Artist's rendering of Cygnus spacecraft approaching the International Space Station. CREDIT: Orbital Sciences Corporation

Orbital Sciences Corp. is one of two private companies that currently hold a contract with NASA to fly unmanned cargo missions to the International Space Station.

The Dulles, Va.-based company's $1.9 billion deal with the space agency requires Orbital to fly eight unmanned cargo missions to the International Space Station using its Antares rocket and Cygnus capsule.

Orbital specialized in launching small satellites for much of the company's history. Recently, the firm has become involved in the manufacturing of missile defense systems. In total, the company has built more than 560 launch vehicles and more than 170 satellites.

Orbital's formal relationship with NASA began in 1983 when the firm signed an agreement to build a Transfer Orbit Stage vehicle that was eventually used during a launch of the space shuttle Discovery. [See Photos of Orbital Sciences' Cygnus and Antares]

By 1991, officials from Orbital signed an $80 million deal allowing NASA to use the company's Pegasus rocket to deliver small payloads into orbit. Pegasus a winged three-stage rocket designed to fly to low-Earth orbit was the first privately developed space launch vehicle.

In the past, the aerospace firm has also signed deals with the U.S. Air Force, Japan's Broadcasting Satellite System Corporation and the Defense Advanced Research Projects Agency.

Cygnus space capsule

Orbital's unmanned Cygnus spacecraft is designed to deliver pressurized crew supplies, scientific experiments and other unpressurized cargo to the space station.

The capsule is currently being built and is scheduled for its first test flight atop the company's Antares rocket in November 2013.

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Orbital Sciences Corporation: Satellites, Rockets and the Space Station