Following the failure of Ariane Flight 157 in December, with the loss of two spacecraft, ESA and Arianespace took the joint decision not to launch Rosetta during its January launch window. This meant that Rosetta’s originally intended mission to Comet Wirtanen had to be abandoned. Scientists and engineers in the programme have been examining several alternative mission scenarios.
Each has been looked at on the basis of the expected scientific return, the technical risks related to using the Rosetta design in the new mission, and the containment of costs.
Of the nine mission scenarios studied by the Rosetta Science Working Team, three have survived to this point and were presented to the delegations of the ESA Member States through the Science Programme Committee at its meeting on 25/26 February. Two mission scenarios (in February 2004 and 2005 respectively) would take Rosetta to a new target comet, Churyumov-Gerasimenko, while another (in January 2004) would take it to its original target, Comet Wirtanen.
All three options are now being studied in detail so that the final decision can be made. A campaign of observations using both the NASA/ESA Hubble Space Telescope and the instruments of the European Southern Observatory is under way to study Comet
Churyumov-Gerasimenko. In this way, astronomers will be able to characterise the comet and perform a mission analysis, also to identify landing scenarios and make a thorough assessment of any hardware modification that would be necessary.
In parallel, ESA is assessing the launch requirements for the various mission scenarios. This will include looking at alternatives to Ariane as back-up options, such as the Russian Proton rocket.
The final decision on Rosetta’s new mission scenario will be made by the ESA Science Programme Committee in May.