U.S. government space officials on Thursday picked incumbents Space Exploration Technologies Corp. and Orbital ATK Inc., along with closely held Sierra Nevada Corp., to ferry cargo back and forth from orbit in the next decade.

National Aeronautics and Space Administration officials said the arrangement, under which each contractor will get at least six unmanned missions to the orbiting international space station, is designed to provide maximum flexibility in price, schedule and mission assurance. Additional missions will be awarded later.

The decision vaults Nevada-based Sierra Nevada, which provides components and systems for space and aerospace applications to commercial and military markets, into the top tier of NASA contractors.

The commercial contracts will be fixed-price, but the agency said the precise costs will depend on when, how many and what types of missions ultimately are ordered.

The maximum total value of the contracts is about $14 billion through 2024, but agency officials said they don’t expect to spend “anywhere close to that.”