Background During the 1986 approach of
Halley's Comet, international space probes were sent to explore the comet, most prominent among them being
ESA's
Giotto. After the probes returned valuable scientific information, it became obvious that follow-ons were needed that would shed more light on cometary composition and answer new questions. Both ESA and
NASA 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 minimising costs. In 1992, after NASA cancelled 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 infeasible with the existing ESA budget, so the mission was redesigned and subsequently approved by the ESA, with the final flight plan resembling the cancelled CRAF mission: an asteroid flyby followed by a comet rendezvous with in-situ examination, including a lander. The
Rosetta mission included generational team management; this allowed mission continuity over the long period of the mission and for special knowledge to be maintained and passed on to future team members. In particular, several younger scientists were brought on as principal science investigators, and regular training sessions were conducted. The planning for the operation of the scientific payload, together with the data retrieval, calibration, archiving and distribution, was performed from the
European Space Astronomy Centre (ESAC), in
Villanueva de la Cañada, near
Madrid, Spain. It has been estimated that in the decade preceding 2014, some 2,000 people assisted in the mission in some capacity.
Rosetta was set to be launched on 12 January 2003 to rendezvous with the comet
46P/Wirtanen in 2011. In May 2003, a new plan was formed to target the comet 67P/Churyumov–Gerasimenko, with a revised launch date of 26 February 2004 and comet rendezvous in 2014. The larger mass and the resulting increased impact velocity made modification of the landing gear necessary.
Launch After two scrubbed launch attempts,
Rosetta was launched on 2 March 2004 at 07:17
UTC from the
Guiana Space Centre in French Guiana, using
Ariane 5 G+ carrier rocket.
Deep space manoeuvres To achieve the required velocity to rendezvous with 67P,
Rosetta used
gravity assist manoeuvres to accelerate throughout the inner Solar System. The comet's orbit was known before
Rosetta launch, from ground-based measurements, to an accuracy of approximately . Information gathered by the onboard cameras beginning at a distance of were processed at ESA's Operation Centre to refine the position of the comet in its orbit to a few kilometres. The first
Earth flyby was on 4 March 2005. On 4 July 2005, imaging instruments on board observed the collision between the comet
Tempel 1 and the impactor of the
Deep Impact mission. On 25 February 2007, the craft was scheduled for a low-altitude flyby of
Mars, to correct the trajectory. This was not without risk, as the estimated altitude of the flyby was a mere . 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 manoeuvre was therefore nicknamed "The Billion Euro Gamble". The flyby was successful, with
Rosetta even returning detailed images of the surface and atmosphere of the planet, and the mission continued as planned. In observations made on 7 and 8 November,
Rosetta was briefly mistaken for a
near-Earth asteroid about in diameter by an astronomer of the
Catalina Sky Survey and was given the
provisional designation . Calculations showed that it would pass very close to Earth, which led to speculation that it could impact Earth. However, astronomer
Denis Denisenko recognised that the trajectory matched that of
Rosetta, which the
Minor Planet Center confirmed in an editorial release on 9 November. The spacecraft performed a close flyby of asteroid
2867 Šteins on 5 September 2008. Its onboard cameras were used to fine-tune the trajectory, achieving a minimum separation of less than . Onboard instruments measured the asteroid from 4 August to 10 September. Maximum relative speed between the two objects during the flyby was .
Rosetta third and final flyby of Earth happened on 12 November 2009 at a distance of . On 16 March 2010,
Rosetta performed observations of the dust tail of the object
P/2010 A2. Together with observations by
Hubble Space Telescope, it helped to confirm that P/2010 A2 is not a comet, but an asteroid, and that the tail most likely consists of particles from an impact by a smaller asteroid. On 10 July 2010,
Rosetta flew by
21 Lutetia, a large
main-belt asteroid, at a minimum distance of km ( mi) at a velocity of . The flyby provided images of up to per pixel resolution and covered about 50% of the surface, mostly in the northern hemisphere. The 462 images were obtained in 21 narrow- and broad-band filters extending from 0.24 to 1 μm. After leaving its hibernation mode in January 2014 and getting closer to the comet,
Rosetta began a series of eight burns in May 2014. These reduced the relative velocity between the spacecraft and 67P from . Prior to
Rosetta deep space hibernation period, two of the spacecraft's four
reaction wheels began exhibiting increased levels of "bearing friction noise". Increased friction levels in Reaction Wheel Assembly (RWA) B were noted after its September 2008 encounter with asteroid Šteins. Two attempts were made to relubricate the RWA using an on-board oil reservoir, but in each case noise levels were only temporarily lowered, and the RWA was turned off in mid-2010 after the flyby of asteroid Lutetia to avoid possible failure. Shortly after this, RWA C also began showing evidence of elevated friction. Relubrication was also performed on this RWA, and methods were found to temporarily increase its operating temperature to better improve the transfer of oil from its reservoir. In addition, the reaction wheel's speed range was decreased to limit lifetime accumulated rotations. These changes resulted in RWA C performance stabilising. During the spacecraft's Deep Space Hibernation flight phase, engineers performed ground testing on a flight spare RWA at the
European Space Operations Centre. After
Rosetta exited hibernation in January 2014, lessons learned from the ground testing were applied to all four RWAs, such as increasing their operating temperatures and limiting their wheel speeds to below 1000 rpm. After these fixes, the RWAs showed nearly identical performance data. These changes allowed the four RWAs to operate throughout
Rosetta mission at 67P/Churyumov–Gerasimenko despite occasional anomalies in their friction plots and a heavy workload imposed by numerous orbital changes. In total eight burns were used to align the trajectories of
Rosetta 67P with the majority of the deceleration occurring during three burns:
Delta-v of on 21 May, on 4 June, and on 18 June. The surface layout of 67P was unknown before
Rosetta arrival. The orbiter mapped the comet in anticipation of detaching its lander. On 14 July 2014, the OSIRIS on-board imaging system returned images of the comet which confirmed its irregular shape. By 25 August 2014, five potential landing sites had been determined. On 15 September 2014, ESA announced Site J, named
Agilkia in honour of
Agilkia Island by an ESA public contest and located on the "head" of the comet, as the lander's destination.
Philae lander of the
comet 67P/Churyumov–Gerasimenko on 12 September 2015 one of the most dramatic cliff collapses captured during the Rosetta mission.
Philae detached from
Rosetta on 12 November 2014 at 08:35 UTC, and approached 67P at a relative speed of about . It initially landed on 67P at 15:33 UTC, but bounced twice, coming to rest at 17:33 UTC. Confirmation of contact with 67P reached Earth at 16:03 UTC. On contact with the surface, two
harpoons were to be fired into the comet to prevent the lander from bouncing off, as the comet's escape velocity is only around . Analysis of telemetry indicated that the surface at the initial touchdown site is relatively soft, covered with a layer of granular material about deep, and that the harpoons had not fired upon landing. After landing on the comet,
Philae had been scheduled to commence its science mission, which included: • Characterisation of the nucleus • Determination of the chemical compounds present, including amino acid
enantiomers • Study of comet activities and developments over time After bouncing,
Philae settled in the shadow of a cliff, Contact was briefly and intermittently reestablished several months later at various times between 13 June and 9 July, before contact was lost once again. There was no communication afterwards, and the transmitter to communicate with
Philae was switched off in July 2016 to reduce power consumption of the probe. Knowing its exact location provides information needed to put Philae's two days of science into proper context. On 23 June 2015, at the same time as a mission extension was confirmed, ESA announced that end of mission would occur at the end of September 2016 after two years of operations at the comet.
Rosetta began a descent with a 208-second thruster burn executed on 29 September 2016 at approximately 20:50
UTC. Its trajectory targeted a site in the Ma'at region near an area of dust- and gas-producing active pits. Impact on the comet's surface occurred 14.5 hours after its descent manoeuvre; the final data packet from
Rosetta was transmitted at 10:39:28.895 UTC (
SCET) by the OSIRIS instrument and was received at the
European Space Operations Centre in Darmstadt, Germany, at 11:19:36.541 UTC. The spacecraft's estimated speed at the time of impact was ,
Rosetta computer included commands to send it into safe mode upon detecting that it had hit the comet's surface, turning off its radio transmitter and rendering it inert in accordance with
International Telecommunication Union rules. == Spacecraft ==