DULLES, Va.June 7, 2005--Orbital Sciences Corporation (NYSE:ORB) reached a significant operational milestone late last week when the company delivered its 500th space and launch system since the company was founded 23 years ago. As one of the most active developers of many types of satellites and rocket systems and the clear leader in the market for smaller-sized, more affordable and responsive space systems, Orbital has averaged one product delivery to customers every 17 days since 1982. The pace of operational activity has also been on a steep upward trajectory over the past decade, with 342 of the company's 500 deliveries taking place in the last 10 years alone, or about one delivery every 10 days since mid-1995.

"We are very proud to have served our customers with numerous, innovative and reliable space and launch systems for the past 23 years," said Mr. David W. Thompson, Orbital's co-founder, Chairman and Chief Executive Officer. "As one of only a handful of successful companies in the space and missiles industry born in the last several decades, Orbital's 500th delivery is a special milestone for all those employees, past and present, who have contributed so much to meeting our customers' needs."

Orbital achieved its 500th delivery when the company delivered and launched two Vandal short-range target vehicles for the U.S. Navy on Thursday, June 2. Included in the 500 space and launch vehicles that Orbital has designed, built and tested for a variety of government and commercial customers are these major types:

    --  93 Satellites. Orbital's satellite deliveries include 7
        geosynchronous-orbit commercial communications spacecraft, 17
        small- to medium-class (between 250 and 3,000 kg.) low-Earth
        orbit satellites and 69 microsatellites (under 250 kg.). These
        spacecraft were built for a range of national security, civil
        government and commercial customers in order to perform
        defense, space science, Earth observation, technology
        demonstration and fixed, mobile and broadcast communications
        missions.

    --  25 Other Space Systems. Space system deliveries in this
        category include 10 major payloads aboard the Space Shuttle
        (including space support equipment for four Hubble servicing
        missions) and 15 major subsystems delivered to other satellite
        manufacturers.

    --  66 Space and Interceptor Launch Vehicles. As the undisputed
        leader in the market for smaller-sized rocket systems, Orbital
        has built 39 Pegasus space and hypersonic research launch
        vehicles, 17 Orbital Boost Vehicle (OBV) missile defense
        interceptor boosters and 10 Taurus and Minotaur space launch
        vehicles.

    --  107 Major Target Launch Vehicles. Used to test the U.S.
        theater and national missile defense systems, Orbital has
        built and launched 10 long-range strategic target rockets and
        97 medium-range tactical target rockets for a variety of U.S.
        military customers.

    --  209 Other Small Rockets. Orbital has carried out a variety of
        scientific sounding rocket launches for NASA, universities and
        other research centers that now total 130 missions. Orbital
        has also emerged as the country's leader in ramjet-powered,
        low-altitude targets for the U.S. Navy, having delivered 71
        such systems over the last five years, as well as conducting
        eight other small targets and sounding rocket launches,
        primarily for the U.S. Department of Defense.

Mr. Thompson continued his remarks, saying, "Today, Orbital is busier than at any time in our history. With a growing contract backlog and a workforce approaching 3,000 employees, we expect to continue to be one of the industry's most active developers and manufacturers in the years ahead. We look forward to reaching our 1,000th space and launch system delivery in less than half the time it took to reach or first 500th delivery milestone."

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.


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

    SOURCE: Orbital Sciences Corporation