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NASA Technical Memorandum 105559AIAA-92-1264

Mission and Sizing Analysis for the Beta IITwo-Stage-to-Orbit Vehicle

Shari-Beth Nadell, William J. Baumgarten, and Stephen W. AlexanderLewis Research CenterCleveland, Ohio

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Prepared for the1992 Aerospace Design Conferencesponsored by the American Institute of Aeronautics and Astronautics, Inc.Irvine, California, February 3-6, 1992

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https://ntrs.nasa.gov/search.jsp?R=19920012304 2019-12-27T16:33:57+00:00Z

MISSION AND SIZING ANALYSIS FOR THE BETA II TWO-STAGE-TO-ORBIT VEHICLE

Shari-Beth NadellWilliam J. Baumgarten__Stephen W. Alexander

NASA Lewis Research Center, Cleveland, Ohio 44135

Abstract

NASA Lewis Research Center studied ahorizontal takeoff and landing, fully reusable,two-stage-to-orbit (TSTO) vehicle capable oflaunching and returning a 10,000 lb payload to lowEarth polar orbit using low-risk technology. Thevehicle, called Beta II, was derived from theUSAF/Boeing Beta vehicle, a TSTO study vehiclecapable of launching a 50,000 lb payload to lowEarth polar orbit. Development of Beta II from theUSAF/Boeing Beta vehicle occurred in a series ofiterations during which the size of the vehicle wasdecreased to accommodate the smaller payload, thestaging Mach number was decreased from 8.0 to 6.5,and the rocket propulsion system was removed fromthe booster. The final Beta II vehicle consisted of arocket powered orbiter and an all airbreathingbooster. The gross takeoff weight of the Beta IIvehicle was approximately 1.1 Mlb. In addition to itsbaseline mission, the Beta II vehicle was capable ofdelivering approximately 17,500 lb to the SpaceStation with the same takeoff gross weight. Themission and sizing analysis performed to arrive atthe Beta II vehicle is discussed.

Introduction

Recently, much emphasis has been placed ondeveloping a viable single-stage-to-orbit (SSTO)vehicle to transfer payloads to orbit. One suchvehicle is the National Aerospace Plane (NASP). Analternate concept to SSTO is the two-stage-to-orbitvehicle. Technology development for TSTO vehiclesdoes not involve as great a risk as that for SSTOvehicles. TSTO vehicle concepts are, therefore,potentially more viable using current or near-termtechnology than SSTO concepts.

NASA Lewis Research Center initiated a studyto investigate a near-term (i.e., developed using 1995

Aerospace Engineer, Member AIAA

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technology) vehicle for delivering payloads to orbit.A TSTO concept was selected over SSTO based onthe chosen technology level. The study guidelinesmandated horizontal takeoff and landing and thatboth the booster and orbiter be fully reusable. TheTSTO vehicle would be developed to deliver andreturn a 10,000 lb payload to low Earth polar orbit(100 n. mi.). This payload capability would capturea large part of projected NASA payloadrequirements. A survey of past TSTO studiesrevealed the Beta vehicle (Figure 1), developed bythe U.S. Air Force (USAF) at Wright Laboratoryand Boeing Aerospace and Electronics (ref. 1), ashaving incorporated guidelines and technology limitssimilar to those of the NASA study. The Beta studyvehicle was therefore chosen as the starting point forthe development of the NASA Lewis TSTO baselinevehicle, called Beta II.

The main goal of the study was to develop theBeta II vehicle to perform the design mission with areasonable minimum takeoff gross weight. Areasonable minimum weight was defined as thatwhich would enable operation from a conventionalrunway. A takeoff gross weight of approximately1 Mlb, similar to a large commercial transport, wasjudged to satisfy this requirement. In addition, thepossibility of performing the boost phase using an allairbreathing propulsion system in place of thecombined airbreathing and rocket propulsion foundon the USAF/Boeing Beta vehicle would beinvestigated. It was believed that this modificationwould decrease the gross weight of the vehicle andsimplify ground handling operations. Development ofBeta II from the USAF/Boeing Beta vehicle by theNASA Lewis TSTO team was supplemented by theU.S. Air Force at Wright Laboratory and theBoeing Defense and Space Group (refs. 1, 2). Themission and sizing analysis performed in-house atNASA Lewis Research Center to arrive at the BetaII vehicle and the methods used are discussed below.

Beta II Development

Development of Beta II from the USAF/BoeingBeta study vehicle occurred in a series of iterationsduring which several modifications were made. Theprocess followed during the Beta II development,along with important intermediate results, isdepicted in Figure 2 and described below.

The initial configuration for the NASA LewisTSTO study was the USAF/Boeing Beta vehicleshown in Figure 1. The USAF/Boeing Beta studyvehicle featured a lifting body orbiter embedded intothe underside of the booster stage. The lifting bodyorbiter provided large cross-range capability, whilethe embedded configuration offered expedient matingand staging procedures. The Beta vehicle wasdeveloped to deliver a 50,000 lb payload into lowEarth polar orbit with a gross weight at takeoff ofapproximately 2 Mlb. Included in the gross weight ofeach vehicle stage was a small growth margin equalto 2 percent of the orbiter dry weight and2.5 percent of the booster dry weight (ref. 1). Thisadded weight accounts for the difference whichinevitably appears between the predicted weight ofa vehicle and its actual weight due to misinterpretedtechnology trends, manufacturing limits, etc.

Beta booster propulsion consisted of two ramjets,eight Advanced Tactical Fighter (ATF) turbofans,and one Space Shuttle Main Engine (SSME). OneSSME modified with a two-position nozzle forimproved performance powered the orbiter. Theorbiter rocket, booster rocket, and boosterairbreathing propulsion system provided thrustduring the initial ascent. The main function of theATF turbofans, however, was to provide power fortransporting the orbiter between launch sites.Therefore, the contribution of the ATF turbofans tothe initial ascent of the USAF/Boeing Beta vehiclewas minimal. Propellant, both liquid oxygen (LOX)and liquid hydrogen (LH2), would be transferredfrom the booster to the orbiter during ascent toensure that the orbiter tanks were full at separation.The Beta vehicle staged at Mach 8.0 and 100,000 ft.After separation the booster, powered by theturbofans, would return to the airfield; the orbiterSSME would provide the remaining impulse requiredto obtain orbit. Upon completion of the mission, theorbiter would return to Earth for a non-powered,shuttle-like, landing.

As indicated on Figure 2, the NASA LewisTSTO development effort began by performing two

sets of initial trade studies, one with the orbiterstage and one with the booster, to determine some ofthe basic vehicle characteristics that would be usedthroughout the study. These initial studies wereperformed with a TSTO vehicle based on the USAFBoeing configuration but scaled parametrically toproduce results for the particular trade underinvestigation. The propulsion (including SSMEperformance) and aerodynamic data developed bythe U.S. Air Force and Boeing for the Beta studyvehicle were employed for these studies (ref. 1). Thefirst trade study involved determining the initialorbiter thrust-to-weight ratio (T/W), i.e., the T/Woccurring at orbiter rocket ignition, that wouldproduce a minimum gross weight. Designing theorbiter at this initial, or staging, thrust-to-weightwould further the goal of developing a vehicle witha minimum takeoff gross weight. The thrust andweight of the rocket engine used for this trade studywere scaled such that the rocket was operating at amaximum thrust level at ignition. This thrust levelwas held constant throughout the trajectory. Thesecond set of trade studies included investigating thepossibility of removing the rocket propulsion systemfrom the booster stage. If feasible, this modificationcould result in decreased vehicle gross weight andsimplified ground handling operations. Thecombination of airbreathing propulsion systems(turbofan ramjet) on the booster which would enablethe vehicle to perform the initial ascent withoutrocket assist was then determined. Additional tradestudies included varying the staging Mach number ofthe vehicle and decreasing the orbiter payload tomeet NASA Lewis study guidelines.

Upon completion of the initial trade studies, thedecision was made to study two TSTO vehiclesderived from the USAF/Boeing Beta vehicle butincorporating the NASA Lewis payload and missionguidelines. In addition, the initial staging Machnumber of 8.0, thought to be optimistic for a low-risk airbreathing propulsion system, was decreased.A staging Mach number of 6.5 was chosen for thefirst vehicle, referred to as Beta-131. Prior experienceat NASA Lewis suggested that Mach 6.5 was theoperational limit of hydrogen fueled ramjets using1995 technology. The second vehicle, Beta-132, wouldbe designed to stage at Mach 4.5. In addition, theramjets on the Beta-132 vehicle would be fueled withhydrocarbon fuel (JP-7) instead of hydrogen. Priorexperience again suggested that Mach 4.5 was theoperational limit of the ramjets when utilizing non-cryogenic hydrocarbon fuel. Both vehicles wouldperform the initial ascent without rocket assist. The

orbiters would retain the SSME used on theUSAF/Boeing Beta orbiter and would be designed atthe initial thrust-to-weight determined to beoptimum, except where this would require thrustlevels higher than that available from the SSME(maximum vacuum thrust of 516,000 lb). When thisoccurred, the thrust of the SSME would beconstrained to the maximum value and the initialthrust-to-weight of the orbiter allowed to vary.

The results from the analyses of the Beta-131 andBeta-132 vehicles, indicated in Figure 2, were studiedto determine which direction the NASA Lewis TSTOstudy would follow next. As previously stated, one ofthe goals of the study was to develop a vehicle witha minimum gross takeoff weight subject to studyguidelines and technology requirements. The Beta-B1vehicle, staging at Mach 6.5, had a lower takeoffgross weight than Beta-B2, staging at Mach 4.5 andusing only hydrocarbon fuel. The Beta-131 vehiclewas therefore chosen for further study.

At this juncture in the study, the opportunitywas taken to modify and refine the Beta-B1 vehicle.First, the orbiter was changed from a lifting body toa more conventional wing-body configuration. Thenew orbiter configuration was proposed by Boeingand offered greater structural efficiency than thelifting body design but decreased cross-rangecapability. Large cross-range capability had been oneof the requirements of the original USAF/BoeingBeta study. The NASA Lewis study, however, wasmore interested in developing a low weight vehiclethan one with a large cross-range capability.Therefore, the orbiter configuration change wasbeneficial for this study. Growth margins wereincreased to 10 percent of the orbiter dry weight and20 percent of the booster dry weight (ref. 1). Thesevalues were also suggested by Boeing and were moreappropriate for the technology level assumed.Airbreathing propulsion (refs. 3,4) and vehicleaerodynamic data developed for the USAF/BoeingBeta vehicle were replaced by data developed atNASA Lewis for the Beta-131 configuration. Thisincluded the substitution of turbojets currently beingstudied for high speed civil transports (HSCT) forthe smaller ATF turbofan engines. Similartechnology requirements between the HSCT andTSTO studies and decreased development costs dueto parallel efforts were the elements considered inthis decision. Finally, the volume and weight of theJP propellant required to return the booster from thestaging point to the airfield and expended duringtakeoff were included in the analysis. Although

included in the USAF/Boeing Beta study, thebooster return fuel had not been considered in theBeta-B studies. Neither the USAF/Boeing Betastudy nor the Beta-B studies had included takeofffuel volume and weight. Though important in thefinal analysis, these were not considered to be majorfactors in the Beta-B decision process.

The final results of the study, after incorporatingthe modifications described above, appear inFigure 2. Details of the Beta II vehicle developmentare discussed in the following sections.

Analysis Tools and Methods

Four analysis codes were used to perform themission and sizing studies for developing the Beta IIvehicle. These were the Configuration Sizingprogram (CONSIZ), the Solid Modeling AerospaceResearch Tool (SMART), the Optimal Trajectoriesby Implicit Simulation program (OTIS), and theVehicle Integrated System Analysis program (VISA).The interaction between these analysis codes isdepicted in Figure 3. Due to the complexity of theanalysis procedure, the orbiter and booster weremodeled and studied separately. A brief descriptionof the codes and the analysis procedure appearsbelow.

Orbiter sizing and weight analysis was performedwith CONSIZ (ref. 5). CONSIZ provided a flexiblemethod for calculating orbiter weight, scaling orbiterdimensions, and scaling the payload size for a fixedorbiter dry or gross weight. Weight estimatingrelations, orbiter dimensions, and orbiter packagingcharacteristics (i.e., tank efficiency, volume, etc.)were put into CONSIZ. The latter two of theseinputs were generated by the SMART code (ref. 6).SMART is a general solid modeling program for thelayout and geometric analysis of aerospace vehicles.Orbiter dimensions, volumes, and areas werecalculated using SMART. In addition, changes inorbiter dimensions resulting from the analysis wereput into SMART for visually checking sizing results.

CONSIZ was developed mainly for sizing rocketpowered vehicles. Booster sizing was thereforeperformed with VISA, a tool which simulates theaerodynamic, weight, and trajectory performance forboth rocket and airbreathing powered vehicles. VISArequires a nominal trajectory as input. Empiricalweight models modified for the technology levelassumed in this study were used within VISA to

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calculate weights and scale the vehicle based on thetrajectory. As with the orbiter, changes in boosterdimensions predicted by VISA were put intoSMART for a visual check of the analysis results.

Trajectory optimization for both the orbiter andbooster was performed with OTIS (ref. 7). OTIS isa program for simulating and optimizing point masstrajectories of various aerospace vehicles withprovisions made for free and fixed end constraints,specified waypoints, and path constraints. For thisstudy, OTIS was used to find optimal trajectorieswhile satisfying maximum dynamic pressure, engineoperation points, and staging Mach numberconstraints. Analysis of the orbiter occurred in thefollowing manner. The initial vehicle definition wasinput to CONSIZ and SMART. Orbiter grossweight, calculated using CONSIZ, and initial grossthrust were transferred to OTIS and the trajectoryanalysis was performed. The resulting burnoutweight was used to calculate the mass ratio (grossweight divided by burnout weight), which was thenpassed back to CONSIZ. Iterations were performeduntil the gross weight converged. Analysis of thebooster was accomplished using OTIS to determinethe optimum trajectory and VISA to scale the initialvehicle accordingly based on this trajectory.Iterations between OTIS and VISA were performeduntil the vehicle could complete the mission withinthe guidelines of the given propulsion system,aerodynamics, and mission constraints. Initial tradestudies were performed with OTIS and VISA in asimilar manner.

Airbreathing propulsion data was calculated in-house at NASA Lewis using the NASA EnginePerformance Program, (NEPP, previously known asNNEP89, ref. 8) for the prediction of the HSCTturbojet performance and RAMSCRAM (ref. 9) forthe prediction of ramjet performance. Vehicleaerodynamic data were calculated in-house using theAerodynamic Preliminary Analysis System (ref. 10).The results of these analyses were incorporated intothe mission studies during the refinement of theBeta-131 vehicle to produce Beta II.

Initial Trade Studies

The mission and sizing analysis of the TSTOvehicle began with two sets of studies. First, theoptimum initial thrust-to-weight for the orbiter wasdetermined. The second set of initial studies,

performed on the booster, included investigating theeffects of changing the staging Mach number anddecreasing the orbiter payload on the boosterpropulsion system. In addition, the propulsionsystem mix (ratio of turbofan to ramjet thrust) onthe booster was optimized for an all airbreathingascent to staging. The results of these studies wereused in the development of the Beta-B and Beta IIvehicles. This discussion presents the assumptionsand results of these initial studies.

Orbiter Thrust-To-Weight Optimization

As discussed above, one of the study goals was todevelop a TSTO vehicle optimized for minimumtakeoff gross weight. Designing the orbiter foroptimum staging thrust-to-weight would help obtainthis goal. Therefore, a study was conducted todetermine the optimum T/W for an orbiter similarto the USAF/Boeing Beta configuration but carryinga 10,000 lb payload. The optimum orbiter trajectoryfound with OTIS was used in VISA. The T/W ratioof the orbiter was varied and the orbiter gross weightdetermined. The results of this study are shown inFigure 4. It should be noted that the graph inFigure 4 is normalized with the optimum pointcorresponding to a relative gross weight of unity andan initial T/ W ratio of 1.17. As discussed previously,the rocket engine thrust and weight were scaled foreach orbiter T/W such that the rocket operated atmaximum thrust at staging. This thrust level wasthen maintained throughout the trajectory. Thisanalysis was repeated for various staging Machnumbers; all produced an initial T/W ofapproximately 1.17. Orbiter design at this optimuminitial T/W occurred in subsequent analyses exceptwhere the required thrust exceeded the limitations ofthe SSME. In this case, the orbiter thrust-to-weightwas allowed to vary.

Booster Propulsion System Optimization Analysis

The next set of trade studies investigated theeffects of modifying the USAF/Boeing Beta vehicleto meet the NASA Lewis study goals on the boosterpropulsion system. These modifications includeddecreasing the staging Mach number, eliminating therocket system from the booster, and decreasing theorbiter payload weight. The remaining airbreathingpropulsion system mix (ratio of turbofan to ramjetthrust) was then optimized to perform the initialascent without rocket assist for a minimum takeoffgross weight vehicle.

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The first modification made to the USAF/BoeingBeta vehicle (represented by the first bar inFigure 5) was the reduction of the staging Machnumber from 8 to 6.5. Mach 6.5 was judged as thefeasible limit for the hydrogen fueled ramjets at thetechnology level assumed in the NASA Lewis TSTOstudy. As the staging Mach number decreased,orbiter weight and size increased since it nowperformed a larger part of the mission. The physicalsize of the booster and, therefore, the boosterstructural weight, increased to accommodate thelarger orbiter. The takeoff gross weight (TOGW) ofthis vehicle (represented by the second bar inFigure 5) was therefore larger than that of theoriginal USAF/Boeing vehicle.

The next step in the study involved determiningif rocket propulsion was necessary during the boostphase of the mission. The rocket propulsion providedan Isp of 460 sec, much lower than the ramjet Isp ofapproximately 4000 sec. Therefore, eliminating therocket propulsion would potentially reduce theoverall weight of the vehicle. The size of theairbreathing propulsion systems would need to beincreased, however, to provide the thrust required toaccelerate through the transonic region. As shown inthe third bar in Figure 5, removing the rocket fromthe booster did result in a large reduction in TOGWover the configurations with rocket propulsion. Thisreduction resulted from a decrease in the propellantrequired for the booster. Employing onlyairbreathing propulsion systems for the initial ascenteliminated the need for liquid oxygen in the boosterand reduced the necessary amount of liquid hydrogenin the booster by half.

The effect of reducing the orbiter payloadcapability from 50,000 to 10,000 lb was then studied.As shown in the fourth bar in Figure 5, this resultedin a large decrease in both the orbiter weight and inthe overall vehicle TOGW. However, this reductionwas not in proportion to the payload weightreduction. This was a result of the non-linearrelation between payload weight and vehiclestructural weight.

Finally, the staging Mach number was reducedfrom 6.5 to 4.5 and the LH2 fuel used in the ramjetwas replaced with JP-7 fuel. This produced an effectsimilar to that of the first Mach number reductionfrom 8.0 to 6.5. The TOGW of the vehicle increaseddue to the heavier orbiter and the reduced Isp of theJP fueled ramjets. This effect is shown in the lastbar of Figure 5.

The results of the trade study indicated that theelimination of rocket propulsion during the initialascent was beneficial in reducing the TOGW.However, as previously discussed, the rocketpropulsion provided a large percentage of the thrustduring the boost phase of the USAF/Boeing Betavehicle. To compensate for this loss, the thrustproduced by the airbreathing propulsion systems wasincreased and optimized to produce a minimumTOGW vehicle. This was accomplished by sizing theturbofan and ramjet thrusts independently of oneanother. A family of vehicle takeoff thrust-to-weightversus TOGW curves was produced for varyingcombinations of turbofan and ramjet thrust levels.An example of this is shown in Figure 6. Each curveproduced an optimum vehicle T/W ratio, whichcorresponded to a minimum TOGW and ratio ofturbofan takeoff thrust to maximum ramjet thrust.The locus of the optimum points in Figure 6 areshown in Figures 7 and 8. Figure 7 indicates theoptimum vehicle T/W ratio was 0.55. Figure 8shows the optimum turbofan to ramjet thrust ratioto be approximately 0.60. The results of this studywere used as a guide to size the booster airbreathingpropulsion system for the Beta-B1, Beta-B2, andBeta II configurations.

Beta-B Vehicle Development

Following the initial trade studies, two TSTOvehicle concepts were identified for analysis. Bothvehicle configurations were derived from the USAFBoeing Beta study vehicle. Both would be designedto deliver and return a 10,000 lb payload to lowEarth polar orbit. Finally, both vehicles would bedesigned to perform the initial ascent utilizing onlyairbreathing propulsion. These vehicles were termedBeta-B1 and Beta-B2. Beta-B1 staged at Mach 6.5;Beta-B2 staged at Mach 4.5. The goal of the studycontinued to be the development of a vehicle withminimum takeoff gross weight utilizing 1995technology.

Vehicle Trajectory

The ascent trajectories for the Beta-B1 andBeta-B2 vehicles appear in Figure 9. The twotrajectories were very similar: the dynamic pressurewas constrained to a maximum of 1500 lb/ft 2 , theramjets began producing thrust at Mach 1, theturbomachinery operated up to Mach 3 and, unlikethe USAF/Boeing Beta vehicle trajectory, the orbiterSSME did not fire until staging. Both the Beta-B1

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and Beta-132 vehicles executed a dive near thetransonic region, trading potential energy for kineticenergy to overcome the high transonic drag of thevehicle. Both trajectories also show a period oforbiter acceleration at slightly decreasing altitudedirectly following staging before a traditional rockettrajectory was followed. This was a result of theorbiter lifting body configuration; when optimizingthe orbiter trajectory, OTIS took advantage of thelift-to-drag ratio of the orbiter (approximately 3) toaccelerate the orbiter in the atmosphere. TheBeta-131 and Beta-132 trajectories differed at thestaging point. For the Beta-131 vehicle, stagingoccurred at Mach 6.5 and at an altitude of100,000 ft. The Beta-132 staged at Mach 4.5 and87,000 ft. The altitude at staging was decreased forthe Beta-132 vehicle to produce a staging dynamicpressure of 700 lb/ft 2 . This pressure was consistentwith that of the Beta-B1 orbiter and was highenough to assure sufficient ramjet performance at thestaging point.

Orbiter Analysis and Results

The Beta-131 and Beta-132 orbiters weredeveloped to perform the design mission with aminimum gross weight. A payload bay volume of3000 0 was assumed and held constant whilescaling the vehicle. An additional 400 ft 3 was heldconstant to account for crew compartment volume.The weights of the SSME and its associated systemswere held constant as the vehicle was sized, as werepersonnel and personnel system weights. As discussedabove, a small growth margin equal to two percentof the orbiter dry weight was included in the weightof each orbiter. This value was used in the originalUSAF/Boeing vehicle definition and was retainedduring this part of the NASA Lewis analysis. Theinitial thrust-to-weight of the Beta-131 orbiter wasfixed at the optimum value of 1.17 by throttling theSSME. For the Beta-132 orbiter, however, the thrustrequired to obtain a T/W value of 1.17 was greaterthan the thrust available from the SSME. Therefore,the thrust of the SSME on the Beta-132 orbiter wasconstrained to a maximum value of 516,000 lb andthe thrust-to-weight was allowed to vary. Theresulting staging T/W for the Beta-132 orbiter was1.04. The thrust level of the SSME was heldconstant for both orbiters throughout the trajectory.

The gross weights of the orbiters are shown inFigure 10 with that of the original Beta orbiter. Asexpected, the decrease in payload weight led to alarge decrease in the gross weight of the orbiter.

Staging at Mach 6.5 produced the lightest orbiter(Beta-131) with a gross weight of approximately359,000 lb. The Beta-132 orbiter was heavier with agross weight of 498,000 lb. This was due to theincreased fuel requirements at the lower stagingMach number and to the inability to operate at theoptimum thrust-to-weight ratio. The Beta-131 andBeta-132 results are represented by the second andthird bars in Figure 10, respectively. As shown in thefigure, the fuel required for ascent from staging toorbit constitutes a large part of the orbiter grossweight for all three vehicles.

Booster Analysis and Results

The Beta-131 and Beta-132 boosters were designedfor minimum takeoff gross weight to transport therespective orbiters to staging. The orbiter volumeswere treated as fixed payload volumes for theboosters. Personnel and personnel systems weightswere held constant as was the orbiter weight. Agrowth margin equal to 2.5 percent of the boosterdry weight was included in the booster weightdefinition, as discussed above. Similar to the orbitergrowth margin, this low value was retained from theoriginal USAF/Boeing Beta vehicle definition. Thispart of the NASA Lewis study was conducted withthe propulsion and aerodynamic data developed forthe USAF/Boeing Beta vehicle (ref. 1). The fuelburned by the vehicle during takeoff, and thatneeded to return the booster from the staging Machnumber and altitude to the airfield, were notincluded in the analysis of the Beta-B boosters.These were not considered major factors in this partof the NASA study. The ramjets on the Beta-131booster were fueled with LH2. Those on the Beta-132booster utilized JP fuel.

Gross weights for the Beta-131 and Beta-B2boosters, which include the orbiter weights asbooster payload, are presented in Figure 11 withthat of the USAF/Boeing Beta booster. The decreasein orbiter payload weight again resulted in vehicleswith gross weights much lower than that of theUSAF/Boeing Beta. Staging at Mach 6.5 producedthe Beta-131 booster with a gross weight ofapproximately 641,000 lb. The Beta-132 booster,staging at Mach 4.5, was heavier with a gross weightof approximately 927,000 lb. The increased weight ofthe Beta-132 orbiter over that of the Beta-131 orbitercaused the Beta-132 booster structural weight toincrease. The Beta-131 and Beta-132 booster grossweights are represented by the second and third barsin Figure 11, respectively.

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At this point in the study, a decision was madeto determine which vehicle, Beta-131 or Beta-132,would undergo further development. The goal ofdeveloping a vehicle with a reasonable takeoff grossweight would be best achieved by choosing the lowerweight Beta-13 vehicle. This would allow for weightgrowth which could occur as the vehicle was refined.The hydrogen fueled Beta-B1 vehicle, staging atMach 6.5 with a TOGW of 641,000 lb, was thereforechosen for further study and refinement into theBeta II baseline TSTO vehicle.

Beta II Vehicle Development

The final NASA Lewis TSTO vehicle, Beta II,evolved from the Beta-B1 vehicle. This evolutionincluded: a change in the orbiter configuration, theincrease of both the orbiter and booster growthmargins, the replacement of both the USAF/BoeingBeta aerodynamic and airbreathing propulsion datawith in-house results, and the inclusion of takeoffand booster return fuel.

Beta II Configuration

The final Beta II configuration appears inFigure 12. Although Beta II is very similar to theoriginal USAF/Boeing Beta configuration, itincorporates many different design features. Due tothe elimination of both the booster rocket and thenecessity for transferring propellant to the orbiterrocket, no oxidizer is required on the booster. Asdiscussed above, the Beta II orbiter is a wing-bodydesign, unlike the lifting body orbiter found in theUSAF/Boeing vehicle. The Beta II orbiter has acylindrical body that, while decreasing thecross-range capability of the orbiter, gives greaterstructural efficiency than the lifting body design. Inaddition, the Beta II orbiter is easier to "package"into the booster because of its slimmer, cylindricalshape. Figure 12 shows that the orbiter includes afolding canard in the forward part of the body. Thisis necessary for control during landing (ref. 1).

Vehicle Trajectory

The trajectory for the Beta II vehicle appears inFigure 9. It is similar to that for the Beta-131orbiter. However, the wing-body configuration hada lower lift-to-drag ratio (approximately 2.1) thanthe Beta-131 lifting body orbiter. The orbitertrajectory therefore followed a traditional rockettrajectory directly following staging. A three-G

acceleration limit was imposed on the Beta II orbiterafter staging. Upon reaching that limit, the SSMEwas throttled to maintain a constant three-Gacceleration until orbital insertion.

Beta II Orbiter Analysis and Results

The Beta II orbiter was optimized to perform thedesign mission with a minimum gross weight. Thepayload volume, 3000 ft 3 , remained constant.Volumes and weights held fixed for the Beta-B1orbiter analysis were likewise fixed. A significantchange in the Beta II orbiter analysis was theincrease of the growth margin from 2 to 10 percentof the orbiter dry weight. This value was suggestedby Boeing as more appropriate for this vehicle typeand the technology level assumed. The stagingthrust-to-weight of the Beta II orbiter was fixed at1.17 and the SSME thrust held constant, similar tothe Beta-131 orbiter, except where the three-G limitwas imposed.

A comparison of the Beta II orbiter gross weightwith the Beta-131 orbiter weight is shown inFigure 10 (fourth and second bars, respectively). Ascan be seen, the two orbiter gross weights werenearly identical. The weight increase that resultedfrom the larger growth margin for the Beta II orbiterwas offset by the greater structural efficiency of thewing-body design. The Beta II orbiter completed themission with a gross weight of approximately359,000 lb, similar to the Beta-131 orbiter.

Beta II Booster Analysis and Results

The Beta II booster was designed for minimumtakeoff gross weight to carry the Beta II orbiter toan altitude of 100,000 ft and a staging Mach numberof 6.5. Similar to both Beta-B vehicles, the orbitervolume and weight were treated as payload and werefixed. The propulsion system on the Beta II boosterwas similar to that of the Beta-131, however, theATF turbofans from the USAF/Boeing Beta boosterwere replaced with larger turbojets (60,000 lb thrustcurrently being studied for high speed civiltransports. The appropriate propulsion data wasused in the analysis. Aerodynamic results calculatedat NASA Lewis for the Beta-131 configuration wereused in this part of the analysis in place of theUSAF/Boeing Beta results. The growth margin forthe Beta II booster was increased from the originalvalue of 2.5 to 20 percent of its dry weight. Similarto the orbiter growth margin, this value wasdetermined to be much more realistic for the

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complexity assumed in this study. Estimates of thefuel expended during takeoff and that needed forreturning the booster from the staging point to theairfield were found with OTIS and VISA and wereincluded in this part of the study.

A comparison of the Beta II and Beta-B1 boosterweights (including the orbiter weights as boosterpayloads) is shown in Figure 11 (fourth and secondbars, respectively). As can be seen, the takeoff grossweight of the Beta II booster is almost twice that ofthe Beta-131 booster. This large increase resulted inpart from the increased growth margin discussedabove. The application of refined aerodynamicresults to the study also led to an increase in thebooster gross weight. The Beta II booster body(Figure 12) had a greater fineness ratio than theUSAF/Boeing Beta booster; the width of the Beta IIbooster nacelles, however, did not decrease from thatof the Beta nacelles in the same proportion. The arearuling of the Beta II booster was thus less ideal thanthat of the USAF/Boeing booster, resulting ingreater transonic drag and an increase in grossweight. Finally, the addition of takeoff and boosterreturn fuel led to a further increase in the Beta IIbooster gross weight above that of the Beta-B1booster.

In spite of these weight increases, the Beta IIvehicle was able to complete the design mission ofdelivering and returning a 10,000 lb payload to lowEarth polar orbit with a gross weight ofapproximately 1.1 Mlb utilizing only airbreathingpropulsion for the initial ascent. Thus, the Beta IIvehicle satisfies the study goals and requirements.

Payload Capability to Space Station Orbit

The design mission to low Earth polar orbit(100 n. mi.) was chosen to maintain continuity withother similar studies. However, the ability of theTSTO system to deliver payload to the SpaceStation (28.5 degree inclination, 180 n. mi. circularorbit) and possibly to a low circular equatorial orbit(100 n. mi.), is also of interest for many futureNASA missions. Examples of these are Space Stationresupply or rescue missions and satellite servicing. Inaddition, the ability of the orbiter to carry payloadwhen forced to stage at a Mach number lower thanits design value was of interest. This would enablevehicle operation even if the airbreathing propulsionsystems on the booster were not able to meet theirpredicted high speed performance level in the near

term. The payload carrying capability of theBeta-B1 orbiter, designed for Mach 6.5 staging, wasinvestigated for three orbits— polar, Space Station,and equatorial—for staging Mach numbers rangingfrom 4.5 to 6.5. At the time this study wasimplemented, definition of the Beta II vehicle hadnot been completed. However, it was judged that theresults obtained for the lifting body Beta-131 orbitercould be extended to the Beta II wing-body orbiter.

This analysis was performed with the assumptionthat the orbiter dry weight and gross weightremained constant. Thus, neither orbiter nor boosterredesign was considered allowable. The effect ofstaging at different Mach numbers or to differentorbits on the booster gross weight was not studied.It was assumed that the orbiter would be staged inthe proper position to obtain its orbit efficiently.OTIS was used to determine the fuel required for theorbiter to reach each orbit when staging fromvarious Mach numbers. CONSIZ was then employedto determine the change in payload weight thatresulted from the differing fuel requirements.

The results of this study are shown in Figure 13.The dotted line indicates the point at which redesignof the orbiter internal packing, i.e., resizing of thefuel tanks and payload bay, would be required tofulfill the mission. For payloads above the dottedline, no repackaging would be necessary. For thosebelow the dotted line, resizing of the fuel tanks andpayload bay and repackaging would be necessary tocomplete the mission. As can be seen, performing thedesign mission to low Earth polar orbit when stagingat a Mach number below 6.5 would requirerepackaging of the orbiter. This result was expected,since the Beta-131 orbiter was designed for staging atMach 6.5. The maximum payload capability of theorbiter ascending to a nominal Space Station orbit isapproximately 17,500 lb when staging at Mach 6.5.A 20,000 lb payload could be delivered to a lowequatorial orbit at the same staging Mach number.

Future Refinements

The Beta II vehicle was developed as a baselinevehicle for further NASA Lewis TSTO studies. Theseinclude: a more detailed analysis of the Beta IIaerodynamic characteristics, particularly in thetransonic region; a detailed structural and thermalanalysis of the booster airbreathing propulsionsystem; an investigation of the optimum stagingMach number; an analysis of the takeoff and landing

8

field requirements, and a cost analysis. In addition,study of a non-cryogenic TSTO vehicle similar toBeta II is planned (ref. 2).

3. Snyder, C.A.; Maldonado, J.J.: The Designand Performance Estimates for the PropulsionModules for the Booster of a TSTO Vehicle.AIAA Paper 91-3136, Sept. 1991.

Summary

NASA Lewis Research Center investigated aTSTO vehicle called Beta II. Beta II was derivedfrom the USAF/Boeing Beta study vehicle, also aTSTO system. In accordance with study guidelines,Beta II was developed using near-term (i.e., 1995)technology to deliver and return a 10,000 lb payloadto low Earth polar orbit. In addition, it wasdetermined that the boost phase of the mission, fromtakeoff to Mach 6.5 and 100,000 ft, could be com-pleted using only airbreathing propulsion systems.Beta II was shown to be capable of completing thedesign mission while meeting study requirements andgoals with a minimum takeoff gross weight ofapproximately 1.1 Mlb. This result, slightly greaterthan large commercial transports, was judged to bereasonable for this vehicle type. The optimum initialthrust-to-weight of the Beta II orbiter was found tobe 1.17; the minimum gross weight of the Beta IIorbiter at this T/W was shown to be approximately359,000 lb. In addition to completing its baselinemission, the Beta II vehicle was shown to be capableof delivering approximately 17,500 lb to the SpaceStation.

The Beta II TSTO vehicle provides a baseline forfuture NASA Lewis studies. Further investigation ofthe Beta II characteristics will lead to a betterdefined vehicle as well as provide information whichcan be used in similar TSTO studies.

4. Midea, A.C.: Mach 6.5 Air Induction SystemDesign for the Beta II Two-Stage-to-OrbitBooster Vehicle. AIAA Paper 91-3196, Sept.1991.

5. Lepsch, R.A.; Stanley, D.O.; Cruz, C.I.;Morris, Jr., S.J.: Utilizing Air-Turborocket andRocket Propulsion for a Single-Stage-to-OrbitVehicle. AIAA Paper 90-0295.

6. McMillan, M.L.; Rehder, J.J.; Wilhite,A.W.; Schwing, J.L.; Spangler, J.; Mills, J.C.:A Solid Modeler for Aerospace Vehicle Design.AIAA Paper 87-2901, Sept. 1987.

7. Vlases, W.G.; Paris, S.W.; Lajoie, R.M.;Martens, P.J.; Hargraves, C.R.: OptimalTrajectories By Implicit Simulation Version2.0. WRDC-TR-90-3056, Dec. 1990.

8. Plencner, R.M.; Snyder, C.A.: TheNavy/NASA Engine Program (NNEP89)—AUser's Manual. NASA TM-105186, 1991.

9. Burkardt, L. A.; Franciscus, L. C.:RAMSCRAM—A Flexible Ramjet/ScramjetEngine Simulation Program. NASA TM-102451,1990.

10. Bonner, E.; Clever, W.; Dunn, K.; Divan, P.;Sova, G.: Aerodynamic Preliminary AnalysisSystem II, Parts I and II. NASA CR-182076,182077, Apr. 1991.

R eferPn rPc

1. Paris, S.W.; Wetzel, E.D.; Meadowcroft, E.T.;Weldon, V.A.; Kotker, D.J.; Williams, D.P.;Dunn, B.M.; Twitchell, S.; Vlases, W.G.:Research Vehicle Configurations forHypervelocity Vehicle Technology. WRDC-TR-90-3003, Volumes I and II, Apr. 1990,Volume IIA, July 1991.

2. Plencner, R.M.: Overview of the Beta II Two-Stage-to-Orbit Vehicle Design. AIAA Paper91-3175, Sept. 1991. Figure 1. USAF/Boeing Two-Stage Beta Vehicle.

9

USAF/Boeing BetaGrose Weight . 2.0 MIbStaging Mach a 8.0Payload .60,0001bBooster Propulsion a 8 ATF Turbofans/ 2 Ramjets/ 1 SSMEOrbiter Propulsion a 1 SSME (2 position nozzle)

Initial Trade Studies Performed with Intermediate Vehicle:- Optimize Orbiter Thrust-to-Weight- Optimize Booster Propulsion System

Staging Mach 6.6

NASA Beta-B1

Gross Weight a 0.64 MlbPayload • 10,0001bBooster Propulsion a 8 ATF Turbofans/ 2 RamjetsOrbiter Propulsion . 1 SSME

Mach 4.6

NASA Beta-B2

Gross Weight a 0.93 MlbPayload a 10,000 lbBooster Propulsion a 8 ATF Turbofans/ 2 RamjetsOrbiter Propulsion • 1 SSME

Vehicle Refinements:- Redesign Orbiter- Increase Growth Margin- Incorporate New Aerodynamics

and Propulsion Data- Account for Booster Takeoff

and Return Fuel

NASA Beta IIGrow Weight a 1.1 MlbStaging Mach . 6.6Payload a 10,0001bBooster Propulsion . 10 HSCT Turbojets/ 2 RamjetsOrbiter Propulsion a 1 SSME

Figure 2. Progression from USAF/Boeing Betato NASA Lewis Beta H.

10

CONSIZ I_ Vol.. Areas , SMART

.^—^ Orbiter Analysis

Booster Analysis

OTIS 1 (Mach, Alt.) '— I VISA

Figure 3. Data Flow Between Analysis Programs.

1.25

on 1.2

!a^

m 1.15

1.1

D

4(95 L

.4 .6 .8 1 1.2 1.4 1.6

Thrust to Weight Ratio (T/W)

Figure 4. Gross Weight of an Orbiter WithVarying Staging Thrust-to-Weight Ratio.

12Q Orbiter

1 Booster Structure

Booster Fuel8 Booster Oudiuer

6

P42

0-Payload (klb) 60 60 60 10 10Stage Mach 8.0 6.6 6.6 6.6 4.6

Airbreathing T/W .144 .154 .626 .670 .606Boost Rocket T/W .472 .604 0 0 0Boost Propellants JP/H2/02 JP/H /O JP/H s JP/H 2 JP

Figure 5. TOGW for Various BoosterPropulsion System Configurations.

11

.400

a

WH

0O

a^

Takeoff Thrust To Weight Ratio (T/W)

Figure 6. Optimal Booster T/W andTurbojet to Ramjet Thrust Ratio.

.oa

.06

.04

.02

1

.98.3 .4 s .D J .9

Takeoff Thrust To Weight Ratio (T/W)

Figure 7. Relative TOGW for BoosterWith Varying Thrust-to-Weight Ratio.

F ^

D

4 ,

300000

Beta-B2

4

Manmum Ramjet Thrust

Figure 8. Relative TOGW for Booster WithVarying Turbofan /Ramjet Thrust Ratio.

Orbiter200000 Beta II

Beta-B1M 160000

^

Staging

100000

60000Booster

00 6 10 16 20 26 30

Mach

Figure 9. NASA Lewis Beta Trajectories.

12

D PayloadOrbiter FuelGrowth MarginEmpty Wt.

C

CA

mm

ChN

Mated Configuration

Redesign Required

C 20000bp 16000

Q, 10000

6000

0

-6000

Equatorial Orbit

Space StationOrbit

Polar Orbit

USAF Beta-B1 Beta-B2 Beta IIBeta

Figure 10. Gross Weight of NASA Lewis Orbiters

USAF Beta-BI Beta-B2 Beta IIBeta

Figure 11. Gross Weight of NASA Lewis Boosters.

Booster Stage Orbiter Stage

Figure 12. NASA Lewis Beta II General Layout.

26000No Redesign Required

4.6 6 6.6 6 6.6

Stage Mach Number

Figure 13. Beta-BI Orbiter Payload Capabilityfor Various Orbits.

13

Form Approved_FREPORT DOCUMENTATION PAGE OMB No. 0704-0188Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources.gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of thiscollection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for information Operations and Reports, 1215 JeffersonDavis Highway, Suite 1204, Arlington. VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.

1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 3- REPORT TYPE AND DATES COVERED

1992 Technical Memorandum4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Mission and Sizing Analysis for the Beta 11 Two-Stage-to-Orbit Vehicle

W U —505-69-406. AUTHOR(S)

Shari-Beth Nadell, William J. Baumgarten, and Stephen W. Alexander

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATIONREPORT NUMBER

National Aeronautics and Space AdministrationLewis Research Center E-6883Cleveland, Ohio 44135-3191

9. SPONSORING/MONITORING AGENCY NAMES(S) AND ADDRESS(ES) 10. SPONSORING/MONITORINGAGENCY REPORT NUMBER

National Aeronautics and Space AdministrationWashington, D.C. 20546-0001 NASA TM— 105559

Corrected Copy

11. SUPPLEMENTARY NOTES

Prepared for the 1992 Aerospace Design Conference sponsored by the American Institute of Aeronautics and Astronautics,Inc., Irvine, California, February 3-6, 1992. Responsible person, Shari-Beth Nadell, (216) 977-7035.

12a. DISTRIBUTION/AVAILABILITY STATEMENT 12b. DISTRIBUTION CODE

Unclassified - UnlimitedSubject Categories 15 and 5

13. ABSTRACT (Maximum 200 words)

NASA Lewis Research Center studied a horizontal takeoff and !anding, fully reusuable, two-stage-to-orbit (TSTO)vehicle capable of launching and returning a 10,000 pound payload to low Earth polar orbit using low-risk technology.The vehicle, called Beta 11, was derived from the USAF/Boeing Beta vehicle, a TSTO study vehicle capable of launchinga 50,000 pound payload to low Earth polar orbit. Development of Beta II from the USAF/Boeing Beta vehicle occurredin a series of iterations during which the size of the vehicle was decreased to accommodate the smaller payload, thestaging Mach number was decreased from 8.0 to 6.5, and the rocket propulsion system was removed from the booster.The final Beta 11 vehicle consisted of a rocket powered orbiter and an all airbreathing booster. The gross takeoff weightof the Beta 11 vehicle was approximately L I million pounds. In addition to its baseline mission, the Beta If vehicle wascapable of delivering approximately 17,500 lb to the Space Station with the same takeoff gross weight. The mission andsizing analysis performed to arrive at the Beta 11 vehicle is discussed.

14. SUBJECT TERMS 15. NUMBER OF PAGES

Aircraft design; Airbreathing boosters; Reusable launch vehicles; Hypersonic aircraft 1616. PRICE CODE

A0317. SECURITY CLASSIFICATION 18, SECURITY CLASSIFICATION 19. SECURITY CLASSIFICATION 20- LIMITATION OF ABSTRACT

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