The 3rd and 4th Full Operational Capability satellites will be the 7th and 8th Galileo satellites launched, alongside the 2 FOC and 4 IOV spacecraft already in orbit. The Galileo constellation is ESA’s satellite navigation system and is expected to be completed by 2020. Galileo will provide Europe with an alternative to the American GPS and Russian GLONASS constellations, but will be interoperable with both systems.