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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs Appendix D Background Information on the Delta IV and Atlas V Families of Large Launch Vehicles RS-68 BOOSTER ENGINE FOR DELTA IV In the early 1990s, Rocketdyne initiated development of the first new indigenous booster-class engine in the United States in more than 25 years. The engine was designated the RS-68 and was ultimately selected to power the Delta family of evolved expendable launch vehicles (EELVs) that was developed for the Air Force by the Boeing Space Systems Company. The RS-68 is a conventional bell nozzle, LOx LH2 booster engine that develops 650,000 lb of sea level thrust. During the design and development phases, this engine utilized a simplified design philosophy (compared with, for example, the Apollo rocket engines and the space shuttle main engine (SSME)), significantly reducing parts count (again, compared with current cryogenic engines worldwide). Rocketdyne also claims that this overall simplified design approach resulted in lower development and production costs. The engine is capable of being throttled to 60 percent of full power level. The RS-68 is the largest LOx/H2 engine in the world today. The engine uses a simple, open gas generator cycle with a regeneratively cooled main chamber. The turbine exhaust gases can be vectored on command to provide roll control capability for the Delta IV family of launch vehicles. The engine was designed, developed, and certified in a little over 5 years, and the first RS-68 flew on the first Delta IV launch in late 2002. At 656,000 lb of sea level thrust, the RS-68 develops the equivalent of 17 million hp (the equivalent of 11 Hoover Dams at full power generation). The RS-68 has far fewer parts than the SSME, which greatly contributes to its lower production costs. It has only 11 major components, including the main combustion chamber (MCC), single oxygen and hydrogen turbopumps, gimbal bearing, injector, gas generator, heat exchangers, and fuel exhaust duct. This amounts to a reduction of parts from SSME of over 80 percent and a reduction in hand-touched labor by 92 percent. The development cycle time was also much reduced, and the nonrecurring costs were claimed to be reduced by a factor of five compared to those of previous cryogenic engines. The engine stands 17 feet tall, is 8 feet in diameter, and has a quadrapod thrust frame that mates it to the Delta IV common booster core first stage. The engine performance and operating characteristics are summarized in Table D-1. RL-10B-2 ENGINE FOR DELTA III AND IV UPPER STAGES The RL-10 engine, developed by Pratt &Whitney in the late 1950s, was the world’s first LOx/LH2-fueled rocket engine operated in space. The RL-10 engine, used on stages (Nova A-3, Nova B-3, and Saturn IV) and on launch vehicles (Nova A, Nova B, Saturn B-1, Saturn C-2, Saturn C-3, and Saturn I), weighed 131 kg and developed an I sp of 410 sec. The engine operated with a nominal chamber pressure of 348 psi and provided a T/W ratio of 44.63. Since the first successful launch of an Atlas/Centaur RL-10 in November of 1961, Pratt &Whitney has developed nine different models of the RL-10 engine family. The RL-10
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs has earned the reputation of being a highly reliable, safe, and high-performing cryogenic upper-stage engine for a wide variety of upper stages for a large number of U.S. EELVs. TABLE D-1 RS-68 Engine Major Performance and Operating Characteristics Thrust Level Characteristic 100% 60% Thrust (thousand lbf) At vacuum 745 650 At sea level 440 345 Weight 14,560 Engine mixture ratio 6.0 6.0 Isp (sec) At vacuum 410 365 At sea level 410 365 Chamber pressure 1,410 836 Expansion ratio E 21.5 During the past four decades, the RL-10 engine family has placed more than 150 government, military, and commercial payloads into space. The RL-10 has provided propulsion for a wide variety of rocket configurations, including those in the Saturn, Titan, Atlas, and Delta launch vehicle families. Payload size and mission configuration were used to determine the best engine model for each vehicle configuration. The RL-10B-2 is a derivative of the successful RL-10 engine. It features the world’s largest carbon-carbon extendible nozzle. This high expansion nozzle enables the RL-10B-2 to operate nominally with a chamber pressure of 633 psi and develops an Isp of 465.5 sec. This engine can lift payloads up to 30,000 lb and currently powers the upper stage of the medium and heavy-lift configurations of Boeing’s Delta IV launch vehicle in addition to the upper stage of the Delta III. Current RL10 engine models and their supported vehicles are RL-10A-4-2 (Atlas V), RL-10-4 and RL-10-4-1 (Atlas II, IIA, IIAS, III and IIIB) and RL-10A-3-A (Titan IVB). The full family of flight-certified RL-10-XX engines is listed in Table D-2, along with their respective key design features. TABLE D-2 Comparison of RL-10 Engine Models Characteristic A-1 A-3 A-3-1 A-3-3 A-3-3a A-4 A-5 A-4-1 B-2 Vacuum thrust (lb) 15,000 15,000 15,000 15,000 16,500 20,800 14,560 22,300 24,750 Chamber pressure (psia) 300 300 300 395 475 578 485 610 644 Thrust/weight 50 50 50 50 54 67 61 Expansion ratio 40:1 40:1 40:1 57:1 61:1 84:1 43:1 84:1 285:1 Specific impulse (sec) 422 427 431 442 444 449 368 451 466.5 Flight Nov. June Sept. Oct. Nov. Dec. Aug. Feb. May certification date 1961 1962 1964 1966 1981 1990 1992 1994 1998 GRAPHITE EPOXY MOTOR FOR DELTA BOOSTERS ATK Thiokol originally developed the graphite epoxy motor (GEM) for the Delta II launch vehicle for the Air Force and Boeing. GEM 40 boosters were used to increase the launch capability of the Delta II. The GEM 46 is a larger derivative of the highly reliable GEM 40 and will be used on the Delta III. This motor has increased length, diameter, and vectorable nozzles on three of the six ground-start motors.
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs The motor has also been used on the Delta II Heavy. More recently, GEM 60 motors were developed for the Delta IV EELV. These 70-ft motors provide auxiliary liftoff capability for the Delta IV M+ vehicles. State-of-the-art automation, robotics, and process controls are used to produce GEMs. Cases are filament wound by computer-controlled winding machines using high-strength graphite fiber and durable epoxy resin. Critical processes (e.g., case bond application, propellant mixing, motor casting) are performed using an extensive network of computerized and robotic facilities to ensure accurate control of manufacturing. The delivered products are consistent, reliable, repeatable, and of high quality. The current GEM family of motors now includes these: GEM 40, for Delta II boosters, GEM 46, for Delta III boosters, and GEM 60, for Delta IV boosters. The 60-in.-diameter GEM motor is a strap-on booster system developed to increase the payload-to-orbit capability of the Delta IV M+ launch vehicles. Two and four strap-on motor configurations of the GEM 60 can be flown on the Delta IV M+ vehicles. The motor features a +5 degree canted, moveable nozzle assembly. This motor is a third-generation GEM with both fixed and vectorable nozzle configurations. The Delta IV launch vehicle family’s inaugural flight occurred in November 2002 and was the first flight of the Air Force’s EELV program. Table D-3 summarizes operation and performance characteristics of the GEM 60 vectorable nozzle motor. TABLE D-3 Performance and Operating Characteristics of the GEM 60 Vectorable Nozzle Motor Characteristic Value Characteristic Value Motor dimensions (in.) Weight (lbm) Diameter 60 Total loaded 74,158 Length 518 Propellant 65,471 Motor performance, 73°F nominal Case 3,578 Burn time (sec) 90.8 Nozzle 2,187 Average chamber pressure (psia) 818 Other 2,922 Total impulse (lbf-sec) 17,950,000 Burnout 8,346 Burn time average thrust (lbf) 197, 539 Temperature limits, Nozzle Operation (°F) 30-100 Housing material 4340 Steel Propellant designation QEY 87% solids HTPB Exit diameter (in.) 43.12 Production status Production Expansion ratio, average 11.0 RD-180 BOOSTER ENGINE FOR THE ATLAS V FIRST STAGE The engine that powers the first stage of the Atlas V EELV is the RD-180. The RD-180 is a two-thrust chamber version of the original Russian RD-170 (four chambers), which is used to power the first stage of the Yuzhnoye/Yuzhmash Ukrainian manufactured Zenit launch vehicle. This engine provides the required performance, operability, and reliability of the RD-170 in a size (933,400 lbf of vacuum thrust) that meets the booster needs of the Atlas V version of the EELV (first used in the United States to successfully power all the Atlas III launches). The RD-180 is a total propulsion unit/engine system with hydraulics for control valve actuation and thrust vector gimbaling, pneumatics for valve actuation and system purging, and a thrust frame to distribute loads, all self contained as part of the engine. The engine, which employs a LOx lead start, a staged combustion cycle, and a LOx-rich turbine drive, delivers 10 percent better performance than kerosene (RP-1)-fueled operational U.S. booster engines and can provide relatively clean, reusable operation (beyond one mission duty cycle).
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs After a highly competitive procurement process, Lockheed Martin selected the RD-180 engine to provide the booster propulsion for its Atlas III launch vehicle and the Atlas V for the Air Force's EELV. The RD-180 is a staged-combustion cycle engine. The two thrust chambers can gimbal ±8 degrees. The engine has a health monitoring and life prediction system. The fewest possible interfaces are utilized between the launch pad and vehicle (pneumatic and hydraulic systems are self-contained, electrical panels consolidated, and a thrust frame simplifies the mechanical interface). The engine offers relatively clean operations with a staged-combustion, oxidizer-rich preburner and oxidizer start and shutdown modes that eliminate the potential for coking and unburned kerosene pollution. Between 40 and 100 percent continuous throttling allows real-time trajectory matching and engine checkout on the pad before launch commit. The RD-180 was developed and qualified in 42 months at a much lower cost than past U.S. booster engine developments because of the strong flight-proven RD-170 heritage. A schematic of the RD-180 dual-nozzle engine is shown in Figure D-1. FIGURE D-1 RD-180. SOURCE: AIAA. RL-10A-4-2 ENGINE FOR ATLAS V SECOND STAGE The RL-10A-4-2 (used on the Centaur IIIB upper stage and the Atlas IIIB and Atlas V launch vehicle) is a LOx/LH2 closed expander. It is equipped with a single turbine and a gearbox that drive the two pumps. It also has dual direct spark ignition and can be flown with a fixed or extendable nozzle. The engine operates nominally with a chamber pressure of 610 psi and develops an Isp of 451 sec. This engine’s performance and operating characteristics are summarized in Table D-4.
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A Review of United States Air Force and Department of Defense Aerospace Propulsion Needs TABLE D-4 Performance and Operating Characteristics of the RL10A-4-2 Characteristic Value Weight w/nozzle (lb) 386 Length, approx. (in.) 91.5 Nozzle extension (in.) 20 Nozzle area ratio 84:1 Isp vacuum (sec) 451 Thrust (lb) 22,300 Propellants LOx/LH2 Nominal mixture ratio, oxider/fuel 5.5:1
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