The fourth Galileo satellite arrived at Cayenne Airport in French Guiana on August 17, while the third satellite arrived at the facility on August 7.
The satellites will be operating from medium orbit 33 about 140 miles above the Earth.
Having four satellites is the minimum number required for navigational fixes, enabling full system testing whenever they are all visible in the sky.
These validation tests will be followed by the deployment of more satellites and ground segment to achieve “Full Operational Capability.”
The European Space Agency (ESA) said back in December of last year that its first Galileo satellite transmitted test signals across its full spectrum.
Twenty-two of the planned satellites are being built by OHB in Germany, which is responsible for the platforms and final satellite integration. The U.K.’s Surrey Satellite Technology will be producing the payloads for the satellites.
EADS Astrium in Germany built the first four Galileo satellites and produce the platforms, while Astrium U.K. built the payloads.
The four Galileo satellites were assembled and tested in Rome by Thales Alenia Space.