— Latest Pegasus Mission Is 28th Consecutive Successful Launch Over 16-Year Period —

— Company’s Air-Launched Rocket Accurately Deploys NASA’s Newest Heliophysics Science Satellite Into Low-Earth Orbit —

(Dulles, VA 27 June 2013) — Orbital Sciences Corporation (NYSE: ORB) announced today that its Pegasus(R) rocket successfully launched the Interface Region Imaging Spectrograph (IRIS) satellite for the National Aeronautics and Space Administration (NASA). The IRIS spacecraft was deployed into its targeted orbit approximately 400 miles above the Earth and early results confirm that the satellite is operating as anticipated at this stage of its mission.

The launch of the Pegasus rocket originated from Vandenberg Air Force Base (VAFB), California when Orbital’s’ L-1011 “Stargazer” carrier aircraft took off from the airfield at approximately 6:30 p.m. (PDT). Following a one-hour preplanned positioning flight, the Pegasus rocket was released at approximately 40,000 feet from Orbital’s L-1011 “Stargazer” carrier aircraft at 7:27 p.m. (PDT). After a 13-minute powered flight sequence, Pegasus launched the 440-pound IRIS satellite into its polar, sun-synchronous Earth orbit.

“The Pegasus rocket carried out another successful mission for NASA today, extending its record of consecutive successful missions to 28 over a 16-year period,” said Mr. Ron Grabe, Orbital’s Executive Vice President and General Manager of its Launch Systems Group. “We are proud of our launch team and are pleased to have contributed to a successful beginning of this important NASA heliophysics science mission.”

The launch of IRIS marks the 45th overall mission for the Pegasus program. Its launch history now includes 42 launches to orbit, which collectively have deployed more than 80 satellites for Earth and space science missions overseen by NASA; military and technology demonstration spacecraft for the U.S. Department of Defense; and communications and imaging satellites for commercial customers. Pegasus technology has also been used to launch three hypersonic flight experiments in Earth’s stratosphere for NASA’s HyperX program.

IRIS is a NASA Small Explorer (SMEX) mission designed to observe how solar material moves, gathers energy and heats up as it travels through a little-understood region in the Sun’s lower atmosphere. This interface region between the Sun’s photosphere and corona powers its dynamic million-degree atmosphere and drives the solar wind. The interface region also is where most of the Sun’s ultraviolet emission is generated that impacts the near-Earth space environment and Earth’s climate.

About the Pegasus Rocket

Pegasus is the world’s leading launch system for the deployment of small satellites into low-Earth orbit. Its patented air-launch system, in which the rocket is launched from beneath Orbital’s “Stargazer” L-1011 carrier aircraft over the ocean, reduces cost and provides customers with unparalleled flexibility to operate from virtually anywhere on Earth with minimal ground support requirements. It is the world’s only small space launch vehicle that is certified with NASA’s Payload Risk Category 3, which the space agency reserves for its highest value space missions.

About Orbital

Orbital develops and manufactures small- and medium-class rockets and space systems for commercial, military and civil government customers. The company’s primary products are satellites and launch vehicles, including low-Earth orbit, geosynchronous-Earth orbit and planetary spacecraft for communications, remote sensing, scientific and defense missions; human-rated space systems for Earth-orbit, lunar and other missions; ground- and air-launched rockets that deliver satellites into orbit; and missile defense systems that are used as interceptor and target vehicles. Orbital also provides satellite subsystems and space-related technical services to government agencies and laboratories.

More information about Orbital can be found at http://www.orbital.com. Follow the company on Twitter @OrbitalSciences.

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Contact:
Barron Beneski (703) 406-5528
Public and Investor Relations
beneski.barron@orbital.com

Note to Editors:

1. For more information about the Pegasus rocket, please visit:
http://www.orbital.com/SpaceLaunch/Pegasus/

2. For more information about NASA’s IRIS mission, please visit:
http://www.nasa.gov/mission_pages/iris/index.html

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