2126 GMT (4:26 p.m. EST)
Stephane Israel, Arianespace's chairman and CEO, confirms all four O3b satellites are healthy after today's launch. But the Soyuz rocket's Fregat upper stage did not send signals to a ground station as expected.

The launch company is waiting on data on the orbit achieved by the rocket before confirming the mission was a full success.

Today's launch is the first flight of a Soyuz/Fregat from French Guiana since an Aug. 22 launch failure that left two European Galileo navigation satellites in the wrong orbit. Arianespace initially declared that launch successful, only to learn later the Fregat upper stage ran into trouble during the flight.

2109 GMT (4:09 p.m. EST)
Telemetry is being received from the second pair of O3b satellites, according to Arianespace.
2059 GMT (3:59 p.m. EST)
The second pair of O3b satellites should be deploying now from the Fregat upper stage.
2056 GMT (3:56 p.m. EST)
Arianespace confirms signals have been received from the first two O3b satellites, and they are flying in the correct orbit.
2051 GMT (3:51 p.m. EST)
The Fregat upper stage should now be firing attitude control thrusters to move away from the two satellites it dropped off earlier. The separation burn will be followed by deployment of the remaining two satellites.
2049 GMT (3:49 p.m. EST)
Arianespace's commentator says ground controllers may have received signals from two of the O3b satellites.
2038 GMT (3:38 p.m. EST)
The third burn of Fregat should now be complete, and the first two O3b satellites should have separated by now. Arianespace is waiting for telemetry to confirm the events occurred.
2029 GMT (3:29 p.m. EST)
The Fregat engine should be firing again to circularize its orbit at an altitude of 7,830 kilometers (4,865 miles) with an inclination of 0.04 degrees.
2020 GMT (3:20 p.m. EST)
The third burn of the Fregat upper stage is scheduled to begin in about 9 minutes. This engine firing should last about 5 minutes to inject the O3b satellites into a near-circular orbit about 4,865 miles above Earth.

Two satellites will jettison from the dispenser shortly after the burn is complete, then Fregat's thrusters will briefly reignite to achieve appropriate spacing between the satellites before deployment of the other two spacecraft.

1910 GMT (2:10 p.m. EST)
T+plus 33 minutes. The Fregat upper stage has turned off its engine again after reaching an elliptical transfer orbit flying more than 11,400 kilometers downrange from the Guiana Space Center.

Arianespace says they have confirmed a nominal shutdown of the Fregat engine via telemetry.

This begins an 81-minute coast before igniting again to circularize the orbit at 2029 GMT (3:29 p.m. EST).

We will pause our coverage now while the Fregat is in a ballistic coast phase.

1900 GMT (2:00 p.m. EST)
T+plus 23 minutes. The Fregat engine has ignited again as planned, now flying over Africa.
1851 GMT (1:51 p.m. EST)
T+plus 14 minutes, 30 seconds. The Fregat engine has shut down on time. This first of four burns was supposed to place the O3b satellites into a parking orbit with a high point of 141 miles (227 kilometers), a low point of 95 miles (153 kilometers), and an inclination of 5.15 degrees.

The second Fregat burn will begin at T+plus 22 minutes, 50 seconds. These maneuvers are required to put the O3b satellites in the correct circular orbit over the equator at an altitude of 4,865 miles.

1848 GMT (1:48 p.m. EST)
The hydrazine-fueled Fregat upper stage is now firing to propel itself into a parking orbit. This burn should last about 4 minutes.
1846 GMT (1:46 p.m. EST)
T+plus 9 minutes, 55 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, 23 seconds to boost the O3b satellites into a parking orbit.
1846 GMT (1:46 p.m. EST)
T+plus 9 minutes. The Soyuz is now flying in range of a ground station in Brazil as the third stage engine prepares for shutdown.
1844 GMT (1:44 p.m. EST)
T+plus 7 minutes. The third stage RD-0124 engine is firing as planned. Altitude is 181 kilometers and downrange distance is 986 kilometers.
1842 GMT (1:42 p.m. EST)
T+plus 5 minutes, 15 seconds. At an altitude of 160 kilometers and a velocity of 3.92 kilometers per second, the Soyuz rocket's second stage has shut down and separated. Third stage ignition is also confirmed.
1841 GMT (1:41 p.m. EST)
T+plus 4 minutes. The rocket's 13.5-foot ST-type nose fairing has jettisoned now that the launcher is out of the lower atmosphere.
1839 GMT (1:39 p.m. EST)
T+plus 2 minutes. The four strap-on boosters of the Soyuz rocket have separated at an altitude of approximately 37 miles. The core stage continues firing.
1837 GMT (1:37 p.m. EST)
LIFTOFF of the Soyuz rocket with four satellites for O3b Networks, linking the developing world via broadband.
1836 GMT (1:36 p.m. EST)
T-minus 15 seconds. Ignition of the Soyuz rocket's engines.
1836 GMT (1:36 p.m. EST)
T-minus 1 minute. The Soyuz will transition to internal power 40 seconds before liftoff.
1835 GMT (1:35 p.m. EST)
T-minus 2 minutes. The upper umbilical mast servicing the Soyuz rocket's four satellite payloads is being disconnected from the launcher.
1833 GMT (1:33 p.m. EST)
T-minus 4 minutes. The exact liftoff time is 1837:00 GMT (1:37:00 p.m. EST; 3:37:00 p.m. local time).
1831 GMT (1:31 p.m. EST)
T-minus 6 minutes. The launch key has been installed inside the launch control center, beginning the Soyuz rocket's synchronized countdown sequence.
1829 GMT (1:29 p.m. EST)
T-minus 8 minutes. The Soyuz rocket family has flown 1,832 times since the 1950s, and this is the 10th time the venerable launcher will fly from outside the territory of the former Soviet Union.
1826 GMT (1:27 p.m. EST)
T-minus 10 minutes. All systems are reporting a "go" status for an on-time launch this afternoon.

It is currently 3:27 p.m. in French Guiana.

1825 GMT (1:25 p.m. EST)
The official video stream from the Guiana Space Center is beginning now.

The four 700-kilogram O3b satellite are being configured for launch.

1822 GMT (1:22 p.m. EST)
T-minus 15 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.

1807 GMT (1:07 p.m. EST)
T-minus 30 minutes. If weather or a technical snag prevents liftoff at 1837 GMT (1:37 p.m. EST), there is another instantaneous launch opportunity 33 minutes later at 1910 GMT (2:10 p.m. EST). This time allows the Soyuz rocket to reconfigure its inertial guidance and navigation system for a new launch trajectory.
1750 GMT (12:50 p.m. EST)
The 174-foot-tall mobile gantry at the Soyuz launch pad has been retracted to launch position about 260 feet from the rocket.
1737 GMT (12:37 p.m. EST)
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.

Today's launch is the 10th 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.

1707 GMT (12:07 p.m. EST)
90 minutes until launch. 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 the O3b 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 an easterly 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 three burns before releasing the first pair of O3b satellites into a circular orbit 4,865 miles (7,830 kilometers) above Earth over the equator.

See our launch timeline for more details.

1637 GMT (11:37 a.m. EST)
T-minus 2 hours. Fueling of the three Soyuz core stages continues with no problems. Some statistics on today's flight:

Some statistics on today's flight:

1450 GMT (9:50 a.m. EST)
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.

0830 GMT (3:30 a.m. EST)
Arianespace has authorized Thursday's launch of a Soyuz rocket from French Guiana with the third quartet of broadband communications satellites for O3b Networks.

Liftoff from the Soyuz launch pad in the northwest sector of the Guiana Space Center on the northern coast of South America is set for 1837 GMT (1:37 p.m. EST; 3:37 p.m. local time).

Four satellites for O3b Networks Ltd. are inside the Soyuz rocket's nose fairing, ready to begin testing in orbit before going into service early next year. The satellites join eight satellite launched on two previous Soyuz liftoffs from French Guiana in June 2013 and July 2014.

The satellites launching Thursday will expand O3b's reach, giving the company access to customers in nearly 180 countries from a unique equatorial orbit 5,000 miles above Earth.

The Soyuz rocket will fly in the Soyuz 2-1b version - also known as the Soyuz ST-B configuration, with a modernized digital control system, an upgraded RD-0124 third stage engine and an ST-type payload fairing with a diameter of 13.4 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 east 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 O3b satellites on a suborbital trajectory before giving way to the Fregat engine for a series of burns to put the spacecraft in the proper orbit.

Deployment of the satellites will occur two-at-a-time at 2037 GMT (3:37 p.m. EST) and 2059 GMT (3:59 p.m. EST), according to Arianespace.

The launch is targeting an orbit with an altitude of about 4,865 miles and an inclination of 0.04 degrees.

Four satellites designed to broadcast high-speed Internet signals to the developing world are mounted on top of a Russian-made Soyuz rocket for liftoff Thursday from the Guiana Space Center in South America.

Read our full story.

Russian rocket technicians working in the French Guiana jungle transported a three-stage Soyuz booster to its launch pad Monday and erected it upright for liftoff Thursday with four communications satellites for O3b Networks.

Read our full story.