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Shuttle ready for third launch attempt

The space shuttle Columbia, twice kept earthbound by mechanical problems within a day of its scheduled launching, is set to soar into space today with a medical laboratory and a cargo of human and animal patients. The mission, which is to examine the medical aspects of space flight, was pronounced ready for flight Tuesday by controllers at NASA's Kennedy Space Center here. But the mission was threatened once again with delays.

Air Force weather forecasters were concerned Tuesday about a cool front moving in from Canada that increased the chance of excessive cloudiness, thunderstorms and lightning in the launching area.

There was a 50 percent chance of unacceptable weather that would delay a liftoff scheduled for 8 a.m., the beginning of a two-hour launching window, but a 60 percent chance of favorable conditions during the entire period, the forecasters said.

Technicians also noticed a loose piece of foam insulation on the giant external fuel tank attached to the orbiter spacecraft. After reattaching the insulation, engineers ran tests of the bonding strength of the repair before deciding to pump a half million gallons of liquid hydrogen and liquid oxygen fuel into the tank.