On 13 November 2009 Rosetta will swing by Earth and pass within 2500 km of Earth's surface. The manoeuvre is the fourth and last in a series of gravity assists and will provide the spacecraft with the required orbital boost to set course for the mission's final destination: comet 67P/Churyumov-Gerasimenko.

Since its launch on 2 March 2004 Rosetta has made a long journey through the inner Solar System and has already performed three planetary gravity assists.

Gravity assists
Earth 4 March 2005

Mars 25 February 2007

Earth 13 November 2007

Earth 13 November 2009

The third and final Earth swingby will, coincidently, occur exactly two years after the previous gravity assist in November 2007. When completed, the four swingby's together will have provided the spacecraft with the orbital energy required to escape the inner Solar System and travel out to nearly the orbit of Jupiter for a rendezvous with comet 67P/Churyumov-Gerasimenko in 2014.

The Earth swingby is critical for the success of the overall mission. During the swingby the highest priority is therefore given to spacecraft operations. However, science observations of the Earth and Moon, with several instruments on both the Rosetta orbiter and Philae lander, are also planned during this swingby.

Plotting the course
A dedicated navigation campaign is underway to ensure the spacecraft is on the right trajectory for the third Earth swing-by (see also status report no. 121 in right-hand menu). The flight dynamics team at ESOC determines what, if any, course adjustments need to be made.

Information on Rosetta's current trajectory comes from telemetry transmitted by Rosetta and from Doppler and ranging data received from the ESA and NASA ground stations that are tracking the spacecraft regularly.

Four specific time slots are reserved for trajectory correction manoeuvres (TCM) should they be needed. The first and primary TCM has been successfully performed on 22 October, three weeks before closest approach. The three additional time slots for possible further refinement of the spacecraft's approach trajectory are at 1 week, 1 day and 6 hours before closest approach (see the timeline above).

During a TCM Rosetta fires its four 10-Newton axial thrusters for a precisely determined length of time, to impart the required change in the spacecraft's velocity vector.

Preparing for the third Earth swingby: End of hibernation and check-out activities
In preparation for the Earth swingby, the Rosetta spacecraft was reconfigured to active cruise mode on 8 September 2009, following an extended period of hibernation in passive cruise mode.

These hibernation periods are part of the normal mission planning and are introduced because of the long mission duration (more than 10 years between launch and the arrival of Rosetta at comet 67P/Churyumov-Gerasimenko). During the hibernation periods all instruments are switched off.

The end of the hibernation on 8 September was directly followed by standard check-out activities of both the spacecraft and instruments (on the orbiter as well as the lander). The instruments were switched on in turn to perform software updates and verifications in preparation for the swing-by operations. The check-out activities were completed in early October.

Details of these preparatory activities can be found in status reports numbers 118 through 120 (see related link in the right-hand menu).

Next stop: asteroid Lutetia
After the third Earth swingby Rosetta will be on the long final leg of its journey towards comet 67P/Churyumov-Gerasimenko. Before reaching this final destination Rosetta will mark another milestone when the spacecraft performs a flyby of asteroid Lutetia on 10 July 2010.

Several instruments on the Rosetta orbiter and the Philae lander will study asteroid Lutetia from the unique vintage point during the flyby.

For most of the remainder of its cruise through the outer Solar System, Rosetta will be configured in deep space hibernation, from July 2011 to January 2014.

Two major trajectory manoeuvres are planned right before and after the deep space hibernation. These will synchronize Rosetta's orbit with that of comet 67P/Churyumov-Gerasimenko, leading up to the spacecraft's rendezvous with the comet in May 2014.