NASA's post-shuttle plans for ferrying cargo - and eventually crew - to the International Space Station rely on private industry to not only design and build the spaceships, but also to foot a substantial share of the costs.
The first company to successfully emerge from the process was California-based Space Exploration Technologies, or SpaceX, which so far has made a test fight and two supply runs to the station. SpaceX also is among three firms developing space taxis to fly station crew members under a related NASA program.
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On Wednesday, a second firm, Orbital Sciences Corp., will attempt to follow SpaceX to the station's door. Launch of Orbital Sciences' Antares rocket and Cygnus cargo capsule is scheduled for 10:50 a.m. EDT from a commercial spaceport on Wallops Island, Va.
If the launch goes as planned, the Cygnus would reach the station on Sunday and remain attached to the outpost for about a month. Unlike SpaceX's Dragon capsules, which return to Earth intact, Cygnus spacecraft are designed to burn up in the atmosphere during re-entry.