Orbital Set to Launch Pegasus Rocket Carrying Company-Built Autonomous Rendezvous Spacecraft for NASA.

DULLES, Va. -- Orbital Sciences Corporation (NYSE:ORB)

--Complex Mission to be Carried Out Entirely With Orbital's Space Technology, Including Two Company-Built Satellites, On-Board Rendezvous Sensors and the Space Launch Vehicle --

--36th Mission for the Pegasus Air-Launched Rocket to Originate from Vandenberg Air Force Base, California --

Orbital Sciences Corporation (NYSE:ORB) announced today that it is in final preparations to launch the National Aeronautics and Space Administration (NASA)'s Demonstration of Autonomous Rendezvous Technology (DART) spacecraft aboard a Pegasus rocket. The mission is scheduled to take place on Tuesday, October 26, 2004, from Vandenberg Air Force Base, CA (VAFB) during an available seven-minute launch window that extends from 11:15 a.m. to 11:22 a.m. (Pacific). This operational schedule is subject to the completion of final testing and other pre-launch activities, as well as acceptable weather conditions in the VAFB area at the time of the launch.

About the Pegasus Launch Vehicle

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 at approximately 40,000 feet, reduces cost, improves performance and provides customers with unparalleled flexibility to operate from virtually anywhere on Earth with minimal ground support requirements. Orbital has launched the Pegasus rocket from six sites around the world, including VAFB; Edwards Air Force Base, CA; Cape Canaveral, FL; Wallops Island, VA; Kwajalein Atoll in the Central Pacific region; and the Spanish Canary Islands. The DART mission will be the 36th flight of the Pegasus rocket since its introduction in 1990. The Pegasus launch vehicle is provided by Orbital under contract to NASA's Kennedy Space Center, FL.

About the DART Spacecraft

Orbital designed, developed, manufactured and tested the DART spacecraft for NASA's Marshall Space Flight Center in Huntsville, AL. The DART spacecraft will demonstrate key hardware and software technologies that will allow one spacecraft to rendezvous with and conduct close-proximity operations near another in-orbit spacecraft. While previous U.S. space rendezvous and docking missions have been piloted by astronauts, the unmanned DART spacecraft will have only on-board computers and data from sensors to perform its rendezvous and close-proximity maneuvers functions.

Along with NASA's Marshall Center, Orbital also engineered, manufactured and tested the advanced laser guidance sensor that the DART spacecraft will use to carry out its final rendezvous and close-proximity maneuvers with its target. Marshall pioneered the basic video laser technology in the late 1990's, which Orbital subsequently qualified for space applications at its Technical Services Division in Greenbelt, MD.

Future applications of the technologies that the DART mission is demonstrating may be used in manned and unmanned missions of the U.S. space program that require in-space assembly, servicing, docking or other autonomous rendezvous operations. The DART spacecraft is nearly six feet long with a diameter of about three feet and weighs about 500 pounds.

About the DART Mission

Following its launch aboard Pegasus into a targeted 475-mile polar orbit, the DART spacecraft will locate and rendezvous with the mission's target satellite, the Multiple-Path Beyond-Line-of-Sight Communications (MUBLCOM) spacecraft that has completed its mission and is operating well beyond its design life. The MUBLCOM satellite was also built by Orbital for the Defense Advanced Research Projects Agency and was launched aboard a previous Pegasus mission in 1999.

Once the DART spacecraft achieves orbit and locates and rendezvous with MUBLCOM, it will perform several close-proximity operations such as approaching to as close as 15 feet and moving away from the satellite on different vectors, as well as performing circumnavigation maneuvers using data provided by its onboard sensors. The entire DART mission will be performed without human intervention and will be completed within 24 hours.

About Orbital

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 satellites and launch vehicles, including geostationary and low-orbit 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, the Pegasus space launch vehicle and the DART spacecraft can be found at http://www.orbital.com

Notes to Editors:

--NASA TV will cover live the Pegasus launch of the DART spacecraft. NASA TV is broadcast on AMC-9, transponder 9, C-band, located at 85 degrees West Longitude. The frequency is 38880.0 MHz. Polarization is vertical and audio is monaural at 6.8 MHz.

--Orbital will link to NASA's web-based pre-launch and live coverage of the DART mission from the company's web site at www.orbital.com