## 1 Introduction  
Galileo--the first European global navigation satellite system providing worldwide positioning, navigation and timing services--has been under extensive development since the early 2000s. The first two experimental satellites--GIOVE-A and GIOVE-B--were launched in 2005 and 2008, respectively. The satellites were the part of the Galileo System Test Bed (GSTB) [1]. After the initial delay of the programme, in recent years we can observe acceleration of the system development. The final constellation will comprise 30 satellites in total, evenly spread on three medium earth orbits including 24 operational plus two spare satellites per plane defining 24/3/1 Walker constellation [2; 3]. At present (October 2017) the Galileo constellation consists of 18 satellites; however, this includes one with \"not unusable\", two with \"testing\" and one with \"not available\" status. The current constellation consists of satellites belonging to in-orbit validation (IOV) and full operational capability (FOC) phases. The former phase, which has already been accomplished, used four satellites launched in 2011 and 2012 to validate the system. The latter comprises operational satellites launched from 2014 onwards. On 22 August 2014, the first two FOC satellites (GSAT0201-E18 and GSAT0202-E14), also named Doresa and Milena, respectively, were unintentionally injected into a wrong orbit. The failure was caused by a technical problem--specifically, by an interruption of propellant supply to the thrusters. On the next day, it was announced that the actual inclination of these satellites' orbits is \(\sim\)5\({}^{\circ}\) lower than the nominal one. Furthermore, the eccentricity of the orbit reached 0.29, which is much higher than the nominal one of 0.0002. Therefore, these satellites were in December 2014 and March 2015 moved by a series of correction manoeuvres into an improved, but still highly eccentric, orbit. This, however, consumed a significant amount of the on-board fuel. Afterwards, the satellites started transmission of the navigational signals [4]. Selected parameters of the actual and nominal E14 & E18 Galileo orbits are listed in Table 1.  
The open question is the potential contribution of the first pair of FOC satellites to the Galileo services and applications. Due to format restrictions of the orbital parameters, E14 and E18 satellites are not included in the broadcast navigation message. Specifically, actual deviations of the semimajor axis and eccentricity exceed the nominal values by far over the limit. Accepting the premise that the maximum value of the eccentricity applied to the broadcast navigation message is 0.03125, the actual value exceeds the limit and reaches the level of 0.16. The nominal value of the semimajor axis (29,600 km) deviates by a value of 1620 km, which also exceeds the limit of 87 km. These facts seem to prevent the application of the E14 & E18 satellites to real-time solutions. Notwithstanding this, the satellites' observations may be applied to post-processing applications, since several GNSS analysis centres provide post-mission products such as satellite clock corrections and orbits. As former studies showed, the quality of such E14 & E18 orbits may be considered as not worse than that of nominal FOC and IOV satellites [5]. Moreover, the eccentricity of the satellite orbits offers several possibilities for scientific applications including general relativity studies. It is recognised that an elliptic orbit of a satellite causes a periodic modulation of the gravitational redshift [6]. This phenomenon may be investigated by taking advantage of the high stability of the on-board H-maser clocks and the high eccentricity of the E14 & E18 orbits [7]. Furthermore, satellite observations may be used in a number of post-mission surveying, geodetic, and geodynamics applications, which is, in a sense, the goal of this paper. Since the initial phases of the Galileo program, the observational data were applied and analysed in several ways.