The space shuttle Discovery has been cleared for a Monday morning blastoff to begin one of NASA's last scheduled flights of its reusable space plane fleet.
Top NASA officials cleared Discovery for launch during a final preflight review here at the shuttle's seaside launch site at the Kennedy Space Center. Liftoff is set for 6:21 a.m. EDT (1021 GMT).
"In essence, the countdown is in great shape and we're not tracking any issues for launch," NASA test director Pete Nickolenko told reporters in a prelaunch briefing.
Mission managers did discuss minor anomalies from NASA's recent shuttle solid rocket booster test in Utah and a few other glitches, but none are expected to pose any concern for Discovery's launch.
Discovery has an 80 percent chance of good launching weather, with the potential for fog posing the only concern.
The shuttle is slated to launch just before sunrise, making it the last scheduled shuttle launch in darkness. The shuttle's ascent into space may be visible, weather permitting, to skywatchers all along the East Coast of the United States (how to spot the shuttle launch).
NASA shuttle weather officer Kathy Winters said the liftoff should be beautiful.
"After the vehicle launches, we should get a nice sunrise right along the plume," Winters said, adding that the effect would light up Discovery in mid-flight.
NASA plans to fly just four final shuttle missions, including Discovery's, to complete the space station's construction before retiring the three-orbiter fleet in the fall. After that, NASA will have to rely on Russian Soyuz spacecraft to ferry astronauts to the space station until commercially built American spaceships become available.
Commanded by veteran spaceflyer Alan Poindexter, Discovery's four-man, three-woman crew is poised to fly a 13-day mission to the International Space Station to deliver a nearly 27,000-pound cargo pod. Three spacewalks are planned to replace an old station gyroscope and deliver a large ammonia coolant tank.
NASA currently plans to try to launch Discovery twice in a row before the agency would stand down for three days to top off the shuttle's propellant tanks and avoid a rocket traffic jam later in the mission, when an unmanned Air Force rocket is slated to launch a secretive space plane prototype near the shuttle's landing day.
If all goes well, Discovery's Monday launch will come on Easter Monday — one day after the arrival of a Russian Soyuz ferrying three new crewmembers to the station. The Soyuz launched Friday and is due to dock at the orbiting laboratory on Easter Sunday.
Mission managers said they have not changed any launch countdown scheduling or any other preparation work due to the Christian holiday.