Efforts of Russian space officials to salvage the Phobos-Grunt mission have not been successful and in a worst case scenario, the spacecraft could re-enter the Earth's atmosphere but will not likely hit a populated area.

Experts, however, cannot agree as to when exactly the craft could come falling back to Earth. Some reports said it could fall out of the orbit in a week or two, while the NASA has suggested that it could maintain its orbit until December.

The RIA Novosti reported that according to Vladimir Popovkin, head of the Russian space agency, the spacecraft could fall into the Earth but it won't harm anyone.

"There are 7.5 metric tons of fuel in the aluminium tanks on board. We have no doubts that they will explode [and destroy the probe] upon re-entry," Popovkin told RIA Novosti. "It is highly unlikely that its parts would reach Earth."

In another report, Major General Vladimir Uvarov, a former top space expert in the Russian Armed Forces told the Rossiiskaya Gazeta newpaper: "In my opinion, the Phobos-Grunt probe has been lost. This probability is very high. At any rate, it is much higher than the chances for reactivating the probe," Major General Uvarov said.

The Phobos-Grunt mission's problems arose when the engines that were supposed to propel the spacecraft towards Mars failed to ignite after the launch. It has been orbiting the planet, running only on reserve battery power since Wednesday, and is losing both altitude and speed each time it completes an orbit.

Russian space officials, together with scientists from the ESA and NASA had been trying to re-establish contact with Phobos-Grunt but this has been unsuccessful.

The Daily Mail reported that according to Roscosmos spokesman Alexei Kuznetsov, since the problem with the Phobos-Grunt probe is likely a hardware failure, not a software-related issue, that there was little chance that they would be able to fix the damage.

"I think we have lost the Phobos-Grunt," Uvarov said. "It looks like a serious flaw. The past experience shows that efforts to make the engines work will likely fail."

With officials preparing for the worst, attention is now focused on the nitrogen teroxide and hydrazine fuel onboard the 14.6 ton spacecraft.

Russian officials are hoping that the fuel will remain in its liquid form during re-entry, exploding before it reaches the ground. However, former NASA scientist and current space consultant James Oberg reportedly said that the fuel could freeze, survive re-entry, and create a serious environmental hazard upon impact.