The potential payload gains due to airbreathing propulsion are evaluated for a one-and-one-half stage reusable vertical-takeoff ballistic space transporter with a gross mass of 155 Mg. The system consists of a returnable ring of turborocket/ramjet engines added as a half-stage to the structure of a 130 Mg, single-stage, vertical-takeoff-vertical-landing, pure-rocket transporter considered in an earlier industry study. High-pressure topping-cycle rockets are used part-time in parallel with the airbreathers, with hydrogen/oxygen propellants used for both. With fixed takeoff mass and airbreathing engines, the main variables were the rocket thrusts and burning times, cycle change and staging points, and the injection angle at 100-m altitude. State-of-the-art technology was assumed. Trajectories free from constraints, except acceleration limits, allowed optimal propulsion system use. Propulsion performance maps, ascent trajectories, and weight breakdowns are given. Payload fractions up to 7.8% of gross mass were obtained for the airbreathing vehicle, which is very high for this size class compared with expendable two-stage rocket transporters.

Hybrid Rocket/Airbreathing Propulsion for Ballistic Space Transportation

Three structural concepts are studied: (1) a state-of-the-art insulated aluminum skin-stringer structure; (2) a near-art insulated evacuated aluminum-alloy honeycomb structure; and (3) an advanced evacuated Rene 41 honeycomb hot structure. Each is evaluated for its thermostructural performance for each of the flight profiles (ascent, entry, and a recall or abort). Results indicate that (1) the state-of-the-art structure encounters negligible thermal stress; (2) the near-art structure has acceptable thermal stresses; and (3) the advanced structure will have thermal stress levels above the material allowables.

Thermostructural analysis of three structural concepts for reusable space vehicles

Energy analysis of high speed vehicle systems

This paper reports the results of a conceptual study to define the performance potential, scaling relationships, and research needs of a hypersonic missile concept formulated about an airframe-integrated propulsion system. A baseline missile design is developed and the rationale for selecting a heat-sink structural approach is described. Modifications to a NASA-Langley-developed fixed-geometry, modular scramjet are presented that may be required to achieve the dual-mode, "hydrocarbon-fueled" engine operational characteristics utilized in predicting missile performance potential. A heat-sink structure is shown to be a viable concept for Mach 6 missiles for ranges of up to 200 n.mi. A heat-sink structure protected by multiwall heat shields is suggested as a potentially attractive system for long-range cruise missiles. Airframe-integrated propulsion systems are shown to offer potentially large benefits for missiles that require high maneuverability. The use of the missile forebody for generating inlet precompression as well as lift and use of the afterbody as a high-expansion ratio, low-drag nozzle also offer improved missile cruise performance. It is concluded that technologies being developed for hypersonic aircraft, with appropriate modifications, also can be useful for hypersonic, airbreathing, lifting missiles.

Performance Potential and Research Needs of a Hypersonic, Airbreathing, Lifting Missile Concept

Future Space Transportation Systems (FSTS) are being studied to identify critical technology needs for timely development of FSTS with the following goals: 150,000-lb payload, long life, fully reusable, all-weather operational capability, and durable structures and systems to minimize refurbishment, maintenance, and cost. Two structural concepts for the FSTS second-stage orbiter were analyzed considering cyclic life, fracture mechanics, thermo-structural and aerodynamic thrust loads, propellant compatibility and operational flexibility. These two orbiter concepts were compared on the basis of weight and ability to meet structural goals. The first concept involves only incremental advancements over current structural technology. The second concept involves more advanced structural technology. The first concept has two blade-stiffened aluminum cryogenic tanks suspended within an insulated aluminum airframe structure. The advanced concept has a blade-stiffened aluminum tank/thrust structure supporting a hot advanced carbon-carbon (ACC) aeroshell structure. The weight advantage and potential for meeting the structural goals make the advanced concept attractive for FSTS consideration.

Structural concepts for future space transportation system orbiters

Results of a preliminary study of a space transport concept are presented. The concept consists of a winged orbiter containing ascent propellants and two small turbojet-powered winged boosters, used for acceleration to supersonic speeds. The concept offers full reuse and horizontal takeoff from numerous existing airports. With current structure and rocket technology, this transport concept has lower gross weight for a selected payload than single-stage-to-orbit concepts, which require structural advancements. Discussion includes alternatives to the baseline space transport concept which improve performance; such as advanced structures, dual-fuel rockets, and lightweight scramjets for the orbiter. A concept of using a stretched shuttle orbiter instead of an all-new configuration is discussed for two payload-class vehicles.

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J. A. Martin

Papers

A fully reusable, horizontal takeoff space transport concept with two small turbojet boosters