Rosetta (spacecraft)
Rosetta is a former space probe built by the European Space Agency that launched on 2 March 2004. Along with Philae, its lander module, Rosetta performed a detailed study of comet 67P/Churyumov–Gerasimenko. During its journey to the comet, the spacecraft performed flybys of Earth, Mars, and the asteroids 21 Lutetia and 2867 Šteins. It was launched as the third cornerstone mission of the ESA's Horizon 2000 programme, after SOHO''Cluster and XMM-Newton. The total cost of the mission was about €1.3 billion.
On 6 August 2014, the spacecraft reached the comet and performed a series of manoeuvers to eventually orbit the comet at distances of. On 12 November, its lander module Philae performed the first successful landing on a comet, though its battery power ran out two days later. Communications with Philae were briefly restored in June and July 2015, but due to diminishing solar power, Rosetta communications module with the lander was turned off on 27 July 2016. On 30 September 2016, the Rosetta'' spacecraft ended its mission by hard-landing on the comet in its Ma'at region.
Name
The probe was named after the Rosetta Stone, a stele of Egyptian origin featuring a decree in three scripts. The lander was named after the Philae obelisk, which bears a bilingual Greek and Egyptian hieroglyphic inscription. A comparison of its hieroglyphs with those on the Rosetta Stone catalysed the deciphering of the Egyptian writing system. Similarly, it was hoped that these spacecraft would result in better understanding of comets and the early Solar System. In a more direct analogy to its namesake, the Rosetta spacecraft also carried a micro-etched pure nickel prototype of the Rosetta disc donated by the Long Now Foundation. The disc was inscribed with 6,500 pages of language translations.Mission overview
The spacecraft consisted of the Rosetta orbiter, which featured 12 instruments, and the Philae lander, with nine additional instruments. The Rosetta mission orbited Comet Churyumov–Gerasimenko for 17 months and was designed to complete the most detailed study of a comet ever attempted.Rosetta was launched on 2 March 2004 from the Guiana Space Centre in Kourou, French Guiana, on an Ariane 5 rocket. In 2007, Rosetta made a Mars gravity assist. The spacecraft also performed two asteroid flybys: of 2867 Šteins in September 2008 and of 21 Lutetia in July 2010.
Rosetta reached Comet Churyumov–Gerasimenko in May 2014. It performed a series of manoeuvres to enter orbit between then and 6 August 2014, when it became the first spacecraft to orbit a comet. Rosetta ''Philae'' lander successfully made the first soft landing on a comet nucleus when it touched down on Comet Churyumov–Gerasimenko on 12 November 2014.
Mission firsts
The Rosetta mission achieved many historic firsts. On its way to comet 67P, Rosetta passed through the main asteroid belt, and made the first European close encounter with several of these primitive objects. Rosetta was the first spacecraft to fly close to Jupiter's orbit using solar cells as its main power source. Rosetta was the first spacecraft to orbit a comet nucleus, and was the first spacecraft to fly alongside a comet as it headed towards the inner Solar System. Previous missions had conducted successful flybys of seven other comets. It became the first spacecraft to examine at close proximity the activity of a frozen comet as it is warmed by the Sun. Shortly after its arrival at 67P, the Rosetta orbiter dispatched the Philae lander for the first controlled touchdown on a comet nucleus. The robotic lander's instruments obtained the first images from a comet's surface and made the first on-site analysis of its composition.History
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 mission. The ESA project was the follow-on Comet Nucleus Sample Return 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. After the spacecraft launch, Gerhard Schwehm was named mission manager; he retired in March 2014.
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 spacecraft was controlled from the European Space Operations Centre, in Darmstadt, Germany. 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, 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 built in a clean room according to COSPAR rules, but "sterilisation 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 project scientist.
Rosetta was set to be launched on 12 January 2003 to rendezvous with the comet 46P/Wirtanen in 2011. This plan was abandoned after the failure of an Ariane 5 ECA carrier rocket during Hot Bird 7's launch on 11 December 2002, grounding it until the cause of the failure could be determined. 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. Aside from the changes made to launch time and target, the mission profile remained almost identical. Both co-discoverers of the comet, Klim Churyumov and Svetlana Gerasimenko, were present at the spaceport during the launch.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.
The second Earth flyby was on 13 November 2007 at a distance of. 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 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. Lutetia was also observed by the visible–near-infrared imaging spectrometer VIRTIS, and measurements of the magnetic field and plasma environment were taken as well.
On 8 June 2011, the spacecraft was transferred into a spin stabilised mode and all electronics except the onboard computer and the hibernation heaters were switched off for the planned 31 months of hibernation. 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.