{"id":4851,"date":"2014-01-19T17:49:41","date_gmt":"2014-01-19T09:49:41","guid":{"rendered":"http:\/\/stuif.com\/blog\/?p=4851"},"modified":"2022-07-06T13:02:35","modified_gmt":"2022-07-06T05:02:35","slug":"wake-up-rosetta","status":"publish","type":"post","link":"https:\/\/stuif.com\/blog\/?p=4851","title":{"rendered":"Wake up, Rosetta!"},"content":{"rendered":"

Almost ten years ago, in March 2004, the European Space Agency (ESA<\/a>) launched a spacecraft with an ambitious mission: to orbit and land on a comet. The spacecraft was called Rosetta. Once in orbit around the comet, a small probe, called Philae, would be launched to make a soft landing on the comet. In this artist impression you see Rosetta in orbit and Philae on its way down to the comet.<\/p>\n

\"Rosetta<\/a><\/p>\n

Destination of Rosetta is the comet\u00a067P\/Churyumov\u2013Gerasimenko<\/a>\u00a0This “dirty snowball” as comets are sometimes called, was discovered in 1969. It has a diameter of 4 km and orbits the Sun with a period of 6.45 year. Comet orbits are very elliptical, when they are close to the sun, some of the comet material evaporates and gives rise to the famous comet tail. At the moment this comet is on its way to the Sun, reaching its closest distance (perihelion) in August 2015.\u00a0Here is a model of the comet nucleus, generated from images taken by the Hubble telescope.<\/p>\n

\"Nucleus<\/a><\/p>\n

If everything goes as planned Rosetta will reach comet\u00a067P\/Churyumov\u2013Gerasimenko in May 2014. A few months later, in November 2014, the probe will land on the surface of the comet. End of mission in December 2015.<\/p>\n

Why does it take so long to reach the comet? Have a look at this diagram, where you see the orbit of the comet (red), the orbits of Earth and Mars (green and blue) and the flight path of Rosetta (dashed line).<\/p>\n

\"Rosetta<\/a><\/p>\n

The reason for the complicated flight path is that it is not feasible to give the spacecraft enough speed at launch to reach its target. To give the spacecraft its required speed, one or more so-called gravitational slingshots<\/a>\u00a0are needed.The\u00a0principle\u00a0is\u00a0this: steer the spacecraft close to a planet or moon. Because these objects have their own (high) speed, the force of gravitation can give extra speed to the spacecraft. \u00a0A simple analogy can be found in sports. When a ball hits a stationary held tennis racket, the speed of the ball will basically remain the same (only reversed). But when the player moves the racket towards the ball, the ball will bounce back with a much higher speed.<\/p>\n

Rosetta has used four of these slingshots, marked in the diagram above \u00a0Three times with Earth (2,4,6) and once with Mars (3). Imagine how accurately the scientists have to steer!<\/p>\n

Actually they did it in a clever way so there were a few bonuses..:-) The second slingshot by Earth (4) was performed in such a way that the path of Rosetta would cross the path of an asteroid, Steins, on 5 September 2008! Perfect to test if all equipment was still working correctly. Here is an image of this rather small (diameter ~ 6 km) asteroid, taken by Rosetta during the fly-by (5 in the diagram). Closest distance between the two ~ 800 km, distance from the Sun more than 300 million km. Amazing.<\/p>\n

\"Stein<\/a><\/p>\n

The last slingshot brought Rosetta in a very elliptical orbit, similar to the target comet. This is necessary because the spacecraft must approach the comet with a low relative speed, otherwise it can not go into orbit around the comet<\/p>\n

Again a bonus, a spectacular one. The path of Rosetta crossed the orbit of another asteroid, a big one (diameter ~ 120 km), called Lutetia. Here is a picture. Asteroids are as old as the solar system, what an inferno it must have been in the beginning, noticing the surface pockmarked with craters.<\/p>\n

\"Lutetia\"<\/a><\/p>\n

The very elliptical orbit of Rosetta after the last slingshot, means that it is moving very far from the Sun. And it depends on the Sun for it uses solar power. The engineers came with an ingenious solution, they let Rosetta go into hibernation<\/span>!<\/p>\n

On 9 June 2011, they sent a signal to Rosetta to switch off all instruments, keeping only the main computer and some heating alive, and starting a timer. It worked, because from then on the spacecraft did not send any signals.<\/p>\n

For more than two and a half years there has been no communication with Rosetta! The timer has been programmed to give Rosetta a wake up call on 20-1-2014 at 10.00 GMT. The wake up process will take many hours. The controlled spinning has to be stopped, the antenna has to be pointed to earth etc, etc. It is expected that the first signal should reach Earth around 17:30-18:30 GMT (Malaysia time is GMT + 8 hours).<\/p>\n

You can follow the events on Monday 20-1-2014 via live streaming (starts 9:15 GMT):<\/p>\n