DULLES, Va., June 1 /PRNewswire/ -- Orbital Sciences Corporation (NYSE: ORB) announced today that it is preparing to launch the National Aeronautics and Space Administration's (NASA's) X-43A "Hyper-X" research aircraft on June 2, 2001. The X-43A will be boosted to a predetermined altitude and velocity by a modified Pegasus rocket launched from NASA's B-52 carrier aircraft off the coast of California. The available window for the mission extends from 1:00 to 4:00 p.m. Pacific Time with a targeted launch time of 1:30 p.m. The launch schedule is subject to completion of final pre- launch testing, as well as to acceptable weather conditions at the Edwards Air Force Base, California launch site.

The Hyper-X program is a five-year, $185 million effort to demonstrate future hypersonic propulsion and airframe technologies. While vehicles with conventional rocket engines carry oxygen on board, the air-breathing X-43A scramjet ingests and compresses oxygen from the atmosphere using the vehicle's uniquely shaped airframe. This type of propulsion system could potentially increase payload capacity on future vehicles since no onboard supply of oxidizer would be required. The X-43A research vehicle was developed by NASA and Micro Craft Inc. of Tullahoma, Tennessee and the program is administered jointly by NASA's Dryden and Langley Research Centers.

Orbital's Launch Systems Group in Chandler, Arizona is building three Pegasus-derivative rockets for the Hyper-X program. In this specialized application, the Pegasus rocket's second and third stages have been eliminated, as has the payload fairing, which is normally used to protect satellite payloads. Instead of being encapsulated in a payload fairing, the X-43A research vehicle and its adapter ride atop the front of a specially configured Pegasus first-stage solid rocket motor. A newly developed thermal protection system protects the Pegasus composite structures against severe heating loads associated with lower-altitude hypersonic operations. Other modifications to Pegasus include upgraded first stage guidance and an avionics repackaging that permits ballasting of the booster for hypersonic flight conditions up to Mach 10.

On launch day, following takeoff from Edwards AFB, the B-52 carrier aircraft will fly to a predetermined point over the Pacific Ocean on the Navy sea range and release the Hyper-X launch vehicle and X-43A research vehicle "stack." After a five-second free-fall, the rocket motor will ignite and quickly accelerate the 41,400-pound stack to supersonic speeds. Approximately 90 seconds after ignition, at an altitude of approximately 95,000 feet and speed of Mach 7, the X-43A will separate from the launch vehicle to conduct its mission.

The Hyper-X team has successfully achieved a number of program milestones in a short timeframe. The X-43A research vehicle and booster were first mated in January, a comprehensive NASA Independent Review was completed in February, and a successful combined systems and taxi test was carried out in March. On April 28, NASA and Orbital successfully conducted a two and a half-hour captive carry flight on the B-52 aircraft. This flight verified the flutter properties of the Hyper-X stack in a representative flight environment, the Hyper-X launch vehicle avionics and control hardware and the Hyper-X airborne support equipment. This flight also served as a complete dress rehearsal for the launch operations, including a simulated launch at the nominal launch location and with nominal flight conditions. Following tomorrow's mission, two additional flight tests are planned for late 2001 and 2002.

Orbital is one of the world's leading manufacturers of low-cost space systems, including satellites, launch vehicles, electronics and sensors, and satellite ground systems. Orbital is also involved with satellite-based networks that provide wireless data communications and high-resolution Earth imagery to customers all around the world.

More information about Orbital can be found at http://www.orbital.com .

CONTACT: Barron Beneski, 703-406-5528, or beneski.barron@orbital.com, or
Investors: Tim Perrott, 703-406-5997, or perrott.tim@orbital.com, both of
Orbital Sciences Corporation.
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SOURCE Orbital Sciences Corporation

/NOTE TO EDITORS: High resolution photos (300+ dpi) of the Hyper-X launch vehicle and the X-43A research aircraft are available for publication on Orbital's web site at: http://www.orbital.com/News/Images/Hyper-X/hyper-x.htm

An online mission information kit can also be found on Orbital's web site at: http://www.orbital.com/News/NextMission/index.html/

CONTACT: Barron Beneski, 703-406-5528, or beneski.barron@orbital.com, or Investors: Tim Perrott, 703-406-5997, or perrott.tim@orbital.com, both of Orbital Sciences Corporation/