Russian Federal Space Agency experts are puzzled by the rising orbit of the Phobos-Grunt unmanned Mars probe, Roscosmos deputy head Vitaly Davydov said on Tuesday.

The probe was launched on November 9 but its engines have not put it on course for the Red Planet. The craft, designed to bring back rock and soil samples from the Martian moon Phobos, is currently moving along a so-called support orbit and has been rising by up to one kilometer a day.

"Unfortunately, we still don't have any telemetric information from the spacecraft so we don't understand what's going on," Davydov said.

"The most interesting part is that Phobos-Grunt is on an oriented flight course but, according to our data, something unusual is happening with it."

He suggested that the spacecraft's control system might still be functional or there could have been a fuel leak, causing its orbit to rise.

A Russian expert earlier said one reason for the spacecraft's unexpected behavior could be the aerodynamic resistance of its solar batteries acting as wings and pushing it up.

According to another industry expert, Phobos-Grunt will not fall to Earth until mid-March because of its rising orbit.

All attempts to receive a signal from the spacecraft have so far been unsuccessful.

According to NASA, Russia has failed all 17 attempts to study the Red Planet since 1960.

The most recent failure occurred in 1996, when Russia lost its Mars-96 orbiter during launch.

Source: RIA Novosti