NASA scrambled on Wednesday to deal with two power problems at the International Space Station that could delay future missions and make it even harder to finish building the orbiting outpost before the space shuttles retire.

Both issues competed for the precious little spacewalking time that’s left in Discovery’s mission, which already was extended a day after the first problem cropped up last weekend. Spacewalks were scheduled for Thursday and Saturday.

Astronauts Scott Parazynski and Douglas Wheelock were getting ready on Wednesday to spend the mission’s fourth spacewalk, thoroughly inspecting a malfunctioning rotary joint that keeps the station’s solar panels turned toward the sun. But that task may be pre-empted if NASA can figure out how to repair a giant solar wing that ripped as it was being unfurled on Tuesday. The tear forced the space agency to halt the process before the wing was fully extended.

Until at least one of the problems is resolved, the station won’t be able to generate enough power to support the new equipment, such as a European lab that is supposed to be delivered by Atlantis in December. Delaying the mission would set back other deliveries, including the planned February installation of a new Japanese lab.

NASA is up against a hard 2010 deadline for completing the space station and retiring the three remaining shuttles. The solar wing damage marred an otherwise hugely successful day. Two of shuttle Discovery’s crew had just finished a seven-hour spacewalk to install the beam that holds the wings.

Astronauts took pictures of the wing tear, but NASA engineers couldn’t tell what caused the damage, space station flight director Heather Rarick said. “Until we know what we think the cause is, maybe until we get some better pictures, I don’t think we really have any solid leads on how to fix it yet,” Rarick said.

Earlier space station program manager Mike Suffredini said astronauts could cut whatever might be snagging the solar wing and possibly sew up the tear.