Orbit Propagation Python Libraries

This study was started as part of a two-months research internship at ISAE-SUPAERO. The code & documentation from the original study are available on the 2022-research-internship branch, while the article written as part of this study can be found here.

Abstract

As part of an effort to streamline the space mission design workflow of the CREME satellite mission into a single-language process, this study provides a list of open-source Python libraries capable of orbit propagation and a comparison of their feature set. Two libraries selected as prime candidates are compared across three different force models with trusted reference tools based on their numerical results, computation time and ease of use. Both are found to be suitable options for different use cases, with faster and more modular computations being their strongest advantages, whereas the reference tools remain particularly compelling for their accessibility when used independently.

Table of Contents

• Introduction
• Features
• Libraries
• Validation tools
• Features comparison

Introduction

The goal of this research internship is to compare various python libraries able to perform orbit propagation of satellites and select the most appropriate one to be implemented in the CREME space mission design workflow based on its ease of use, feature set, performance and accuracy.

Features

The following features are investigated:

• Orbit propagation
  • Keplerian
  • With J2, J3, J4+ effects
  • With drag
  • With other perturbations (+ SRP, 3rd body, etc.)
• Eclipses prediction
• Ground station visibility prediction
• Export of ECEF states

Libraries

The following libraries have been found:

• astropy not a library for orbit propagation
• poliastro
• tudatpy
• skyfield only does SGP4 propagation
• orbit-predictor (mostly SGP4 propagation)
• Orbitdeterminator (does basic propagation, but no eclipses or communication windows prediction)
• orbdetpy (prediction of communication windows but not eclipses)
• Orekit python wrapper

Validation tools

Results are to be validated with the following tools:

• Celestlab & CelestlabX on Scilab
• GMAT

Features comparison

Abbreviations :

• OP : Orbit propagation
• GS : Ground station

Feature	poliastro	Tudatpy	Orbit Predictor	Orbitdeterminator	orbdetpy	Orekit (py)
Propagation language	Python	C++	Python/C++(SGP4)	Python/C++(SGP4)	Java	Java
OP - Keplerian	✅	✅	✅	✅	✅	✅
OP - J2	✅	✅	✅	✅	✅	✅
OP - J3	✅	✅	❌	❌	✅	✅
OP - J4+	❌	✅	❌	❌	✅	✅
OP - Drag	✅	✅	❌	✅	✅	✅
OP - 3rd body	✅	✅	❌	❌	✅	✅
OP - SRP	✅	✅	❌	❌	✅	✅
OP - SGP4	❌	❌	✅	✅	❌	✅
OP - Other perturbations	❌	✅	❌	❌	✅	✅
Eclipses	✅	✅	✅	❌	❌	✅
GS visibility	❌	❌	❌	❌	✅	✅
ECEF export	❌	✅	✅	✅	✅	✅

Validation tools force models

Celestlab

Model	Earth gravity	Other bodies gravity	Atmospheric drag	Solar radiation pressure
Keplerian	Point mass	❌	❌	❌
Secular J2	Only secular effects of J2 on AOP, RAAN and MA	❌	❌	❌
Eckstein-Hechler	Zonal harmonics up to J6, no tesseral terms	❌	❌	❌
Lyddane	Zonal harmonics up to J5	❌	❌	❌
STELA	Degree and order up to 15	Moon & Sun	✅	✅

GMAT

Model	Earth gravity	Other bodies gravity	Atmospheric drag	Solar radiation pressure
Customizable	✅	✅	✅	✅

Validation models

Spherical gravity model : "zonal harmonics only" --> order m = 0. Degree up to chosen value.

Tudatpy

To compare with Celestlab and GMAT

Orbit	Earth gravity	Other bodies gravity	Atmospheric drag	Solar radiation pressure	Celestlab equivalent
keplerian	Point mass	❌	❌	❌	Keplerian
earthZonalJ5	Zonal harmonics up to J5 (degree l=5, order m=0)	❌	❌	❌	Lyddane
complete	Spherical harmonics degree and order = 15	Moon & Sun point mass	✅	✅	STELA

Poliastro

To compare with Celestlab (Keplerian only) and GMAT

Orbit	Earth gravity	Other bodies gravity	Atmospheric drag	Solar radiation pressure	Celestlab equivalent
keplerian	Point mass	❌	❌	❌	Keplerian
earthZonalJ3	Zonal harmonics up to J3 (degree l=3, order m=0)	❌	❌	❌	❌
complete	Zonal harmonics up to J3 (degree l=3, order m=0)	Moon & Sun point mass	✅	✅	❌

Models used

Feature	poliastro	Tudatpy	Celestlab	GMAT
Atmospheric density model	Jacchia77	NRLMSISE-00	NRLMSISE-00	JacchiaRoberts & MSISE-90
Earth gravity field	J2/J3 only	GOCO05c	EGM96	EGM96