[meteorite-list] Mars Express Radar Ready to Work

[Ron Baalke]

http://www.esa.int/SPECIALS/Mars_Express/SEMEV82DU8E_0.html

Mars Express radar ready to work
European Space Agency 
22 June 2005

ESA PR 34-2005. MARSIS, the Mars Advanced Radar for Subsurface and
Ionosphere Sounding on board ESA's Mars Express orbiter, is now fully
deployed, has undergone its first check-out 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 day to 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 Prof. 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