Unreliable? The Mars Science Laboratory. Credit: NASA/JPL-CALTECH

The launch of the Mars Science Laboratory, a one-tonne rover, has been delayed from October 2009 until late 2011.

NASA officials were concerned by the reliability of the motor units that drive both the rover's wheels and the joints of its robotic arm. The mission to look for signs of past life on Mars was slated to cost $1.6 billion when it was authorized in 2006, but now it is predicted to need between $2.2 billion and $2.3 billion to enable it to run until 2014. NASA expects to have to delay other missions to help cover the cost.

The increasing expense of Mars exploration prompted Ed Weiler, NASA's associate administrator for science, to announce that the agency will partner with the European Space Agency on future major missions.