude distortion. In the simulation experiment, two typical pulsars (PSR B0531

Analysis on time of arrival precision in X-ray pulsar-based navigation

X-ray pulsar-based navigation method is a promising autonomous navigation method. The research has been done for nearly 30 years. Several key techniques about this method are the research hotspots now. One of the key techniques is estimation of the time of arrival (TOA) in pulsars signal processing. The precision of the TOA would affect the precision of X-ray pulsar-based navigation. Using Monte Carlo method, we analyze the impact of the precision of TOA by some parameters. The Results show that the earth ephemerid errors would affect the precision of TOA in the single estimation. About the pulsars characteristic parameters, pulsar position and its rotation period are the main factors that affect the precision of TOA. In order to keep the precision, the time delay of the detector should be calibrated and the background noise should be restrained. Results of the paper could make contribution to the precision analysis of the X-ray pulsar-based navigation.

Spacecraft autonomous navigation via inter-spacecraft relaying communication for Mars prober

With the development of deep space exploration, the requirements of accuracy and real time for navigation services become higher, so that the traditional ground based network can hardly meet the users needs. And the accuracy of existing autonomous navigation method, such as celestial navigation, cannot meet the requirement either. In order to improve the performance of autonomous navigation for deep space prober, a navigation method based on inter-satellite link and starlight angle is proposed in this article. The prober determines its position by communicating with other spacecrafts and observing the star. This navigation method is illustrated by an example of Mars exploration mission. To verify the feasibility of this method, simulation is used to analyze its accuracy in this paper. The results show that the Mars prober can reach the position accuracy of 100m, which is much higher than the traditional celestial navigation which only measure the starlight angle. Meanwhile, the selection strategy of communication object is given after analyzing the variance matrix at steady-state. The accuracy of this method will be improved along with the increasing of onboard spacecrafts. This kind of autonomous navigation will significantly contribute to the deep space exploration mission in the future.

Performance comparison among the autonomous navigation methods for constellation around the earth-moon libration points via the Fisher information matrix

The Fisher information matrix is applied to evaluate the performance of three different navigation methods for the constellation around the libration points. Where the X-ray pulsar relative navigation is the main method, and the starlight Doppler relative navigation and the intersatellite links are integrated with it respectively. Their measurement quantities are respectively the time difference of arrival (TDOA), the starlight Doppler shift and the pseudo-range. Results show that only the accuracy of starlight Doppler shift reach the magnitude of 0.01m/s, can the addition of the starlight Doppler relative navigation effectively improve the performance of the X-ray pulsar relative navigation. In addition, the X-ray pulsar relative navigation / intersatellite-integrated navigation method has the highest navigation precision and fastest convergence rate.

X-ray pulsar-based navigation method using one sensor and modified time-differenced measurement

X-ray pulsar-based navigation method using one sensor (XNAVO) could fix the position of satellites by sequentially observing X-ray pulsars at the cost of loading one X-ray sensor, which drops the demand on the loading capability of satellite and is feasible for practice. However, subjected to the current research status of astronomical measure and the radiation mechanism of pulsar, there are unexpected systematic biases in XNAVO, which would greatly worsen the positioning performance of XNAVO. In addition, the systematic biases compensation methods previously proposed for X-ray pulsar-based navigation using three sensors would fail when being applied to XNAVO, due to the sequential observation strategy. In order to solve the problem, this paper introduces a positioning algorithm for XNAVO based on the modified time-differenced measurement. The propagation of systematic biases is analysed, revealing the systematic biases behave a quasi-periodical variation. Thus, a modified time-differenced measurement is proposed in accordance of the quasi-periodicity. A navigation filter that propagates sigma points to generate the improved time-differenced measurement model without linearisation has been given. The results of simulation have shown that the proposed method could reduce the major impact of investigated systematic biases.

Hardware In-Loop System for X-ray Pulsar-Based Navigation and Experiments

X-ray pulsar-based navigation uses natural objects, the neutron star, in space as the navigation signal source. The advantages of the method are navigation information is complete, and the reliability and autonomy are high. It is a research hot spot at present both at home and abroad. As a result of the X-ray signal from the pulsars is very weak, it cannot penetrate the thickset atmosphere. In order to validate the pulsar navigation algorithms closer to the real conditions on ground, the special Hardware in-Loop System should be used to do the experiments. This paper adopted the system “Tianshu-II” which is developed by National University of Defense Technology and Xi’an Institute of Optics and Precision Mechanics research institute. A series of X-ray pulsar-based navigation experiments are carried out. Experimental results show that the algorithms are reliable. They are verified to be effective in the hardware-in-the-loop simulation.

Profile bias’ influence in x-ray pulsar based navigation

X-ray pulsar-based navigation is a novel autonomous navigation method. The pulsar is a kind of neutron star rotating with high speed. Its angle position is stationary in space and its rotation period is extremely stable. In space, the signal with extremely stable period could be detected. Its long-term stability is higher than the atomic clock in state-of-the-art. Therefore, the signal of the pulsars in X-ray waveband could be used for the autonomous navigation of the spacecrafts. The signal’s profile is a necessary parameter to estimate the navigation information. In this paper, the impact on the navigation precision caused by the flux bias of the signal’s profile is analyzed. The impact is not severely proved in theory and simulation.

Design of the Performance Evaluation Software for X-ray Detectors

At present, the X-ray pulsar-based technology is on the step of space verification. It is badly in need of the deep analysis of the craft-carried detector’s performance. In addition, the developing departments need the key parameters that influence the performance of the X-ray pulsar-based navigation most. This paper designed a software system which can be used to evaluate the detector’s performance. The system can simulate the received photon characteristics with high precision by setting the detector parameters and observed pulsar parameters. Furthermore, it would analyze performance influences to the X-ray pulsar-based navigation by the detector’s key parameter, so that the detector performance could be effectively evaluated.

A Method of X-ray Pulsar-Based Navigation for Constellation in Libration Points

A method of X-ray pulsar-based navigation for satellites constellation in Halo orbit is given in this article. The dynamics of libration point orbits offer many opportunities for flexible, low-energy trajectories, and missions around libration points are arising. Autonomous navigation is necessary for spacecraft autonomy in libration point, as well as significantly benefits China’s deep space missions. In this paper, the state equation is established according to the dynamic characteristic in the libration point orbit. The difference of pulse arrival time to different satellites can be regarded as the measurements in the measurement equation. Unscented Kalman filter is applied to estimate the state of the system. Simulations demonstrate that this method is feasible for autonomous navigation for satellites constellation in the Sun–Earth libration point orbit. Comparing X-ray pulsar-based method with the traditional inter-satellite links navigation principle, satellites constellation rotation can be solved. Combining inter-satellite links and pulsar measurements in the UKF filter, the state of the system can be estimated more precisely and in a more quick way.