0557 GMT (1:57 a.m. EDT)
Spacecraft separation! Both Galileo satellites have been released from the Fregat upper stage.

Arianespace chairman and CEO Stephane Israel says it will take another 30 minutes or so to verify the satellites are in the correct orbit and confirm the success of tonight's mission.

Ground controllers will analyze signals from the satellites to determine their location in space.

The long wait to confirm the outcome of the launch stems from an embarrassing premature announcement of a successful flight in August 2014, when a closer look at data revealed the Fregat stage placed two Galileo satellites in an off-target orbit.

0552 GMT (1:52 a.m. EDT)
T+plus 3 hours, 47 minutes. Arianespace confirms the successful ignition and cutoff of the second Fregat burn. This firing was designed to circularize its orbit at about 14,600 miles altitude.
0540 GMT (1:40 a.m. EDT)
Deployment of the two Galileo satellites is expected at 0556 GMT (1:56 a.m. EDT).
0537 GMT (1:37 a.m. EDT)
T+plus 3 hours, 29 minutes. The second ignition of the Fregat upper stage is less than 10 minutes away.
0232 GMT (10:32 p.m. EDT on Thurs.)
T+plus 24 minutes. The Fregat engine has shut down on time. This first of two burns was supposed to place the Galileo satellites into a parking orbit with a low point just above the atmosphere and a high point of about 23,500 kilometers (14,600 miles).

The second Fregat burn will begin at about T+plus 3 hours, 39 minutes to place the Galileo satellites into a circular orbit at an altitude of 23,522 kilometers (14,619 miles) at an inclination of 57.39 degrees.

0224 GMT (10:24 p.m. EDT on Thurs.)
No problems reported so far in this burn of the Fregat-MT main engine.
0219 GMT (10:19 p.m. EDT)
The hydrazine-fueled Fregat upper stage is now firing to propel itself into a transfer orbit. This burn should last about 13 minutes.
0217 GMT (10:17 p.m. EDT on Thurs.)
T+plus 9 minutes, 40 seconds. The Soyuz third stage and Fregat upper stage have now separated. The first burn of the Fregat upper stage begins at T+plus 10 minutes, 24 seconds to boost the Galileo satellites into an elliptical transfer orbit.
0217 GMT (10:17 p.m. EDT on Thurs.)
T+plus 9 minutes. The Soyuz is now flying in range of a ground station in the Atlantic Ocean as the third stage engine prepares for shutdown.
0215 GMT (10:15 p.m. EDT on Thurs.)
T+plus 7 minutes, 30 seconds. The third stage RD-0124 engine is firing as planned. Altitude is 182 kilometers and downrange distance is 1,185 kilometers.
0213 GMT (10:13 p.m. EDT on Thurs.)
T+plus 5 minutes, 15 seconds. The Soyuz rocket's second stage has shut down and separated. Third stage ignition is also confirmed.
0212 GMT (10:12 p.m. EDT on Thurs.)
T+plus 4 minutes. The rocket's 13.4-foot ST-type nose fairing has jettisoned now that the launcher is out of the lower atmosphere.
0210 GMT (10:10 p.m. EDT on Thurs.)
T+plus 2 minutes. The four strap-on boosters of the Soyuz rocket have separated at an altitude of approximately 30 miles. The core stage continues firing.
0208:10 GMT (10:08:10 p.m. EDT on Thurs.)
LIFTOFF of a Soyuz rocket, carrying two Galileo navigation satellites to grow Europe's positioning network into double digits.
0207 GMT (10:07 p.m. EDT on Thurs.)
T-minus 15 seconds. Ignition of the Soyuz rocket's engines.
0207 GMT (10:07 p.m. EDT on Thurs.)
T-minus 1 minute. The Soyuz will transition to internal power 40 seconds before liftoff.
0206 GMT (10:06 p.m. EDT on Thurs.)
T-minus 2 minutes. The upper umbilical mast servicing the Soyuz rocket's two satellite payloads is being disconnected from the launcher.
0204 GMT (10:04 p.m. EDT on Thurs.)
T-minus 4 minutes. The exact liftoff time is 0208:10 GMT (10:08:10 p.m. EDT; 11:08:10 p.m. local time).
0202 GMT (10:02 p.m. EDT on Thurs.)
T-minus 6 minutes. The launch key has been installed inside the launch control center, beginning the Soyuz rocket's synchronized countdown sequence.
0200 GMT (10:00 p.m. EDT on Thurs.)
T-minus 8 minutes. The Soyuz rocket family has flown 1,846 times since the 1950s, and this is the 12th time the venerable launcher will fly from outside the territory of the former Soviet Union.
0158 GMT (9:58 p.m. EDT on Thurs.)
T-minus 10 minutes. All systems are reporting a "go" status for an on-time launch this afternoon.

It is currently 10:58 p.m. in French Guiana.

0152 GMT (9:52 p.m. EDT on Thurs.)
Today's launch will use the Soyuz 2-1b, or Soyuz ST-B, version of the venerable Russian booster, featuring advanced digital avionics and an upgraded RD-0124 third stage engine. Thrust from 32 engine nozzles on the first stage will generate more than 900,000 pounds of thrust at liftoff.
0148 GMT (9:48 p.m. EDT on Thurs.)
The official video stream from the Guiana Space Center is beginning now.

The two 715-kilogram (1,576-pound) Galileo satellite are being configured for launch.

0138 GMT (9:38 p.m. EDT on Thurs.)
T-minus 30 minutes. The launch team has loaded more than 500,000 pounds of liquid oxygen and kerosene propellant into the rocket this afternoon, plus hydrogen peroxide to drive the engines' gas turbines and liquid nitrogen to keep the propellant tanks pressurized.

The Soyuz countdown sequence begins 6 minutes, 10 seconds prior to liftoff, then the Fregat upper stage will transition to internal power five minutes before launch.

The umbilical arm servicing the upper stage and payloads will pull away at T-minus 2 minutes, 25 seconds. The Soyuz rocket is operating on internal power at T-minus 40 seconds, and the final servicing mast retracts from the rocket 20 seconds later.

The ignition sequence of the Soyuz rocket's kerosene-fueled core stage and four strap-on boosters begins 17 seconds before liftoff, and all engines should be at full thrust three seconds before launch.

0125 GMT (9:25 p.m. EDT on Thurs.)
The two satellites launching today will expand Europe's growing Galileo navigation system and kick off a series of rapid-fire launches of up to six satellites per year through 2020 to build out the network.

The 1,577-pound satellites mounted side-by-side on top of the Soyuz rocket were manufactured by OHB System of Bremen, Germany. They carry L-band navigation payloads supplied by Surrey Satellite Technology Ltd.

Once deployed from the launcher's Fregat-MT upper stage, the satellites will extend their solar arrays and begin a week-long phase of initial activations and tests.

The satellites will be allowed to drift into their final positions within Plane A of the Galileo constellation and will enter service in about three months.

The satellites join four other Galileo satellites launched in 2011 and 2012 to validate the network's design -- in space and on the ground.

Two Full Operational Capability, or FOC, satellites launched into the wrong orbit by a Soyuz/Fregat booster in August 2014 are also being incorporated into the Galileo fleet. The satellites should be able to be full-fledged members of the Galileo system even though their orbits do not match the orbits of the network's other spacecraft.

Another pair of satellites launched in March brought the total number of Galileo spacecraft in orbit to eight. Tonight's launch adds the ninth and 10th members.

Fourteen more Galileo satellites are being built and tested to launch on Soyuz and Ariane 5 rockets through 2018 to populate the constellation, which will eventually consist of 30 satellites in orbit at a given time, including spares.

0108 GMT (9:08 p.m. EDT on Thurs.)
One hour until launch.

The European-funded, Russian-built pad is located about eight miles northwest of the Ariane 5 and Vega launch pads at the Guiana Space Center. Engineers selected the Soyuz launch site based on terrain, geology and a location away from Ariane facilities to ensure they did not interfere with each other.

It took three years and cost European governments $800 million to build the Soyuz launch facility, which is known by its French acronym ELS. Other than the 17-story mobile servicing tower and four lightning masts, the launch pad is modeled after the Soyuz launch pad at the Baikonur Cosmodrome in Kazakhstan.

This evening's launch is the 12th Soyuz to fly from ELS.

The Soyuz pad includes blue and yellow umbilical arms and hold-down petals at the base of the rocket. On the back side of the pad is a deep flame trench dug out of granite bedrock. The facility also houses living quarters for Russian workers and a launch control center.

The Soyuz site lies closer to the town of Sinnamary than Kourou, which is more typically associated with the spaceport.

0038 GMT (8:38 p.m. EDT on Thurs.)
90 minutes until launch. Fueling of the Soyuz rocket with kerosene and liquid oxygen is nearing completion. Topping of the Soyuz propellant tanks with liquid oxygen and liquid nitrogen pressurant continues, and filling of the rocket's kerosene tanks is complete.

The next milestone in the countdown will be retraction of the Soyuz rocket's mobile gantry. Engineers are currently configuring the servicing tower to move to a point about 260 feet from the Soyuz rocket.

The Soyuz rocket with Galileo satellites on-board is a modernized version of the venerable Russian launcher with an automated digital control system and an upgraded RD-0124 third stage engine. It also has a flight termination system that can receive commands from safety officials on the ground in the event of a mishap, a key difference between the Soyuz rockets flying from French Guiana and Russian launch sites.

The Soyuz launching this evening is known as the Soyuz ST-B or Soyuz 2-1b configuration.

Other upgrades for Soyuz launchers based in French Guiana include an S-band telemetry system, modifications to cope the the humid tropical climate, and valves in the rocket's fuel tanks to allow empty stages to sink in the Atlantic Ocean. Soyuz launches from Kazakhstan or Russia drop their stages on land.

After liftoff, the rocket will go through pitch and roll programs to align with a northeasterly trajectory from the launch pad near Sinnamary, French Guiana. After a nearly 10-minute flight powered by the Soyuz rocket's three core stages, a Fregat-MT upper stage will take over for two burns before releasing the pair of Galileo satellites into a circular orbit 14,615 miles (23,522 kilometers) above Earth at an inclination of 57.39 degrees.

See our launch timeline for more details.

0008 GMT (8:08 p.m. EDT on Thurs.)
T-minus 2 hours. Fueling of the three Soyuz core stages in French Guiana continues with no problems.

Some statistics on today's flight:

2330 GMT (7:30 p.m. EDT)
The Russian State Commission has convened to review the status of launch preparations and given the "go" to inject kerosene and liquid oxygen propellants into the 151-foot-tall Soyuz rocket, which is housed inside a 174-foot-tall mobile gantry about 8 miles northwest of the spaceport's Ariane 5 and Vega launch facilities.

The launch team has completed electrical checks after turning on the Soyuz rocket's avionics systems, and the process to fill the three-stage launcher with liquid oxygen and kerosene has begun.

Fueling should be complete about two hours before liftoff.

0401 GMT (12:01 a.m. EDT)
Senior managers met Wednesday and gave the green light for the liftoff of a Soyuz rocket late Thursday, carrying the next two Galileo navigation satellites into orbit for Europe's independent navigation system.

The Soyuz ST-B rocket will blast off at 0208:10 GMT Friday (10:08:10 p.m. EDT; 11:08:10 p.m. French Guiana time Thursday), soaring into orbit from the European-run spaceport in French Guiana.

It will mark the 12th launch of the venerable Russian rocket from the Guiana Space Center, and its fifth mission from the tropical space base to serve the Galileo network. The launch is the second Soyuz flight of the year from French Guiana.

Two 1,577-pound (715-kilogram) Galileo navigation satellites built by OHB of Bremen, Germany, are packaged inside the Soyuz rocket's nose cone.

Upgrades to the Soyuz rocket featured on Thursday's launch include a modernized digital flight control system, an RD-0124 third stage engine, and a ST-type payload fairing with a diameter of nearly 13.5 feet.

Following a state commission meeting of mission managers, the Soyuz rocket will be filled with liquid oxygen and kerosene propellants beginning about four hours before liftoff, according to information released by Arianespace, the commercial operator for Soyuz rocket missions in French Guiana.

The launch pad's 174-foot-tall mobile gantry will be retracted about an hour before launch, moving into position about 260 feet from the Soyuz rocket.

After a computerized sequence, the 151-foot-tall launcher will ignite its main engines and blast off, turning northeast from the French Guiana spaceport and shedding strap-on boosters less than two minutes into the mission.

The Soyuz rocket's second and third stages will accelerate a Fregat upper stage and the four Galileo satellites on a suborbital trajectory before giving way to the Fregat engine for two burns to put the spacecraft in the proper orbit.

Deployment of the satellites from a specially-designed dispenser on the Fregat upper stage will occur simultaneously at 0556 GMT (1:46 a.m. EDT), according to Arianespace.

The launch is targeting a circular orbit with an altitude of about 14,615 miles (23,522 kilometers) and an inclination of 57.39 degrees.

The next pair of spacecraft to join Europe's Galileo navigation system are positioned for liftoff late Thursday aboard a Soyuz rocket. These photos chronicle the preparation of the satellites for launch at the Guiana Space Center.

Read our full story.

The next pair of spacecraft to join Europe’s growing Galileo navigation system, a civilian-run analog to the U.S. military’s Global Positioning System, will be added to the tip of a Russian Soyuz booster overnight Monday after the rocket’s rollout earlier in the day in French Guiana.

Read our full story.