# Precise Real-Time Navigation of LEO Satellites Using a Single-Frequency GPS Receiver and Ultra-Rapid Ephemerides

## TL;DR

This paper presents a method for precise real-time navigation of LEO satellites using a single-frequency GPS receiver and ultra-rapid ephemerides, achieving sub-meter accuracy without complex matrix operations.

## Contribution

It introduces a novel combination of measurement techniques and a sequential Kalman filter to enhance real-time orbit determination accuracy for LEO satellites.

## Key findings

- Achieved 0.50 m 3D position accuracy in real flight tests.
- Attained 0.55 mm/s velocity accuracy.
- Validated method with data from China's SJ-9A satellite.

## Abstract

Precise (sub-meter level) real-time navigation using a space-capable single-frequency global positioning system (GPS) receiver and ultra-rapid (real-time) ephemerides from the international global navigation satellite systems service is proposed for low-Earth-orbiting (LEO) satellites. The C/A code and L1 carrier phase measurements are combined and single-differenced to eliminate first-order ionospheric effects and receiver clock offsets. A random-walk process is employed to model the phase ambiguities in order to absorb the time-varying and satellite-specific higher-order measurement errors as well as the GPS clock correction errors. A sequential Kalman filter which incorporates the known orbital dynamic model is developed to estimate orbital states and phase ambiguities without matrix inversion. Real flight data from the single-frequency GPS receiver onboard China's SJ-9A small satellite are processed to evaluate the orbit determination accuracy. Statistics from internal orbit assessments indicate that three-dimensional accuracies of better than 0.50 m and 0.55 mm/s are achieved for position and velocity, respectively.

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Source: https://tomesphere.com/paper/1704.02094