(DULLES, VA 29 AUGUST 1997) -- Orbital Sciences Corporation (NASDAQ: ORBI) today announced that, for the second time in less than a month, its Pegasus XL rocket successfully launched a satellite into its targeted low-Earth orbit. The two missions in August represent the most rapid back-to-back missions conducted in the Pegasus program's seven-year operational history. Today's launch operation was the third consecutive success for the Pegasus rocket this year and the program's 17th mission overall. Orbital deployed the U.S. Department of Energy's (DOE) Fast On-orbit Recording of Transient Events (FORTE) satellite in today's Pegasus mission.

This morning's launch operation originated from Vandenberg Air Force Base, California (VAFB) when Orbital's L-1011 Pegasus carrier aircraft took off at approximately 7:00 a.m. PDT. The aircraft flew off the California coast to a predetermined location at 39,000 feet over the Pacific Ocean where the Pegasus XL rocket was released at approximately 8:00 a.m. After an 11 minute and 17 second flight, Pegasus deployed DOE's FORTE satellite into a 800 by 800 circular orbit, inclined at 70.0 degrees.

Mr. David W. Thompson, Orbital's Chairman and Chief Executive Officer, said, "Our launch team deserves a great deal of credit for conducting two successful Pegasus launches in less than a month. Today's launch adds another entry to Pegasus' growing list of achievements. By the end of 1997, we plan to expand that list, with three more Pegasus launches scheduled to take place this year."

The FORTE satellite is a 468 lb. spacecraft that was designed and built in New Mexico for DOE at the Los Alamos National Laboratory and the Sandia National Laboratories. It was originally designed as a test-bed spacecraft for treaty-monitoring technology for use as part of the United States' nuclear detection system, supporting the country's efforts to curb the proliferation of nuclear weapons around the globe. The spacecraft will also serve in another capacity by assisting scientific researchers with their investigations into the Earth's ionosphere and the physics of lightning. The FORTE satellite will record optical flashes and radio-frequency emissions generated by lightning storms. This same data will also give scientists a new tool for climate modeling and weather prediction.

Orbital is a space and information systems company that designs, manufactures, operates and markets a broad range of affordable space and ground infrastructure systems, satellite access products and satellite services. These include launch vehicles, satellites, space sensors and instruments, satellite ground systems and software, satellite-based navigation and communications products, and satellite-delivered communications and Earth-imaging services.

To learn more about the FORTE satellite, visit the FORTE home page at: http://nis-www.lanl.gov/nis-projects/forte.