Two astronauts will float outside the International Space Station Saturday on the last spacewalk of their mission, one aimed at performing some last few maintenance chores on the orbiting laboratory.

Clad in bulky NASA spacesuits, Discovery shuttle astronauts Danny Olivas and Christer Fuglesang plan spend 6 1/2 hours working outside the space station to prepare the orbital outpost for future missions.

The spacewalk is slated to begin at 4:49 p.m. EDT (2049 GMT). It is the third and last spacewalk of Discovery's 13-day mission to the space station to boost the space station's supplies and science gear.

"I think the challenge is really to not lose eyes on the goal, and that is basically to conduct three safe and successful EVAs," Olivas said in a news conference late Friday using NASA's term for spacewalks. "We have two under our belts ... but two behind us doesn't mean that the third one is going to be as much or even more of a challenge."

Saturday's spacewalk includes a hodgepodge of maintenance tasks to replace broken components and prepare the space station for the arrival of spare parts and a new room over the next year. The astronauts plan to replace a broken part of the station's attitude control system and an old circuit breaker, as well as install new navigation antennas and deploy a vital spare parts attachment point.

Olivas and Fuglesang also plan to string a set of 60-foot (18-meter) power and data cables along the space station's hull to support a new module slated to arrive early next year. The cables can be stiff in space and hard to handle, mission managers said.

"They can get to be like a bundle of snakes so we have a good plan in place on how to route these and how to secure them," said Zeb Scoville, NASA's lead spacewalk officer for Discovery's mission.

Saturday's spacewalk will mark the fifth career excursion for both Olivas and Fuglesang. Fuglesang, who is Swedish and represents the European Space Agency, has already performed more spacewalks than any other European astronaut and expected Saturday's excursion to be his last.

"It will also feel a little bit sad because there won't be any more chances," said Fuglesang, who is making his second spaceflight, in a news conference late Friday. "But I'll try to enjoy the moment as much as I can and focus on the work I have to do."

The current spacewalk record is held by Russian cosmonaut Anatoly Solovyov with 16 spacewalks and more than 80 hours of orbital work.

Discovery launched toward the space station last week to deliver new science gear, supplies and a treadmill named after comedian Stephen Colbert. The shuttle also ferried a new crewmember for the station's six-person crew.

Discovery is due to undock from the space station on Tuesday and return to Earth on Thursday.

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SPACE.com is providing complete coverage of Discovery's STS-128 mission to the International Space Station with Managing Editor Tariq Malik and Staff Writer Clara Moskowitz in New York. Click here for shuttle mission updates and a link to NASA TV. Live spacewalk coverage begins at 3:50 p.m. EDT.