The Aerojet LR87 was a liquid-propellant rocket engine that played a significant role in the United States’ space and missile programs from the late 1950s through the early 2000s. Developed by Aerojet, the LR87 was used as the main engine for the first stages of various Titan intercontinental ballistic missiles (ICBMs) and launch vehicles. The engine’s unique twin-chamber design and versatility in using different propellant combinations made it a reliable workhorse for the Titan family of rockets.
Development and Design
Aerojet began developing the LR87 in the late 1950s as part of the U.S. Air Force’s Titan ICBM program. The engine was designed to be the first production rocket engine capable of burning three common liquid rocket propellant combinations: liquid oxygen/RP-1, nitrogen tetroxide/Aerozine 50, and liquid oxygen/liquid hydrogen. This versatility allowed the LR87 to be adapted for various applications and missions, ensuring its longevity in the rapidly evolving aerospace industry.
The LR87 featured a unique configuration, consisting of twin motors with separate combustion chambers and turbopump machinery. Although considered a single unit, the engine was never flown or designed to operate as a single combustion chamber engine. This twin-chamber design provided increased reliability and thrust for the Titan rockets, as well as redundancy in case of a single chamber failure.
The engine operated on an open gas-generator cycle and utilized regeneratively cooled combustion chambers. For each thrust chamber assembly, a single high-speed turbine drove the lower-speed centrifugal fuel and oxidizer pumps through gearing, ensuring high turbopump efficiency. This configuration reduced fuel consumption in the gas generator and improved the engine’s specific impulse, resulting in better overall performance.
The LR87’s combustion chambers were constructed using a tubular wall design, with the propellant flowing through tubes that formed the chamber walls. This regenerative cooling method helped to maintain the structural integrity of the chambers during operation, while also preheating the propellant before injection into the combustion chamber. The injectors used a combination of impinging and coaxial elements to ensure efficient mixing and atomization of the propellants.
Variants and Applications
LR87-3
The LR87-3 variant, used on the Titan I ICBM, burned liquid oxygen and RP-1. This combination provided a high specific impulse and was well-understood due to its extensive use in other rocket engines of the era. The LR87-3 produced a sea-level thrust of approximately 1,500 kN (340,000 lbf) per chamber, for a total of 3,000 kN (680,000 lbf) at liftoff.
Following the retirement of the Titan I missile program, these engines saw no further use. However, the LR87-3 was also tested with nitrogen tetroxide/Aerozine 50 and liquid oxygen/liquid hydrogen propellant combinations, making it one of the few engines to have been run on three different propellant combinations. These tests demonstrated the engine’s adaptability and laid the groundwork for future variants.
LR87-5 and LR87-7
For the Titan II ICBM and Gemini launch vehicle, Aerojet developed the LR87-5 and LR87-7 variants, respectively. These engines used nitrogen tetroxide and Aerozine 50 propellants for improved storability at the request of the U.S. Air Force. The switch to hypergolic propellants allowed for simpler engine controls, solid-propellant cartridges for turbopump start-up, simplified injectors, and autogenous pressurization.
The LR87-5 and LR87-7 produced a sea-level thrust of approximately 1,900 kN (430,000 lbf) per chamber, for a total of 3,800 kN (860,000 lbf) at liftoff. The LR87-7 featured additional redundancies and safety features to meet human-rating certification requirements for the Gemini program, ensuring the safety of the astronauts during their missions.
The use of the LR87-5 and LR87-7 in the Titan II and Gemini programs demonstrated the engine’s reliability and performance capabilities. The Titan II ICBM served as a critical component of the United States’ nuclear deterrent during the Cold War, while the Gemini program laid the foundation for the Apollo missions and the eventual moon landings.
LR87-9 and LR87-11
The LR87-9 and LR87-11 variants were used on various Titan III launch vehicles, with the LR87-11A being used on the Titan IV A/B. These versions featured increased thrust and nozzle area ratios, requiring heavier turbopumps, pipes, and other components to accommodate the higher performance.
The LR87-9 produced a sea-level thrust of approximately 2,100 kN (470,000 lbf) per chamber, for a total of 4,200 kN (940,000 lbf) at liftoff. The LR87-11 further increased the thrust to approximately 2,400 kN (540,000 lbf) per chamber, resulting in a total liftoff thrust of 4,800 kN (1,080,000 lbf).
The Titan III and Titan IV launch vehicles were used for a variety of military and civilian payloads, including reconnaissance satellites, communications satellites, and interplanetary probes. The increased performance of the LR87-9 and LR87-11 variants allowed these vehicles to carry heavier payloads to higher orbits, expanding the capabilities of the Titan family.
Manufacturing and Testing
Aerojet manufactured the LR87 engines at its facility in Sacramento, California. The company invested heavily in advanced manufacturing techniques and quality control measures to ensure the engines met the stringent requirements of the U.S. Air Force and NASA.
Each LR87 engine underwent rigorous testing before being approved for flight. This testing included individual component tests, such as turbopump and injector tests, as well as full-scale engine hot-fire tests. These tests were conducted at Aerojet’s facilities and at U.S. Air Force and NASA test sites, such as Edwards Air Force Base in California and the Marshall Space Flight Center in Alabama.
The extensive testing program helped to identify and resolve any issues with the engines, ensuring their reliability and performance in flight. The data gathered during these tests also provided valuable insights for future engine development and improvement.
Legacy and Conclusion
The Aerojet LR87 engine family played a crucial role in the success of the Titan missile and launch vehicle programs. Its unique twin-chamber design and ability to burn various propellant combinations made it a versatile and reliable engine for over four decades. The LR87’s development also paved the way for the creation of the LR-91 engine, which was used in the second stage of the Titan missiles and launch vehicles.
The LR87’s contributions to the Titan program were significant, with the engine powering various ICBMs and launch vehicles that served critical roles in the United States’ military and civilian space programs. The Titan I and Titan II ICBMs formed a key part of the country’s nuclear deterrent during the Cold War, while the Gemini program, powered by the LR87-7, laid the groundwork for the Apollo missions and the eventual moon landings.
The Titan III and Titan IV launch vehicles, powered by the LR87-9 and LR87-11 variants, were instrumental in launching numerous military and civilian payloads, including reconnaissance satellites, communications satellites, and interplanetary probes. These missions helped to advance our understanding of the Earth, the solar system, and the universe beyond.
Although the LR87 is no longer in use, its legacy as a powerful and adaptable rocket engine remains significant in the history of American rocketry. The engine’s development and success demonstrate the ingenuity and dedication of the engineers and scientists at Aerojet and the U.S. Air Force, who worked tirelessly to push the boundaries of rocket technology.
The LR87’s influence can still be seen in modern rocket engine designs, which continue to build upon the lessons learned and advancements made during its development and operation. As we continue to explore space and push the limits of human achievement, it is important to remember the contributions of engines like the LR87 and the people who made them possible.
