Europe’s Galileo satellite navigation system will come a giant leap nearer completion on Tuesday 12 December, as four more Galileo satellites are launched into orbit by Ariane 5.

Liftoff from Europe’s Spaceport in Kourou, French Guiana is scheduled for 18:36 UTC (19:36 CET, 15:36 local time), carrying Galileo satellites 19–22.

The launcher’s attitude and trajectory are controlled by the two onboard computers, located in the Ariane 5 vehicle equipment bay (VEB).

About seven seconds after start of the ignition of the main stage cryogenic engine at T-0, the two solid-propellant boosters are ignited, enabling liftoff. The launcher first climbs vertically for six seconds, then rotates towards the East. It maintains an attitude that ensures the axis of the launcher remains parallel to its velocity vector, in order to minimize aerodynamic loads throughout the entire atmospheric phase until the solid boosters are jettisoned.

The fairing protecting the payload is jettisoned at T+225 seconds.

The flight of the Ariane 5 lower composite, comprising two solid boosters and the cryogenic main stage, will last about nine minutes. This stage then separates from the upper stage and falls back into the Pacific Ocean, off the coast of Peru. The storable propellant upper stage will ignite its own engine at this point, to bring the upper composite – comprising the Galileo satellites and their dispenser – into a transfer orbit. Following this initial ignition, the upper composite is spun up for a ballistic phase lasting 3 hours and 8 minutes. At a predetermined point in this orbit, the upper stage will again ignite its engine for a little more than six minutes, to reach a circular separation orbit. Once stabilized, the dispenser will release the first two satellites, followed by the second pair 20 minutes later. The upper stage will be passivated at the end of the mission. The Galileo satellites will then perform a maneuver to increase their altitude and reach the operational orbit at 23,222 km.

At orbital injection, the launcher will have attained a velocity of approximately 3,000 meters/second, and will be at an altitude of 22,925 kilometers, 300 km. under Galileo’s operational orbit.

The first Livestream transmission is scheduled for 18:10 GMT (19:10 CET), covering the liftoff, ascent and first phases of flight.