Enlarge NASA/AFP/Getty Images U.S. astronaut Tom Marshburn, lower right, tightens some bolts outside the International Space Station. Astronauts from space shuttle Endeavour ventured into open space on the mission's second spacewalk aimed at helping complete the International Space Station. CAPE CANAVERAL (AP)  The astronauts aboard the shuttle-station complex celebrated the 40th anniversary of man's first moon landing with their own spacewalk Monday, heading outside to stockpile some big spare parts. In the second outing of their mission, David Wolf and Thomas Marshburn anchored a 6-foot dish antenna on the international space station for future use, then did the same with a hefty pump and an engine for a rail car. The spacewalk unfolded 40 years to the day that two other astronauts —Neil Armstrong and Buzz Aldrin— strolled the moon's dusty surface. It was the 202nd spacewalk by Americans since the Apollo 11 lunar excursion. Inside Mission Control, a clock counted down to 4:17 p.m. ET, the moment the Eagle set down on the Sea of Tranquility on July 20, 1969. It wasn't until two hours later, as the spacewalk was ending, that the astronauts made note of this "special day." Earlier in the day at a Washington news conference, some of the Apollo astronauts, including Aldrin, suggested the $100 billion poured into the space station had not yielded much and that the outpost would be better used as a testbed for human missions to Mars and even asteroids. "We've spent a lot of money up there for almost nothing," said Apollo 13 commander Jim Lovell. "It's almost a white elephant and until we can really get a return on our investment of that particular project, then it was money wasted." Meanwhile, the $15.6 million space station toilet that broke down Sunday was up and running again, after the crew added some new parts. The commode — one of three on the linked station and shuttle Endeavour — was out of action for about 24 hours. NASA wanted the station commode working again as soon as possible. With a record number of people on board — 13 — having three working toilets is crucial. Complicating matters was the fact that Endeavour cannot eject any waste water while it's docked to the space station. The water would spray all over the porch attached two days ago to the Japanese lab, and possibly corrode it. With the toilet fixed, there was no longer any worry about coming close to filling Endeavour's waste water tank. There were a few moments of concern midway through the seven-hour spacewalk, however, when Marshburn reported that one of the hooks on his safety tethers was not anchored to the station. The antenna work was held up while he reeled his 85-foot tether back out, trying not to drag the line against critical equipment. Despite everything, he remained connected to the station the entire time. The antenna and other spare parts that were attached to the space station were hauled up by Endeavour. It was grueling work for the spacewalkers because of the tight clearances. NASA wants to have as many extra pieces up there as possible so that when the shuttles stop flying next year, the station will be able to get along without their big deliveries. None of the other spacecraft that visits the outpost can hold nearly as much cargo as the shuttle. Monday's spacewalk was much quieter than the one Saturday. Loud static filled the airwaves throughout the earlier excursion, the result of improperly positioned microphones in an astronaut's helmet. The cap with those microphones will not be used again. Three more spacewalks are planned during Endeavour's station visit, which ends July 28. Copyright 2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed. Guidelines: You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. Read more