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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.
This begins an 81-minute coast before igniting again to circularize the orbit at 2048 GMT (4:48 p.m. EDT).
We will pause our coverage now while the Fregat is in a ballistic coast phase.
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.
It is currently 3:45 p.m. in French Guiana.
The four 700-kilogram O3b satellite are being configured for launch.
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.
See our launch timeline for more details.
"I think satellite launches are unique, and this one obviously is a very important moment for O3b," Collar said. "There's a real feeling of building excitement. We've got a bunch of our customers down here with us, and we took them right up to the launch pad this morning and had them get really get up close and personal with the rocket, with our satellites, and with the fairing. It makes it very real for them and to see that connection was magical for us. It's a great feeling of excitement here."
O3b's mission is to provide high-speed Internet connectivity to the developing world. The satellites fly in a unique orbit 5,000 miles over the equator, reaching customers in a band between 45 degrees north and 45 degrees south latitude.
The satellites host Ka-band antennas to broadcast services to customers out of reach of terrestrial broadband networks, boosting data throughput and connection speeds in homes, businesses, schools and hospitals.
O3b's name is short for the "other 3 billion," referencing the approximate number of people without reliable, high-speed Internet connections.
Today's launch will send up the second set of four satellites for O3b. The identical spacecraft, built by Thales Alenia Space of Italy, weigh about 700 kilograms, or 1,543 pounds at launch.
The satellites launching today will join four satellites put in orbit on another Soyuz flight in June 2013.
"We need eight satellites up in orbit in order to provide the full global coverage. We've already launched commercial service on the first four, but we're limited in the number of places on Earth that we can provide service with only four satellites," Collar said. "With four more, we can now truly go global and deliver service to all of the customer that we have signed and all the prospects that we have in our pipeline.
"It's very important because it's essentially the launch that allows us to launch full commercial service and really start rolling out the highly differentiated value proposition that we've got for our customers," Collar said.
According to Collar, the satellites will be in service around the first of September after a month of in-orbit testing and maneuvers required to put the spacecraft in the correct positions within O3b's constellation.
"By the first of September, we will be lighting up services on the full constellation," Collar said.
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 morning's launch is the eighth 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.
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.
Some statistics on today's flight:
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.
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 1855:56 GMT (2:55:56 p.m. EDT; 3:55:56 p.m. local time). If weather or technical issues prevent an on-time launch, there is another one-second opportunity at 1928:56 GMT (3:28:56 p.m. EDT; 4:28:56 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 in August. The satellites join another quartet launched for O3b in June 2013.
The satellites launching Thursday will give O3b near-global reach, serving 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. If launch occurs in the first opportunity Thursday, deployment of the satellites will occur two-at-a-time at 2056 GMT (4:56 p.m. EDT) and 2118 GMT (5:18 p.m. EDT), according to Arianespace.
The launch is targeting an orbit with an altitude of about 4,865 miles and an inclination of 0.04 degrees.
The satellites will beam high-speed connectivity to customers out of reach of terrestrial networks, an aspiration spelled out in the company's name, which stands for the "other three billion," referring to the number of people without access to the Internet.
The startup is based in Britain's Channel Islands.
Thursday's launch will put O3b's second quartet of satellites into orbit, following launch of the first four spacecraft in June 2013.
It will mark the eighth flight of Russia's venerable Soyuz launcher from the European-run Guiana Space Center on the northern coast of South America. Soyuz flights from French Guiana are managed by Arianespace.
Liftoff is set for 1855:56 GMT (2:55:56 p.m. EDT) from the purpose-built Soyuz launch pad at the space base. Launch is scheduled for 3:55 p.m. local time in French Guiana.
If weather or a technical problem prevents an on-time liftoff, a second instantaneous launch opportunity is available at 1928:56 GMT (3:28:56 p.m. EDT).
Rollout operations began around sunrise Monday, keeping with tradition dating back to the dawn of Russia's space program.
The three-stage rocket -- missing its payload fairing and Fregat-MT upper stage -- was transferred laying down on top of a transporter-erector system on rail tracks for the 700-meter (2,300-foot) journey from its integration building to the launch pad.
By midday, the Soyuz was lifted vertical over the launch pad's cavernous flame trench carved out of granite bedrock. The rocket is suspended in place by four large support arms.
Technicians will roll the launch pad's mobile service gantry around the Soyuz rocket later Monday to prepare for the arrival of the mission's payload.
Ground crews planned to transport the four O3b satellites and the Fregat upper stage from a nearby clean room to the launch pad Monday evening for lifting into the facility's gantry. Technicians will delicately maneuver the satellites inside the Soyuz nose shroud over the launcher's third stage overnight. 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.
The Fregat upper stage will release the four spacecraft more than two hours after liftoff in a unique orbit about 5,000 miles over the equator.
O3b satellites will reach customers across the planet between 45 degrees north and south latitude. Officials say O3b offers the benefits of fiber-optic lines without the costs to maintain them.
The second launch for O3b Networks was delayed from September 2013 to allow engineers to investigate a problem with the first set of satellites launched last year.
The four satellites were already at the launch base for liftoff in September, but officials elected to ship the spacecraft back to their factory at Thales Alenia Space in Rome to repair a defect in their communications systems.
O3b launched commercial service with its four in-orbit satellites in the Cook Islands in March.
The company says tests with customers have attained throughput of up to 1.6 gigabits per second and round trip latency below 150 milliseconds, beyond the system's designed capabilities.