# Autonomous Orbit Determination Using Epoch-Differenced Gravity Gradients and Starlight Refraction

## TL;DR

This paper presents a novel autonomous orbit determination method combining epoch-differenced gravity gradients and starlight refraction, improving accuracy for low-Earth satellites in GPS-denied environments.

## Contribution

It introduces an integrated approach using epoch-differenced gravity gradients and starlight refraction with an extended Kalman filter for precise orbit estimation.

## Key findings

- Achieved 100 m position accuracy in semi-simulation tests.
- Demonstrated effectiveness of starlight refraction in along-track error correction.
- Showed bias elimination through epoch differencing of gravity gradients.

## Abstract

Autonomous orbit determination via integration of epoch-differenced gravity gradients and starlight refraction is proposed in this paper for low-Earth-orbiting satellites operating in GPS-denied environments. The starlight refrac-tion can compensate for the significant along-track position error using solely gravity gradients and benefit from the integration in view of accuracy improvement in radial and cross-track position estimates. The between-epoch dif-ferencing of gravity gradients is employed to eliminate slowly varying measurement biases and noises near the orbit revolution frequency. The refraction angle is directly used as measurement and its Jacobian matrix is derived from an implicit observation equation. An information fusion filter based on sequential extended Kalman filter is devel-oped for the orbit determination. Truth-model simulations are used to test the performance of the algorithm and the effects of differencing intervals and orbital heights are analyzed. A semi-simulation study using actual gravity gra-dient data from the Gravity field and steady-state Ocean Circulation Explorer (GOCE) combined with simulated starlight refraction measurements is further conducted and a three-dimensional position accuracy of better than 100 m is achieved.

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Source: https://tomesphere.com/paper/1702.01937