Astronauts at the International Space Station have completed the second spacewalk of five, during the shuttle Endeavour's 11-day mission at the station.  

Astronauts Dave Wolf and Tom Marshburn undertook a 6-hour, 53-minute spacewalk Monday to conduct maintenance work at the station.  The walk coincided with the 40th anniversary of man's landing on the moon.

Wolf and astronaut Tim Kopra completed the first spacewalk of the mission during a 5.5-hour operation Saturday.  They installed an external platform on the massive Japanese lab at the space station. The lab is known as Kibo, or "hope."

The platform will allow scientists to conduct experiments in the vacuum of space.

With the shuttle crew's visit, there are 13 astronauts aboard the space station, the most ever.  Kopra is taking the place of Japan's Koichi Wakata, who has been on the space station since March.