# Galileo Single Point Positioning Assessment Including FOC Satellites in Eccentric Orbits
## 1 Introduction  
On 15 December 2016, with 18 satellites in orbit, Europe's satellite navigation system Galileo was declared operational and started offering its initial services to public authorities, businesses, and citizens. When Galileo will be fully operational, the constellation will consist of 24 satellites plus spares in Medium Earth Orbit (MEO) at an altitude of 23,222 km. Eight active satellites will occupy each of three orbital planes inclined at an angle of 56 degrees to the Equator. The satellites will be spread evenly around each plane and will take about 14 h to orbit the Earth. Two further satellites in each plane will be a spare on stand-by should any operational satellite fail. Currently (April 2019), Galileo is in its Full Operational Capability (FOC) phase; 22 FOC satellites were launched up to the start of 2019 in addition to the four IOV (In-Orbit Validation) launched between2011 and 2012. The navigation signals of these satellites are transmitted on five frequencies, E1, E5a, E5b, E5, and E6. Only three IOV satellites are operational because E20 was declared unavailable since 27 May 2014 [1] when a power anomaly led the E5 and E6 signals to a permanent loss of power. After this failure, all IOV satellites were backed-off, and thus, their signals have less transmitted power than the FOC satellites. Nineteen FOC satellites were declared operational; one (E22) was removed from active service on December 2017 for constellation management purposes, while the first two FOC satellites, Doresa (E14) and Milena (E18), were under test. These two satellites were launched on 22 August 2014 at 9:27 local time in French Guiana by a Soyuz STrocket. The two satellites were left in a non-nominal highly-elliptical orbit characterized by an apogee of 25,900 km and a perigee of 13,713 km, with an inclination with respect to the Equator of 49.69 degrees instead of planned circular medium-Earth orbits at an altitude of 23,222 km with an inclination of 55.04 degrees. The wrong injection orbits made the two satellites not usable for navigation missions; thus, the European Space Agency (ESA) planned a rescue mission to make the two satellites usable [2; 3]. Starting from November 2014-February 2015, the satellites made a series of maneuvers in order to raise the low point of their orbits by 3500 km and making their orbits more circular. Satellites in new orbits overfly the same location on the ground every 20 days. This is different from a normal Galileo repeat pattern of 10 days; however, it makes possible a synchronization of their ground tracks with the rest of the Galileo constellation. Thus, the revised orbit (reported in Table 1) allowed ESA to switch on the satellites' navigation payload. On 5 August 2016, beginning at 00:00 UTC, GSAT0201 (E18) and GSAT0202 (E14) started broadcasting navigation messages for testing purposes (for details, see the notice advisory to Galileo users [[https://www.gsc-europa.eu/notice-advisory-to-galileo-users-nagu-2016030](https://www.gsc-europa.eu/notice-advisory-to-galileo-users-nagu-2016030)]([https://www.gsc-europa.eu/notice-advisory-to-galileo-users-nagu-2016030](https://www.gsc-europa.eu/notice-advisory-to-galileo-users-nagu-2016030))). At the end of the mission, the European Space Agency on 8 October 2016 requested to provide feedback on usage of these satellites ([[http://galileognss.eu/tag/sat-6/](http://galileognss.eu/tag/sat-6/)]([http://galileognss.eu/tag/sat-6/](http://galileognss.eu/tag/sat-6/))). GNSS errors can be divided into errors that can be corrected by using differential techniques or not. The ephemeris error belongs to the first group [4], while the multipath error to the second. Therefore, before proceeding to the analysis performed in the positioning domain, the authors already analyzed these satellites considering these two aspects.