Max Planck Institute for Solar System Research | 2011 Jun 08
Rosetta comet probe enters hibernation in deep spaceThree years before its arrival the camera system on board the space probe Rosetta renders the first images of its destination.
Approximately 163 million kilometers still separate ESA's spacecraft Rosetta from comet Churyumov-Gerasimenko, its 2014 target. Despite this remarkable distance, scientists from the Max Planck Institute for Solar System Research (MPS) in Germany have succeeded in obtaining the first images of the remote destination using the onboard camera system OSIRIS. These pictures were generated during the tests performed by the team during the last weeks. After the successful completion of these tests, Rosetta will now start its almost three year hibernation period: In order to save energy on the last part of the way offering only little sunlight, all systems will be powered down.
In these first images comet Churyumov-Gerasimenko appears as a single point of light covering only a few pixels. "But the pictures already give us a good idea of where we are headed", says Dr. Holger Sierks from MPS, OSIRIS Lead Investigator. "In addition, they are a remarkable proof of the camera's performance. We had not expected to be able to create first images from so far away".
Comet Churyumov-Gerasimenko is extremely faint. Its brightness is approximately a million times less then that of the faintest star that can be discerned from Earth with the naked eye. Astronomers studying the comet from Earth use the European Southern Observatory's Very Large Telescope in Chile, one of the world's most powerful telescopes with a main mirror diameter of eight meters. OSIRIS's mirror measures only approximately ten centimeters in diameter.
In order to make the comet visible despite these challenges, an exposure time of 13 hours was necessary. "All in all, we took 52 images with OSIRIS, each exposed for 15 minutes", explains Dr. Colin Snodgrass from MPS, responsible for data processing. Since within a period of a few hours the comet moves relative to the background of fixed stars, the first step was to align all of the images and correct for this motion. After further refined steps of data processing (for example subtracting the fixed stars) the researchers were able to catch a first glimpse of their destination.
Before they get a chance at a second glimpse, it will, however, be a long wait. The systems on board Rosetta will be powered down today for approximately three years. In this way the solar panel powered spacecraft saves energy while it is far from the Sun - until it reawakens in the spring of 2014 and takes a next look at "its" comet.
The spacecraft Rosetta has been en route to comet Churyumov-Gerasimenko since 2004. OSIRIS, the scientific camera system on board, was developed and built under the lead of the MPS in cooperation with a team bringing together members of six European countries. It consists of a wide- and a narrow-angle camera. The camera system is operated by scientists from MPS.
ESA Space Science | 2011 Jun 08
The final command placing ESA's Rosetta comet-chaser into deep-space hibernation was sent earlier today. With virtually all systems shut down, the probe will now coast for 31 months until waking up in 2014 for arrival at its comet destination.
Today's dramatic event marks the end of the hugely successful first phase of Rosetta's ten-year cruise and the start of a long, dark hibernation during which all instruments and almost all control systems will be silent.
The deep sleep is made necessary by the craft's enormous distance from the Sun and the weakness of the sunlight falling on its solar panels, which cannot produce enough electricity to power the probe fully.
Arcing through millions of kilometres of space
Between now and January 2014, Rosetta will arc unattended through millions of kilometres of cold, distant space, heading toward a rendezvous with 67-P/Churyumov-Gerasimenko.
Only the computer and several heaters will remain active. These will be automatically controlled to ensure that the entire satellite doesn't freeze as its orbit takes it from 660 million km from the Sun out to 790 million km and back between now and 2014.
"We sent the command via NASA's 70 m Deep Space Network station in Canberra, Australia, ensuring the signal was transmitted with enough power to reach Rosetta, which is now 549 million km from Earth," said ESA's Spacecraft Operations Manager Andrea Accomazzo.
"We'll monitor via ESA's 35 m station at New Norcia in Australia for a few days to see if any problems occur, but we expect to receive no radio signal until 2014. Rosetta's on her own now."
Wake up call in 2014
On 20 January 2014, a timer will wake the slumbering spacecraft, which will then transmit a signal to Earth to announce that its revival.
Mission controllers will then spend several weeks gradually warming up and reactivating the spacecraft in preparation for its rendezvous with the comet in July 2014.
Mission controllers at ESOC, ESA's Space Operations Centre, Darmstadt, have spent most of the past year preparing for hibernation.
A special hibernation mode of the spacecraft was designed by engineers at EADS Astrium, the main industrial prime contractor that build Rosetta, to allow it to survive the large distances from the Sun during its cruise.
All of the scientific instruments were switched off by the end of March. In April and May, with Rosetta orbiting at more than 600 million km from the Sun, tests were conducted with the solar arrays to confirm that sufficient power would be available for today's hibernation.
Final shut-down command sent today
At 08:00 UT (10:00 CEST) today, Rosetta automatically started spinning, which will stabilise the probe while the normal attitude control system is off throughout hibernation, and at 12:58 UT (14:58 CEST) the final shut-down command was sent. Confirmation of successful entry into hibernation came at 14:13 UT (16:13 CEST) when radio contact was lost, as expected.
"With flybys of asteroids Steins in 2008 and Lutetia in 2010, Rosetta has already delivered excellent scientific results," says Paolo Ferri, Head of ESOC's Solar and Planetary Mission Operations Division.
"Hibernation is a necessary step to reach the final target. We are now looking forward to 2014, when Rosetta becomes the first spacecraft to track the life of a comet as it arcs in toward the Sun."
