DULLES, Va., Feb 4, 2002 /PRNewswire-FirstCall via COMTEX/ --

- HESSI Mission Will Be 31st Flight of Company's Air-Launched Rocket -

Orbital Sciences Corporation (NYSE: ORB) today announced that it is in final preparations to launch the National Aeronautics and Space Administration's (NASA) High Energy Spectroscopic Imager (HESSI) satellite aboard the company's Pegasus(R) rocket. The launch is currently scheduled to take place on Tuesday, February 5, 2002 and will originate from Cape Canaveral, FL.

The available launch window for the HESSI mission extends from 3:21 p.m. to 5:21 p.m. (EST), with a targeted launch time of 3:26 p.m. on Tuesday. This operational schedule is subject to the completion of final pre-launch activities, as well as acceptable weather conditions at Cape Canaveral.

The powered flight sequence for the HESSI mission is expected to take approximately 9 1/2 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 HESSI spacecraft into a circular orbit 373 miles (600 kilometers) above the Earth, inclined at 38 degrees to the equator.

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. For the HESSI launch, the Florida Space Authority provided logistical and facility support for Orbital's launch team, which is primarily based in California and Virginia.

The HESSI mission will be the 31st flight of the Pegasus rocket and its first mission in 2002. Several other Pegasus missions are currently scheduled for 2002, including the launch of NASA's GALEX and SORCE scientific satellites and ORBIMAGE's OrbView-3 high-resolution imaging satellite.

The mission of the HESSI satellite is to help researchers understand what triggers a solar flare and how it releases energy through massive explosions in the atmosphere of the Sun. The HESSI spacecraft will use its imaging instrument to produce the first high-fidelity color videos of solar flares during the periods of their highest energy emissions.

Orbital is one of the world's leading developers and manufacturers of affordable space systems for commercial, civil government and military customers. The company's primary products are spacecraft and launch vehicles, including geostationary and low-orbit satellites 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, beneski.barron@orbital.com.

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SOURCE Orbital Sciences Corporation

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

URL:              http://www.orbital.com
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