-- Two Minotaur IV Vehicles to Boost Hypersonic Test Vehicles for

                               DARPA --

DULLES, Va.Dec. 14, 2006--Orbital Sciences Corporation (NYSE:ORB) today announced that it has been awarded a $27 million contract for two Minotaur IV launch vehicles by the U.S. Air Force Space and Missiles Systems (SMC) Space Development and Test Wing (SDTW). The SDTW organization responsible for this contract is the 3rd Space Test Squadron (3STS). The two new missions will be used to support the FALCON program, which is being carried out by the Defense Advanced Research Projects Agency (DARPA). The Minotaur IV rockets will launch DARPA's Hypersonic Test Vehicle (HTV) technology demonstration systems, HTV-2a and HTV-2b, in 2008 and 2009, respectively.

The Minotaur IV launch vehicles will deliver the HTVs to a precise point in space, after which the test vehicles will be separated to then autonomously carry out guided test flights at hypersonic velocities. This contract covers the second and third Minotaur IV launch vehicles to be awarded by SMC and represents the 19th and 20th orders placed for the Minotaur family of launch vehicles.

About Orbital's Minotaur Product Line

Orbital's Minotaur product line was developed under the U.S. Air Force's Orbital/Suborbital Program (OSP). The initial five-year OSP contract was competitively awarded to Orbital in 1997 and the company also won the follow-on 10-year OSP-2 contract in 2003. The Minotaur I and II launch vehicles were the original members of Orbital's Minotaur family of launch vehicles, which includes both space launch vehicles and long-range suborbital vehicles for missile defense and other specialized launch missions. There have been ten successful launches of Minotaur I and II vehicles to date.

The Minotaur vehicles are specifically designed to be capable of launching from all U.S. spaceports, including government and commercial launch sites in Alaska, California, Florida and Virginia. Due to the minimal amount of specialized infrastructure that is required to support Minotaur launches, they can also be employed at other U.S. launch sites.

The Minotaur IV space launch configuration combines Orbital's commercial launch vehicle technologies, including upper stage rocket motors, structures, avionics and other elements, with government-supplied lower-stage rocket motor stages to create responsive, reliable and low-cost launch systems for U.S. government sponsored payloads. The Minotaur IV incorporates a standard 92-inch fairing from Orbital's Taurus(TM) booster and supports dedicated or shared launch missions. Capable of boosting satellites weighing up to 3,800 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 Air Force Space and Missile Systems Center in late 2008.

In addition to the Minotaur I and IV space launch vehicles, Orbital's Minotaur product line also includes:

    --  Minotaur II - A three-stage suborbital rocket, used as a
        target vehicle for testing U.S. missile defense systems and
        related missions. There have been five successful Minotaur II
        flights to date with three additional launches scheduled in
        2007.

    --  Minotaur III - A three-stage suborbital rocket also used to
        deliver suborbital technology demonstration payloads or as a
        target vehicle for testing U.S. missile defense systems and
        similar missions.

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

    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 can be found at http://www.orbital.com

Note to Editors:

High-resolution photos of the Minotaur I rocket launches and an artists rendering of the Minotaur IV are available on Orbital's website at: http://www.orbital.com/NewsInfo/Images/SpaceLaunch/index.html

More information about the Minotaur IV launch vehicle can be found at: http://www.orbital.com/SpaceLaunch/MinotaurIV/index.html


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

    SOURCE: Orbital Sciences Corporation