Rosetta is a European Space Agency (ESA) mission designed to rendezvous with comet Wirtanen and perform remote sensing investigations. It will carry two probes to land on the comet's surface and perform in-situ measurements. Flybys of two asteroids on the way to the comet are also planned. After launch in January 2003, Rosetta will fly out to Mars for a gravity assist and return for an Earth flyby approximately 3 years after launch. A flyby of the mainbelt asteroid 3840 Mimistrobell will occur about 300 days later, followed by a second gravity-assist Earth flyby. A flyby of asteroid 2530 Shipka will take place approximately 2,100 days after launch.
After the asteroid flyby, the spacecraft enters a heliocentric drift phase to intercept the comet at a point close enough to allow communication with the Earth. The spacecraft will lower its velocity relative to that of Comet P/Wirtanen from 100 meters/second at 500,000 kilometers to a speed low enough to allow it to go into an elliptic polar orbit about the nucleus, using the images of the comet as it gets closer to fine-tune the approach. This will occur in August 2011, about 3,150 days after launch. A landing site will be chosen and the probes, named RoLand and Champollion, will be released in August 2012. The probes will land at a relative velocity of less than 5 meters/second and will transmit data from the surface over the next 84 hours to the spacecraft, which will relay it to Earth. The spacecraft will remain with the comet and make observations through perihelion on 21 October 2013.
Rosetta's design is based on the existing Eurostar telecommunications satellite. The spacecraft will be approximately 2 meters on a side. Two 24 square meter solar panel "wings" extend from opposite sides of the cube. A steerable 2 m diameter parabolic dish antenna is attached to one side, and the probes will be mounted on two other sides. The solar panels will provide 472 W at a distance of 5.2 AU from the Sun, with energy storage provided by 7 A-hr nickel-cadmium batteries. Rosetta will utilize an S-band telecommand uplink and an X-band telemetry and science-data downlink.
The scientific instruments on Rosetta will include a remote imaging system, a visible and IR spectral and thermal mapper, a gas and ion mass-spectrometer, a cometary mass analyzer, a scanning electron microprobe, a dust production rate and velocity analyzer, an electron density and temperature probe, and a solar wind flux monitor. The probe surface science packages include: an accelerometer; a permittivity probe; a thermal and evolved gas analyzer; a gamma-ray spectrometer; an alpha-proton-X-ray spectrometer; a neutron spectrometer; a gas chromatograph/mass spectrometer; an in-situ imaging system involving a dozen cameras and a microscope; and instruments attached to spikes which will penetrate below the surface. The surface packages might also include drills, coring devices and surface sample collectors. Also under consideration is a radio sounding tomographic experiment to study the comet nucleus.