ATK wins Orbital Sciences order for space transport vehicle WASHINGTON (Reuters) - Alliant Techsystems Inc (ATK.N) on Tuesday said it had won an order from Orbital Sciences Corp (ORB.N) to provide solid rocket motors for a new air-launched space transport system that is part of Microsoft co-founder Paul Allen's latest venture. Blake Larson, president of ATK Aerospace Group, gave no details on the size and scope of the contract, but told Reuters the deal was "certainly substantial." "It further enhances and expands other commercial elements of our propulsion business," Larson said. ATK is seeking to take on more commercial projects to diversity its portfolio at a time when the U.S. military budget is set to flatten or decline. There was no immediate comment from Orbital Sciences. Allen's Stratolaunch Systems tapped Orbital Sciences in June to develop the new transport system which will use a large aircraft to launch satellites, cargo and possibly humans, into space. Stratolaunch plans to launch test flights in 2016, and may fly its first mission in 2017 or 2018. ATK said it would provide the first and second stage propulsion for the Air Launch Vehicle. The company will also design and develop and flight hardware for initial Stratolaunch missions. ATK has built more than 1,600 commercial solid rocket motors for a wide array of launch vehicles, including Orbital Sciences' Pegasus, Taurus, Minotaur and Antares launch vehicles. Scott Lehr, vice president and general manager of ATK's Defense and Commercial Division, said the company would use materials including high-strength, low-weight graphite composite cases and advanced propellants for the Orbital Sciences project. Editing by Miral Fahmy