Launch of Europe's ambitious Rosetta mission to orbit a comet and deliver a tiny lander onto the icy surface has been postponed yet again -- this time by insulating foam that detached from the Ariane 5 rocket's main stage.

The Ariane 5 rocket will launch Rosetta. Credit: ESA/CNES/Arianespace

Originally scheduled for blastoff in January 2003, Rosetta was grounded by concerns with the Ariane 5 in the wake of a failed launch and missed its window to reach comet Wirtanen.

After reprogramming the mission to target another comet, Thursday morning's initial launch attempt was thwarted by high-altitude wind conditions.

While preparing for another countdown Thursday evening, the foam trouble prompted officials to halt the launch. This delay is expected to stretch into early next week.

To make repairs and perform a thorough inspection of the main stage, the Ariane 5 must be rolled off the launch pad and returned to its assembly building.

The rocket's main stage uses super-cold liquid hydrogen and liquid oxygen to feed the Vulcain 1 engine during the first 10 minutes of flight. The stage is covered with insulation to protect the cryogenic propellants inside -- a concept similar to the foam on space shuttle external tanks.

There is not yet a sense of urgency to get Rosetta airborne. The available period in which the craft can embark on its trek to comet Churyumov-Gerasimenko extends to March 17.

Rosetta will travel 10 years before arriving at its destination, becoming the first spacecraft to orbit a comet. A lander called Philae will separate from the Rosetta mothership and land on the comet's nucleus for detailed research.

An artist's concept shows the Rosetta orbiter and its lander. Credit: EADS Astrium

Comets are believed to be time capsules holding important clues about the birth of the solar system and its early development. The Rosetta mission seeks to understand the properties of comets and the processes that take place inside them.

"Working in unison, the lander and the orbiter will revolutionize our understanding of comets," Rosetta project scientist Gerhard Schwehm said. "They will lead to amazing discoveries about the most primitive building blocks of the solar system."