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The Aerojet Rocketdyne RS-25, otherwise known as the Space Shuttle Main Engine (SSME), is a liquid-fuel cryogenic rocket engine that was used on NASA's Space Shuttle and is planned to be used on its successor, the Space Launch System. Built in the United States by Rocketdyne, the RS-25 burns cryogenic liquid hydrogen and liquid oxygen propellants, with each engine producing of thrust at liftoff. Although the RS-25 can trace its heritage back to the 1960s, concerted development of the engine began in the 1970s, with the first flight, STS-1, occurring on April 12, 1981. The RS-25 has undergone several upgrades over its operational history to improve the engine's reliability, safety and maintenance load. The engine produces a specific impulse (''I''sp) of in a vacuum, or at sea level, has a mass of approximately , and is capable of throttling between 67% and 109% of its rated power level in one-percent increments. The RS-25 operates under temperatures ranging from to 3300 °C (6000 °F).〔 On the Space Shuttle, the RS-25 was used in clusters of three engines mounted in the aft structure of the Orbiter, with fuel being drawn from the external tank. The engines were used for propulsion during the entirety of the spacecraft's ascent, with additional thrust being provided by two solid rocket boosters and the orbiter's two AJ10-190 Orbital Maneuvering System engines. Following each flight, the engines were removed from the orbiter, inspected and refurbished before being reused on another mission. ==Components== The RS-25 engine consists of various pumps, valves and other components which work in concert to produce thrust. Fuel (liquid hydrogen) and oxidizer (liquid oxygen) from the Space Shuttle external tank entered the orbiter at the umbilical disconnect valves, and from there flowed through the orbiter's main propulsion system (MPS) feed lines; whereas in the Space Launch System (SLS), fuel and oxidizer from the rocket's core stage will flow directly into the MPS lines. Once in the MPS lines, the fuel and oxidizer each branch out into separate paths to each engine (three on the Space Shuttle, up to five on the SLS). In each branch, prevalves then allow the propellants to enter the engine.〔 Once in the engine, the propellants flow through low-pressure fuel and oxidizer turbopumps (LPFTP and LPOTP), and from there into high-pressure turbopumps (HPFTP and HPOTP). From these HPTPs the propellants take different routes through the engine. The oxidizer is split into four separate paths: to the oxidizer heat exchanger, which then splits into the oxidizer tank pressurization and pogo suppression systems; to the low pressure oxidiser turbopump (LPOTP); to the high pressure oxidizer preburner, from which it is split into the HPFTP turbine and HPOTP before being reunited in the hot gas manifold and sent on to the main combustion chamber (MCC); or directly into the main combustion chamber (MCC) injectors. Meanwhile, fuel flows through the main fuel valve into regenerative cooling systems for the nozzle and MCC, or through the chamber coolant valve. Fuel passing through the MCC cooling system then passes back through the LPFTP turbine before being routed either to the fuel tank pressurization system or to the hot gas manifold cooling system (from where it passes into the MCC). Fuel in the nozzle cooling and chamber coolant valve systems is then sent via preburners into the HPFTP turbine and HPOTP before being reunited again in the hot gas manifold, from where it passes into the MCC injectors. Once in the injectors, the propellants are mixed and injected into the main combustion chamber where they are ignited. The burning propellant mixture is then ejected through the throat and bell of the engine's nozzle, the pressure of which creates the thrust.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Space Shuttle main engine」の詳細全文を読む スポンサード リンク
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