A Minimal Architecture for Real-Time Lunar Surface Positioning Using Joint Doppler and Ranging

A positioning solution for users on the lunar surface is required for the success of upcoming missions. Technological advancements have enabled the use of accurate range and Doppler measurements from a lunar orbiter. This article introduces a filtered approach of joint Doppler and ranging (JDR), a minimal architecture that requires as few as one lunar orbiter to perform 3D positioning of lunar surface vehicles. The simulated performance of JDR and Doppler-based positioning methods is compared. Two lunar satellites are simulated: The lunar relay satellite (LRS) in a 12-h frozen orbit with its apogee above the lunar south pole, and the lunar reconnaissance orbiter in a 2-h Polar orbit. The analysis interval is 8 h over a single LRS ground pass. The ground pass has only a few intervals where both satellites are visible to the user and reference station on the lunar south pole. Navigation nodes are simulated with synchronized clocks for all methods. Measurement and satellite ephemeris errors are embedded into a Monte Carlo simulation to evaluate 3D positioning error. The relative JDR method obtains the lowest and most consistent overall 3D root mean squared error, averaging around 10–15 m. The absolute positioning methods are limited by satellite orbit height and other factors. Ultimately, JDR is able to provide reasonably accurate positioning knowledge to users with a minimal required infrastructure. Though this article introduces JDR on the Moon, the same architecture can be applied for other celestial bodies like Venus, Mars, Titan, and asteroids.