PASADENA, Calif. - Both of NASA (news - web sites)'s aging Mars rovers have been experiencing problems but continue to explore opposite sides of the Red Planet, the Jet Propulsion Laboratory said Wednesday. A semiconductor component aboard the Spirit rover did not power up while commands were being executed on Aug. 1, affecting the ability to use its three spectrometer instruments. Engineers believe the problem likely involves the timing of instruction signals reaching the component, called a gate array, within microseconds of each other. If that is confirmed, the likely solution would be to insert a delay between the signals,...