(AP) -- A pair of astronauts finished installing a fresh storage tank outside the International Space Station on Tuesday, accomplishing a main mission objective that required three spacewalks.
Rick Mastracchio hooked up the fluid lines for the ammonia tank as soon as he and Clayton Anderson floated out early Tuesday morning on the final spacewalk of shuttle Discovery's mission. He was done within minutes.
"Very nice work, Rick," astronaut Dorothy Metcalf-Lindenburger radioed from inside.
The ammonia and nitrogen hoses should have been connected during Sunday's spacewalk. But the astronauts had trouble attaching the new tank to the space station because of a stubborn bolt, and some chores had to be put off.
Flight controllers began activating the tank - part of the space station's cooling system - as soon as the lines were in place. The spacewalkers paused to take pictures.
"Look over here," Anderson told Mastracchio. "Oh, baby, you're going to want to take this one to the grandkids."
Their next big chore was to put the old, virtually empty tank aboard Discovery so it can be returned to Earth next week. NASA will fill it and fly it back up this summer as a spare.
The space agency wants to stockpile as many big parts up there as possible. Only three shuttle missions are left after this one, and there will be limited room on the much smaller Russian, European and Japanese cargo ships that will be supplying the station until its projected end in 2020.
President Barack Obama will outline his objectives for NASA's human spaceflight program Thursday during a visit to Kennedy Space Center. He's already axed his predecessor's effort to return astronauts to the moon.
At the start of Tuesday's spacewalk, Mastracchio had a little trouble opening the hatch. Mission Control asked them to check the handle before they left the air lock. Everything seemed to be in place.
Discovery will depart the space station Saturday and return to Earth on Monday.
NASA is keeping the shuttle docked an extra day in order to move up a survey of the wings and nose, a routine search for micrometeorite damage. The shuttle's main antenna is broken, and so the laser images must be sent down from the station. Normally, the inspection is conducted after a shuttle leaves.
Explore further: Russia announces plan to build new space station with NASA