The delay, the second in 24 hours, further reduced the number of launch attempts that can be feasibly undertaken before the final launch deadline of March 17. Theoretically a launch window of a few seconds exists each day. However, the availability of cryogenic fuel at Europe's Guiana Space Center and the need to permit tired launch crews to rest means that the rocket will have no more than six or seven realistic attempts to launch Rosetta by March 17 - the last day it can be launched and still reach its intended target, said Jacques Louet, head of science projects at the European Space Agency (ESA).

Jean-Yves Le Gall, chief executive of the Arianespace launch consortium, said Feb. 27 that this would be plenty of time to launch Rosetta, which already missed its January 2003 launch window -- and was forced to find a new target comet -- because of reliability issues that kept the Ariane 5 vehicle grounded early in 2003.

ESA Director-General Jean-Jacques Dordain said Feb. 27 that the agency remains confident that Rosetta, whose total budget is 1 billion euros ($1.25 billion), will make its Ariane 5 launch deadline. "The problem is identified and the solution is simple. We will leave a couple of days later on a 10-year trip. The satellite is in good shape."

Le Gall said a piece of thermal protection covering the cryogenic fuel tank was found on the launch platform during a routine inspection of the area late Feb. 26. The rocket's pre-dawn Feb. 26 launch attempt had been cancelled because of high winds in the upper atmosphere. The piece of insulating foam, measuring 10 by 15 centimeters, had likely fallen off the tank after the cryogenic fuel tank was emptied in response to the 24-hour weather delay.

The Ariane 5 rocket's main cryogenic stage contains about 158,000 kilograms of liquid oxygen and liquid hydrogen. The tank is fueled several hours before launch. To keep the fuel cold and to prevent ice from forming on the tank's exterior in the warm, humid air of this equatorial launch base, the tank is covered with foam insulation.

Gases sometimes are trapped in the small spaces between the tank and the insulation. Le Gall said it is likely that when the tank was emptied and the tank's surface temperature rose, this gas expanded and forced the  separation of the foam insulation.

The rocket will be returned to its assembly hall and its entire cryogenic tank inspected to assure that no other pieces of insulation have become partially unglued. Replacement foam will be added to the spot where the insulation fell off. Once added the replacement foam  takes about 36 hours to solidify.

Le Gall said even a small exposed area of the fuel tank cannot be tolerated. If the missing piece had not been detected, ice would have formed on the tank just before launch and could have become a danger to the rocket if it fell off during launch.