Strong, high-altitude winds forced the launch of Europe鈥檚 comet-chasing Rosetta spacecraft to be called off early on Thursday morning.
The launch was halted 20 minutes and 40 seconds before Rosetta was scheduled to blast-off at 0436 local time from Kourou in French Guiana.
Mission managers will attempt the launch again on Friday at about the same time, but if more problems develop, they can try once every day until 17 March.
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Winds between 10 and 15 kilometres above the launch site arose about two hours before the scheduled lift-off at 0736 GMT. But managers of the Ariane-5 launch rocket were concerned about the direction of the wind, not its force.
鈥淭he launch vehicle can fly whatever the speed of the wind,鈥� said Jean-Yves Le Gall, chief executive officer of Arianespace, the rocket鈥檚 manufacturer. 鈥淭he concern is where the debris will fall down if we have problems in flight.鈥�
ESA science director David Southwood took the news in his stride but says he felt like he was 鈥渁ll dressed up and nowhere to go鈥�. Still, he acknowledged the importance of following the protocol for possible debris damage. 鈥淵ou have to think of every eventuality,鈥� he said. 鈥淏etter safe than sorry is a good approach.鈥�
Rainy season
Usually there are two launch opportunities per day, each separated by 20 minutes, from this site just north of the equator. But to maximise the use of fuel on the launch vehicle, Rosetta has just one chance to launch per day.
Gravitational calculations have set Friday鈥檚 launch for 0736 and 50 seconds, one second after Thursday鈥檚 intended time. The launch window to reach Rosetta鈥檚 target 鈥� Comet 67P/Churyumov-Gerasimenko, or Chury 鈥� will end on 17 March. Mission planners had aimed for the earliest launch opportunity in case problems arose.
Roberto Lo Verde, a spokesman for ESA, says that lightning and low clouds that block mission controllers鈥� view of the launch vehicle are other weather factors that can scupper a launch. The launch window to reach Comet Chury falls during the rainy season in Kourou, and the hours preceding Thursday鈥檚 scheduled launch were filled with rain.
鈥淵ou come to the tropics, and it rains and you get winds,鈥� said Southwood. 鈥淓verything was looking good two hours ago. Tomorrow is another day.鈥�
Gravitational fields
Rosetta has suffered more than its share of delays. Originally conceived in 1985, the mission was approved in 1993 and was due to launch in January 2003 to rendezvous with Comet Wirtanen. But Rosetta鈥檚 managers decided to postpone the mission after a new version of the Ariane-5 launch rocket blew up in December 2002. The mission was redesigned entirely with a new flight path and a new comet.
This is the first mission to attempt to orbit and land on a comet. Rosetta will take ten years to reach Chury. During its long voyage it will fly three times round the Earth and once around Mars, using the gravitational fields of these planets to slingshot itself into the correct path for the rendezvous.
A few months after the spacecraft meets Chury, it will release a small cube-shaped lander on to the comet鈥檚 icy core. The orbiter will then spend two years circling Chury as it travels back towards the Sun.
