DULLES, Va.April 17, 2006--Orbital Sciences Corporation

     Six Orbital-Developed Weather-Monitoring MicroStar Satellites
         Activated and In Check-Out for Taiwan's Space Agency

  Flight Brings the Minotaur Rocket Product Line's Launch Record to a
                Perfect Ten-for-Ten Over Last Six Years

Orbital Sciences Corporation (NYSE:ORB) announced today that its Minotaur I space launch vehicle successfully delivered six small scientific satellites into low-Earth orbit in a mission that originated from Vandenberg Air Force Base (VAFB), CA on April 14. The space mission, known in the United States as the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC), consists of an array of six small-sized remote-sensing satellites, collectively called the FORMOSAT-3 program by its owner and operator, the National Space Program Office (NSPO) in Taiwan.

The mission originated Friday evening at approximately 6.40 p.m. (PDT) when the Minotaur rocket ignited its first stage motor and lifted-off from its West Coast launch site. Approximately 10 minutes later, the Minotaur I fourth stage and satellites were placed into their targeted orbit approximately 500 kilometers above the Earth's surface, inclined at 72 degrees to the equator. Over the next nine minutes, the six satellites were separated from the rocket's final stage one spacecraft at a time.

The FORMOSAT-3/COSMIC satellites were developed, manufactured and tested under a collaborative project between Taiwan's civilian space agency, the National Space Program Office; several agencies of the U.S. Government, including the National Science Foundation and the U.S. Air Force; and the University Corporation for Atmospheric Research (UCAR). NSPO and UCAR selected Orbital in 2001 to jointly develop and manufacture the six spacecraft, which are based on Orbital's MicroStar(TM) product line. During their first several days in space, the initial satellite in-orbit checkout process has been progressing as planned. Once it is completed, the satellites will be maneuvered to form a global constellation that will collect data on the Earth's atmosphere that can be used to improve weather forecasting, climate monitoring and understanding of the ionosphere.

Friday's launch was the fifth flight of the Minotaur I space launch vehicle, all of which have been successful. In addition, the launch demonstrated two "firsts," including being the first space launch vehicle to use a new low-cost, lightweight Orbital Flight Computer that was developed by the company in-house. The FORMOSAT-3/COSMIC launch vehicle also incorporated a low-cost telemetry subsystem that utilizes the U.S. Government's Tracking and Data Relay Satellite System (TDRSS). The TDRSS telemetry system was flown on the Minotaur vehicle to provide real-time telemetry once the launch vehicle was beyond the range of ground-based receivers.

The Minotaur launch was the tenth consecutive successful flight of the Minotaur family of space and suborbital launch vehicles since the program's first flight in January 2000. Minotaur I space launch vehicles have put a total of 20 satellites into orbit in five fully successful missions. Minotaur II rockets have also carried out five target vehicle missions in support of U.S. missile defense programs. The Minotaur product line, including its newest Minotaur III, IV and V variants, currently has another seven launches on contract for space and suborbital missions over the next three years.

About the FORMOSAT-3/COSMIC Spacecraft

The six FORMOSAT-3/COSMIC spacecraft are based on Orbital's MicroStar small satellite platform, first introduced in 1995 and updated with new technology over the last several years. Weighing only 70 kg (150 lbs.) each, the satellites carry three scientific instruments: an advanced Global Positioning System (GPS) occultation receiver, an ionospheric photometer and a tri-band beacon. During their expected five-year operational lifetime, the satellites will form a global array to collect approximately 2,500 measurements every 24 hours of Earth's atmosphere's temperature and water vapor profiles from ground-level to the ionosphere. The satellites will convert GPS radio occultation measurements into a precise worldwide set of weather and climate-change data that will be available to scientists and forecasters within a few hours of the observations.

About Orbital's Minotaur Launch Vehicles

The Minotaur space launch vehicle used in the successful launch of the FORMOSAT-3/COSMIC satellites is a member of Orbital's Minotaur family of space and suborbital launch vehicles. Minotaur rockets are flight-proven and are currently capable of supporting the Department of Defense's Operationally Responsive Space (ORS) launch requirements. Minotaur rockets have already supported rapid call-up operations (in four days), as well as extended durations on alert. They are designed for high launch availability, so launch site conditions and upper level winds are less of a launch constraint than with typical launch vehicles.

Minotaur launch vehicles are also designed to be flexible in meeting unique customer requirements. Customers are offered several payload fairing size options from which to choose, the ability to launch multiple payloads, various upper-stage motor options, tight launch window capabilities (measured in minutes) and minimal ground support requirements to allow launches to be conducted from austere locations.

In addition to the Minotaur I space booster, Orbital's Minotaur product line also includes:

    Minotaur II - A three-stage suborbital rocket, used as a strategic
    target vehicle for testing U.S. missile defense systems and
    related missions. Orbital offers Heavy and Light variants of
    Minotaur II in order to meet unique customer needs.

    Minotaur III - A very high-accuracy four-stage suborbital rocket
    capable of launching payloads up to 6,500 lbs. The vehicle can be
    used for testing hypersonic vehicles and as a strategic target
    vehicle for U.S. missile defense systems or similar missions.

    Minotaur IV - A four-stage space launch vehicle, used to place
    U.S. Government-sponsored satellites, weighing up to 4,000 lbs.,
    into low-Earth orbit. The first Minotaur IV mission is currently
    under contract to launch the Space-Based Surveillance System
    (SBSS) satellite for the U.S. Air Force.

    Minotaur V - An enhanced-performance version of the Minotaur IV
    space launch vehicle that may be used to launch government
    satellites, weight up to 800 lbs., into geosynchronous orbit and
    other higher-energy orbits for missions related to national
    defense, space exploration and other activities beyond low-Earth
    orbit.

About the FORMOSAT-3/COSMIC Spacecraft

The six FORMOSAT/COSMIC spacecraft are based on Orbital's MicroStar small satellite platform, first introduced in 1995 and updated with new technology over the last several years. Weighing only 70 kg (150 lbs.) each, the satellites carry three scientific instruments: an advanced Global Positioning System (GPS) occultation receiver, an ionospheric photometer and a tri-band beacon. During their expected five-year operational lifetime, the satellites will form a global array to collect approximately 2,500 measurements every 24 hours of Earth's atmosphere's temperature and water vapor profiles from ground-level to the ionosphere. The satellites will convert GPS radio occultation measurements into a precise worldwide set of weather and climate-change data that will be available to scientists and forecasters within a few hours of the observations.

About Orbital

Orbital develops and manufactures small space systems for commercial, civil government and military customers. The company's primary products are satellites and launch vehicles, including low-orbit, geostationary-orbit and planetary spacecraft for communications, remote sensing and scientific missions; ground- and air-launched rockets that deliver satellites into orbit; and missile defense boosters 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 and the Minotaur launch vehicle product line can be found at http://www.orbital.com

Note to Editors:

A high-resolution photo of the Minotaur rocket that carried out the FORMOSAT-3/COSMIC mission is available at: http://www.orbital.com/NewsInfo/Images/SpaceLaunch/index.html


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

    SOURCE: Orbital Sciences Corporation