NASA space shuttle Discovery astronauts wrapped up their third and final spacewalk this morning after successfully attaching a new ammonia tank to the International Space Station.

During a six-hour, 24-minute spacewalk this morning, Mission Specialists Rick Mastracchio and Clayton Anderson also relocated a portable foot restraint and readied cables on the backbone of the station for installation of a spare Space to Ground Ku-Band antenna .

The astronauts did hit have difficulty securing a used-up ammonia tank that had been removed from the station walls in the space shuttle's cargo bay. The trouble forced a delay in the spacewalk, forcing NASA to postpone plans to "retrieve a light-weight adapter plate assembly from the Columbus laboratory."

The astronauts were able to finally secure the old ammonia tank in preparation for its return to earth aboard the shuttle, and to complete the installation of a new one outside the space station. The ammonia tank is part of the space station's cooling system

Various shuttle missions over the past year have been focusing on bringing new equipment, spare parts and supplies to the space station. NASA is trying to stock it up before its space shuttle fleet, which has been the cargo workhorse for the station, is retired. The last shuttle flight is scheduled for September, though NASA's Inspector General recently issued a report predicting that the final flight will be pushed back to some time next year.

Discovery was launched early in the early morning hours on Monday, April 5 from Kennedy Space Center in Florida, carrying about 17,000 pounds of supplies and equipment to the space station.

Late last week NASA officials added a day to the now 14-day mission. The astronauts will use the extra day in space to conduct an inspection of the shuttle's heat shield.

The crew did a standard check of the heat shield the day after the shuttle was launched. However, a malfunctioning Ku-Band antenna on Discovery meant that the information could not be sent immediately down to Mission Control for analysis. The follow-up inspection will be conducted while the shuttle is docked to the space station so communication instruments on the station can send the data to Earth.