XLR81

XLR81

Standard Agena D 108 being delivered to final assembly area. Would later become Gemini Agena target vehicle 5003.
Country of origin	United States
Date	1957
First flight	1963-07-12
Last flight	1984-04-17
Manufacturer	Bell Aerosystems Company
Application	upper stage engine
Associated L/V	Thor, Thorad, Atlas and Titan
Predecessor	Bell 8081
Successor	Bell 8247
Status	Retired
Liquid-fuel engine
Propellant	RFNA / UDMH
Mixture ratio	2.55
Cycle	Gas generator
Configuration
Chamber	1
Nozzle ratio	45
Performance
Thrust (vac.)	71.2 kN (16,000 lbf)
Chamber pressure	3.49 MPa (506 psi)
Isp (vac.)	293 s
Burn time	265 s
Restarts	2
Gimbal range	+/-2.5°
Dimensions
Length	2.11 m (83.2 in)
Diameter	0.90 m (35.5 in)
Dry weight	134 kg (296 lb)
Used in
RM-81 Agena

The Bell Aerosystems Company XLR81 (Model 8096) was an American liquid-propellant rocket engine, which was used on the Agena upper stage. It burned UDMH and RFNA fed by a turbopump in a fuel rich gas generator cycle. The turbopump had a single turbine with a gearbox to transmit power to the oxidizer and fuel pumps. The thrust chamber was all-aluminum, and regeneratively cooled by oxidizer flowing through gun-drilled passages in the combustion chamber and throat walls. The nozzle was a titanium radiatively cooled extension. The engine was mounted on an hydraulic actuated gimbal which enabled thrust vectoring to control pitch and yaw. Engine thrust and mixture ratio were controlled by cavitating flow venturis on the gas generator flow circuit. Engine start was achieved by solid propellant start cartridge.

Starting as an air-launched missile engine and finishing as a multi-mission general propulsion for the space age, the basic design went through a series of iterations and versions that enabled it to have a long and productive career.