ATK’s CASTOR 30 Motor Supports Successful Antares(TM) Test Flight

Arlington, Va., April 21, 2013 – ATK’s (NYSE: ATK) CASTOR(R) 30 upper stage solid rocket motor supported the successful flight of Orbital Sciences Corporation’s (NYSE:ORB) Antares rocket as it lifted off from NASA’s Wallops Flight Facility in Virginia at 5:00 p.m. EDT with the Cygnus mass simulator payload. This was the test flight of the new Antares launch vehicle.

“This is a great day for the Antares team,” said Scott Lehr, vice president and general manager of ATK’s Defense and Commercial Division. “We congratulate Orbital for a successful test flight today. ATK is proud to be a part of their Antares team, and we look forward to helping Orbital successfully carry out its first cargo resupply mission to the International Space Station (ISS) later this year.”

ATK’s CASTOR 30 was developed in response to a market need for a large-diameter upper stage motor. It has the flexibility to serve markets as diverse as space launch, prompt global strike and operationally responsive space. In support of today’s launch, the motor fired for approximately 153 seconds and produced 73,000 pounds of maximum thrust to loft the Cygnus mass simulator payload into the proper orbit. The heavily instrumented payload will gather data about the launch environment aboard Antares. In addition, four small “pico satellites” were deployed from two dispensers that are integrated with the mass simulator.

Orbital has designed, built and tested the Antares medium-class space launch vehicle, as well as partnered with NASA to develop the Cygnus cargo spacecraft under NASA’s Commercial Orbital Transportation Services (COTS) program. NASA initiatives like COTS are helping develop a robust U.S. commercial space transportation industry, with the goal of achieving safe, reliable and cost-effective transportation to and from the ISS and low-Earth orbit.

Following the successful completion of the COTS demonstration mission to the ISS around mid-year, , Orbital will begin regular cargo resupply flights to the orbiting laboratory through NASA’s Commercial Resupply Services contract beginning in the fall.

A key partner supporting ATK through development and production of the CASTOR 30 motor is Moog in East Aurora, New York, which produced the thrust vector control (TVC) system. The TVC system was developed to have common hardware for future use on other ATK motors.

ATK is an aerospace, defense, and commercial products company with operations in 21 states, Puerto Rico, and internationally. News and information can be found on the Internet at www.atk.com.

Certain information discussed in this press release constitutes forward-looking statements as defined in the Private Securities Litigation Reform Act of 1995. Although ATK believes that the expectations reflected in such forward-looking statements are based on reasonable assumptions, it can give no assurance that its expectations will be achieved. Forward-looking information is subject to certain risks, trends and uncertainties that could cause actual results to differ materially from those projected. Among those factors are: changes in governmental spending, budgetary policies and product sourcing strategies; the company’s competitive environment; the terms and timing of awards and contracts; and economic conditions. ATK undertakes no obligation to update any forward-looking statements. For further information on factors that could impact ATK, and statements contained herein, please refer to ATK’s most recent Annual Report on Form 10-K and any subsequent quarterly reports on Form 10-Q and current reports on Form 8-K filed with the U.S. Securities and Exchange Commission.