PARIS — The Russian space agency, Roscosmos, on Jan. 12 said its large Phobos-Grunt spacecraft, which failed to leave low Earth orbit after its Nov. 8 launch, likely would re-enter the Earth’s atmosphere on Jan. 15 or Jan. 16.

With an estimated weight of more than 13,000 kilograms including fuel, Phobos-Grunt would be the largest spacecraft to make an uncontrolled atmospheric re-entry since NASA’s 6,000-kilogram Upper Atmosphere Research Satellite (UARS) broke up over the Pacific Ocean in September.

Roscosmos had said earlier that it expected Phobos-Grunt, designed to return samples to Earth from Mars’ largest moon, would mostly burn up as it plummeted through the atmosphere, but that 20 to 30 pieces weighing a total of no more than 200 kilograms were likely to hit the Earth’s surface.

As of Jan. 12, Roscosmos said the pieces that survived, notably the small lander that was designed to bring back Phobos samples, could come down off the east coast of southern Africa.

But Roscosmos said pinpointing a precise time and location of re-entry would be impossible until just hours before the spacecraft hit the upper atmosphere, and even then may not be predictable.

In the case of UARS, NASA officials were at pains to determine exactly where pieces fell in the Pacific Ocean even after the event.

Brian Weeden, technical director and orbital debris expert at the Secure World Foundation, a Washington think tank, said that even the U.S. Air Force’s Space Surveillance Network of ground-based radars are unable to predict when and where a satellite will break up in the atmosphere on re-entry.

In a Jan. 12 interview, Weeden said the publicly available data about Phobos-Grunt suggested that its aluminum fuel tanks would quickly succumb to the stress of re-entry, eliminating toxic fuel as a risk if the breakup occurred over land.

Similarly, he said the several kilograms of radioisotope Cobalt-57 on board were almost certain to be obliterated as the spacecraft crashed through the atmosphere. Given the small amount of Cobalt-57 and the likely protective measures Russian designers took in packaging it, Weeden said, the radioactive material should not be viewed as a special concern.

A spacecraft like Phobos-Grunt, whose orbit was relatively circular — according to Roscosmos, on Jan. 12 its flight path had an apogee of 193.9 kilometers and a perigee of 163.5 kilometers — could enter the atmosphere at just about any point in its orbit, Weeden said. For Phobos-Grunt, that means an area anywhere between 51.4 degrees north latitude and 51.4 degrees south latitude.

Weeden said that several hours before Phobos-Grunt was to enter the atmosphere it was possible that the Joint Space Operations Center at Vandenberg Air Fore Base, Calif., which tracks man-made orbital objects, would be able to warn any inhabited areas that may be in the Phobos-Grunt debris field.

Beyond that, he said, the expansion and contraction of the atmosphere due to solar activity, and the wind conditions in the upper atmosphere in the region of the spacecraft’s re-entry, combine to make it impossible to make accurate predictions.

“As much as we would like to believe we can make these calculations with high accuracy, we can’t,” Weeden said. “Predicting exactly when and where an object will land on the ground is beyond our capacities.”

It is unclear what if any effect the loss of Phobos-Grunt will have on Russia’s space science program, which has already suffered in the past decade as Russia has focused on satellite navigation and space-based telecommunications.

But one possible beneficiary could be the stalled U.S.-European joint Mars exploration program, called ExoMars. With NASA hesitating to commit to the project, which calls for launches in 2016 and 2018, the 19-nation European Space Agency (ESA) and NASA have opened talks with Roscosmos about Russia joining ExoMars as a third partner.

ESA Director-General Jean-Jacques Dordain said Jan. 9 that Roscosmos appears ready to take part in ExoMars, notably by providing a heavy-lift Proton rocket for the 2016 mission, designed to carry an ESA-built telecommunications orbiter to Mars, and a European entry, descent and landing capsule.

Russian instruments likely would be added to this package.

Dordain said Russian authorities have said they are looking for a fresh long-term space project with ESA now that Russia’s Soyuz rocket has been successfully operated from Europe’s Guiana Space Center in French Guiana, on the northeast coast of South America. ExoMars, he said, could be it.

A decision on ExoMars is expected sometime in February, once NASA has a better idea of its 2013 budget and its ability to finance the project.



ESA Abandons Effort To Contact Russia’s Stranded Mars Probe

European Tracking Antenna Loses Contact with Phobos-Grunt

ESA Makes Contact with Russia’s Stranded Phobos-Grunt Spacecraft

Peter B. de Selding was the Paris bureau chief for SpaceNews.