Rosettas launch profile would require the Ariane 5 rockets upper stage to undertake its first-ever ballistic coast phase before being ignited, a two-hour-long sequence that Arianespace Chief Executive Jean-Yves Le Gall has said presents several challenges.

Those challenges were known years ago, when Arianespace agreed to undertake the Rosetta launch. But the company and its industrial contractors, and a separate board of inquiry, have been forced to conduct a thorough review of all aspects of the Ariane 5 in light of the Dec. 11 launch failure. Le Gall said he would not launch Rosetta unless Arianespace was certain it had satisfied itself that the vehicle was sound.

A board of inquiry concluded that the Dec. 11 failure was caused by a failure of the nozzle on the rockets Vulcain-2 main-stage engine.

Rosetta had not been slated to ride aboard this new version of the Ariane 5. But the vehicle intended to launch the probe cannot be considered standard in the sense of having flown many times before. In addition to having a unique mission profile, the vehicle has undergone modifications to its equipment bay and electrical system.

David Southwood, science director at the European Space Agency, has said missing the late-January launch window likely would mean placing Rosetta in storage for months as another comet is found, and a new mission examined. He said the cost of such a delay could be between 50 million and 100 million euros ($50 million to $100 million).