Rosetta (spacecraft)

Rosetta is a spacecraft of the European Space Agency, which has the comet 67P/Tschurjumow-Gerasimenko as a target. Launched on March 2, 2004 by an Ariane 5 G happened, built by EADS Astrium in Friedrichshafen probe after several swing-by maneuvers at Earth and Mars, the asteroid ( 2867 ) Šteins and (21) Lutetia and then spent two and a half years in "hibernation " ( Deep Space Hibernation ).

In August 2014, the probe is to pivot into an orbit around the comet Churyumov- Gerasimenko and map it to another approach in August to prepare for the landing of Philae. This 100 kg heavy ballistic Lander will touch down in November on the comet and start experiments allow conclusions on the nature of comets, and thus on the early solar system.

The name refers to the Rosetta stone of Rosetta, which allows managed to decipher Egyptian hieroglyphics. The name of the lander Philae refers to an island in the Nile on which an obelisk was found that helped in the decipherment of the Rosetta Stone. There is a prototype of the so-called Rosetta Disk, a five -centimeter disc of a nickel alloy, on the approximately 15,000 pages of text with information for over 2,500 languages ​​are etched into microscopic size on board.

The mission will cost a total of about one billion euros, the most important of the 17 nations involved carries Germany which around 290 million euros.

• 5.1 Interference in orbit around the comet
• 5.2 Orientation and Navigation in comets near

Beginnings of the Mission

Originally the launch of Rosetta was planned on 13 January 2003 and as a target the comet 46P/Wirtanen was provided. Because of difficulties with the Ariane 5 rocket program of the launch was postponed for a year.

On 26 February 2004, the launch from Kourou Space Center in French Guiana has been postponed at short notice because of violent winds aloft and the next day due to a defect in the heat shield again. March 2, 2004 at 8:17 CET clock finally lifted the launcher Ariane 5 G from the type with the three- tonne spacecraft on board.

History of the flight

No existing launcher is able to bring such a heavy payload directly on the orbit of a comet. These are earth and comet in the gravitational potential of the sun too far apart. Rather, the Ariane upper stage Rosetta brought out only on a near-earth orbit around the sun, so essentially from the gravitational potential of the earth. This is marked with "1" in the diagram opposite. After a few days it was clear that the desired path was made just enough so that Rosetta's fuel supply would be enough for all mission objectives, in particular for the path corrections of the two planned close flybys of the asteroid.

A year later, on 4 March 2005, Rosetta flew a first swing-by maneuver, in which the probe is approaching the Earth's surface up to 1,900 km. The probe was easily flown before this encounter " 2 " outside the Earth's orbit and dragged from the earth and accelerated. Then they went away relatively quickly to the outside and lost less energy than they had previously received from the earth. Your path now crossed at "3 " that of the planet Mars, which they there for another round and course corrections on 29 September ( DELTA.v = 32 m / s) and 13 November 2006 ( 0.1 m / s) at a very narrow swing-by hit. This meeting on 25 February 2007, a minimum distance of only 250 km slowed Rosetta 2.19 km / s, which made the subsequent interaction with the earth all the greater. This interaction with " 4/6 " consisted of two matches each on November 13 of the years 2007 and 2009, with intervals of 5295 or 2481 km. The energy gain is reflected in the increase of the semimajor axis of the orbit to approximately 1.6 and 3.1 AE - AE 3.5 is the value for the comet 67P/Tschurjumow-Gerasimenko, which the probe approaches since then.

Observations on the road

Observation of Deep Impact

Rosetta observed the Deep Impact on July 4, 2005, about 80 million kilometers distance transverse to the illumination by the sun. In particular, Rosetta's ALICE UV spectrometer was the best instrument of its kind, which stood for the observation of this event are available.

Flyby of asteroid ( 2867 ) Šteins

September 5, 2008 Rosetta happened at "5 ", ie at the inner edge of the asteroid main belt, the 4.6 -kilometer ( 2867 ) Šteins at a relative speed of 8.6 km / s With a new for ESA optical navigation method of the flyby succeeded in the planned distance of 800 km. For the calculation of correction maneuvers the two navigation cameras ( NAVCAM ) and the scientific camera OSIRIS made ​​repeated images of the asteroid before the star background. During the flyby data both with the optical camera OSIRIS and with the VIRTIS spectrometer were collected. For this purpose the probe must be rotated so that the communication antenna is not pointed to the earth. After 90 minutes of silence, the first telemetry data confirmed the success of the maneuver. The subsequently published images show a brilliant -shaped body with a large number of impact craters. For results, see ( 2867 ) Šteins.

Flyby of asteroid Lutetia

Rosetta happened on 10 July 2010 "7" to about 100 km asteroid (21 ) Lutetia with 3162 km distance and a relative speed of 15 km / s

In addition to researching Lutetia - the asteroid is characterized by huge craters, ridges and landslides as well as several hundred meters large rock - served the flyby also a test of the scientific instruments of Rosetta, as well as one of the ten experiments the lander Philae in very cold conditions, 407 million kilometers away from the sun and 455 million kilometers from Earth.

Hibernation

Rosetta's energy supply by solar cells was a novelty for missions beyond the Mars orbit. With the radiation intensity that decreases with the square of distance from the sun, also decreases the recoverable electric power. The very large size solar modules allowed in March 2011, just a first look at the real target of the mission, the comet 67P/Tschurjumow-Gerasimenko, from about 1 AU distance. However, the further rapprochement came in a wide arc that reached almost to the orbit of Jupiter with a maximum of 790 million km Sun distance. For the 31 months beyond about 660 million km Sun distance (from " 8" to "9" in the diagram above ), so the probe was in a sleep mode ( Deep Space Hibernation ), in which the low power available only the " life support " served (on-board computer and some heating elements for the scientific payload ).

On January 20, 2014 Rosetta woke scheduled for this idle state and has since been prepared for the rendezvous.

Technology and instruments

The basic structure of Rosetta consists of a housing made of an aluminum alloy having 2.8 m × 2.1 m × 2.0 m in size, with the scientific instruments (about 165 kg in total ) support is mounted on the upper side and the bus modules to the base are. On the side of a 2.2-meter parabolic antenna for communication ( S-band and X-band with 10-22000 bits per second), the five -part solar boom with 32 m span (32 square meters and 850 W of power are in a distance of 3.4 AU and 395 W applied at 5.25 AE) and about 100 kg lander. The drive system consists of 24 dual-fuel engines, each with ten Newton thrust, for about 1670 kg of fuel on board.

On board the Rosetta eleven instruments:

• The ultraviolet spectrometer ALICE will look for various noble gases, their distribution tells something about the ambient temperature during the formation 4.5 billion years ago. This is the only U.S. instrument of the Rosetta probe, an evolved version of Alice is also found in the New Horizons spacecraft use.
• The imaging system OSIRIS (Optical, Spectroscopic and Infrared Remote Imaging System) with two cameras: wide angle with 12 ° × 12 ° and 2.2 ° telephoto × 2.2 ° field of view. Each with mirror optics, filter wheel and 4- megapixel sensor. In order to orient and photography in particular the particle cloud and the surface of the comet down to 2 cm resolution at closest approach on 1 km distance, in visible and near infrared spectral regions. Also to search for a landing site for the lander.
• VIRTIS ( Visible and Infrared Thermal Imaging Spectrometer ) is to shoot medium to low -resolution images of the comet's nucleus, from which it can be concluded on the spatial distribution of elements found.
• The instrument MIRO (Microwave Spectrometer for the Rosetta Orbiter ) to measure the outgassing rate of the comet nucleus and the distribution functions for airspeed and excited states for the molecules CO, CH3OH, NH3, H216O, H217O and H218O. After these molecules lookout was kept in the vicinity of the asteroids. This high-resolution molecular spectroscopy is done in numerous fixed in 0.5 - mm - band frequencies. In addition, there are and the 1.9 - mm tape broadband channels for the measurement of temperature and temperature gradient at the surface of the celestial body visited.
• ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) consists of a magnetic - DFMS and a time of flight mass spectrometer RTOF, the ions and neutral gas detected. Thus, for example, the composition of the comet barely existent atmosphere and interactions of the particles can be determined.
• For the investigation of comet dust is also determined with a mass spectrometer, the abundances of elements, isotopes and molecules COSIMA ( Cometary Secondary Ion Mass Spectrometer).
• The high-resolution scanning probe microscope MIDAS (Micro - Imaging Dust Analysis System) can depict the fine structure of individual dust particles.
• The RPC (Rosetta Plasma Consortium) includes ion and electron detectors, and a magnetometer. Measure physical properties of the core and the coma, and the interaction between coma and solar wind.
• The consert experiment ( Comet Nucleus Sounding Experiment by Radio wave transmission) explored the structure of the comet nucleus.
• Giada (Grain Impact Analyser ) examines the coma and determines the number, size and speed of the dust grains therein.
• By using the communication system determines RSI ( Radio Science Investigation ), the gravitational field of the nucleus and from its mass and mass distribution.

Another ten instruments are on board the lander, enter their data on Rosetta as a relay station to the ground. The scientific data are stored on a solid-state memory with 25 GBit ( minimum capacity at the end of the mission).

Challenges and specifics of the mission

By Rosettamission is breaking new ground in some areas of space research. The mission profile is characterized by several features.

Interference in orbit around the comet

To study the comet to be swung into orbit around him. Among other things, the gravitational potential of the comet is to be measured, which is very different in the vicinity of a central potential and cause observable perturbations. In this case, additional effects have to be considered:

• The radiation pressure of the sun
• The coma of the comet formed near the sun by outgassing from active sites of the comet. The particle causes an acceleration. Also, by the (stationary ) particle cloud around the comet a deceleration of the probe occur.
• The tidal force of the Sun.

Orientation and navigation in comets near

By the large duration of the communication signals is not possible directly to control from the ground. Probe and lander must therefore be able to act autonomously. In particular, concerns the position control.

Trivia

The Minor Planet Center, the observed near-Earth asteroids, in a circular of 8 November 2007 published the discovery of an object that would pass very close to Earth, and forgave him the catalog name 2007VN84. It quickly became apparent that in reality the Rosetta spacecraft was observed in their approach to the second swing-by maneuver on the ground. The designation was therefore withdrawn.

In addition, the research team in early November 2007 discovered a body of Rosetta seemed to follow. The distance was reduced to a few 100,000 km flyby of Earth on November 13. Having lost components of the probe could be excluded itself, an object of the earth's orbit crossing Apollo asteroids was suspected.