DULLES, Va., July 18 /PRNewswire/ -- Orbital Sciences Corporation (NYSE: ORB) announced today that it is preparing to launch the U.S. Air Force's MightySat II satellite aboard a Minotaur rocket on Wednesday, July 19, 2000. The MightySat II mission represents the second launch of the Minotaur rocket, which successfully delivered 11 small satellites into their targeted orbits on its inaugural flight in January 2000.

Orbital developed the four-stage Minotaur rocket for the Air Force's Orbital/Suborbital Program (OSP) using U.S. Government-supplied Minuteman II motors that have been decommissioned as a result of arms reduction treaties. The deactivated rocket motors serve as the vehicle's first and second stages. Its third and fourth stages, as well as its guidance and control system, use technology from Orbital's Pegasus XL rocket. Orbital is under contract to the Air Force to provide integrated Minotaur launch vehicles and to perform launch operations to deliver small military satellites to orbit.

On launch day, the available window for the Minotaur mission extends from 4:09 p.m. to 5:35 p.m. Eastern time, with a targeted launch time of 4:09 p.m. This schedule is subject to the completion of final pre-launch testing, as well as acceptable weather conditions at the Vandenberg Air Force Base (VAFB), California launch site.

The operational sequence for the mission is expected to take about 11 minutes, from the time the Minotaur launcher's first stage engine ignites to the time that the satellite payload is deployed. The Minotaur rocket is expected to deliver the satellite into a circular, sun-synchronous orbit approximately 297 nautical miles (550 kilometers) above the Earth, inclined at 97.6 degrees to the equator.

The 263-pound (120-kilogram) MightySat II satellite was built by Spectrum Astro, Inc. of Gilbert, Arizona for the Air Force Research Laboratory (AFRL). A follow-on to the Orbital-built MightySat I satellite, which was successfully launched from the Space Shuttle in late 1998, MightySat II will provide a space-based platform for demonstrations of advanced AFRL space system technologies such as a solar array concentrator and a Fourier Transform Hyperspectral Imager.

Orbital is one of the largest space technology and satellite services companies in the world, with 1999 total enterprise revenues (including revenues from unconsolidated affiliates) of approximately $915 million. The company, headquartered in Dulles, Virginia, employs about 5,500 people at major facilities in the United States, Canada and several overseas locations.

Orbital is the world's leading manufacturer of low-cost space systems, including satellites and space robotics, launch vehicles, electronics and sensors, satellite ground systems and related digital infrastructure. Its Magellan subsidiary is a pioneer in satellite-based navigation and communications products for consumer and industrial markets. Through its ORBCOMM and ORBIMAGE affiliates and ORBNAV subsidiary, Orbital is also a major operator of satellite-based networks that provide data communications, high- resolution imagery and automotive information services to customers around the world.

For more information on the MightySat II program, visit http://www.vs.afrl.af.mil/vsd/mightysatII.

For more information on the Minotaur launch vehicle, visit http://www.losangeles.af.mil/SMC/PA/Fact_Sheets/minotaur_fs.html. SOURCE Orbital Sciences Corporation

/NOTE TO EDITORS: To learn more about Orbital and the Minotaur rocket, as well as to access its recent press releases, please visit its web site at http://www.orbital.com/

CONTACT: Barron Beneski of Orbital Sciences Corporation, 703-406-5000, or email: Beneski.barron@orbital.com/