A rendering of Galileo FOC-M7 satellites. Image provided by Arianespace.
Four new satellites for Europe’s Galileo GNSS constellation have been successfully launched from French Guiana on December 13 at 05:37 AEDT.
Four of the remaining six satellites required to complete the full 24-strong Galileo constellation are Medium Earth Orbit (MEO), Galileo FOC-M7 satellites 19 to 22.
The Flight VA240 mission was be carried out by French-headquartered launch company Arianespace with the heavy launch vehicle Ariane 5, under contract to the European Space Agency (ESA).
Cutaway of Ariane 5 ES heavy launcher fairing. Image provided by Arianespace.
Oversight of the Galileo constellation was transferred from the ESA to the European GNSS Agency (GSA) in July 2017, making this launch the first Galileo launch to be presided over by the GSA, with full responsibility for the operation of satellites 19-22 after their separation from the launch vehicle.
The mission’s duration from liftoff to separation was 3 hours and 55 minutes. Galileo came online in December 2016, and the constellation’s next four satellites are due to be deployed in mid-2018.
Flight VA240 tech specs
The launcher’s attitude and trajectory are controlled by the two onboard computers, located in the Ariane 5 vehicle equipment bay.
About seven seconds after start of the ignition of the main stage cryogenic engine at T-0, the two solid-propellant boosters 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.
A rendering of an Ariane 5 ES heavy launcher. Image provided by Arianespace.
The flight of the Ariane 5 lower composite, comprising two solid boosters and the cryogenic main stage, lasted about nine minutes. This stage then separated from the upper stage and fell back into the Pacific Ocean, off the coast of Peru. The storable propellant upper stage then ignited its own engine, to bring the upper composite – comprising the Galileo satellites and their dispenser – into a transfer orbit.
Following this initial ignition, the upper composite was spun up for a ballistic phase lasting 3 hours and 8 minutes. At a predetermined point in this orbit, the upper stage again ignited its engine for a little more than six minutes, to reach a circular separation orbit. Once stabilized, the dispenser released the first two satellites, followed by the second pair 20 minutes later. The upper stage waspassivated 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 kilometres.
At orbital injection, the launcher will have attained a velocity of approximately 3,000 meters/sec-ond, and will be at an altitude of 22,925 kilometres, 300 kilometres under Galileo’s operational orbit.
