具有多物理特性的X射线脉冲星导航地面验证系统

导航地面验证是X射线脉冲星导航研究必不可少的环节.针对导航算法验证需要真实连续的脉冲星信号的需求,同时避免X射线调制及探测难度大、成本高的问题,提出了一种基于可见光源的X射线脉冲星导航地面验证系统.该系统利用太阳系质心处脉冲星信号模型和航天器轨道信息,建立航天器处实时光子到达速率函数,再通过硬件系统转换成电压信号,利用该电压控制线性光源输出,最后经衰减、探测及甄别后获得航天器处的实时光子到达时间序列.该时间序列不仅具有导航脉冲星的轮廓特性、自转特性,还包括空间传播时间效应及宇宙X射线背景.本系统利用半物理装置对可见光进行调制及衰减,实时判断轨道各位置处导航脉冲星的可见性,实现X射线脉冲星信号传播过程的模拟.该系统提供四路可控输出信号,支持多种导航模式的验证.仿真系统的性能分析和功能验证结果表明,该系统具有良好的性能,可提供真实便捷的地面验证环境.

Ground verification system of X-ray pulsar navigation with multi-physical properties

Navigation ground verification is an essential part of X-ray pulsar navigation (XPNAV) research. Aiming at the need of real and continuous pulsar signals for navigation algorithm verification, and to avoid the difficulties and high costs of X-ray modulation and detection, we propose an XPNAV ground verification system based on visible light source. In this system, the pulsar signal model at the solar system barycenter and the orbit information are used to establish the real-time photon arrival rate function at a spacecraft, and then the rate function is digitized and converted into voltage signal by the designed hardware system to drive a linear light source. After the processes of light attenuation, signal detection and pulse discrimination are experienced, the real-time photon time of arrivals (TOAs) at a spacecraft can be achieved. These photon TOAs contain characteristics of the pulsar profiles and frequency, the time propagation effect in the solar system, and cosmic X-ray background. The system uses semi-physical devices to modulate and attenuate visible light, and judges whether the spacecraft can observe the navigation pulsar according to the real position, thereby realizing the simulation of X-ray propagation in space. At present, the detection method of pulsar observation with single detector include detection of single pulsar, time division detection of multiple pulsars, and simultaneous detection of multiple pulsars. The system has four channels, each of which has three output modes mentioned above, and can support the verification of multiple navigation modes. This system consists of signal simulator and controller, single photon generator and detector, single photon screening and time tagging, and navigation algorithm verification. This paper presents the testing results of the system characteristics, the authenticity of the simulated photon arrival time series and the navigation verification. Monte Carlo experiments show that the recording accuracy of photon arrival time is 10 ns and the delays of the four channels are (11 ±2), (15 ±4), (14 ±3), and (16 ±4) \${\text{μ}}{\rm{s}}$\, respectively. The multi-physical properties of simulated photon arrival time series are introduced in detail, including photon flux, shape of observation profile, pulsar frequency characteristics and Doppler shift. The position and velocity errors of autonomous navigation algorithm test are 13.587 km and 14.277 m·s^-1, respectively, with an orbital altitude 26610 km and within 10 h. The ground verification system adopts master-slave control mode, the master computer mainly implements parameter setting and navigation algorithm verification, and the slave computer mainly carry out pulsar signal simulation. The communication based on TCP/IP protocol is applied to realize parameter transmission and real-time control between the master and slave computers in navigation verification process. The results of performance and functional test show that the system is available to accomplish the simulation of photon TOAs of X-ray pulsars at a spacecraft in real time and implement the ground verification of XPNAV.