N° 34-2005 – Paris, 22 June 2005

Mars Express radar ready to work

MARSIS, the Mars Advanced Radar for Subsurface and Ionosphere Sounding onboard
ESA’s Mars Express orbiter, is now fully deployed, has undergone its first
checkout and is ready to start operations around the Red Planet. With this
radar, the Mars Express orbiter at last has its full complement of instruments
available to probe the planet’s atmosphere, surface and subsurface structure.

MARSIS consists of three antennas: two ‘dipole’ booms 20 metres long, and one
7-metre ‘monopole’ boom oriented perpendicular to the first two. Its importance
is that it is the first- ever means of looking at what may lie below the surface
of Mars.

The delicate three-stage phase of radar boom deployment, and all the following
tests to verify spacecraft integrity, took place between 2 May and 19 June.
Deployment of the first boom was completed on 10 May. That boom, initially
stuck in unlocked mode, was later released by exploiting solar heating of its
hinges.

Taking advantage of the lessons learnt from that first boom-deployment, the
second 20-metre boom was successfully deployed on 14 June. Subsequently, ESA’s
ground team at the European Space Operations Centre (ESOC) in Darmstadt,
Germany, commanded the non-critical deployment of the third boom on 17 June,
which proceeded smoothly as planned.

MARSIS’s ability to transmit radio waves in space was tried out for the first
time on 19 June, when the instrument was switched on and performed a successful
transmission test.

The instrument works by sending a coded stream of radio waves towards Mars at
night, and analysing their distinctive echoes. From this, scientists can then
make deductions about the surface and subsurface structure. The key search is
for water. But MARSIS's capabilities do not stop there. The same methods can
also be used by dayto probe the structure of the upper atmosphere.

Before starting its scientific observations, MARSIS has to undergo its
commissioning phase. This is a routine procedure for any spacecraft instrument,
necessary to test its performance in orbit using real targets in situ. In this
case, the commissioning will last about ten days, or 38 spacecraft orbital
passes, starting on 23 June and ending on 4 July.

During the commissioning phase, MARSIS will be pointed straight down (nadir
pointing mode) to look at Mars from those parts of the elliptical orbit where
the spacecraft is closest to the surface (around the pericentre). During this
phase, it will cover the areas of Mars between 15° S and 70° N latitude. This
includes interesting features such as the northern plains and the Tharsis
region, so there is a small chance of exciting discoveries being made early on.

On 4 July, when the commissioning operations end, MARSIS will start its nominal
science observations. In the initial phase, it will operate in survey mode. It
will make observations of the Martian globe’s night-side. This is favourable to
deep subsurface sounding, because during the night the ionosphere of Mars does
not interfere with the lower-frequency signals needed by the instrument to
penetrate the planet's surface, down to a depth of 5 kilometres.

Through to mid-July, the radar will look at all Martian longitudes between 30° S
and 60° N latitude, in nadir pointing mode. This area, which includes the
smooth northern plains, may have once contained large amounts of water.

The MARSIS operation altitudes are up to 800 kilometres for subsurface sounding
and up to 1200 kilometres for studying the ionosphere. From mid-July, the
orbit's closest approach point will enter the day-side of Mars and stay there
until December. In this phase, using higher frequency radio waves, the
instrument will continue shallow probing of the subsurface and start atmospheric
sounding.

“Overcoming all the technical challenges to operate an instrument like MARSIS,
which had never flown in space before this mission, has been made possible
thanks to magnificent cooperation between experts on both sides of the
Atlantic,” said Professor David Southwood, ESA's Science Programme Director.
“The effort is indeed worthwhile as, with MARSIS now at work, whatever we find,
we are moving into new territory; ESA’s Mars Express is now well and truly one
of the most important scientific missions to Mars to date,” he concluded.

Note to editors

The MARSIS instrument was developed by the University of Rome, Italy, in
partnership with NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California.
The instrument team is led by Professor Giovanni Picardi. It is the first
instrument to actually look below the surface of Mars, using low frequency
microwaves reflected by the different layers of matter. Among its primary
objectives are the attempt to detect underground water ice and the
characterisation of terrains underneath layers of sediment. In addition, MARSIS
will conduct large-scale altimetry mapping and provide data on the planet’s
ionosphere, as this electrically-charged region of the upper atmosphere reflects
radio waves too.

Mars Express was launched on 2 June 2003 and reached the Red Planet on Christmas
Day that same year. MARSIS was planned to deploy its three antenna booms in
April 2004, towards the end of the orbiter’s commissioning phase. Computer
simulations pointed to a risk that the booms could lash back and harm the
spacecraft and its instruments during deployment. ESA therefore delayed
deployment until the boom supplier (JPL) and the spacecraft prime contractor
(Astrium, France) together with ESA’s experts had conducted further analyses and
simulations of boom behaviour during deployment and the possible impact on the
spacecraft. Once the magnitude of the risk involved had been assessed and the
relevant mitigation scenarios defined, ESA decided to proceed with releasing the
MARSIS antennas in May 2005.
For more information contact:

Fred Jansen
ESA, Mars Express Mission Manager
E-mail: fjansen @ rssd.esa.int

Agustin Chicarro
ESA, Mars Express Project Scientist
E-Mail : agustin.chicarro @ esa.int

ESA Media Relations Division
Tel. :+33(0)1.53.69.7155
Fax : +33(0)1.53.69.7690