Spacewalk starts amid preps for early departure

Spacewalkers Clay Anderson and Dave Williams are heading outside the International Space Station as crewmates inside the visiting shuttle Endeavour prepare for a potential early departure from the outpost.

Anderson and Williams switched their spacesuits to internal battery power at 9:17 a.m. EDT, marking the official start time for the fourth and final excursion of the Endeavour's mission to the station.

You can watch the spacewalk unfold here in The Flame Trench. Simply click the link below the Mission Webcast headline to launch our NASA TV viewer. Start up time is about 20 seconds.

Williams will be answering to the call sign "EV-2" and is wearing a pure white spacesuit. Anderson is "EV-3" and is wearing a suit with broken red horizontal stripes on its legs.

Tracy Caldwell will be orchestrating the spacewalk from inside the joined shuttle-station complex, which is circling 215 miles above Earth.

The original timeline for the spacewalk is here: EVA_4_Detailed_timeline.pdf.

The astronauts aim to complete all the major tasks on the timeline with the exception of some work with debris shields on the outside of the U.S. Destiny lab and the U.S. Unity module. They had planned to bolt down the shields, which now are simply tied down, but the work was dropped to hasten preps for a possible shuttle departure from the station around 7:56 a.m. Sunday.

Crewmates inside the shuttle and the station are hustling to finish hauling supplies and equipment between a Spacehab module in Endeavour's cargo bay and the station. The hurry-up is aimed at closing hatches between the joined spacecraft at 5 p.m. today. The crews now are scheduled to bid adieu at 4:46 p.m.

The latest version of the NASA TV schedule for STS-118 -- Rev O -- details times for major mission operations today. Note that the schedule beyond crew wake-up on Sunday is TBD: tvsked_revo.pdf.

The rush is being triggered by Hurricane Dean, which is churning through the Caribbean and could threaten NASA's Mission Control Center at Johnson Space Center in Houston.

Click to enlarge the 8 a.m. track from the National Hurricane Center in Miami:

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A decision on a possible early undocking is expected to be made at the 2 p.m. Mission Management Team meeting today. A post-MMT news briefing will be webcast live here in The Flame Trench beginning at 5 p.m. EDT.

NOTE ON IMAGES: Click to enlarge the NASA screen grab (top) that shows astronauts Dave Williams (in the pur white suit) and Clay Anderson (in the suit with broken red stripes on its legs) as they floated out of the outer hatch of the U.S. Quest airlock at the International Space Station. You can also click to enlarge the National Hurricane Center track on Hurricane Dean.