Rosetta is the first mission designed to both orbit and land on a comet. Rosetta comprises an orbiter and a lander. The spacecraft carries eleven scientific experiments to complete the most detailed study of a comet ever attempted.

Rosetta's name comes from the famous Rosetta stone, that almost 200 years ago led to the deciphering of Egyptian hieroglyphics. In a similar way, scientists hope that the Rosetta spacecraft will unlock the mysteries of how the Solar System evolved.

Rosetta's launch had been originally scheduled for January 2003 on board an Ariane-5 rocket. Rosetta's target then was Comet Wirtanen, and the encounter had been planned to occur in 2011. However, following the failure of the Ariane Flight 157 in December 2002, with the loss of two spacecraft, ESA and Arianespace took the joint decision not to launch Rosetta during its January 2003 launch window. This meant that Rosetta's intended mission to Comet Wirtanen had to be abandoned.

In May 2003 a new target comet and launch date for Rosetta were selected: the spacecraft will be launched in February 2004 and will meet its new target comet, Churyumov-Gerasimenko, in 2014.

Objectives
ESA's Rosetta spacecraft will be the first to undertake the long-term exploration of a comet at close quarters. After entering orbit around Comet 67P/Churyumov-Gerasimenko, in 2014, the spacecraft will release a small lander onto the icy nucleus. Rosetta will orbit the comet for about a year as it heads towards the Sun. Once it has passed its perihelion (closest distance to the Sun), Rosetta will keep orbiting the comet for another half year.

Comets have essential information about the origin of our Solar System because they are the most primitive objects in the Solar System and their chemical composition has not changed much since their formation. Comets' compositions therefore reflect that of the Solar System when it was very young and still 'unfinished', more than 4600 million years ago. By orbiting Comet 67P/Churyumov-Gerasimenko and landing on it, Rosetta will allow us to reconstruct the history of our own neighborhood in space.

Rosetta will also help to discover whether comets contributed to the beginnings of life on Earth. Comets are carriers of complex organic molecules that - delivered to Earth through impacts ­ perhaps played a role in the origin of life. Moreover, 'volatile' light elements carried by comets may also have played an important role in forming the Earth's oceans and atmosphere.

During its trek to Comet 67P/Churyumov-Gerasimenko, Rosetta will make two excursions into the main asteroid belt that lies between the orbits of Jupiter and Mars. Scientists have identified some possible target asteroids along Rosetta's path. One or more of them will be selected in the course of the mission for a close fly-by.

Cost
The total cost of the mission is close to 1 thousand million Euros. This includes, the launch, the spacecraft, the scientific payload (instruments and lander) and operations.

The cost of the Rosetta launch delay is 70 million Euros.

Launch
Rosetta will be launched in late February 2004 on board an Ariane-5 from Europe's spaceport in Kourou, French Guiana.

Mission timeline
Launch: scheduled for late February 2004
First Earth gravity assist/fly-by: March 2005
Mars gravity assist: February 2007
Second Earth fly-by: November 2007
Third Earth fly-by: November 2009
Comet Churyumov-Gerasimenko rendezvous manoeuvre: May 2014
Landing on the comet: November 2014
Escorting the comet: December 2015

Planned mission lifetime
Rosetta's mission will last for 12 years until December 2015

Spacecraft

Design
Rosetta resembles a large aluminium box. The scientific instruments are mounted on the 'top' of the box - the Payload Support Module - while the subsystems are on the 'base' or Bus Support Module. On one side of the Orbiter is a 2.2-metre diameter communications dish - the steerable high-gain antenna - while the Lander is attached to the opposite face. Two enormous solar wings extend from the other sides. Both these panels can be rotated through +/-180 degrees to catch the maximum amount of sunlight.

Mass
Approximately 3000 kilograms (fully fuelled) including 1670 kilograms propellant, 165 kilograms of scientific payload for the orbiter and the lander weighs 100 kilograms.

Dimensions
Main spacecraft 2.8 x 2.1 x 2.0 metres, on which all subsystems and payload equipment are mounted. Two 14-metre long solar panels with a total area of 64 square metres.

Industrial involvement
Prime contractor is Astrium, Germany, the leader of an industrial team involving more than 50 contractors from 14 European countries and the United States. There is also Canadian participation in the ESA 35-metre Deep Space Antenna in Australia. Throughout Europe, about 1000 people have been involved in the development of Rosetta.

What's on board?

Orbiter

The orbiter's scientific payload includes 11 experiments, in addition to the lander. Scientific consortia from institutes across Europe and the United States have provided these state-of-the-art instruments.

Ultraviolet Imaging Spectrometer - ALICE ALICE will analyse gases in the coma and tail and measures the comet's production rates of water and carbon monoxide or dioxide. It will provide information on the surface composition of the nucleus.

Principal Investigator: S. A. Stern, SwRI, Boulder, Co., United States.

Comet Nucleus Sounding Experiment - CONSERT CONSERT will probe the comet's interior by studying radio waves that are reflected and scattered by the nucleus.

Principal Investigator: W. Kofman, LPG, Grenoble, France.

Cometary Secondary Ion Mass Analyser - COSIMA COSIMA will analyse the characteristics of dust grains emitted by the comet, such as their composition and whether they are organic or inorganic.

Principal Investigator: J. Kissel, MPAe, Katlenburg-Lindau, Germany.

Grain Impact Analyser and Dust Accumulator - GIADA GIADA will measure the number, mass, momentum, and velocity distribution of dust grains coming from the comet nucleus and from other directions (reflected by solar radiation pressure).

Principal Investigator: L. Colangeli, Oss. Astronomico di Capodimonte, Naples, Italy.

Micro-Imaging Dust Analysis System - MIDAS MIDAS will study the dust environment around the comet. It will provide information on particle population, size, volume, and shape.

Principal Investigator: W. Riedler, IWF, Graz, Austria.

Microwave Instrument for the Rosetta Orbiter - MIRO MIRO will determine the abundances of major gases, the surface outgassing rate, and the nucleus subsurface temperature.

Principal Investigator: S. Gulkis, NASA-JPL, Pasadena, CA., United States.

Optical, Spectrocopic and Infrared Remote Imaging System - OSIRIS OSIRIS is a Wide-Angle Camera and Narrow-Angle Camera to obtain high-resolution images of the comet's nucleus.

Principal Investigator: H.U. Keller, MPAe, Katlenburg-Lindau, Germany.

Rosetta Orbiter Spectrometer for Ion and Neutral Analysis - ROSINA ROSINA will determine the composition of the comet's atmosphere and ionosphere, the velocities of electrified gas particles, and reactions in which they take part.

Principal Investigator: H. Balsiger, University of Bern, Switzerland.

Rosetta Plasma Consortium - RPC RPC will measure the physical properties of the nucleus; examine the structure of the inner coma; monitor cometary activity; and study the comet's interaction with the solar wind.

Investigators: A. Eriksson, Swedish Institute of Space Physics, Uppsala, Sweden; J. Burch, SwRI, San Antonio, TX., United States; K-H Glassmeier, TU Braunschweig, Germany; R. Lundin, Swedish Institute of Space Physics, Kiruna, Sweden; J. G. Trotignon, LPCE/CNRS, Orleans, France; C. Carr, Imperial College, United Kingdom.

Radio Science Investigation - RSI Using shifts in the spacecraft's radio signals, RSI will measure the mass, density, and gravity of the nucleus; define the comet's orbit; and study the inner coma.

Principal Investigator: M. Patzold, University of Cologne, Cologne, Germany.

Visible and Infrared Mapping Spectrometer - VIRTIS VIRTIS will map and study the nature of the solids and the temperature on the surface of the nucleus. It will also identify comet gases, characterise the physical conditions of the coma, and help identify the best landing sites.

Principal Investigator: A. Coradini, IFSI, Rome, Italy.

Lander

Design
The lander structure consists of a baseplate, an instrument platform, and a polygonal sandwich construction, all made of carbon fibre. Some of the instruments and subsystems are beneath a hood that is covered with solar cells. An antenna transmits data from the surface to Earth via the orbiter. The lander carries nine experiments, with a total mass of about 21 kilograms. It also carries a drilling system to take samples of subsurface material.

Alpha Proton X-ray Spectrometer - APXS Lowered to within 4 centimetres of the ground, APXS will detect alpha particles and X-rays that will provide information on the elemental composition of the comet's surface.

Principal Investigator: R. Rieder, MPCH, Mainz, Germany.

Rosetta Lander Imaging System- CIVA/ROLIS Rolis: is a CCD camera to obtain high-resolution images during descent and stereo panoramic images of areas sampled by other instruments. Six identical micro-cameras will take panoramic pictures of the surface. A spectrometer will study the composition, texture, and albedo (reflectivity) of samples collected from the surface.

Principal Investigators: J. P. Bibring, IAS, Orsay, France, S. Mottola, DLR, Berlin, Germany.

Comet Nucleus Sounding - CONSERT CONSERT will probe the internal structure of the nucleus. Radio waves from CONSERT will travel through the nucleus and will be returned by a transponder on the lander.

Principal Investigator: W. Kofman, LPG, Grenoble, France.

Cometary Sampling and Composition experiment - COSAC One of two evolved gas analysers. It will detect and identify complex organic molecules from their elemental and molecular composition.

Principal Investigator: H. Rosenbauer, MPAe, Katlenburg-Lindau, Germany.

Evolved Gas Analyser - MODULUS PTOLEMY Another evolved gas analyser that will obtain accurate measurements of isotopic ratios of light elements.

Principal Investigator: I. Wright, Open University, United Kingdom.

Multi-Purpose Sensor for Surface and Subsurface Science - Mupus Mupus will use sensors on the lander's anchor, probe, and exterior to measure the density, thermal, and mechanical properties of the surface.

Principal Investigator: T. Spohn, University of Munster Germany.

Rosetta Lander Magnetometer and Plasma Monitor - Romap A magnetometer and plasma monitor that will study the local magnetic field and the comet / solar wind interaction.

Principal Investigators: U. Auster, DLR, Berlin, Germany and I. Apathy, KFKI, Budapest, Hungary.

Sample and Distribution Device - SD2 SD2 will drill more than 20 centimetres into the surface, will collect samples and deliver them to different ovens or for microscope inspection.

Principal Investigator: A. Ercoli Finzi, Polytecnico, Milano, Italy.

Surface Electrical, Seismic and Acoustic Monitoring Experimens - SESAME Three instruments will measure properties of the comet's outer layers. The Cometary Acoustic Sounding Surface Experiment will measure the way sound travels through the surface. The Permittivity Probe will investigate its electrical characteristics, and the Dust Impact Monitor will measure dust falling back to the surface.

Principal Investigators: D. Möhlmann, DLR, Cologne, Germany, W. Schmidt, FMI, Helsinki, Finland, I. Apathy, KFKI, Budapest, Hungary.

Operations

Mission Operations Centre: European Space Operations Centre (ESOC), Darmstadt, Germany.

Prime Ground Station: ESA Deep Space Antenna in New Norcia, near Perth, Australia.

Science Operations Centre: European Space and Technology Centre (ESTEC), in Noordwijk, The Netherlands. Co-located at European Space Operations Centre (ESOC), Darmstadt, Germany for prime mission phases.

Lander Control Centre: DLR, Cologne, Germany.

Lander Science Centre: CNES, Toulouse, France.