* Astronomy

ESA's comet chaser mission Rosetta took these infrared and visible images of Earth and the Moon, during the Earth fly-by of 4/5 March 2005 while on its way to Comet 67P/Churyumov-Gerasimenko.

THE ROSETTA MISSION

 

Europe's comet-chasing probe Rosetta has launched successfully into space on a daring journey to chase and land on a comet. at 0717 GMT on the 2^nd March. The launch of Europe's Rosetta space mission, which aims to chase and then land on a comet, has been delayed due to bad weather and technical problems. The probe is due to depart from Kourou in French Guiana on the first stage of its 7bn-kilometre, 10-year journey to reach the comet Churyumov-Gerasimenko.

In 2014, Rosetta will reach the comet and deliver a lander to its surface.
The £600m spacecraft on an Ariane 5 G+ rocket was due to launch at 0736 GMT on Thursday 26^th February (and on the 27^th) and there were two launch opportunities, at 07:17 and 07:37 GMT on March 2nd.

The Rosetta mission had a launch instant rather than a launch window. This means it can only launch at 07:36 GMT. With a launch window, mission controllers can try later on the same day if conditions improve. Once up in space, Rosetta will be placed in orbit around Earth before departing for the outer Solar System. The Ariane rocket consists of boosters, a core section, or stage, an upper stage and the probe itself. The probe and upper stage are known collectively as the stack. Two minutes after lift off, the rocket jettisoned its boosters leaving the rest of the rocket to ascend to a height of 4,000km.

After about 10 minutes, the rocket begins to fall back towards Earth. As this happens, the core stage separates from the stack.

 

 

The core re-enters the atmosphere while the stack remains in orbit, using the Earth's gravity to build up velocity for Rosetta's "escape". After a further two hours, the upper stage separates from Rosetta, leaving the probe to begin its journey.
During the course of its 10-year journey, the probe will round the Sun four times before reaching 67P/Churyumov-Gerasimenko. The probe will perform three close fly-bys of the Earth and one of Mars in "slingshot" manoeuvres that will use the planets' gravity to help the probe build up speed. Rosetta will need this extra velocity if it is to intercept the comet as it streaks past Jupiter towards the Sun.
Over half of the 3,000 kg spacecraft's mass is fuel, to enable it to complete its epic trip around the Solar System.
By May/June of 2014, Rosetta will enter orbit around the comet and begin edging towards its nucleus. The orbiter's cameras will then map the nucleus in detail to help scientists choose a suitable landing site. After this has been chosen, Rosetta will despatch its lander Philae to the comet's surface. Approaching the nucleus at walking speed, Philae will fire two harpoons to anchor itself down. During Rosetta's rendezvous with the comet, commands from Earth will take about 50 minutes to reach the spacecraft. So the probe has been designed with a degree of autonomy, allowing it to think for itself. Rosetta will have to cope with temperatures that fall to -150 Celsius beyond the planet Jupiter. The mission is due to end in December 2015.

LIVE Real-Player stream of the Rosetta mission.
RE-RUN Real-Player stream of the Rosetta Launch.
Launch Clip of Ariane 5 G+ rocket .

latest photo of 67P/Churyumov-Gerasimenko.

Rosetta is named after the stone that explained Egyptian hieroglyphics, thus laying bare the culture of the Pharaohs to modern eyes.
Its lander, Philae, is so called after an obelisk that itself provided a key to understanding Rosetta.

On Mar 11, 2004 The European Space Agency selected a pair of asteroids of high scientific interest, well within the fuel budget, that Rosetta will fly past on its way to meet up with Comet 67P/Churyumov-Gerasimenko.

The first target is Steins, which is only a few kilometres across will be visited by Rosetta on 5 September 2008 at a distance of just over 1700 kilometres. This encounter will take place at a relatively low speed of about 9 kilometres per second during Rosetta's first excursion into the asteroid belt between the orbits of Mars and Jupiter.
The second asteroid is Lutetia; a 100 km asteroid which Rosetta will pass within about 3000 kilometres on 10 July 2010 at a speed of 15 kilometres per second. This will be during Rosetta's second passage through the asteroid belt. Rosetta will obtain spectacular images as it flies by these primordial rocks. Its onboard instruments will provide information on the mass and density of the asteroids, thus telling us more about their composition, and will also measure their subsurface temperature and look for gas and dust around them.
The selection of these two excellent targets was made possible by the high accuracy with which the Ariane 5 delivered the spacecraft into its orbit. This of course leaves sufficient fuel for the core part of the mission, orbiting Comet 67P/Churyumov-Gerasimenko for 17 months when Rosetta reaches its target in 2014.

 

Rosetta Status Report 3 May 2004:

For the first time the spacecraft was rotated such that the payload could point towards the Earth. This gave MIRO and VIRTIS the opportunity to take calibration measurements using the Earth as a target. Close monitoring of the thermal environment continues, and the experience with the Earth pointing attitude has resulted in a further restriction on the range of allowed attitudes. The Sun is now allowed in a range from ñ4 to +50 degrees from the +X axis in the X/Z plan, at least until after perihelion is reached on 25 May.

Philae's Challenge:     Landing on Powder or Ice?

Rosetta's lander Philae will do something never before attempted: land on a comet. But how will it do this, when the kind of surface it will land on is unknown? With the surface composition and condition largely a mystery, engineers found themselves with an extraordinary challenge; they had to design something that would land equally well on either solid ice or powder snow, or any state in between. In the tiny gravitational field of a comet, landing on hard icy surface might cause Philae to bounce off again. Alternatively, hitting a soft snowy one could result in it sinking. To cope with either possibility, Philae will touch as softly as possible. In fact, engineers have likened it more to docking in space.
Landing on a comet is nothing like landing on a large planet, you do not have to fight against the pull of the planet's gravity, and there is no atmosphere. The final touching velocity will be about one metre per second. That is near a walking pace. However, as anyone who has walked into a wall by mistake will tell you, it is still fast enough to do some damage. So, two other strategies have been implemented. Firstly, to guard against bouncing off, Philae will fire harpoons upon contact to secure itself to the comet. Secondly, to prevent Philae from disappearing into a snowy surface, the landing gear is equipped with large pads to spread its weight across a broad area - which is how snowshoes work on Earth, allowing us to walk on powdery falls of snow. When necessity forced Rosetta's target comet to be changed in Spring 2003 from Comet Wirtanen to Comet 67P/Churyumov-Gerasimenko, the landing team re-analysed Philae's ability to cope. Because Comet Churyumov-Gerasimenko is larger than Wirtanen, three times the radius, it will have a larger gravitational field with which to pull down Philae.
In testing it was discovered that the landing gear is capable of withstanding a landing of 1.5 metres per second - this was better than originally assumed. In addition, Rosetta will gently push out the lander from a low altitude, to lessen its fall. In the re-analysis, one small worry was that Philae might just topple, if it landed on a slope at high speed. So the lander team developed a special device called a ëtilt limiter', and attached it to the lander before lift-off, to prevent this happening. In fact, the unknown nature of the landing environment only serves to highlight why the Rosetta mission is vital in the first place. Astronomers and planetary scientists need to learn more about these dirty snowballs that orbit the Sun.

-- Edited by Blobrana on Friday 16th of October 2009 10:42:12 PM