Bound For 2014 Rendezvous With Comet
The team working on
ESA's Rosetta mission have been particularly busy in November.
Activities are underway to set the spacecraft's trajectory, and
prepare the on-board instruments ready for the next major mission
milestone: the swing-by of planet Mars in February 2007.
Since its launch in March 2004, Rosetta has been bouncing around
the inner solar system on a trajectory that will eventually lead it
to its final destination in the first half of 2014 -- comet 67P
Churyumov-Gerasimenko. As the three-ton spacecraft could not be set
by its launcher onto a trajectory that would take it directly to
the comet, a series of four planetary gravity-assisted maneuvers
were introduced into the mission design.
Swing-bys allow a spacecraft to gain energy in a 'natural' way,
by exploiting the gravitational energy of massive planetary bodies
such as planets, similar to the way in which a slingshot is used to
release a stone. The Mars swing-by in February next year is the
second of these maneuvers for Rosetta, as the first Earth swing-by
took place in March 2005. After next February's Mars swing-by, the
next Earth swing-by will take place on November 13, 2007.
To aim Rosetta precisely at Mars, two deep-space maneuvers were
carried out on 29 September and 13 November of this year. Rosetta
will make its closest approach to Mars on 25 February when it will
be just 250 km above its surface.
Close vicinity to the
planet is essential for the spacecraft to make the most efficient
use of the swing-by -- however, this also makes the maneuver
very complex. Mission controllers at ESA's European Space
Operations Center (ESOC) in Germany are carefully monitoring the
spacecraft's path in space and preparing to perform trajectory
correction maneuvers 16 and 7 days before Rosetta makes its closest
approach to Mars.
Rosetta's close vicinity to Mars will also provide an excellent
opportunity to take a close look at the planet. Using the on-board
instruments both on the orbiter and the Philae lander, the Rosetta
scientists will be able to calibrate their instruments and
complement ESA's Mars Express data by carrying out a 'mini'
observation campaign in the weeks around the Mars swing-by. Science
operations will start at the beginning of January 2007, and be
'formally' concluded at the end of March.
Looking at Mars
In preparation for the Mars' observation, earlier this week
mission controllers at ESOC commenced a full series of instrument
checks. These operations, which included switching on the
instruments and checking their pointing performance, will last
about a month.
Between 2 and 3 January 2007 Rosetta will 'warm-up' its on-board
camera OSIRIS to take a look at the asteroid 21-Lutetia that lies
between the orbits of Mars and Jupiter in the Asteroid Belt. The
purpose of this 36-hour observation campaign is to understand the
rotation direction of the asteroid. This valuable information will
enable scientists to characterize this target so that Rosetta can
study it in greater detail in July 2010, when the spacecraft will
pass within about 2000 km of the asteroid.
Rosetta will be able to observe Mars from about 20 hours before
it makes its closest approach to about a few weeks after. Before
making its close approach to Mars, priority will be given to
spacecraft operations. If the in-flight tests planned for 7 January
reveal that the spacecraft's illumination and thermal conditions
are not favorable for its own navigational security, then all the
science operations that are to be carried out before it makes its
close approach will have to be cancelled.
In any event, just
around the time of closest approach, the orbiter's instruments will
be switched off for about three hours, and the spacecraft will be
put in eclipse mode. This is to prepare the spacecraft for a period
of eclipse that will last for 25 minutes and take place as Rosetta
goes behind Mars and enters its shadow. During this eclipse period
the solar arrays will not 'see' the Sun and will not be able to
produce any power.
However, a few scientific instruments on the Philae lander will
still be operating and taking measurements during the eclipse as
the lander has its own independent power system. This is because
once the lander is on the surface of the comet, ready to carry out
its mission, it has to survive autonomously without the orbiter's
support.
Rosetta will use its imaging system and imaging spectrometers to
gather data about the surface and atmosphere of Mars and its
chemical composition. It will also collect data about the
atmosphere's interaction with the solar wind and the Martian
radiation environment, and it will image the two natural satellites
of Mars: Phobos and Deimos.
During the Mars swing-by, Rosetta's velocity and trajectory will
also be accurately measured to check if any anomalous spacecraft
acceleration can be observed.