# Hybrid SGP4 orbit propagator

## TL;DR

This paper introduces a hybrid propagation method that extends the validity of TLEs for satellite orbit prediction by combining standard SGP4 with an error correction model, enhancing accuracy over longer periods.

## Contribution

It proposes a non-intrusive hybrid TLE approach that incorporates an error model to improve orbit propagation accuracy and extend TLE validity without major system changes.

## Key findings

- Extended TLE validity significantly improves orbit prediction accuracy.
- Hybrid SGP4 reduces propagation errors over longer time horizons.
- Method is compatible with existing TLE distribution systems.

## Abstract

Two-Line Elements (TLEs) continue to be the sole public source of orbiter observations. The accuracy of TLE propagations through the Simplified General Perturbations-4 (SGP4) software decreases dramatically as the propagation horizon increases, and thus the period of validity of TLEs is very limited. As a result, TLEs are gradually becoming insufficient for the growing demands of Space Situational Awareness (SSA). We propose a technique, based on the hybrid propagation methodology, aimed at extending TLE validity with minimal changes to the current TLE-SGP4 system in a non-intrusive way. It requires that the institution in possession of the osculating elements distributes hybrid TLEs, HTLEs, which encapsulate the standard TLE and the model of its propagation error. The validity extension can be accomplished when the end user processes HTLEs through the hybrid SGP4 propagator, HSGP4, which comprises the standard SGP4 and an error corrector.