SCISAT-1 Mission Will be the Fourth Pegasus Launch in 2003 and
35th in the Program’s History

Orbital Sciences Corporation (NYSE:ORB) today announced that it is
in final preparations to launch the Scientific Satellite (SCISAT-1)
Atmospheric Chemistry Experiment (ACE) spacecraft for the National
Aeronautics and Space Administration (NASA) and the Canadian Space
Agency (CSA) aboard the company’s Pegasus(R) rocket. The launch is
currently scheduled to take place on Tuesday, August 12, 2003 from
Vandenberg Air Force Base (VAFB), California during an available
launch window that extends from 10:05 p.m. to 11:02 p.m. (EDT). The
targeted launch time is approximately 10:10 p.m. This operational
schedule is subject to the completion of final pre-launch activities,
as well as acceptable weather conditions at VAFB at the time of the

The powered flight sequence for the SCISAT-1 mission is expected
to take approximately 11 minutes, from the time the Pegasus rocket is
released from the L-1011 carrier aircraft to the time that the
satellite is deployed into orbit. Orbital plans to launch the
330-pound SCISAT-1 spacecraft into a polar orbit approximately 400
miles above the Earth, inclined at 73.9 degrees to the equator.

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.

The SCISAT-1 mission will be the 35th flight of the Pegasus rocket
and its fourth mission in 2003. Earlier this year, Pegasus carried out
three successful launches, each carrying an Orbital-built satellite,
including SORCE in January, GALEX in April, and OrbView-3 in June,
which was the 20th consecutive successful mission for the Pegasus

About SCISAT-1

The SCISAT-1 spacecraft was developed under a cooperative program
between NASA and CSA. The Canadian government selected ACE for the
scientific mission for the SCISAT-1 spacecraft. The major scientific
goal of the ACE instrument is to measure and understand the chemical
processes that control the distribution of ozone in the Earth’s
atmosphere, especially at high altitudes.

The data gathered by SCISAT-1 will help Canadian scientists and
policy makers assess existing environmental policy and develop
protective measures for improving the health of the Earth’s atmosphere
and preventing further ozone depletion. The SCISAT-1 mission is
designed to last at least two years.

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

More information about Orbital can be found at