PARIS -- The three-pronged radar instrument aboard Europe's Mars Express satellite has been fully deployed and put through initial tests and is expected to start operations in July following a 10-day commissioning period, the European Space Agency (ESA) announced June 22.

The radar, featuring two 20-meter and one 7-meter boom antennas, is designed to study Mars' atmosphere and to look up to 5 kilometers beneath its surface for water. Its deployment had not been completed until now because of concerns that the antennas would snap back toward the satellite's body while they were being unfolded, damaging the satellite or its other instruments.

Mars Express, launched in June 2003, arrived in Mars orbit in December 2003.

With deployment and initial checkout completed, the Mars Advanced Radar for Subsurface and Ionosphere Sounding, or Marsis, instrument will undergo detailed tests of its observing power.

Starting July 4, it should be ready for operations. An initial subsurface examination is expected to be possible for about two weeks.

After that, the Mars Express satellite's orbit will carry it out of optimal range for this work, and Marsis will be used for atmospheric sounding.

The satellite's orbit is expected to take it closer to the planet's surface starting in November. Subsurface soundings can be made when Mars Express is no more than 800 kilometers from the martian surface. The satellite's orbit varies between 260 and 11,000 kilometers in altitude.