Astronauts on Tuesday moved a solar array to its new position on the International Space Station, a key step to ensuring the station maintains its power supply.

Space shuttle Discovery astronauts Scott Parazynski and Doug Wheelock began a spacewalk on Tuesday morning at 4:45 a.m. ET to guide the station's robotic arm operators in moving a truss carrying the solar arrays to the port side of the station. They then bolted the massive structure in place.

Spacewalker Doug Wheelock exits the U.S. Quest joint airlock to begin the mission's third spacewalk.
(NASA TV)

The truss carries solar panel arrays, which have provided power for seven years, from their old location at the centre of the station. The astronauts began unfurling the panels Tuesday their full length of 73 metres from tip to tip, but stopped short when a rip was spotted in the second panel. They sent down photos of the rip so that NASA can evaluate the extent of the damage.

Getting the panels up and running has become even more important for the crews of Discovery and the space station since a malfunction was discovered in a rotary joint on a separate set of solar panels on the opposite side of the station. The rotary joint allows the solar panels to tilt in the direction of the sun.

Before the spacewalk was completed, Parazynski inspected the rotary joint on the newly installed array to see what a perfectly functioning unit looks like compared with the malfunctioning one.

On a Sunday spacewalk astronauts found what appeared to be metal shavings inside the malfunctioning starboard rotary joint. NASA officials said it would remain in a parked position until the problem is resolved. The joint, which was installed in June, has been experiencing electrical current spikes for nearly two months.

To provide time for the inspection, NASA has added an extra day to the mission. Discovery is now set to return to Earth on Nov. 7.

Should repairs be required, NASA said they would take place after Discovery departed.

On Friday, astronauts Stephanie Wilson, Clay Anderson and Daniel Tani installed an Italian-built connection module called Harmony to a temporary home on the station.

Harmony will be moved in front of the U.S. Destiny Laboratory on the station before the next shuttle flight arrives with the European Space Agency's Columbus module around Dec. 8.

Once the move is complete, Harmony will serve as the connection between Destiny and two new laboratories, Columbus and the Japanese Kibo module, which is set to arrive in two pieces, in February and April.