The Dragon spacecraft is packed with nearly 2.1 tons of scientific experiments, provisions and maintenance items.

The cargo riding up to the space station includes a new Boeing-built docking adapter packaged inside the Dragon capsule's unpressurized trunk. The docking system will be used by commercial crew spaceships being developed by SpaceX and Boeing for launches as soon as 2017.

The launch of the first of two International Docking Adapters, or IDAs, is part of a wholesale reconfiguration of the U.S. segment of the space station to prepare for the arrivals of commercial crew vehicles. A storage module was transferred from one location to another on the space station in May, and spacewalks later this year will wire up and connect the docking adapter to the forward docking port on the outpost's Harmony module, the same site that received visiting space shuttles.

Chris Ferguson, a former shuttle astronaut and Boeing's director of crew and mission operations, said it was "interesting and ironic" the Boeing-made adapter is launching aboard a cargo capsule owned by the aerospace giant's rival SpaceX.

"I think this is a great element in the partnership that we have going forward," Ferguson said. "Later this year, we'll see the second docking adapter go up. Clearly, we're all in this together. It's a partnership with the commercial crew program, and with the various vendors, and we're eagerly seeking to reclaim the business of delivering crew and cargo back to the space station from U.S. soil."

SpaceX is also keen on getting the docking system on the station.

"It's a key stepping stone for us," said Hans Koenigsmann, SpaceX's vice president of mission assurance. "If you put this on the station, that is the part that Crew Dragon (SpaceX's human-rated spaceship) is designed to actually attach with. I think it's a really important and significant piece of hardware that we're bringing up."

All told, the SpaceX cargo capsule will deliver equipment to support 35 scientific investigations on the space station, plus another 30 or more student-led experiments, according to NASA.

Today's launch marks SpaceX's seventh operational resupply run to the space station under a 15-mission contract with NASA covering cargo services through 2017.

Check out photos of the Falcon 9 rocket on the launch pad earlier this morning.

Fueling of the Falcon 9 rocket is underway at Cape Canaveral's Complex 40 launch pad.

The two-stage rocket burns RP-1 fuel -- a high-refined kerosene -- and liquid oxygen during today's nine-minute launch sequence.

Today's flight marks the 19th launch of a Falcon 9 rocket since debuting in June 2010. It's the 14th mission of the improved Falcon 9 v1.1 version, which made its inaugural launch in September 2013 from Vandenberg Air Force Base.

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SpaceX and NASA technicians loaded the final items into the pressurized hull of the Dragon supply ship Saturday, closed the hatch and lifted the Falcon 9 rocket vertical ahead of launch at 10:21 a.m. EDT (1421 GMT).

The privately-owned spacecraft will deliver nearly 2.1 tons of supplies and experiments to the International Space Station.

Time-sensitive cargo installed hours before Sunday's scheduled launch included fresh food for the space station's three-person crew. The residents typically consume non-perishable food, but ground crews send up fresh fruit and other goodies to the crew aboard cargo ships.

Weather conditions for Sunday's launch continue to look favorable, with a 90 percent chance of acceptable conditions, according to a U.S. Air Force forecast team.

A few clouds at 2,500 feet and scattered clouds at 22,000 feet are in the forecast for Sunday's 10:21 a.m. EDT (1421 GMT) launch opportunity. Winds will be from the southwest at 12 to 17 mph, and the temperature at launch time is predicted to be 84 degrees Fahrenheit.

Light winds aloft are also forecast.

Thunderstorms could pop up in the afternoon, but well after Sunday's launch time.

"Although lightning chances remain high in the afternoon and evening, given the time of launch, weather violation threat is low," says the official launch forecast issued by the Air Force's 45th Weather Squadron. "The primary weather concern is early cumulus development."

If the launch does not occur Sunday, the conditions slightly worsen Monday, with a 30 percent chance of violating weather constraints.

Fair weather is also expected at the Falcon 9 booster's landing zone in the Atlantic Ocean northeast of Cape Canaveral. Meteorologists expect 50 percent cloud coverage, southwest winds of 20 knots, and waves of 5 to 7 feet.

Ground crews plan to load the final cargo into SpaceX's Dragon supply ship Saturday after the capsule's Falcon 9 rocket booster briefly fired up on the launch pad at Cape Canaveral for a flight readiness check.

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Keeping with its mantra of fly, fix and fly again, SpaceX says it has resolved a valve problem that kept one of its Falcon 9 boosters from successfully touching down on a barge in the Atlantic Ocean in April, ahead of another landing attempt after a launch from Cape Canaveral set for Sunday.

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