NASA mission managers moved liftoff up to the opening of a 10-minute launch window to avoid a sea breeze thunderstorm that was closing in on the spaceport.
Liftoff had been set for 5:15 p.m. EDT (2115 GMT). Launching at that preferred time would have saved fuel during the climb to orbit, but mission managers wanted to prevent the possibility of a second consecutive launch delay.
An initial bid to get Discovery airborne was thwarted Thursday by stormy weather.
"Yesterday we had a good vehicle and the weather didnt permit an attempt. Today we have both, so we wish you good luck on your mission," NASA shuttle launch director Mike Leinbach told the shuttle crew minutes before they set sail for the station.
"And to the Expedition Three crew, fare well."
"Thank you very much," Discovery mission commander Scott Horowitz replied. "Tell the Expedition Two guys: `Stand by, were on our way."
Powered by twin solid rocket boosters and three liquid-fueled main engines, Discovery rumbled off its oceanfront launch pad, rolled onto its back and then thundered along a flight path that paralleled the U.S. eastern seaboard.
The earthshaking, eight-and-a-half-minute ascent provided a late afternoon sky-show for thousands of local residents and tourists on public roadsides, beaches and parks as well as thousands of workers and visiting VIPs at KSC.
Now cruising along at 25 times the speed of sound, Discovery is due to dock at the station Sunday after what amounts to a two-day orbital chase.
The changing of the guard at the station will come a day later. Culbertson and his crew will take the helm of the outpost once their custom-made seat-liners are set up within a Russian Soyuz spacecraft serving as an emergency lifeboat at the complex.
That work, along with checkouts of the partial pressure spacesuits the so-called Expedition Three crew would wear aboard the Soyuz, will mark the start of a four-month tour focused more on research than outpost assembly.
Coming amid a preplanned pause in station construction, Culbertson and his colleagues will carry out 50 U.S. and Russian science experiments.
Two Progress re-supply ships will be launched during their stay, and a visiting Russian crew will deliver a new Soyuz lifeboat and then return to Earth in the craft now at the outpost.
But the only assembly work will come in mid-September when a Russian airlock is delivered to the station and then outfitted during three spacewalks.
Key to all that work: Unpacking several tons of luggage for Culbertson and his crew, a job that will require mounting a shuttle-borne shipping container on the side of the outpost.
Wielding the shuttles 50-foot (15-meter) robot arm, Discovery mission specialist Patrick Forrester will lift an Italian-built cargo carrier from the shuttles cargo bay before attaching it to a berthing port on the stations Unity module.
More than three tons of food, clothing, supplies and research gear and science experiments then will unloaded from the pressurized module, one of three built by the Italian Space Agency at a cost of $450 million.
Just as important: Packing up Usachev and his crew for the return trip home.
Some 2,000 pounds (607 kilograms) of crew luggage, surplus station gear and garbage will be loaded into the shipping container before it is stowed back in the shuttle for a return trip to Earth.
The restocking of the station, meanwhile, is considered crucial. Unlike two previous station expeditions, no shuttle visits are scheduled during the time Culbertson and his crew will be living and working aboard the station.
"This is a little different for us in that we dont have the frequent shuttle flights," said NASA deputy station project manager Bill Gerstenmaier. "So we need to make sure things are in place."
Two five-hour spacewalks also will be performed during Discoverys stay at the station.
Forrester and fellow mission specialist Daniel Barry will mount a pallet of ammonia coolant tanks on the stations $600 million U.S. electric power tower during the first excursion, which will be staged next Thursday.
Weighing in at 1,200 pounds (540 kilograms), the ammonia tanks will provide a backup supply of coolant for the air conditioning system housed in the stations U.S. Destiny science laboratory.
The second sortie which will take place Aug. 18 primarily will involve stringing cables outside the $1.4 billion research lab. The 45-foot (13.6-meter) electrical lines will serve as a back-up to power cables that will be hooked up to critical heaters on a station truss segment that is to be launched to the outpost aboard shuttle Atlantis early next year.
With shuttle pilot Rick Sturckow at the controls and Usachev and his crew in tow Discovery is scheduled to depart the station Aug. 20, heading off on a two-day trip back to Earth.
Culbertson and his crew, meanwhile, are scheduled to remain in space until Dec. 9.
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