Proposed Orbital Products for Positioning Using Mega-Constellation LEO Satellites.

Ahmed El-Mowafy,Kan Wang

doi:10.3390/s20205806

Abstract

With thousands of low Earth orbit (LEO) satellites to be launched in the near future, LEO mega-constellations are supposed to significantly change the positioning and navigation service for ground users. The goal of this contribution is to suggest and discuss the feasibility of possible procedures to generate the LEO orbital products at two accuracy levels to facilitate different positioning methods—i.e., Level A orbits with meter-level accuracy as LEO-specific broadcast ephemeris, and Level B orbits with an accuracy of centimeters as polynomial corrections based on Level A orbits. Real data of the LEO satellite GRACE FO-1 are used for analyzing the error budgets. For the Level A products, compared to the orbital user range errors (OUREs) of a few centimeters introduced by the ephemeris fitting, it was found that the orbital prediction errors play the dominant role in the total error budget—i.e., at around 0.1, 0.2 and 1 m for prediction intervals of 1, 2 and 6 h, respectively. For the Level B products, the predicted orbits within a short period of up to 60 s have an OURE of a few centimeters, while the polynomial fitting OUREs can be reduced by a few millimeters when increasing the polynomial degree from one to two.

Highlights

Global navigation satellite systems (GNSSs) currently provide positioning, navigation and timing (PNT) services to users in different areas
The signals from mega-constellation low Earth orbit (LEO) satellites, currently in developement with satellites continuously being launched, are nowadays becoming attractive for navigation purposes. Since these LEO satellites are primarily used for communications, to enable positioning, it is proposed that either additional payloads are added to these satellites to provide GNSS-like signals or employ their signals as signals of opportunity for positioning (SOOP) [1]
Different from the GNSS satellites that are located at the medium Earth orbits (MEOs), the LEO satellites at lower latitudes of about 300 to 1500 km [2] are able to provide ground users with much stronger signals, which enables positioning in GNSS-challenging areas and makes the signals more resilient against jamming [3]

Summary

Introduction

Global navigation satellite systems (GNSSs) currently provide positioning, navigation and timing (PNT) services to users in different areas. The signals from mega-constellation low Earth orbit (LEO) satellites, currently in developement with satellites continuously being launched, are nowadays becoming attractive for navigation purposes. Since these LEO satellites are primarily used for communications, to enable positioning, it is proposed that either additional payloads are added to these satellites to provide GNSS-like signals or employ their signals as signals of opportunity for positioning (SOOP) [1]. Different from the GNSS satellites that are located at the medium Earth orbits (MEOs), the LEO satellites at lower latitudes of about 300 to 1500 km [2] are able to provide ground users with much stronger signals, which enables positioning in GNSS-challenging areas and makes the signals more resilient against jamming [3]. A large number of LEO satellites launched or to be launched in the near future by companies such as Iridium, Globalstar, SpaceX, OneWeb, Samsung and Boeing does benefit the overall satellite geometry and the position dilution of precision (PDOP), the fast-moving LEO satellites and the rapidly changing geometry can reduce the long convergence time in the precise point positioning (PPP) [4]

Objectives

Results

Conclusion