(Updates possible landing times, paragraph 8)

By Irene Klotz

CAPE CANAVERAL, Fla., June 21 (Reuters) - NASA will try again on Friday to bring the U.S. space shuttle Atlantis and seven astronauts home after bad weather prevented its planned landing in Florida on Thursday.

The shuttle has been in orbit since June 8 to install a pair of solar power wings on the International Space Station and prepare the outpost for new laboratories built by Europe and Japan.

Flight directors had two opportunities to land the shuttle on Thursday but the Kennedy Space Center was socked in by thick clouds and threatened by thunderstorms -- typical summer weather for the sultry subtropical Florida peninsula.

"We looked at it as hard and long as we think is reasonable," astronaut Tony Antonelli radioed from mission control to Atlantis commander Frederick Sturckow, explaining the decision to skip Thursday's landing opportunities.

The shuttle has enough fuel and supplies to stay in space until Sunday, but it cannot land in rain because it could damage the thousands of ceramic tiles that protect its belly from the fiery heat of re-entry.

After Thursday's wave-off, Sturckow fine-tuned the shuttle's orbit with a brief engine burn to position it for an extra landing opportunity on Friday at the backup runway at Edwards Air Force Base in California.

Atlantis could land at Edwards, in the Mojave Desert north of Los Angeles, if Florida's bad weather persists.

The first possible touchdown at Kennedy Space Center on Friday will be at 2:18 p.m. EDT (1818 GMT) and a second at 3:55 p.m. (1955 GMT), although flight directors could decide to use that flyover to divert Atlantis to California, with a possible landing there at 3:49 p.m. EDT (1949 GMT).

Additional California landing opportunities are at 5:23 p.m. EDT (2123 GMT) and 6:59 p.m. EDT (2259 GMT).

STORMY WEATHER

Weather conditions at both sites are questionable, with forecasts calling for more rain and clouds at Kennedy Space Center and high winds at Edwards.

"We're going to be fighting the same challenges at KSC. At Edwards, the winds are going to pick up," Antonelli said. "We are going to try to land tomorrow."

While NASA battled weather on the ground, its Russian partners in the $100 billion space station program wrestled with the outpost's balky computers.

The primary system shut down last week while astronauts were hooking up the station's new solar panels.

Station commander Fyodor Yurchikhin and flight engineer Oleg Kotov were able to bypass suspect circuitry and eventually revive the computers, which are needed to keep the station properly positioned in orbit.

The station crew disconnected two of the three computer systems on Thursday from the jumper cables used to bypass the circuits but failed to restart the network.

A third computer system remained operational.

The cause of the computer crash, which raised the prospect the station might have to be temporarily abandoned, remains a mystery.

The Atlantis mission, which was delayed from March after the shuttle's external fuel tank was damaged in a hailstorm in late February, is the first of four shuttle flights scheduled this year.

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