Orbital Set to Launch NASA's Space Technology 5 Spacecraft aboard Pegasus Rocket; ST5 Mission Will be the First Pegasus Launch in 2006 and 37th in the Program's 16-Year History.

DULLES, Va. -- Orbital Sciences Corporation (NYSE:ORB) today announced that it is in final preparations to launch the Space Technology 5 (ST5) scientific spacecraft for the National Aeronautics and Space Administration (NASA) aboard the company's Pegasus(R) rocket. The launch is currently scheduled to take place on Wednesday, March 15, 2006 from Vandenberg Air Force Base (VAFB), California, during an available launch window that extends from 8:57 to 10:19 a.m. (EST). The targeted mission launch time is 9:02 a.m. (EST). This operational schedule is subject to the completion of final pre-launch activities, as well as acceptable weather conditions at VAFB at the time of the launch.

The powered flight sequence for the ST5 mission is expected to take approximately 11 minutes, from the time the Pegasus rocket is released from its L-1011 carrier aircraft to the time that the three ST5 satellites are deployed into orbit. Orbital plans to launch the 55-pound spacecraft into a highly elliptical orbit of 186 by 2,796 miles above the Earth at an inclination of 105.6 degrees to the equator.

About Pegasus

Pegasus is the world's leading launch system for the deployment of small satellites into low-Earth orbit. Its patented air-launch system, in which the rocket is launched from beneath Orbital's "Stargazer" L-1011 carrier aircraft over the ocean, reduces cost and provides customers with unparalleled flexibility to operate from virtually anywhere on Earth with minimal ground support requirements.

For the ST5 mission, Orbital will employ a unique satellite deployment system called the Pegasus Support Structure, which is a spring-loaded mechanism that intentionally spins the satellites at preset time intervals in order to create a formation-flying group of spacecraft in low-Earth orbit.

The ST5 mission will be the 37th flight of the Pegasus rocket and the first of two planned missions in 2006. Later in the year, Orbital is scheduled to launch NASA's Aeronomy of Ice in the Mesosphere (AIM) spacecraft, which is now in production at Orbital's Dulles, Virginia satellite manufacturing facility.

About ST5

NASA's New Millennium Program's ST5 spacecraft consists of three microsats that are designed to validate, in actual flight conditions, innovative technology concepts that may reduce risks to future science missions. The ST5 mission will demonstrate the ability of small satellites to perform research-quality science by taking measurements of the Earth's magnetic field using highly sensitive magnetometers.

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 Pegasus rocket are available on Orbital's website at: http://www.orbital.com/NewsInfo/Images/index.html

--Launch Day Press Coverage - On launch day, media representatives should meet at the Vandenberg main gate at 4:30 a.m. (PST) to be escorted to the viewing room of the NASA Mission Director's Center located at Building 840 on South Vandenberg Air Force Base. From there, media may follow the L-1011 departure, flight and launch of Pegasus/ST5. Assuming a successful flight of the Pegasus, a post-launch news conference will not be held. However, launch vehicle and spacecraft representatives will be available afterward to informally answer questions from the media.

--NASA Television Launch Coverage of Pegasus/ST5 - Live coverage on NASA Television of the Pegasus/ST5 launch will begin at 7:30 a.m. (EST) on March 15 and continue through spacecraft separation from the Pegasus vehicle, which occurs approximately 10 minutes after launch. Live launch commentary and audio of the Pegasus/ST5 briefings will be available on the "V circuits" that may be dialed at 321/867-1220, 1240, 1260.