NASA’s efforts to clear the way for the Spirit rover to reach Mars’ surface have so far failed, and engineers are considering alternative routes for maneuvering the six-wheeled robot off its lander, scientists said Thursday morning. NASA planned to try one more time to gather up the deflated air bags that cradled Spirit during landing but now blocks the ramp engineers want to use as the rover’s exit to the Martian soil. “We were not successful in doing that yesterday,” said Matt Wallace, mission manager for Spirit’s sixth day of operations.