U.S. Space Agency Orders Two Pegasus and Two Taurus Rockets for Scientific
Missions in 2006 and 2007

(Dulles, VA) – Orbital Sciences Corporation (NYSE: ORB) announced today that
the National Aeronautics and Space Administration (NASA) has ordered four space
launch vehicles, including two Pegasusuand two TaurusĀ® rockets, for U.S.
government scientific satellite missions scheduled to be launched over a
two-year period beginning in 2006. The orders were placed under the Small
Expendable Launch Vehicles Services (SELVS) contract that was awarded to
Orbital by NASA’s Kennedy Space Center in 1998.

The two new Pegasus vehicles will be used to launch the satellites designated
for NASA’s Space Technology-8 (ST-8) and Small Explorer-10 (SMEX-10) missions.
The two Taurus missions are scheduled to launch NASA satellites that Orbital
is currently developing and manufacturing at its Dulles, VA facility. The
first of the two new Taurus rockets will launch the GLORY satellite for
NASA’s Goddard Space Flight Center. The second Taurus rocket will launch the
Orbiting Carbon Observer satellite for the Jet Propulsion Laboratory.

With these new launch vehicle orders, NASA is continuing a 12-year relationship
with Orbital for Pegasus and derivative rockets, which began in 1991. During
this time, the space agency has purchased 25 Pegasus, Taurus and
related launch vehicles for a wide range of Earth and space science and
technology demonstration missions. Fourteen of these launches have been
carried out to date, while another 11 are planned from 2004 to 2008.

“Orbital is very pleased with NASA’s continued commitment to our space launch
vehicle products,” said Mr. David W. Thompson, Orbital’s Chairman and Chief
Executive Officer. “We look forward to continuing the excellent working
relationship that our launch vehicle team has established with its NASA
counterparts. Together, our shared goal is to reliably support the
scientific community’s use of small satellites for highly productive Earth
and space science investigations.”

About the Pegasus Launch System

Pegasus is the world’s leading launch system for the deployment of small
satellites weighing up to 1,000 pounds 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.

First launched in 1990, Pegasus is the world’s 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 21 consecutive successful Pegasus
missions carried out since 1997.

About the Taurus Launch System

Orbital developed the ground-launched Taurus vehicle to provide a
cost-effective, reliable means of launching satellites weighing up to 3,000
pounds into low-Earth orbit. First launched in 1994, Taurus incorporates
advanced structural and avionics technology proven on Pegasus and other
operational launch systems and is designed for easy transportability,
offering customers rapid-response launches from a wide range of locations.

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, 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.