Abstract

The spacecraft nicknamed Vespucci is the first GPS III satellite launched in December 2018. Numerous receivers of the global International GNSS Service network tracked the signals of this new generation of GPS spacecraft from January to July 2019. This data set serves as the basis for analysis of broadcast ephemeris performance and clock stability, as well as solar radiation pressure and satellite antenna phase center models. Different empirical orbit models are tested, and box-wing models are developed based on approximate dimensions, mass, and assumed optical properties. The box-wing models show in general a better performance than the empirical models. Compared to Block IIF satellites, the stability of the GPS III rubidium clock is higher for integration times up to 10 s. At longer integration times, the stability of both clocks is similar but the GPS III clock does not suffer from frequency-specific line bias variations that affect the apparent IIF clock. Estimated antenna phase center offsets agree on the centimeter level with the calibrations published by the manufacturer. Measurements with a 30-m high-gain antenna revealed that the satellite did not stop signal transmission in July 2019 but switched to non-standard codes and codes beyond the tracking capabilities of commercial GNSS receivers. Prior to this hibernation mode, a 70 days test without broadcast ephemeris update was conducted during which the user range error increased to roughly 1 km.

Highlights

  • The first GPS III spacecraft is named after the Italian explorer Amerigo Vespucci

  • In contrast to the previous generation of Block IIF satellites with Boeing as prime contractor, the GPS III spacecraft are manufactured by Lockheed Martin, which already built the Block IIR and IIR-M satellites

  • Metadata for GPS III are currently limited to approximate mass and body dimensions (Alexander and Martin, 2018) as well as satellite antenna phase center offsets (PCOs) and intersignal correction parameters (Lockheed Martin, 2019b)

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Summary

Introduction

The first GPS III spacecraft is named after the Italian explorer Amerigo Vespucci. It was launched on December 23, 2018, from Cape Canaveral with a Falcon-9 rocket. Metadata for GPS III are currently limited to approximate mass and body dimensions (Alexander and Martin, 2018) as well as satellite antenna phase center offsets (PCOs) and intersignal correction parameters (Lockheed Martin, 2019b). The optical properties of the satellite surfaces that are required for solar radiation pressure modeling are currently not publicly available. It is not clear if the dimensions of the satellite body given in Alexander and Martin (2018) refer to the solid box of the satellite or if they refer to an envelope including, e.g., the antenna panel.

Signal transmission and broadcast ephemerides
Navigation signals
Broadcast ephemerides
Orbit determination
Solar radiation pressure modeling
Orbit analysis
20 ECOM-2
Clock stability
Satellite antenna phase center offsets
Findings
Outlook
Full Text
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