(Editor's Note: An Orbital Sciences Antares rocket carrying an unmanned Cygnus spacecraft exploded just after launch on Oct. 28, 2014. Orbital representatives are now trying to assess the cause of the massive failure. Had it been successful, the launch would have kicked off the company's third official resupply mission to the International Space Station for NASA. Read more about the Antares failure: Antares Rocket Explosion: Full Coverage and Investigation)
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.
Cygnus comes equipped with two sets of solar arrays on either side of the service module that power the command control and communications hardware of the robotic capsule once launched and deployed.
The capsule's design draws on previously tested spaceflight technology crafted by Orbital's engineers. The spacecraft's designers incorporated avionics systems from LEOStar and GEOStar satellites into Cygnus and the power and propulsion systems used by GEOStar as well.
In all, the capsule is expected to carry up to 5,952 pounds (2,700 kilograms) of pressurized cargo when it is launched atop an Antares rocket to the space station.
Orbital's Antares rocket — formerly called the "Taurus II" — is a two-stage launch vehicle designed to deliver cargo to low-Earth orbit. The aerospace firm will use the rocket to launch their Cygnus space capsule to the International Space Station during cargo missions.
When upright, the rocket is 131 feet (40 m) tall, and the rocket's dual AJ26 rocket engines are designed to provide 680,000 pounds of thrust. Antares' first test launch occured on April 18, 2013.
An Antares rocket exploded moments after launching from a pad located at NASA's Wallops Flight Facility in Virginia. The launch was expected to deliver a Cygnus spacecraft to the International Space Station, however, the massive failure destroyed the unmanned space probe. Antares performed four successful flights before the failure on Oct. 28, 2014.
On Nov. 5, 2014, Orbital representatives announced that they are likely planning to discontinue the use of the AJ26 engines for Antares. Orbital plans to replace the engines for the next generation Antares rocket by 2016. The company is going to buy time on other launch providers in order to complete their contract with NASA.
Missile defense systems
Orbital has conducted close to 50 major launches for the U.S. Missile Defense Agency, the Air Force, the Army and the Navy to enhance missile defense systems in the country.
The firm also manufactures and supplies "interceptor boosters" to intercept possible missiles launched against the United States.
Orbital also builds target vehicles that can be used in simulations designed to test the efficacy of the missile defense systems.
Orbital is not the only company that has a cargo deal with NASA. The California-based commercial spaceflight firm SpaceX has successfully flow two of its 12 contracted unmanned cargo missions to the space station under its $1.6 billion contract with the space agency.
— Miriam Kramer, SPACE.com Staff Writer