U2 kicked off their first tour in three years last night, rocking a 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.

Watch footage from the show.

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 show.

The group, 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 US 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.

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.