UNCLASSIF IE D//PW r^UF F TCTW ^^S^^TCE T Defense Intelligence Reference Docum ent Acquisition Threat Support March 2010 : 1 D ecember 2009 .-08-1001-006 Space Access: W here W e've Been . . . and W here W e Could G o UNCLASSI F IE D //rOH OFFIC IAL USE 8NW UNCLASSIF IE D//rQn OFFIC IAL UPC ONC T Space Access: W here W e've Been . . . and W here W e Could G o Prepared by: Acquisition Support Division (DW O-3) Defense W arning Office Directorate for Analysis Defense Intelligence Agency Author: AAP Person 67 Adm inistrative Note COPYRIGH T WARNING: Further dissemination of the photographs in this publication is not authorized. This product is one in a series of advanced technology reports produced in FY 2009 under the D efense Intelligence Agency, D efense W arning O ffice's Advanced Aerospace W eapon System Applications (AAW SA) Program. Comments or questions pertaining to this document should be addressed to|AAP Person 1 ~[ AAW SA Program Manager, D efense Intelligence Agency, ATTN: CLAR/D W O -3, Bldg 6000, W ashington, D C 20340-5100. UNCLASSIF IE D//rQn OFFIC IAL UG E ONLY UNCLASSI F I E D//TO R OmC IAL USE ONLY ■ Contents Introduction................................................................................................................v Propulsion Perspective.................... 1 H ypersonic Configuration Concepts....................................................... 2 Therm odynam ics and M aterials.............................................................. 16 The Qu Tube................................................................................................ 23 Rocket Propulsion....................................................................................... 25 Up-and-Down Operations.........................................................................................30 Launch Options.............................................. 33 Atm ospheric Variations..................................................... 35 Conclusion.............................. 37 Appendix A: H istorical Perspective...................................... 43 Appendix B: Aeropropulsion Integrated Vehicle............................ 46 Appendix C: TAV Operational Costs................................. 47 Appendix D: Landing E llipses for H ypersonic G liders..............................................48 F igures F igure 1. H ardware F low............................................... vi F igure 2. Im pact of Air-Breathing Rocket..................................................................1 F igure 3. H SVS H ypersonic Cruise Aircraft Showing True Skin Tem perature ...........3 F igure 4. H ypersonic Rocket-Powered G lider H ypersonic Air-Breathing Cruiser.....4 F igure 5. Delta-Lifting Body Designs..................................... 5 F igure 6. M artin M arietta X -24 A & B Research G liders...................... 7 F igure 7. Detailed Design Analyses Show the W eight Trends are as M uch a F unction of Configuration F am ily as Lift-to-Drag Ratio ........... .........9 F igure 8. H igh-Perform ance H ypersonic G lide Aircraft........................ 10 F igure 9. NASA Langley W ing-Body Configuration W B-004 with Critical Areas for W ing Bodies Identified..... 11 F igure 10. F DL-7C/D and F DL-7M C Lifting-Body Configuration...............................12 F igure 11. F DL-7C/D with a DuPont Retractable Inward-Turning Inlet..................12 F igure 12. Com parison of F DL-7C/D and M odel 176................................................13 F igure 13. Sufficient Cross Range (L/D) M eans There is No W aiting to Return.....14 F igure 14. H ypersonic G lider Characteristics...........................................................15 F igure 15. Both Delta Planform Lifting Body (Dynasoar) and M odel 176 Offer Superior Landing Perform ance... 16 F igure 16. M cDonnell Aircraft Com pany Roll-Bonded Titanium Structure.............17 iii UNCLASSIF IE D/ /£Q£-QE E 1C1AJ—LLS^QhLLX UNCLASSIF IE D//FOR OFFIC IAL USE ONLY F igure 17. M odel 176 in the M cDonnell Douglas H ypervelocity Im pulse Tunnel ....18 F igure 18. F DL-7C/D, M odel 176 E ntry Tem perature Distribution.........................19 F igure 19. E ven At M ach 12, E m bedded Vortices in the Boundary Layer Alter the Local H eat Transfer.................................. ...19 F igure 20. Therm ographic Phosphor Im age of M odel 176 at Near-M axim um Angle of Attack..................................... 20 F igure 21. F rom L/D M axim um to M axim um Angle of Attack, There Is Always a Cool Sub-layer Adjacent to the W all....................... 20 F igure 22. This 1988 SE P Bordeaux SiC/SiC Panel Could Sustain Tem peratures of up to 3,000°F ..........................................................................21 F igure 23. UBE Corporation's Tyranno Cloth.................................... 21 F igure 24. A Porous Nickel Tip Oozing W ater.................................... 21 F igure 25. F DL ASSE T F light-Tested F rom Orbital Speeds to E valuate 1960s M aterials................................................................................22 F igure 26. H eat Pipe Shuttle Leading E dge Designed and Built by M cDonnell Douglas Astronautics................................. ...22 F igure 27. Boost-G lide Strategic Vehicle with Pratt & W hitney X LR-129 Rocket E ngine Installed......................................... 25 F igure 28. X LR-129.................................................................. 25 F igure 29. Two Rocket Air-Breathing Rocket Cycles to M ach 5.5.............. .....27 F igure 30. H OTOL E volution: F rom Aerodynam ic Optim um Configuration to Practical Launcher Configuration...........................................................27 F igure 31. LACE Air-Breathing Rocket............................. .29 F igure 32. The F DL-7 Class of Vehicles.................................. .........29 F igure 33. Takeoff and Landing Speeds of M inim um -Sized Launchers..................30 F igure 34. H orizontal launch Not Practical Unless W eight Ratio Less Than F our ...31 F igure 35. Propellant Tanks That Are Not Reentry Vehicles G reatly Reduce System W eight................................... 33 F igure 36. Sim ple H orizontal Integration and Vertical Launch Provides Rapid Launch Capability.......................... ...34 F igure 37. A Vertical Launch Com plex Provides Vertical Toss Back Booster Recovery and H orizontal Landing F acilities for the H ypersonic G liders 34 F igure 38. A 1964 M DC Astronautics, St. Louis, Briefing.................... 35 F igure 39. E arth's Atm osphere................. .36 F igure 40. F DL-5 Scale M odel of A Stage and One-H alf................... .....37 F igure 41. The F DL-7 and M odel 176 Class of H ypersonic G liders ..... ...37 F igure 42. H ypersonic Decelerating....................................... 38 F igure 43. W here W e Are Today.................................... 39 F igure 44. W here W e Could Be If W e Can Recapture the E ngineering Confidence and E xpertise of the Apollo/Saturn V E ra............................40 F igure 45. TAV Operational Costs.................................. 47 F igure 46. Landing E llipse........................................... 48 Tables Table 1. Characteristics of Selected F light Dynam ics Laboratory H ypersonic G lider Configurations During the 1958-68 Tim efram e................. .....6 Table 2. E lem ents of the Space Infrastructure Shown in F igure 44 ........................41 iv UNCLASSIF IE D//FOR OFFIC IAL USE ONLY UNCLASSIF IE D//FOR OmOIAL USE ONLY Space Access: W here W e've Been . . . and W here W e Could G o Introduction Developm ent of com m ercial access to space by our budding space­ faring civilization is a straightforward effort dom inated by propulsion and reliability. The initial focus should be on schedulable, dependable access to and from low E arth orbit (LE O). F or years we have known the m eans to accom plish such a task but have lacked a dedicated organized effort. The key requirem ent is to develop a robust and not necessarily a low-cost infrastructure, without which com m ercial exploitation of LE O and the m oon will not be possible. This is a m atter of skill; operational hardware based on durable, reliable, and dem onstrated com ponents; and operational system s. It is not necessarily a m atter of technology. H owever, technology discovery and developm ent are necessary for future space travel beyond E arth's environs. This paper addresses these issues by providing a running account of the historical details associated with the developm ent of the m yriad system s proposed and tested to provide access to space. Am ong the m any advances in space access that will be possible in the future,1 the key technology developm ents will be in the area of propulsion, because without these we are confined to our solar system by flight tim es lim ited to a project team 's functional life. The Pioneer spacecraft were fortunate to be m onitored for 20 years. H owever, the issue facing our spaceflight organizations is the lack of a durable, consistent, schedulable, and frequent hardware system to and from space assets such as the International Space Station. In October 1958, the author's job in the vertical wind tunnel at W right-Patterson Air F orce Base abruptly changed; hypersonic and high-tem perature flows becam e a new focus. W hat was then the Aircraft Laboratory was to becom e the Air F orce F light Dynam ics Laboratory (AF F DL), with a focus on space flight. Al Draper of the AF F DL began working with a select group of aerospace firm s on hypersonic gliders. The initial requirem ent from the Air F orce was to quickly find operational access to space. Technology application, hardware design and fabrication with an innovative application, and extending the industrial capabilities of the tim e were very m uch the issue, as exem plified by the Lockheed A-12/SR-71. W hen asked about space access at the tim e, a group of Aerospace Corporation v UNCLASSI F IE D//FOR OFFIC IAL USE ONLY UNCLASSIF IE D//FOR OFFIC IAL USE ONLY veterans responded, " It was not a technology issue; it was a hardware issue." In a keynote address to the Aeronautical Revolutionary Concepts W orkshop sponsored by the Vehicle Applications Panel of the National Research Council and held at NASA Am es in July 1984, then-Assistant Secretary of Com m erce for Productivity, Technology, and Innovation Dr. D. Bruce M errifield identified the problem of translating ideas into products as preparing technology for product m anufacture. Dr. M errifield drew an analogy between this step and M ajor League Baseball's farm system , which prepares skilled but untrained players for the m ajor leagues. The United States assigns projects to accom plish technology tasks so the flow of production­ ready hardware is always im proving and is not fixed (see F igure 1). Innovation Focus: Preparation of Technology for Application ’< *«»« ^Xffi™ «*c.« preparation tor application in United States No Gap in transformation to production 1983 Innovation in Aeronautics Workshop, NASA AME S Or.D . Bruce Merrifield D ept me nt of Commerce Assistant Secretary for Productivity. Technology and Innovation F igure 1. H ardware F low Saturn I and Saturn V could be readied for a m oon flight in such a short tim e because m ost of their hardware was based on a frozen design, proven production processes, and adaptation of existing hardware. Using a sim ilar approach, current industrial capabilities can create the next practical system for accessing space. In the late 1950s and early 1960s, the U.S. Air F orce was working toward an operational capability analogous to its B-52 fleets: flight operations when required or " on dem and." After NASA was assigned vi UNCLASSI F IE D//MB QEMC IAh USE QNb* UNCLASSIF IE D//TOW OFFIC IAL USB ONLY responsibility for space access, that Air F orce's focus switched to surveillance, com m unication, and G lobal Positioning System satellites. In the late 1950s, there existed a predisposition—forced by the m ilitary com petition between the United States and the form er Soviet Union—to use rockets derived from m ilitary ballistic m issiles. That decision curtailed efforts to develop alternatives to chem ical rockets together with practical com m ercial developm ents. W ith the orbiting of Sputnik, the aircraft path to space, as represented by the X series of planes, ended with the X -15. W ith the X -15's dem ise, all efforts to fly aircraft to space ended, replaced by the m ore fam iliar (but less practical) strategy of loudly blasting to space with expendable rockets derived from undertested ballistic m issile hardware, as docum ented in early failures. Like their ballistic m issile progenitors, current expendable rockets can be launched only once. W ith the exception of the experim ental Delta Clipper developed and operated by W illiam G aubatz and the late Pete Conrad, no operational launcher has ever successfully aborted. In this context, a reusable launcher is sim ply an expendable with som e parts reused a few tim es. Thus, neither the United States nor the Soviet Union/Russia has ever realized a truly com m ercial approach to space travel, although the Soviets cam e close to taking the first step with the since-term inated E nergia/Buran system . Both the United States and the Soviet Union/Russia historically have generated a large num ber of concepts that could fly directly to space and return on a sustained, frequent, scheduled basis. An all-up air breather such as the NASP was to solve that problem and fly directly to space and return. Developing an operational m ach 12 to 14 aircraft with air-breathing propulsion presents a serious design, engineering, and fabrication challenge analogous to the SR-71 Blackbird. vii UNCLASSI F IE D//FOR OFFIC IAL USE ONLY UNCLASSIF IE D//TOR OFFIC IAL UG E ONLY Propulsion Perspective In exiting Earth's atmosphere, the propulsion system and configuration are inexorably linked. A hypersonic glider exits the atmosphere on either a rocket booster or a first stage of a two-stage-to-orbit aircraft. As such, it usually exits the atmosphere quickly, and the key exit design considerations are the high transonic aerodynamic and the mechanical loads encountered in the exit trajectory. W hether for a new rocket launcher or the U.S. space shuttle, the phenomenon is the same: the peak mechanical loads occur during exit. In this case, the exit aerodynamics are important but not vital. The vital aerodynamics and thermodynamics (aerothermodynamics) are in the entry glide, where thermal loads are maximal and must be controlled. The vehicle must always be controlled in flight so its attitude and direction are within limits set by the aerothermodynamics. The angle-of-attack limits are very close for high-performance hypersonic gliders, as their glide angle of attack is 11 to 15 degrees, not the 45 degrees of the space shuttle. Even the Russian Buran had a lower glide angle of attack than the shuttle; a TsAGI report given to the author by Vladimir Neyland shows it to have been about 30 to 35 degrees.2 Like the Buran, the high-performance glider is best controlled by an automatic integrated flight control system that monitors the thermodynamic state of the vehicle, as well as its aerodynamic and trajectory states. The sensor array provides real-time information to the control system that can maintain the correct attitude in a manner a human controller could not accomplish. So it is this phase of the flight that designs the hypersonic glider. The exception is when powered by an air-breathing rocket (HO TO L, Skyion, and LACE), which must remain lower in the atmosphere until reaching the air­ breathing rocket transition to conventional rocket. The configuration for the air-breathing rocket is different, as it must have a retractable air inlet in the mach 0 to 5 range but does not determine the vehicle configuration. The impact is significant, as the carried oxidizer is reduced in the heaviest initial portion of the flight, as shown in Figure 2 for a D elta Clipper-type design with an aerospike nozzle tested by Konstantin Feotkiskov. The example is from a Senior Capstone D esign Study Team from Parks College, Saint Louis All Rocket 5 .35 ton payload 334 ton 101 ton TOG W 28 6 ton 15.9 ton OEW 678 m2 4 28 m2 Spten F igure 2. Im pact of Air-Breathing Rocket University, circa 1992, and is based on the engineering reports the author was permitted to read from the library of Konstantin Feotkiskov, an aerospace designer and cosmonaut. The question, as always, is, why bother with air-breathing systems at all if they are that much of a challenge? The answer is to consider a partial air-breathing system based on available hydrogen/oxygen rockets that operate to about mach 5.5. It operates in a flight region where the carried oxidizer quantities are the greatest. An operational system is sought that is capable of a large number of flights per year. The fewer resources required for launch, the greater ease with which the system can operate and the greater potential to operate from more bases. 1 UNCLASSI F IE D//FOR OFFIC IAL USE ONLY UNCLASSIF IE D//FOR OmC IAL USE ONLY The Russian design bureaus are to thank for arriving at a concept that eliminated the noisy and hazardous air-breather takeoff and for increasing the operational flexibility of the British HO TO L concept. Glebe Lozino-Lozinski had a concept for a spacecraft with a 7-metric-ton payload carried atop an Antonov An-225, with a second An-225 carrying the liquid hydrogen and launch facilities and staff.3 The An-225 was in fact a mobile launch facility; it could literally launch a satellite for any facility that could accommodate a B-747 or an MD C-11. W ith Rolls Royce or General Electric engines, the An-225 becomes a more easily maintained vehicle with better altitude performance. The An-225's empennage is modified from the An-124's single vertical and horizontal empennage to an 'H' configuration. This permits the powered hypersonic glider to easily lift off the top of the vehicle, as the MBB Sanger wind tunnel test demonstrated. Most commercial transport aircraft larger than ERJ 170 are potential mobile launch platforms for space tourism, point-to-point cargo, or orbital facilities support. Most of the commercial passenger equipment can be removed, with just enough equipment remaining for a launch crew. The fuselage is strengthened and fitted with external mountings for the hypersonic glider. The landing gear need not be modified, as the same maximum weight as the commercial transport will be maintained. The flight control system would be adapted to automatically maintain the correct launch trajectory until separation. A second modified transport would be modified to carry the liquid hydrogen and liquid air to fuel the hypersonic vehicle, along with maintenance and support crew. The intent is to use the automatic launch checkout the author witnessed at Baikanour in 1988, wherein a Soyuz that arrived on its train carrier at 0500 hours launched carrying a Progress capsule at 1715 hours the same day. That should make a local launch possible within hours of arriving at the specified airport launch departure site. These two elements can provide a commercial space launch facility that requires no special or dedicated operational base. H ypersonic Configuration Concepts The configuration and the propulsion system are linked through aerothermopropulsion integration. This approach is not new, as a wide spectrum of configurations and concepts existed in the 1960s. O ne such McD onnell Aircraft Company concept is shown in Figure 3. This potential operational mach 12 cruise vehicle was developed for the U.S. government as a strike reconnaissance vehicle taking off from a U.S. Air Force base. The concept was to provide on-demand reconnaissance in force operations. However, as was the case with all such efforts in the 1960s, none of the aircraft derived from the "flight-to-space" efforts reached a hardware stage. Individuals working on these projects were convinced that the industrial capability existed to design and fabricate these vehicles, and that such vehicles were technically feasible. The concepts varied widely among different nations, but all had as their goal a transportation system to space that had commercial potential. This discussion is provided to discriminate between rocket-powered hypersonic gliders and hypersonic cruisers with an air­ breathing propulsion system. 2 UNCLASSI F IE D//FOR OmC IAL USE ONEY UNCLASSIF IE D//rOR OFFIC IAL USE ONLY F igure 3. H SVS H ypersonic Cruise Aircraft Showing True Skin Tem perature A wide variety of configurations for recoverable spacecraft are possible. But if the requirements for a transportation system capable of traveling to and returning from space are to be met, the configurations spectrum is significantly narrowed. Two basic configuration types emerge. O ne configuration is for a hypersonic glider powered by either rocket or air-breathing rocket cycle propulsion that can operate as air-breathing propulsion to mach 5.5 or less. A versatile variable-capture, inward-turning inlet4 can be integrated with the vehicle configuration derived from the FD L series of hypersonic gliders developed by the U.S. Air Force Flight D ynamics Laboratory (AFFD L)5 and the work of the McD onnell D ouglas Astronautics Company. Because of the mass ratio to orbit, these configurations are vertical takeoff and horizontal landing vehicles, exemplified by the upper-left vehicle in Figure 4. This vehicle is usually an upper stage in a two-stage-to-orbit rather than a single-stage-to-orbit vehicle. 3 U N CLASSI F I E D/^BM UM M «AI ..rrAi.oz UNCLASSIF IE D//TOW OFFIC IAL UD E OhL¥ F igure 4. H ypersonic Rocket-Powered G lider and H ypersonic Air-Breathing Cruiser The second configuration is for air-breathing propulsion systems operating at between mach 6 and mach 14 that require a propulsion-configured vehicle, where the underside of the vehicle is an integral part of the propulsion system (forming most of the air­ capturing inlet). This is typified by the lower-right vehicle in Figure 4. The thermally integrated, air-breathing, combined-cycle configuration concept is derived from the McD onnell D ouglas (St. Louis) Advanced D esign organization. The vehicle concept initially conceived in the late 1950s and early 1960s was an air-breathing propulsion- configured vehicle accelerated by a main rocket in the aft end of the body, as shown in Figure 3. The vehicle's underside is the propulsion system; the engine is in the engine module. Both basic shapes are functions of tau—that is, for a given planform area, the cross­ sectional distribution is determined by the volume required. Tau was reported in D . Kuchemann's book on supersonic aerodynamics6 as: ^lotal s15 3 plan (1) The only configuration discussed in the book in any detail is the rocket-powered hypersonic glider. The hypersonic glider has greater near-term potential to become an operational system, considering the failure of the National Aerospace Plane (NASP) to reach a functional hardware stage. 4 UNCLASSI F IE D//F hP n^rrTAi iicemmiv UNCLASSIF IE D//FOR OFFIC IAL UD E ONW W hatever goes into orbit must enter the atmosphere many times if it is to be a sustained-use vehicle. If it is to be a commercial vehicle, then the flexibility to land wherever the commercial customers are is essential. Consider how successful FedEx, UPS, or D HL would be if there were only two pickup and delivery sites in the United States and a few more elsewhere in the world. A ballistic capsule has even fewer landing options, and a saltwater landing and recovery is too costly to be commercially feasible. W hat is needed is a hypersonic glider with the flexibility to enter when necessary, without waiting, and to land at different operational bases, just as a transport might. There were three serious competitors in the United States with respect to hypersonic glider configurations: the AFFD L at W right-Patterson Air Force Base, the McD onnell D ouglas Corporation (MD C), and the Lockheed Corporation. NASA Ames and NASA Langley were also generating hypersonic configurations, but NASA's views on hypersonic gliders (fundamentally research and development projects) and their glide range requirements differed from those of the three organizations listed above. That difference is clearly exemplified by the difference between the operational requirements of an experimental aircraft (such as X-l, X-2, X-10, X-15, or X-20) that flies infrequently and at the convenience of the research organization and those of an operational Air Force or Navy aircraft that must be able to fly on any day in almost any weather when needed (also a Russian spacecraft operational rule). From the middle of the 1960s to the early 1970s, the U.S. Air Force and NASA had disagreements over the operational capability of these aircraft and their requirements. As a result, each went its own development direction, and much of the originality and practicality of the AFFD L concepts has not been reflected in the space access configurations developed by NASA. There was a final attempt to apply the AFFD L's philosophy of a high lift-to-drag (L/D ) ratio delta planform configuration to the NASA space shuttle, as detailed in the article "A D elta Shuttle O rbiter" in the January 1971 issue of Astronautics and Aeronautics.7 Figure 5 shows the array of delta planform configurations the AFFD L considered during the 1958-68 timeframe. F igure 5. Delta-Lifting Body Designs. Array of delta-lifting body designs shows configuration is not limited to high hypersonic lift-to-drag ratios, high cross range, and large size.8 5 UNCLASSI F IE D//FOR OFFIC IAL USE ONL¥ UNCLASSI F IE D/yrOR OmC IAL USE ONLY The AFFD L's approach was to design a hypersonic performance configuration that would minimize the waiting time in orbit to return to the continental United States (CO NUS). This resulted in configurations with sharper leading edges and smaller nose radii than found in NASA and Russian configurations. All of the material, structural, and thermodynamic details related to the sharper configurations were tested and verified in ground test facilities and flight tests (BGRV and ASSET). Characteristics of selected AFFD L hypersonic glider configurations are identified in Table 1. Table 1. Characteristics of Selected Flight Dynamics Laboratory Hypersonic Glider Configurations During the 1958-68 Timeframe # M odel Observation I FDL -24B Flat bottom, sharp leading edges, conventional tails, as designed 2 All Body Glider, similar to Russian B OR vehicles Upturned spatular nose, conventional tails 3 ASSET Test vehicle to evaluate aerodynamics, thermodynamics and materials, based on nose of DynaSoar 4 FDL-7M C Flat bottom, sharp leading edges, variable geometry wing, experimentally developed tail X configuration 5 Blunt nose, wing-body DynaSoar type configuration 6 Spainrlar N ose V ersion of DynaSoar type First integration of 2-dimensional nose (less drag) on a hypersonic glider (R.D. Newmann) 7 FDL-8 Flat bottom, sharp leading edges, outboard tails 8 HL -10 N ASA Ames flat up-swept with bottom, round upper body, high dihedral angle tails 9 X-24A NASA L angley round body, high dihedral angle tails 10 Star B ody based on Russian Star Body type configuration Configuration 2 was a higher wing-loading, relatively blunt all-body with an upswept spatular nose that is not unlike Russia's Bor series of Lozino-Lozinski hypersonic gliders. W hen the author was at W right-Patterson, interest in this waned quickly because of the limited cross range available. Because of the longitudinal extent of the former Soviet Union compared with the United States, the minimum L/D ratio to ensure a landing on the continental land mass was less for the former Soviet Union than it was for the United States—1.7 for the Soviet Union versus 2.7 for the United States. Configuration 3 was a subscale research vehicle to evaluate the thermodynamic and materials for hypersonic gliders. The nose and leading edge radii were full-scale size. ASSET was successfully flown on a Thor intermediate-range ballistic missile (IRBM) booster. O ne that was recovered after an ocean landing is on display in the U.S. Air Force Museum in D ayton, O hio. Configuration 6 was the first two-dimensional nose applied to a conventional winged-body (configuration 5) in the United States. Configuration 4 was a product of cooperation between the AFFD L (Alfred D raper) and McD onnell D ouglas Astronautics Company (Robert Masek) to develop a vehicle to support the Manned O rbiting Laboratory (MO L). This concept was briefed to the U.S. 6 UNCLASSI F IE D//F OP ^^ti-tai iicemmiv UNCLASSIF IE D//FOA OFFIC IAL USE ONLY Air Force in 1964, and elements of that configuration will be shown later. The intent was a 9- to 12-person vehicle for crew rotation that could alternatively carry supplies to the orbital station on a regular, frequent schedule (about one flight per week per vehicle). The variable geometry switchblade wing permitted landing with heavy loads returning from space and eventually horizontal takeoff. The experimentally determined configuration feature was the tail configuration. This configuration was wind tunnel tested and demonstrated inherent stability and control at speeds ranging from mach 22 to landing speed. Configuration 6 was a product of cooperation between the AFFD L (Richard D . Neumann) and McD onnell D ouglas Astronautics Company (Robert Krieger) to reduce the drag of hypersonic gliders. Based on the physics that a two-dimensional wedge has less drag than a right circular cone of the same volume, these engineers devised the "spatular leading edge." The wind-body configuration formed the basis of the X-20 and D ynaSoar configurations that had a limited hypersonic L/D ratio, primarily because of drag. W ith the spatular nose, the nose wave drag could be reduced by 35 to 40 percent, thus increasing the hypersonic L/D ratio. Configuration 6 was derived from the conventional wing body, configuration 5. Configuration 10 is an adaptation of the Russian "Star Body" concept that can enter in one of three orientations and need not always have one side facing the flow (compression side). The theory was that in a damaged situation, one of the three sides would be available for a safe entry. The limitation of this configuration concept is a small internal volume and a high ratio of wetted (surface) area per planform area that reduces the hypersonic L/D ratio. The X-24B was based on the FD L-8 configuration. The different approaches to hypersonic glider configuration are best exemplified by Figure 6. The X- 24A, built by Martin Marietta at its D enver, Colorado, facilities, is a round fuselage configuration with outboard high-dihedral-angle vertical tails. All the configurations of this type have serious lateral-directional stability problems at low speeds and tend to roll about the horizontal axis through the fuselage. O ne designer, the Russian Glebe Lozino-Lozinski, solved the problem by employing variable dihedral tails. The AFFD L solved the problem by using nonround configurations; that is, F igure 6. M artin M arietta X -24 A & B Research G liders. X-24A based on USAF PRIME configuration. the quest for high hypersonic L/D ratios led to the solution of the low speed problem. Under an AFFD L program, Martin Marietta modified the X-24A into a flat-bottomed configuration with trailing edge elevons called the X-24B, shown in Figure 6. Comments by Bill D ana, the NASA pilot who flew the X-15 and the X-24A/B, about the change in the slow speed performance of the X-24B confirmed the advantage of the AFFD L approach.9 7 UNCLASSI F IE D//B OB nESTC IM USE ONI Y UNCLASSIF IE D//rOR OFFIC IAL USE ONLY The design parameters that largely determine a spacecraft's weight are its configuration and the amount of wetted or surface area relative to the planform area. The hypersonic gliders shown in Figure 5 have differing values of wetted area to planform area. Another important factor is the presence of wings, such as for configurations 5 and 6, which are wing bodies with a relatively thin wing or no wing, such as the lifting­ body FD L-class hypersonic glider (configurations 2, 4, or 7). In this case the lifting bodies have a shape advantage that reduces the amount of surface area that is thin or subject to high heating. In the 1960s, when the U.S. Air Force's high-performance lifting body was competing with NASA's modest-performance wing body, there was much debate regarding the weight of these lifting concepts compared with that of a ballistic capsule (see Appendix A). At that time, with the large sea-recovery fleets, ballistic capsules were the only entry vehicles in either the United States or the former Soviet Union. A number of studies in the early-to-mid-1960s attempted to rectify and quantify the weight of a lifting entry vehicle compared with a ballistic capsule. In all the discussion in the Mercury, Gemini, and Apollo programs, the cost of the sea recovery was almost taken for granted, so the focus was on the cost of the vehicle itself, not the entire vehicle system. The government assembled a chart representing the relative weight of hypersonic entry systems—from ballistic to high-performance (high L/D ratio) gliders—collected from contractor and government reports. The relative weight was the system weight compared with that of a ballistic capsule with the same payload capacity. The result was a correlation curve that showed the high- performance wing-body gliders could weigh as much as twice what a comparable payload ballistic capsule weighed. This correlation was based on the L/D ratio of the vehicle. Apollo has an L/D ratio of about 0.5, but the system was still a ballistic vehicle with a very limited cross range. O ne correlation of the data is: W/Wo =l + 0.1259