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ESA's Rosetta Spacecraft Wakes Up from long Hibernation

January 20, 2014

ESA's Rosetta orbiter has woken up from a 31-month Hibernation on Monday to begin an ambitious year of operations to become the first craft to rendezvous with a comet, follow it as it makes its close approach to the Sun and deploy the Philae lander onto its surface. 

Launching atop an Ariane 5G+ rocket on March 2, 2004, Rosetta set sail on a long journey headed for a ten-year cruise through the solar system to eventually link up with Comet 67P/Churyumov–Gerasimenko in order to deploy the lander and escort the comet during its close encounter with the sun. To reach its destination, Rosetta had to complete a complex series of engine burns and flybys of Earth and Mars to boost its orbit around the sun for the Rendezvous with 67P more than ten years after launch.

Image: ESA/ATG Medialab

The 3,000-Kilogram spacecraft made its first critical engine burn on May 10, 2004 followed by smaller maneuvers to set the stage for the first Flyby of Earth on March 4, 2005. 

Image: CNES

Rosetta's Trajectory

Earth as seen during the final Flyby

After this initial boost given to the spacecraft by Earth, Rosetta was in an orbit that took it beyond the orbit of Mars for a flyby on February 25, 2007. Rosetta was then inbound again, heading for its second Earth flyby that occurred on November 14, 2007 and again increased the vehicle's orbital velocity around the sun, also increasing the aphelion of the orbit. Once in this orbit, Rosetta was set for a flyby of asteroid 2876 Šteins. Zipping by at a relative speed of 31,000 Kilometers per hour, Rosetta came as close as 800 Kilometers to the asteroid. This flyby was used to test out the instrument suite of the spacecraft and lander.

The Rosetta orbiter is equipped with a 165-Kilogram payload package comprised of 11 instruments consisting of optical imagers, spectrometers, particle analyzers, dust sensors and microwave instruments. Philae, the small 100-Kilogram lander, carries ten instruments that include panoramic and microscopic imagers, gas analyzers, a drill and sampling system, a radio sounder, surface & subsurface probes, a magnetometer and plasma monitor as well as electrical, acoustic and dust impact monitoring equipment. These instruments were operated during the flybys of Mars and Earth and the close-encounters with asteroids. 

After its flyby of Steins, Rosetta traveled back to the inner Solar System and performed its third and final Earth flyby coming as close as 2,481 Kilometers on November 13, 2009, further boosting its orbit around the sun to place Rosetta on its trajectory to 67P. Along the way, the spacecraft completed another flyby of an asteroid after observing other bodies from a distance. On July 10, 2010, Rosetta flew past asteroid 21 Lutetia and again used its instruments for several days before and after the approach. 

Following its final planned flyby, Rosetta was on a path towards aphelion more than five Astronomical Units from the Sun. As no spacecraft events were planned from that point on and solar power generation is limited that far from the sun, Rosetta was sent into a deep sleep of two and a half years on June 8, 2011. 

In its Hibernation Mode, Rosetta was only powering its computer running core functions and hibernation heaters - all other systems were completely turned off as Rosetta ventured out to a point 790 million Kilometers from the sun. While in hibernation, Rosetta was spin stabilized. Throughout hibernation, no communications were possible with the spacecraft and the Mission Team on Earth had no insight into the status of the spacecraft for two and a half years. 

On Monday at 10 UTC, the onboard computer triggered the wake-up sequence which was a carefully designed process to ensure Rosetta would get back to a safe configuration. The procedure included the activation of the core systems of the spacecraft including heaters and avionics. The sequence was programmed to slowly warm up the vehicle's systems to make sure none would be damaged as a result of a sudden temperature change. 

The Attitude Determination and Control System was activated and Rosetta slowed down its spin rate, determined its attitude using its star-trackers and performed a re-orientation to point to Earth before starting to power on transmitters to send its first signal back to Earth approximately seven hours after waking up. Being sent from a point 807 million Kilometers from Earth, Rosetta's signal traveled 44 minutes and 53 seconds before reaching Earth where NASA's 70-meter Deep Space Station at Goldstone (DSS-14) was listening for it starting around 14:35 UTC on Monday. DSS-43, Canberra, Australia started listening at 18:15 UTC.

At ESOC, all eyes were on the screens displaying the spectrum analyzer as Goldstone was scanning for Rosetta's signal which was anticipated to arrive between 17:30 and 18:30 UTC if everything had gone nominally aboard the spacecraft. 

For the first 45 minutes of the first acquisition window, only noise showed up on the screens and the mood among the many guests at ESOC started to get tense, but such a delay was not unexpected as there were a number of scenarios that could lead to Rosetta starting to transmit later.

Rosetta's carrier signal arrived at 18:17 UTC and was relayed from Goldstone & Canberra to the European Space Operations Center in Germany where Mission Controllers quickly confirmed that Rosetta had woken up as expected and went into a planned Safe Mode. This acquisition of signal confirmed that Rosetta was alive after its long hibernation, but a lot of work lies ahead for the Mission Team. Over the coming days and weeks, teams will first establish two-way communications with the X-Band System of the spacecraft and then start downlinking housekeeping telemetry to assess the health of all spacecraft systems. 

Photo: ESA Web TV

Above: Goldstone picks up ambient noise as teams wait for Rosetta's signal
Below: Rosetta's signal shows up as prominent peak in the spectrum

Photo: ESA Web TV

Once all systems are fully operational and Rosetta has transitioned from a Safe Mode to nominal operations, the 11 orbiter and 10 lander instruments can be activated again for re-commissioning and calibrations that will take several weeks to complete. 

Image: ESA/ATG Medialab

As Rosetta gets closer to comet 67P, the instruments will start gathering data and the spacecraft will complete a series of maneuvers to link up with the 4-Kilometer wide comet. Rendezvous maneuvers will begin in May as Rosetta's imagers start tracking the comet to precisely determine its trajectory. 

In August, Rosetta will arrive in its operational orbit from where the spacecraft will perform its science mission that will begin with extensive mapping of the comet to find a suitable landing site for the Philae lander.

In November, the lander will be deployed for a touchdown on the surface. Upon contact, Philae will be secured on the surface using harpoons. Once at the surface, Philae will begin its mission which will be the first in-situ examination of the nucleus of a comet. Philae will characterize the chemical composition of the nucleus and characterize its physical properties. Also, comet activities and surface evolution over time as the comet gets closer to the sun will be studied. 

While Philae is performing close-up science on the surface, Rosetta will continue science operations in orbit using its remote sensing instruments and direct sensing systems to study the comet as it travels in its orbit, starting to get closer to the sun for the perihelion passage on August 13, 2015. 

Comets are of particular interest to scientists because they may hold information on the early stage of the Solar System. Considered basic building blocks of the Solar System, Comets likely brought Water to planet Earth and possibly delivered the ingredients for the formation of life. Rosetta will perform an unprecedented close-up study of comet 67P to unlock the secrets that it might hold to learn more about the formation and evolution of the Solar System.

The Rosetta mission is expected to last until late 2015. 

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