Monostatic laser Doppler velocimeter for ISRO’s future space docking missions

A compact, high-accuracy Doppler-based velocity sensor, called Monostatic Laser Doppler Velocimeter (mLDV), is under development using fiber optic technology and coherent homodyne detection, which significantly enhances sensitivity to velocity changes compared to conventional detection methods. By employing a Phase Diversity Receiver (PDR) that separates incoming signals into in-phase and quadrature-phase (I/Q) components, the mLDV provides more precise measurements than traditional systems. We successfully demonstrated the sensor's performance from 0.5 to 20 meters, achieving an accuracy of less than 2 millimeters/second for speeds up to 5 meters/second. Considering the approach velocity of 10 millimeters/second in the Indian Space Research Organization (ISRO) space docking experiment SPADEX1, the mLDV's improved accuracy offers significant gains in docking precision and reliability. This paper outlines the sensor's design, configuration, and preliminary test results.