The space shuttle Discovery is set for launch Monday, with weather conditions appearing mostly favorable, NASA officials said Saturday.

"In essence, countdown's in great shape, and we're not tracking any issues," said Pete Nickolenko, launch director, at an afternoon news conference from Kennedy Space Center in Florida.

The launch is on track for a 6:21 a.m. ET launch Monday, he said.

"The weather does look good for Monday, the only concern we have ... is a chance for some fog," shuttle weather officer Kathy Winters said. She said there has been fog in the area for the past few days, although she said it did look like conditions were beginning to improve.

Discovery, with its crew of seven astronauts, will carry supplies and science equipment for the international space station's laboratories. The 13-day mission has three planned spacewalks, with work that includes replacing an ammonia tank assembly and retrieving a Japanese experiment from the station's exterior.

It is scheduled to arrive at the space station on Wednesday, and return to Earth on April 18 at 8:35 a.m. ET.

After this mission, there are only three shuttle missions remaining before the space shuttle fleet is retired.

NASA noted that the Discovery's mission will mark the first time that four women have been in space at one time. Three women - mission specialists Stephanie Wilson, Dorothy Metcalf-Lindenburger and Naoko Yamazaki - make up part of the Discovery's crew, while NASA astronaut Tracy Caldwell Dyson will already be at the space station.

The launch comes three days after Russian spacecraft Soyuz TMA-18, carrying Dyson and Russian cosmonauts Alexander Skvortsov and Mikhail Kornienko, blasted off to the international space station from a Kazakhstan facility.

The space station, which orbits the Earth at a height of some 250 miles, is due to be finished next year and is about 90 percent complete.