More than half a billion euros (650 million dollars) and Europe's bid to rival the United States and Russia in the lucrative market for satellite launches will be riding on the mammoth rocket.

"The consequences of a failure would be quite serious," Francois Auque, chief executive officer of EADS Space, the subsidiary of the European aeronautics and space giant EADS, said on Friday.

"We need a successful 10-tonne launcher in order to stay competitive."

EADS has a 27.03-percent stake in Arianespace, which operates and markets the Ariane range of launchers designed by the European Space Agency (ESA).

The Ariane 5 ECA, with a capacity to place up to 10 tonnes of payload into orbit, failed catastrophically on its maiden flight in December 2002.

It veered offcourse after liftoff and had to be blown up over the Atlantic, destroying its half-billion-dollar satellite cargo.

A painstaking inquiry into the disaster pinned the blame on a cooling system in the ECA's Vulcain-2 motor, an upgraded version of the Vulcain-1 engine that powers the standard 6.8-tonne Ariane 5.

Backed by pledges of 550 million euros (715 million dollars) from ESA's stakeholder nations, a programme was initiated to fix the problem.

It culminates on Saturday -- launch window between 1949 and 2110 GMT -- when the ECA is scheduled to take aloft a triple payload weighing 8.3 tonnes.

The piece of commercial freight is the 3.6-tonne satellite XTAR-EUR, due to provide government and military communications for the United States and Spain in a footprint ranging from eastern Brazil to Singapore.

There is also a small Dutch satellite, Sloshsat, weighing 127 kilospounds) to test the dynamics of fluids in orbit. The third item is called Maqsat-B2 -- essentially a 3.6-tonne water container, which is being added to help boost the payload and test the rocket's handling.

The commercial interest in the ECA is productivity. A launch costs about 150 million euros (195 million dollars), so if two or three satellites can be launched in one go, the costs per satellite are far cheaper than with a single payload.

US corporations have likewise gone in for the huge end of the market.

There is Boeing's Delta 4 Heavy, which made its test flight last December 21, with the capacity to put between 6.4 and 24 tonnes of cargo into space depending on the distance to orbit.

There is also Lockheed Martin's Atlas 5, which made its inaugural flight in 2002, and which has an advertised payload capacity of between 4.9 and 20.5 tonnes.

However, apart from launches for government agencies, the market remains somewhat in the doldrums, partially because the bust of the late 1990s telecoms boom left a lot of cheap, surplus satellite capacity around.

In 2003, Arianespace recorded profits of 9.2 million euros (11.96 million dollars), after three successive years of losses, on a turnover of 559 million euros (726 million dollars). It expects to break even for 2004, with a turnover of about 700 million euros (910 million dollars), Arianespace's CEO, Jean-Yves Le Gall said in December.

To complete its range, Arianespace has been diversifying to the middle and lower size of rockets, turning to Russia to provide its Soyuz rocket for services at Kourou, and is developing the small rocket Vega, due for launch in

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