CAPE CANAVERAL, Fla. - The weather looks good for NASA?s planned Saturday launch of the shuttle Discovery to deliver a massive new laboratory to the International Space Station.

?Everything is coming together for launch and that includes the weather,? said shuttle weather officer Kathy Winters during a morning briefing here at NASA?s Kennedy Space Center. ?There?s an 80 percent chance of good weather on Saturday.?

Discovery is set to lift off from a seaside launch pad tomorrow at 5:02 p.m. EDT (2102 GMT) to haul the $1 billion Japanese Kibo laboratory toward the space station. The shuttle?s seven crewmembers, led by commander Mark Kelly, are scheduled to perform three spacewalks to install the new room during their planned 14-day mission.

If Discovery does not launch tomorrow, the weather begins to deteriorate, with an increased chance of thunderstorms delaying the launch.

?If we do happen to delay 24 hours we start to get a little more concerned,? Winters said. ?There?s a 30 percent chance of KSC weather prohibiting launch.?

If the shuttle?s liftoff is delayed by 48 hours, the chances of bad weather disrupting the launch rise to 60 percent.

Plans for launch appear to be progressing smoothly, with no last-minute issues hindering preparations. Shuttle workers have packed away a last-minute addition, a spare toilet pump for the space station?s bathroom, so astronauts aboard the outpost can repair the space toilet in orbit. The station?s toilet went on the fritz last week and astronauts need the new pump to restore it to full service.

?I?m really happy to report that all of our systems are in great shape, we?re tracking no issues and we?re right on track,? NASA test director Jeff Spaulding said today.

The rotating service structure, the giant metal shroud surrounding the space shuttle on its launch pad, is set to be retracted tonight at 8:30 p.m. EDT (2430 GMT). Discovery?s communications system will be checked out today, with ground crews set to perform final configurations on the shuttle and stow the last of the crew equipment later today.

Discovery astronauts are in for a somewhat quiet day today as they attend final briefings and take some time off to rest and visit with their families before their adventure planned for tomorrow. Engineers are expected to begin fueling Discovery?s 15-story external tank for launch at about 7:37 a.m. EDT (1137 GMT) tomorrow.

Discovery?s Saturday launch will mark NASA?s third shuttle flight this year aimed at delivering a new orbital room to the space station. Astronauts installed Europe?s Columbus lab at the station in February, with another mission in March to deliver a small storage room for Japan?s tour bus-sized Kibo. NASA plans to launch up to five shuttle missions this year, including a flight to overhaul the Hubble Space Telescope and cargo flight to the space station.

NASA will broadcast the planned launch of Discovery's STS-124 mission live on NASA TV, beginning at 12:00 p.m. EDT (1600 GMT) on Saturday. Click here for SPACE.com's shuttle mission updates and NASA TV feed.