Delta-P

For the mathematical term symbolizing a change in pressure, see ΔP.

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 continued to serve as the second stage for subsequent Delta 2000 and Delta 3000 flights for 17 years, with its last usage on February 8, 1988. It is propelled by a single TRW TR-201 rocket engine, fueled by Aerozine 50 and dinitrogen tetroxide,^[1] which are hypergolic.

Delta-P

Manufacturer	TRW and McDonnell Douglas
Country of origin	United States
Used on	Delta 1000 Delta 2000 Delta 3000
General characteristics
Height	5.9 m (19 ft)[1]
Diameter	2.4 m (7.9 ft)[1]
Gross mass	6,954 kg (15,331 lb)[1]
Engine details
Powered by	1 TR-201
Maximum thrust	43.63 kN (9,810 lbf)[1]
Specific impulse	319 seconds (3.13 km/s)[1]
Burn time	431 seconds[1]
Propellant	Aerozine 50 / N2O4

The Delta-P traces its heritage to the Apollo Lunar Module's Descent Propulsion System. The TR-201 engine is the Descent Propulsion System modified to be a fixed thrust engine.^[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. The Delta-K was then exclusively used on the second stage for the Delta 4000, Delta 5000, and subsequent Delta II.