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WEDNESDAY, AUGUST 28, 2013 A European Ariane 5 rocket is on the launch pad after a 1.7-mile rail journey this morning at the Guiana Space Center in South America.

The 17-story launcher arrived at the launch pad around midday after being towed from its final assembly building by a heavy-duty Titan truck.

After its arrival at the ELA-3 launch zone near the Atlantic coast of French Guiana, the Ariane 5 rocket was to be connected to the launch pad via electrical, communications and plumbing lines ahead of the start of the launch countdown early Thursday.

The launcher's payload fairing contains the Eutelsat 25B/Es'hail 1 and GSAT 7 communications satellites for satellite operators Eutelsat and Es'hailSat - of Paris and Qatar - and the Indian Navy.

It will mark the fourth of five planned Ariane 5 launches this year, and the 71st Ariane 5 flight overall since 1996.

Liftoff is scheduled for 2030 GMT (4:30 p.m. EDT; 5:30 p.m. local time) at the opening of a 50-minute launch window.

Final Ariane 5 countdown procedures are scheduled to begin around 0900 GMT (5 a.m. EDT). A check of electrical systems was scheduled to occur around 1300 GMT (9 a.m. EDT).

Workers will also put finishing touches on the launch pad, including the closure of doors, removal of safety barriers and configuring fluid lines for fueling.

The launch team will begin the process to fuel the rocket with super-cold liquid hydrogen and liquid oxygen propellants at 1540 GMT (11:40 a.m. EDT). First, ground reservoirs will be pressurized, then the fuel lines will be chilled down to condition the plumbing for the flow of super-cold liquid hydrogen and liquid oxygen, which are stored at approximately minus 423 degrees Fahrenheit and minus 298 degrees Fahrenheit, respectively.

It will take approximately two hours to fill the Ariane 5 core stage tanks.

A similar procedure for the Ariane 5's cryogenic upper stage will commence at 1640 GMT (12:40 p.m. EDT).

Chilldown conditioning of the Vulcain 2 first stage engine will occur at 1740 GMT (1:40 p.m. EDT), and a communications check between the rocket and ground telemetry, tracking and command systems is scheduled for 1920 GMT (3:20 p.m. EDT).

The computer-controlled synchronized countdown sequence will begin seven minutes before launch to pressurize propellant tanks, switch to on-board power and take the rocket's guidance system to flight mode.

The Vulcain 2 engine will ignite as the countdown clock reaches zero, followed by a health check and ignition of the Ariane 5's solid rocket boosters seven seconds later to send the 1.7 million-pound launcher skyward.

Five seconds after blastoff, the rocket will begin pitching east from the ELA-3 launch pad, surpassing the speed of sound less than a minute into the mission. The Ariane 5's twin solid rocket boosters will jettison 2 minutes and 23 seconds after liftoff.

Once above the dense atmosphere, the launcher's payload fairing will fall away at an altitude of about 66 miles. The Ariane 5's first stage will shut down 8 minutes, 46 seconds after liftoff, followed moments later by stage separation and ignition of the hydrogen-fueled cryogenic HM7B upper stage engine.

The rocket's upper stage will fire for nearly 16 minutes, accelerating to a velocity of 20,969 mph miles to reach an orbit with a planned high point of 22,325 miles and a targeted low point of 154 miles.

The release of Eutelsat 25B/Es'hail 1 is scheduled for 27 minutes, 45 seconds. The rocket's barrel-shaped Sylda 5 dual-payload adapter will be jettisoned a few minutes later.

GSAT 7 will separate from the lower portion of the payload stack at 34 minutes, 26 seconds.

THURSDAY, AUGUST 29, 2013 1755 GMT (1:55 p.m. EDT) Fueling of the Ariane 5 rocket with cryogenic liquid hydrogen and liquid oxygen is underway, and chilldown of the first stage's Vulcain 2 main engine has begun to prepare the engine for its 9-minute firing in today's mission.