• SORCE Mission will be 32nd Flight of Company's Air-Launched Rocket -

  • Solar Observation Satellite Developed and Built by Orbital -

DULLES, Va., Jan. 23 /PRNewswire-FirstCall/ -- Orbital Sciences Corporation (NYSE: ORB) today announced that it is in final preparations to launch the National Aeronautics and Space Administration's (NASA) Solar Radiation and Climate Experiment (SORCE) satellite aboard the company's Pegasus(R) rocket. The launch is currently scheduled to take place on Saturday, January 25, 2003 and will originate from Cape Canaveral, FL. The available launch window for the SORCE mission extends from 3:10 p.m. to 4:08 p.m. (Eastern Standard Time), with a targeted launch time of 3:15 p.m. on Saturday. This operational schedule is subject to the completion of final pre-launch activities, as well as acceptable weather conditions at Cape Canaveral at the time of the launch.

The powered flight sequence for the SORCE 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 315 kilogram (693 pound) SORCE spacecraft into a circular orbit 645 kilometers (400 miles) above the Earth, inclined at 40 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 SORCE mission will be the 32nd flight of the Pegasus rocket and its first mission in 2003. Several other Pegasus missions are currently scheduled for this year, including the launch of the Galaxy Evolution Explorer (GALEX) satellite for Jet Propulsion Laboratory, the SCISAT scientific spacecraft for NASA/Kennedy Space Center and the Canadian Space Agency, and the OrbView-3 high-resolution imaging satellite for ORBIMAGE.

About SORCE

Orbital designed and built the SORCE satellite at its Dulles, VA manufacturing facility for NASA under contract to the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder, Colorado. The SORCE program merges two previous scientific efforts: the Solar- Stellar Irradiance Comparison Experiment/Solar Atmospheric Variability Explorer (SOLSTICE/SAVE) mission and the Total Solar Irradiance Mission (TSIM). The SORCE satellite is based on the company's state-of-the-art LEOStar platform and will carry four instruments on board.

The mission of the SORCE satellite is to provide state-of-the-art measurements of incoming x-ray, ultraviolet, visible, near-infrared and total solar radiation. The measurements provided by the SORCE spacecraft will address long-term atmospheric change, climate prediction, atmospheric ozone and ultraviolet-B radiation. These measurements are critical to the study of the Sun, its effect on Earth's atmosphere and its influence on mankind.

Orbital is one of the world's leading developers and manufacturers of 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

For More Information Contact:

Barron Beneski (703) 406-5528

Public and Investor Relations

beneski.barron@orbital.com SOURCE Orbital Sciences Corporation

-0- 01/23/2003

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

Live television coverage of the Pegasus-SORCE mission will be broadcast on NASA TV beginning at 2:00 p.m. (EST). NASA will also webcast the launch at: http://www.ksc.nasa.gov/

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