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A01-34302

AIAA 2001 -3594

Dual Moveable Nozzle Thrust VectorControl Program Status

Henry N. DoveyATK Thiokol PropulsionP.O. Box 707, M/S 230Brigham City, UT 84302-0707

37th AIAA/ASME/SAE/ASEEJoint Propulsion Conference and Exhibit

July 8-11,2001Salt Lake City, Utah

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PAPER #2001-3594

DUAL MOVEABLE NOZZLE THRUST VECTOR CONTROLPROGRAM STATUS

Henry N. Dovey, MemberSenior Program Manager, Technology Programs

andSteven R. Wassom, Ph.D., Member

Senior Staff Engineer, Systems EngineeringThiokol Propulsion

P.O. Box 707 MS 230Brigham City, UT 84302-0707

Rich Schroeder, MemberPresident

General Dynamics OTS (Versatron, Inc.)511 Grove Street

Healdsburg, CA 95448

AbstractThe Integrated High Payoff Rocket

Propulsion Technology (IHPRPT) Dual MovableNozzle Thrust Vector Control Program, sponsoredby the Naval Air Warfare Center WeaponsDivision, NAWCWD, China Lake, was establishedto combine conventional external fin aerodynamiccontrol with solid rocket motor thrust vector control(TVC) to improve tactical missile agility. Thesystem uses two omni-axial movable nozzles forhigh-agility 3-axis (pitch, yaw, roll) control in allflight regimes. Dual blast tube assembliesintegrated into a common aft motor closure allowfor efficient packaging. A compact electro-mechanical control actuation system (CAS), and aunique patented linkage that couples the motionsof the nozzles and fins are packaged around theDual Nozzle hardware. The program hascompleted the design and hardware developmentphases. CAS hardware has been manufacturedand is currently undergoing bench level testingwith a Dual Nozzle bench test system. Theprogram will culminate with a static test of the CAS

and Dual Moveable Nozzle system on a 7"diameter tactical rocket motor. Testing will beconducted at the NAWCWD/China Lake testfacility.

Introduction

Advances in foreign adversary aircraftdictate a need for improvements in the energymanagement and control authority of nextgeneration air-launched tactical missiles. Missilesmust have improved range and lethality toovercome the aircraft. Advanced control systemsare needed that can accomplish the futuremissions, which will require greater range andmaneuverability. These systems must achieve thesystem performance goals while reducing cost andweight versus current state-of-the-art (SOTA)systems.

Conventional aerodynamic control systemswith fins provide pitch, yaw, and roll control (knownas 3-axis control). These systems are inadequateat low Mach numbers and high angles of attack.1

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Three-axis thrust vector control (TVC) has beenused to overcome aircraft and their advancedweapons systems. TVC is achieved by using arocket motor with multiple nozzles or byincorporating jet vanes into a single nozzle. Someof the representative 3-axis TVC systems fortactical missiles are shown in Table 1.

Table 1. Current 3-Axis Control Systems

NAMEMk72

Harpoon DemoSea Sparrow

Vertical LaunchASROCAIM-9X

Evolved SeaSparrow

TYPE4 nozzles2 nozzlesJet VaneJet Vane

Jet VaneJet Vane

DIAMETER21 inches

13.5 inches8 inches

13.8 inches

5 inches10 inches

The design approach for existing systemshas a number of shortcomings. These designs aretypically limited to large diameter rocket motorsthat are not typical of short- and medium-range air-to-air missiles. These systems also use separatefin and TVC actuators, which significantly increasethe cost, weight, and volume of the system. Jetvane systems also incur inherent losses due to:

• Drag• Packaging length impacts on propellant

loading

Inert weight is added to the system as a result ofthe packaging issues. A significant decrease insystem mass fraction results from the largersystem. Jet vanes are also limited in their controlauthority by the size of vane that will fit into thenozzle exit cone or exit plane.

IHPRPT Background

A consortium of government and industrycreated the IHPRPT initiative in 1995 to double thecapability of propulsion by the year 2010. Threespecific phases were established, each with anattendant set of goals to be reached by the years2000, 2005, and 2010. A specific area for TacticalPropulsion Technology was established to develop

and demonstrate technology for advancedpropulsion systems that address emerging needs.The IHPRPT Dual Moveable Nozzle Thrust VectorControl program was created for Phase I todemonstrate an innovative aerofin and thrustvector control system that improves missileperformance and control authority in all flightregimes.

System Performance and Cost Comparison

Since no production-level baseline exists foran air-to-air tactical rocket motor with 3-axis TVC,a hypothetical baseline design was developed forthe IHPRPT program. The configuration uses a 7-inch diameter production tactical solid rocket motorwith an aerofin control section, augmented with anaft-mounted jet vane TVC system. Sizing for thesystem was derived from an approach developedby NAWC1. The set of implicit equations uses thethickness/chord ratio, aspect ratio, and leadingedge bluntness recommended by NAWC. Theequations calculate the gas properties at the vaneleading edge and the aerodynamic coefficients forside force and drag. The coefficients have beensubstantiated using the Missile DATCOM program.The procedure has been calibrated with the jetvane systems used on VLA and Sea Sparrow, andhas also been validated with measurements fromstatic test.

Designs were created for the DualMoveable Nozzle and CAS to reflect a flight weightproduction system. Thermal and structuralanalyses were conducted on the flightconfiguration. A lightweight closure and blast tubedesign were established and analyzed. Flexbearing and exit cone geometries were notchanged. CAS system electronics and batterieswere packaged around the dual blast tube systemwith sufficient clearance to eliminate thermal andmechanical interference issues associated withmotor operation. This design was assessedagainst the Jet Vane baseline.

A comparison between the designimprovements of the flight weight system over thebaseline and the Phase I IHPRPT goals is shownin Table 2. The design meets the goals withconsiderable margin. The Dual Moveable Nozzlesystem would also easily meet the IHPRPT costobjective of a 25% cost reduction for severalreasons. First, the most expensive part of thesystem is the actuation system, and as previously

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discussed, many cost-saving techniques havebeen employed in the design and fabrication of theactuators. Also, because of the mechanicalcoupling of fins and nozzles, the number of controlchannels has been reduced from a maximum of 8(4 fins and 4 jet vanes) to 4.

Table 2. Comparison with Baseline

Parameter

Length

Weight

DeliveredImpulse

MassFraction

Improvement

44.9%

25.2%

16.3%

1 1 .4%

IHPRPTPhase I Goal

20%

20%

3%

10%

Program Plan

The actual program to develop a DualNozzle with integrated thrust vector and aero-fincontrol was initiated in March 1998 by ThiokolPropulsion. Government management of theprogram is being conducted through the Naval AirWarfare Center at China Lake, California.

The program was divided into threephases with a planned period-of-performance offorty-two months. The first program phase wouldaccomplish the requirements and performancedefinition leading to a final engineering designpackage for the Dual Nozzle and control system.The design would include an assessment of apotential.flight weight system with layouts for allhardware and electronic items. The second phasewould fabricate test hardware and accomplishbench level testing of the flex bearings (FB) andthe CAS. Bench testing would be accomplishedusing simulated loading of the hardware. The thirdphase is to include the integration of the CAS withthe Dual Nozzle hardware leading to a final statictest on a tactical solid rocket motor. The

assembled system is to be subjected to a systemcheckout using a pressurized test fixture tosimulate motor pressure. The static test duty cyclewill be accomplished at the bench test level. Thecomplete system will be removed from the benchtest fixture as a unit and will be installed on therocket motor. The static test is to be accomplishedat a government test facility at China Lake.

Phase

The initial program phase consisted of thefollowing: 1) development of the system designrequirements, 2) analysis of the design approachusing 3-D and kinematic models, 3) developmentof a flight weight design demonstrating systempackaging, 4) Dual Nozzle to CAS interfacedefinition, 5) definition of static test interfacesincluding TVC duty cycle, and 6) development ofthe static test design package. The formal designphase of the program was completed in Decemberof 1999. Customer approval was received for thedesign and the Phase II test program. Programdetails for the first phase have been previouslyreported2

System Performance Goals

System performance goals wereestablished for the program based onrequirements for advanced tactical air-to-airmissiles. Fin and nozzle deflection goals wereobtained from a kinematics analysis of the systemrequirements. Final design requirements for thestatic test hardware were obtained from theballistic and interface definition for the test article.System environments were developed fromcurrent tactical air launched systems and includeda temperature range of -65°F to +135°F. Thecombination of requirements was established earlyin the program and used to design and analyze theprogram hardware.

Moveable Nozzle Joint Trade Study

Early in Phase I, a trade was conductedfor trapped ball and flex bearing joints.Technology improvements and historicalinformation were evaluated for both designoptions. A trapped ball joint was deemed to havethe greatest potential for future growth in high-

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pressure motors but presented a significant designproblem associated with the unpredictability ofbreakaway forces associated with "stiction" torque.The flex bearing using advanced materialstechnology was assessed and found to have theleast risk. The team selected the flex bearing.

Phase II

The second phase of the programconsisted of hardware fabrication and subsystembench level tests. Thiokol Propulsion wasresponsible for the fabrication of the Dual Nozzlehardware, bench test simulation hardware for theGAS bench test, and bench level testing of the flexbearing assemblies. Versatron fabricatedhardware and electronic components for the CASand accomplished bench level testing of the CASsystem.

Figure 1 shows the static test hardwarethat has been manufactured and bench tested forthe Dual Nozzle system. Metal components arefabricated from steel alloys. Plastic componentsuse proven tactical rocket motor materials.

Dual Nozzle

Closure and Blast Tube components aremanufactured from high strength steel. A boltedjoint was used for the blast tube to closure toprovide for ease of assembly, and eliminate thedevelopment of a more costly manufacturingprocess. The design utilizes heavyweighthardware for static test. A flight weight design hasbeen developed and analyzed for this application.

Insulation

The nozzle and blast tube insulation ismolded in low-erosion areas for cost savings, whileplies of material are laid-up on a pre-determinedangle for high-erosion areas. The blast tubes aredesigned for high Mach numbers, whichcontributes to more compact packaging. The blasttube insulation also incorporates a specialgeometry to protect the flex bearing splitline. Boththe high Mach number blast tube and the splitlineprotection have been demonstrated on previousThiokol internal research & development (IR&D)tests.

Flex Bearing

The flex bearing design includes stainlesssteel shims and elastomer pads sandwichedbetween stainless steel end rings. The pads are asilicone elastomer with an operating temperaturerange of -65° F to 165° F. Thiokol developed theelastomer and bond system used in the design.Six flex bearings were fabricated, and successfullycompleted bench testing. Two bearings wereselected for the final static test motor, two for theCAS bench test, and the final two bearings willundergo structural capability testing

Figure 1. Dual Nozzle Hardware

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Nozzle/Exit Cone

The nozzle and exit cone are comprised ofstainless steel shells with plastic insulationmaterial. For the tactical rocket system being usedin the demonstration test, packaging constraintslimit the exit diameter, which results in some lossof expansion ratio. The throat diameter is drivenby the government-specified 7-inch rocket motorballistics, since this motor was chosen for thestatic test. Related studies have shown thatsmaller packaging (down to 5.5 inch diameter) maybe achieved with higher motor pressures andsmaller throats. Higher pressures may result inthe selection of a trapped-ball type bearing insteadof a flex bearing.

Electromechanical Control Actuation System

Actuation system requirements for thecoupled system do not significantly exceed therequirements for a fin only system. While theoverall performance is state of the art, severalconfigurations of each element have beenproduced and demonstrated on Department ofDefense (DoD) technology programs over the past8 years. The following sections describe the majorelements of the CAS.

Motor/Gearbox

The compact and high efficiency gearingconsists of a spur gear train followed by a bevelgear. The overall ratio is greater than 300:1 andthe efficiency is approximately 90%. The totalvolume of this arrangement is very smallcompared to ball-screw and clevis approaches andallows packaging around the otherwise unusedvolume between blast tubes and batteries. Thevery high power density motor is Versatron's "Lo-J"brushless DC motor. Versions of this motor havebeen demonstrated to exceed 2 HP/cu-in. Whilecurrent missile configurations do not demand thispower level, significant margins will exist forapplication to other systems.

The overall packaging of the servo systemaccommodates two (2) production thermalbatteries inside a two-piece clamshell structurepackaged around the two blast tubes.

Electronics

The high power density motor and compactgearbox arrangement results in ample volume forpackaging off-the-shelf electronic components.This is critical in achieving the target unitproduction cost savings compared to existingsystems. The overall electronics architectureleverages many years of development. The loopclosure and communication functions areimplemented on a single low power digital boardthat is optically isolated from the high power motorcontrol electronics. The processor selected has aninternal pulse width modulation generator. Theprocessor loop closure operates at high frequencyresulting in minimal phase lag due to digital delays.The power stage uses commercial grade fieldeffect transistor (FET) switches to implement thehigh power motor drives. These FETs are drivenby proprietary switching logic to maintain efficiencyat the relatively high motor speeds. Theelectronics package has been designed with adigital controller. The program hardware will usean off-the-shelf analog controller for the static testhardware. Schematically, the electronics havebeen demonstrated on a number of programsincluding HAVEDASH, BOA, and two NAWCWDsponsored small business innovative research(SBIR) programs.

The power stage operates from the twothermal batteries. The batteries are in seriesresulting in a high side operating voltage of240VDC. As noted above, the low power loopclosure circuit is isolated from the high powercircuits and operates from externally suppliedpower. The high power switches are mounteddirectly to a heat sink that is integral to the actuatorhousing. Since the missile skin, blast tubes andbatteries all represent a heat source, the heat sinkis sized with enough thermal mass to dissipate thepower losses generated in the FETs during theduty cycle.

TVC Mechanism

The thrust vector control (TVC) mechanismhas been demonstrated over the past 10 yearsthrough a combination of IR&D, SBIR, and othergovernment contracted programs. While allhardware implementations have been with a singlemoveable nozzle, the mechanism operationremains essentially the same for the dual nozzleconfiguration.

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The mechanism represents a very volumeefficient method for vectoring the nozzle within theotherwise unused volume of the boat tail. Themechanism results in nozzle vectoring proportionalto the algebraic sum of the rotation of the fins. Rollmotion of the fins causes the nozzles to move inopposite directions, generating a roll moment withno net pitch/yaw thrust vector. The magnitude ofthe roll moment is proportional to the roll motion ofthe fins. The mechanical ratio of differential fintravel to roll moment is determined by nozzlespacing and linkage geometry.

Figure 2 shows the CAS assembled aroundthe Dual Nozzle bench test simulator.

Figure 2. CAS Bench Test Assembly

CAS Bench Testing

A bench level test program is beingconducted at Versatron to evaluate systemperformance. To date, Versatron has completedbench top (un-powered) verification of the systemfor travel limits, TVC coupling, nozzle and yokeplate motion, and preliminary gear train efficiency.Controller integration and debug was also

completed. All four of the fin servos wereintegrated and tested under full power. Fin axisloop closure was completed with gain andcompensation settings optimized for no-load finconditions. These closures will be reevaluatedwith the addition of TVC loads. Travel limits andbasic motor performance were verified underpower. A minor problem was discovered in thepotentiometer reference circuit. As currently built,the controller could not drive all fourpotentiometers at once. The issue was correctedin the controller.

Future Versatron work will include:

• Integration of TVC mechanism whileunder closed loop, powered condition

• Characterization of servo andmechanical stiffness and backlash forinput to the simulation

• Loaded fin axis testing• Unloaded TVC testing• Loaded TVC testing• Duty Cycle validation• IATVC System Acceptance Test

Phase

Phase III tasks shall include the integratedsystem testing for the CAS & Dual Nozzlehardware. A system integration test will beconducted using a pressurized test kettle tosimulate rocket motor pressure. The integratedCAS and Dual Nozzle system will be subjected tothe program duty cycle. An evaluation of systemperformance and acceptability for static test will bemade from this integrated test.

Upon successful completion of the systemlevel checkout, the integrated system will beremoved from the test stand and assembled to thestatic test rocket motor. Leak testing of the motoris to be performed to ensure the integrity of systemseals. The motor will be installed in a test standthat provides for six degrees of freedom for motorperformance measurement. A modified duty cycleis to be conducted on the system after assembly tothe motor to establish proper system operation.The motor static test will be accomplished,completing the major tasks for this program phase.

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Conclusions

A program is in place that has developedand will demonstrate an advanced vehicle controlsystem for tactical rocket motors. This systemincludes coupled fin and motor thrust vectorcontrol to accomplish improved missilemaneuverability under all flight regimes. Thesystem incorporates technologies into a designthat exceeds the IHPRPT Phase I goals for air-launched tactical solid rocket motors. Finaldemonstration of the technology will supportplanner needs for future weapon systems.

Acknowledgment

The Naval Air Warfare Center WeaponsDivision, China Lake, California, sponsored thiseffort under the direction of Mr. John Bratcher,Program Manager.

References

1. Ripley-Lotee, M. J., and O'Neil, S. M., "JetVane Thrust Vector Control - A NeglectedTechnology with New Horizons," 1980 JANNAFPropulsion Meeting, CPIA Publication 315, Vol. IV,pp. 345-370.

2. Wassom, S. R., Dovey, H. N., Kuwana, M. B.,Schroeder, R., "Dual Movable Nozzle ThrustVector Control Program: Phase I Status," 1999JANNAF Rocket Nozzle TechnologySubcommittee Meeting, Salt Lake City, UT.

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