Other critics of the deal included U.S. Democratic Senator Elizabeth Warren, who asked the FTC to examine the internal firewalls Lockheed said it would put in place to prevent it from gaining a competitive advantage over its peers.
Lockheed had said it accounted for 33% of Aerojet's sales and argued that the deal would reduce costs for the Pentagon and the U.S. taxpayer.
Rocket motors like those made by Aerojet are used in everything from the homeland defensive missile system to Stinger missiles.
Aerojet develops and manufactures liquid and solid rocket propulsion, air-breathing hypersonic engines and electric power and propulsion for space, defense, civil and commercial applications. Its customers include the Pentagon, NASA, Boeing, Lockheed Martin, Raytheon and the United Launch Alliance.