Wake up, Rosetta!

Almost ten years ago, in March 2004, the European Space Agency (ESA) 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.

Rosetta and Philae

Destination of Rosetta is the comet 67P/Churyumov–Gerasimenko This “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. Here is a model of the comet nucleus, generated from images taken by the Hubble telescope.

Nucleus of 67P

If everything goes as planned Rosetta will reach comet 67P/Churyumov–Gerasimenko 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.

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).

Rosetta flight path

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 are needed.The principle is this: 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.  A 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.

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

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.

Stein asteroid

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

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.


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!

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.

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).

You can follow the events on Monday 20-1-2014 via live streaming (starts 9:15 GMT):

More information can be found on the ESA Wake Up Rosetta page. They have done a good publicity job. For example they have organised a Wake Up Rosetta competition for the general public. You can create a video and submit it (until tomorrow). Here is the Facebook page where you can view the contributions. And vote for your favourite!

Tomorrow will be a nerve-wrecking and nail-biting day for many scientists!

UPDATE 21-1-2014

Rosetta has woken up! Yesterday at 18:20 GMT a big applause started in the ESA control room, when a spike appeared in the spectrum analyser. It was the first signal from Rosetta, which had traveled for 45 minutes to reach Earth, 800 million km away.. In Malaysia it was already 2:20 am but I could not sleep, had to watch…:-) Here are two screenshots from the live blog

The signal

Hello World, I am awake

This was a sign of life, next step will be to receive a health report. What a brilliant achievement.

Another update

A friend sent me a link to an ESA webpage: Where is Rosetta An animation of the path of Rosetta through the Solar System. Breathtakingly beautiful. You can zoom in and out, tilt, etc. The page takes time to load, but really worth the effort !


5 thoughts on “Wake up, Rosetta!

  1. Fingers crossed tomorrow, they were talking about it on the Stargazing Programme recently on the Television here in the UK. I think The Jodrell Bank Observatory here in the UK is involved in the wakeup call. As a Amateur Radio operator, I am still amazed that we can send Radio signals so far out into space to remotely control such a small speck that is Rosetta.

    • As I understand it, Earth can not send a wake up call! During hibernation Rosetta is spinning, the antenna is not pointing to Earth, etc. It is the timer in Rosetta itself that has to give the wake up signal. It will stop the spinning, orient itself on the stars, find out where Earth is, point the antenna in the right direction, etc. There is nothing scientists can do than wait for a signal from Rosetta. And bite their nails, probably…:-)

      • That’s even MORE impressive! As another amateur radio operator (W6DBZ)–although inactive for many years–I find it awesome to imagine the complexity of designing the hardware and software to calculate the relative position of Earth from celestial observations (I had to learn celestial navigation when I was in the U.S. Navy in the 1950’s). But then, the entire project is almost beyond belief!

        • Hi Don,
          One of the members in my radio club, works at the Mullard Space Laboratories, here in Southern England. and has been involved in the project.
          At our Sunday chin wag meet today, he was explaining as Jan has said that it is Rossetta that has to wake itself up. Once it hopefully comes out of hibernation, it will then go into a engineering mode to bring up the required systems to be able to tell the world it wide awake. As he explained its going to be another expensive Cock up if it stays in Hibernation, will watch with anticipation tomorrow.
          73,’ Robert

  2. At 18:20 GMT on 20-1-2014, a green spike appeared on the spectrum analyser in the Rosetta control room. A thundering applause. Rosetta had woken up. It must have been nerve-wrecking for the scientists and engineers. What a brilliant success.

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