嫦娥五号任务中的多通道多比特VLBI信号采集记录与传输一体化技术

Integration of very long baseline interferometry data acquisition, recording, and transmission with multichannel and multibit for CE-5 mission

对接收到的观测信号进行实时采集记录与传输是甚长基线干涉测量(VLBI)的重要技术环节.在嫦娥五号任务中, VLBI终端需要同时采集记录轨道器、上升器、着陆器等多个目标探测器发出的测控信号、数传信号并分时采集记录河外射电源信号.由于探测器信号频点多、动态范围大、频谱形式复杂,现有天文VLBI终端不能满足探月与深空探测的需求.我们针对嫦娥五号探测器信标特点,开展了多通道、多比特信号采集、记录与传输一体化技术研究;提出了可变频率多项滤波器组算法,可在很宽的频段范围内,灵活设置信号频点,并能获得平坦的幅度特性与线性相位特性.采用该技术研制的新型采集记录与传输一体化VLBI终端,具备16个基带通道,能够实时采样、记录嫦娥五号多个探测器用于VLBI测轨的全部测控与数传信标,并能够通过网络将数据实时传送至VLBI中心,确保了在嫦娥五号多种信标复杂电磁环境下的VLBI测轨.相比以往天文终端,其实时性、测量精度和可靠性都有大幅提高,极大地支持了我国嫦娥五号首次月球采样返回关键段测轨任务的圆满完成.为适应未来射电源与探测器的宽窄带观测需求,新型采集记录与传输一体化VLBI终端还具备多比特量化功能.

Real-time signal acquisition, recording, and transmission are the important functions of very long baseline interferometry(VLBI). In the Chang’e-5(CE-5) mission, a VLBI backend is required to connect the telemetry, track and command(TT&C) beacons, data signals from multiple probes, such as the orbiter, ascender, and lander, and signals from the extragalactic radio source in time. Due to the multiple frequency points, large dynamic range, and complex spectrum form of the probe signals, existing VLBI astronomical backends do not meet the requirements of lunar exploration and deep space exploration. According to the characteristics of the beacon of CE-5 probes, we researched the integration technology of multichannel and multibit signal acquisition, recording, and transmission. This paper proposes a frequency tunable polyphase-filter bank algorithm, which can flexibly set frequency and obtain flat amplitude and linear phase characteristics in a wide band. The novel integrated VLBI backend developed by this technology contains 16 channels,which can sample and record all the TT&C and data signals from CE-5 probes in real time and transmit the VLBI data to the VLBI center through the network. It ensures successful VLBI measurement in the complex electromagnetic environment of CE-5 multi beacons. Compared with the previous astronomical backends, the real-time performance,measurement accuracy, and reliability of the novel integrated VLBI backend are greatly improved, which support the successful completion of China’s first lunar sampling return mission of CE-5. The novel integrated VLBI backend also has the function of multibit quantization to meet the needs of wide and narrow observation of future radio sources and probes.