Q&A with Michel Denis, ExoMars flight director

A Russian rocket released two Galileo navigation satellites nearly 15,000 miles above Earth early Friday, adding to a growing fleet giving Europe an independent space-based positioning system tracking automobiles, airplanes and cell phone-carrying people around the world.

An Ariane 5 rocket took off from French Guiana Friday with the heaviest interplanetary science probe ever launched, kicking off a $1.7 billion European Space Agency mission on a decade-long quest to Jupiter’s icy moons in search of environments that could be habitable for life.

Arianespace is returning an Ariane 5 rocket — loaded with three U.S.-built satellites — back to its final assembly building in French Guiana to replace a suspect sensor on the vehicle that prompted officials to cancel a launch attempt Friday. Arianespace said Monday that the swap will delay the launch until around Aug. 14.