Engineering:Ascent Propulsion System

Ascent Propulsion System (APS)

Apollo LM Ascent Engine
Country of origin	United States
Date	1964–72
Manufacturer	Bell Aircraft / Rocketdyne
Application	Lunar Ascent Stage/Spacecraft propulsion
Predecessor	Bell 8247
Successor	RS-18
Status	Retired
Liquid-fuel engine
Propellant	N2O4 / Aerozine 50
Cycle	Pressure-fed
Configuration
Chamber	1
Performance
Thrust (vac.)	3,500 pounds-force (16 kN)
Thrust-to-weight ratio	19.44
Isp (vac.)	311 seconds (3.05 km/s)
Dimensions
Length	47 inches (120 cm)
Diameter	34 inches (86 cm)
Dry weight	180 pounds (82 kg)
Used in
Lunar Module as Ascent Engine

Apollo 17 LM Ascent Stage

The Ascent Propulsion System (APS) or Lunar Module Ascent Engine (LMAE) is a fixed-thrust hypergolic rocket engine developed by Bell Aerosystems for use in the Apollo Lunar Module Ascent Stage. It used Aerozine 50 fuel, and N₂O₄ oxidizer. Rocketdyne provided the injector system, at the request of NASA, when Bell could not solve combustion instability problems.

Origins

The LMAE traces its origin to the earlier Bell Aerosystems engines (8096, 8247) used in the RM-81 Agena, the United States rocket upper stage and satellite support bus developed by Lockheed initially for the canceled WS-117L reconnaissance satellite program. The Agena served as an upper stage for several defense, intelligence, and exploration programs: SAMOS-E, SAMOS-F (ELINT Ferret) and MIDAS (Missile Defense Alarm System) military early-warning satellites, Corona photo intelligence program, and the Ranger and Lunar Orbiter lunar probes.

The Lockheed Agena target vehicle using the Bell 8247 engine was qualified for 15 restarts for NASA's Project Gemini.

A total of 365 Agena rockets were launched by NASA and the US Air Force between February 28, 1959 and the last Agena D launched on 12 February 1987, configured as the upper stage of a Titan 34B.

Development

During the spring of 1963, Grumman hired Bell to develop the Lunar Module ascent engine, on the assumption that Bell's experience in development of the Air Force Agena engine would be transferable to the Lunar Module requirements. Grumman placed heavy emphasis upon high reliability through simplicity of design, and the ascent engine emerged as the least complicated of the three main engines in the Apollo space vehicle, including the LM descent and CSM service propulsion system engines.

Embodying a pressure-fed fuel system using hypergolic (self-igniting) propellants, the ascent engine was fixed-thrust and nongimbaled, capable of lifting the ascent stage off the Moon or aborting a landing if necessary.

The engine developed about 3,500 pounds-force (16 kN) of thrust, which produced a velocity of 2,000 meters per second from lunar launch, to LOR, and CM docking. It weighed 180 pounds (81.6 kg), with a length of 47 inches (119.4 cm) and diameter of 34 inches (86.4 cm).

According to the Science Channel's documentary Moon Machines, the fuel and oxidizer were so corrosive that the engines had to be rebuilt after each firing. This meant that each ascent from the Moon was performed with an engine that had not been test-fired prior to flight.

RS-18 Engine

Rocketdyne brought the Lunar Module Ascent Engine (LMAE) out of its 36-year retirement, now designated as RS-18, and reconfigured this non-throttleable hypergolic engine to use LOX/Methane for NASA Exploration Systems Architecture Study (ESAS) engine testing in 2008.

References

 This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration.

External links

• NASA Technical Note: October 24, 1972
• Apollo Lunar Module Propulsion Systems Overview, NASA