Abstract: In terms of the characteristics of radio signals typically emitted by spacecraft in high Earth orbit space and cislunar space during orbital maneuvers, passively receiving and processing techniques for radio signals are employed to achieve sensitive andrapid motion monitoring of spacecraft in orbit. The common technical methods used for spacecraft in orbit motion monitoring are analyzed，and a passive monitoring strategy based on radiometric measurements is proposed. Firstly, based on the operational characteristics of the transmitted telemetry, data transmission, and carrier signals from the target spacecraft, the target spacecraft signal is tracked and received by radio receiving antennas. Secondly, the target spacecraft downlink radio signal is sampled and recorded by the sampling and recording equipment. Subsequently, this paper focuses on the processing and analysis of the target's downlink signals by software-defined radio mode, accurately extracting sensitive features related to the target's motion such as signal frequency, amplitude, and phase changes. The orbit control quantity estimation algorithm based on open-loop Doppler frequency is proposed to evaluate the target's motion state. Finally, the effectiveness of the motion monitoring is assessed. The results indicate that accurate and sensitive monitoring of the orbital maneuvers and attitude adjustment processes of Earth high orbit spacecraft has been achieved based on actual experiment. The starting and ending time of the orbit control is accurately monitored, and the orbit control quantity in the line of sight direction of the station is estimated to be 4.1m/s, suggesting that this Earth high orbit spacecraft adopted a small thrust continuous orbit change mode for orbital maneuvers. The signal monitoring of the lunar spacecraft orbit maneuver process is realized, and its frequency, amplitude and phase characteristics are extracted respectively, and the orbit control quantity in the line of sight direction of the station is estimated to be 0.91m/s. The spacecraft motion monitoring method based on radiometric measurements effectively compensates for the limitations of traditional radar and optical measurements in monitoring spacecraft motion and complements them. This method is suitable for a variety of new application scenarios, and provides a feasible technical solution for the future monitoring of earth high orbit and cislunar space spacecraft.

Key words: spacecraft, motion monitoring, orbit attitude change, radio measurement, open-loop measurement, signal processing