TV grab on Aug. 18, 2007 shows astronauts Clayton Anderson and Dave Williams conducting their final spacewalk of Endeavour mission outside the International Space Station. (Xinhua Photo/AFP) Photo Gallery>>>

    WASHINGTON, Aug. 18 (Xinhua) -- Astronauts Clayton Anderson and Dave Williams wrapped up the fourth or final spacewalk of Endeavour mission on Saturday, following the successful completion of a series of tasks outside the International Space Station (ISS).

    Anderson, an ISS flight engineer, and Williams, an Endeavour mission specialist, began the spacewalk at 9:17 a.m., 44 minutes ahead of schedule. The spacewalk, initially slated to run about 6.5 hours in duration, lasted for about five hours.

    Overnight, mission managers decided to shorten the spacewalk so that the crews can close the hatches earlier. The decision preserves the option to have Endeavour undock from the station on Sunday and prepare for a landing on Tuesday, one day ahead of scheduled landing on Wednesday.

    The earlier landing is being considered in the event approaching Hurricane Dean threatens the Houston area. It could allow an opportunity for the shuttle to land before Mission Control, Houston, would be shut down in preparation for a storm.

    However, mission managers will review the forecast for Dean and mission activities Saturday afternoon during their daily meeting and assess their options before making a final decision later in the day.

    During Saturday's spacewalk, Anderson and Williams installed a shuttle inspection boom stand on the station, retrieved a pair of materials exposure experiments for return to Earth, and secured an S-band antenna mount. They also installed a wireless sensor system antenna before wrapping up the spacewalk.

    The two spacewalkers were very careful during the excursion and checked their spacesuit gloves with more frequency after their fellow spacewalker found a small hole on one of his gloves on Wednesday, curtailing a spacewalk that day.

    As the shuttle-station complex passed over a daylit Earth, the spacewalkers paused in their work to gaze at Hurricane Dean, which is roaring toward Jamaica and the Gulf of Mexico with an intensity just under the threshold of Category 5 and could be extremely devastating.

    "Hoo man, you can't miss that," Williams said from his perch outside the ISS. "Holy smokes, that's impressive."

    "Scary," Anderson said of the storm. "It's only impressive whenit's not coming to you."

    Another dramatic episode took place three hours into the five-hour spacewalk when a fire alarm sounded inside the station.

    The station crew rushed to check and only found out that it wasa false alarm. The interruption did not affect the spacewalk.