The Delta-K was an American rocket stage, developed by McDonnell Douglas and Aerojet.

It continued to serve as the second stage for subsequent variants of the Delta rocket.

It was propelled by a single AJ10-118K rocket engine, fueled by Aerozine 50 and dinitrogen tetroxide,[1] which are hypergolic.

The Delta-K had a long heritage to the first Able stage used in Project Vanguard.

As of 25 May 2008, 138 have been launched,[4] and excluding one which was destroyed by the explosion of a lower stage, none have failed.