US defense group Northrop Grumman will buy out the rocket and missile maker Orbital ATK (Frankfurt: AD9S.F - news) in a deal worth $9.2 billion, the firms said on Monday.

The announcement comes around two weeks after industrial conglomerate United Technologies acquired aerospace supplier Rockwell Collins (NYSE: COL - news) in a $30 billion deal.

"Northrop Grumman will acquire Orbital ATK for approximately $7.8 billion in cash, plus the assumption of $1.4 billion in net debt," the companies said in a statement.

The transaction, which is expected to close in the first half of 2018, has been approved by the companies' boards of directors but is still subject to regulatory and Orbital shareholder approval.

Northrop is valued at $46.5 billion, while Orbital -- which specializes in making rocket launchers and missiles, including for Elon Musk's SpaceX -- is valued at $6.3 billion.

The deal comes amid high tensions with North Korea and as American defense firms are under pressure to maintain their profit margins while customers demand better value for money.

In 2015, Northrop won an $80 billion mega-contract from the US military for the Long Range Strike Bomber planned for the mid-2020s.