A Mars probe's tank is expected to melt during re-entry, so there's no need for a missile intercept, like in 2008, experts say.
Russia's failed Mars probe is due to fall to Earth on Sunday or Monday.
The spacecraft, stranded after a botched launch on Nov. 8, has more than 10 tons of toxic rocket fuel aboard.
The fuel is expected to incinerate during the plunge through the atmosphere, eliminating the need for a missile intercept.
When a botched launch stranded a U.S. spy satellite close to Earth four years ago, the military took action.
Concerned that the satellite's rocket fuel could pose a contamination risk if the uncontrollable spacecraft re-entered the atmosphere over populated areas, the Pentagon ordered the Navy to shoot down the crippled bird so any debris would land harmlessly in the ocean.
The operation was successful and the threat from 100 pounds of rocket fuel averted.
On Sunday, Russia's failed Phobos-Grunt Mars probe, which carries more than 10 tons of propellant, is expected to plunge back to Earth, though experts say this time the fuel, despite its great mass, isn't as much of a concern.