Nuclear Brayton cycle powerplants for space applications.
Parametric analysis and system optimization of nuclear reactor heated Brayton cycle space power plants, discussing turbomachinery performance and shielding weight factors
NUCLEAR SHIELDING↗
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Bonded orthotropic strips with cracks
The elastostatic problem for a nonhomogeneous plane which consists of two sets of periodically arranged dissimilar orthotropic strips is considered. It is assumed that the plane contains a series of collinear cracks perpendicular to the interfaces and is loaded in tension away from and perpendicular to the cracks. The problem of cracks fully imbedded into the homogeneous strips is considered. The singular behavior of the stresses for two special crack geometries is studied. The first is the case of a broken laminate in which the crack tips touch the interfaces. The second is the case of cracks crossing the interfaces. An interesting result found from the analysis of the latter is that for certain orthotropic material combinations the stress state at the point of intersection of a crack and an interface may be bounded whereas in isotropic materials at this point stresses are always singular. A number of numerical examples are worked out to separate the primary material parameters influencing the stress intensity factors and the powers of stress singularity, and to determine the trends regarding the influence of the secondary parameters. Some numerical results are given for the stress intensity factors in certain basic crack geometries and for typical material combinations.
Delale, F.↗
Crossed, Small-Deflection Energy Analyzer for Wind/Temperature Spectrometer
Determination of neutral winds and ion drifts in low-Earth-orbit missions requires measurements of the angular and energy distributions of the flux of neutrals and ions entering the satellite from the ram direction. The magnitude and direction of the neutral-wind (or ion-drift) determine the location of the maximum in the angular distribution of the flux. Knowledge of the angle of maximum flux with respect to satellite coordinates (pointing) is essential to determine the wind (or ion-drift) vector. The crossed Small-Deflection Energy Analyzer (SDEA) spectrometer (see Figure 1) occupies minimal volume and consumes minimal power. Designed for upper atmosphere/ionosphere investigations at Earth altitudes above 100 km, the spectrometer operates by detecting the angular and energy distributions of neutral atoms/molecules and ions in two mutually perpendicular planes. In this configuration, the two detection planes actually cross at the spectrometer center. It is possible to merge two SDEAs so they share a common optical axis and alternate measurements between two perpendicular planes, and reduce the number of ion sources from two to one. This minimizes the volume and footprint significantly and reduces the ion source power by a factor of two. The area of the entrance aperture affects the number of ions detected/second and also determines the energy resolution. Thermionic emitters require heater power of about 100 mW to produce 1 mA of electron beam current. Typically, electron energy is about 100 eV and requires a 100-V supply for electron acceleration to supply an additional 100 mW of power. Thus, ion source power is at most 200 mW. If two ion sources were to be used, the ion source power would be, at most, 400 mW. Detector power, deflection voltage power, and microcontroller and other functions require less than 150 mW. A WTS (wind/ temperature spectrometer) with two separate optical axes would consume about 650 mW, while the crossed SDEA described here consumes about 350 mW. The entrance aperture has a diameter of 0.004 in. (0.10 mm) to provide the required energy resolution between 0.05 and 0.15. This design (see Figure 2) provides a WTS occupying a volume less than 40 cm(sup 3), on a footprint of diameter about 1.5 in. (38 mm). The Crossed SDEA offers many advantages in the measurements of neutral wind and ion drifts in the Earth's thermosphere. As such, it will be useful in future commercial satellites dedicated to monitoring the ionosphere with a view to improving the integrity and predictability of GPS operations.
Herrero, Federico A.↗
Bonded orthotropic strips with cracks
The elastostatic problem for a nonhomogeneous plane which consists of two sets of periodically arranged dissimilar orthotropic strips is considered. First, the problem of cracks fully imbedded into the homogeneous strips is considered. Then, the singular behavior of the stresses for two special crack geometries is studied in some detail. The first is the case of a broken laminate in which the crack tips touch the interfaces. The second is the case of cracks crossing the interfaces. A number of numerical examples are worked out in order to separate the primary material parameters influencing the stress intensity factors and the powers of stress singularity, and to determine the trends regarding the influence of the secondary parameters. Finally, some numerical results are given for the stress intensity factors in certain basic crack geometries and for typical material combinations.
Delale, F.↗
Effects off system factors on the economics of and demand for small solar thermal power systems
Market penetration as a function time, SPS performance factors, and market/economic considerations was estimated, and commercialization strategies were formulated. A market analysis task included personal interviews and supplemental mail surveys to acquire statistical data and to identify and measure attitudes, reactions and intentions of prospective SPS users. Interviews encompassed three ownership classes of electric utilities and industrial firms in the SIC codes for energy consumption. A market demand model was developed which utilized the data base developed, and projected energy price and consumption data to perform sensitivity analyses and estimate potential market for SPS.
Source record↗
Thermionic reactors for electric propulsion - Parametric studies.
Parametric study of in-core thermionic power plants for electric propulsion, describing factors affecting transmission lines and power conditioning equipment
Gietzen, A. J.↗
The effect of material heterogeneity and random loading on the mechanics of fatigue crack growth
This paper reviews experimental work on the influence of variable amplitude or random loads on the mechanics and micromechanisms of fatigue crack growth. Implications are discussed in terms of the crack driving force, local plasticity, crack closure, crack blunting, and microstructure. Due to heterogeneity in the material's microstructure, the crack growth rate varies with crack tip position. Using the weakest link theory, an expression for crack growth rate is obtained as the expectation of a random variable. This expression is used to predict the crack growth rates for aluminum alloys, a titanium alloy, and a nickel steel in the mid-range region. It is observed, using the present theory, that the crack growth rate obeys the power law for small stress intensity factor range, and that the power is a function of a material constant.
Srivatsan, T. S.↗
Solar power
This paper describes categories of solar technologies and identifies those that are economic. It compares the private costs of power from solar, wind, nuclear, coal, oil, and gas generators. In the southern United States, the private costs of building and generating electricity from new solar and wind power plants are less than the private cost of electricity from a new nuclear power plant. Solar power is more valuable than nuclear power since all solar power is available during peak and midpeak periods. Half of the power from nuclear generators is off-peak power and therefore is less valuable. Reliability is important in determining the value of wind and nuclear power. Damage from air pollution, when factored into the cost of power from fossil fuels, alters the cost comparison in favor of solar and wind power. Some policies are more effective at encouraging alternative energy technologies that pollute less and improve national security.
Walton, A. L.↗
Application of high power lasers to space power and propulsion
The transmission of laser power over long distances for applications such as direct conversion to propulsive thrust or electrical power is considered. Factors discussed include: problems inherent in transmitting, propagating, and receiving the laser beam over long ranges; high efficiency, closed-cycle, continuous wave operation; advancement of CO2 laser technology; and compatibility with photovoltaic power conversion devices.
Nored, D. L.↗
A modular electric power system test bed for small spacecraft
In the new climate of smaller, faster, and cheaper space science satellites, a new power system topology has been developed at the NASA Lewis Research Center. This new topology is based on a series connected boost converter (SCBC) and can greatly affect the size, weight, fault tolerance, and cost of any small spacecraft using photovoltaic solar arrays. The paper presents electric power system design factors and requirements as background information. The series connected boost converter topology is discussed and several advantages over existing technologies are illustrated. Besides being small, lightweight, and efficient, this topology has the added benefit of inherent fault tolerance. A positive ground power system test bed has been developed for the TROPIX spacecraft program. Performance of the SCBC in the test bed is described in detail. SCBC efficiencies of 95 percent to 98 percent have been measured. Finally, a modular, photovoltaic regulator 'kit' concept is presented. Two SCBC's are used to regulate solar array charging of batteries and to provide 'utilitytype' power to the user loads. The kit's modularity will allow a spacecraft electric power system to be built from off-the-shelf hardware; resulting in smaller, faster, and cheaper spacecraft.
Button, Robert M.↗
Site dependent factors affecting the economic feasibility of solar powered absorption cooling
A procedure was developed to evaluate the cost effectiveness of combining an absorption cycle chiller with a solar energy system. A basic assumption of the procedure is that a solar energy system exists for meeting the heating load of the building, and that the building must be cooled. The decision to be made is to either cool the building with a conventional vapor compression cycle chiller or to use the existing solar energy system to provide a heat input to the absorption chiller. Two methods of meeting the cooling load not supplied by solar energy were considered. In the first method, heat is supplied to the absorption chiller by a boiler using fossil fuel. In the second method, the load not met by solar energy is net by a conventional vapor compression chiller. In addition, the procedure can consider waste heat as another form of auxiliary energy. Commercial applications of solar cooling with an absorption chiller were found to be more cost effective than the residential applications. In general, it was found that the larger the chiller, the more economically feasible it would be. Also, it was found that a conventional vapor compression chiller is a viable alternative for the auxiliary cooling source, especially for the larger chillers. The results of the analysis gives a relative rating of the sites considered as to their economic feasibility of solar cooling.
Bartlett, J. C.↗
Site-dependent factors affecting the economic feasibility of solar powered absorption cooling
A procedure has been developed which can be used to determine the economic feasibility of solar powered absorption cooling systems. This procedure has been used in a study to investigate the influence of the site-dependent parameters on the economic feasibility of solar absorption cooling. The purpose of this study was to make preliminary site selections for solar powered absorption cooling systems. This paper summarizes the results of that study.
Bartlett, J. C.↗
Radiation damage in proton irradiated indium phosphide solar cells
Indium phosphide solar cells exposed to 10 MeV proton irradiations were found to have significantly greater radiation resistance than either GaAs or Si. Performance predictions were obtained for two proton dominated orbits and one in which both protons and electrons were significant cell degradation factors. Array specific power was calculated using lightweight blanket technology, a SEP array structure, and projected cell efficiencies. Results indicate that arrays using fully developed InP cells should out-perform those using GaAs or Si in orbits where radiation is a significant cell degradation factor.
Weinberg, I.↗
Human Factors and Information Operation for a Nuclear Power Space Vehicle
This paper describes human-interactive systems needed for a crewed nuclear-enabled space mission. A synthesis of aircraft engine and nuclear power plant displays, biofeedback of sensory input, virtual control, brain mapping for control process and manipulation, and so forth are becoming viable solutions. These aspects must maintain the crew's situation awareness and performance, which entails a delicate function allocation between crew and automation.
Trujillo, Anna C.↗
Chapter 12: Materials for Liquid Propulsion Systems
Earth to orbit launch vehicles are propelled by rocket engines and motors, both liquid and solid. This chapter will discuss liquid engines. The heart of a launch vehicle is its engine. The remainder of the vehicle (with the notable exceptions of the payload and guidance system) is an aero structure to support the propellant tanks which provide the fuel and oxidizer to feed the engine or engines. The basic principle behind a rocket engine is straightforward. The engine is a means to convert potential thermochemical energy of one or more propellants into exhaust jet kinetic energy. Fuel and oxidizer are burned in a combustion chamber where they create hot gases under high pressure. These hot gases are allowed to expand through a nozzle. The molecules of hot gas are first constricted by the throat of the nozzle (de-Laval nozzle) which forces them to accelerate; then as the nozzle flares outwards, they expand and further accelerate. It is the mass of the combustion gases times their velocity, reacting against the walls of the combustion chamber and nozzle, which produce thrust according to Newton's third law: for every action there is an equal and opposite reaction. Solid rocket motors are cheaper to manufacture and offer good values for their cost. Liquid propellant engines offer higher performance, that is, they deliver greater thrust per unit weight of propellant burned. They also have a considerably higher thrust to weigh ratio. Since liquid rocket engines can be tested several times before flight, they have the capability to be more reliable, and their ability to shut down once started provides an extra margin of safety. Liquid propellant engines also can be designed with restart capability to provide orbital maneuvering capability. In some instances, liquid engines also can be designed to be reusable. On the solid side, hybrid solid motors also have been developed with the capability to stop and restart. Solid motors are covered in detail in chapter 11. Liquid rocket engine operational factors can be described in terms of extremes: temperatures ranging from that of liquid hydrogen (-423 F) to 6000 F hot gases; enormous thermal shock (7000 F/sec); large temperature differentials between contiguous components; reactive propellants; extreme acoustic environments; high rotational speeds for turbo machinery and extreme power densities. These factors place great demands on materials selection and each must be dealt with while maintaining an engine of the lightest possible weight. This chapter will describe the design considerations for the materials used in the various components of liquid rocket engines and provide examples of usage and experiences in each.
Halchak, John A.↗
Paraffin Phase Change Material for Maintaining Temperature Stability of IceCube Type of CubeSats in LEO
The MLA and IFA of the instrument on the IceCube require a 20 C temperature and a thermal stability of +/-1 C. The thermal environment of the ISS orbit for the IceCube is very unstable due to solar beta angles in the -75deg to +75deg range. Additionally the instrument is powered off in every eclipse to conserve electrical power. These two factors cause thermal instability to the MLA and IFA. This paper presents a thermal design of using mini paraffin PCM packs to meet the thermal requirements of these instrument components. With a 31 g mass plus a 30% margin of n-hexadecane, the MLA and IFA are powered on for 32.3 minutes in sunlight at a 0deg beta angle to melt the paraffin. The powered-on time increases to 38 minutes at a 75deg (+/-) beta angle. When the MLA and IFA are powered off, the paraffin freezes.
CubeState↗
Comparing Trash Disposal and Reuse Options for Deep Space Gateway and Mars Missions
Taking out the trash at NASA's newly proposed Deep Space Gateway (DSG) will not be a trivial task. While not the most important aspect of planning this cislunar outpost, there are several options that should be carefully considered since they may affect the crew as well as mission mass and volume. This study extends an earlier one, which focused on waste disposal options for a Mars Transit Vehicle. In that study, gasifying and venting trash along the way was found to noticeably reduce propellant needs and launch mass, whereas keeping processed trash on board in the form of radiation shielding tiles would significantly lower the crew's radiation dose during a solar particle event. Another favorable strategy was packing trash in a used logistics module for disposal. Since the DSG does not need much propulsion to maintain its orbit and Orion will be present with its own radiation storm shelter at the Gateway, the driving factors of the waste disposal trade study are different than for the Mars mission. Besides reviewing the propulsion and radiation shielding factors, potential drivers such as mass, power, volume, crew time, and human factors (e.g. smell) were studied. Disposal options for DSG include jettison of a used logistics module containing waste after every human stay, jettison of the same logistics module after several missions once it is full, regular disposal of trash via an airlock, or gasifying waste products for easier disposal or reuse. Conversely, a heat melt compactor device could be used to remove water and stabilize trash into tiles which could be more compactly stored on board and used as radiation shielding. Equivalent system mass analysis is used to tally the benefits and costs (mass, volume, power, crew time) of each case on an equivalent mass basis. Other more subjective factors are also discussed. Recommendations are made for DSG and Mars mission waste disposal.
Ewert, Michael↗
Assessment of Aerodynamic Challenges of a Variable-Speed Power Turbine for Large Civil Tilt-Rotor Application
The main rotors of the NASA Large Civil Tilt-Rotor notional vehicle operate over a wide speed-range (100% at take-off to 54% at cruise). The variable-speed power turbine, when coupled to a fixed-gear-ratio transmission, offers one approach to accomplish this speed variation. The key aero-challenges of the variable-speed power turbine are related to high work factors at cruise, where the power turbine operates at 54% of take-off speed, wide incidence variations into the vane, blade, and exit-guide-vane rows associated with the power-turbine speed change, and the impact of low aft-stage Reynolds number (transitional flow) at 28 kft cruise. Meanline and 2-D Reynolds-Averaged Navier- Stokes analyses are used to characterize the variable-speed power-turbine aerodynamic challenges and to outline a conceptual design approach that accounts for multi-point operation. Identified technical challenges associated with the aerodynamics of high work factor, incidence-tolerant blading, and low Reynolds numbers pose research needs outlined in the paper
Welch, Gerand E.↗