Late Saturday night, NASA's Mars Science Laboratory spacecraft successfully fine-tuned its course to better zero in on its target entry point into the Martian atmosphere on landing day. Two brief thruster firings totaling about seven seconds altered the spacecraft's velocity slightly, by about one-fortieth of one mile per hour (one centimeter per second). This trajectory correction maneuver—the fourth since MSL's launch—adjusted the point at which Curiosity will enter the Martian atmosphere by about 13 miles (21 kilometers). On landing day, MSL can steer enough during its flight through the upper atmosphere to correct for a miss of the target entry point by a few miles and still land within its target ellipse. Mission engineers and managers rated the projected 13-mile miss big enough to warrant a correction maneuver. Telemetry and tracking data indicate the maneuver was successful. MSL will have two further opportunities for additional course corrections during the final 48 hours before landing, if needed.