Yuichiro Kitagawa, LSAS Tec; Guifre Molera Calves, HENSOLDT Australia & University of Tasmania; Koji Wakamori, LSAS Tec; Yosuke Yamamoto, LSAS Tec; Masahiro Yamatani, MCC Corporation
Keywords: Lunar orbit, Cislunar, Passive RF sensor, TDOA /FDOA, High Accuracy Orbit Determination
Abstract:
In recent years, there has been growing interest in the Cislunar region in the fields of space development and security, making the safe and sustainable monitoring of this region an important challenge.
Traditional spacecraft orbit determination has mainly relied on radar and optical observations, but recently, there is growing expectation for the use of observation data from passive RF sensors that receive S-band and C-band radio waves emitted by spacecraft.
In this paper, we extend orbit determination using TDOA/FDOA to be applicable in lunar orbit and the cislunar region.
Passive RF sensors have the advantage of being able to track spacecraft regardless of time of day or weather conditions if radio waves are received, being able to detect satellite maneuvers in real-time. They also enable high-precision orbit determination by using long baseline observation networks and high-gain antennas. Therefore, they are expected to have superior tracking capabilities compared to conventional radar and optical observations.
In the Lunar orbit and Cislunar region, optical observations are challenging due to sunlight reflection from the lunar surface. However, with the advantages of passive RF sensors, it is expected to eliminate this issue and make observation in the Cislunar region feasible.
In this study, TDOA and FDOA calculated using S-band observation data from the KPLO (Korean Pathfinder Lunar Orbiter) obtained with a 12m diameter passive RF sensor of the South Guardian Sensor Network which has a baseline length of ~ 2000 km each, were used to determine the orbit of the lunar orbiter. The achieved orbit determination accuracy was ~ 500m in the In-Track/Radial direction and ~ 3500m in the Cross-Track direction (3σ).
Using this technique, it will be possible to determine the orbits of satellites in lunar orbit and in the cislunar region with high accuracy.
In the future, it will be possible to form an ultra-long baseline network by combining the South Guardian Sensor Network with Northern Hemisphere sensors, which is expected to further improve the orbit determination accuracy.[1]
This paper demonstrates the effectiveness of passive RF sensors for orbit determination in the Cislunar region and highlights the potential contribution to future space mission monitoring.
Reference:
[1] François Thevenot et al., Cislunar Orbit Determination using passive RF sensors: 2024 Advanced Maui Optical and Space Surveillance Technologies Conference (AMOS)
Date of Conference: September 16-19, 2025
Track: Cislunar SDA