NASA's delayed Mars Science Laboratory mission (pictured) is experiencing further problems as it jostles for space in a crowded launch schedule.

The nuclear-powered rover, which will search for evidence of past life on Mars, is due to launch at the end of 2011, two years later than planned.

But the mission's first possible launch window, in October, would be tightly constrained by the August 2011 launch of Juno, a mission to study Jupiter's magnetic and gravitational fields. A second launch window is available in December, but that would favour landing sites in Mars's northern hemisphere, potentially reopening the debate over what part of the planet the rover should explore. Resolving the dilemma could add US$50 million to the already vastly over-budget mission, now expected to cost up to $2.3 billion over its lifetime.