[meteorite-list] Rosetta Warms Up for Mars Swing-By

[Ron Baalke]

http://www.esa.int/esaCP/SEMNJ8D4VUE_index_0.html

Rosetta warms up for Mars swing-by
European Space Agency 
29 November 2006

This month the team working on ESA's Rosetta mission have been
particularly busy. 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-tonne 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 manoeuvres 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
manoeuvres 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 13 November 2007.

To aim Rosetta precisely at Mars, two deep-space manoeuvres 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
manoeuvre complex. This is why mission controllers at ESA's European
Space Operations Centre (ESOC) in Germany are carefully monitoring the
spacecraft's path in space and preparing to perform trajectory
correction manoeuvres 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
characterise 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 favourable 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.

 
For more information
 
Gerhard Schwehm, ESA Rosetta Mission Manager
Email: gerhard.schwehm @ esa.int

Andrea Accomazzo, ESA Rosetta Spacecraft Operations Manager
Email: andrea.accomazzo @ esa.int