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This paper explores some of the many considerations which enter into the choice of a specific spacecraft propulsion system for a particular application. The environment and its influence on propulsion requirements are discussed in general terms, characteristics of several propellant combinations are presented and an example of a typical ambitious mission is used. ...A general conclusion is that the state of the art of spacecraft propulsion technology must advance on a broad front in the time period prior to project definition in order to provide the technological options which allow significant optimization of the complete project propulsion system. ...A general conclusion is that the state of the art of spacecraft propulsion technology must advance on a broad front in the time period prior to project definition in order to provide the technological options which allow significant optimization of the complete project propulsion system.

THE NUCLEAR turboelectric ion propulsion system operates as follows: 1. A nuclear reactor supplies thermal energy to a vapor boiler. 2. ...Electric propulsion systems can be used in a wide variety of space missions, including satellite sustainers, lunar cargo transport, and interplanetary missions.*

The prop-fan propulsion system is being investigated as part of the NASA Aircraft Energy Efficiency program which includes both analytical studies and experimental tests.

It is compared with the chemical rocket and the nuclear turboelectric ion propulsion system. In developing the concept for this low-power rocket, NASA engineers concentrated on attaining low weight and high hydrogen temperature, and on solving problems concerned with automatic control and operation of high-temperature reactors.

A method that exploits certain properties of a recirculating gas has been investigated as a means of achieving a sustained accelerative vector force without either the expulsion of mass from or a reaction against an external mass by the accelerated body. A theory of operation is presented that defines the capabilities and limitations of the method, and which has resulted in functioning prototypes. The prototype devices require only a source of electric power and a means of cooling to achieve an internally generated, externally measurable accelerative vector force that is sustained for as long as power is supplied to the device.

Experimental data on performance and cooling from sea level and altitude firing tests of fluorine/oxygen mixtures with light-hydrocarbon fuels are presented. The majority of the work has been oriented toward pressure-fed rocket applications, with testing at 5000-lb vacuum thrust and 100-psia chamber pressure. Work in progress is at chamber pressures of 250 and 500 psia, being oriented toward pump-fed rocket applications. High delivered specific impulse levels have been demonstrated. One problem, apparently unique to these propellants, is that performance at the optimum mixture ratio is extremely sensitive to incomplete mixing.

To achieve this goal, NASA has analyzed a hybrid body wing aircraft with a turboelectric distributed propulsion system. The propulsion system must be designed to operate at the highest possible efficiency in order to meet the reduced fuel burn goal. ...High density components are required to minimize the weight of the electric propulsion system while meeting the high power demand. Minimizing the electric propulsion system weight helps to reduce the amount of fuel required for propulsion. ...NASA's N3-X aircraft design under the Research and Technology for Aerospace Propulsion Systems (RTAPS) study is being designed to meet the N+3 goals, one of which is the reduction of aircraft fuel burn by 70% or better.

The general problem of applying propulsion systems to supersonic aircraft is discussed briefly and it is shown that neither turbojets nor ramjets are entirely satisfactory when used by themselves. ...In order to avoid the confusion resulting from the comparison of propulsion system performance using the special parameters associated with each type of engine, performance is compared along operating altitude-Mach number paths in terms of thrust and specific fuel consumption only. ...The combined propulsion system arrived at offers promise of good performance, light weight, low cost, and simple installation.

Propulsion system controls have been steadily increasing in complexity to meet the regulation and limiting requirements of current and future turbine engines. ...This requirement further increases the sensing, computational and regulation functions of the propulsion system control. In the past, electronic controls have played a subordinate role because of the severe turbine engine flight environment and the computational needs of the engine could usually be met by hydromechanical components. ...With this insight, more timely planning and execution of state-of-the-art advances in propulsion system control technology can be accomplished to meet the functionability, performance, and confidence goals of future propulsion system hardware.

The Waste Management/Rocket Propulsion System appears capable of satisfying many propulsion requirements; for example, orbit change maneuvers, aerodynamic drag makeup, midcourse correction, terminal braking, and auxiliary and emergency propulsion. ...To date, spacecraft designers have considered life support systems and rocket propulsion systems as independent subsystems of a manned spacecraft. The Integrated Waste Management/Rocket Propulsion System concept developed by Rocket Research Corp. under NASA Contract NAS 1–6750, has demonstrated that human waste products can form a useful propellant ingredient and provide propulsion, as well as be an effective means of removing and sterilizing spacecraft waste. ...The Integrated Waste Management/Rocket Propulsion System concept developed by Rocket Research Corp. under NASA Contract NAS 1–6750, has demonstrated that human waste products can form a useful propellant ingredient and provide propulsion, as well as be an effective means of removing and sterilizing spacecraft waste.

Incorporation of an advanced technology, high-speed turboprop propulsion system into future air transports can achieve significant reductions in operating costs through large reductions in fuel consumption. ...The advantages of the propfan aircraft, in light of ever-increasing fuel shortages and fuel cost increases, have resulted in several NASA-sponsored research programs to verify propulsion performance and develop the required technology base. Continuation and escalation of these activities must be accomplished to ensure incorporation of the propfan into the next generation of commercial air transports.

ATR with extended precooling (Tout=100K) is examined in more detail. For propulsion systems including different types of engines, running simultaneously the concept of LH2 heat sink capacity concentration for turbojet air precooling is proposed.

The Space Shuttle Orbiter vehicle employs two earth storable bipropellant propulsion subsystems to provide orbit maneuvering and vehicle attitude control. Respectively, these are the Orbit Maneuvering Subsystem (OMS) and the Reaction Control Subsystem (RCS). ...The OMS is made up of two normally independent propulsion subsystems in removable pods. Each contains a 6000 lb. thrust rocket engine, propellant tankage, and necessary feed and control componentry. ...Like the OMS, the RCS modules are totally self-contained propulsion subsystems.

In addition, a study was performed to compare candidate lox/HC propulsion system concepts and to evaluate major system/component design options. The data generated provide quantitative substantiation of trends previously experienced with hypergolic propellants and with a lox and rocket propellant combination.

Two decades of turboprop technology advances are discussed along with their application to a Prop-Fan propulsion system for modern high-speed commercial aircraft. The Prop-Fan propulsion system features a small diameter, multibladed propulsor geared to an advanced gas turbine engine. ...Several advanced technologies in the airframe and propulsion disciplines have been identified by NASA, with the turboprop being one of these. Two decades of turboprop technology advances are discussed along with their application to a Prop-Fan propulsion system for modern high-speed commercial aircraft.

In a search for potential methods of reducing future air transport fuel consumption, advanced conventional turbofan and more unconventional propulsion systems were examined. Early results encouraged a more detailed evaluation of an advanced Brayton cycle gas generator in a turbofan engine or geared to an advanced multi-bladed, small diameter propeller.

The NASA Small Transport Aircraft Technology (STAT) Propulsion Study was established to identify technology requirements and define the research and development required for new commuter aircraft.

Surface tension principles applicable to the design of propellant management devices for static retention and dynamic control of space propulsion system propellants are discussed. The characteristics of ideal propellant retention and control (management) systems are introduced as criteria for judging proposed designs.

A series hybrid-electric propulsion system has been designed for small rapid-response unmanned aircraft systems (UAS) with the goals of improving endurance, providing flexible and responsive electric propulsion, and enabling heavy fuel usage. ...A series hybrid-electric propulsion system has been designed for small rapid-response unmanned aircraft systems (UAS) with the goals of improving endurance, providing flexible and responsive electric propulsion, and enabling heavy fuel usage. The series hybrid architecture used a motor-driven propeller powered by a battery bank, which was recharged by an engine-driven generator, similar to other range-extended electric vehicles. ...Development of the hybrid propulsion system is ongoing, with current efforts focused on reducing system mass, packaging, and gearing up for a future hardware demonstration.