-- Company to Design, Manufacture, Test and Operate New $40 Million Low-Earth Orbit Space Science Satellite --

DULLES, Va.Jul. 8, 2009-- Orbital Sciences Corporation (NYSE:ORB) announced today that it has been selected by the National Aeronautics and Space Administration (NASA) to design, manufacture, integrate and test a new low-Earth orbit (LEO) space science satellite that will study X-ray polarization in space. Under the $40 million contract, Orbital will provide the spacecraft bus and conduct mission operations for the Goddard Space Flight Center’s (GSFC) Gravity and Extreme Magnetism (GEMS) mission. The GEMS contract was awarded to Orbital under the space agency’s Small Explorer (SMEX) series of cost efficient and highly productive space science satellites. Orbital has built several other SMEX satellites for NASA, including the in-orbit GALEX, AIM and IBEX spacecraft, and is currently developing the NuSTAR spacecraft that is scheduled for launch in 2011. The GEMS mission is being led by the project’s Principal Investigator Dr. Jean Swank and is being managed by GSFC. It is currently scheduled to launch no later than 2015.

“Orbital is very pleased to be able to continue our support for NASA’s SMEX program with our selection by the Goddard Space Flight Center to build and operate the GEMS satellite,” said Mr. Mike Miller, Orbital’s Senior Vice President for Science and Technology satellite programs. “With our proven capabilities to build and deploy very reliable satellites to support the nation’s space science research, we are looking forward to working with Dr. Swank and her team on another important mission.”

The GEMS satellite will be the first observatory to systematically measure X-ray polarization which encodes information about the structure of cosmic sources, unlocking a previously hidden astrophysical world. Previous space-based X-ray observatories have been insensitive to polarization, which refers to the direction of the electric field of electromagnetic waves. Polarization measurements will allow scientists to study scattering, magnetic fields and strong gravitational fields.

“The collaboration among the GEMS participants during the study phase resulted in a strong team that was selected by NASA from among several other proposed missions to go forward with its important scientific research,” said Dr. Swank. “Over the next several years, we look forward to completing the satellite and flying a mission that will add important and useful new information to the study of astrophysics.”

The purpose of the GEMS mission is to help scientists answer fundamental questions about the universe, such as: Where is energy released near black holes? What is the origin of X-ray emissions from pulsars? What is the magnetic field structure in high energy nebulae? The GEMS team will make the data from the mission readily accessible to the astrophysics community and the general public on NASA’s High Energy Astrophysics Science Archive Research Center website at: http://heasarc.gsfc.nasa.gov/

The GEMS satellite will be based on Orbital’s proven LEOStar-2 TM spacecraft bus design. GEMS will be the eighth satellite to be based on the LEOStar-2 platform. Other LEOStar-based satellites that Orbital has built or currently has in development for NASA include the four SMEX satellites mentioned above, plus the Dawn interplanetary spacecraft that was launched in 2007 and the SORCE Earth science satellite that is currently in its seventh year of operation.

In addition to its program management role, NASA’s GSFC will provide the X-ray polarimeter instrument and oversee the Science Operations Center, science data processing, systems engineering and education and public outreach. Other program partners include NASA’s Ames Research Center, the University of Iowa and ATK, Inc.

About Orbital

Orbital develops and manufactures small- and medium-class rockets and space systems for commercial, military and civil government customers. The company’s primary products are satellites and launch vehicles, including low-Earth orbit, geosynchronous-Earth orbit and planetary spacecraft for communications, remote sensing, scientific and defense missions; human-rated space systems for Earth-orbit, lunar and other 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 provides satellite subsystems and space-related technical services to government agencies and laboratories. More information about Orbital can be found at http://www.orbital.com

Note to Editors:

A high-resolution artist concept of the GEMS satellite in orbit, courtesy of NASA, is available on Orbital’s website at: http://www.orbital.com/NewsInfo/ImagesMultimedia/Images/SatelliteSpaceSystems/index

Source: Orbital Sciences Corporation

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