PARIS -- The second of two 20-meter-long radar booms on Europe's Mars Express satellite will be deployed the week of June 13, an event that should permit the spacecraft to begin looking deep beneath Mars' surface for water, the program's manager said June 8.

Fred Jansen, Mars Express mission manager at the European Space Agency (ESA), said the release of the second Marsis boom antenna will be prepared by orienting the satellite toward the sun to permit the boom to warm up first.

The first Marsis antenna failed to lock fully into position when it was unfolded in May and was deployed May 10 only after it was exposed to the sun. Mission managers concluded that one of the antenna's joints had become stiff after such a long period in stowed position. Mars Express was launched in June 2003.

Because of concerns that the Marsis boom antennas could damage other Mars Express experiments in the event of a whiplash during deployment, the antennas remained stowed to give the six other sensors time to gather information about Mars' atmosphere and surface.

Jensen said in an interview that Mars Express will be made ready for the second boom antenna's deployment starting June 13, with the antenna to be unfolded over a two-day period starting June 15.

If all goes well, the third and final radar boom, this one just 7 meters long, will be deployed on June 20, followed by a three-week testing period.

Jensen said that once successfully deployed, the Marsis radar will spend the first five months taking readings mainly of Mars' atmosphere rather than peering deep beneath its surface. The satellite's orbit between now and November is such that lighting conditions are not favorable to take subsurface readings.

Deployment of the second 20-meter boom also will permit ESA ground controllers to fly the satellite in its normal mode. Since the first boom's deployment, Mars Express has been kept in "robust" mode to compensate for the minor disequilibrium resulting from having only one of the two unfolded.

European science managers in September are expected to approve a 23-month extension of the Mars Express mission, to December 2007, with the Marsis radar soundings to be the highlight of the next two years' operations.