ALBERT

Beschreibung: Experience with many spacecraft configurations boosted by a variety of launch vehicles indicates that the maximum loads experienced throughout most of the structure are inertial in origin. These loads arise from the dynamic elastic response of the flight vehicle to the transient disturbances of launch and flight, and are highly dependent on the dynamic characteristics of both the spacecraft and the launch vehicle. It has proved to be most advantageous, in the analysis of this critical dependency of loads upon vehicle dynamic properties, to establish a mathematical model in terms of normal mode characteristics. In this way, the vibration behavior of an elastomechanical structure (or substructure) can be described by means of the so-called modal or natural degrees of freedom. The conduct of a mode survey test and the use of a suitably test-verified model in loads analyses is essential to the flight worthiness certification process of space systems. The desirability of such tests is confirmed by the fact that, almost invariably, significant deficiencies in the analytical models are revealed by the results. Therefore, this experimental program was undertaken to determine those properties of a solid-propellant rocket motor (SRM) which are required to characterize a dynamic model. Random ambient-excited accelerations were measured at a series of stations along the motor for the purpose of identifying the motor beam-like stiffnesses in bending, shear, and torsion. From a system identification point of view, it is significant that stiffness properties of a subsystem (the motor) are determined from modes of the full system (motor/stand configuration) using mode shape data of the subsystem only. This contrasts with traditional system identification approaches which rely upon complete system mode shapes.

Beschreibung: The orbiting shadowing analysis computer program was developed by NASA in order to assess the shadowing effects on various power systems. The algorithms, the inputs and outputs are discussed. Examples of typical shadowing analysis, performed for the International Space Station Freedom, the International Space Station Alpha and the joint United States/International Mir Solar Dynamic Flight Experimental Project are presented.

Beschreibung: The topics addressed are: (1) phobos power plant; (2) fusion power/propulsion system; (3) surface power from an orbiting spacecraft; (4) RTG replacement; (5) MHD-thermoelectric burst reactor; (6) TAU Voyage power/propulsion device; (7) ESCAPE to ODYSSEY.

Beschreibung: The Texas A&M Nuclear and Aerospace engineering departments have worked on five different projects for the NASA/USRA Advanced Design Program during the 1987/88 year. The aerospace department worked on two types of lunar tunnelers that would create habitable space. The first design used a heated cone to melt the lunar regolith, and the second used a conventional drill to bore its way through the crust. Both used a dump truck to get rid of waste heat from the reactor as well as excess regolith from the tunneling operation. The nuclear engineering department worked on three separate projects. The NEPTUNE system is a manned, outer-planetary explorer designed with Jupiter exploration as the baseline mission. The lifetime requirement for both reactor and power-conversion systems was twenty years. The second project undertaken for the power supply was a Mars Sample Return Mission power supply. This was designed to produce 2 kW of electrical power for seven years. The design consisted of a General Purpose Heat Source (GPHS) utilizing a Stirling engine as the power conversion unit. A mass optimization was performed to aid in overall design. The last design was a reactor to provide power for propulsion to Mars and power on the surface. The requirements of 300 kW of electrical power output and a mass of less than 10,000 Rg were set. This allowed the reactor and power conversion unit to fit within the Space Shuttle cargo bay.

Beschreibung: The damage potentials to the space shuttle orbiter caused by the high velocity particles contained in the exhaust plume of an upper stage is discussed. In particular, the particle size distribution and composition, the velocity of the particles and the expected contribution from shuttle launched upper stages are addressed. Particle size estimates based on historical data are compapred with those derived from upper stage motor performance testing. The particle velocities as determined by the best available plume computational technique are presented. The shuttle is scheduled to launch approximately 135 upper-stages over its lifetime looking at the currently scheduled flights and averaging over a yearly basis yields the contribution of particulates from the uper-stages. On the average, 91,645 llbs of Al2O3 will be ejected on each launch. The analysis to determine how much of this 91,645 lbs will remain in orbit or the decay rate is yet to be accomplished.

Beschreibung: Results of the liquid rocket booster study initiated by NASA to define an alternative to solid rocket boosters, are presented. The prime study contractors, Martin Marietta Corporation and General Dynamics, have identified liquid rocket booster configurations that can increase shuttle performance to 70 klb. These boosters will provide improved reliability, hold down, verification prior to vehicle release, engine-out and abort capabilities. Phasing of these boosters into Space Transportation System (STS) operations without adversely affecting flight rate is described.

Beschreibung: The redesigned solid rocket motor of the Space Shuttle is described. Improvements over the model that led to the loss of the Space Shuttle Challenger are outlined. Scale and full-size tests carried out to verify the quality of the redesign are described. A unique feature of the test program is the introduction of deliberate flaws into some test articles. Post-flight evaluation of the redesigned boosters show excellent results.

Beschreibung: A contactless method for the determination of the free-carrier density and the composition distribution across the thickness of 3-5 multi-layer solar cell structures, using the Raman scattering method, is developed. The method includes a step analysis of Raman spectra from optical phonons and phonon-plasmon modes of different layers. The method provides simultaneous measurements of the element composition and the thickness of the structure's layers together with the free-carrier density. The results of measurements of the free-carrier density composition distributions of the liquid phase epitaxy grown AlGaAs/GaAs and GaSb solar cell structures are presented and discussed.

Beschreibung: The photovoltaic array space power (PASP)-Plus solar cell flight experiment is described, and the observed performances of different solar cell types during the first six months of their operation, are summarized. The solar cell types include single crystal and amorphous silicon, GaAs, several multijunction cell types, indium phosphide and GaAs/GaSb concentrator cells. The radiation degradation experienced by some of the solar cell types agrees with theoretical predictions. Other samples, including silicon, are degraded less than predicted. Effects, including the increase in temperature of all the experiments and the effect of sun glint on cell measurement, are discussed.

Beschreibung: The conceptual design and experimental results for two types of space application concentrator photovoltaic modules, employing reflective optical elements, are presented. The first type is based on the use of compound parabolic concentrators, the second type is based on the use of line-focus parabolic troughs. Lightweight concentrators are formed with nickel foil coated silver with a diamond-like carbon layer protection. Secondary optical elements, including lenses and cones, are introduced for a better matching of concentrators and solar cells. Both types of modules are characterized by concentration ratios in the range 20x to 30x, depending on the chosen range of misorientation angles. The estimated specific parameters of these modules operating with single junction AlGaAs/GaAs solar cells are 240 W/sq m and 3 kg/sq m.

Beschreibung: Two contact systems for use on shallow junction InP solar cells are described. The feature shared by these two contact systems is the absence of the metallurgical intermixing that normally takes place between the semiconductor and the contact metallization during the sintering process. The n(+)pp(+) cell contact system, consisting of a combination of Au and Ge, not only exhibits very low resistance in the as-fabricated state, but also yields post-sinter resistivity values of 1(exp -7) ohms-sq cm, with effectively no metal-InP interdiffusion. The n(+)pp(+)cell contact system, consisting of a combination of Ag and Zn, permits low resistance ohmic contact to be made directly to a shallow junction p/n InP device without harming the device itself during the contacting process.

Beschreibung: The effects of irradiation of In(0.53)Ga(0.47)As/InP (InGaAs/InP) solar cells illuminated through a transparent InP substrate with 1 MeV electrons were measured. These solar cells were developed for bottom cells in tandem solar photovoltaic cell structures. Some InGaAs/InP heterostructures with four layers were grown by liquid phase epitaxy. The structure of the solar cells allowed lightly doped materials in n and p photoactive layers to be used. The base dopant levels ranged from 1.10(exp 17) to 5.10(exp 17) cm(exp -3). The open circuit voltage and the short circuit current were moderately degraded after irradiation with 10(exp 16) cm(exp-2) 1 MeV electrons. This behavior is explained in terms of the device structure and the n and p layer thicknesses.

Beschreibung: The in-flight tests and the operational sequences of the Superfluid Helium On-Orbit Transfer (SHOOT) experiment are outlined. These tests include the transfer of superfluid helium at a variety of rates, the transfer into cold and warm receivers, the operation of an extravehicular activity coupling, and tests of a liquid acquisition device. A variety of different types of instrumentation will be required for these tests. These include pressure sensors and liquid flow meters that must operate in liquid helium, accurate thermometry, two types of quantity gauges, and liquid-vapor sensors.

Beschreibung: NASA's Lewis Research Center is developing a highly automated system for the generation, storage and distribution of electrical power aboard the projected Space Station. This autonomous power system will employ conventional algorithms, enhanced by expert systems, to schedule power, allocate energy, diagnose causes of failure, propose goals, prepare plans for their implementation, evaluate their consequences, and select optimum plans for their execution. While crew-interactive expert systems will be ready for the initial Space Station, total system autonomy is expected to require additional development time.

Beschreibung: The relationship between the exploration of space and the availability of abundant power supplies is discussed. It is proposed that nuclear power will be needed to satisfy the power demands of manufacturing facilities in LEO, and power demands for the year 2000 are projected to be 300 KW(e). The capabilities and development of the Space Station are described; the use of nuclear power for the Station and various reactor location configurations are studied. The power requirements that will be necessary for the development of lunar resource bases and the exploration of Mars and other planets are considered; the advantages of nuclear power are examined.

Beschreibung: During ground testing of the Space Shuttle Main Engine (SSME), there have been twenty-six major incidents resulting in substantial hardware damage and loss. Historical characteristics, advances in detection technology, and advances in computing technology led to plans for study of an advanced real time SSME test stand failure detection system which would reduce damage and preserve evidence when a failure with major incident potential occurs. This detection system will speed recognition of dangerous engine operation, and quicken the shutdown decision. The scope of this study, SSME characteristics, SSME test history, the problem definition, and some technical issues will be addressed herein.

Beschreibung: An evaluation is made of technology development prospects for launch vehicle, orbit transfer vehicle, satellite, and planetary exploration spacecraft propulsion systems being contemplated by NASA and its research contractors. Attention is given to such electric propulsion systems as arcjet, pulsed plasma, ion, and resistojet thrusters, as well as to solar thermal heat exchanger powerplants, beamed energy propulsion systems, and ultra-advanced nuclear fission and fusion propulsion concepts.

Beschreibung: A brief summary is presented of a NASA study contract and in-house investigation on Growth Space Station missions and appropriate nuclear and solar space electric power systems. By the year 2000 some 300 kWe will be needed for missions and housekeeping power for a 12 to 18 person Station crew. Several Space Station configurations employing nuclear reactor power systems are discussed, including shielding requirements and power transmission schemes. Advantages of reactor power include a greatly simplified Station orientation procedure, greatly reduced occultation of views of the earth and deep space, near elimination of energy storage requirements, and significantly reduced station-keeping propellant mass due to very low drag of the reactor power system. The in-house studies of viable alternative Growth Space Station power systems showed that at 300 kWe a rigid silicon solar cell array with NiCd batteries had the highest specific mass at 275 kg/kWe, with solar Stirling the lowest at 40 kg/kWe. However, when 10 year propellant mass requirements are factored in, the 300 kWe nuclear Stirling exhibits the lowest total mass.

Beschreibung: A number of attractive options are available for the Space Station Power System. These include a photovoltaic system or solar dynamic system for power generation, batteries or fuel cells for energy storage and ac or dc for power management and distribution. These options are being explored during the present preliminary design and definition phase of the Space Station Program. Final selections are presently targeted for January 1986.

Beschreibung: The ram impact of low earth orbital atomic oxygen causes oxidation of spacecraft materials including polymers such as polyimides. The rate of oxidation is sufficiently high to potentially compromise the long term durability of Kapton solar array blankets. Ion beam sputter deposited atomic oxygen protective coatings of aluminum oxide, silicon dioxide, and codeposited silicon dioxide with small amounts of polytetrafluoroethylene were evaluated both in RF plasma asher tests and in low earth orbit. Deposition techniques, mechanical properties, and atomic oxygen protection performance are presented.

Beschreibung: The solar array for the Venus Radar Mapper mission will operate in the high temperature, high intensity conditions of a low Venus orbit environment. To fulfill the performance requirements in this environment at minimum cost and mass while maximizing power density and packing factor on the panel surface, several features were introduced into the design. These features included the use of optical surface reflectors (OSR's) to reduce the operating temperature; new adhesives for conductive bonding of OSR's to avoid electrostatic discharges; custom-designed large area cells and novel shunt diode circuit and panel power harness configurations.

Beschreibung: The paper considers the present status of solar thermal dynamic space power technologies and projects the various attributes of these systems into the future, to the years 2000 and 2010. By the year 2000, collector weights should decrease from 1.25 kg/sq m (1985 value) to about 1.0 kg/sq m. The specific weight is also expected to decrease from 6.0 kg/kw. By the year 2010, slight improvements in the free piston Stirling energy conversion system are postulated with efficiencies reaching 32 percent. In addition, advanced concentrator concepts should be operational.

Beschreibung: The regenerative fuel cell, a candidate technology for the Space Station's energy storage system, is described. An advanced development program was initiated to design, manufacture, and integrate a regenerative fuel cell Space Station prototype (RFC SSP). The RFC SSP incorporates long-life fuel cell technology, increased cell area for the fuel cells, and high voltage cell stacks for both units. The RFC SSP's potential for integration with the Space Station's life support and propulsion systems is discussed.

Beschreibung: The Space Station power system selection process is described with attention given to management organization and technical considerations. A hybrid power system was chosen because of the large life cycle cost savings. The power management and distribution system that was chosen was the 400 Hz system.

Beschreibung: A preliminary feasibility assessment of the integration of reactor power system concepts with a projected growth Space Station architecture was conducted to address a variety of installation, operational, disposition and safety issues. A previous NASA sponsored study, which showed the advantages of Space Station - attached concepts, served as the basis for this study. A study methodology was defined and implemented to assess compatible combinations of reactor power installation concepts, disposal destinations, and propulsion methods. Three installation concepts that met a set of integration criteria were characterized from a configuration and operational viewpoint, with end-of-life disposal mass identified. Disposal destinations that met current aerospace nuclear safety criteria were identified and characterized from an operational and energy requirements viewpoint, with delta-V energy requirement as a key parameter. Chemical propulsion methods that met current and near-term application criteria were identified and payload mass and delta-V capabilities were characterized. These capabilities were matched against concept disposal mass and destination delta-V requirements to provide a feasibility of each combination.

Beschreibung: The regenerative fuel cell system (RFCS), designed for application to the Space Station energy storage system, is based on state-of-the-art alkaline electrolyte technology and incorporates a dedicated fuel cell system (FCS) and water electrolysis subsystem (WES). In the present study, emphasis is placed on the WES portion of the RFCS. To ensure RFCS availability for the Space Station, the RFCS Space Station Prototype design was undertaken which included a 46-cell 0.93 cu m static feed water electrolysis module and three integrated mechanical components.

Beschreibung: Under NASA sponsorship, JPL is developing advanced, high rate Li-SOCl2 cells for future space missions. As part of this effort, Li-SOCl2 cells of various designs were examined for performance and safety. The cells differed from one another in several aspects, such as: nature of carbon cathode, catalysts, cell configuration, case polarity, and safety devices. Performance evaluation included constant-current discharge over a range of currents and temperatures. Abuse-testing consisted of shortcircuiting, charging, and over-discharge. Energy densities greater than 300 Wh/Kg at the C/2 rate were found for some designs. A cell design featuring a high-surface-area carbon cathode was found to deliver nearly 500 Wh/Kg at moderate discharge rates. Temperature influenced the performance significantly.

Beschreibung: The performance of a 12 V, 40 ampere-hour bipolar battery during various charge current, discharge current, temperature, and pressure operating conditions is investigated. The cell voltages, temperatures, ampere-hours, and watt-hours derived from the charge/discharge cycle tests are studied. Consideration is given to battery voltage and discharge capacity as a function of discharge current, the correlation between energy delivered on a discharge and battery temperature, battery voltage response to pulse discharges, and the voltage-temperature relationship. The data reveal that the bipolar Ni-H battery is applicable to high power systems.

Beschreibung: Two solar array designs developed for the Advanced Photovoltaic Solar Array program are described. The goal of the program is to develop solar arrays with higher mass specific power and power density and good robustness. The specific design requirements are: a beginning-of-life value of 130 W/kg, and end-of-life goals of 105 W/kg and 110 W/sq m. The two array-wing designs consisted of a single blanket. The differences in the blanket material (25 micron-thick Kapton versus 50 micron-thick carbon-loaded Kapton), solar cells (100 micron-thick wrap around versus 50 micron-thick 2 x 4 cm planar contact cells), and performance objectives (proposed industry requirements versus mission objectives) of the two designs are examined.

Beschreibung: The development of ultrathin silicon solar cell array modules from initial design to flight testing is discussed. Three 80-cell modules were subjected to the thermal soak test, the LEO thermal cycle test, and the solar array flight experiment, and six 48-cell welded modules were evaluated in the geosynchronous orbit thermal cycle test. It is observed that the electrical performance of the modules was not affected by the different environmental conditions. The automatic assembly of the cell modules, in particular the welding and solar cell glassing operation, is described. The specific power capabilities of Kapton, Kapton-Kevlar-Kapton, Kapton-graphite-Kapton, and Kapton-graphite-aluminum honeycomb-graphite solar array designs are assessed.

Beschreibung: The power systems for the Space Station manned core and platforms that have been selected in definition studies are described in this paper. The selected system for the platforms uses silicon arrays and Ni-H2 batteries. The power system for the manned core is a hybrid employing arrays and batteries identical to those on the platform along with solar dynamic modules using either Brayton or organic Rankine engines. The power system requirements, candidate technologies, and configurations that were considered, and the basis for selection, are discussed.

Beschreibung: Each Common Module (CM) of the Space Station must be capable of handling a 50 kW electricity supply, 25 kW for transmission and 25 kW for consumption. The power must be handled and managed by on-board systems, a necessity that dovetails with the objectives of Public Law 98-371, which mandates that the Space Station push the state of the art of automation and AI. Expert systems will be needed to handle the large data flow for the power system and to ensure that the system degrades gracefully. Features of the first expert systems expected for the power system, i.e., a dynamic load planner/scheduler and energy storage subsystem management, fault diagnosis/analysis, health status/trend analysis, and orbital replacement advisor expert systems, are described. Finally, growth Space Station expert systems applications are discussed.

Beschreibung: Past and future progress in the performance of control systems for large, liquid rocket engines typified such as current state-of-the-art, the Shuttle Main Engine (SSME), is discussed. Details of the first decade of efforts, which culminates in the F-1 and J-2 Saturn engines control systems, are traced, noting problem modes and improvements which were implemented to realize the SSME. Future control system designs, to accommodate the requirements of operation of engines for a heavy lift launch vehicle, an orbital transfer vehicle and the aerospace plane, are summarized. Generic design upgrades needed include an expanded range of fault detection, maintenance as-needed instead of as-scheduled, reduced human involvement in engine operations, and increased control of internal engine states. Current NASA technology development programs aimed at meeting the future control system requirements are described.

Beschreibung: A prototype 25 lb sub f gaseous oxygen/gaseous hydrogen thruster for Space Station propulsion application was designed and fabricated by Rocketdyne and endurance tested at the NASA/Marshall space Flight Center. The thruster incorporates a regeneratively cooled thrust chamber with a nozzle exit area ratio of 30, a 12-element coaxial injector, a spark igniter, and close-coupled propellant valves. Test results indicate that all major technology issues for long-life gaseous oxygen/gaseous hydrogen thrusters for Space Station application have been resolved.

Beschreibung: The results of a pre-development component demonstration program on the use of a gas generator-driven turbopump that increases the Space Shuttle's Orbital Maneuvering Engine (OME) operating pressure are given. Tests and analysis confirm the the capability of the concept to meet or exceed performance and life requirements. Storable propellant upper stage concepts are also discussed.

Beschreibung: Attention is given to the goals and preliminary determinations of the SP-100 program, whose objective is the design of space and lunar base nuclear powerplants capable of generating 100-1000 kW(e) for two years, with potential growth to 7 years. Current program studies are focusing on design concepts and the development status evaluation of critical technology. The dimensions of an SP-100 powerplant must allow transportation aboard the Space Shuttle. Reactor, heat conversion cycle, heat transfer medium, and thermal rejection system alternatives are discussed.

Beschreibung: NASA's planned Space Station has projected power requirements in the 75-300 kW range; attention is presently given to the range of power system configurations thus far proposed. These are a silicon solar cell system incorporating regenerative fuel cell or battery storage, with a 10-year lifetime, a solar-dynamic power system with phase-change or regenerative fuel cell energy storage, and a combination of these two alternatives. A development status evaluation is also given for the propulsion systems that may be used by next-generation boosters. These include such novel airbreathing systems as turboramjets, air liquefaction cycle rockets, airturboramjet/rockets, and supersonic combustion ramjets.

Beschreibung: Two propulsion systems have been selected for the Space Station: O/H rockets for high thrust applications and the multipropellant resistojets for low thrust needs. These thruster systems integrate very well with the fluid systems on the station. Both thrusters will utilize waste fluids as their source of propellant. The O/H rocket will be fueled by electrolyzed water and the resistojets will use stored waste gases from the environmental control system and the various laboratories. This paper presents the results of experimental efforts with O/H and resistojet thrusters to determine their performance and life capability.

Beschreibung: Reflective surfaces for Space Station power generation systems are required to withstand the atomic oxygen-dominated environment of near earth orbit. Thin films of platinum and rhodium, which are corrosion resistant reflective metals, have been deposited by ion beam sputter deposition onto various substrate materials. Solar reflectances were then measured as a function of time of exposure to a RF-generated air plasma.

Beschreibung: The development of a three-dimensional inelastic analysis methodology for the Space Shuttle main engine (SSME) structural components is described. The methodology is composed of: (1) composite load spectra, (2) probabilistic structural analysis methods, (3) the probabilistic finite element theory, and (4) probabilistic structural analysis. The methodology has led to significant technical progress in several important aspects of probabilistic structural analysis. The program and accomplishments to date are summarized.

Beschreibung: Extraterrestrial resources for space processing of chemicals, in general, and propellants, in particular, are explored quantitatively. It is seen that, for several candidate space mission scenarios, space processing of both space resources and earth-carried resources can make decisive differences in the mission success for a given payload. To fix ideas and demonstrate trends, the specific case of water splitting to extract oxygen, discard (or use without storage) the resulting hydrogen, and burn earth-carried noncryogenic liquid fuel(s) in a simple rocket motor, designed for periodic thrusting, is treated in some detail. Experimental hardware is assembled and demonstrated to perform adequately, besides showing compactness of the space-packaged 'capsule' module that is self-contained. Building upon previous studies, the concept of in situ propellant production (ISPP) is reexamined in light of more recent energy and materials technologies. Missions to comets and Mars Sample Return are mentioned as candidate scenarios. The mission duration, reliability-repairability of hardware, resource availability in low earth orbit (LEO), and the thrust requirements are considered in turn. It is seen that space storage of hydrogen for extended durations (5-10 years) involves problems that require detailed studies, besides involving many presently unanswered issues. A study of the energy option in LEO and in deep space is developed in simple terms. The different solar, radioisotope, and nuclear power sources are mentioned. Storage and handling of raw and processed chemicals are considered.

Beschreibung: Probabilistic structural analysis methods are particularly useful in the design and analysis of critical structural components and systems that operate in very severe and uncertain environments. These methods have recently found application in space propulsion systems to improve the structural reliability of Space Shuttle Main Engine (SSME) components. A computer program, NESSUS, based on a deterministic finite-element program and a method of probabilistic analysis (fast probability integration) provides probabilistic structural analysis for selected SSME components. While computationally efficient, it considers both correlated and nonnormal random variables as well as an implicit functional relationship between independent and dependent variables. The program is used to determine the response of a nickel-based superalloy SSME turbopump blade. Results include blade tip displacement statistics due to the variability in blade thickness, modulus of elasticity, Poisson's ratio or density. Modulus of elasticity significantly contributed to blade tip variability while Poisson's ratio did not. Thus, a rational method for choosing parameters to be modeled as random is provided.

Beschreibung: The design and performance of a arcjet nuclear electric propulsion spacecraft, suitable for use in a space reactor power system (SRPS) flight experiment, are outlined. The vehicle design is based on a 92-kW ammonia arcjet system operating at a specific impulse of 1050 s and an efficiency of 45 percent. The arcjet/gimbal system, power processing unit, and propellant feed system are described. A 100-kW SRPS is assumed and the spacecraft mass is baselined at 5250 kg, excluding the propellant and propellant feed system. A radiation/arcjet efflux diagnostics package is included in the performance analysis. This spacecraft, assuming a Shuttle launch from Kennedy Space Center, can perform a 35-deg inclination change and reach a final orbit of 35,860 km with a 120-day trip time, thus providing a four-month active load for the SRPS. Alternatively, a Titan IV launch could provide a mass margin of 120 kg to a 1000km, 58-deg final orbit in 74 days.

Beschreibung: The major requirements and guidelines that affect the manned Space Station configuration and the power systems are explained. The evolution of the Space Station power system from the NASA program development feasibility phase through the current preliminary design phase is described. Several early station concepts are described and linked to the present concept. The recently completed phase B tradeoff study selections of photovoltaic system technologies are described. The present solar dynamic and power management and distribution systems are also summarized for completeness.

Beschreibung: A new concept for a Space Station power system is proposed which reduces the drag effect of the solar panels and eliminates eclipsing by the Earth. The solar generator is physically separated from the Space Station, and power transmitted to the station by a microwave beam. The power station can thus be placed high enough that drag is not a significant factor. For a resonant orbit where the ratio of periods s:p is a ratio of odd integers, and the orbital planes nearly perpendicular, an orbit can be chosen such that the line of sight is never blocked if the lower orbit has an altitude greater than calculatable mininum. For the 1:3 resonance, this minimum altitude is 0.5 r(e). Finally, by placing the power station into a sun-synchronous orbit, it can be made to avoid shadowing by the Earth, thus providing continuous power.

Beschreibung: During the conceptual design phase a 20-kHz power distribution system was selected as the reference for the Space Station. The system is single-phase 400 VRMS, with a sinusoidal wave form. The initial user power level will be 75 kW with growth to 300 kW. The high-frequency system selection was based upon considerations of efficiency, weight, safety, ease of control, interface with computers, and ease of paralleling for growth. Each of these aspects will be discussed as well as the associated trade-offs involved. An advanced development program has been instituted to accelerate the maturation of the high-frequency system. Some technical aspects of the advanced development will be discussed.

Beschreibung: A brief history of the development of electrical power systems from the earliest manned space flights illustrates a natural trend toward a growth of electrical power requirements and operational lifetimes with each succeeding space program. A review of the design philosophy and development experience associated with the Space Shuttle Orbiter electrical power system is presented, beginning with the state of technology at the conclusion of the Apollo Program. A discussion of prototype, verification, and qualification hardware is included, and several design improvements following the first Orbiter flight are described. The problems encountered, the scientific and engineering approaches used to meet the technological challenges, and the results obtained are stressed. Major technology barriers and their solutions are discussed, and a brief Orbiter flight experience summary of early Space Shuttle missions is included. A description of projected Space Station power requirements and candidate system concepts which could satisfy these anticipated needs is presented. Significant challenges different from Space Shuttle, innovative concepts and ideas, and station growth considerations are discussed. The Phase B Advanced Development hardware program is summarized and a status of Phase B preliminary tradeoff studies is presented.

Beschreibung: The Space Station represents the next major U.S. commitment in space. The efficient delivery of power to multiple user loads is key to that success. In 1969, NASA Lewis Research Center began a series of studies with component and circuit developments that led to the high frequency bi-directional, four quadrant resonant driven converter. Additional studies and subsequent developments into the early 1980's have shown how the high frequency ac power system could provide overall advantages to many aerospace power systems. Because of its wide versatility, it also has outstanding advantages for the Space Station Program and its wide range of users. High frequency ac power provides higher efficiency, lower cost, and improved safety. The 20 kHz power system has exceptional flexibility, is inherently user friendly, and is compatible with all types of energy sources - photovoltaic, solar dynamic, rotating machines or nuclear Lewis distribution system testbed. The testbed demonstrates flexibility, versatility, and transparency to user technology as well as high efficiency, low mass, and reduced volume.

Beschreibung: Two computational techniques commonly employed in the calculation of rocket and thruster expansion plumes are assessed. These are the method of characteristics (MOC), which is derived from the continuum Euler equations, and the direct simulation Monte Carlo (DSMC) method, which adopts a discrete particle approach. These techniques vary both in the computational expense and in the accuracy and detail of the solutions that they provide, depending upon the regime of application. The assessment is made with reference to the plume expanding from a small monopropellant hydrazine thruster and concentrates on the isentropic core of the jet for the flow regime lying between the continuum and free molecular limits. It is found that the more numerically intensive DSMC method offers the better correspondence to the available experimental data. In addition, large differences in typical impingement effects such as drag force and heat transfer are found at the free molecular limit of the plume expansion for the two predictive techniques. It is concluded that accurate estimation of impingement potential may only be achieved through application of the discrete particle method.

Beschreibung: The rudiments of a rocket thruster that receives its enthalpy from a remote energy source, a laser, are described. An experimental study is discussed that provides details of the physics for assessing the feasibility of using hydrogen plasmas for accepting and converting this energy to enthalpy. A plasma ignition scheme that uses a pulsed CO2 laser has been developed and the properties of the ignition spark documented, including breakdown intensities in hydrogen. A complete diagnostic system, capable of determining plasma temperature and the plasma absorptivity for subsequent steady-state absorption of a high-power CO2 laser beam, is developed and demonstrative use is discussed for the preliminary case study, a 2 atm laser-supported argon plasma.

Beschreibung: Previous studies have shown that many desirable planetary exploration missions require large injection delta-V. Solar Thermal Rocket (STR) propulsion, under study for orbit-raising applications may enhance or enable such high-energy missions. The required technology of thermal control for liquid hydrogen propellant is available for the required storage duration. Self-deploying, inflatable solar concentrators are under study. The mass penalty for passive cryogenic thermal control, liquid hydrogen tanks and solar concentrators does not compromise the specific impulse advantage afforded by the STR as compared to chemical propulsion systems. An STR injection module is characterized and performance is evaluated by comparison to electric propulsion options for the Saturn Orbiter Titan Probe (SOTP) and Uranus Flyby Uranus Probe (UFUP) missions.

Beschreibung: In preparation for the development of a manned space station program of advanced technology and development to make new advanced propulsion options available for the initial space station in the 1990's is described. This paper reviews the objectives of the advanced technology and development program in propulsion, describes its origin and how it relates to the forthcoming development program. The advanced propulsion and fluid management systems to be investigated in the program are discussed along with the rationale for their selection. Finally, the systems test program is discussed.

Beschreibung: A propulsion module to augment the Centaur G-Prime and the Aerobraked OTV (AOTV) injection energy (C sub 3) was studied. The characteristics and performance of a variety of Earth-storable and cryogenic propulsion systems are presented. A pump-fed, cryogenic O2/H2 propulsion system enables the elimination of a three-year delta V Earth gravity assist (delta VEGA) maneuver for several planetary missions currently under consideration by the NASA. This trip time reduction can significantly reduce mission support costs, reduce spacecraft (S/C) life requirements and potentially increase the probability of mission success. This study also shows that an O2/H2 propulsion module, developed for Centaur C sub 3 augmentation can be used with a space-based AOTV in the return mode, allowing the reuse of the high-value AOTV while still delivering the required high-injection energy for direct planetary missions. The propulsion module performance was estimated for a space shuttle delivery capability to LEO of 65,000 lb sub m and 75,000 lb sub m. The required minimum thrust level to minimize gravity losses was also determined. For several currently planned NASA planetary missions, the Centaur G-Prime injection energy is augmented by a delta VEGA maneuver. For these missions, direct injection by the Centaur cannot provide a shorter trip time than the delta VEGA injection trip time.

Beschreibung: A research and technology program for advanced high pressure, oxygen-hydrogen rocket propulsion technology is presently being pursued by the National Aeronautics and Space Administration (NASA) to establish the basic discipline technologies, develop the analytical tools, and establish the data base necessary for an orderly evolution of the staged combustion reusable rocket engine. The need for the program is based on the premise that the USA will depend on the Shuttle and its derivative versions as its principal Earth-to-orbit transportation system for the next 20 to 30 yr. The program is focused in three principal areas of enhancement: (1) life extension, (2) performance, and (3) operations and diagnosis. Within the technological disciplines the efforts include: rotordynamics, structural dynamics, fluid and gas dynamics, materials fatigue/fracture/life, turbomachinery fluid mechanics, ignition/combustion processes, manufacturing/producibility/nondestructive evaluation methods and materials development/evaluation. An overview of the Advanced High Pressure Oxygen-Hydrogen Rocket Propulsion Technology Program Structure and Working Groups objectives are presented with highlights of several significant achievements.

Beschreibung: Several samples are presented of CFD-generated flow ribbon images of fuel flow in the SSME. The images result from simulations of H2 flow through a design iteration of the main injector, the hot gas manifold and the fuel bowl section. The color-coded ribbons provide three-dimensional perspectives which indicate the direction and orientation of the flow and the velocity magnitude in intervals along the flow path.

Beschreibung: An evaluation is made of the various technologies that have been considered for incorporation into the NASA Space Station's solar power system. A major feature of the system is noted to be the use of both 25 kW capacity of photovoltaic power and two 25-kW turbine-driven generators based on the heating of a working fluid by a mirror concentrator dish. Fuel cells will be used to store excess electrical energy, together with nickel-cadmium batteries. The selection of this manned Space Station power system was arrived at through a comparison of six different configurations.

Beschreibung: In previous tests of liquid oxygen cooling of hydrocarbon fueled rocket engines, small oxygen leaks developed at the throat of the thrust chamber and film cooled the hot gas side of the chamber wall without resulting in catastrophic failure. However, more testing is necessary to demonstrate that a catastropic failure would not occur if cracks developed further upstream between the injector and the throat, where the boundary layer has not been established. Since under normal conditions cracks are expected to form in the throat region of the thrust chamber, cracks must be initiated artificially in order to control their location. Several methods of crack initiation are discussed here.

Beschreibung: An experimental investigation was conducted to determine the thrust performance attainable from high-area-ratio rocket nozzles. A modified Rao-contoured nozzle with an expansion area of 1030 was test fired with hydrogen-oxygen propellants at altitude conditions. The nozzle was also tested as a truncated nozzle, at an expansion area ratio of 428. Thrust coefficient and thrust coefficient efficiency values are presented for each configuration at various propellant mixture ratios (oxygen/fuel). Several procedural techniques were developed permitting improved measurement of nozzle performance. The more significant of these were correcting the thrust for the aneroid effects, determining the effective chamber pressure, and referencing differential pressure transducers to a vacuum reference tank.

Beschreibung: Aluminum oxide particles from the exhaust of the Space Shuttle were collected immediately after the launch of the SEPEX mission and during the descent over the altitude interval of 7.6-4.6 km. The SEM examination revealed that the particles were spherical and ranged in diameter from about 0.1 micron to 10 microns. Results from the energy dispersive analysis (by an X-ray method) and of the particle chemistry (by electron spectroscopy) confirmed that the particles were predominantly composed of aluminum and oxygen. The particle size distribution of the Al2O3 was bimodal, with one observed peak centered near 2.0 microns; the other distribution mode centered at a diameter of less than 0.3 micron, but could not be accurately located. A mass median diameter was slightly less than 2 microns. Evaluation of ice nucleation activity revealed only a small fraction (about 1 ppm) of active ice nuclei among the Al2O3 particulates.

Beschreibung: A Microwave Electric Propulsion (MEP) concept is developed for an unmanned Orbit Transfer Vehicle (OTV). The concept is based on the use of beamed microwave power and on an extrapolation of ion thruster technology. Beamed microwave power transmission is discussed in terms of its relationship to spacecraft propulsion. Characteristics of an MEP OTV are determined and performance is evaluated by comparison to a variety of alternative propulsion systems for the completion of a ten-year mission model.

Beschreibung: Advanced space propulsion systems are required to meet projected Air Force needs through the year 2000. Most of these missions require a large, on-orbit impulse capability. High specific impulse (I sub sp) electric engines can provide this impulse while consuming relatively little propellant. An arcjet engine system, which operates in the range of 800 to 2000 s I sub sp, is a promising candidate to meet these projected Air Force mission needs. This electric propulsion system is ideally suited to missions currently under consideration, such as the Space-based Radar and other space platforms, because sufficient power is already installed for other functions on the spacecraft. Also, arcjet systems are attractive for NASA near-term, low-cost Mariner Mark II missions to Saturn and Uranus. Development of arcjet engines was an Air Force and NASA-sponsored activity that proceeded vigorously from its inception during the late 1950's up to the mid-1960's when the programs were terminated. This paper describes thermal arcjet technology as it was developed over two decades ago and points to the direction this technology development should proceed in the future. In particular, operation with storable propellants such as ammonia and hydrazine are considered. The performance, applicability and advantages of these systems in terms of increased payload and/or decreased trip times are discussed.

Beschreibung: Tests were conducted to investigate the effect of vacuum facility pressure on the performance of small thruster nozzles. Thrust measurements of two converging-diverging nozzles with an area ratio of 140 and an orifice plate flowing unheated nitrogen and hydrogen were taken over a wide range of vacuum facility pressures and nozzle throat Reynolds numbers. In the Reynolds number range of 2200 to 12,000 there was no discernable viscous effect on thrust below an ambient to total pressure ratio of 1000. In nearly all cases, flow separation occurred at a pressure ratio of about 1000. This was the upper limit for obtaining an accurate thrust measurement for a conical nozzle with an area ratio of 140.

Beschreibung: Experiments were performed to determine the compatibility of materials and propellants for electro-thermal thrusters. Candidate propellants for resistojet propulsion include carbon dioxide, methane, hydrogen, ammonia, and hydrazine. The materials being examined are grain stabilized platinum for resistojets for space station and rhenium for high performance resistojets for satellites. Heater mass loss and deterioration of materials were evaluated. A coiled tube of platinum, with yttria dispersed throughout the base material to inhibit grain growth, was tested in carbon dioxide at 1300 C for 2000 hr. Post-test examination indicated the platinum-yttria heater would last over 100,000 hr with less than 10 percent mass loss. Short-term compatibility tests were conducted to test the integrity of the platinum-yttria in hydrogen, methane, carbon dioxide/methane mixtures and ammonia environments. In each of these 100 hr tests, the platinum-yttria mass change indicated a minimum coil life of 100,000 hr. Facility related effects were investigated in materials tests using rhenium heated to high temperatures. Vacuum facility water reduction was monitored using a mass spectrometer. In vacuum environments obtained using only diffusion pumping and those obtained with the assistance of cryogenic equipment there were mass gains in the rhenium heaters. These mass gains were the result of the high amount of oxygen and water contained in the gas. Propellant purity and preferred test facility environments are discussed.

Beschreibung: This paper describes the considerations given to selection of 20 and 50 A h nickel-cadmium cells and batteries for NASA/Goddard's Solar Max and Landsat D missions. Results of cell and battery manufacturer testing and improvements in design required by NASA standard specifications are shown. Operation of three batteries in parallel using a single voltage limit/current taper charge control system is described along with suggestions for optimizing life and uniformity. The results of three years of in-orbit operation is presented.

Beschreibung: The design of the power system for supplying the Space Station with insolation-generated electricity is the main Phase B task at NASA-Lewis Center. The advantages and limitations of two types of power systems, the photovoltaic arrays (PV) and the solar dynamic system (SD), are discussed from the points of view of cost, overall systems integration, and growth. Subsystems of each of these options are described, and a sketch of a projected SD system is shown. The PV technology is well developed and proven, but its low efficiency calls for solar arrays of large areas, which affect station dynamics, control, and drag compensation. The SD systems would be less costly to operate than VP, and are more efficient, needing less deployed area. The major drawback of the SD is its infancy. The conservative and forgiving designs for some of its components must still be created and tested, and the development risks assessed.

Beschreibung: The experimental and analytical efforts performed for fracture control of the Space Shuttle auxiliary power unit (APU) wheel are described and a summary of fracture mechanics concepts relevant to safe-life analysis of fatigue loaded parts is given. An environmental crack growth test program is conducted by NASA on candidate wheel materials exposed to decomposed hydrazine which is found to be no more severe in causing crack growth than an environment of high-temperature air. Details of the crack growth testing and the safe-life analysis are presented. The results show that special nondestructive examination is needed for the APU wheel to meet the required mission life for either the maximum design or expected speed-range operations.

Beschreibung: The main objective of this study is to develop a new test method that is suitable for the assessment of the resistance of aerospace cables to arc tracking for different specific environmental and network conditions of spacecrafts. This paper reports the purpose, test conditions, test specimen, test procedure, and test acceptance criteria of seven different (200-250 mm long) cables.

Beschreibung: This report contains viewgraphs on arc tracking tests in various aerospace environments. It has the following six sections: LeRC arc tracking tests parameters, apparatus, sample description, procedure, arc tracking test results, and discussion.

Beschreibung: The results of the testing of wire insulation materials for space applications is presented in this report. The wire insulations tested were partially fluorinated polyimide, extruded ETFE, extruded PTFE, PTFE tape, and PTFE/Kapton. The tests performed were flammability tests, odor tests, compatibility tests with aerospace fluids, offgassing tests, and thermal vacuum stability tests.

Beschreibung: The objectives of the NASA Wiring for Space Applications program were to investigate the effects of atomic oxygen (AO), ultraviolet (UV) radiation, and AO with UV synergistic effects on wire insulation materials. The AO exposure was on the order of 10(exp 21) atoms/sq cm and the vacuum UV radiation was on the order of 10,000 ESH. The results of these tests are presented in this document

Beschreibung: The electrical power wiring tests results from the NASA Wiring for Space Applications program are presented. The goal of the program was to develop a base for the building of a lightweight, arc track-resistant electrical wiring system for aerospace applications. This new wiring system would be applied to such structures as pressurized modules, trans-atmospheric vehicles, LEO/GEO environments, and lunar and Martian environments. Technological developments from this program include the fabrication of new insulating materials, the production of new wiring constructions, an improved system design, and an advanced circuit protection design.

Beschreibung: Oxidizer propellant systems for liquid-fueled rocket engines must meet stringent cleanliness requirements for particulate and nonvolatile residue. These requirements were established to limit residual contaminants which could block small orifices or ignite in the oxidizer system during engine operation. Limiting organic residues in high pressure oxygen systems is particularly important. The current method of cleanliness verification used by Rocketdyne requires an organic solvent flush of the critical hardware surfaces. The solvent is filtered and analyzed for particulate matter, followed by gravimetric determination of the nonvolatile residue (NVR) content of the filtered solvent. The organic solvents currently specified for use (1,1,1-trichloroethane and CFC-113) are ozone-depleting chemicals slated for elimination by December 1995. A test program is in progress to evaluate alternative methods for cleanliness verification that do not require the use of ozone-depleting chemicals and that minimize or eliminate the use of solvents regulated as hazardous air pollutants or smog precursors. Initial results from the laboratory test program to evaluate aqueous-based methods and organic solvent flush methods for NVR verification are provided and compared with results obtained using the current method. Evaluation of the alternative methods was conducted using a range of contaminants encountered in the manufacture of rocket engine hardware.

Beschreibung: The Solid Rocket Motors (SRM) used by NASA to propel the Space Shuttle employ gimballing nozzles as a means for vehicular guidance during launch and ascent. Gimballing a nozzle renders the pressure field of the exhaust gases nonaxisymmetric. This has two effects: (1) it exerts a torque and side load on the nozzle; and (2) the exhaust gases flow circumferentially in the aft-dome region, thermally loading the flexible boot, case-to-nozzle joint, and casing insulation. The use of CFD models to simulate such flows is imperative in order to assess SRM design. The grids for these problems were constructed by obtaining information from drawings and tabulated coordinates. The 2D axisymmetric grids were designed and generated using the EZ-Surf and GEN2D surface and grid generation codes. These 2D grids were solved using codes such as FDNS, GASP, and MINT. These axisymmetric grids were rotated around the center-line to form 3D nongimballed grids. These were then gimballed around the pivot point and the gaps or overlaps resurfaced to obtain the final domains, which contained approximately 366,000 grid points. The 2D solutions were then rotated and manipulated as appropriate for geometry and used as initial guesses in the final solution. The analyses were used in answering questions about flight criteria.

Beschreibung: A two-year feasibility and test program to solve the problem of unburned confined hydrogen at the Vandenberg Space Launch Complex Six (SLC-6) during Space Shuttle Main Engine (SSME) firings is discussed. A novel steam inerting design was selected for development. Available sound suppression water is superheated to flash to steam at the duct entrance. Testing, analysis, and design during 1987 showed that the steam inerting system (SIS) solves the problem and meets other flight-critical system requirements. The SIS design is complete and available for installation at SLC-6 to support shuttle or derivative vehicles.

Beschreibung: The appearance of visible objects in the exhaust plume of space shuttle main engines (SSME) during test firings is discussed. A program was undertaken to attempt to identify anomalous material resulting from wear, normal or excessive, of internal parts, allowing time monitoring of engine condition or detection of failure precursors. Measurements were taken during test firings at Stennis Space Center and at the Santa Suzanna facility in California. The results indicated that a system having high spectral resolution, a fast time response, and a wide spectral range was required to meet all requirements, thus two special systems have been designed and built. One is the Optical Plume Anomaly Detector (OPAD). The other instrument, which is described in this report, is the superspectrometer, an optical multichannel analyzer having 8,192 channels covering the spectral band 250 to 1,000 nm.

Beschreibung: The goal of this work is to develop and test thin-film thermocouples for Space Shuttle Main Engine (SSME) components. Thin-film thermocouples have been developed for aircraft gas turbine engines and are in use for temperature measurement on turbine blades up to 1800 F. Established aircraft engine gas turbine technology is currently being adapted to turbine engine blade materials and the environment encountered in the SSME, especially severe thermal shock from cryogenic fuel to combustion temperatures. Initial results using coupons of MAR M-246 (+Hf) and PWA 1480 have been followed by fabrication of thin-film thermocouples on SSME turbine blades. Current efforts are focused on preparing for testing in the Turbine Blade Tester at the NASA Marshall Space Flight Center (MSFC). Future work will include testing of thin-film thermocouples on SSME blades of single crystal PWA 1480 at MSFC.

Beschreibung: The development of probabilistic structural analysis methods is a major part of the SSME Structural Durability Program and consists of three program elements: composite load spectra, probabilistic finite element structural analysis, and probabilistic structural analysis applications. Recent progress includes: (1) the effects of the uncertainties of several factors on the HPFP blade temperature pressure and torque, (2) the evaluation of the cumulative distribution function of structural response variables based on assumed uncertainties on primitive structural variables, and (3) evaluation of the failure probability. Collectively, the results obtained demonstrate that the structural durability of critical SSME components can be probabilistically evaluated.

Beschreibung: Advanced auxiliary propulsion system (APS) technology has the potential to both, increase the payload capability of earth-to-orbit (ETO) vehicles by reducing APS propellant mass, and simplify ground operations and logistics by reducing the number of fluids on the vehicle and eliminating toxic, corrosive propellants. The impact of integrated cryogenic APS on vehicle payloads is addressed. In this system, launch propulsion system residuals are scavenged from integral launch propulsion tanks for use in the APS. Sufficient propellant is preloaded into the APS to return to earth with margin and noncomplete scavenging assumed. No propellant conditioning is required by the APS, but ambient heat soak is accommodated. High temperature rocket materials enable the use of the unconditioned hydrogen/oxygen in the APS and are estimated to give APS rockets specific impulse of up to about 444 sec. The payload benefits are quantified and compared with an uprated monomethyl hydrazine/nitrogen tetroxide system in a conservative fashion, by assuming a 25.5 percent weight growth for the hydrogen/oxygen system and a 0 percent weight growth for the uprated system. The combination and scavenging and high performance gives payload impacts which are highly mission specific. A payload benefit of 861 kg (1898 lbm) was estimated for a Space Station Freedom rendezvous mission and 2099 kg (4626 lbm) for a sortie mission, with payload impacts varying with the amount of launch propulsion residual propellants. Missions without liquid propellant scavenging were estimated to have payload penalties, however, operational benefits were still possible.

Beschreibung: The generation and deposition of carbon was studied in the Carbon Deposition Program using subscale hardware with LO2/Liquid Natural Gas (LNG) and LO2/Methane propellants at low mixture ratios. The purpose of the testing was to evaluate the effect of methane purity and full scale injection density on carbon deposition. The LO2/LNG gas generator/preburner testing was performed at mixture ratios between 0.24 and 0.58 and chamber pressures from 5.8 to 9.4 MPa (840 to 1370 psia). A total of seven 200 second duration tests were performed. The LNG testing occurred at low injection densities, similar to the previous LO2/RP-1, LO2/propane, and LO2/methane testing performed on the carbon deposition program. The current LO2/methane test series occurred at an injection density factor of approximately 10 times higher than the previous testing. The high injection density LO2/methane testing was performed at mixture ratios between from 0.23 to 0.81 and chamber pressures from 6.4 to 15.2 MPa (925 to 2210 psia). A total of nine high injection density tests were performed. The testing performed demonstrated that low purity methane (LNG) did not produce any detectable change in carbon deposition when compared to pure methane. In addition, the C* performance and the combustion gas temperatures measured were similar to those obtained for pure methane. Similar results were obtained testing pure methane at higher propellant injection densities with coarse injector elements.

Beschreibung: Vacuum Microelectronic devices can be described as vacuum transistors or micro-miniature vacuum tubes, as one chooses. The fundamental reason behind this new technology is the very large current densities available from field emitters, namely as high as 10(8) A/sq cm. Array current densities as high as 1000 A/sq cm have been measured. Total electron transit times from source to drain for 1 micron feature size devices have been predicted to be about 150fs. This very short transit time implies the possibility of submillimeter wave transmitters and rectennas in devices which can operate with reasonably high voltages and which are small in size and are lightweight. In addition, they are expected to be extremely radiation hard and very temperature insensitive. That is, they are expected to have radiation hardness characteristics similar to vacuum tubes, and both the high temperature and low temperature limits should be determined by the package. That is, there should be no practical intrinsic temperature or carrier freezeout problems for devices based on metals or composites. But the technology is difficult to implement at the present time because it is based on 300 to 500 angstrom radius field emitters which must be relatively uniform. There is also the need to understand the non-equilibrium transport physics in the near-surface regions of the field emitters.

Beschreibung: The concept of a pyro thruster, combining an automatic structural attachment with quick disconnect and thrusting capability, is described. The purpose of the invention is to simplify booster installation, disengagement, and jettison functions for the U.S. Air Force Advanced Launch Systems (ALS) program.

Beschreibung: Vehicle/engine analysis studies have identified the High/Dual Mixture Ratio O2/H2 Engine cycle as a leading candidate for an advanced Single Stage to Orbit (SSTO) propulsion system. This cycle is designed to allow operation at a higher than normal O/F ratio of 12 during liftoff and then transition to a more optimum O/F ratio of 6 at altitude. While operation at high mixture ratios lowers specific impulse, the resultant high propellant bulk density and high power density combine to minimize the influence of atmospheric drag and low altitude gravitational forces. Transition to a lower mixture ratio at altitude then provides improved specific impulse relative to a single mixture ratio engine that must select a mixture ratio that is balanced for both low and high altitude operation. This combination of increased altitude specific impulse and high propellant bulk density more than offsets the compromised low altitude performance and results in an overall mission benefit. Two areas of technical concern relative to the execution of this dual mixture ratio cycle concept are addressed. First, actions required to transition from high to low mixture ratio are examined, including an assessment of the main chamber environment as the main chamber mixture ratio passes through stoichiometric. Secondly, two approaches to meet a requirement for high turbine power at high mixture ratio condition are examined. One approach uses high turbine temperature to produce the power and requires cooled turbines. The other approach incorporates an oxidizer-rich preburner to increase turbine work capability via increased turbine mass flow.

Beschreibung: Characterization of liquid rocket engine injector elements is an important part of the development process for rocket engine combustion devices. Modern nonintrusive instrumentation for flow velocity and spray droplet size measurement, and automated, computer-controlled test facilities allow rapid, low-cost evaluation of injector element performance and behavior. Application of these methods in rocket engine development, paralleling their use in gas turbine engine development, will reduce rocket engine development cost and risk. The Alternate Turbopump (ATP) Hot Gas Systems (HGS) preburner injector elements were characterized using such methods, and the methodology and some of the results obtained will be shown.

Beschreibung: Recent hot fire testing at the Marshall Space Flight Center (MSFC) has indicated the swirl-coaxial element to be a viable candidate for the STBE injector. Plans are to test the current 40K lbf thrust injector at the higher chamber pressure and colder fuel temperature which are anticipated for STBE. A cold flow program to characterize the swirl coax element over a range of operating points was conducted. The results are presented and compared to the hot fire data. Predictions for compatibility, performance and stability are then presented for the uprated test conditions.

Beschreibung: A LOX/LH2 high/variable mixture ratio booster upper stage is described. The engine has high thrust-weight ratio as a booster and high specific impulse as an upper stage engine. Operation at high mixture ratio utilizes the propellants at high bulk density. The engine may use multiple turbopump-preburners for higher thrust ratings. The engine uses the full flow cycle to obtain minimum turbine inlet temperatures for a given chamber pressure and to avoid interpropellant shaft seals and other single point failure modes. A portion of the liquid hydrogen is used to regeneratively cool the thrust chamber assembly. The warmed hydrogen coolant is then used to drive the fuel boost turbopump. All propellants arrive at the gas-gas injector ready to burn. Shear mixing of the parallel flowing high velocity, low density fuel-rich gases with the high density, low velocity oxidizer-rich gases provides complete combustion with a modest chamber volume. Combustion stability is assured by the injection of the heated fuel-rich gases and the comparatively low volume ratio of the propellants before and after combustion. The high area ratio nozzle skirt is fitted with a low area ratio nozzle skirt insert for optimum low altitude performance. The overall engine characteristics make it a candidate for ALS, Shuttle-C, LRB, and SSTO applications.

Beschreibung: Studies have indicated that xenon ion propulsion systems can enable the use of smaller earth-launch vehicles for satellite placement which results in significant cost savings. These analyses have assumed the availability of advanced, high power ion thrusters-operating at about 10 kW or higher. A program was initiated to explore the viability of operating 50 cm diameter ion thrusters at this power level. Operation with several discharge chamber and ion extraction grid set combinations was demonstrated and data were obtained at power levels to 16 kW. Fifty cm diameter thrusters using state of the art 30 cm diameter grids or advanced technology 50 cm diameter grids allow discharge power and beam current densities commensurate with long life at power levels up to 10 kW. In addition, 50 cm diameter thrusters are shown to have potential for growth in thrust and power levels beyond 10 kW.

Beschreibung: The concept of the Earth as a closed ecological system is addressed from the point of view of the availability and use of energy from space and its potential influence on the economies of both developed and developing countries. The results of past studies of the solar power satellite (SPS) are reviewed, and the current international activities exploring various aspects of an SPS are mentioned. The functions of an SPS, including collection of solar energy in orbit, conversion to an intermediate form of energy, transmission of energy from orbit to Earth, and conversion to useful energy in the most appropriate form are discussed. Directions for future developments are addressed including a suggested planning framework. Salient aspects of SPS technologies are presented, and the potential benefits of the uses of lunar materials for the SPS construction are outlined. Scenarios within the context of international participation in a global SPS system are presented. The conclusion is drawn that an SPS system is one of the few promising, globally applicable power generation options that has the potential to meet energy demands in the 21st Century and to achieve the inevitable transition to inexhaustible and renewable energy sources.

Beschreibung: Recent developments in high energy lasers, adaptive optics, and atmospheric transmission bring laser propulsion much closer to realization. Proposed here is a reference vehicle for study which consists of payload and solid propellant (e.g. ice). A suitable laser pulse is proposed for using a Laser Supported Detonation wave to produce thrust efficiently. It seems likely that a minimum system (10 Mw CO2 laser and 10 m dia. mirror) could be constructed for about $150 M. This minimum system could launch payloads of about 13 kg to a 400 km orbit every 10 minutes. The annual launch capability would be about 683 tons times the duty factor. Laser propulsion would be an order of magnitude cheaper than chemical rockets if the duty factor was 20 percent (10,000 launches/yr). Launches beyond that would be even cheaper. The chief problem which needs to be addressed before these possibilities could be realized is the design of a propellant to turn laser energy into thrust efficiently and to withstand the launch environment.

Beschreibung: Some large scale power beaming applications are proposed for the purpose of stimulating research. The first proposal is for a combination of large phased arrays on the ground near power stations and passive reflectors in geostationary orbit. The systems would beam excess electrical power in microwave form to areas in need of electrical power. Another proposal is to build solar arrays in deserts and beam the energy around the world. Another proposal is to use lasers to beam energy from earth to orbiting spacecraft.