|Operator||European Space Agency|
|Major contractors||European Space Agency|
|Mission type||Comet Orbiter/Lander|
|Launch date||March 2, 2004 at 07:17 UTC|
|Launch vehicle||Ariane 5G+|
|Mission duration||9 years, 2 months, and 15 days elapsed|
|Flyby of||Earth, Mars, 2867 Šteins, 21 Lutetia|
Rosetta consists of two main elements: the Rosetta space probe and the Philae lander. The spacecraft was launched on 2 March 2004 on an Ariane 5 rocket and will reach the comet by mid-2014. The space probe is intended to orbit and perform long-term exploration of the comet at close quarters. On 10 November 2014 the Philae lander will attempt to land and perform detailed investigations on the comet's surface. Both the probe and the lander carry a large complement of scientific experiments designed to complete the most detailed study of a comet ever attempted.
The probe is named after the Rosetta Stone, as it is hoped the mission will help form an idea of how the solar system looked before planets formed. The lander is named after the Nile island Philae where an obelisk was found that helped decipher the Rosetta Stone. The spacecraft has already performed two successful asteroid flyby missions on its way to the comet. In 2007, Rosetta performed a Mars swingby (flyby), and returned images. The craft completed its fly-by of asteroid 2867 Šteins in September 2008 and of 21 Lutetia in July 2010, and is presently in "hibernation" mode and on-target for its final destination. The spacecraft will remain in this state until 20 January 2014 when the hibernation exit sequence will be initiated.
In 2007, as it approached Earth for a fly-by, the spacecraft was briefly designated a minor planet 2007 VN84 due to it being misidentified as an asteroid (see below).
Mission timeline 
This is the planned timeline for the mission after its launch:
- First Earth flyby (March 4, 2005)
- Mars flyby (February 25, 2007)
- Second Earth flyby (November 13, 2007 )
- Flyby of asteroid 2867 Šteins (September 5, 2008)
- Third Earth flyby (November 13, 2009)
- Flyby of asteroid 21 Lutetia (July 10, 2010)
- Deep-space hibernation (June 2011 - January 2014)
- Comet approach (January–May 2014)
- Comet mapping / Characterisation (August 2014)
- Landing on the comet (November 2014)
- Escorting the comet around the Sun (November 2014 - December 2015)
- End of mission (December 2015)
Rosetta's current location can be found on the ESA website.
During the 1986 apparition of the Comet Halley, a number of international space probes were sent to explore the cometary system, most prominent among them being ESA's highly successful Giotto. After the probes returned a treasure-trove of valuable scientific information it was becoming obvious that follow-ons were needed that would shed more light on the complex cometary composition and resolve the newly opened questions.
Both NASA and ESA started cooperatively developing new probes. The NASA project was the Comet Rendezvous Asteroid Flyby (CRAF) mission. The ESA project was the follow-on Comet Nucleus Sample Return (CNSR) mission. Both missions were to share the Mariner Mark II spacecraft design, thus minimizing costs. In 1992, after NASA axed CRAF due to budgetary limitations, ESA decided to develop a CRAF-style project on its own. By 1993 it was evident that the ambitious sample return mission was unfeasible with the existing ESA budget, so the mission was redesigned, with the final flight plan resembling the canceled CRAF mission, an asteroid flyby followed by a comet rendezvous with in-situ examination, including a lander.
Rosetta was built in a clean room according to COSPAR rules, but "Sterilisation [was] generally not crucial since comets are usually regarded as objects where you can find prebiotic molecules, that is, molecules that are precursors of life, but not living microorganisms, " according to Gerhard Schwehm, Rosetta's Project Scientist.
However, this plan was abandoned after a failure of the planned launch vehicle Ariane 5 on December 11, 2002. A new plan was formed to target the comet Churyumov–Gerasimenko, with launch on February 26, 2004 and rendezvous in 2014. The larger mass and the resulting increased impact velocity made modification of the landing gear necessary. After two cancelled launch attempts, Rosetta was launched on March 2, 2004 at 7:17 GMT. Besides the changes made to launch time and target, the mission profile remains almost identical.
The first flyby of Earth occurred on March 4, 2005.
On February 25, 2007, the craft was scheduled for a low-altitude bypass of Mars, to correct the trajectory after the first launch in 2003 was delayed by one year. This was not without risk, as the estimated altitude of the flyover manoeuvre was a mere 250 km (155 miles). During that encounter the solar panels could not be used since the craft was in the planet's shadow, where it would not receive any solar light for 15 minutes, causing a dangerous shortage of power. The craft was therefore put into standby mode, with no possibility to communicate, flying on batteries that were originally not designed for this task. This Mars manœuvre was therefore nicknamed "The Billion Euro Gamble". Fortunately, the flyby was successful and the mission continued as planned.
The spacecraft performed a close flyby of asteroid 2867 Šteins on September 5, 2008. Its onboard cameras were used to fine-tune the trajectory, achieving a minimum separation of less than 800 km (497 miles). Onboard instruments measured the asteroid from August 4 to September 10. Maximum relative speed between the two objects during the flyby was 8.6 km/s (19,240 mph).
The asteroid's orbit was known before Rosetta's launch, from ground-based measurements, to an accuracy of approximately 100 km. Information gathered by the onboard cameras beginning at a distance of 24 million km will be processed at ESA's Operation Center to refine the asteroid's position in its orbit to a few kilometers.
Rosetta's third and final flyby of Earth happened on November 12, 2009.
In May 2014, the Rosetta craft will enter a slow orbit around the comet and gradually slow down in preparation for releasing a lander that will make contact with the comet itself. The lander, named "Philae", will approach Churyumov–Gerasimenko at relative speed around 1 m/s and on contact with the surface, two harpoons will be fired into the comet to prevent the lander from bouncing off. Additional drills are used to further secure the lander on the comet.
Once attached to the comet, expected to take place in November 2014, the lander will begin its science mission:
- Characterisation of the nucleus
- Determination of the chemical compounds present, including enantiomers
- Study of comet activities and developments over time
The exact surface layout of the comet is currently unknown and the orbiter has been built to map this before detaching the lander. It is anticipated that a suitable landing site can be found, although few specific details exist regarding the surface.
The spectroscopical investigation of the core is done by four instruments.
- ALICE (an ultraviolet imaging spectrograph). The UV spectrograph will search for the abundance of noble gas in the comet core, from which the temperature during the comet creation could be estimated. The detection is done by an array of potassium bromide and caesium iodide photocathodes. The 3.1 kg instrument uses 2.9 watts and was produced in the USA, and an improved version is used in the New Horizons.
- OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System). The camera system has a narrow-angle lens (700 mm) and a wide-angle lens (140 mm), with a 2048x2048 pixel CCD chip. The instrument was constructed in Germany.
- VIRTIS (Visible and Infrared Thermal Imaging Spectrometer). The Visible and IR spectrometer is able to make pictures of the core in the IR and also search for IR spectra of molecules in the coma. The detection is done by a mercury cadmium teluride array for IR and with a CCD chip for the Visible range. The instrument was produced in Italy, and improved versions were used for Dawn and Venus express.
- MIRO (Microwave Instrument for the Rosetta Orbiter). The abundance and temperature of volatile substances like water, ammonia and carbon dioxide can be detected by MIRO via their microwave emissions. The 30 cm radio antenna was constructed in Germany, while the rest of the 18.5 kg instrument was provided by the USA.
The interior of the comet is probed by the CONSERT instrument.
- CONSERT (Comet Nucleus Sounding Experiment by Radiowave Transmission). The CONSERT experiment is the only experiment on board the ROSETTA mission which will provide information about the deep interior of the comet. The Consert radar will perform tomography of the nucleus by measuring electromagnetic wave propagation between the Philae lander and the Rosetta orbiter through the comet nucleus. This allows it to determine the comet's internal structure and deduce information on its composition. The lander and orbiter electronics were provided by France and both antennas were constructed in Germany.
Gas and particles 
- ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis). The instrument consists of a double-focus magnetic mass spectrometer DFMS and a reflectron type time of flight mass spectrometer RTOF. The DFMS has a high resolution (can resolve N2 from CO) for molecules up to 300 amu. The RTOF is highly sensitive for neutral molecules and for ions.
- MIDAS (Micro-Imaging Dust Analysis System). The high-resolution atomic force microscope will investigate the dust particles which are deposited on a silicone plate.
- COSIMA (Cometary Secondary Ion Mass Analyser). COSIMA analyses the composition of dust particles by secondary ion mass spectrometry, after the surface is cleaned by indium ions. It can analyse ions up to a mass of 4000 amu.
- GIADA (Grain Impact Analyser and Dust Accumulator) 
Solarwind interaction 
Major events and discoveries 
- March 2 – ESA's Rosetta mission was successfully launched at 07:17 UTC (08:17 Central European Time). The launcher successfully placed its upper stage and payload into an eccentric coast orbit (200 x 4,000 km). About two hours later, at 09:14 UTC, the upper stage ignited its own engine to reach escape velocity in order to leave the Earth’s gravity field and enter heliocentric orbit. The Rosetta probe was released 18 minutes later. ESA’s Operations Centre (ESOC) in Darmstadt, Germany, established contact with the probe shortly after that.
- May 10 – The first and most important deep space maneuver was successfully executed to adjust the course of the space craft, with a reported inaccuracy of 0.05%.
- March 4 – Rosetta executed its first planned close flyby of Earth. The Moon and the Earth's magnetic field were used to test and calibrate the instruments on board of the spacecraft. The minimum altitude above the Earth's surface was about 1,954.7 km at 22:09 UTC and images of the space probe passing by were captured by amateur astronomers.
- July 4 – Imaging instruments on board observed the collision between the comet Tempel 1 and the impactor of the Deep Impact mission.
- February 25 – Mars swing-by. Philae's ROMAP (Rosetta Lander Magnetometer and Plasma Monitor) instrument measures the complex Martian magnetic environment, while Rosetta's OSIRIS (Optical, Spectroscopic, and Infrared Remote Imaging System) took various images of the planet using different photographic filters. While in Mars' shadow most of the instruments were turned off and the Philae lander was autonomously running on batteries. During this operation the ÇIVA instrument on the lander took pictures of Mars. Among others, both actions were meant to test the spacecraft's instruments. The spacecraft used the gravity of Mars to change course towards its second Earth flyby in November.
- November 8 – Misidentification of Rosetta space craft as an asteroid (see below).
- September 5 – Flyby of asteroid 2867 Šteins. The spacecraft passed the main-belt asteroid at a distance of 800 km and the relatively slow speed of 8.6 km/s.
- November 13 – Last swingby (gravity assist passage) of Earth. The spacecraft made its closest approach (perigee passage) at 2481 km altitude over 109°E and 8°S - just off the coast of the Indonesian island of Java, at 07:45 UTC.
- March 16 - Observation of the dust tail of the asteroid P/2010 A2. Together with observations of Hubble space telescope it could be confirmed that the P/2010 A2 is not a comet but an asteroid and the tail most likely consists of particles from an impact of a smaller asteroid.
- July 10 - Flew by and photographed the asteroid 21 Lutetia.
- June 8 - The spacecraft was transferred into a spin stabilized mode and all electronics except the onboard computer and the hibernation heaters were switched off.
Misidentification as an asteroid 
In November 2007, during its second flyby, the Rosetta spacecraft was mistaken for a near-Earth asteroid and given the designation 2007 VN84. Based upon images taken by a 0.68-meter telescope of the Catalina Sky Survey, an astronomer 'discovered' the spacecraft and misidentified it as an asteroid about 20 meters in diameter, and performed a trajectory calculation showing that it would make its closest flyby of the Earth at a distance of 5,700 kilometers on November 13, 2007. This extremely close approach (in astronomical terms) led to speculation that 2007 VN84 might be at risk of impacting the Earth. However, astronomer Denis Denisenko recognized that the trajectory matched that of the Rosetta probe, which was performing a flyby of Earth en route to its rendezvous with a comet. The Minor Planet Center later confirmed in an editorial release that 2007 VN84 was actually the spacecraft.
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|Wikimedia Commons has media related to: Rosetta (spacecraft)|
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