AIM Mission Was 24th Consecutive Successful Launch for Pegasus

       AIM Spacecraft Operating as Expected Early in its Mission

    Company Carries Out Two Space Launches on Consecutive Days From
                   East and West Coast Launch Sites

DULLES, Va.April 26, 2007--Orbital Sciences Corporation (NYSE:ORB) announced today that its Pegasus(R) space launch vehicle successfully launched the Aeronomy of Ice in the Mesosphere (AIM) scientific satellite for the National Aeronautics and Space Administration (NASA). Orbital designed, built and tested the AIM spacecraft at its satellite manufacturing facility in Dulles, Virginia. In a mission that took place on Wednesday, April 25 from Vandenberg Air Force Base (VAFB), California, the 440-pound AIM spacecraft was accurately delivered into its targeted orbit approximately 375 miles above the Earth, inclined at 97.77 degrees to the equator.

The powered flight sequence for the AIM mission took just over 10 minutes, from the time the Pegasus rocket was released from its L-1011 carrier aircraft at approximately 1:26 p.m. PDT to the time that the satellite was deployed into orbit. The AIM mission was the 38th launch of the Pegasus rocket since its debut in 1990 and its 24th consecutive successful mission since 1997.

Orbital also noted that yesterday's successful Pegasus launch from VAFB on the U.S. West Coast came just one day after its Minotaur space launch vehicle team successfully launched the U.S. Missile Defense Agency's NFIRE satellite from NASA's Wallops Flight Facility, on the East Coast. The successful launch of NFIRE was the seventh flight of the Minotaur I rocket, all of which have been successful.

About Pegasus

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.

Pegasus is the only small launch vehicle to have earned NASA's Category 3 certification, which allows the U.S. space agency to launch its most valuable payloads aboard the rocket. A Category 3 certification is achieved through a long-term record of highly reliable launch services, such as the current record of 24 consecutive successful Pegasus missions carried out over the last 10 years.

About the AIM Satellite

The AIM spacecraft was designed, manufactured and tested at Orbital's Dulles, Virginia satellite manufacturing facility. The spacecraft program is being overseen by prime contractor Hampton University of Hampton, Virginia, assisted by the University of Colorado and Virginia Tech University. The AIM mission is part of NASA's ongoing series of Small Explorers (SMEX) missions that use smaller-sized satellites to carry out Earth and space science missions.

The AIM mission is a two-year program to study polar mesospheric clouds, which are the highest altitude clouds that form in the Earth's atmosphere. Mesospheric clouds create an icy membrane about 50 miles above the surface at the edge of space. These clouds, which are visible from the ground with the naked eye, form in the spring and summer at higher latitudes and have been seen for over a century, reflecting the Sun's light in the twilight sky. The mission's primary goal for the three onboard instruments is to explain why these clouds form and discover what is causing them to appear more frequently and at lower latitudes.

About Orbital

Orbital develops and manufactures small space systems for commercial, civil government and military customers. The company's primary products are satellites and launch vehicles, including low-orbit, geosynchronous and planetary spacecraft for communications, remote sensing and scientific missions; ground- and air-launched rockets that deliver satellites into orbit; and missile defense boosters that are used as interceptor and target vehicles. Orbital also offers space-related technical services to government agencies and develops and builds satellite-based transportation management systems for public transit agencies and private vehicle fleet operators. More information about Orbital can be found at http://www.orbital.com.


    Note to Editors:

    --  High-resolution photos of the Pegasus rocket and AIM satellite
        are available on Orbital's web site at:
        http://www.orbital.com/NewsInfo/Images



    CONTACT: Orbital Sciences Corporation
             Barron Beneski, 703-406-5528
             Public and Investor Relations
             beneski.barron@orbital.com

    SOURCE: Orbital Sciences Corporation