Washington - Two NASA astronauts began the second spacewalk of the Atlantis mission on Saturday to complete another round of chores outside the International Space Station (ISS). Astronauts Mike Foreman and Randy Bresnik were to add more storage capacity on the station shell to hold parts and supplies.
A false alarm aboard the ISS had delayed the start of their spacewalk by more than an hour.
The alarm woke up both crews two hours after they went to sleep and warned them of a drop in pressure. This caused the ventilation system to shut down automatically, which in turn activated a fire alarm.
NASA said there was no danger to the astronauts, but decided to delay the spacewalk for an hour to give the crew time to get more sleep.
After the Atlantis mission, only five more shuttle flightsto the ISS remain before the programme is retired in 2010, and there is a rush to maximize the heavy lifting capability of the shuttle to ferry backup supplies to the orbiting station.
Since storage is a premium inside the station,new carriers are being attached outside for the equipment on the current mission.
During the first spacewalk on Thursday, two astronauts installed a backup antenna to the outside of the station and completed other maintenance work.
Thefinal spacewalk of the mission is slated for Monday. Atlantis is to disembark on Tuesday and arrive back on Earth next Friday.
It will leave behind two containers with12,360 kilogrammes of spare parts: Gyroscopes that help keep the ISS at the proper altitude in space; an extra hand for the station's robotic arm; a gas tank for providing oxygen to the airlock during spacewalks; parts for the station's cooling system.
NASA is at work on developing the next generation spacecraft with an eye on returning humans to the moon or travelling to Mars and beyond. But full support for the plans is still pending in the halls of government.
