Ariane propulsion from nose to tail
Extremely powerful propulsion systems are needed to tear the Ariane 5 launcher away from Earth's gravity. Safran* companies have risen to this challenge by providing both cryogenic rocket engines (Snecma) and solid rocket motors (Herakles).
Closely watched rocket engines
start of the synchronized (automated) launch sequence. In just over seven minutes, the Ariane 5 heavy-lift launcher will lift off to boost two telecommunications satellites into orbit.
The total weight to be boosted into space is over 775 metric tons, or 1.7 million pounds.
At the Guiana Space Center, the launch base in Kourou, French Guiana (South America), Alain and Guillaume, two Safran propulsion engineers, are excited but still focused on the job at hand. They monitor the operation of the engines powering this huge rocket: the Vulcain 2 cryogenic engine powering the main stage, and the solid rocket motors in the strap-on boosters.
From assembly of these powerplants all the way to ignition, they take part in a series of meticulous checks to make sure no problems occur: leak tightness, electrical connections, torque, valves, telemetry, fluids, etc.
Just four short hours ago, they were still monitoring the very delicate operation of loading main stage propellants and making sure they were correctly pressurized
At T-1', they take part in the final remote checks. They have to stay alert up to the last second, because the stakes, as always, are huge: the latest success of Europe's heavy launcher. Safran's engines* blast this rocket off the launch pad with a combined thrust of nearly 3 million pounds.
4, 3, 2, 1…
The onboard computer starts the ignition sequence for the Vulcain®2 cryogenic engine.
Fueled by liquid propellants (25 metric tons of liquid hydrogen and nearly 150 metric tons of liquid oxygen) in two main-stage tanks, the Vulcain 2 provides part of the liftoff thrust. But its main role comes after liftoff.
Ignition of the two solid boosters
They provide 90% of total liftoff thrust. They each contain some 240 metric tons of solid propellant, a combination of an oxidizer and a fuel.
As it climbs through the atmosphere, the launcher is steered by movable nozzles on the boosters and the Vulcain®2 engine. Steering is provided by servo-actuators, which are also controlled by the onboard computer.
Flight control not only sets the launcher on the right flight path, but also maintains its balance.
The launcher climbs straight up for the first five seconds of flight, then "rotates" in the direction needed to inject its satellites into orbit.
"All systems go" during these decisive early moments of the mission. Alain and Guillaume both breathe a sigh of relief, while staying focused on the next steps in the mission.
of Ariane 5's thrust at liftoff is provided by Safran's boosters
of propellant provided by Safran for each Ariane 5 launch
72 hectares (178 acres)
as large as 150 football fields
T + 2'17''
the boosters are jettisoned
After using up all their propellant, burned at a rate of 3.5 metric tons/second, the solid boosters are jettisoned. The launcher is now at an altitude of nearly 70 km and is continuing its flight at more than 2,000 meters/second (7,200 km/h) – about six times the speed of sound. Once it climbs above the dense lower parts of the Earth's atmosphere, it can also jettison its fairing (the streamlined structured that protects the payload), which no longer serves a purpose.
At 170 km, after some 8 minutes of flight, the main stage engine shuts down and this stage is also jettisoned, with the launcher now traveling at 25,000 km/h. The stage falls back into the Atlantic, off the African coast.
The upper-stage HM7B cryogenic engine, also made by Safran, takes over to provide the speed increase needed to inject the satellites into orbit. Tracked by Alain and Guillaume, the HM7B operates for over 16 minutes, increasing the launcher's speed to 33,500 km/h!
At about 27 minutes after liftoff and an altitude of more than 1,000 km, the first satellite is released. It will be followed eight minutes later by the second satellite. Mission accomplished! Back at the launch base, everybody shakes hands and applauds. The Safran team joins in their enthusiasm, but they're already planning ahead for the next launch.