"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.