Today's launch of Flight 158 with the Rosetta spacecraft will be delayed by a few days to allow for a minor repair to the external thermal protection on Ariane 5’s core cryogenic stage.
Arianespace reports that a visual inspection of the cryogenic core stage detected that a 10 X 15-cm piece of the protection was missing, giving reason for the countdown to be stopped. The inspection was made prior to the start of the stage’s fuelling. This thermal protection insulates the stage’s cold cryogenic propellants against the warmer external environment.
To replace the missing piece of insulation, Ariane 5 will be moved on its mobile launch table back to the Spaceport’s Final Assembly Building, where a new block of thermal protection will be installed. Once the new piece is in place, the adhesive requires approximately 36 hours for its drying/curing process.
Both the launcher and the Rosetta spacecraft remain in a 'safe' mode.
Resumption of the Flight 158 countdown is planned for the beginning of next week.