Airbus Defence and Space

The Rosetta mission - in search of pristine matter

The Rosetta spacecraft is on its long 10-year flight to the comet "Churyumov-Gerasimenko" . Once there , for approximately 13 months, it will orbit this tailed comet at distances as close as one kilometre and will explore it in considerable detail. At the same time, a small lander, a kind of “mini-lab”, will be put down on the comet's surface for scientific investigations and analysis.

Rosetta will sail through the planetary system

Rosetta is the third of ESA’s four major Planetary Cornerstone missions . In terms of engineering, it ranks among the most difficult projects that are feasible today.

The flight path itself already calls for new technical solutions. Even the thrust of the powerful Ariane 5 rocket is not sufficient to take the spacecraft straight to the comet. To get onto the right flight path the probe must gain momentum four times from the gravity fields of Mars and the Earth. Rosetta swings by Mars in February 2005, the Earth in March 2005, November 2007 and again in 2009. Only after the fourth swing-by manoeuvre Rosetta is catapulted into the outer regions of the planetary system, where it encounters the comet “67P”, as Churyumov-Gerasimenko is also called. Thus, Rosetta reaches a maximum distance of approximately 800 million kilometres from the Sun and about 950 million kilometres from the Earth. It will be the first time a solar-powered probe has ever travelled such distances.

In between these events, Rosetta is largely on its own and must operate faultlessly and, to a large degree, autonomously. This is why the avionics, provided by Airbus Defence and Space was so complex technically. It contains the software for the on-board computers and the attitude control system. However, the biggest single item in the development programme was the instrument platform, which was also the responsibility of Airbus Defence and Space.

Observation of asteroids during fly-by

Before its encounter with the comet "Churyumov-Gerasimenko", Rosetta flies through the asteroid belt and will be able to examine closely at least one asteroid as it passes. Asteroids are bits of rock which orbit the Sun primarily in the area between the orbits of Mars and Jupiter. They are thought to be the building blocks of a planet which could not be formed on account of Jupiter's enormous gravitational forces. Therefore, these bodies are also called planetoids or minor planets. Astronomers know very little about them and expect to obtain valuable information on their composition and creation from the data provided by Rosetta.

Destination – Comet "67P/Churyumov-Gerasimenko"

The rendezvous manoeuvre with "67P" will be initiated in May 2014. In August 2014, more than ten years after launch, Rosetta will have reached its destination and inserted itself into an orbit around the comet which will then be approximately 675 million kilometres from the Sun.

At this point the surface will be able to be examined from a distance of only a few kilometres. For the first time, scientists, and the public, will be able to see what the surface of a comet looks like. Details down to one metre should be clearly visible using the camera that was built by the Max-Planck Institute for Aeronomy in Katlenburg/Lindau, the experts who also developed the successful camera for the Giotto spacecraft.

Simultaneously, spectrometers will scan the surface in various spectral bands down to infrared. This data will be used to determine the mineral and chemical composition of the surface. The surface is expected to have the appearance of a dirty, crusted icy desert.

Halley’s Comet revealed long canyons, wide craters and up to 900-metre high hills. Nobody knows whether "Churyumov-Gerasimenko" will look the same.

The camera on board the orbiter will also be used to look for level terrain, so that Rosetta can deploy its lander on the surface in November 2014. The lander was developed under the leadership of the German Aerospace Centre (DLR).

Although "Churyumov-Gerasimenko" is about four times larger than comet "Wirtanen", the original destination, the lander must still be anchored to the surface. Otherwise there is a danger that the lander might break away from the comet's surface. However the higher gravitational attraction of "67" is not necessarily an advantage because a higher mass also translates into a higher approach and impact speed – for which the lander's legs were not originally designed. This problem was resolved by a special shock-absorbing system, a development in which Airbus Defence and Space, Friedrichshafen, was also involved.

The lander will carry a series of complex instruments for the analysis of surface samples and a camera to take panoramic pictures. The camera was developed by the Berlin-based DLR Institute of Planetary Exploration in co-operation with researchers in France. It is even planned to lower a micro-camera into a borehole to determine the structure of the comet’s crust.

While Rosetta is in orbit the comet will approach the Sun. It will ‘wake up’ from its ice cold hibernation and start to heat up. Gases will evaporate from its surface and from within and will draw out particles of dust. and will thus form a coma and a tail. The eleven measuring instruments on board Rosetta will then begin the study of the gas and dust clouds.

Approximately one year after Rosetta’s encounter, the comet, "67P", will have reached the orbital point nearest the Sun, where it is most active. A few months after this, the spacecraft will have completed its mission. "Churyumov-Gerasimenko" will then withdraw again into the outer, icy regions of the planetary system.

For the first time, scientists will have the opportunity to see "live" how a cometary surface evolves in the course of the "seasons". The pictures taken by Giotto of Halley’s comet appeared to show that huge gas jets spout out of the crevasses in the surface. Rosetta will show this process in much more detail and so help to unravel further the mysteries that surround the comets.

Comets - the archives of primeval times

The data gathered will be of inestimable value to the scientific community, as the instruments on board the lander will, in a way, tap into an archive which has preserved material unaltered from the time of the formation of the solar system. Pristine matter cannot be found on any other celestial body with the possible exception of some asteroids.

Comets, by comparison, are so small that no geological processes, such as erosion or plate tectonics, take place. There are presumably billions of cometary nuclei that slowly move around the Sun far outside Pluto's orbit. It is only when one of them ventures into the inner solar system that it will heat up so that gas will evaporate and it will appear as a tailed star in the sky.

Comets spend most of their "lives" in the outer reaches of the solar system where temperatures drop to nearly absolute zero. The cometary material is thus preserved in a deep-freeze state. Scientists therefore hope that Rosetta will help them determine the chemical composition of protosolar nebula in order to further explore the creation of our solar system and thus of the Earth. In other words: Rosetta will be looking for the very roots of man’s existence, the formation of life.

67P – Churyumov-Gerasimenko

The comet Churyumov-Gerasimenko was detected in 1969. Initially, Klim Churyumov examined a picture of the comet Comas Solá taken by Swetlana Gerasimenko and detected the comet on it. P67 is about three kilometres by five and rotates about its one axis once in about twelve hours. It takes approximately six and a half years to complete one Sun orbit and its distance from the Sun varies from between 194 and 858 million kilometres. . In preparation for the Rosetta mission, "Churyumov-Gerasimenko", which is regarded as a "dusty" comet was inspected in detail by the Hubble Space Telescope. In March 2003, one of Hubble’s cameras took some 60 images so that astronomers could get a rough idea of the comet's shape, which is similar to a rugby ball.