DULLES, Va.Aug. 22, 2006--Orbital Sciences Corporation (NYSE:ORB):

    --  First High-Power STAR(TM) Spacecraft to be Launched in
        September for Australian Satellite Operator

    --  Delivery of 10th Company-Built GEO Satellite in Last Five
        Years Marks the Beginning of Busy Launch Period Through 2008

Orbital Sciences Corporation (NYSE:ORB) announced today that the company-built Optus D1 geosynchronous (GEO) communications satellite has been delivered to the space launch complex in Kourou, French Guiana, where it is scheduled to be launched aboard an Arianespace Ariane 5 rocket in September. The Optus D1 satellite is the first of two high-power satellites that Orbital is building for Optus Networks of Australia. The second satellite, Optus D2, is scheduled for completion and launch in 2007. Both of the Optus satellites are based on Orbital's new STAR 2.4 platform, which can generate nearly five kilowatts of payload power, making them the most powerful commercial communications satellites that Orbital has produced. The Optus program's design, manufacturing and testing activities are being carried out at Orbital's state-of-the-art satellite production facility in Dulles, Virginia.

"We are looking forward to launching, testing and commissioning the new D1 satellite for Optus," said Dr. Ali Atia, head of Orbital's GEO satellite business unit. "The STAR satellite platform has evolved to higher power and more complex payload capabilities in a careful and deliberate fashion over the past couple of years. We are now able to offer customers a wider selection of standard platforms, from our classic two kilowatt payload power small satellites to the high-end of the small range at about five kilowatts payload power. All of these STAR models use proven technology and offer reliable performance at attractive prices and are delivered, on average, in a 24-month timeframe."

Over the next several weeks, a team of engineers from Optus, Arianespace and Orbital will work together to integrate the satellite with the launch vehicle and perform an extensive series of tests and inspections to ensure that the combined systems of the satellite and rocket are working properly.

Orbital is one of the leading suppliers of GEO communications satellites, which are based on the STAR family of smaller GEO satellite platforms and are capable of accommodating most types of commercial communications payloads. For many applications, the STAR design is an attractive alternative to the larger, more costly GEO satellites offered by other industry suppliers. STAR satellites are smaller and significantly less expensive to manufacture and launch, making them a perfect fit for customers in the early stages of building their business or for established companies that wish to replace or add capacity to their network.

Customer demand for Orbital's STAR GEO satellites has been robust over the past several years. In 2005 and early 2006, Orbital received orders for STAR satellites from U.S.-based PanAmSat, the Horizons joint venture between JSAT of Japan and PanAmSat, Telenor of Norway, Measat of Malaysia and SES Americom of the U.S. Including the Optus D1 spacecraft, Orbital is now in varying stages of design, manufacturing and testing of eight commercial GEO satellites that will be launched over the next two years.

About Orbital

Orbital develops and manufactures small rockets and space systems for commercial, military and civil government customers. The company's primary products are satellites and launch vehicles, including low-orbit, geosynchronous-orbit 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.

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


    Note to Editors:

    --  A high-resolution image of the Optus satellite is available on
        Orbital's web site at:
        http://www.orbital.com/NewsInfo/Images/GEO



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

    SOURCE: Orbital Sciences Corporation