Sending a package to outer space is not as simple as dialing a parcel company. But it's getting there.

If all goes well, on Wednesday morning a privately owned robotic spaceship, the Cygnus, will blast off from Wallops Island, Va., to deliver cargo to NASA astronauts living on the International Space Station. Crews in space have already received three loads of freight on robotic spaceships belonging to California-based SpaceX, but Cygnus is owned by a rival firm. And that means that Wednesday's flight will mark a milestone of its own: the beginning of competition in the high-stakes business of supplying astronauts in orbit.

"When two companies have done it, it will prove that we have an industry, not just one success," says James Muncy, a commercial space policy consultant. But the fact that companies are tackling the job doesn't mean the risk has disappeared: "Spaceflight is hard. It's really important not to crash a spacecraft into the space station."

The Cygnus, developed by Orbital Sciences Corporation, hasn't been tested even once in zero gravity, but the rocket that will blast Cygnus into orbit had a nearly flawless trial run in April, and the Cygnus must pass a series of rigorous maneuvering tests in space before it's allowed to approach the space station, an orbiting laboratory designed to support a crew of six. No one cares to re-stage the terrifying 1997 crash of a Soviet cargo ship into Russia's space station, Mir.

If Cygnus proves itself worthy, on Sunday it will creep toward the station until it's a mere 36 feet away, allowing crewmembers Luca Parmitano and Karen Nyberg to grab the ship with the station's robotic arm. The pair will anchor Cygnus onto the station, then open the hatch to the visiting vehicle and unload the 1,500 pounds of supplies tucked inside it.

"It's a new vehicle, and you have to expect that something could go wrong, and you have to be ready for all scenarios," Nyberg told the Associated Press on Monday. Even so, she and her two crewmates are "really, really excited" about the ships' arrival, partly because Cygnus will drop off care packages from home.

Until recently, private industry had little incentive to get involved in the space delivery business. The space shuttle, the station wagon of space vehicles, seated seven and boasted a trunk big enough for 50,000 pounds of gear. Russia's Soyuz spaceship regularly trundles three passengers to orbit, and Japanese, European and Russian robotic ships haul cargo to station crews. But when the shuttle retired in 2011, NASA turned to industry to keep the U.S. space program from having to rely entirely on foreign partners.

So far SpaceX's Dragon capsule has delivered two loads of supplies to the station, and the company and two others are testing new spacecraft to ferry astronauts off the Earth.

The International Space Station's robotic arm pushes SpaceX's Dragon capsule away for release March 26, 2013.(Photo: NAsa via AFP/Getty Images)

"For a long time … we've seen a lot of promises and PowerPoint presentations about proposed (private) spacecraft," says Jeff Foust, senior analyst at technology consulting firm Futron. "Now we're seeing those Power Points turn into actual hardware."