The Delta-P is an American rocket stage, developed by McDonnell Douglas and TRW, first used on November 10, 1972 as the second stage for the Delta 1000 series.
It is propelled by a single TRW TR-201 rocket engine, fueled by Aerozine 50 and dinitrogen tetroxide,[1] which are hypergolic.
The Delta-P traces its heritage to the Apollo Lunar Module's Descent Propulsion System.
[2] The Descent Propulsion System was first fired in flight during the Apollo 5 mission, in a low Earth orbit test on January 22, 1968.
As the supply of these surplus Apollo engines was depleted, the Douglas/Aerojet Delta-K upper stage was introduced in the Delta 3000 program.