CAPE CANAVERAL, Fla. -- Europe's largest satellite ever built was safely delivered into polar orbit Thursday, riding atop an Ariane 5 rocket that needed this successful shot to recover from a failure last summer.

An Ariane 5 lifts off Thursday night from the Guiana Space Center carrying Envisat into polar orbit. Image from Arianespace TV and used with permission.

The mission was considered critical not only for Arianespace -- the European commercial launch firm that hasn't flown an Ariane 5 rocket since a botched launch in July -- but also for all of Europe, which shared in the cost and construction of the $2 billion Envisat environmental research platform.

"Bravo Europe! Congratulations," Jean-Marie Luton, Arianespace's top manager, said after the satellite delivery mission was declared complete. "It's the success of European space in its entirety that we can celebrate here this evening."

Some ten years in the making and weighing in at 17,844 pounds (8,111 kilograms), Envisat is the biggest and heaviest spacecraft ever constructed on the European continent. It required Arianespace to use its tallest nose cone to protect the satellite at launch.

As a result, it was a 165-foot-tall (50.4 meters) rocket that blasted off from the Guiana Space Center's ELA-3 launch pad at precisely 8:07:59 p.m. EST (0107.59 Friday GMT).

Flying a course of due north from the South American spaceport, the Ariane 5 took nearly 27 minutes to inject Envisat into its proper orbit, an orbit that will allow the spacecraft to train its sensors on Earth's entire surface once every three days.

Equipped with an array of ten instruments, Envisat will monitor the land, oceans, atmosphere and even Earth's ice caps, seeking to gather data on how our climate is changing over time and perhaps evidence on what is causing those changes to take place.

"This is the most sophisticated laboratory ever put in space to study the Earth and monitor the environment," said Jose Achache, director of the European Space Agency's Earth observation program. "It's going to be wonderful for the scientific community."

According to Envisat officials, the spacecraft's five-year mission will help try to answer several questions, including:

• Is the ozone hole growing?

• What concentrations of greenhouse gases are to be found in the atmosphere?

• What is the state of the El Nio current in the Pacific Ocean?

• What is the state of the rain forest?

• How fast are the ice caps melting?

Achache said Envisat's data, when combined with information gathered by other satellites past and present, will be used by European lawmakers to help set environmental policy.

Return to flight

Meanwhile, Arianespace officials are breathing a sigh of relief following Thursday's launch, which marked the first use of the next-generation Ariane 5 booster since a July mishap with the rocket's upper stage left two satellites in useless orbits.

"Everybody was quite tense and even stressed because this launch was a very important launch," Luton said. "With the orbiting of Envisat, Ariane 5 is back again, on track and perfectly operational."

The trouble began on July 12 when an Ariane 5 upper stage engine never developed proper thrust after ignition. As a consequence, the European Space Agency's Artemis experimental communications satellite and Japan's Broadcasting Satellite Systems Corp. BSAT-2B were stranded in an orbit that was too low.

While the Artemis satellite is using its onboard thrusters -- both chemical and ion -- to climb up to its intended orbit, where it can still achieve limited success in its mission, the BSAT-2B spacecraft was considered a total loss and a replacement is scheduled to be launched in 2003.

Analysis on the ground, meanwhile, revealed that the problem with the upper stage was caused by the unwanted presence of water in fuel lines. The water came from tests by the manufacturer to make sure the plumbing could withstand certain pressures.

"The troubleshooting was a bit of a challenge, particularly early on, because they had trouble recreating the anomaly," said Clayton Mowry, president of the Washington, D.C.-based Arianespace, Inc., which markets Ariane launch services in the United States. "From there it was easy to implement a solution and comprehensive plan to make sure we wouldn't have that problem again."

While the Ariane 5 remain grounded and underwent more than 300 engine test firings, Arianespace continued to launch Ariane 4 rockets and juggled its customers along the way, in one case moving INSAT-3C from a scheduled Ariane 5 ride to an Ariane 4 launched on Jan. 23.

By the numbers, Ariane 5 has now launched 11 times and experienced three failures, scoring a 72.7 percent success rate. While that is lower than the rates boasted by its sister rocket and its competitors, Arianespace officials remain confident that their trust is well placed in the Ariane 5.

"It's a mature system despite the upper stage anomaly we experienced. It's not a test rocket by any stretch. We think it's far advanced in comparison, say, to the EELVs," Mowry said, referencing the U.S. Atlas 5 and Delta 4 rockets, which are scheduled for their inaugural missions this year from Cape Canaveral.

"For us to be competitive in the future we needed to upgrade our capabilities and that's why we have the Ariane 5," Mowry said.