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

The Ariane 5 rocket suffered major engine trouble before going out of control and exploding over the Atlantic Ocean during Wednesday's botched launch, Arianespace officials said today.

After lifting off from its jungle launch pad in French Guiana, South America, the European-made rocket was headed for a 36-minute trek to Earth orbit carrying a cargo of two communications satellites.

It was the maiden flight of the Ariane 5 ECA rocket, a more powerful version of the Ariane 5 with a modified first stage engine and brand new cryogenic upper stage. The enhancements allow the new vehicle to loft nearly twice the payload than the previous Ariane 5 configuration.

The first hint of problems during Wednesday's flight occurred at 96 seconds when telemetry from the rocket showed a slight pressure decrease in the Vulcain 2 first stage engine's cooling system.

The flight continued as the twin solid rocket boosters burned out and were jettisoned from the Ariane 5's cryogenic first stage at +2 minutes, 17 seconds.

Between +2 minutes, 58 seconds and +3 minutes, 6 seconds, a "major problem" in the Vulcain 2's firing was observed and the rocket's flight control was disturbed.

"During that period (there was) a problem in operating of the engine, which was at the origin, of course, of the problem with the control of the launch," Arianespace CEO Jean-Yves Le Gall, speaking through a translator, told reporters today. "But right now the reasons behind this problem in the engine have not been clearly established."

At +3 minutes, 7 seconds, the rocket's nose cone that shielded the payload during the climb through Earth's atmosphere was jettisoned. However, the rocket wasn't properly positioned when the two-piece shroud separated.

"The maneuver of fairing jettisoning should happen when the launcher has an attitude and trajectory which are as stable as possible. During jettisoning of the fairing, the trajectory and the attitude were not stabilized."

Immediately after the nose cone was released, the rocket lost control at altitude of about 150 km.

"From that moment on, it started a fully erratic trajectory."

By +7 minutes, 35 seconds, the destruct explosives on the Ariane 5 were triggered to break up the pieces of the doomed rocket.

"The launcher gets in the situation where the safeguard procedure must announce the order to destroy the launcher...When the destruction order is given, the launcher is at an altitude of 69 km and landed, of course, in the Atlantic Ocean at 800-1,000 km away from Guiana.

"These are the facts. This is what happened yesterday in the evening. Today, my teams are going on working to try and understand in a more precise way why we had this unfortunate series of events that ended in the failure of the mission."

Le Gall said it is too soon to pin the blame entirely on the Snecma-made Vulcain 2 engine.

"It's a bit early to say that the Vulcain engine failed. We observed there was a problem in the way it operated. It was disturbed. But we cannot say whether it's due to a failure of the engine itself.

"The Vulcain engine operates in a very specific environment and what we observed here, as far as the problem is concern, might have a different origin. The origin might not be due to a wrong operating of the Vulcain engine."

An independent investigation commission will be set up Friday and begin its work Monday.

"This commission will have two assignments. It will have to clearly explain and tell us if what happened will have consequences on the Ariane 5 launcher -- its basic version. Second, it will us when we can start again launching this Ariane 5 version. We will analyze the results immediately when we get them."

That basic version -- the Ariane 5G with the original Vulcain engine that has flown multiple times -- is scheduled to launch the European Space Agency's Rosetta comet spacecraft on January 12. Officials and scientists are faced with just 20 days to launch the ambitious robotic mission on the proper course to the comet.

"(The failure board) will have to see whether the anomaly we had yesterday will or will not have consequences on our basic, classical Ariane 5. It seems no, but that has to be confirmed.

"Rosetta will be launched. That is what is most probable. We have to understand what happened first, but we will launch it on the 12th of January as planned."

Next Tuesday's planned flight of the Ariane 4 rocket is not expected to be impacted. It will place the Lockheed Martin-built NSS 6 telecommunications satellite into space for operator New Skies Satellites.

"Yesterday's anomaly has no consequence whatsoever on this particular launch. I discussed that point yesterday with our client and our client did confirm that we would launch."

This was the fourth Ariane 5 mishap in 14 flights.

The first Ariane 5 met a disastrous end about 40 seconds after blastoff in June 1996 when a guidance system error caused the massive booster to go out of control and explode. The Ariane 502 rocket did achieve orbit in October 1997, but was also lower than planned due to a premature shutdown of the first stage main engine. After a final test flight was successfully flown, the next-generation rocket made six commercial missions before failing in July 2001 due to an upper stage engine malfunction.

The Ariane 4 has just two more launches left before it is retired, a decision Arianespace made in favor of Ariane 5. Getting the Ariane 5 back in full service is critical for the company's survival.

"We are determined to go on. We've had difficulties in the past, we had another difficulty today. It's a difficult job. We'll find the solution, overcome the difficulty and we will go on."