-- Latest Mission Is 26^th Consecutive Successful Launch for Pegasus --

-- Scientific Satellite to Study the Heliosphere is Performing as Expected Early in its Mission --

Orbital Sciences Corporation (NYSE: ORB) announced today that its Pegasus^® rocket successfully launched the company-built Interstellar Boundary Explorer (IBEX) satellite for the National Aeronautics and Space Administration (NASA) into its intended highly elliptical orbit. Early results indicate that the satellite is operating as expected at this stage of its mission. Orbital designed, manufactured and tested the IBEX satellite at its Dulles, VA satellite manufacturing facilities. Orbital is teamed with the Southwest Research Institute (SwRI) of San Antonio, TX, which is managing the IBEX scientific program, with mission funding provided by NASA. The successful launch by the Pegasus rocket was the 26^th consecutive successful mission for the Pegasus program since 1997 and the 40^th overall flight of the company’s unique air-launched system since its introduction in 1990.

“We are very pleased to support NASA and Southwest Research Institute on this important scientific project,” said Mr. David W. Thompson, Orbital’s Chairman and Chief Executive Officer. “The IBEX program was another ‘dual’ mission for our satellite and launch vehicle engineering teams, building on our history of carrying out missions for which Orbital was responsible for the satellite design, development, manufacturing and testing, as well as the launch services with our Pegasus and Taurus rockets. Once the IBEX satellite completes its in-orbit testing and begins to deliver data to the scientific team, it will join a growing list of other Orbital-supported dual missions for NASA, including the AIM, GALEX, SORCE and ACRIMSAT science satellites built by Orbital and launched aboard our rockets.”

The Pegasus/IBEX mission took place on Sunday, October 19, originating from the U.S. Army’s Reagan Test Site, Kwajalein Atoll, which is a part of the Marshall Islands in the mid-Pacific Ocean. Following a one-hour preplanned positioning flight, the Pegasus rocket was released from Orbital’s L-1011 carrier aircraft at approximately 1:47 p.m. (EDT). After an 8-minute and 15-second powered flight sequence by the Pegasus rocket, the IBEX satellite flight system, which weighed approximately 1,000 lbs. at launch and included the spacecraft and its associated propulsion system, was accurately deployed into its targeted initial orbit 125 miles above the Earth. Shortly after separation from Pegasus, the IBEX satellite’s independent propulsion system burned for just over a minute to propel it into its initial elliptical orbit.

Over the next several weeks, the IBEX satellite’s onboard hydrazine thrusters will fire to maneuver the spacecraft into its final highly elliptical final orbit of 200,000 by 4,400 miles. Upon completion of the orbit positioning process, the apogee of IBEX’s orbit will extend 80% of the distance to the Moon from Earth.

About the IBEX Mission

For the IBEX program, Orbital is teamed with the SwRI’s Principal Investigator Dr. David McComas. The IBEX mission is funded through NASA’s Small Explorers (SMEX) science satellite program, which is managed by the Goddard Space Flight Center in Greenbelt, MD.

The mission of the IBEX satellite program is to make the first comprehensive image map of the boundary between the Solar System and interstellar space, where hot solar winds collide with the cold expanse of space. Measuring this interstellar interaction is important for understanding man’s protection from galactic cosmic rays, which are energetic particles from beyond the Solar System that could pose health risks to future astronauts exploring deep space. The satellite will employ two narrow-band image sensors (IBEX-Hi and IBEX-Low) to detect neutral atoms, enabling Dr. McComas and his scientific team to map the boundary between the Solar System and interstellar space.

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.

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.

Notes to Editors:

Orbital Sciences Corporation
Barron Beneski (703) 406-5528
Public and Investor Relations
beneski.barron@orbital.com