2. Orbital Sciences Corporation
Orbital Sciences, founded in 1982, is building its Antares rocket to deliver cargo to the space station and perform commercial satellite launches. Using up to three stages, the rocket is designed to carry up to 6.1 metric tons to low-Earth orbit.
In addition, the company is building a pressurized cargo craft, dubbed Cygnus, to ride atop Antares. It is designed to carry up to 2.7 metric tons of cargo to the space station. Unlike SpaceX's Dragon capsule, designed to return cargo to the ground as well as deliver it to the space station, Cygnus is a one-and-done craft, like the unmanned resupply craft the Russians, Japanese, and Europeans use.
In all, Orbital Sciences has a stable of four rockets, including its Taurus ground-launched rocket and its Pegasus rocket, which is launched from the underside of a modified Lockheed L-1011 airliner. Pegasus was first launched in 1990 and can loft hardware weighing up to 1,000 pounds.