Orders in prospect after failure of uprated model, while preparations for Rosetta asteroid-comet explorer progress

Arianespace is expected to order further basic models of its Ariane 5 launch vehicle following the failure of the uprated variant on its 11 December maiden flight. The decision will allow the company to continue operating two launch vehicle models rather than phase out the basic Ariane 5G by year-end after six more launches.

The European launch services company had planned to operate one launcher, the improved "10t" Ariane 5 ECA, from 2004, but this is beginning to look like a risky strategy in the highly competitive commercial launch market. Arianespace's workhorse Ariane 4 will be phased out after one more launch early this year.

Preparations are going ahead, meanwhile, for the Ariane 5G launch of the European Space Agency's Rosetta asteroid-comet explorer during a 19-day flight window that opens on 12 January. The launch vehicle for Flight 158 was moved to the final-assembly facility at the Kourou, French Guiana, launch site in mid-December, but final clearance is pending a go-ahead from an inquiry board investigating the failure of Flight 157.

The board was scheduled to report its results on 6 January, with the cause of the failure expected to be linked to changes introduced with the uprated Ariane 5 ECA, clearing the basic model for launch.

Approving the Ariane 5G for launch is critical if ESA's €700 million ($700 million) Rosetta is to accomplish its ambitious mission to become the first spacecraft to orbit the nucleus of a comet and place a lander on its surface. To reach its target - the comet Wirtanen - in May 2012, the Astrium-built spacecraft needs to use gravity-assist fly-bys of Mars in August 2005, and Earth in November 2005 and November 2007.

The complex trajectory means that the 12-31 January window includes only six days when a launch is possible, and only two specific times each day when the launch can be attempted. Even then, the launch must be accurate to within a second. If the gravity-assist opportunities are lost, Rosetta will not be able to reach Wirtanen and a new mission will have to be devised for the spacecraft.

During its planned flight to Wirtanen, Rosetta will fly by the asteroids Otawara in July 2007 and Siwa a year later. The craft will reach the region of Wirtanen in November 2011 and its relative velocity will be reduced gradually to 10km/s, enabling the craft to enter orbit around the nucleus, suspected to be 600m (1,970ft) in diameter.

Rosetta's 100kg (220lb) lander will have an equivalent weight of 1kg on the comet's low-gravity surface, and will have to deploy roped harpoons to anchor itself. The lander will take samples, using a drill to penetrate 200mm (8in) into the comet's surface.


Source: Flight International