modification and verification testing of a russian nk-33...

AIAA 98-3361

MODIFICATION AND VERIFICATION TESTING OF A RUSSIAN NK-33 ROCKET ENGINEFOR REUSABLE AND RESTARTABLE APPLICATIONS

J. Hulka*. J.S. Fordef, R.E. Werling*Aerojet, Sacramento, CA

V.S. Anisimov5, V.A. Kozlov", I.P. KositsinttN.D. Kuznetsov SSTC, Samara, Russia

PRA 044-98

ABSTRACT

Flight-qualified liquid propellant rocket enginesfrom the Russian lunar launch program were received atAerojet, modified to include reusable and restartablefeatures with modern instrumentation and controls, andtest fired to verify the modifications. The NK-33 liquidoxygen/kerosene propellant rocket engine was designedand manufactured by Samara State Scientific andProduction Enterprise "TRUD" (now known as N.D.Kuznetsov Samara Scientific and Technical Company) ofSamara, Russia, for the Soviet N-l launch vehicle. Thisstaged combustion engine delivered high pressure (2109psia chamber pressure) and high performance (331seconds vacuum delivered specific impulse) that hadnever been available in the West for an hydrocarbonengine. Aerojet imported 36 NK-33 engines, along with9 NK-43 engines, an upper stage version of the sameengine, from N.D. Kuznetsov SSTC. The first of the NK-33 engines was modified for use on the Kistler K-llaunch vehicle. Modifications included replacement ofpyrotechnic initiated valves with solenoid actuatedvalves; replacement of electromechanical actuators forthrust and mixture ratio control; redesign of purge supplysystems; replacement of solid propellant for theturbopump start spinup and the main chamber igniters;redesign and replacement of the thrust frame for additionof a gimbal and thrust vector control mount; addition ofvalves, pyrotechnics, and plumbing to restart the engine;and replacement of instrumentation and wiring harnesses.This engine was successfully test fired at Aerojet to verify

* Engineering Specialist, Sr. Member AIAAf Lead Engineer, NK-33 Engine Modifications* Program Manager, NK-33 Engine Modifications1 Chief Designer" Department Head, Engine Control Systemsn Department Head, Turbomachinery

Copyright 1998 by Aerojet and N.D. Kuznetsov SSTC.Astronautics, Inc., with permission.

the new components and configurations, and to begincharacterization of engine durability for the reusableKistler vehicle. This paper describes the modifications tothe original Russian engine, and reports the results oftesting to date.

INTRODUCTION

The NK-33 engine, a 350,000 Ibf thrust class liquidoxygen/kerosene staged combustion engine, was designedand manufactured in the 1960s by the Russian designbureau now known as N.D. Kuznetsov SSTC.1 The NK-33 engine was a flight qualified, significantly upgradedversion of the NK-15, the engine that supplied the mainpropulsion for the boost propulsion stage of the SovietN-l lunar launch vehicle.2 For the N-l boost stage flightprofile, the NK-15 was ignited at sea level and operatedabout 120 seconds, producing a nominal sea level thrustof 339,000 Ibf (154 metric tons) with a sea level deliveredspecific impulse of 297 lbf-sec/lbm, and a nominalvacuum thrust of 378,000 Ibf (172 metric tons) with avacuum delivered specific impulse of 331 lbf-sec/lbm.

The NK-15 engine, originally developed for singleuse, was redesigned to increase component life andinclude reusable features for conducting acceptance andstage tests along with a cost effective qualification testprogram for the N-l and future vehicles.1 Majorimprovements on this new engine, the NK-33, were sealupgrades, addition of a TEA preburner start system, andpurge systems to allow multiple starts. The NK-33

Published by the American Institute of Aeronautics and

1American Institute of Aeronautics and Astronautics

engines, which were to have been used on subsequent N-lflights, completed extensive qualification testing, withnearly 100,000 seconds of testing accumulated on morethan 200 engines, following nearly 90,000 seconds oftesting on nearly 600 engines for NK-15 development andproduction prior to the first flight of the N-l.

In 1995, Aerojet brought an NK-33 engine to itsliquid rocket test facility and conducted a series of tests aspart of its Evolved Expendable Launch Vehicle (EELV)proposals.3 The objectives of these benchmark tests were:

Verify engine performance and operabilitywith liquid oxygen/RP-1 propellants fromthe U.S.

Verify engine functionality after twentyyears of storage.

Demonstrate engine performance at Atlasinlet conditions.

Demonstrate Atlas firing duration andprofile.

Demonstrate the ability of Aerojet andN.D. Kuznetsov SSTC to cooperate withtechnical, logistical, and political issuesand successfully test a Russian liquidrocket engine in the United States.

Five tests were successfully conducted on theBenchmark Test Program, ranging in power level from58% to 113%, for a total duration of 408 seconds.Including the acceptance test in Russia, this engine wastested for a duration of 450 seconds. The success of thistest program demonstrated the robustness of the flightqualified engine and convinced Aerojet to pursue its usein the Western launch vehicle market. The excellentspecific impulse performance of this staged combustionengine, exceeding the performance of the gas generatorcycle engines currently available in the West by 20 to 30seconds (or 15 to 20 at equivalent mixture ratios andexpansion ratios), showed that the engine could becomean enabling feature of the new and improved launchvehicles being developed in the Western market.

Modifications to the NK-33 engine for a Westernflight vehicle were subsequently initiated for the KistlerK-l flight vehicle.4 These modifications included newfeatures for interface to and control by the K-l vehicle,and variations of the original Russian engine to enhanceoperability for use on a reusable vehicle.

The modified engine, renamed AJ26-58, was thentested at the Aerojet E-5 liquid propellant rocket testfacility in a special verification test program designed todemonstrate that the modified NK-33 engine would meet

the Kistler performance requirements, and that themodifications would not alter steady-state performance ortransient operation of the engine. The specific objectivesof the verification program were:

Verify chilldown, start, and shutdownsequences with modified enginecomponents.

Verify new purge systems with modifiedengine components.

Verify test-to-test repeatability of steady-state and transient operating conditions.

Verify capability of new electro-mechanical actuators to control enginepower level and mixture ratio as predicted.

Verify capability to operate with subcooledU.S. RP-1 to be used on Kistler vehicle.

Verify capability to start with low engineinlet pressures expected for Kistler vehicleupper stages.

Verify capability and repeatability ofrestart.

Verify capability to start, operate, andshutdown with new engine controller.

Collect data to evaluate engine lifecharacteristics.

At the publication deadline for this paper, five testsof the Verification Test Program have been conducted.This paper will present the results of these tests alongwith the results of the benchmark tests from 1995, whichto date have been unpublished. The NK-33 engine and itsmodifications will be described in detail, along with itsoperating and performance characteristics.

NK-33 ENGINE DESCRIPTION

The NK-33 is a staged combustion, pump-fed liquidpropellant rocket engine that uses oxidizer-richcombustion gas to drive a single stage turbine.' Similar tomany Russian liquid rocket engines, the main fuel andoxidizer pumps are driven by a single, spline-coupledshaft and contained within a single housing with multiplebolted pieces.

Engine performance parameters are listed in Table I.For the Kistler vehicle, the main combustion chamber willoperate at a nominal mixture ratio of 2.59 and nominalchamber pressure (defined as 100% power level) of 2109psia.4 At these conditions, the preburner will operate at anominal mixture ratio of 58 and chamber pressure of4670 psia, with a combustion gas temperature of 670 R.Without operation of the mixture ratio valve, the mixtureratio of the engine will increase as the power level is

American Institute of Aeronautics and Astronautics

reduced, to about 2.75 at 75% chamber pressure level,and about 2.90 at 50% chamber pressure level.Activation of the mixture ratio control valve will provide20% control capability in mixture ratio over the wholethrust range. For the Kistler vehicle, however, the lowerrange is limited by the standard inlet conditions andnominal mixture ratio to about -5%.

Engine repeatability, based on Russian qualificationtest history and acceptance test instrumentation accuracy,is expected to be +/- 1% on thrust, +/- 1.5% on mixtureratio, and +/- 1% on specific impulse.

For the Kistler vehicle, there will be two differentmodified versions of NK-33 engines one basic, renamedAJ26-58; and one restartable, renamed AJ26-59.

Basic Engine

The fluid schematic of the basic modified NK-33engine is shown in Fig. 1. The turbopump is an inlineassembly containing oxidizer boost and main pumps, fuelboost and main pumps, a gas main turbine, and a gas startturbine all within a single bolted housing. All of theoxidizer is provided to the preburner, while most of thefuel is provided to the main combustion chamber coolantjacket. A high pressure, high speed gear driven kick stagepump delivers a small quantity of high pressure fuel to thepreburner.

Combustion devices include a liquid/gas coaxialelement main injector, regeneratively-cooled mainchamber, regeneratively-cooled nozzle, liquid/liquid swirlelement preburner, solid propellant pyroignitors for themain chamber, and a solid propellant cartridge to supplygas to a start turbine to prespin the turbopump prior toignition.

There are three different ignition systems on theengine. The preburner is ignited by a slug oftriethylaluminum/triethylborane (TEA/TEB), a hypergolicpropellant with oxygen, that precedes the fuel into thepreburner during the start transient. The maincombustion chamber is ignited by three solid propellantpyroigniters that fire into the chamber through ports onthe periphery of the fuel manifold. The main chamberpyroigniters and the solid propellant in the turbopumpstart cartridge are themselves ignited by squib initiators.

The engine is mechanically controlled by an arrayof nitrogen-actuated pneumatic valves, electropneumaticpilot valves (EPV), electromechanically actuatedregulation valves, and differential pressure hydraulicallysequenced main valves. After the preburner fuel shutoff

valve is opened and the start purge is initiated by openinga pneumatic valve on the engine, no other valves on theengine need to be externally actuated to provide forengine startup. Pressure-sequenced valves start the flowof oxidizer into the preburner and the main flow of fuelinto the main combustion chamber coolant jacket once thestart cartridge is prespinning the TPA. "Cutter valves"with blades actuated by gas from the start cartridge cutdiaphragms on the TEA/TEB ampoules, and start thesecondary flow of fuel into the preburner, although thepressure developed by the kickstage pump during startcartridge operation is also normally sufficient to rupturethe diaphragms.

To shutdown, the preburner fuel shutoff valve ispneumatically closed and the shutdown purge valve onthe engine is pneumatically opened. When the preburnerfuel shutoff valve is closed, the engine shuts off. Forredundancy to close the preburner fuel shutoff valve, theshutdown purge is hydraulically tied to the actuationcircuit of the preburner valve.

The pneumatic valves are controlled by supplyingor removing voltage to the corresponding EPV. Nitrogenis then provided to or removed from the main valveactuation cavity through the EPV, causing the pneumaticvalve to operate.

Thrust or power level of the engine is controlled byregulating the fuel flowrate to the preburner. Theposition of the valve that controls this flowrate iscontrolled by an electromechanical actuator (EMA). Thisvalve also ensures a benign and controlled engine startwith the use of internal hydraulic packages that strictlyregulate preburner fuel flowrate during bootstrap.

Mixture ratio through the main combustion chamberis controlled by regulating the fuel flowrate to the mainchamber. The position of the valve that controls thisflowrate is also controlled by an EMA.

A purging system displaces propellants from thecavities of the engine and its assemblies, preventingaccumulation of combustible mixtures and removingpropellant from the internal engine cavities at shutdown.There are 3 interfaces to the engine that supply nitrogenpurge one a low flowrate at two levels (0.0044 to 0.010lbm/sec) to the interpropellant seal (IPS), and the othertwo high flowrate (4.5 and 2.5 lbm/sec, respectively) forstart and shutdown purging. The purging system hasbeen modified from the Russian version of the NK-33 toeliminate on-board bottles of compressed gas and controlvalves, and now includes only electropneumatic valves


and check valves. The start and shutdown purge controlvalves are identical new valves.

Two internal fluid tapoffs are available on theengine, one of which will be used for the Kistler vehicleand during the verification test program. A high pressurefuel tapoff from the main fuel pump discharge will beused on the Kistler vehicle to supply fluid to power thethrust vector control system. Oxygen-rich turbine exhaustgas, used in the Russian vehicle for oxygen tankpressurization gas supply, is also available but will not beused by the Kistler vehicle, although the port will remainavailable on the modified engine for other applications.

Restartable Engine

The fluid schematic of the modified restartable NK-33 engine is shown in Fig. 2. The schematic is verysimilar to the basic engine except for a few variations.There are dual main chamber igniters and dual startcartridges, two parallel TEA ampoules, and two sets ofcutter valves. There is an additional valve supplying thetwo TEA ampoules in the preburner supply line, and thereis a parallel fuel supply line between the second TEAampoule and a new, dual preburner shutoff valve.

These modifications essentially do not alter theoriginal engine transients, so the first start and firstshutdown of the restartable engine are exactly the same asfor the basic engine. For the second start of therestartable engine, the 3-way valve and dual preburnervalve are switched to the opposite leg of the preburnerfuel supply system, and the second start then proceedsexactly as the first start. The second shutdown is exactlythe same as the first shutdown except that the secondvalve of the dual preburner valve is deactivated, ratherthan the first.

Engine Layout

The layout of the basic NK-33 engine is shown inFigs. 3 and 4. The turbopump is connected to the headend of the combustion chamber by the main turbineexhaust duct. The preburner is mounted directly to themain turbine housing which is connected to the oxidizerpump. The turbopump start cartridge is located at theopposite end of the turbopump, connected to the fuelpump. The parallel arrangement of thrust chamber andturbopump was a carefully engineered design to carryload, provide rigidity, and reduce weight.' Modificationshave not disturbed the maximum length of the originalengine, and slightly increased the maximum diameter.

The engine layout of the restartable NK-33 engine isshown in Figs. 5 and 6. The dual start cartridge is an in-line series design that replaces the single start cartridge onthe turbopump opposite the preburner. The dual mainchamber igniters are also in-line series designs that fit intothe existing ports on the main combustion chamber. Bothof these pyrotechnic devices incorporate burst diaphragmsto separate the multiple ignition components.

Hardware Components

Turbopump

The turbopump assembly (TPA) consists of twoindependent units: an oxygen boost pump and mainpump with the main turbine; and fuel boost pump, mainpump, and kickstage pump with the start turbine. Bothmain pumps are centrifugal. The low pressure, low speedoxidizer boost pump has a hydraulic drive connection tothe main oxidizer pump. The low pressure, low speedfuel boost pump is gear driven by the main fuel pump.The mechanical connection between the fuel and oxidizerpump shafts is provided by a spline connection on theshaft. An interpropellant seal prevents the migration ofpropellants into unlike pump cavities.

The pump housings are made from aluminum sandcastings, except the high pressure housings which areforgings made from aluminum. Both low speed inducersand the oxidizer hydraulic turbine are made frominvestment cast aluminum, while all high speed inducersand impellers are made from investment cast chrome-nickel steel, except the high speed fuel inducer which ismade from a titanium alloy. Low speed and main shaftsare made from stainless steel, except for the fuel boostpump shaft which is made from a titanium alloy. Theturbine housing is made of an Inconel equivalent, and thestart cartridge housing is made of titanium.

On the oxidizer pump side of the TPA is a rotoraxial thrust balancing device to balance the axial forces ofthe rotor. Oxygen flow through a regulating passageprovides automatic unloading of the axial forces alongwith individual adjustment capability for each engine.

Radial ball bearings support the TPA rotors. Fuelpump bearings are cooled with fuel, and oxygen pumpbearings, which are made from stainless steel, are cooledwith oxygen. The fuel bearing cages are made of bronze,while the oxidizer bearings have teflon separator cages.


Preburner

The preburner provides oxygen-rich combustion gasto the TPA turbine, and this gas is then further combustedin the main combustion chamber. The preburner isdesigned with multiple axial zones for oxidizer injectionand mixing, with the majority of oxidizer injecteddownstream from the injector face. Baffles downstreamof the injector face provide high frequency combustiondamping.

The preburner injector uses a combination oftangential swirl injection elements and showerheadelements for each propellant. The preburner walls arecooled with liquid oxygen which is then injected at thechamber periphery before the entrance into the turbinenozzles.

The preburner chamber shells and manifolds aremade of stainless steel. The injection elements andfaceplate are made from a chrome copper alloy.

Thrust Chamber Assembly

The combustion chamber is an inseparable welded-brazed assembly, and consists of subassemblies for theoxidizer gas manifold, main injector, chamber housing,upper nozzle, middle nozzle, lower nozzle, propellantsupply ducts, and pyroigniter ports.

The oxidizer gas manifold, made of an Inconelequivalent, directs the oxidizer-rich turbine drive gasfrom the turbine discharge to the main injector. Themanifold contains a flange that attaches the chamber tothe engine thrust takeout structure. A spherical plate inthe oxidizer stream upstream of the injector providesadditional propellant distribution prior to injection.

The main injector consists of upper and lowerstainless steel parts that are welded together. The warmoxidizer-rich gas from the turbine exhaust is suppliedaxially, and the fuel is supplied radially from the maincombustion chamber regenerative coolant circuits. Maininjector elements are coaxial in nature with fuel swirl.The outer row of injection elements is biased for massand mixture ratio stratification. There are no baffles,acoustic cavities, or other stability devices in the maincombustion chamber. Combustion stability in the maincombustion chamber was achieved by proper distributionof propellants across the injector face and in thecombustor volume.1 Since very early in the NK-15development, there have been no instances of combustioninstability in the main combustion chamber.1

The chamber housing is a brazed and weldedassembly consisting of a stainless steel external jacket, achrome copper alloy slotted internal liner, and a stainlesssteel fuel inlet manifold. Fuel from the pump dischargeenters the coolant jacket aft of the throat and splits in twodirections, up the main chamber and down the nozzle.The coolant in the main chamber flows through milledchannels in the liner upstream past the throat section untilrejoining with the fuel coolant used to cool the lowernozzle. Some of this fuel is then injected into thecombustion chamber through two rows of tangentialorifices located in the chamber barrel downstream of theinjector face. The remainder is then directed to the lowerfuel manifold in the main injector.

The nozzle of the NK-33 combustion chamberconsists of upper, middle, and lower sections. Eachnozzle section has inner and outer shells made of stainlesssteel which are fabricated and inspected separately. Theinner shell of the upper nozzle is slotted to form coolantpassages, and the outer shell is brazed to the inner shell toform the outer wall closure of the coolant passages. Themiddle and lower nozzle sections are divided bycorrugated sections that define the coolant passages. Thethree nozzle sections are inspected individually and thenwelded together.

Engine Valves

Automatic control assemblies form the primaryelements of the control, regulation, and purging systems.The control system provides propellant flowrate to theengine lines during chilldown, startup, and shutdown,while the regulation system maintains proper flowrateduring steady-state operation.

The oxidizer chilldown valve, located on theoxidizer pump discharge upstream of the preburner inletand main oxidizer shutoff valve, provides a bleed pathfrom the engine during oxidizer pump chill down.

The main oxidizer shutoff valve provides the startand shutoff for the oxidizer system, opening or closingdepending upon the differential pressure between theoxidizer pump discharge and inlet. The main fuel shutoffvalve provides flow to the main combustion chambercoolant jacket, opening or closing depending upon thedifferential pressure between the fuel pump discharge andinlet. The preburner fuel shutoff valve supplies fuel tothe preburner, and when closed shuts the engine down.Fuel flow to the preburner is started when the diaphragmson the TEA/TEB ampoule are punctured.


The Russian thrust regulation valve was fitted with anew electromechanical actuator to provide throttlecapability over the range from 49% chamber pressure to123% chamber pressure. This valve also strictly controlsfuel flowrate to the preburner during the initial portion ofthe start transient to provide benign pressure andtemperature environments in the engine,

The Russian mixture ratio regulation valve wasfitted with a new electromechanical actuator to provide a20% range of mixture ratio control. The actual minimummixture ratio is dependent upon the mixture ratio valveitself, rather than the range of the actuator, dependingupon where the nominal is set. For the Kistler vehicle at100% power level, the mixture range is about -5%/+15%.

Since the requirements for on/off functions andflowrate regulating functions were divided betweenseparate systems, both systems were optimized for thesevery different design requirements. The division of thesefunctions contributes to the high reliability andcontrollability of the NK-33 and NK-43 engines.

Description of the Engine Modifications

The Russian NK-33 and NK-43 engines have beenmodified for installation and operation on the Kistler K-llaunch vehicle.4 Modifications on the basic engine aresummarized in Table II. Additional modificationsrequired to produce a restartable NK-33 configuration aresummarized in Table III.

All new components have undergone qualificationtesting at the component level. For valves, EMAs,pyrotechnics, and sensors this testing included thermalcycling, performance verification, and vibration testing.All new components, with the exception of the gimbal,were incorporated into the engine and are being verifiedat the engine level in the Verification Test Program. Thethrust frame and gimbal were statically tested to ultimateloads on the component level.

Engine Valves

The original NK-33 and NK-43 engines used threepyrotechnic valves that, when actuated, were eitherpermanently closed or opened. Replacement of theactuator or the complete valve was required to hot fire theengine again. One of the first modifications was toremove the pyrotechnic actuation on these valves, andreplace them with gaseous pneumatic actuation controlledby solenoids. Consequently, two of the pyrotechnic-actuated valves were completely replaced, and on thethird the actuator was replaced.

The liquid oxygen (LOX) chilldown valve providedthe capability to thermally condition the oxygen pumpwith tank head pressure prior to hot fire. In the originalvalve, a pyrotechnic charge was fired to wedge a piston inthe valve and permanently seal the normally open bleed.To provide multiple chilldown cycles without having tochange the valve, this valve was completely replaced witha pneumatic valve remotely piloted by a solenoid valve.Piloting medium was gaseous nitrogen. The valve bodywas made from Inconel for improved liquid oxygencompatibility and to handle 6000 psia oxidizer dischargepressure in the event of valve operation failure.

On the original engine, another pyrotechnic-actuated valve provided purge to the main combustionchamber during the engine shutdown from an on-boardhigh pressure nitrogen bottle. In this valve, a pyrotechniccharge was fired to wedge a piston in the valve andpermanently open the nitrogen bottle discharge. Since theshutdown purge will now be provided from the vehicle,this valve was completely replaced with an internallypiloted solenoid actuated valve. The on-board nitrogenpurge bottles and regulation system were removed, whichconsiderably lightened the gimbaled engine mass.

The third pyrotechnic actuated valve on the originalengine stopped fuel flow to the preburner and precipitatedengine shutdown. In this normally open valve, apyrotechnic charge was fired from a bolt-on actuator towedge the poppet and close the valve outlet. This single-use bolt-on pyrotechnic actuator was replaced with agaseous nitrogen driven actuator controlled by a remotelymounted solenoid pilot valve. To retain the flow featuresof the valve, only the pyrotechnic actuator was replaced.The pilot valve will be powered open prior to engineoperation, providing nitrogen to the preburner fuel valveactuator and opening the valve. The solenoid will ventthe actuator when engine shutdown is commanded. Toensure correct timing with the onset of the shutdownpurge into the preburner fuel injector manifold, whichwas initiated by opening the shutdown purge valve, thepurge was tied into the preburner fuel shutoff valveactuator outlet. Thus the shutdown purge will assist inclosing the preburner shutoff valve by pressurizing theactuator to the normally closed valve position.

Another valve was added to the engine that controlsthe start purge flow. This valve is identical to theshutdown purge valve, and allows the start purge to beprovided from the vehicle.

For the restartable NK-33 engine, two new valveswere added to provide a parallel TEA/TEB preburnerignition system. A single inlet, dual outlet ("3-way")


valve allows selection of the appropriate TEA/TEB leg.This valve will be normally shunted to the initial usecircuit. During the shutdown of the first burn and prior torestart, the valve will be shuttled to the second position bya pilot solenoid valve that is remotely mounted, andenergized during the entire second burn. The other newvalve is a completely new dual preburner shutoff valve atthe opposite ends of the TEA/TEB supply lines. Thisdual valve is a similar design to the single preburnershutoff valve but includes two parallel valves in a singletitanium housing, with two inlets and one outlet.

The solenoid pilot valves are common valvescurrently in production. These solenoid valves wereremotely mounted on the engine to reduce vibrationlevels and provide thermal isolation.

Electromechanical Actuators

Externally commanded changes to mixture ratio andthrust are performed by electromechanical actuators(EMAs) which change the flow area of the mixture ratioand thrust control valves. New EMAs have replaced theexisting Russian actuators to provide electricalcompatibility with U.S. launch vehicle powerrequirements, and to increase the control range. The twoactuators are similar in design except for the matinginterfaces and internal gear ratios. The actuators useharmonic drives with a 60:1 gear ratio for the thrustcontrol actuator and a 160:1 gear ratio for the mixtureratio control actuator. Both actuators incorporatevibration isolation into the mating interfaces similar to theRussian actuators. Individual actuator weight is 11 lbm.

Both actuators are closed-loop devices with theelectronics for both actuators located in a vehicle-mounted actuator controller. Controller weight is 17 lbm.The actuator controller is electronically redundant, withinputs of primary or secondary channel selection,redundant power inputs, and analog position commands.The controller uses position and velocity output in closedloop control to provide the required position. Controlleroutput includes actuator velocity, position, and torqueapplied to the actuator.

When configured for the Kistler K-l vehicle, thethrust actuator will be allowed a thrust range of 68% ofchamber pressure. The maximum end-to-end range is76% of chamber pressure. Thrust change can becommanded up to a rate of 135% chamber pressure persecond, given sufficient engine inlet pressures to precludecavitating the pumps.

The mixture ratio actuator will be allowed a rangeof about 0.5 units of mixture ratio. When configured forthe Kistler K-l vehicle, the actual range about thenominal mixture ratio is about -0.15/+0.35 due to enginebalance considerations. Mixture ratio range can becommanded up to a rate of 5% of full scale range persecond.

Main Combustion Chamber Igniters

New main combustion chamber igniters wererequired because on the original engines these igniterswere pyrotechnic based and hence consumable. Eventhough there were no ignition failures with the originalRussian design, the new igniters were designed to provideabout 30% more caloric output over the same actuationduration to increase ignition reliability with subcooledRP-1. The igniters for the restart engine have the samebasic design as the nonrestartable engine but with a burstdisk separating the initial charge from the second charge.Both igniters use a fuel-rich magnesium and teflonpropellant to provide afterburning in the main chamberduring the oxidizer-rich ignition period.

Thrust Mount

The original NK-33 and NK-43 thrust takeoutstructures were tubular with four attachment points to thesquare pattern vehicle structure. To provide capability togimbal the engine, this frame was removed and replacedwith a new frame specially designed and built for theKistler vehicle. The new thrust mount, shown in Fig. 7,was designed and fabricated by N.D. Kuznetsov SSTC in1997 to meet the gimbaled and static thrust load of theNK-43 engine. To reduce development costs, the NK-33engine will use the same thrust mount. The cast steelalloy frame is a 3-piece construction for retrofitting theframe to the existing engine without disassembly of theturbopump assembly from the thrust chamber. The framehas a 2-piece split ring that bolts together around theturbine exhaust duct and to the existing thrust chambertakeout flanges. A conical shell attaches to the two halfrings and tapers to interface with the gimbal bearing. Thethrust frame also includes two titanium attachment armsfor attaching hydraulic actuators to provide gimbalingmotion.

Gimbal

A spherical gimbal bearing located at thecombustion chamber head, together with flexibleelements on pressurant supply lines, allow for the engineto be gimbaled. Requirements for the Kistler K-l vehiclecall for a gimbal range of +/- 6 degrees.4 The gimbal


bearing is modified from the bearing for the space shuttlemain engine (SSME). Modifications include shorteningthe bearing for improved integration into the Kistlervehicle, and replacing the titanium alloy used for thecryogenic environment on the SSME with a readilyavailable and less expensive titanium alloy. Otherwise,bearing material is the same as used on the SSME. Thegimbal block will be acceptance tested to obtain aconsistent coefficient of friction.

The engine was tested during the verification testprogram without the gimbal and gimbal actuators. Thetest facility used a flexible mount to eliminate unrealisticside loads on the thrust frame.

Engine Controller

A new engine control system is being developed forthe Kistler K-l vehicle. Each engine on the vehicle willhave a separate dedicated controller. This new controllerwill house sequencing commands to start and shutdownthe engine, circuitry to condition signals from the engine-mounted flight sensors, and software to monitor enginehealth during the start transient prior to liftoff. Controllerweight currently is about 65 lbm which includes theenvironmental box and all internal cards and harnesses.Harness weight between the engine and controller isabout 20 lbm for the basic engine and 24 lbm for therestartable engine.

The engine controller will maintain control over allengine-mounted components that affect engine operation,including the two EMAs, the several solenoid pilot valvescontrolling pnenumatically actuated valves, and theinitiator squibs that ignite the pyroigniters and startcartridge. Electrical power conversion and distributionfunctions are included. Each engine controller is poweredfrom seven vehicle power busses - triple busses forelectronics power and dual busses for both utility powerand pyrotechnic power.

The engine controller has redundant channels toprevent single-point failure in case of controllermalfunction. A third channel acts as a bus controller andprovides decision authority when the two channelsdisagree. The processor is responsible for coordinatingall control operations and monitoring the sensors forproper engine operation. Control system components thatare not performing properly are identified and appropriateaction is initiated. In this way the engine controllerprovides self-monitoring capabilities.

The engine controller conditions and records datafrom flight sensors located on the engine. The engine-

mounted sensor suite includes commercially availablepressure, temperature, speed, and acceleration sensors.The engine flight sensors chosen for the Kistler K-lvehicle, which are similar to the sensors used in theRussian flight program, are listed in Table IV.

The engine-mounted control units and sensors areindividually connected to the engine controller through amultiple-cable wiring harness, connector bulkhead, andmultiple cables. The interconnect cables include multipleconductor power and signal lines and are shielded.

The data collection and conditioning system hasbeen tested during the Verification Test Program, and inupcoming tests the sequencing operations will be verified.During the test program the operation of the enginecontroller was directed by a PC-compatible Pentium-based system located in the control room. This electricalground support equipment (EGSE) served as the interfacebetween the engine controller and the test facility andoperators. On the Kistler vehicle, the vehicle controllerwill serve this function.

Engine Characteristics

Engine Weight

Modified NK-33 engine weights are shown in TableV. Dry weights include the weight of all themodifications added to the engine, including the gimbalblock, but do not include the engine controller and theelectronic control box for the EMAs, nor vehicledependent items such as propellant feedlines and thermalshielding. The wet pre-fire weights include all the dryweight plus the solid propellant weight and the liquidpropellant weight in the engine up to the main shutoffvalves. The wet operating weights include all the dryweight plus the liquid propellant weight in the engine,minus the solid propellant mass that had been consumedduring the start transient.

Start Sequence

The engine system requires thermal conditioning(chilldown) of the oxidizer pump before firing to stabilizeoxidizer flow components at cryogenic temperatures and"avoid temperature shocks and gasifying of propellantsduring start. The chilldown is performed by bleedingoxygen through the system at a controlled rate. Duringtests at Aerojet, the time required for the thermalconditioning of the engine was typically 15 to 20 minutesfor normal boiling point oxidizer (-297 F), and 10 to 15minutes for subcooled oxidizer (-310 F).


The following description is a typical sequence ofevents during engine chilldown. The engine controllermaintains control of the oxidizer chilldown valve.Commands are transferred from the vehicle or facilitycontroller to the engine controller through a MIL-STD-1553 bus. Sequence times are described before enginestart (E/S):

1. (E/S -180 minutes)Begin engine purging with the low

flowrate (0.0044 lbm/sec) IPS purge.2. (E/S -120 to 150 minutes)

Initiate fuel fill and drainoperations

3. (E/S -10 to 15 minutes)Initiate low flowrate oxygen

circulation. Oxygen is supplied up tothe main oxidizer shutoff valve anddisposed from the engine through thechilldown valve and recirculationpiping. The oxygen flowrate duringthis period is about 3 lbm/sec.

Final conditioning before the engine autosequencestart is conducted according to the following procedure:

4. (E/S - 2 to 3 minutes)Initiate higher flowrate oxygen

circulation by increasing propellantinlet pressures to values specified atstartup. The flowrate at this time isabout 6 lbm/sec.

Initiate engine purging with highflowrate (0.011 lbm/sec) IPS purge.

5. (E/S -1 minute)Verify that oxygen inlet

temperature and oxygen bleed outlettemperature are within specification.

At approximately 45 seconds prior to engine start,the engine controller initiates preignition sequenceactivities, which include the following events:

6. (E/S - 45 seconds)Perform internal self-check of

engine controller. Engine controllerwill signal test facility if transfer of testcontrol is or is not accepted.

Verify valve positions.Verify sensor signals.Verify pyrotechnics continuity.Select EM A command channel B,

and move mixture ratio valve and thrust

control valve out of position and backinto position.

Select EMA command channel A,and move mixture ratio valve and thrustcontrol valve out of position and backinto position.

At this time, the following components andconditions have been verified by the engine controllerprior to engine start:

Controller functions EMA operation Solenoid valve operation Engine IPS purge inlet pressure

The following conditions are then verified by thevehicle controller to test facility prior to engine start:

Engine tank pressure (to verifyengine inlet pressure)

Engine main chamber walltemperature

The engine chamber wall temperature is monitoredprior to firing to preclude excessive chilling of thecombustion chamber liner, which may occur due toexcessive oxidizer leakage through the turbine seal.

Engine timing during the start transient is shown inFig 8. The ignition system start is monitored by theengine controller which verifies normal operation beforeallowing the throttle to full power. Engine start includesthe following events which are controlled by the enginecontroller:

7. (E/S - 5 seconds)Open preburner fuel shutoff valve.

8. (E/S - 2 seconds)Open engine start purge valve.

9. (E/S -1.3 seconds)Verify start purge inlet pressure

downstream of engine start purge valve.10. (E/S - 0.50 seconds (latest))

Close LOX chilldown valve.11. (E/S - 0.40 seconds)

Ignite first of three maincombustion chamber pyroigniters.

12. (E/S - 0.39 seconds)Ignite second of three main

combustion chamber pyroigniters.13. (E/S - 0.38 seconds)

Ignite third of three maincombustion chamber pyroigniters.


14. (E/S - 0 seconds)Ignite start cartridge.

15. (E/S + 1.3 seconds)Verify satisfactory ignition and

operation with main injector fuelmanifold pressure, turbine outlettemperature, and turbopump rotorspeed.

Close start purge valve on engine.

If the engine has not reached a satisfactoryintermediate power level at E/S + 1.3 seconds, the enginecontroller will command a normal shutdown.

At the time E/S +1.5 seconds, the engine internalhydraulics have attained steady-state operation, and theengine is ready to be commanded to a different powerlevel or mixture ratio. During the boost phase of theKistler vehicle, a thrust increase command is given toeach engine to synchronize the power levels of the threefirst stage engines at the time E/S +1.5 seconds, and thenthe thrust increase to full power is commanded at E/S +1.75 seconds. On the flyback stage and the second stageof the Kistler vehicle, the engine is commanded to fullpower at the time E/S + 1.5 seconds.

Start Performance Characteristics

For normal starts of the NK-33 engine, whereengine power is increased up to full power within 2seconds after command to ignite the start cartridge, theminimum allowable propellant temperature and pressureconditions at the engine interface required during enginestart are shown in Figs. 9 and 10 for RP-1 and liquidoxygen, respectively. Slumps or other pressurereductions at engine inlets are not allowed to go lowerthan the pressures shown in these figures. In a specialcase being developed for the Kistler vehicle altitudeengine starts, as described later, an early portion of thestart transient is being allowed to exceed the requirementsin Figs. 9 and 10.

The NK-33 engine is capable of starting with thesespecified inlet conditions, transient temperatureconditions, and the specified range of inlet ductingwithout supplementary pressurization or otheraugmentation during transient flow conditions.

The NK-33 engine is capable of withstandingmaximum pressure limits at the engine/vehicle interfaceof 327 psia (23 kgf/cm2) for the oxidizer inlet and 284psia (20 kgf/cm2) for the fuel inlet. These pressuresinclude the maximum conditions of transient and steady-state operation during all phases of engine operation.

Steady-state Performance Characteristics

The NK-33 engine inlet temperature and pressurerequirements for mainstage (steady-state) operation arealso shown in Figs. 9 and 10 for RP-1 and liquid oxygen,respectively. Kistler steady-state standard inlet conditionsfor the NK-33 verification engine are shown in Table VI.

There are no special inlet flow requirements (e.g.,straight run, vane, strut spacing, etc., to minimize flowdistortion) at the RP-1 or oxygen pump inlet interfaces.

Shutdown Sequence

The engine is capable of normal shutdown with thesame inlet pressure and temperatures as shown in Figs. 9and 10, and without any supplementary pressurization.The engine is capable of normal shutdown, upon receiptof appropriate signal, from any engine operatingcondition. The engine is capable of benign shutdown (nodamage external to the engine) in the event of loss ofvehicle fluids, including propellants.

For the reusable application of the Kistler vehicle,the engine is throttled down to intermediate power (about55% of full power chamber pressure) prior to shutdown.This throttle period is expected to last from 1 to 5seconds. The standard shutdown sequence, commandedby the engine controller, shuts the engine down after theengine power level has been reduced.

From the 55% power level, engine shutdown (E/SD)proceeds with the following events:

1. (E/SD - 0 seconds)Open shutdown purge valve on

engine.Close preburner fuel shutoff valve

on engine.2. (E/SD + 2 seconds)

Close shutdown purge valve onengine.

The engine will shutdown from 55% power level to10% of mainstage chamber pressure within 0.8 seconds,+/- 0.3 seconds.

The emergency shutdown sequence is exactly thesame as the standard shutdown sequence except that theengine power is not throttled back to 55%.


AEROJET E-5 TEST FACILITY

Tests of the original NK-33 engine in 1995 and ofthe modified engine in 1998 were conducted at arefurbished test facility at Aerojet originally used forTitan I engine testing. The E-zone facility at Aerojet hasalso been used for LOX/hydrocarbon and LOX/hydrogenthrust chamber development testing in the last 10 years.The NK-33 tests were conducted vertically at test stand E-5 at sea level conditions. A deflector plate approximately15 feet below the exit of the nozzle turned the exhaustplume into a flame pit from which the hot gasses wereremoved from the area. The modified NK-33 enginemounted on the test stand is shown in Figure 11.

The E-5 test facility is capable of moderate durationLOX/RP-1 test firings. The LOX tank holds 20,000gallons, and the fuel tank, although also sized for 20,000gallons, is only site-licensed for 10,000 gallons.Maximum duration at full power for NK-33 enginefirings is about 200 seconds.

The oxygen tank and the oxygen feedlines arevacuum jacketed. Storage and operation with subcooledliquid oxygen temperatures down to -315 F has beendemonstrated in the verification testing. The oxygenfeedlines are 12 inch diameter except for a flowmetersection with parallel 8 inch diameter pipes. The fuelfeedlines are 10 inch diameter except for a flowmetersection with parallel 8 inch diameter pipes. Flowrate wasmeasured by redundant 8 inch FlowTec turbineflowmeters for both oxidizer and fuel.

A propellant subcooling skid has been developed byAerojet for use in the Kistler program. The skid usesliquid nitrogen to subcool oxygen from -297 F to -310 F,and cold gaseous nitrogen to subcool the liquid RP-1from ambient temperature to -30 F.

The vertical position E-5 does not have capability tomeasure thrust. Thrust was calculated with measurementsof engine inlet flowrate and main combustion chamberpressure, together with thrust coefficients provided byN.D. Kuznetsov SSTC. During development andqualification of the NK-33 engines in Russia, thrust wasmeasured at a sea level facility so the thrust coefficientwas empirically generated. The 3a accuracy of the thrustmeasurement provided by the Russian testing wasestimated to be +/- 0.5%, from which the 3

The fourth benchmark test was a 168 seconddemonstration of a complete Atlas duty cycle at therequired engine inlet pressures. The engine ramp to fullpower was controlled by the thrust control valve actuator,and the engine ran at 78%, 86%, and 103% power levelsat various times in the test profile.

The fifth benchmark test was a 150 seconddemonstration of engine capability to operate at about114%, the maximum required power level for EELV withthis engine. The engine ran at 113% power level for 130seconds, and at 103% power level for 10 seconds beforeand after operation at 113%.

A summary of the data from this test series isprovided in Table VII. The 1995 test data and theRussian acceptance test data for this engine had excellentagreement, showing that the engine operated withoutdegradation after storage of 20 years. Specific impulseagreed within 0.6%, providing a very satisfyingjustification of the published Russian performance. Theengine proved to be very durable, even at power levels ashigh as 113%.

VERIFICATION TEST RESULTS

Following the success of the Benchmark TestProgram, the path for testing the modified NK-33 enginewas considerably simplified. The operability of the basicengine after a long storage had been proven, and thecapability of the test facility had been demonstrated.Aerojet engineers had become familiar with theprocedures and operating characteristics of the NK-33engine, and facility personnel with the handling of theengine.

The Verification Test Program was designed toprovide the maximum amount of data on a variety ofobjectives with a single engine. To date, five tests havebeen conducted with the modified engine. Measuredchamber pressure and mixture ratio profiles for each ofthese tests, along with the commanded thrust control andmixture ratio control valve angle positions, are shown inFigs. 12 to 16.

The first test was a repeat of the original Russianacceptance test for this engine, except with normalboiling point liquid oxygen and ambient temperature U.S.RP-1, for a duration of 44 seconds. Thrust and mixtureratio commands were provided to the engine through thenew EMAs. This test was a significant milestone tocheck out the new purge valves, plumbing, preburnervalve actuator, thrust frame, and ignition hardware thathad been put on the engine. All new hardware operated

satisfactorily. The main combustion chamber igniterssuffered minor erosion through an inner casing,precipitating a minor redesign prior to the next test.

The second test was a long duration test to verifymodified engine capability to operate for the full Kistlervehicle boost phase duration. Thrust and mixture ratiowere varied extensively, verifying the capability of theEMAs to operate under load as expected. The test wastreated as a rehearsal of a flight profile after anacceptance test, with the engine balance carefullyprogrammed to deliver Kistler first stage operatingconditions -- a chamber pressure of 2019 psia and amixture ratio of 2.587. In addition, conditions at startwere carefully monitored to compare start transientparameters with the first test. Start cartridge propellanttemperature was conditioned for the 24 hour period priorto the test to the same temperature as on the first test. Allstart transient parameters pressure slumps at pumpinlets, ignition times of preburner and main combustionchambers, pressure and temperature rises in the engine,and operating parameters at intermediate stage, werewithin 2% of the parameters for the first test. Variousengine internal operating parameters, including pumpdischarge temperatures, turbine outlet temperatures, andmain chamber pressures are shown in Fig. 17.

The third test was a moderate duration test toevaluate the capability of the new propellant subcoolingfacility to deliver subcooled propellants, and the engine toperform with them. The subcooled oxidizer temperatureof -310 F is the nominal temperature for Russianoperation, while the subcooled fuel temperature of -30 Fis colder than the Russian nominal temperature but stillwithin the range of Russian test history. The test was shutdown prematurely due to buildup of ice in a filter in thethrust control valve when throttling down to a lowerpower level. An investigation of the test facility showedexcessive moisture had built up in the RP-1 supplysystem, which created ice particles when the RP-1 wassubcooled to -30 F. Subsequent activities to remove themoisture from the RP-1 have been identified, and thesubcooled fuel system will be reactivated when themoisture has been removed. There was no damage to theengine as a result of the ice buildup in the valve, whichsimply powered the engine down by restricting fuel to thepreburner, resulting in an aborted test due to low powerlevel.

The fourth test was a significant development in theKistler program. One of the Kistler vehicle requirementsto the engines was to start with inlet pressures lower thanthe requirements shown in Figs. 9 and 10 and lower thanhad been tested during engine development. With these


inlet pressures at start, both the oxidizer pump and thefuel pump were expected to cavitate during the starttransient. Consequently, tests were required to evaluatethe ability of the engine to start under these conditions.Due to the configuration of the E-5 facility, sufficientlylow oxidizer inlet pressures at start could not be generatedwith subcooled temperatures, so a test was constructedwith normal boiling point oxygen, taking into account thedifference in vapor pressure between -310 F and -297 F.

Results from this test showed that although both theoxidizer and fuel pumps were cavitating, the enginestarted and operated at intermediate stage power withinnormal characteristics. Figs. 18 through 20 presentcomposites of various engine parameters during the starttransient for all five verification tests. Chamber pressurewas essentially unaffected, as shown in Fig. 18, and therewere no turbine speed excursions, as shown in Fig. 19.The engine inlet pressures, however, were depressed for asubstantially longer time than during other tests, as shownin Fig. 20. Examination of pump characteristics showedthat during the initial portion of the start transient, thepump had delivered only 4% of its nominal noncavitatinghead rise. Comparison with transient analyses of vehiclestarts showed that this test, in terms of inlet pressuredepression, was an excellent simulation of the Kistler K-lsecond stage start, where inlet pressures are expected tobe lowest at start.

The fifth verification test was a long duration testdesigned primarily to add duration for evaluation ofengine life. Subcooled oxygen was used. The shutdownwas designed to duplicate the Kistler second stageshutdown, which has an extended constant throttle downfrom full power and a dwell period prior to shutting theengine off. Unfortunately, a facility redline for flamebucket cooling water pressure stopped the test 10 secondsprematurely.

A summary of the data from the Verification TestSeries is provided in Table VIII. Sea level specificperformance fell well within the NK-33 nominal range of297 +/- 3 seconds. Comparison of the transients betweenthe benchmark testing and the verification testing showedvirtually no differences. The engine start transientenvelope had not been changed due to the modificationsto the engine.

CONCLUSIONS

A flight qualified liquid propellant rocket enginefrom the Russian lunar launch program has been broughtto the West, modified for attachment to and control by theKistler K-l, a reusable launch vehicle currently in

development in the United States, and successfully testfired at Aerojet. The changes made to the originalRussian engine included replacement of three pyrotechnicactuated valves with solenoid actuated valves,replacement of two electromechanical actuators, redesignof the purge supply system including removal of on-engine purge gas supply bottles and replacement ofcontrol valves, replacement of the solid propellant formain chamber ignition and start turbine spin up, redesignand replacement of the thrust frame for addition of agimbal and TVC mount, and replacement of all sensorsand wiring harnesses.

The tests reported in this paper comprise about halfof the test matrix designed to verify the changes made tothe original engine. Tests that have been conductedinclude evaluation of Kistler K-l vehicle boost phaseduration, operation with subcooled fuel, capability tocontrol thrust and mixture ratio to Kistler specifications,and capability to start the engines with very low inletpressures expected during the restart stage and secondstage start of the Kistler vehicle. The low inlet pressurestart of the NK-33 engine is a significant new capabilitythat has now been demonstrated. This type of startdemonstrates the robustness of the engine, especially inthe critical area of transients.

Modifications to the NK-33 engine have notchanged performance parameters, transient operation, or,to date, durability of the original, flight-qualified engine.This is a critical goal of the engine modification program,whose intent is to maintain the flight-qualified status ofthe engine despite changing some of the enginecomponents and features.

FUTURE PLANS

The verification test program is planned to becompleted in July and August of 1998. The engine willbe modified while on the test stand into the restartableconfiguration, which includes new valves, pyrotechnics,and plumbing. Upcoming tests include evaluation of thecapability to restart the engine at sea level, integration ofthe engine controller for sequencing operations, andextended duration to evaluate engine life.

Following the completion of the verificationprogram, the first set of four engines for the first KistlerK-l launch vehicle will be assembled and acceptancetested. This set of engines includes two basic modifiedNK-33 (AJ26-58) engines, one restartable NK-33 (AJ26-59) engine, and an NK-43 (AJ26-60) engine. The NK-43is an NK-33 powerhead and thrust chamber with analtitude nozzle. The engine will be acceptance tested at


sea level with the use of a vacuum jacket around thelower nozzle, and without a gas diffuser, based onexperience developed in Russia with this engine in theearly 1970s. Even at sea level, the gas flow in the largenozzle flows nearly full due to the high chamber pressureprovided by the stage combustion cycle. The vacuumjacket is a provision to get the engine through the starttransient without damaging the nozzle. The acceptancetests and the remaining verification tests will be reportedin a future paper.

ACKNOWLEDGMENTS

Forrester, Harvey Howard, Jack Knutsen, Pat Leeds,Rubin Placencia, Roy Sanders, Tony Sanders, DaveSimon, Rick Simonsen, Troy Smith, Jack Standen, DaleVandershaaf, Fred Ward, Jack Winhall, and GeorgeWong. Translators and interpreters who have providedthe critical link between these engineers and their Russiancolleagues are Natasha Bearden and Irena Yermilova.Additional technical help and translation was provided byV.A. Bolshakov, Department Head, External Relationsfor N.D. Kuznetsov SSTC.

REFERENCES

For such an extensive undertaking as modifying andtesting a large liquid propellant rocket engine, there aremany people at Aerojet to acknowledge for theirsubstantial efforts towards making it happen. Inengineering, Ed Bair, William Baker, Jim Bouris, JimBoyd, Bill Campbell, Bryan Campbell, Don Culver, MarkEager, Greg Etzel, Joe Fasl, Ken Freese, Ted Gehrig,Floyd Hensen, Rosemary Hernandez, Larry Hoffman, WilHolzmann, Earl Jansa, Emil Leuders, Greg Lui, JoeMello, Dave Merchant, Thinh Nguyentat, Lynne Nickels,Dave Saltzman, Andy Smith, Russ Thomas, ChuckVallance, Garrett Wagner, Steve Walker, Gary Weeks,Gary Westman, and Mei Yee. In manufacturing, CliffAbbott, Tom Hubbard, Miguel Martinez, John Schneider,and Pete Womble. In test, Bill Baker, Brian Ballen, PeteCova, Ed Classon, Richard Classon, Mark Dvorak, Martin

1. Kuznetsov, N.D., "Closed Cycle Liquid PropellantRocket Engines," AIAA Paper No. 93-1956, June, 1993.

2. Johnson, N.L, "The Soviet Reach for the Moon," 2ndEdition, c. Cosmos Books, ISBN 1-885609-03-5, 1995.

3. Judd, D.C., "Final Report For: AJ26-NK33A LiquidRocket Engine Test Preparation Program," CooperativeAgreement RS5-089004, GenCorp Aerojet, December 7,1995.

4. Limerick, C., J. Andrews, R. Starke, R. Werling, J.Hansen, and C. Judd, "An Overview of the K-l ReusablePropulsion System," AIAA Paper No. 97-3120, July,1997.

Table I.Nominal Modified NK-33 Engine (AJ26-58,59) Performance Parameters*

ParametersSea level delivered thrustVacuum delivered thrustSea level delivered specific impulseVacuum delivered specific impulsePropellant flowrate into main combustion chamber

- Oxidizer-Fuel

TVC fuel tapoff flowrateMain combustion chamber pressureMain combustion chamber mixture ratioPreburner combustion chamber pressurePreburner combustion chamber mixture ratioPreburner outlet temperatureNozzle exit area ratio

UnitsIbfIbf

lbf-sec/lbmlbf-sec/lbm

Ibm/secIbm/seclbm/seclbm/sec

psia

psiaF-

Value340,000379,000

29733111448253195.0

21092.59467058670

27.7:1* at Kistler vehicle standard inlet conditions for 100% power level


Table HModifications for Basic NK-33 (AJ26-58) and NK-43 (AJ26-60) Engines

ComponentThrust and MR valveactuators

Pyrotechnic valves (3)

N2 storage bottlesStart purge valveShutdown purge valveStart and shutdown checkvalvesSensorsWiring harness

Thrust mount

Gimbal bearingFluid interface panel

Start cartridge and MCCigniter solid propellant

ModificationUse U.S. -produced 28 volt EM As

Replace LO2 chilldown, shutdownpurge, and preburner shutdownpyrotechnic actuation with solenoidvalvesRemove bottles (2)Add new piloted solenoid valveAdd new piloted solenoid valveAdd valves in generic start/shutdownpurge linesReplace with U.S. sensorsReplace with U.S. compatibleharnessReplaced with new mount

Add bearingAdd panel

Replace with U.S. ordnance

Modification RationaleIncrease actuation range, makecompatible with U.S. power, RussianEMA availabilityImprove reusability

Supply gasses from vehicle/facilityGeneric start/shutdown purge lineGeneric start/shutdown purge lineEliminate potential backflow

U.S. compatibilityU.S. compatibility

Vehicle interface, gimbalrequirementsVehicle gimbal requirementsImprove gimbal capability bygrouping lines that cross gimbalplane; isolate pilot valvesRussian availability

Table IHAdditional Modifications for Restartable NK-33 Engines (AJ26-59)

ComponentStart cartridge housingMain combustionchamber igniter housingTEA/TEB ampouleCutter valves

TEA/TEB ampouleselection valvePreburner fuel supply line

Preburner fuel shutoffvalveFuel bleed line fromsecond cutter valve

ModificationReplace with dual start cartridge unitReplace with dual pyrotechnic chargeunitAdd parallel ampouleAdd cutter valves to parallelTEA/TEB ampouleAdd 3-way valve

Add parallel line from TEA outletcutter valve to preburner shutoffvalveReplace with dual solenoid valve

Add line

Modification RationaleRequire second turbopump start spinRequire second main combustionchamber ignitionRequire second preburner ignitionIsolate second TEA/TEB ampoule;provide second start identical to firstSelect appropriate TEA/TEB ampoule

Avoid shutdown purge cleanlinessrequirements

Isolate second TEA/TEB line

Bleed fuel into preburner supply linethe same as for first start


Table IV.Modified NK-33 and NK-43 Engines (AJ26-58,59,60) Flight Sensor Suite

Parameters

Main combustion chamber pressureMain injector fuel manifold pressureOxidizer pump discharge pressureFuel pump discharge pressureFuel kickstage pump discharge pressureTurbine outlet temperatureTurbopump shaft speedStart purge engine inlet pressureShutdown purge engine inlet pressureInterpropellant seal pressurePreburner fuel injector dynamic pressureMain chamber jacket temperaturePreburner injector vibrationMain chamber vibrationTTO reference junction temperature

No. ofsensors

121113421112113

Acronym

PCPFJPODPFD

PFDKSTTONT

PSPIPSDPIPIPS

PFJPBRTSCHW

GXPBGXCHRTA

Table V.Modified NK-33 Engine Weights

Parameters

Dry weight - pre-fireWet weight - pre-fireWet weight - operatingWet weight - second operating

Units

IbmIbmIbmlbm

Basic Engine *AJ26-58

310433353409N/A

Restartable *AJ26-59

3216344735213505

* Note: engine weights include gimbal block, but do not include enginecontroller, EMA controller, or vehicle dependent items such aspropellant feedlines and thermal shielding.

Table VIStandard Inlet and Engine Tuning Conditions

ParametersOxidizer inlet pressureOxidizer inlet temperatureFuel inlet pressureFuel inlet temperatureFuel inlet densityFuel tapoff flowrateOxidizer hot gas tapoff flowrate

UnitspsiaF

psiaF

lbm/ftA3Ibm/secIbm/sec

Soviet N-l56.9-31056.9

553.42.48.5

K-l LAP35.2-31020.6-3052.65.0*

0

K-1OV35.2-31020.6-3052.65.0*

0* Note: Used to power TVC system


Table VH1995 Benchmark Test Program Data Summary

AveragedTimePeriod

TestNumber tavg

seconds

1 4 to 9.914 to 22

2 10 to 2028 to 3839 to 41

3 24 to 25

4 2.6 to 3.215 to 3545 to 597510130166 to 168

5 4 to 81510135

140.5 to 145.2

MainChamberPressure

PCpsia

16652162

218816571762

1215

18252177164621641654

217723782162

Percent ofNominalChamberPressure

We%

78.9102.5

103.878.683.5

57.6

86.5103.278.0102.678.4

103.2112.8102.5

EngineInlet

OxidizerFlowrate

WoIbm/sec

661839

854658696

N/G

723851654845656

855926846

EngineInletFuel

Flowrate

WfIbm/sec

242318

324239256

W/G

269325239325243

323358323

EngineInlet

MixtureRatio

MR-

2.732.64

2.632.752.72

N/G

2.692.622.732.602.70

2.642.592.62

Calc'dSea Level

Thrust

FslIbf

259460347660

352270258110276630

N/G

285900349860255740347310256940

350390385760347570

Percent ofNominal

Sea LevelThrust

Wsl~%~

76.4102.4

103.876.081.5

N/G

84.2103.175.3102.375.7

103.2113.6102.4

Calc'dSea LevelSpecificImpulse

l dIbf-sec/lbm

287.3300.5

299.1287.6290.4

N/G

288.3297.5286.3296.9285.9

297.5300.4297.3

EngineInlet

OxidizerPressure

Pospsia

93.379.4

77.190.688.1

80.2

72.563.974.959.370.8

85.978.384.9

EngineInletFuelTemp

TosF

-293.9-294.0

-294.2-294.1-294.1

-282.4

-290.0-293.6-293.6-293.5-293.3

-293.1-293.4-293.3

EngineInletFuel

Pressure

Pfspsia

89.981.6

76.483.481.9

87.4

53.352.058.650.556.0

83.477.484.5

EngineInletFuel

Temp

TfsF

6363

616262

63

5256565757

586162

OxidizerPump

DischargePressure

Podpsia

38095516

556837874138

2467

43525654376656233810

669165275657

FuelPump

DischargePressure

Pfdpsia

29084240

436528933165

1942

33584359287943462946

443751384409

TurbineRotorSpeed

NtRPM

1458017870

181501455015280

11740

1579018190145801818014710

182601974018250

TurbineOutletTemp

TtoF

372610

635394441

244

410632408668489

611753654

Table VIE1998 Verification Test Program Data Summary

Percent of EngineAveraged Main Nominal Inlet

Time Chamber Chamber OxidizerPeriod Pressure Pressure Flowrate

Engine Engine Percent of Calc'dIntet Inlet Calc'd Nominal Sea LevelFuel Mixture Sea Level Sea Level Specific

Flowrate Ratio Thrust Thrust Impulse

ThrustEngine Engine Engine Engine Oxidizer Fuel Vector

Inlet Inlet Inlet Inlet Pump Pump Turbine Turbine ControlOxidizer Fuel Fuel Fuel Discharge Discharge Rotor Outlet TapoffPressure Temp Pressure Temp Pressure Pressure Speed Temp Flowrate

Test* iass

seconds

1 10 to 2030 to 3943 to 44

2 15 to 2540 to 5060 to 7085 to 95100101101151012513510145

3 8W1029 to 3442 to 47

4 8 to 1016102135 to 4054 to 59

5 19102429103444104954 to 5974 to 7984 to 8994 to 9910410109119101241341013914410149

Espsia225116931823

2112210721122113219620322027

117020962095

1045104810501051

20772071206020632068206221022105202020212060

%i%

106.780.386.4

100.199.9100.1100.2104.196.396.1

55.599.499.3

49.649.749.849.8

98.598.297.797.898.197.899.799.895.895.897.7

WeIbm/sec

862654700

8208308198138437S5789

497820814

440438432427

820818827826812811826826802797810

mIbm/sec

349256278

317307317322338308303

N/G311315

150148151153

305308298295307309316313294297304

MB-

2.472.562.52

2.592.702.582.522.502.552.61

N/G2.642.58

2.922.972.872.78

2.692.662.772.802.652.622.612.642.732.682.66

EslIbf

361830262980285870

338890339380338910338370352870324160323940

N/G336500335590

149600150300150230149950

334070332740331940332560332090330730337710338680324160323830330670

%Fsl%

106.577.484.1

99.799.899.799.5103.895.495.3

N/G99.098.7

44.044.244.244.1

98.397.997.797.897.797.399.499.695.495.397.3

ISJUtlIbf-sec/lbm

298.8289.1292.4

297.9298.3298.3298.0298.9296.7296.8

N/G297.5297.3

253.6256.7257.8258.4

297.3296.7296.3296.8296.9296.4297.0297.5296.0296.1296.8

EflSpsia

81.894.991.7

85.684.884.283.580.584.983.3

66.846.045.5

42.147.048.751.1

86.885.985.986.285.785.083.984.386.685.883.6

IfiS.F

-295.2-295.3-295.3

-294.6-294.6-294.6-294.7-294.7-294.7-294.7

-314.5-314.9-314.9

-294.9-295.2-295.3-295.3

-311.8-311.8-310.8-309.4-309.3-309.3-309.3-309.2-309.2-309.2-309.1

ESSpsia

76.881.679.4

62.362.160.757.955.257.054.5

51.144.040.8

26.927.628.127.8

64.563.593.062.259.858.756.555.356.254.053.0

usF

414040

44444444444444

-8-36-37

57504949

464747485052S354555555

eastpsia

575437214141

5284533852895262558849704992

231351305107

2033204720402024

50945089513551375082507452235227494849275069

EMpsia

451228423165

4138425641214046430638013865

173140223947

1543154915251497

36843666377837963667364637523776360837723677

atRPM

182601438015230

17500176401750017430180301686016920

110101694016870

10550105101051010450

1673016720168701688016740167301701017020165201647016730

BaF

616369429

542528534528566493483

164498502

157152160165

460464459457474473489487444449466

WtueIbm/sec

000

0000000

000

0000

0.54.74.80.50.54.74.80.50.50.50.5


VSSSSJ&SSSSSSSSSSSSSSJfSSSSJV,I

FLUID GIMBALEDINTERFACE INTERFACE

PANEL

LEGEND

HO FILTER

g CHECK VALVE

fj ORIFICE

fU SOLENOID VALVE

ACCELEROMETER

PRESSURETRANSDUCERp. TEMPERATURE^ MEASUREMENT

ROTOR SHAFTSPEED FUEL SEALCAVITY DRAIN

, L02 CHLLCOWNr. DRAIN

OX SEALCAVITY DRAIN

Figure 1. Schematic of the Modified BasicNK-33 Engine (AJ26-58)

FEEDSYSTEMINTERFACE

\

FLUIDINTERFACE

LEGEND

[J FILTER

g CHECK VALVE

Qj ORIFICE

E3T1 SOLENOID VALVE

@ ACCELEROMETER

PRESSURETRANSDUCER,-. TEMPERATURE^ MEASUREMENT

ROTOR SHAFTSPEED FUEL SEAL

TURBINEEXHAUSTTAILPIPE

OX SEALCAVITY DRAIN CAVITY DRAIN

Figure 2. Schematic of the Modified RestartableNK-33 Engine (AJ26-59)


MainInjector Main

CombustionChamber

PreburnerFuelShutoffValve

MainOxidiValve Ampoule

FuelOxLzer Fuel Pum"

InletStart Cartridge

Valve

Figure 3. Layout Envelope of the Modified BasicNK-33 Engine (AJ26-58) - Side View

Units = inches

TEA/TEBAmpoule

Main FuelValve

FluidInterfacePanel Units = inches

Figure 4. Layout Envelope of the Modified BasicNK-33 Engine (AJ26-58) - Top View


42.76

- Dual PreburnerFuel Shutoff Valve

Dual TEA/TEBAmpoules

3-WayValve

Dual StartCartridge

Units = inches

Figure 5. Layout Envelope of the Modified RestartableNK-33 Engine (AJ26-59) - Side View

Dual TEA/TEBAmpoul

Units = inches

Figure 6. Layout Envelope of the Modified RestartableNK-33 Engine (AJ26-59) - Top View


13.618

Figure 7a. New Thrust Mount - Side View

Figure 7b. New Thrust Mount - Top View

Initiate Engine Controller Internal Sett-chert

-4S.OEnginCo*AulosStart

-A^

eoilerifiquence

^5.0

* Open Fuel Prebumer Valve

^v-

* Open Engine Start Purge Valve

^S^

-2.0

Verity Start PurgePressure. PSPI

-1.3

-0.4

ignite Main Chamber Pyroigniters

0Engin

Ignite Start Cartridge Close L.OX Pump Chitldown Valve

A1.3

e Comm

Close Engine Start Purge Valve Verify Main Chamber Fuel Pressure PFJ for Ignition Verify Rotor Speed NT and Turbine Outlet Temperature TTO for Operation

1.5anded

* Position Regulator foir 100% Thrust

1.85

100% Thrust Achieved. Minimum Time

100% Tluust

Power Level,Cham

ber Pre

is s

-u 8 8?

Time fromEngine Start,seconds

TOO

Figure 8. Start Transient of the Modified NK-33Engine (AJ26-58, 59)


NK-33 Fuel Inlet Pressure versus Temperature and Power Level

40.0

|30.0.

at10.

10.0.

0.0

Kistl

2r Opei

s>

ating B

Stanc-InletCond

ox

ard

tion

I104%Hi 00%A 75%X55%

-40 -36 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40

Inlet Temperature (F)

Figure 9. RP-1 Engine Inlet Pressure and Temperaturefor Modified NK-33 Engines (AJ26-58,59)

NK-33 Oxidizer Inlet Pressures versus Temperature and Power Level

-320 -315 -310 -305

Inlet Temperature (F)

-295 -290

Figure 10. LOX Engine Inlet Pressure and Temperaturefor Modified NK-33 Engines (AJ26-58 , 59)


Figure 11a. Modified NK33 Engine (AJ26-58) onAerojet Test Stand E-5

Fuel InletHi

Figure 11 b. Modified NK33 Engine (AJ26-58)


R PC-IDE MRI LHRVBL LTCVB

NK33 VERIFICRTION TEST NKP2-Q01-1R-001ENGINE CONTROL PRRRMETERS PLOT ZS

Figure 12. Performance Parameters forVerification Test #001

H PC-ID PSIflE MRI LMRVB DEGREESL UTCVB DEGREES

T1HE (SECOHIJS)

NK33 VERIFICHTIDN TEST NKP2-Q01-1R-002ENGINE CONTROL PRRRMETERS PLOT 25


12 IB PC-ID psinE HR! LHRVB DEGREESL LTCVB

IHC (SECONDS)NK33 VERIFICRTION TEST NKP2-Q01-1R-003ENGINE CONTROL PRRRMETERS PLOT 25


S79.81

fl PC-IDE MRI LHRVBL LTCV8

TIHE (SECONDS!NK33 VERIFICRTION TEST NKP2-Q01-1R-004ENGINE CONTROL PRRRMETERS PLOT 25


24American Institute of Aeronaudcs and Astronautics

2400-

2000-

1

J s 1-

iifenww

Iy

V- Vwi;,*.

! 1 i

. U-i

^MU^OIWU

*I*"*S1

........jMrtgw/

i 1;

...... J........J.........L...... .................

.......JIl]\..J..,.....|.......J........

, kj

: : ;!

tr\... ........

........J... ......

""S,--t\S

; jXi

:

i

n

\

|6oJ O.J : ) ) | ' : | ' | ' , , i , |-ID 20 40 SO 80 100 120 140 160 IB

TIHE ISECOHDS)

" PC-IO PSIB MK33 VERIFICRTION TEST NKP2-Q01-1R-005"5RVB OEGIIEES ENGINE CONTROL PRRRMETERS PLOT 25L LTCVB DEGREES


g-

fi PC-1C8 PFJ-1BC PFD-2BE POD-2BG TTO-2

PSIRPSIflPSIRPSIRDEB F

H TTD-3 DEC FI NT-lfl RPM

100 120 140TIME (SECONDS!

NK33 VERIFICATION TEST NKPZ-QDI-1H-002ENGINE STERDY STRTE PRRRMETERS PLOT 1NEFF DHTfi SYSTEM '

Figure 17. Internal Engine Parameters forVerification Test #002

1 TEST 001 PSIH2 TEST ODZ PSlfi3 TEST 003 PSJfl

PC VS TIMENK33 COMBINED STHRT TRHNSIENTS 200 SPS

Figure 18. Verification Test Start Transient Comparisonof Main Combustion Chamber Pressures


BEgBJET PROPUL5IOH ^ PO M jyt SHCggjEBTOJSBljl

1 TEST 0012 TEST 0023 TEST 0034 TEST 0045 TEST COS

1.5Q 1.75 2.00

RPMRPMRPMRPHRPrt

0-75 1.00 !._TIME (SECONDS)

NT VS TIMENK33 COMBINED STRRT TRRNSIENTS 200 SPS

Figure 19. Verification Test Start Transient Comparisonof Turbopump Shaft Speeds

1 TEST OD1 PSIH2 TEST OD2 PSIfl3 TEST 003 PSJR

PQS-NH VS TIMENK33 COMBINED STRRT TRRNSIENTS ZOO SPS4 TEST 0045 TEST DOS

PSIflPSIR

Figure 20. Verification Test Start Transient Comparisonof Oxidizer Inlet Pressures


modification and verification testing of a russian nk-33...

Documents