An Orbital Sciences Corporation Antares rocket launches the Cygnus cargo ship from Pad-0A at NASA's Wallops Flight Facility on Wallops Island, Virginia on Sunday, July 13, 2014. The commercial mission will deliver supplies to astronauts on the International Space Station.

WALLOPS ISLAND, Va. — A private spaceship packed with astronaut food, science experiments and a fleet of tiny satellites soared into orbit from Virginia's Eastern Shore today (July 13) on an orbital delivery mission to the International Space Station for NASA.

The unmanned Cygnus spacecraft and its towering Antares rocket — the size of a 13-story building — lifted off at 12:52 p.m. (1652 GMT) under partly cloudy skies after stormy weather twice delayed the launch. Both spacecraft and rocket are commercial vehicles built by the aerospace company Orbital Sciences Corp., of Dulles, Virginia. NASA provided live video views of the Antares rocket launch during the liftoff from a seaside pad operated by the Mid-Atlantic Regional Spaceport, or MARS, at NASA's Wallops Flight Facility on Wallops Island, Virginia.

"The countdown was extremely smooth," Bill Gerstenmaier, NASA's chief of human exploration and operations, told reporters. "Just a tremendous launch." [Gallery: Orbital Sciences' Orb-2 Cargo Mission in Photos]

An Orbital Sciences Corporation Antares rocket launches the Cygnus cargo ship from Pad-0A at NASA's Wallops Flight Facility on Wallops Island, Virginia on Sunday, July 13, 2014. The commercial mission will deliver supplies to astronauts on the International Space Station. (Image credit: NASA/Bill Ingalls)

Keeping the station stocked

NASA has relied on private companies and foreign space agencies to keep the space station stocked with supplies since the U.S. space shuttle fleet retired in 2011. Under a $1.9 billion contract with NASA, Dulles, Virginia-based Orbital Sciences will fly eight missions through 2016. Today's flight, dubbed Orb-2, marks the second official Cygnus cargo mission to the station and the fourth launch of an Antares rocket in the last 15 months.

"Keeping [the space station] supplied, keeping it flying, and even, politically, keeping it supported by the various governments around the world continues to be a challenge," Frank Culbertson, a former NASA astronaut and current executive vice president for Orbital Sciences, told reporters ahead of the launch. "But I think that almost everyone involved in it around the world understands the importance of maintaining this foothold on the high ground in space because it is the next stepping to stone to where we're going go next — whether it's the moon, Mars, asteroids or further out into the solar system."

Culbertson said he expects the company's next launch, Orb-3, to take place in October; three more Orbital launches are planned for 2015.

The only other U.S. spaceflight company with a NASA contract to perform resupply missions is Space Exploration Technologies, better known as SpaceX. The Hawthorne, California-based company founded by billionaire Elon Musk has a $1.6 billion deal with NASA for 12 delivery missions. SpaceX launched the third of those flights in April.

Cygnus is carrying more than 3,600 lbs. (1,600 kilograms) of cargo to the station, including some much-needed food to restock the astronauts' pantry, as well as a replacement pump for the Japanese module and some other equipment. Gerstenmaier told reporters he could "breathe a sigh of relief" with the flight.

"It was getting to be where it was a little tense," Gerstenmaier added. "This next year will be really important to us as we establish a cadence of routine flights."

Originally scheduled for a May launch, Orb-2 had been delayed due to technical issues — primarily, a malfunction of an AJ26 engine (the kind that powers Antares) during a test at NASA's Stennis Space Center in Mississippi. Without giving many details, Orbital officials told reporters that the ensuing investigation yielded favorable results.

"We have a lot of confidence that the two engines on Orb-2 are ready to go," Mike Pinkston, Orbital's Antares rocket program manager, told reporters in a pre-launch briefing Saturday (July 12).

The mission suffered more delays during this past week's flight window when bad weather prevented the launch team from readying the rocket. By Saturday, NASA officials estimated that they would see a 90 percent chance of favorable weather conditions for launch — and they expected many spectators along the Eastern Seaboard to have clear view of the rocket as it arced out over the Atlantic Ocean.

"I think we found the secret to getting people's attention here on the Eastern Shore of Virginia, Maryland and Delaware, and that's to launch on a Sunday in July," Culbertson said after the launch, noting the traffic jams around the normally sleepy beach town of Chincoteague.

5,001 manned days on the ISS

The launch comes a day after a manned spaceflight milestone: the 5,000th day humans have lived inside the $100 billion International Space Station.

"In those 5,000 days, not only have we managed to assemble this unique laboratory, but we've been able to conduct 1,600 experiments to date," Kirt Costello, assistant International Space Station program scientist, told reporters here in a briefing on Friday (July 11). "Really it's an amazing feat to be able to already have completed so much science. We are now in a period where utilization is really the prime goal of the space station."

Now that station managers are focused on using the lab rather than building it, commercial companies also have found ways to use the astronaut outpost as a platform for their research. Planet Labs, a San Francisco-based startup that aims to image the whole Earth once a day, is sending a new constellation of 28 small satellites to be deployed from the station via Orb-2. [Planet Labs Photos of Earth from Space]

Today's cargo delivery also includes 15 student science experiments chosen from more than 1,000 proposals through NASA's Student Spaceflight Experiments Program (SSEP). As part of SSEP's so-called Charlie Brown payload, a Girl Scout troop from Hawaii will test the possibility of growing arugula in water; a group of students from New York City will study how mold grows on white bread in microgravity; and an 8th grader from Maryland will look at how water membranes form in space.

The principal investigator of that last experiment, Kevin He, told reporters here today that his project was, in part, inspired by Canadian astronaut Chris Hadfield's viral video in which he showed how strangely water behaves without gravity by wringing out a wash cloth on the space station.

If all goes well, the Cygnus spacecraft will arrive at the International Space Station Wednesday morning (July 16). Astronauts living on board the orbiting lab will capture the vessel with a huge robotic arm, unload the cargo and refill the capsule with trash. The disposable vessel will remain attached to the space station for about 30 days before it is jettisoned toward Earth. After performing a few days' worth of engineering tests in orbit, the vessel will burn up in the planet's atmosphere over the South Pacific, Orbital officials said.

Editor's note: This article was updated Sunday (July 13) at 3:30 p.m. EDT.

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