Evolved expendable launch vehicle system: RS-68 main engine development

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PERGAMON Acta Astronautica 53 (2003) 577-584 www.elsevier.com/locate/actaaslro

EVOLVED EXPENDABLE LAUNCH VEHICLE SYSTEM: RS-68 MAIN ENGINE DEVELOPMENT

David Conley, Capt., USAF SMUMVB

I Norman Y. Lee Aerospace Corporation

Peter L. Portanova Aerospace Corporation

Byron K. Wood Vice President and General Manager

Rocketdyne Propulsion & Power The Boeing Company

Abstract

Delta IV is one of two competing Evolved Expendable Launch Vehicle (EELV) systems being developed in an industry/United States Government partnership to meet the needs of the new era of space launch for the early decades of the 2 1” Century. The Rocketdyne Division of Tbe Boeing Company and the United States Air Force have developed a 650 Klbf sea-level (2.9 MN) class liquid hydrogen/liquid oxygen main engine for the Delta IV family of EELV. The purpose of this paper is to present the innovative approach to the design, development, testing and certification of the RS-68 engine. Q 2003 Published by Elsevier Science Ltd.

EELV Program Acouisition

The primary objective of the EELV program is to acquire a family of expendable launch vehicles to launch the National Mission Model currently serviced by Delta II/III, Atlas II/Ill and Titan IL/IV. EELV’s ultimate objective is to establish the competitive advantage in both the U.S. and the international launch industries while maintaining or improving mission assurance at a significantly reduced launch cost.

EELV uses Cost As Independent Variable (CAIV) to control cost. CAIV is a powerful process in implementing acquisition reform and was emphasized to system developers as an integral part of the system design, development, production, and operation. CAIV provides for aggressive, realistic cost objectives and risk management processes to obtain them. EELV demonstrates how costs can be

reduced through prudent trades of costs against performance. The emphasis on CAIV is a major reason EELV will enable the U.S. commercial launch industry to be more competitive in the international market.’

The EELV acquisition program has served to focus and maximize industry’s involvement and ownership and scope, minimize development risks. capture and employ commercial best practices. The Delta IV with the RS-68 main engine marks the first t ime in nearly thirty years that the U.S. has developed a large cryogenic rocket engine for a new family of launch vehicles.

Execution of a Modular Aonroach to Acouisition

The EELV program began in August 1995, when the U.S. Government awarded $30 mill ion Firm Fixed Price contracts to each of four contractors in a competition to select a single new launch service provider. This original strategy was based on the conclusion that the commercial market could not support two launch systems. In December 1996. the U.S. Government competitively down-selected to two of these contractors, awarding $60 mill ion each to Lockheed Martin and McDonnell Douglas (subsequently acquired by The Boeing Company). The overall EELV program schedule, including modular approach IO acquisition, IS shown in Figure I.

However, the single launch system philosophy changed in 1997 when the Commercial Space Transportation Advisory Committee (COMSTAC) model projected worldwide demand of an average of

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578 D. Conley et ul. /Acta A.stronautica 53 (2003) 577-584

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Figure 1. EELV Program Master Schedule

30 to 40 addressable commercial Geosynchronous Transfer Orbit (GTO) launches per year for, at least, the next twelve years (Figure 2).

Swrcc COMSTAC Commcrcnl Spacecraft Mission Model as of Sqmnhm 1996

Figure 2. COMSTAC Commercial CT0 Market

In addition, the ratio of U.S. Government to commercial launches shifted significantly in favor of commercial launches, to a ratio of approximately three to ~ne.~ Thus, it became clear that the original strategy of down-selecting to only one launch service provider could be modilied. In November 1997, the U.S. Air Force revised the acquisition strategy (Figure 3) to allow for the selection of up to two contractors to proceed into Engineering, Manufacturing and Development (EMD).

Subsequently, the program achieved a major milestone with the formal start of the EMD phase in October 1998. The U.S. Government awarded 5500 million each to Lockheed Martin Corporation and The Boeing Company in innovative partnership and cost-sharing development agreements, whereby development costs are shared between the contractors and the U.S. Government. Rather than the government fully funding the development effort, this partnership approach provided an avenue for the

Figure 3. Acquisition Strategy Change, November 1997

government to invest in each contractor’s development of a national, dual-use launch service that would meet both government and commercial launch requirements.

Execution of the revised strategy also enabled realization of two other significant benefits: competition and assured access to space. Selecting and retaining two EELV launch service providers, maintains competition throughout the life cycle of the EELV program. Competition is a key enabler for the significant recurring cost reduction of at least 25% required by EELV. By obtaining launch services from two providers with a standard payload interface, the U.S. Air Force maintains payload interchangeability between Atlas V and Delta IV and enhances assured access to space, a key facet of both U.S. Government national security and commercial enterprise 3.

Delta IV Familv of Launch Vehicles

The Boeing approach to the EELV is to use the best mature components and processes from existing Delta systems. Assessing the various subsystems for cost reduction, it was determined that the existing Delta booster propulsion system and structure account for over 50% of the entire system cost. Thus, the propulsion was selected for a new development because it is the largest cost subsystem. Boeing selected liquid oxygen/liquid hydrogen engine rather than liquid oxygen/kerosene because LO&I-I* provides more inherently stable combination solutions and a lower thrust requirement due to higher specific impulse.

The Delta IV family of vehicles is built around a Common Booster Core (CBC) powered by the new Boeing-Rocketdyne RS-68 main engine. The RS-68

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is a 650,000 Ibf (2.9 MN) thrust, gas generator cycle engine employing no new technology. The Delta IV cryogenic upper stage uses the Pratt & Whitney RLIOB-2 engine and is very similar to that flown on the Delta III launch vehicle. The Delta IV family of vehicles will have the GTO lift capabit:*y shown in Figure 4.

Figure 4. Delta IV Family of Vehicles

RS-68 Main Eneine Development

Conceptual studies of the RS-68 were an outgrowth of the NASA Space Transportation Main Engine (STME) Project begun in 1988. In that program, NASA and all major U.S. propulsion contractors collaborated in trade studies on propellants, cycles, size, and lessons learned to focus on reduced development cost for a new multi-application engine for the United States4

Boeing has taken an evolutionary approach to Delta IV system development, balancing the use of heritage hardware with development of new hardware. One of the major new developments for Delta IV is the RS-68 main propulsion system. The development schedule is shown in Figure 5.

Figure 5. RS-68 Engine Development Program

STME studies concentrated on a balance between cost and performance, but by the time the program was canceled in 1994, a new engine development cost projection of $1.1 billion with eight and one-half years to accomplish was on the table. Rocketdyne,

recognizing that the price tag and cycle time would never be acceptable to the government, committed significant internal investment to establish an organizational culture, processes, and tools to significantly outperform the STME program forecast.

In 1995, Rockwell International, Rocketdyne’s then- parent company, made the decision to respond to the Air Force EELV program in partnership with .McDonnell Douglas with a new member of the Delta “family,” which had decades of successful launches. Powering the Delta IV would be the RS-68 from Rocketdyne Propulsion and Power. It was not until after the Boeing acquisition of Rockwell, and then McDonnell Douglas, that the foresight for significant private industry investment in a new rocket engine came into being - this based on the firm belief and in- place evidence that Rocketdyne could truly do the job for less than that projected for STME. In 1997, RS- 68 development was started.

To meet the demands of the U.S. Air Force and the Boeing-targeted commercial launch market, the RS- 68 was created in a CAIV environment where cost was the truly independent variable (Figure 6).

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Figure 6. Cost as Independent Variable (CAIV) Key Elements

Compared to the Space Shuttle Main Engine (SSME), the RS-68 has 80 percent fewer parts and is produced for 92 percent less touch labor, in conjunction with a small focused supplier base, yielding a recurring cost one-fourteenth that of an SSME. The engine was developed/certified via eight new, plus four rebuilt, engines, accumulating 183 tests and 18,945 seconds of operation. In addition. live engines were run beyond the maximum mission duty cycle endurance factor limit and three engines were run to over three times the maximum flight duty cycle, including two run to 105 percent power, validating the RS-68’s reuse potential. The engine completed certification testing for its use on Delta IV in October 2001, with the completion of the final

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Certification Compliance Review completed in December 2001.

The RS-68 engine development involved extensive testing of major components including turbopumps, gas generator, injectors, and heat exchanger, with the goal of verifying engine-level performance parameters such as thrust, specific impulse (Isp), mixture ratio, and main combustion chamber pressure (PC). Subsequently, a series of engine hot fire tests were conducted at the Air Force Research Lab (AFRL), Fdwards Air Force Base, California and at the NASA Stennis Space Center (SSC), Mississippi.

The first launch is targeted for Fall 2002 at Cape Canaveral Air Force Station, Florida, from a new launch pad built by Boeing at Space Launch Complex 37 (SLC-37). Equivalent capability will be in place on the west coast at Vandenberg Air Force Base’s Space Launch Complex 6 (SLC-6).

Engine Characteristics

The new RS-68 is certified to operate at, and transition between, full power level and minimum power level upon command from the vehicle. It also conditions pressurization gasses for vehicle fuel and oxidizer propellant tanks, provides pitch and yaw control by gimbaling the main chamber/nozzle and roll control by gimbaling the fuel turbine exhaust roll control nozzles (Figure 7 and Figure IO).

Figure 7. RS-68 Operating, Characteristics

Turbopumps are single-shaft with direct drive turbines. Boost pumps are not required. High- pressure hot gases from the gas generator power in parallel the turbines, which employ integral machined bladed disks (blisk) (Figure 8). The thrust chamber/nozzle assembly consists of a combustion chamber and low-cost ablative nozzle, both utilizing existing, well demonstrated technology. While the main injector is similar, in concept, to the J-2 and SSME engines, it has been greatly simplified by

Figure 8. RS-68 Operating Schematic

reducing injector element density and using fewer unique parts. High-pressure ducting delivers pumped Liquid Hydrogen (LH,) and Liquid Oxygen (LOX) to the injector/thrust chamber assembly through main ball valves utilizing hydraulic actuators for control (Figure 9).

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Figure 9. RS-68 Components

Installation into the vehicle employs the proven thrust frame design philosophy of Rocketdyne’s Thor and RS-27 (Delta II) engines. The RS-68 physical design (Figure 10) has pumps nested in a four-point

Figure 10. RS-68 Engine

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attaching framework fitted to the vehicle thrust section. Outriggers connecting hydraulic actuators to the combustion chamber provide gimbaling of the thrust chamber assembly during engine operation. The two engine gimbal ducts utilize flex sections rather than employing complete bellows construction, Engine start, steady-state operation, throttling and cutoff are controlled by an engine-mounted controller.

3-D Solid-Model-Based Virtual Design

Three-dimensional modeling and’ a wide array of analysis and design tools were implemented on the RS-68 that were simply unav6ilable a generation ago when the Space Shuttle Main Engine was developed. Design optimization codes, including those supporting manufacturing producibility, enhanced the ability to achieve cost reduction and reliability improvement objectives. Further, these tools and disciplines were used in new and cooperative ways by the RS-68 team in a parallel and integrated product development (IPD) environment that yielded extensive sharing of information among IPD team members.

The team shared a common, three dimensional (3-D) geometric model of each component, which allowed all team members to work from the same model to perform their unique analyses and then update the design. As an example, 3-D unsteady computational fluid dynamics (0) analysis was used for turbine evaluation, leading to better quantification of the dynamic environment that allowed decisions early in the design as to the type of nozzles and or the need for damping features. That analysis was then extended to manufacturing for direct machining from the 3-D geometric model through the use of the Rocketdyne Advanced Process Integration Development (RAPID) program (Figure II). The

Figure 11. Digital Driven Design Environment

USC of three-dimensional model databases and stereo lithography (SLA) processes reduced development and fabrication cycle time for soft and production tooling. SLA-driven cost reduction was particularly effective in producing complex metal castings.

An important element in implementing this strategy was the adoption of concurrent engineering, led by an IPT skilled in monitoring numerous metrics such as co% weight, performance, life and quality (Figures 12 & 13).

Figure 12. RS-68 Virtual Design

Figure 13. Model Analysis Cycle Time

As an example, early in the design of a turbopump shaft, a Horizontally Integrated Design System (HIDS) 3-D model for the casting core was fabricated directly and sent to the casting vendor to begin casting trials. Casing these cores, the vendor was to optimize gating and have a direct impact on part design through the incorporation of specific features that ensured better core burnout or fill. Then. as the component design was completed, the core was updated and the probability of a first-time uscable part was increased.

The use of castings to integrate multiple parts into one piece provided the same OI improved functionality while reducing part counts (Figure 14).

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Figure 14. RS-68 Low Cost Fabrication

Testing and Debian Verification

As design concepts solidified into hardware, components were tested as proof of design. The thrust chamber injector was tested at the Marshall Space Fight Center, while the gas generator was tested at the Santa Susana Field Laboratory. During that time, the IA test stand at the AFRL was prepared to perform the blow-down and hot-fire testing of the turbopump test article (TPTA) power pack. After TPTA removal, the first RS-68 prototype engine was installed and tested. Full flight design configured engine testing was started in 1998.

Development and certification time for the RS-68 engine was one-half the cycle time required to develop and certify previous rocket engines. That was realized by breaking the test-fail-fix cycle and using an objective-based variable test/time approach, with component-level testing and won’t-fail designs and processes. Use of facilities at Boeing Rocketdyne, Marshall Space Flight Center, AFRL, and SSC, were key to conducting detailed component, subassembly and subsystem testing. These facilities were able to simulate engine and mission operating nominal and limit conditions.

Engine development testing (Figure 15) was aggressively pursued, providing confirmation of start, mainstage, low and high power level operation, shutdown. and “out-of-envelope” inlet pressures. With a significantly reduced devclopmcnt cycle and the goal of lowering cost, the test development and engine certification process was put on the fast track. In early 2001, development, certification and vehicle qualification testing were occurring simultaneously at three test positions. The results exceeded expectations, especially when compared to historical precedent.

Figure 15. RS-68 Engine Test Program

Robust start, shutdown and transition to steady-state operation sequences were developed and demonstrated in record time. In fact, full power testing (Figure 16) was achieved in only 27 tests, approximately one-fifth the number of tests required on prior engine development programs.

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Figure 16. Full-Pnwer Test Capability Milestones

Engine full-power capability was essential to moving forward with an objective-based test program. The objective-based approach focused on specific engine and mission requirements and operating regimes. Test duration and the total number of tests were adjusted based on verification and certification of these objectives.

The engine and facility digital control systems were designed to provide flexibility and adjustability to optimize engine performance and test facility capability. This flexible and adjustable architecture meant that multiple objectives could be accomplished on one test (one RS-68 engine test is the equivalent of thirteen orificed engine tests). Engine analytical models became key tools that set the test engine and facility operating points and limit settings; these were used to simulate nominal and off-nominal operating conditions. A Taguchi methods/design of experiment approach was employed to establish the specific

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operating set points needed to verify an objective. The objective-based approach and flexible, robust tools led to RS-68 first flight certification in only I83 tests, a factor of nine less than the F-l and a factor of three less than the SSME (Figure 17).

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Figure 17. EnginesTests: First Flight Certification

Engine flight life requirement is 8 starts and 1.200 seconds. During the development and certification program. live engines exceeded twice the flight life requirement. including three that were tested to over three times the required flight life (Figure 18).

Figure IS. BS-68 Endurance Margin

Common Booster Core (CBC) Integration Testing

The RS-68 was fully integrated with the Delta IV Common Booster Core (CBC) design for integrated system testing. Integrated trade studies optimized the

vehicle design and vehicle operation requirements to ensure the engine was truly developed and tested as it would fly. This fully integrated approach paved the way for a very successful CBC static hot fire test series.

A fully functional CBC with an RS-68 was hot-lirc tested at SSC five times. During the series, engine chill and vehicle propellant loading was demonstrated, engine-vehicle communication was verified, operational sequences were finalized and engine hot-tire showed that the engine was indeed ready for flight (Figure 19).

Figure 19. Common Booster Core Testing

Summarv

With flight certification now complete and flight engines in delivery, the metrics for RS-68 development include 5 fold reduced development costs, IO fold reduction in variable development costs, 2 fold reduction in development/certification cycle times, 3 fold reduction in required engine tests, I4 fold reduction in recurring costs and, in addition, the engine surpassed design reliability goals.

As heritage launch systems are phased out, EELV will provide the primary U.S. expendable launch capability. The RS-68 will power the Delta IV family of space launch vehicles at affordable cost for the next 20 years, providing assured access to space.

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BiblioeraDby

1. McKinney, R.W. Colonel, U.S. Ah Force, Portanova, P.L., The Aerospace Corporation, et al., “EELV Meets CAJV”, Aerospace America, May 1999, pages 68-74

2. U.S. Department of Transportation, Commercial Space Transportation Advisory Committee (COMSTAC) Report, 25 July 1996

3. Saxer, R.K., Colonel, Knauf, J.M., Lt Colonel. U.S. Air Force, Drake. L.R., Portanova, P.L., The Aerospace Corporation, “Evolved Expendable Launch Vehicle System: The Next Step in

Affordable Space T~nspOttatiOtI”, f’hf: PrOgrUm

Manuger, March-April 2002, pages 2-15 4. Wood, B.K., The Boeing Company, Rocketdyne

Propulsion & Power, Canoga Park, CA. “Propulsion for the 2 I st Century - RS-68”, AJAA 38th Joint Liquid Propulsion Conference. 8-10 July 2002

Editor’s Note: The authors welcome questions or comments on this article. To contact them, please email: David.S.Conlev@losaneles.af.mil; norman.v.lee@aero.ora; Dete.nortanova@nro.miil: bvron.k.wood@boeina.com