The 15th flight of Ariane 5 is scheduled for April 8. Photo: ESA

Arianespace is setting up for a crucial flight next week of the Ariane 5 rocket that promises to be widely watched throughout the aerospace industry after the last mission of the heavy-lift booster ended in failure and prompted a program-wide review.

The launch provider and its engineering team have worked over the past few months checking hardware and designs of the Ariane 5G basic version of the rocket after an upgraded configuration -- capable of carrying 10 metric tons into geosynchronous transfer orbit -- failed to deliver two payloads in December.

The Ariane 5 ECA that experienced the malfunction has been grounded indefinitely and will likely carry a dummy cargo next time around instead of a paying customer. Arianespace acknowledges one or possibly two test flights may be needed before the 10-ton Ariane 5 version can enter commercial service.

Engineers traced the cause of the botched Dec. 11 launch to a cooling system issue on the first stage's Vulcain 2 main engine. Cooling loops lining the nozzle sprouted a leak, which led to overheating of the engine bell and a loss of integrity. The rocket then flew out of control and impacted in the Atlantic Ocean offshore of the South American launch site.

A Vulcain 2 cryogenic main engine. Photo: Snecma/studio Pons

Investigators ordered officials to not only look into the Ariane 5 ECA Vulcain 2, but also to examine the predecessor Vulcain 1 of the Ariane 5G, even though no faults or problems were located in that design.

This review delayed a number of missions slated for the Ariane 5, most notably ESA's Rosetta comet probe that was due for launch in a specific science window in January. Rosetta is now scheduled to leave Earth no sooner than early 2004. Europe's SMART-1 lunar explorer and a number of commercial spacecraft were also pushed back as a result of the investigation and testing than ran into late winter and early spring.

The last time an Ariane 5G had a launch accident was in July 2001 when an early shutdown of the upper stage left two satellites in the wrong orbit. In all, the basic version of Ariane 5 has suffered two complete failures and another that reached a lower-than-planned altitude during a qualification flight.

That said, Arianespace has shown confidence in the Ariane 5G by ordering additional rockets while the issues with the Ariane 5 ECA are worked out.

"Ariane 5 Generic will handle the lion's share of missions for the near- and medium-term," said Jean-Yves Le Gall, the Arianespace chief executive officer. "Our board of directors has decided to order more of these vehicles. This year, we should launch eight satellites with five standard Ariane 5s. In 2004, we will maintain the pace with four standard Ariane 5s, plus one or two qualification launches of the 10-ton Ariane 5 version."

The Ariane 5 ECA is considered Arianespace's future since it will be needed to loft heavier cargos. In addition to the changes made to the Vulcain main engine, the Ariane 5 ECA features a powerful new cryogenic upper stage that increases the amount of payload that can be hurled into space.

Waiting for the ride to space next week are two communications spacecraft that are to be injected into a highly elliptical geosynchronous transfer orbit before each maneuver into their respective operational positions.

Riding in the lower position within the confines of the Sylda 5 dual payload adapter is the Galaxy 12 spacecraft for American satellite operator PanAmSat.

An artist's concept of Galaxy 12. Credit: Orbital Sciences

Once in its geostationary orbit slot at 74 degrees West over the nation of Colombia, Galaxy 12 will use its 24 C-band transponders to relay telecommunications traffic ranging from multimedia and data networking to direct-to-home programming.

Galaxy 12 will reach customers across the continental United States as well as Alaska and Hawaii throughout its 15-year design life. The 3,872-pound satellite was build by the Orbital Sciences Corporation of Virginia.

Positioned atop the Sylda 5 is the Insat 3A communications satellite to be operated by the Indian Space Research Organization.

With 18 C-band and 6 Ku-band transponders, Insat 3A will beam broadcasts and communications services to users across the Indian subcontinent from its perch above the Bengal Gulf at 93.5 degrees East longitude.

An artist's concept of Insat 3A. Credit: ISRO

Weighing 6,490 pounds at liftoff, Insat 3A also features instruments to aid in meteorology studies and weather forecasting in India. Another transponder is added for search and rescue applications.

Liftoff of the Ariane 5 is slated for the opening of a 41-minute launch window at 2249 GMT (6:49 p.m. EDT) from the ELA-3 launch pad at the Guiana Space Center in Kourou, French Guiana.

This mission will mark the 159th Ariane launch dating back to 1979, the 15th flight of the Ariane 5 rocket and the second Ariane launch of 2003. It will be the first Ariane 5 voyage since the workhorse Ariane 4 retired in February.