The announcement comes after SpaceX CEO Elon Musk publicly criticized ULA for relying on RD-180 engines from Russian suppliers RD AMROSS and NPO Energomash to launch U.S. Air Force missions.

“While the RD-180 has been a remarkable success, we believe now is the right time for American investment in a domestic engine,” said Michael Gass, ULA president and CEO.  “At the same time, given that ULA is the only certified launch provider of our nation’s most important satellites, it is critical that America preserve current capabilities and options while simultaneously pursuing this new engine.”

ULA is expected to select its future concept and engine supplier by the fourth quarter of this year to enable initial launch capability by 2019 of the new system.