After an initial success in December 2010, NASA allowed SpaceX to combine the objectives of the second and third test flights into a single mission, which was successfully carried out last May. That cleared the way for the company's first operational cargo resupply services mission -- CRS-1 -- under the $1.6 billion contract.

"We are required under this contract to fly 20 metric tons up to the International Space Station," said SpaceX President Gwynne Shotwell. "With the way it looks, over the 12 flights we'll be taking up and back about 60 metric tons."

Even with a failure, she said, "given the capacity we have on the Falcon 9 and the Dragon flights, I don't believe there's any chance we won't hit our 20-metric ton target."

The Dragon capsule is 14.4 feet tall and 12 feet wide, with trunk section that extends another 9.2 feet below the capsule's heat shield that houses two solar arrays and an unpressurized cargo bay. The spacecraft can carry up to 7,297 pounds of cargo split between the pressurized and unpressurized sections.

Under a $440 million contract with NASA, SpaceX engineers are working on upgrades to convert the Dragon capsule into a manned spacecraft that can ferry crews to and from the station. SpaceX managers believe they will be ready for initial manned test flights in the 2015 timeframe, assuming continued NASA funding. Two other companies, Boeing and Sierra Nevada, are developing their own spacecraft designs under similar contracts.

For the CRS-1 mission, the Dragon capsule is loaded with 882 pounds of hardware, supplies and equipment including:

* 260 pounds of crew food, clothing, low-sodium food kits and other crew supplies.
* 390 pounds of science gear, including a low-temperature Glacier freezer for experiment samples, fluids and combustion facility hardware, a commercial generic bioprocessing apparatus, cables for the Alpha Magnetic Spectrometer and research gear for the Japanese and European space agencies.
* 225 pounds of space station hardware, including crew health care system components, life support system parts, filters and electrical components
* 7 pounds of computer gear

For its return to Earth, the Dragon spacecraft will be carrying 1,673 pounds of experiment samples and hardware, including:

* 163 pounds of crew supplies
* 518 pounds of vehicle hardware
* 123 pounds of computer gear, Russian cargo and spacewalk equipment
* 866 pounds of science gear and experiment samples, including 400 samples of crew urine.

Smith said "it may be urine to you, but it's gold to us. There's a lot of science that comes out of this."