Throttleable LREs can be used for planetary entry and descent, space rendezvous, orbital maneuvering including orientation and stabilization in space, and hovering and hazard avoidance during planetary landing. Liquid-Propellant Rocket Engines (LREs) are capable of on-command variable thrust or thrust modulation, an operability advantage that has been studied intermittently since the late 1930s. Liquid-Propellant Rocket Engine Throttling: A Comprehensive ReviewĬasiano, Matthew Hulka, James Yang, Virog It is also important to assess the amount of nozzle flow separation that can be tolerated at low thrust levels for ground testing. For valves, it is necessary to design valves and actuators that can achieve accurate flow control at all thrust levels.
For turbomachinery, the primary considerations are to avoid cavitation, stall, surge, and to consider bearing leakage flows, rotordynamics, and structural dynamics. For the combustion chamber, cooling can be an issue at low thrust levels. The key difficulty in throttling liquid rocket engines is maintaining an adequate pressure drop across the injector, which is necessary to provide propellant atomization and mixing. Boost and sustainer engines have demonstrated throttling from 17% to 100% thrust, while upper stage and lunar lander engines have demonstrated throttling in excess of 10% to 100% thrust. Both deep throttling and shallow throttling engines are discussed. This study focuses on liquid rocket engines that have demonstrated operational capability on American space launch vehicles, starting with the Apollo vehicle engines and ending with current technology demonstrations. Next, the engine system is broken down into components to discuss special considerations that need to be made for engine throttling. Three engines are discussed that have successfully demonstrated throttling. A background on liquid rocket engine throttling is provided, along with the basic equations that are used to predict performance. First, an assessment of space mission requirements is performed to determine what applications require engine throttling.
The focus of this study is on engine components, and how the interactions of these components are considered for throttling applications. This is a comprehensive systems study to examine and evaluate throttling capabilities of liquid rocket engines. A Historical Systems Study of Liquid Rocket Engine Throttling Capabilitiesīetts, Erin M.
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