An Ariane 5 rocket is due for launch with two spacecraft Friday, hauling into orbit a traditional fixed communications satellite for Intelsat and an adaptable broadband Internet services payload for U.K.-based Avanti Communications.

The Ariane 5 rocket rolled to the launch pad Thursday. Credit: Arianespace

Both satellites will be ejected from the launcher about a half-hour after liftoff, kicking off months of commissioning and testing before officials press the spacecraft into service.

Intelsat 17 will park itself in permanent position 22,300 miles over the equator at 66 degrees east longitude, moving in range of customers in Europe, Africa, the Middle East, India and other parts of Asia.

The 12,214-pound spacecraft was built by Space Systems/Loral and is designed for operations lasting at least 18 years. Intelsat 17 carries C-band and Ku-band transponders for video distribution and other communications services. It will replace Intelsat 702, which launched in 1994 and has surpassed its original design life.

Intelsat 17 will separate from the rocket first, followed more than seven minutes later by the release HYLAS 1, an innovative satellite testing new technological and institutional methods.

HYLAS 1 is the product of a public-private partnership involving the European Space Agency, EADS Astrium, Avanti Communications of the United Kingdom and an Indian contractor.

The spacecraft weighs 5,666 pounds at launch and includes eight Ka-band and two Ku-band transponders. HYLAS stands for Highly Adaptable Satellite, denoting the craft's unique capability of allocating bandwidth and power to meet the ever-changing demands of the marketplace.

HYLAS 1's mission is to beam broadband Internet services to rural areas across Europe from an orbital location at 33.5 degrees west longitude.

Liftoff of the Ariane 5 rocket is scheduled for 1839 GMT (1:39 p.m. EST) from the ELA-3 launch pad in Kourou, French Guiana. The launch window extends until 2154 GMT (4:54 p.m. EDT).

The 166-foot-tall rocket is tailored for dual-payload missions, and Friday's flight will be the Ariane 5's fifth commercial launch so far this year.

Final countdown procedures are scheduled to begin at 0709 GMT (2:09 a.m. EST). A check of electrical systems is expected around 1109 GMT (6:09 a.m. EST), and the launch team will begin fueling the rocket with super-cold liquid hydrogen and liquid oxygen propellants at 1349 GMT (8:49 a.m. EST).

Chilldown conditioning of the Vulcain 2 first stage engine will occur at 1519 GMT (10:19 a.m. EST), and a communications check between the rocket and ground telemetry, tracking and command systems is scheduled for 1729 GMT (12:29 p.m. EST).

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 20 seconds after liftoff.

Once above the dense atmosphere, the launcher's payload fairing will fall away at an altitude of nearly 70 miles. The Ariane 5's first stage will shut down at 8 minutes, 56 seconds, 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 5.8 miles per second to reach an orbit with a planned high point of 22,236 miles and a targeted low point of 155 miles.

The release of Intelsat 17 is scheduled for 27 minutes, 29 seconds. The rocket's barrel-shaped Sylda 5 dual-payload adapter will be jettisoned a few minutes later.

HYLAS 1 will separate from the lower portion of the payload stack at 34 minutes, 51 seconds.