U2 kicked off their first tour in three years on Tuesday, rocking a raucous Barcelona crowd of around 90,000 and reaching for the stars with a live link-up to the International Space Station.

Featuring one of the biggest concert stages ever built, the U2 360 Tour will visit 31 cities across Europe and North America and entertain an estimated three million people. More dates are expected to be announced in 2010.

Fans surrounded the circular platform inside Barcelona's Nou Camp stadium, allowing for a bigger audience and lower average ticket prices during the global recession.

"All around Spain, all around the world, things are difficult. Thank you for coming back to us again and again," Bono said during the high octane show.

The quartet, one of the world's most successful acts, opened with "Breathe" from their acclaimed new album "No Line on the Horizon," and the crowd came to life with the anthem-style "Magnificent" on a hot summer's night.

U2 mixed old songs and new, playing classics including "Beautiful Day" and "Sunday Bloody Sunday" as well as "Angel of Harlem," which the band dedicated to U.S. pop star Michael Jackson, who died suddenly last week aged 50.

"We wrote this one for Billie Holiday but we are going to play it tonight for Michael Jackson," said Bono. "Unspeakable talent, that's all there is to say, really," he added, and the song morphed into Jackson hits "Man in the Mirror" and "Don't Stop 'Til You Get Enough."

Half way through the concert, U2 linked up by video to the International Space Station.

"Very nice to hear you," said one astronaut as the microphone floated around the cabin.

"Commander, can you see Barcelona?" asked Bono.

"Right now the most beautiful sight in our cosmos is the blue planet earth," came the reply.

GREAT EXPECTATIONS

The tour is reported to be the group's most expensive to date, costing an estimated $100 million, but industry experts suggest it could be money well spent.

Live performance is becoming an increasingly important source of revenue for major acts like U2 as sales of physical CDs declines sharply and online piracy remains rampant.

Billboard, an authoritative music industry publication, believes the U2 360 Tour could become one of the highest grossing ever, possibly eclipsing its 2005-6 Vertigo tour which earned the band $389 million.

The stage, which takes 120 trucks to transport, is another grand statement from U2, which has won more Grammy awards than any other band.

On the Zoo TV tour, huge video screens overloaded fans with flashing images of pop culture. On the PopMart tour, Bono appeared from inside a 12 meter glitterball shaped like a lemon.

The abiding visual memory on this tour is sure to be the "Claw," a four-legged "monster" that towers 50 meters over the band's heads and on which the sound system is mounted.

(China Daily/Agencies July 3, 2009)