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THE REUSABLE LAUNCH VEHICLE TECHNOLOGY PROGRAM AND THE X-33 ADVANCED TECHNOLOGY DEMONSTRATOR
Stephen A. Cook* RLV Technology Program Marshall Space Flight Center Huntsville, Alabama
BACKGROUND An all-rocket SSTO vehicle appears to be the best blend of near-term achievable technology an affordability for low-cost The next generation of U.S. launch vehicles routine space access after the turn-of-the- must dramatically lower the cost of space century. It is an evolutionary, not access. Today, many promising space revolutionary., path that relies on 25 years of missions and experiments are grounded aerospace experience to mature and because of overwhelming launch costs-- demonstrate several advanced technologies only the Nation's highest priority payloads needed to make a new reusable launch are being launched. The cost of space vehicle a cost-effective reality. transportation consumes so many resources (budget, talent, and facilities) that too little remains to undertake the bold endeavors that PROGRAM GOALS AND push technological advancements and OBJECTIVES inspire the imagination and spirit. Reducing the cost of space access would spur the The goal of the Reusable Launch Vehicle Nation's competitiveness and its industrial (RLV) technology program is to mature the might. technologies essential for a next-generation reusable launch system capable of reliably Today's launch systems have major serving National space transportation needs shortcomings that will increase in at substantially reduced costs. significance in the future, and thus are principal drivers for seeking major The primary objectives of the RLV improvements in space transportation. They technology program are to (1) mature tile are too costly; insufficiently reliable, safe, technologies required for the next- and operable; and increasingly losing market generation system, (2) demonstrate the share to international competition. For the capability to achieve low development and United States to continue its leadership in operational cost, and rapid launch the human exploration and wide ranging turnaround times and (3) reduce business utilization of space, the first order of and technical risks to encourage significant business must be to achieve low cost, private investment in the commercial reliable transportation to Earth orbit. development and operation of the next- generation system. The space launch industry is at a crossroad much like the one faced by the fledgling Developing and demonstrating tile airline industry in the early 1930's. An technologies required for a Single Stage to evolutionary technical leap, coupled with a Orbit (SSTO) rocket is a focus of the revolutionary cultural shift, must be made-- program because past studies indicate it has analogous to the DC-3 aircraft--for space the best potential for achieving the lowest launch to become truly routine. NASA's space access cost while acting as an RLV Access to Space Study, in 1993, technology driver (since it also encompasses recommended the development of a fully the technology requirements of reusable reusable single-stage-to-orbit (SSTO) rocket rocket vehicles in general). However, the vehicle as an Agency goal. private sector may ultimately choose the operational RLV configuration to be llown * Senior Member, AIAA Page 2
post-2000 that can compete in an health management/monitoring. Initial internationalmarket. activities are a balance of laboratory experiments, ground testing, and flight testing to establish the capability/limits of Concept Definition candidate solutions. Later efforts (post 1996) begin to develop hardware for flight The concept definition studies develop testing on an advanced technology system sensitivities for the flight vehicle and demonstrator - X-33. technology demonstrator systems and identify the enabling vehicle technology Operations Technologies requirements (i.e., targets). The concept studies will focus on SSTO rocket-powered Operations technologies include operations concepts. Emphasis will be placed on enhancement technologies (e.g., health development, operational costs, and maintenance systems, etc.) and advanced performance. The concept definition avionics (e.g., automated flight control). A process will: goal of the operations enhancement area is to develop and demonstrate technologies • Evaluate the merits of vehicle concepts that will permit automation and the reduce for a given set of mission and system manpower requirements associted with: requirements --with a focus on reduced between flight maintenance, the launch operations costs. complex, and required ground based flight • Provide the operating environments and operations support. A goal of the advanced targets for the candidate technologies as avionics area is to shift the more of the a means for evaluation of the readiness responsbility for mission control from the of the candidates. ground to the flight vehicle.
Propulsion Technologies For the first time within space launch vehicle programs, a detailed reliability, This technology area develops and maintainability, and supportability (RM&S) demonstrates the operational and app,;oach will be established. The RM&S performance characteristics of engine and Program will be carried through the entire main propulsion systems, and defines technology and X-33 / X-34 program derived requirements for an operational development. These are focused on assuring propulsion system. Key obiectives for the that the vehicle can indeed be operated in an RLV propulsion system must be robustness, efficient and cost-effective manner. In operability, high thrust-to-weight ratio, and addition to these specific technology tasks, an affordable development program with the requirements to achieve low operations acceptable risk. The technology component costs (i.e., minimal personnel and cost for development will validate design capability, refurbishment, inspection, and prelaunch define component hardware response, and processing) will be integrated into the other demonstrate manufacturing processes. technology areas.
Vehicle Structural Technologies Flight Demonstrators This program area addresses technology maturation for reusable cryogenic tank Flight demonstration is a key and integral systems, reusable composite primary part of the overall RLV technology program. structures, and thermal protection systems. It is clear that flight demonstration will force The goal is to demonstrate representative the real technology development issues to systems which are manufacturable, operable, surface early m the program, thus and traceable/scaleable to an SSTO system. minimizing technical issues during the more The efforts focus on the integration and life costly full scale development phase. The cycle demonstrations of the load carrying overall objectives which are common to all structure, cryogenic insulation (as required), three demonstrators (DC-XA, X-34, and X- thermal protection material, and associated 33) include: Page 3
• Provide an integrated systems testbed RLV Technology Program Phase I (1994 - for advanced technologies 1996) • Demonstration of capabilities in realistic ground and flight environments The primary objective of the Phase I effort is of a next generation system to demonstrate capability to achieve low • Demonstration of operability, opt:rational cost by bringing a wide range of maintainability, and reusability required tecnnology candidates to a level of maturity for a next generation system sufficient to permit a narrowing of • Demonstration of mass fraction scalable component and materials choices to permit to a full-scale SSTO (X-33 only) cost effective large scale (Phase II) • Demonstration of rapid prototyping technology demonstrations. A prime • Demonstration of the ability to perform emphasis in this activity is demonstration of "faster, better, cheaper" attributes that will enable low operational costs. Multiple technology system concepts will be evaluated in scaled relevant RLV TECHNOLOGY PROGRAM environments. Results will be used to IMPLEMENTATION validate the analytical models which will permit the construction of large scale ground The RLV technology program is an and flight systems in Phase II. The integrated, fast-track approach for reducing technology elements in Phase I range from the technical and business risk in developing subscale materials and components to economical, operational, reusable launch approximately one-third scale hardware that vehicles. An integrated ground and flight can permit concept selections to be made. test program is being implemented to The following technology areas are being characterize key component technologies addressed in this phase: and to validate their systems' capabilities, both from a performance and operations Operations Technologies viewpoint. The program will develop and Graphite Composite Primary validate vehicle, propulsion, and operations Structure technologies. The integrated program is Reusable Cryogenic Tanks shown on Figure l -- RLV Technology Long Life/Low Maintenance TPS Implementation. Advanced Propulsion Systems.
To commit to specific component RLV Technology Program Phase II (1996 technologies for both the flight - End of Decade) demonstrators and the full-scale operational vehicle, it is necessary to demonstrate that In Phase II, large scale hardware will be components have robust and well- developed with a focus the X-33 Advanced understood design margins relative to the Technology Demonstrator (ATD) vehicle. applications for which they are intended. The X-33 is an integrated ground and flight Thus, the ground test program will entail operations demonstration of the critical cycling of the candidate components under technologies required for a SSTO RLV. The realistic environmental conditions to technology development and demonstration establish the acceptable number of flight activities will be focused on flight cycles before deterioration, or failure of the demonstrations of the X-33, supported by components will occur. appropriate ground test. The design of the X-33 and ground test articles will be based The flight test demonstration program (DC- on the results of the Phase I technology XA, X-33, and X-34) will be implemented system selections. Phase II designs will to identify component and system more accurately represent full-scale RLV integration issues in the RLV program that components and will be subjected to more are unresolved by ground test and to confirm realistic flight environments. Ability to the environments that are employed in the achieve low cost operability targets must be ground tests. Page 4
(_ Definition I1_
• X-33 Trades • Ealpae Concept Selec_on • Operations EvaluaUon
• Prlvle Financing • Pohcy aad/_" LegiJtlaaon Reqt_
• _on Period
Figure 1.-- RLV Technology Implementation demonstrated by the X-33. In addition to the technologies that offer the potential for issues addressed in Phase I, SSTO mass expediting the development of technology fraction will be demonstrated. for future next-generation engines will be investigated. Ground-based subscale engine Business and technical information and main propulsion systems demonstrations developed at the end of this phase will will provide a testbed for demonstration of permit Government / private sector decisions operability and performance targets and will on development and operation of a next permit extrapolation of targets from ,generation launch system. demonstrated conditions to full scale. A technology component development activity Propulsion Technologies will validate design concepts, define component hardware response, and Propulsion technology efforts will demonstrate cost-effective manufacturing demonstrate the operational and processes. performance characteristics of candidate engine and main propulsion systems and Candidate engine systems currently define and establish a set of derived identified for reusable vehicles include both requirements for an operable propulsion bipropellant (e.g., LO2/LH2) and ,_vstem. Key targets for the next-generation tripropellant (e.g., LO2/LH2/RP- 1) engines. propulsion system are robustness, Initial studies indicate that tripropellant or operability, high thrust-to-weight ratio, and advanced bipropellant (high thrust-to-weight an affordable development program with configurations) propulsion systems are acceptable risk. Both U.S. and foreign required to achieve sufficient design Page 5
margins. Engine conceptsbeing evaluated corrosion concerns, nonpressurized airframe include a Space Shuttle Main Engine structures will be constructed of graphite (SSME)-derived dual bell, an advanced composite, drawing on current aircraft and aerospike, an advanced full-flow-staged rocket designs. These include both low- and combustion cycle single bell for high-temperature composites. TPS bipropellant,an SSME-derivedbell-annular candidates for acreage areas include both concept,anRD-704-derivedconcept,andan ceramic and metallic concepts. Leading RD-0120-derivedconceptfor tripropellant. edge, nose cone, and control-surface Key technologiesfor all of theseconcepts material candidates include advanced include LO2 rich compatible materials, carbon/carbon and CMC. modularcombustionchamberdevelopment, Table 1 provides an overview of major and the use of advancedCeramic Matrix products in 1995 and 1996. Composite(CMC) materialsin component designs. Table 1 provides an overview of Operations Technologies majorproductsin 1995and1996. To meet the fundamental goal of affordable access to space, a major emphasis will be Vehicle Structural Technologies placed on realizing significant savings in operations cost through advancement in Vehicle structural technologies encompass operations and maintenance technologies reusable cryogenic tank systems, graphite- and processes. Fast turnaround times, small composite structures, and Thermal ground crews, and airline-type maintenance Protection Systems (TPS). The efforts focus will permit operations costs to drop on the operability and integration of the dramatically. load-carrying airframe structure, cryogenic insulation (as required), thermal protection Automated operations technologies will be material, and associated health management applied to the streamlining and simplifying for the next-generation system. Early of the ground and flight operations of the (1994-96) activities will be a balance of next-generation system to achieve cost and laboratory experiments, ground testing, and performance goals. Technologies include flight testing to establish the operability, automated checkout, vehicle health performance, and limits of candidate management/monitoring systems, solutions. Foreign technologies that offer autonomous flight controls and "smart" the potential for expediting the development avionics/guidance navigation. Incorporation of advanced technology for future structural of process enhancements such as one-time systems will be investigated. Later efforts flight certification, hazardous materials (1996-99) will focus on the development of elimination, ground-scheduling systems, and large-scale hardware for flight testing on the a philosophy of reliability-centered X-33. maintenance and minimum operations between flights will contribute to an aircraft- The reusable rocket must return from orbit like operations process. A detailed with its cryogenic propellant tanks, reliability, maintainability, and presenting complex thermal-structural supportability approach will be established challenges. Issues associated with life-cycle and executed throughout the program to effects on the integrated tank system--tank ensure that the vehicle can indeed be wall, cryogenic insulation, and TPS--must operated in an efficient and cost-effective be addressed. Aluminum-lithium (alloys) manner. and graphite-composite tank materials are being considered. To significantly reduce structural mass and alleviate fatigue and Page 6
• Structur,ml and lrPli CY 1985 CY 1898
- P4,.,s_:_e c_ Tank DC-XA G_-Comp. LH2 Tank 8ys. (IdDA) sub-scan Gbr-Comp. LH2 Tank Sys. (Rq CC-XA Ruemn A_LI LO2 Trek SyL-2 (MO/_ StA)-Sclm G¢-Como. LO2 Tank Syl. (MOA) Gr_ LO2 _ (MC_k) Remlable C_/o Irmu/tlon (MOA and RI) Cyro Tank Panele (RI)
- Grephce CompoW.re Pru_w_ S_ure EIC:-XA Inl41tfflrlk (MDA) SulPSca_ tn_ortank Sys. (MDA) Intedank, Wing, and Thud $lr_'luro S,ub-Sea_ IIio_r_ Intertank (MDA-Rtnman) Componim_ and Elements= (RI) PllTamp CompoWta Structure= (MDA) Fu¢ Sle S_ Sy_ Sogrr_t (RI) Ful Scale _ Strucka'e _ Segment (RI) Ful S¢_o W_ 0 SynL Section (RI)
- TPS Inlerf_l Multlocreofl Imltdatlon (M[_t) Plant Artlyl (MD_) Metd/¢ Panehl (MOA) CtSK_ Pan_ Array_ (MDA) C/SIC Pinto (MOA) TAB Pm _ (Rt) TABI _ (RI) TAB _# MLI Panel Arrays (RI) TABI Blanlm_ w0MLI (RI) W-'eqocoo_ng Demo (R0) Allachm_tntT_ Aftk:hNm(AE'r'IB,CMC. RI)
cm_ _ter (_ukn Td-Pm_ _ (Aan:_q • PPopubion Plmllve LO2 Co¢_lllo_tg (MMC) 40 K Nozzle Exlon_K>n (Fiber Mat'ls&RCI) - Main P_opuls=on System LO2 _ Pmve_tlon {MMC) Unl_ll_l Td-Prop lnioclo¢ (Penn State) 10 Elemenl Td-Prop Injector (P&_rJ Uni_emlmt Ox RIoh Ir_'_ (Penn State) Un_ Td-Prop Inject_ (Penn State) Modul_ Comlxmlo_ Cl_ml)em (R'dy_) Unlelecne_ Ox Rich Inlact_ (P_ Stale) Ox Rich Tu_4rm Dm_ (R'dyne) Modu/r _ion Cha_ (R'dyne) Imlogfalocl BI-Prop Prop. Sy_em Tull:,od (RI) Ox Rich Turbllne Drlvo (R'dyml)
Llq-Gll Coeweflion System (MOA) RCS C_ Ma_l Prop' (Fib_ Mat'h_RCI) O2/H2 APU (MDA) - Aumllary Pr'of_lsK>n _ Comp(x_a Valve Body (MDA) I_eormeaDC-XJled-XA Pallet (MDA)MD ,_: Syllmm Incta Table l -- Key 1995 and 1996 Technology Products Flight Demonstrations tank, (2) composite liquid hydrogen tank, (3) cornposite intertank structure, (4) integrated Because they are an integrated system, flight auxiliary propulsion system consisting of a demonstrations force the key technology liquid-to-gas conversion system, (5) development and operations issues to surface, thus minimizing technical and operational risk during the more costly next- modified auxiliary power unit, and (6) =enerat]on-system development phase. hydrogen leak-detection sensors. Each of These are also the key testbeds for proof-of these components will be built to technical system operability and rapid turnaround specifications traceable and scalable to a times. The following paragraphs describe next-generation system and will undergo the planned demonstrators and their ground-checkout testing prior to installation respective roles in the development and in the DC-XA vehicle for mid-1996 flight demonstration of RLV technologies. testing. Testing of the upgraded technology components in flight and natural DC-XA - Experimental Advanced environments will be used to demonstrate system operability. The McDonnell Douglas Delta Clipper- Experimental (DC-X) vehicle, developed X-34 Small Booster Technology and initially demonstrated by the Ballistic Demonstrator Missile Defense Organization, will be The X-34 will be used to investigate transferred to NASA, and advanced technologies that may be incorporated into technology upgrades will be installed, future reusable launch vehicles. This reconfiguring it as the DC-XA. The program, which will be jointly funded with following technology components are the commercial launch industry, minimizes currently planned to be incorporated into the development uncertainties and accelerates vehicle: (1) aluminum-lithium liquid oxygen timetables for validating less costly, more operable and reliable small booster vehicle Page 7 componentsandflight test articles. Orbital minimum, the X-33 will be an autonomous, SciencesCorporation(OSC)wasselectedon suborbital, experimental, single-stage rocket March6, 1995asthedeveloperof theX-34. flight vehicle. As shown in Figure 2, three basic classes of X-33/SSTO are being The X-34 will benefit the overall RLV investigated: vertical takeoff, horizontal programsince it offers the prospectof an landing (VTHL) wing-body, vertical early testbed, including a realistic flight takeoff, horizontal landing (VTHL) lifting- environment, for some of the advanced body, and vertical takeoff, vertical landing componentsthatcould beusedfor thenext- (VTVL) concepts. generationsystem. Thesecomponentsand systemspotentiallyincludethefollowing: • Advanced thermalprotectionsystems (high-temperature nose cap and leadingedges), • Advanced avionics and flight-control /¢ing Body Lifting Body systems,including autonomousreentry andlanding, • Vehicle health monitoring systems, and • Groundoperations/rapidturnaround. i1 Just as important as the technology that it will demonstrate,theX-34 providesanearly Vertical Lander opportunity to demonstrate streamlined managementandprocurement,industrycost Figure 2.-- Basic Classes of X-33/SSTO sharing and lead management, and the Concepts economics of reusability. The X-34 is a logical precursor to a full-scale next- generationreusable launch system. During Phase I, a competitive X-33 concept definition/design activity combined with X-33 Advanced Technoloev Demonstrator --v ongoing technology developments and demonstration, will culminate in the The X-33 is an experimental SSTO rocket downselection of the X-33 concept in FY proof-of-concept demonstrator. The X-33 1996. A wide range of technology system must prove the concept of a next- candidates will be demonstrated to a level of generation system by demonstrating key maturity sufficient to reduce the number of technology, operations, and reliability alternatives, enabling the design and requirements in an integrated flight vehicle. development of a cost-effective, large-scale This program will implement the recently technology demonstrator. Sufficient data released National Space Transportation must be available by the summer of 1996 to Policy, specifically Section III, paragraph support the decision to proceed into the final 2(b): "Research shall be focused on design/development and flight test of the X- technologies to support a decision no later 33 (Phase II). Business and operations than December 1996 to proceed with a sub- planning results from this activity, when scale flight demonstration which would combined with the design maturity and prove the concept of single-stage to orbit." technology status, will serve as major elements in the selection process. Three Critical characteristics of SSTO systems, industry teams were selected on March 6, such as the structural/thermal concept, 1995 to compete during this phase to aircraft-like operations and maintenance develop the X-33: Lockheed/Martin, concepts, flight dynamics, flight loads, McDonnell Douglas / Boeing, and ascent and entry environments, mass Rockwell. fraction, fabrication methods, etc., will be incorporated into the X-33 system. As a Page 8 In Phase II, and based on a Presidential contractual vehicles, such as cooperative decision to proceed, the X-33 will serve as agreements for this joint the flight testbed for large-scale elements of Government/industry ventures approach. critical RLV technologies and is the focus of Both industy and government partners the program leading to the next-generation- contribute cash (or IR&D), in-kind, and system decision by the end of this decade. manpower resources to the effort. This phase will consist of the final design, fabrication, assembly and test of the X-33 Marshall Space Flight Center (MSFC) will system. The X-33 vehicle will be flight serve as the host Center for the program, tested, using a flight envelope expansion which will draw upon the resources of other process and will demonstrate "aircraft like" NASA Centers and the U.S. Air Force operations (minimal ground crew size, short (USAF) to support the effort. The RLV turnaround times, etc.). Flight testing will program will be managed by a small be accomplished at an appropriate test range. program office. Government and contractor Complementary ground based personnel will be minimized in order to demonstrations will round out the demonstrate the effective streamlined technology development efforts required for management approach necessary to reduce the next generation system. development and operations costs. This approach will incorporate the experience The end of the decade decision could result gained from the DC-X program. in an operational vehicle in the 2005 timeframe. However, depending on the The USAF has been designated as the DoD success of the technology development organization which will coordinate and program, the initial next-generation- system manage related DoD investments, including operations date could be sooner. RLV technologies. The cooperative NASAJUSAF technology program will Table 2 describes the minimum set of provide the technology base for future technical requirements for the X-33. A set related applications of both agencies. The of initial requirements for its corresponding USAF, with its expertise in aircraft operational SSTO rocket are shown and are operations, maintenance, and flight testing, subject to later trades to be performed during will bring these complementary disciplines Phase I. to the cooperative RLV activities. With these capabilities, the USAF will provide An overarching requirement is that the X-33 leadership in the RLV flight demonstration system, subsystems, and major components program tbr operations concepts, performing will be designed and tested so as to ensure flight-test range facilitation, flight-test their traceability (technology and general planning, and flight-test operations. design similarity) and scaleability (directly scaleable weights, margins, loads, design, The DC-X program, which preceded this fabrication methods, and testing approaches) effort, was executed by DoD by the to a full scale SSTO rocket system. aggressive application of similar management concepts and principles. PROGRAM MANAGEMENT NASA intends to adapt its internal The NASA RLV technology program is procedures and its relationship with industry being executed in cooperation with the and DoD and apply these concepts and Department of Defense (DoD) and by principles to the RLV program. involving the private sector as partners in planning and evaluating the activities. The The new model for the relationship among management approach provides a full NASA, industry, and DoD is a partnership. understanding of the cost, schedule, and The concept of a partnership embodies development risks before decisions to mutual responsibility for the effort, mutual proceed are made. benefit from the research and design efforts, and mutual contribution of assets to the NASA's approach of forging partnerships execution of the effort. with industry will be reflected in the use of Page 9 Table 2: Minimum X-33 and Corresponding SSTO Requirements Corrt$ ponding X-33 SSTO CAPABLE Performance • Suborbital, reusable rocket-based flight system REQ N/A i • Mission Applications: N/A REQ -- Payload Delivery: Government (Civil/Military) and Commercial Missions. -- Capable of delivering/returning cargo and crew complement to/from the International Space Station (ISS) in accordance with ISS requirements (e.g., minimum sizes, loads, schedule) • • ISS located at 220 nmi (244 nmi max) Altitude and 51.6 ° Inclination. • • Current esthnated payload delivery requirement: 20-25,000 Ibm Launck and Flight Operations • Automated pre-flight and flight operations (launch, ascent, on-orbit, _Q r_Q reentry, landing) • The flight vehicle shall be capable of safely aborting to the launch site GOAL REQ during the ascent phase if required • 7 day maximum mission duration N/A REQ • 7 day ground processing time from landing to launch. GOAL GOAL • 3.5 day ground processing time from landing to launch for reflight under GOAL GOAL emergency conditions. On.Orbit Operation: • The system shall be able to autonomously rendezvous and station keep N/A As REQ with the International Space Station and other orbital spacecraft. • The system shall be able to autonomously dock payloads with the N/A REQ International Space Station. Accommodate Payloads • The flight vehicle shall provide standardized structural, mechanical, N/A REQ electrical, communications, and other interfaces to payload. • 15 ft diameter x 30 ft long cargo bay N/A REQ OPERABLE Schedule Dependability • The probability of launching within TBD days of scheduled is 0.95 GOAL REQ Responsive • Maximize robusmess to adverse weather conditions. REQ P,EQ Supportable • Launch and landing at same location (nominal condition). REQ REQ • The flight vehicle shall be capable of unplanned landing at alternate GOAL _EQ landing sites with minimal support equipment/facilities, e.g. -- No existing cryogenic facilities, launch stands/equipment, etc. -- Self-ferry of flight vehicle between landing and launch sites (add-on engines, landing/n,av lights, etc. equipment allowed). Maintainable • To the extent practical, on-board subsystems required for the flight GOAL REQ vehicle shall be field repairable/replaceable. • Equipment required to repair, process and return vehicle to launch site GOAL REQ shall be transportable. RELIABLE • 0.995 Probability of safe recovery of the flight vehicle per mission. N/A REQ • 0.999 Probability of safe recovery of the human passengers per mission. N/A _Q REQ: Requirement / GOAL: Desirable Attribute N/A: Not Applicable