Analysis of Orbit Determination Error Impact on Clutter Doppler Frequency for Space-Based Early Warning Radar

The accuracy of clutter Doppler frequency in space-based early warning radar (SBR) directly determines moving target detection performance, and satellite orbit determi-nation error is a important cause of clutter Doppler deviation. Taking satellite position and velocity in the Geocentric Celestial Reference System (GCRS) as core variables, this paper derives the analytical expression of clutter Doppler frequency through co-ordinate transformations from GCRS to the International Terrestrial Reference System (ITRS) and then to the North-East-Zenith (NEZ) local coordinate system. The multi-variate function gradient analysis method is used to quantitatively reveal the influ-ence laws of GCRS position and velocity errors on Doppler frequency. Results indicate that satellite velocity error is the linear dominant term of Doppler variation with a constant gradient magnitude of 2/λ, and only the velocity component along the satel-lite–ground line-of-sight contributes to frequency shift. Satellite position error acts as a nonlinear modulation term, whose gradient magnitude is inversely proportional to the satellite–ground distance and coupled with satellite velocity. Under typical SBR oper-ating parameters and BeiDou receiver orbit determination errors, a velocity error of 0.1 m/s causes a Doppler deviation below 1 Hz, and a 10 m position error results in a de-viation less than 1.6 Hz, both negligible in engineering. This research clarifies orbit de-termination error propagation characteristics and provides a theoretical foundation for clutter Doppler accuracy control and orbit precision design of SBR.