DULLES, Va.Nov. 16, 2004--Orbital Sciences Corporation (NYSE: ORB) announced today that its Hyper-X launch vehicle was successfully launched earlier today in a flight test that originated from NASA's Dryden Flight Research Center located at Edwards Air Force Base, California. The Hyper-X launch vehicle uses a modified single-stage winged rocket, originally designed and flight-proven aboard Orbital's Pegasus(R) space launch vehicle, to accelerate NASA's X-43A air-breathing scramjet to approximately 10 times the speed of sound.

Unlike vehicles with conventional rocket engines, which carry oxygen onboard, the air-breathing X-43A scoops and compresses oxygen from the atmosphere using the shape of the vehicle's airframe. This type of propulsion system could potentially increase payload capacity of future launch vehicles and make high-speed passenger travel feasible, since the weight of the onboard supply of oxidizer would be eliminated.

"We are extremely pleased with the results of the second successful flight of the Hyper-X launch vehicle, which powered the X-43A scramjet to a new world speed record for an air-breathing aircraft," said Mr. Ron Grabe, Executive Vice President and General Manager of Orbital's Launch Systems Group. "We congratulate NASA and all the industry partners on this program who have accomplished something no other group has ever done."

The mission's flight operations began when NASA's B-52B carrier aircraft took off and flew a predetermined flight path to a point about 50 miles off the California coast. The Hyper-X launch vehicle was released from the B-52B at 2:35 p.m. (PST) approximately 40,000 feet over the Pacific Ocean. Following rocket motor ignition, the Hyper-X launch vehicle, carrying the X-43A scramjet, accelerated to a velocity of approximately 7,000 miles per hour, or Mach 10 (ten times the speed of sound), and reached an altitude of 110,000 feet. Approximately 90 seconds after ignition, with the booster at a precise trajectory condition, the Hyper-X launch vehicle sent commands to the X-43A scramjet, which then separated from the booster.

Early flight results indicate that the X-43A stabilized, ignited its scramjet and provided good data back to NASA engineers that indicated predicted vehicle performance. After its engine burn, the X-43A executed a number of aerodynamic maneuvers during its ten-minute coast to an ocean impact approximately 850 miles from the launch point. After separation, the spent booster impacted the ocean in a pre-determined splash area.

About Orbital

Orbital develops and manufactures small space and rocket systems for commercial, military and civil government customers. The company's primary products are satellites and launch vehicles, including low-orbit, geosynchronous and planetary spacecraft for communications, remote sensing, scientific and defense missions; ground- and air-launched rockets that deliver satellites into orbit; and missile defense systems 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.

Note to editors: High-resolution photos of the Hyper-X launch vehicle, suitable for publication, are available on Orbital's web site at:

http://www.orbital.com/NewsInfo/Images/AdvancedLaunch/index.html


    CONTACT: Orbital Sciences Corporation
             Barron Beneski, 703-406-5528
             Beneski.barron@orbital.com

    SOURCE: Orbital Sciences Corporation