NASA on Saturday started the countdown again to launch the space shuttle Discovery after extensive troubleshooting to fix the faulty sensor that scuttled the first attempt.

Liftoff is set for 10:39 a.m. Eastern time Tuesday from Kennedy Space Center, with forecasters predicting a 60 percent chance of favorable weather.

Discovery's astronauts arrived in Florida on Friday, saying they hope for dry skies when they climb aboard their spaceship again.

"We hope we can give you a good show," Discovery commander Eileen Collins said. "We're really excited about getting this launch off, we're very prepared, and we'll be talking to you from space."

The main weather issues for Tuesday are isolated showers and clouds in the launch area, said shuttle launch weather officer Katherine A. Winters. She said tropical storm Franklin, a concern earlier, is no longer considered to be a threat.

Discovery's crew is to dock at the international space station to deliver supplies and make a series of spacewalks. The mission is NASA's first shuttle flight in the more than 21/2 years since seven astronauts died aboard Columbia in 2003.

Discovery already was fueled and just hours from liftoff July 13 when a fuel sensor failed to respond to computer commands during routine pre-launch testing. NASA called off the launch.

The agency has not been able to figure out the glitch definitively, but engineers suspect that electromagnetic interference from subtle grounding problems caused the sensor to fail.

The sensor is one of four that alert the shuttle's computers when the external tank is about to run out of hydrogen. The sensors are a precautionary measure, not needed during a normal launch because the tank carries more hydrogen than is required to get into orbit.