The Ariane 5 rocket was being brought back into final assembly building at the European Space Agency's launch pad here, where technicians would replace an insulation tile that broke off from its main fuel tank, Arianespace Director General Jean-Yves Le Gall told the press.

They would also carry out an inspection of the other insulation tiles that cover the tank to see if any were loose, he said.

The rocket will be brought back on to the launch pad and a second launch attempt will take place "overnight Monday or overnight Tuesday" depending on how the repair work and inspection proceed, he said.

"As of today, a launch for early Tuesday seems feasible to me," Le Gall said.

The countdown clock was stopped on Friday three hours, 34 minutes and 29 seconds before blast off.

Rosetta's flight timetable over the next 10 years is so precise that the rocket has to be launched at an exact second in the pre-dawn hours on any day during its three-week launch window, which closes on March 17.

The craft will meet up in deep space with Comet Churyumov-Gerasimenko in 2014 and follow it on its path around the Sun.

The orbiter, equipped with remote sensors to map and probe the comet's surface, will also send down a miniature laboratory to conduct a chemical analysis of its ice and soil, believed to hold complex molecules that could help explain how life began on Earth.

Le Gall said the tile was found in a final inspection of the launch pad.

The tile broke away apparently because of the expansion and contraction of the tank after it was filled with extremely cold liquid hydrogen, and then emptied, following a failed launch attempt on Thursday.

Thursday's launch bid was scrapped because of high altitude winds, which could have scattered debris onto inhabited areas if the rocket blew up or had to be destroyed for some reason.

If the launch window closes, "we can launch [again] in one year's time to the same comet if we have a larger launch vehicle," said John Ellwood, in charge of the Rosetta mission at ESA.

The alternative rockets for this would be the Ariane 5 ECA, a rocket with a 10-tonne launch capacity that this year will undergo a test flight following a disastrous maiden flight in December 2002, and the Russian rocket, the Proton.

Rosetta and its lander, Philae, should have headed off into space more than a year ago towards another target, Comet Wirtanen.

But that mission was scrapped, and another comet chosen, to give engineers time to carry out reliability checks on the standard Ariane 5 launcher which is taking Rosetta into orbit.

SPACE.WIRE