DULLES, Va., June 8 /PRNewswire/ -- Orbital Sciences Corporation (NYSE: ORB) announced today that its latest satellite, the 250-kg Tri-Service Experiments Mission 5 (TSX-5) spacecraft for the U.S. Air Force, is in excellent health following a successful launch aboard a Pegasus rocket on June 7, 2000. As a result of data gathered from initial tests, a team of Air Force and Orbital satellite engineers has determined that the satellite's main systems are performing as expected. The TSX-5 spacecraft is generating full electrical power, indicating that its solar arrays are properly deployed. Additionally, reliable communications between the satellite and its ground control center, located at Kirtland Air Force Base in Albuquerque, New Mexico, have been established. Once further in-orbit tests are completed over the next several weeks, the research experiments aboard the TSX-5 satellite will be activated to begin mission operations.

Mr. Robert R. Lovell, Orbital's Executive Vice President and General Manager of its Space Systems Group, stated, "Orbital is very pleased to have played such a critical role in the successful beginning of the Air Force's TSX-5 mission. Yesterday, Orbital's Pegasus rocket delivered the spacecraft into its targeted orbit and now, after 24 hours of in-orbit operations, it appears to be a very healthy satellite. In addition to these promising early mission results, we look forward to contributing to the overall success of the TSX-5 program with continued in-orbit technical support for the remainder of the mission."

Under a contract from the U.S. Air Force, Orbital designed and built the 250-kg TSX-5 satellite at the company's Washington, D.C. metropolitan area satellite manufacturing facilities. Orbital will also provide technical support for the duration of its one-year mission. The TSX-5 spacecraft carries two research experiments intended to demonstrate advanced space technologies. Orbital has previously developed numerous spacecraft for Air Force space research missions, including APEX, REX II and the STEP series of small satellites.

Orbital is one of the world's leading manufacturers of cost-effective and highly reliable small spacecraft for low-Earth orbit and geosynchronous-Earth orbit missions. The company has built, delivered and launched over 85 satellites for communications, remote imaging and science and technology missions, which have amassed over 300 years of in-orbit experience. Customers for Orbital's satellites include commercial space companies, numerous U.S. Government agencies, as well as international private- and public-sector organizations.

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

/NOTE TO EDITORS: For a photo and artist's rendering of the TSX-5 satellite suitable for publication, visit http://www.orbital.com/News/Images/Satellites/satellites.htm on Orbital's corporate web site.

For more information on the TSX-5 mission, please visit either http://www.orbital.com/News/TSX-5Mission.htm on Orbital's corporate web site or the Air Force's TSX-5 mission web site at http://www.te.plk.af.mil/TSX5Home/TSX5.cfm

To learn more about Orbital, as well as to access their recent press releases, visit their corporate web site at http://www.orbital.com/

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