深空探测用双频连续相位测量技术及在行星射电掩星反演中应用研究

After a series of CE lunar exploration missions, the independent deep space missions are being planed in China, and Mars will be the first target. By using the VLBI radio telescopes of China, this project will study the key techniques of the dual–frequency continuous phase measuring system, which can be used for the planetary radio science exploration and deep space satellite’s orbit determination. The main work include: 1) the high-speed down conversion parallel signal processing; 2) real time tracking of the continuous phase measurements, especially for the low SNR Doppler signal in deep space explorations; 3) the planetary radio occultation inversion technique based on the dual-frequency differential continuous phase observations. For X-band continuous phase observation, the precision with one - hundredth of cycle can be achieved. The high quality tracking data is important to improve the precisions of the retrieved Martian electron density profiles and the orbits of the deep space satellite. High-precision electron density data provide important references to distinguish the noise from the real waves in the faint electron density profiles, and calculation of the key physical parameters in the theoretical ionospheric model. By constructing a one-dimensional ionospheric model, we will study the inflow and outflow variations of the major ions in different altitude ranges, and the diffusion features of the Martian ionosphere. The works in this project will have a breakthrough in the dual-frequency differential tracking system for deep space satellites and occultation inversion of the Martian ionosphere in China.

继一系列的嫦娥月球探测任务之后，我国也在规划独立的深空探测任务，火星将是首要的探测目标。本项目利用天文系统的VLBI 射电天文设备，研究用于行星无线电科学探测和深空飞行器测轨的双波段连续相位测量体系的关键技术，包括：1）超高速下变频同步并行处理算法研究；2）深空低信噪比双频多普勒信号的连续相位实时跟踪测量算法研究；3）基于双频差分连续相位的火星电离层星地掩星反演技术研究。对于X波段连续相位测量，精度可达到百分之一周，这将有助于提高电子密度的反演精度和深空飞行器的测轨精度。高精度的火星电子密度数据为微弱电子密度廓线的判别、日间电离层的波动现象解释以及电离层理论模型中关键物理参数的确定提供重要依据。通过构建一维火星电离层模型，进一步研究不同高度范围内主要离子的流入和流出通量变化和火星电离层的输运特性。本工作将在深空飞行器双频差分跟踪观测体系和火星电离层掩星反演方面取得突破。

本项目应用天文系统的VLBI 射电天文设备，采用双频差动观测模式跟踪行星飞行器的下行无线电载波信号，开展超高速下变频同步并行处理算法研究，开展深空低信噪比多普勒信号连续相位实时跟踪测量算法研究，研制了可提取多通道（2通道或4通道）高分辨率的多普勒频率幅度和相位信息以及基于B/S架构的可配置式软件无线电数字式双频连续相位测量接收机。X波段连续相位测量精度可达到1毫周，这将有助于基于双波段差分观测的深空飞行器测轨及一些行星探测。开展了深空飞行器大范围连续跟踪观测的关键技术研究，实现低信噪比下深空飞行器双波段多普勒频移和连续相位高精度实时解析，采样数据的分辨率达到10MSPS和16bits，多普勒提取间隔从0.01s到60秒。跟踪嫦娥3、火星快车和新视野飞行器的实验结果表明了双频连续相位测量技术的可行性和有效性。本项目还利用上海佘山VLBI射电天线、佳木斯深空站66米射电天线对所研制的深空探测用双频多通道连续相位测量无线电科学接收机进行了应用测试分析，进行了多次行星轨道器的试观测、小型飞行物重力场测量、掩星观测和嫦娥飞行器跟踪观测实验等，得到了一些初步观测结果。本项目将填补我国行星无线电科学的空白。