Astronauts on another spacewalk at the ISS

HOUSTON, July 12 (UPI) -- NASA astronauts took another walk in space Wednesday, this time demonstrating on-orbit health shield repair techniques.

The excursion, which began at 7:20 a.m. EDT, was the third EVA during the shuttle Discovery's current mission at the International Space Station.

The spacewalkers demonstrated repair work on pre-positioned heat shield materials in the payload bay. Among the tools they used were a space-certified caulk gun and a variety of spatulas to manipulate the test materials.

The spacewalk by Mission Specialists Mike Fossum and Piers Sellers also involved testing an infrared camera by performing a 60-second recording of two sample damaged tiles. The camera is designed to capture temperature gradients that will indicate invisible damage.

The spacewalk was coordinated by Pilot Mark Kelly, with Commander Steve Lindsey overseeing shuttle and video systems. Mission Specialists Lisa Nowak and Stephanie Wilson were the robot arm operators.

Mission controllers at the Johnson Space Center in Houston said the shuttle is scheduled to return to Earth on Saturday.