Mission Was 33rd Flight of Air-Launched Pegasus Rocket and its 19th Consecutive SuccessOrbital-Built GALEX Satellite Operating as Planned Early in the Mission

Orbital Sciences
Corporation announced that earlier today, it successfully launched
the National Aeronautics and Space Administration (NASA)’s Galaxy Evolution
Explorer (GALEX) satellite into its targeted orbit aboard the company’s
Pegasus® rocket. The 312-kilogram (690-pound) GALEX scientific satellite,
which Orbital designed and built at its Dulles, Virginia satellite
manufacturing facility, was accurately delivered into its targeted orbit
approximately 690 kilometers (420 miles) above the Earth, inclined at 29
degrees to the equator.

The powered flight sequence for the GALEX mission took about 11 minutes,
from the time the Pegasus rocket was released from its L-1011 carrier aircraft
at approximately 8:00 a.m. (EDT) to the time that the satellite was deployed
into orbit. Preliminary information indicates that the GALEX satellite is
working as planned in the early stages of its mission.

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 19 consecutive successful Pegasus missions carried out since 1997.

The GALEX mission was the 33rd flight of the Pegasus rocket and the second
of four planned missions in 2003. In January, Orbital successfully launched
another company-built satellite, SORCE, for NASA aboard Pegasus. Orbital’s
next launch will be the OrbView-3 high-resolution imaging satellite, which the
company built for ORBIMAGE, in early June. Orbital is also scheduled to
launch the SCISAT scientific spacecraft for NASA/Kennedy Space Center and the
Canadian Space Agency later in 2003.

Orbital develops and manufactures small space systems for commercial,
civil government and military customers. The company’s primary products are
spacecraft and launch vehicles, including low-orbit, geostationary 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.

CONTACT: Barron Beneski, Public and Investor Relations of Orbital
Sciences Corporation, +1-703-406-5528, or Beneski.barron@orbital.com.