Russia has until early December to establish contact with the stranded Phobos-Grunt Mars probe and send it toward the Red Planet, the head of the Russian space ageny said Monday.

Phobos-Grunt's mission was to pick up samples from the surface of Phobos, the largest moon of Mars, and return them to Earth in 2014. Credit: IKI
 
Speaking to reporters after the launch of a three-man crew to the International Space Station, the chief of the space agency said Phobos-Grunt is in control of its flight and is maintaining its orientation toward the sun to generate electricity.

But controllers have not communicated with the probe since it launched Nov. 8. Phobos-Grunt's main propulsion system did not ignite for either of two planned firings to propel itself out of low Earth orbit and on a course to Mars.

Vladimir Popovkin, head of Roscosmos, said the 29,000-pound spacecraft should remain in orbit until January, but the planetary window to reach Mars closes in early December. Launches to Mars are only possible approximately every 26 months when the planets are in the correct position in the solar system.

If engineers can't recover Phobos-Grunt, it will continue flying in orbit and crash back to Earth in the next month or two.

Nicholas Johnson, a NASA orbital debris expert, said Friday he expects Phobos-Grunt to fall back into Earth's atmosphere around late December.

Popovkin said it will only be possible to further pinpoint the timeframe of Phobos-Grunt's re-entry when it reaches an altitude of 180 kilometers, or about 112 miles. As of late Monday, Phobos-Grunt was orbiting between 129 miles and 205 miles above Earth, according to U.S. military tracking data.

The source of the uncertainty in the timing of the potential re-entry is fluctuating solar activity, which can cause the atmosphere to expand and contract, changing the effect of drag on orbiting satellites.

Phobos-Grunt and its propulsion pack are encapsulated inside the Zenit rocket's nose shroud before launch. Credit: Roscosmos
 
Because Phobos-Grunt is in a low-altitude orbit, communications stations only have about seven minutes to attempt to contact Phobos-Grunt on each pass, Popovkin said.

Without two-way communications, engineers are unable to diagnose what went wrong after launch or upload new software and commands to fire Phobos-Grunt's engine.

Popovkin's comments were the first official statement from Roscosmos on the Phobos-Grunt mission since Nov. 9. Russian news reports since then quoted unnamed sources and outside experts, but the leadership of Roscosmos had been silent until Monday.

The space agency chief rejected accusations the Phobos-Grunt probe was launched with design flaws.

Popovkin also stressed a re-entry of Phobos-Grunt would pose no threat to Earth, saying its full load of toxic rocket propellant inside aluminum fuel tanks would explode high in the atmosphere and pose no danger to the public.

Johnson also said aluminum tanks would rupture and explode during re-entry, whether the propellant inside was frozen or liquid. Phobos-Grunt, which was designed to retrieve and return samples from the Mars moon Phobos, carries an entry capsule with a heat shield that could survive and reach the surface.