By Dr David Whitehouse BBC News Online science editor

Engineers and officials are still unsure what caused Europe's new Ariane 5-ECA rocket to fail just three minutes into its maiden flight.

Le Gall: Confident about the future

The launcher blew up when it started to veer off course, dumping two satellites worth more than 600m euros in the Atlantic Ocean.

At a press conference held by rocket operator Arianespace in Kourou, French Guiana, officials said they were establishing an independent commission to look into the accident of Flight 157.

Engineers said there were problems reported during the flight from the new Vulcain-2 rocket motor but they are at present unsure if that was the cause of the failure.

Current difficulties

Officials were adamant that the next flight of Ariane 5, using a "classical" non-enhanced version of the booster, would go ahead in January when the Rosetta comet lander would be launched.

They said the launch of a satellite on an Ariane 4 next Tuesday would also proceed as normal.

"The Flight 157 failure has not affected Arianespace's determination to move ahead and to overcome our difficulties," Arianespace chief executive officer Jean-Yves Le Gall said.

"We will not change our overall strategy, and we are confident about the future."

Pressure problems

At the press conference, Arianespace officials went through the facts of the failure, as they are currently known.

The sequence of failure has been established if not the cause

The first anomaly occurred 96 seconds into the mission when there was a slight drop in the pressure of the coolant system of the Vulcain-2 engine that powers the rocket for the first nine minutes. Engineers are unsure if this is significant.

From 178 seconds into the flight to 186 seconds, the engine speed changed and "a significant flight control perturbation occurred".

At 187 seconds, the faring covering the payload was jettisoned, as expected.

At 196 seconds, a major problem developed in the Vulcain-2 engine but engineers are unsure if its failure was due to a fault inside the rocket engine or in its environment.

The rocket was then in an "erratic trajectory" and started to fall from its altitude of 150 km.

Self-destruct system

At 456 seconds, it had fallen to just 69 km when its auto-destruct mechanism activated.

Wreckage from the rocket fell into the Atlantic, several hundred kilometres off the coast of French Guiana. However, the parachutes that the first two stages would have used to ditch into the sea for later recovery did operate.

This has raised hopes that the boosters can be recovered and examined to see if they contain any clues to the failure. A search for them is underway.

Officials were keen to point out that the January launch of the Rosetta comet mission would go ahead as it is using the "classical" version of Ariane 5 and not the beefed-up version that had failed on Wednesday night.

Weeks away

Rosetta, which will land a spacecraft on Comet Wirtanen, has to take off during a short window starting on 12 January.

The Rosetta mission to land on a comet should go ahead

The commission reviewing the failure will report as soon as possible if Wednesday's loss has any repercussions for the Rosetta launch but officials are confident it will not.

Two launches of the enhanced Ariane 5 were planned for 2003.

At present, they have not officially been postponed as the accident commission is expected to deliver its findings in a few weeks, allowing plenty of time for decisions to be made about forthcoming flights.

The Ariane 5-ECA was carrying Stentor, an experimental telecommunications satellite for the French space agency, CNES, and Hot Bird7, a Eutelsat television broadcast satellite. Both satellites were insured.