DLR hands over Rosetta-Lander to ESA
Astrium built probe travels to the edge of our solar system
Friedrichshafen, 20 November 2001
In January 2003 the Astrium-built European spacecraft Rosetta is to set off in search of pristine matter. It will be launched on its long flight to the comet "Wirtanen" by the European launch vehicle Ariane 5. For approximately one year, it will orbit this comet at a distance of one kilometre and study it in detail. At the same time, a probe will land on the comet's surface, in order to perform surface investigations and analysis. The lander has now been completed by the German Aerospace Center, (DLR) and delivered to the European Space Agency, ESA.
As the prime industrial contractor, Astrium is currently putting this challenging project for ESA into action. Not only the lander, but also the satellite is already completed. As the probe begins its journey from Turin to ESA´s Technical Centre ESTEC in Noordwijk, Holland, the lander is setting off on its journey from Ottobrunn, where it has completed a first series of tests at IABG. The probe and lander will be coupled at ESTEC and will be submitted to an extensive testing programme, during which the launch conditions and those in space will be simulated. This phase of inspection will last until the middle of the following year. Astrium is also involved with Roland: the company is providing support for the systems engineering, quality control and testing and for the sophisticated landing arms.
Rosetta: Tacking through the Planetary System
Rosetta is the third of ESA´s four major planetary missions. In terms of engineering, it ranks among the most difficult projects that are feasible today. It will further expand Europe's leading position in cometary research, which it had attained with the fly-by of Halley's Comet by the space probe Giotto in 1986.
The flight path itself calls for new technical solutions. Even the thrust of the powerful Ariane 5 is not sufficient to directly send the spacecraft on its way to the comet. The probe needs to gather momentum three times in the gravity fields of Mars and the Earth in order to get onto the right course. According to current planning, this will take place in 2005 at Mars and the Earth and once again at the Earth in 2008. Only after the third swing-by manoeuvre will Rosetta be catapulted into the outer regions of the planetary system, where it will encounter the comet Wirtanen.
In between these events, Rosetta will be largely on its own. For this reason, the so-called "Avionics Package", which will also be delivered by Astrium, will be the most technologically complex component. It contains the software for the onboard computers and the attitude control system. Rosetta's ¡§Mind¡¨ and ¡§body¡¨ must be able to operate faultlessly, and to a large degree autonomously. The biggest single item under this contract, however, is the instrument platform, which is also under the responsibility of Astrium.
The Asteroids Otawara and Siwa
However before Rosetta reaches the comet, it will fly past two asteroids: in 2006, it will pass 750 kilometres distant from Otawara and then in 2008, after the second Earth ¡§slingshot¡¨ manoeuvre, it will fly by Siwa at a distance of 1600 kilometres. Asteroids are boulders which are mainly to be found circling in the area between Mars and Jupiter. They are thought to be the building blocks for a planet, which could not form in Jupiter´s powerful gravity field. They are therefore also known as planetoids. Little is known about these bodies and therefore astronomists are hoping for valuable data from Rosetta concerning their composition and formation.
The Wirtanen Comet
In the spring of 2011, the rendezvous-manoeuvre with comet Wirtanen will be initiated and then in the following spring, nine years after the start, the goal will be reached. The most exciting phase of the project will then begin. Wirtanen will, by this time, be 600 million kilometres away from the Earth and 750 million kilometres from the sun. Here, in the icy cold of space, the comet is inactive, meaning that it produces no gas which could form a cover (Coma) or a tail.
During this time, Rosetta will photograph the surface from a distance of one kilometre. For the first time, scientists, and the public, of course, will be able to view the surface of a comet. Details up to one metre in size will be available. The camera was created in the Max-Planck Institute for Aeronomy in Katlenburg/Lindau, Germany. Here are to be found the experts who have already constructed the successful Giotto camera.
At the same time, spectrometers will scan the surface in various spectral ranges down to infrared. The chemical and mineral composition of the comet's surface materials will therefore be determined. The surface is expected to be a dirty, icy waste. Halley's comet was composed of long canyons, wide craters and hills up to 900 metres tall. Nobody knows whether Wirtanen will be similar or not.
The German camera will also look for level terrain, as Rosetta will deploy a lander on the surface shortly after having reached the comet. Originally, two landers had been planned. One, called Champollion, was to be jointly built by France and the USA, the other one, Roland (Rosetta Lander), was planned as an exclusively German project. After the Americans' decision to withdraw from the project, Germany and France have jointly built one lander.
The device, measuring 1x1x1 metres must land smoothly on the surface and be anchored there. The reason is the very slight gravity of the comet, which is only a few kilometres in size. Its gravity field is already so slight, that a coin, when flipped from the comet, would disappear into space, never to be seen again. In this way, the 100 kilograms Roland will weigh merely 3 grams on Wirtanen. During the landing approach, Roland will deploy its three ¡§arms¡¨, (radius 2.8 metres). At the end of each arm is a small ice drill, which will secure the lander to Wirtanen, before harpoons are fired into the surface of the comet. Cables will thus hold Rosetta lander firm.
The Lander has a range of sophisticated instruments for the analysis of soil samples on board. Moreover, a camera will also take panoramic shots. It was created by a collaborative effort between the Institute for Planetary Investigation of the German Aerospace Center (DLR) in Berlin, and French scientists. It is also planned to insert a micro-camera into a borehole, in order to investigate the composition of the comet's crust.
While Rosetta continues its orbit round the comet, it will move closer to the sun. Wirtanen will awaken from its cryosleep and will begin to warm up. Gases will evaporate from the surface and the core. These will carry along dust particles and Wirtanen will thus generate a tail. At this point, the 13 measuring devices on board Rosetta will commence studying the gas and dust. About a year after the probe's arrival, Wirtanen will reach the closest point to the sun on its path, where it will be most active. Shortly afterwards, the satellite's mission will conclude. Wirtanen will return to the icy, outer regions of the solar system.
Scientists will therefore possess a means of following the alterations of the comet's surface through the seasons live. It was possible to determine from the Giotto images, that gas jets shoot from cracks in the surface. Rosetta will provide a follow-on from this and will solve other mysteries which surround the comet.
Comets - Primeval Archives
The measuring data will be of incalculable worth to the scientists, as the lander's instruments will be boring into material which has been exactly preserved since the creation of the solar system. Pristine matter is to be found on no other celestial body, apart from Asteroids. On the Earth and similarly on other planets, the primordial matter out of which the planets were formed has been incessantly altered during the past 4.6 billion years. Chemical, geological and biological processes have transformed atmospheres and rock as well as destroying pristine matter of any kind.
Comets, on the other hand, are so small that geological processes such as erosion or plate tectonics do not occur. There are probably billions of comet cores, which circle the sun slowly, far outside the normal orbit of even the furthest planets. It is only when one of these enters the inner solar system that it heats up sufficiently to produce gas, which appears as a tail in the sky.
Comets, therefore, spend the majority of their lifetimes in the outer reaches of the solar system, where temperatures sink to absolute zero. The comets are „cosmic deep freezers¡§, in which matter is frozen rigid. Scientists hope, therefore, with the aid of Rosetta, to be able to determine the chemical composition of the interstellar medium and to fathom how our solar system and with it, the Earth, came into existence. Rosetta will explore the roots of our existence.
Rosetta's Nomenclature
From this the name of the probe is explained. It refers to the "Rosetta stone" - an Egyptian stone covered with inscriptions, which was discovered by a soldier in Napoleon's army in 1799, near to the Egyptian town of Rosetta. The French savant, Jean-François Champollion succeeded in decoding Egyptian hieroglyphics with the aid of the inscriptions on the stone. That aided historians in determining the roots of our culture.
Friedrichshafen/Ottobrunn, November 20th, 2001
