This disclosure relates generally to the field of space power system, and, in particular, to low specific mass space power system.
Space missions use a space platform to host a mission payload to achieve mission goals. Space platform performance is limited by energy generation capability, available mass and thermal dissipation capability. Space platforms typically use solar photovoltaic cells to convert solar radiative electromagnetic energy into electric energy to serve as the primary power source for the space platform. However, solar radiative energy flux diminishes as the square of the distance from the sun, so many space missions may not have enough energy using traditional methods. In addition, the mass of the platform power source may be severely limited by the launch mass capabilities of current launch vehicles. There is a need for highly mass-efficient solar photovoltaic power systems for space platforms to accomplish desired space mission goals.
The following presents a simplified summary of one or more aspects of the present disclosure, in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated features of the disclosure, and is intended neither to identify key or critical elements of all aspects of the disclosure nor to delineate the scope of any or all aspects of the disclosure. Its sole purpose is to present some concepts of one or more aspects of the disclosure in a simplified form as a prelude to the more detailed description that is presented later.
In one aspect, the disclosure provides apparatus and method for generating solar power. Accordingly, an apparatus including a concentrator, wherein the concentrator includes an optical filter and wherein the optical filter includes a first characteristic of concentrating a filtered light and a second characteristic of passively radiating a rejected light; a photovoltaic (PV) conversion system coupled to the concentrator, wherein the photovoltaic (PV) conversion system includes a plurality of photovoltaic (PV) cells, wherein a majority quantity of the plurality of photovoltaic (PV) cells is spectrally matched to the filtered light.
In one example, the optical filter includes a single spectral window. In one example, the single spectral window reflects or transmits the filtered light. In one example, the single spectral window transmits, absorbs, or reflects the rejected light. In one example, the optical filter is a reflectance/transmittance (R/T) filter. In one example, the optical filter is a transmittance/absorbance (T/A) filter. In one example, the optical filter is a transmittance/reflectance (T/R) filter. In one example, the concentrator is a concave reflector (CR). In one example, the concentrator is a light-channel (LC). In one example, the concentrator comprises a low areal mass density deployable structure.
Another aspect of the disclosure provides a method for solar power generation, the method including filtering a light to generate a filtered light and a rejected light; concentrating the filtered light; and passively radiating the rejected light. In one example, the method further includes concentrating the filtered light to a plurality of photovoltaic (PV) cells. In one example, the concentrating step includes reflecting the filtered light. In one example, the concentrating step includes transmitting the filtered light. In one example, the passively radiating step includes transmitting the rejected light. In one example, the passively radiating step includes absorbing the rejected light. In one example, the passively radiating step includes reflecting the rejected light. In one example, the method further includes generating solar power using the plurality of photovoltaic (PV) cells.
These and other aspects of the present disclosure will become more fully understood upon a review of the detailed description, which follows. Other aspects, features, and implementations of the present disclosure will become apparent to those of ordinary skill in the art, upon reviewing the following description of specific, exemplary implementations of the present invention in conjunction with the accompanying figures. While features of the present invention may be discussed relative to certain implementations and figures below, all implementations of the present invention can include one or more of the advantageous features discussed herein. In other words, while one or more implementations may be discussed as having certain advantageous features, one or more of such features may also be used in accordance with the various implementations of the invention discussed herein. In similar fashion, while exemplary implementations may be discussed below as device, system, or method implementations it should be understood that such exemplary implementations can be implemented in various devices, systems, and methods.
The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.
While for purposes of simplicity of explanation, the methodologies are shown and described as a series of acts, it is to be understood and appreciated that the methodologies are not limited by the order of acts, as some acts may, in accordance with one or more aspects, occur in different orders and/or concurrently with other acts from that shown and described herein. For example, those skilled in the art will understand and appreciate that a methodology could alternatively be represented as a series of interrelated states or events, such as in a state diagram. Moreover, not all illustrated acts may be required to implement a methodology in accordance with one or more aspects.
Space missions are deployed to achieve mission goals, such as communication, navigation, remote sensing, data collection, science exploration, weather monitoring, etc. Space missions may use a space platform, e.g., a satellite or spacecraft, to host a mission payload in support of the mission goals. In one example, the space power system may also be applied to terrestrial applications or to surface applications on other bodies in our Solar System or beyond. One important requirement for the hosting of the mission payload is providing an adequate source of electric energy on the space platform. The source is a space power system, for example, a solar power system. One important space power system is a solar photovoltaic system which employs photovoltaic cells to convert solar radiative energy to electric energy. Since the solar radiative energy has a broadband spectral distribution (i.e., the solar radiative energy is spread over a wide range of wavelengths), solar photovoltaic cells may be matched to the spectrum of the solar radiative energy for maximum energy conversion to electric energy. In one example, the maximum solar radiative energy flux is in the visible part of the electromagnetic spectrum, for example, from about 400 nm to 700 nm wavelength.
In one aspect, space missions have a need for the following example features: low mass, deep space power systems and low specific mass space power systems. In a first example regarding low mass: all space missions strive for mass reduction given the high costs associated with launch, and electric power availability is a critical driver for all types of space missions with higher power allowing greater mission opportunities.
In a second example regarding deep space power systems: conventional solar power systems have diminished utility at distances far away from the sun, while currently available alternative energy sources for deep space missions such as radioisotope thermal generators (RTGs) and nuclear reactors are heavy, costly, and complex.
In a third example regarding low specific mass space power systems: a lightweight power system enables several missions (e.g., data collection, communication, instrument operations, etc.) as well as transformative application of electric propulsion. A critical parameter for a power-limited propulsion system (e.g., an electric propulsion system) is the specific mass, or mass per unit power, of the combined power and propulsion system. In one example, the inverse relation, power per unit mass, which is referred to as specific power, is also defined as an interchangeable figure of merit for space power systems. An equivalent description for a low specific mass space power system is a high specific power space power system. While electric propulsion thrusters are being developed with low specific mass, there are currently no power systems with low specific mass to be used with these thrusters to realize rapid interplanetary missions.
In one example, the low specific mass space power system increases the power production capabilities of photovoltaic (PV) cells by filtering and concentrating sunlight to improve PV junction efficiency and to increase the total power output of a fixed mass of photovoltaic cells.
In one example, the low specific mass space power system may include two primary subsystems: a concentrator and a photovoltaic energy conversion system. These subsystems may be implemented as a single monolithic structure, or multiple modular constituents that may be combined. In one example, the concentrator may include a low areal mass density deployable structure that may include a substrate coated with an optical filter and support constituent structures used to deploy, shape, and orient the concentrator with respect to the photovoltaic energy system and the Sun. In one example control of deployment, shape geometry, or relative orientation is actuated with active or passive feedback control with mechanized components, shape memory alloys, piezoelectric motors, other motor varieties, or structural or electronic elements that respond light or heat stimuli and modifying shape, angle, or orientation of concentrator surfaces or support structures. The concentrator controls the narrowband optical intensity (in watts per meter) at the PV cells by concentrating and thereby increasing the incident optical intensity of filtered light at the PV cells to maximize PV efficiency and power production while allowing for passive cooling at the PV cells, for example without additional or substantial dedicated radiators or active cooling mechanisms.
In one example, the concentrator may include one or more modules which may be individually or collectively deployed and controlled. Each module may include (a) a low areal mass substrate surface constituent to perform sunlight filtering and concentration, (b) structural constituents to facilitate high concentration efficiency and excess heat removal from the system, and/or (c) a passive or active control constituent to deploy, position and orient the reflective surface with respect to the sun, the PV cells and other modules.
In one example, the concentrator may include an optical filter, for example a notch reflection filter, a long-pass filter, a short-pass filter, a dichroic filter, or a band-pass filter, to implement one or more spectral windows. A single spectral window is a contiguous range of wavelengths which allow energy transfer. In one example, the concentrator may include a thin-film material similar to solar sail materials for the reflective filtering and concentration surface substrate. The concentrator may also include a thin-film optical coating commonly used in the optics and laser field that is selected or designed to match corresponding photovoltaic junctions of the PV cells. Depending on the emissivity properties of the surface material selected, a high emissivity coating may be used on the non-reflective or non-transmitting concentrator surface features to enhance residual solar energy dissipation away from the space platform, for example from the PV cells.
In one example, designs may include methods and processes to manufacture large areas of coated thin-film material and methods to ensure the coating quality throughout the lifecycle from production, through launch and deployment, and onto flight operations. Design and methods of operations for deployable structural and control constituents may ensure overall low specific mass and high system efficiency with the potential for lower areal mass density or improved optical filter performance with the use of a metamaterial for the concentrator surface. In one example, the use of nanostructured substrates acting as photonic crystals allows the substrate to function as an optical filter or concentrator waveguide, or a combination thereof.
In the example depicted in
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Single-junction photovoltaics based on indium gallium phosphide (InGaP), for example, exhibit high conversion efficiencies, or external quantum efficiencies, in the 400 nm-650 nm wavelength range, while gallium arsenide (GaAs) single junction photovoltaics exhibit high external quantum efficiencies in the 500 nm-800 nm wavelength range, for example. Dual junction or multi junction cells based on InGaP, GaAs, or other semiconductors like GaInAsP and GaInAs provide alternative options. PV architectures, thin-film PV cells or future PV architectures may be employed to integrate PV junctions and cells into arrays for a low specific mass space power system to reduce overall specific mass with improved efficiency and/or reduced mass. Articulation of the PV cells with respect to the sun, the host spacecraft and the concentrator may be accomplished with static or dynamic, passive or active means, but may be selected for a specific mission to ensure low specific mass and to meet minimum power requirements throughout mission life. One example implementation involves a fixed configuration in which the photovoltaics are held at a constant orientation with respect to the concentrator after deployment, with the entire solar power system gimbaled in one or more axes to face the sun for operations.
Concerning Option 1 (CR.1 and LC.1) implementation example shown in
One example of an optical notch filter for application to any example low specific mass space power system is a dichroic reflector film that reflects sunlight with wavelengths between 450 nm-600 nm, while transmitting other wavelengths in the solar spectrum. Another example is a polychroic reflector that reflects sunlight in multiple spectral bands, for instance wavelengths between 450 nm-600 nm and between 700 nm-850 nm while transmitting the rest. In one example, a long-pass filter designed to transmit all wavelengths longer than a given value and reflect the rest of the solar spectrum is used, since much of the unused solar spectrum is in the long wavelengths. A variety of commercial off-the-shelf optical filters may be used to achieve solar spectrum filtering. In one example, several different optical filters are used to coat a single concentrator, with different optical filters selected with spectral properties according to the sunlight incidence angle with respect to concentrator surface so that resulting optical filtering and concentration occurs with high efficiency and produces spectral windows matching the PV system photovoltaic cells.
These examples of wavelength ranges are given as examples to match PV junction spectral ranges, though for specific implementations, the spectral range of the optical filter may be selected in conjunction with the PV system's photovoltaic junctions. In one example a broad range of optical filters may be used. Many options are available to deposit such films, including R/T, T/A, or TR filters, to a variety of substrate materials that include plastics, polyimides, and other transparent, thin-film media relevant to this example. Deposition options include, for example, ion-beam sputtering, laminating, dyeing, hot-rolling, or direct-depositing. In one example, the substrate is designed with nanostructures or with metamaterials to perform desired optical filtering without the need for additional optical filter coating.
Concerning Option 2 (CR.2 and LC.2) implementation examples shown in
One example of a thermally conductive path is the selection of a concentrator surface material that has high thermal conductivity. Another example involves the use of dedicated thermal conduction pathways built into the concentrator surface, for example, as webbing in the surface constituents or, for example, as a secondary function for the structural constituents or deployment constituents necessary to maintain the shape and orientation of the concentrator surfaces. Emission may take place, for example, across the entire opposite surface of the concentrator away from PV cells that is treated for example with high emissivity coating or other means to ensure a higher emissivity than the surface facing PV cells. In another example, emission of the absorbed thermal energy takes place at isolated thermal emission locations that are facing away from PV cells and that are designed to be more highly emissive than any other feature of the concentrator, for example, with material or coating selections. These isolated emission locations may, for example, be connected with thermally conductive pathways to the absorptive surface constituents receiving excess sunlight.
Concerning Option 3 (CR.3 and LC.3) implementation examples shown in
For both Options 2 and Option 3 shown in
In the example shown in the middle of
Examples of thermally-conductive substrates may include carbon fiber composites, composites with graphite including pyrolytic graphite, graphene, metallics, or other thermal conductors. Examples of high absorptivity, low emissivity materials that may be used on opaque constituents facing the PV system include plated nickel oxide metal, plated black chrome metal, plated black sulfide metal, Solchrome®, copper treated with NaCIO2 and NaOH, Thermafin®'s Black Crystal®, and galvanized metal. Examples of high emissivity materials for use in radiating away excess heat in directions that are not visible to the PV system may include white paints, light colored paints, zinc oxide with sodium silicate, magnesium oxide paint, magnesium/aluminum oxide paint, zinc orthotitanate with potassium silicate, anodized aluminum, potassium fluorotitanate white paint, white zinc oxide paint, titanium oxide white paint with methyl silicone, black paints, dark paints, strongly oxidized iron and steel, black silicates, black plastics, and blackening agents including, for example, graphite colloids. Examples of lightweight substrates may include composites that include carbon fiber composites, epoxied fabrics, or carbon fiber-reinforced plastics. And, examples of highly reflective surfaces may include aluminum coating, silver coating, or silvered or white paint.
In the example 730 at the bottom of
A summary of the different basic examples of the low specific mass space power system is compiled in Table 1. A key design feature which enables a low specific mass is the use of low areal mass density material for sunlight concentration, filtering, and excess heat removal. In addition, in one example, the PV cells are illuminated with narrowband light to maximize the power output per unit mass of the PV cells without requiring active cooling. Table 1 illustrates a set of examples for a low specific mass space power system.
In one set of examples shown in Table 1, the low specific mass space power system includes two subsystems: a concentrator subsystem and a photovoltaic energy conversion system. In one example, the concentrator may include a low areal mass density deployable structure. The function of the concentrator is three-fold: spectral filtering of sunlight, concentration of selected solar spectra onto the photovoltaic energy conversion system, and rejection of excess energy and heat from the power system. The configuration of the concentrator may be, for example: a concave reflector (CR) as described in Table 1,
In one example of the power system using a CR concentrator as shown in
In one aspect, all examples may be implemented at various scales, spanning designs that include a single large concentrator providing all the energy for the power supply system to designs that include many concentrator systems and many PV systems. Likewise, in one aspect, PV modules may be implemented in one example as a single array, or in another example as many arrays.
The dashed box 820 shown at the bottom of
In one example, the deployed concentrator structure has a fixed orientation with respect to the photovoltaic energy conversion system, and the entire structure's orientation with respect to the sun must be controlled, for instance with the photovoltaic surface facing away from the sun, with the reflective surface of the concentrator facing toward the sun. In one example, control of the relative orientation of the concentrator and PV with respect to the Sun is performed with active or passive feedback control involving light-sensing or heat-sensing components. In one example, the concentration factor of a given low specific mass space power system may be altered by varying the distance of the concentrator with respect to the PV system, effectively focusing or defocusing the filtered light. In one example, the concentration factor of a given low specific mass space power system may be altered by varying the shape, geometry, or relative orientation of the concentrator with respect to the PV cells by active or passive means. In one example, the sun-facing side of the photovoltaic surface is mirrored, i.e., coated with a thin-film reflective surface, for instance aluminum, silver, another metallic, or another highly reflective film, to reflect the full solar spectrum and to limit the total absorbed solar energy. In another example, a mirrored structure on the sun-side of the photovoltaics directs sunlight toward the concentrator surface to be filtered, reflected, and focused on the energy conversion side of the photovoltaics. In one example, the energy conversion side of the photovoltaics includes mirrored structures to guide filtered but misdirected sunlight onto the energy conversion area of the photovoltaics. In one example, the mirrored structures double as radiators for the PV system.
In one example, the low specific mass space power system achieves low specific mass through a combination of:
In one example, the low specific mass space power system includes a process by which components including solar sail materials, thin-film optical coating technology or metamaterials, thin-film lenses, spacecraft deployable structures and photovoltaic cells may be combined, relying on the concentrator surface to spectrally filter and concentrate sunlight onto an associated and frequency-matched PV cells, while removing excess heat passively to enable low specific mass space power systems. In one example, the methods of the low specific mass space power system may be applied to space missions as a power unit for electric propulsion systems or for more generalized space mission power systems for use on transportation or surface platforms.
In one example, the low specific mass space power system may be used for on-Earth, near-Earth and cis-lunar missions as well as for Mars and deep space missions. The system is scalable and based on simple component technologies. For example, transformative human and robotic missions may be achievable with the low specific mass space power system. Such a system may optimize optical filter reflection coefficients, beam steering, areal mass density capabilities of deployable structures for the concentrator, PV efficiency and PV specific mass when illuminated by narrowband radiation.
In one example, rapid interplanetary transport from Earth to Mars is one exemplary usage of the low specific mass space power system. While electric propulsion thrusters are used today with existing power supplies for robotic missions, and while there are some low specific mass thruster examples that have been developed or are currently in development, there are currently no power sources with sufficiently low specific mass to enable rapid interplanetary transfers with shorter travel times than traditional chemical or nuclear thermal propulsion systems, for example, among other transformative applications of a combined space power and propulsion system with low specific mass. Another example application includes the application of low specific mass power and propulsion systems for high payload mass fraction deliveries in Earth orbit and beyond. Other example applications of a low specific mass space power system include operations of infrastructure elements or instruments on surface or transporting platforms like in-situ resource utilization plants on the lunar surface, Martian surface, or on other bodies in our Solar System, or for terrestrial power systems on Earth.
The graph 1010 shows the PV power conversion system specific mass assuming either 5 kW/m2 or 10 kW/m2 concentrated filtered sunlight provided by the concentrator. In this example, the PV system is assumed to have a specific mass baseline of 6 kg/kW for standard photovoltaic cells and 0.6 kg/kW for thin-film photovoltaic cells, assuming 30% PV conversion efficiency ηPV for operations at 1 AU with unfiltered, un-concentrated sunlight. The three graphs in 1020 show an example for concentrator system specific mass αconc dependency on the combined areal mass density of the concentrator system, which includes surface, structural and control constituents. The three graphs in 1020 correspond to operations at 1.0 AU (graph 1020A), 1.5 AU (graph 1020B), and 5.2 AU (graph 1020C) from the Sun, corresponding to: operations on or near Earth or the Moon; operations on or near Mars; and operations in the vicinity of Jupiter, respectively. In 1020, the sensitivity of concentrator system specific mass αconc to combined concentrator and PV system efficiency ηconcηPV is depicted by varying the combined efficiency ηconcηPV as well as the concentrator system areal mass density. In one example, the concentrator efficiency ηconc is the product of optical filter power fraction ηopt (fraction of solar power filtered by the surface) and the steering efficiency ηsteer (fraction of filtered power that is properly steered onto the PV cells). The three graphs in 1030 show an example for the sensitivity of combined PV system and concentrator system specific mass αPV+αconc as a function of concentrator system areal mass density and filtered light concentration factor. In 1030, three graphs depict an example low specific mass space power system with ηconcηPV=0.2, ηsteer=0.85, and ηPV=0.45 corresponding to a combined efficiency ηconcηPV=0.077. The three graphs in 1030 correspond to operational distances from the Sun of 1.0 AU (graph 1030A), 1.5 AU (graph 1030B), and 5.2 AU (graph 1030C). A horizontal gray dashed line in each of the three graphs in 1030 depicts the specific mass of a standard PV power system without concentration or sunlight filtering, assuming the use of a PV system that operates with ηPV=0.3 when exposed to unfiltered, unconcentrated sunlight, and which has a specific mass of 6 kg/kW when operating at 1.0 AU from the Sun. The black lines with varying thickness in the plots 1030 depict the combined specific mass αPV+αconc of examples for low specific mass space power system as a function of concentrator system areal mass density and filtered light concentration factor. The concentration factor is depicted with the thickness of the line, and is noted in the legend of 1030. In one example, the filtered light concentration factor is the ratio of the effective concentrator system area (the area of sunlight filtered and concentrated when measured in a plane normal to the sunlight incidence) to the effective PV system area (the collective photovoltaic cell area exposed to filtered light).
In one example, the low specific mass space power system specific mass, a, depends, in part, on the sum of the concentrator specific mass, αconc, and the PV system specific mass, αPV. For example, a standard PV system, i.e. not a thin-film PV system, may have a specific mass of 6 kg/kW at 1.0 AU with a PV efficiency of 30% assuming unfiltered and un-concentrated sunlight. The same reference PV system has, for example, a specific mass of 14 kg/kW at 1.5 AU assuming 30% PV efficiency when illuminated by unfiltered and un-concentrated sunlight. If a PV system with these properties were to be included in a low specific mass space power system near or far from Earth or the Moon, and the concentrator system illuminates the PV system by concentrated filtered and concentrated sunlight, a higher PV conversion efficiency is expected as well as a higher electrical power output from the PV system. For example, a PV system illuminated by 10 kW/m2 filtered and concentrated sunlight may have a PV efficiency of ηPV=45%. This example corresponds to a PV specific mass of 0.54 kg/kW. This example is depicted as a star in 1010. An example concentrator with areal mass density of 20 g/m2 operating with combined concentrator and PV system efficiency ηconcηPV=7.5% corresponds to a concentrator specific mass of 0.20 kg/kW, 0.45 kg/kW, and 5.3 kg/kW for operations at a distance from the Sun of 1.0 AU, 1.5 AU, and 5.2 AU, respectively. These example concentrator specific masses are shown with stars in each of the three graphs in 1020 for operations at a distance from the Sun of 1.0 AU, 1.5 AU, and 5.2 AU, respectively. When the PV and concentrator specific masses are combined for an operational environment and concentrated filtered light intensity, the total estimated specific mass a of the low specific mass space power system can be calculated for an example. For a filtered light concentration intensity at the PV system of 10 kW/m2, the low specific mass space power system specific mass for operations at 1.0 AU from the Sun (on or near Earth or the Moon), is α=αPV+αconc=0.54 kg/kW+0.20 kg/kW=0.74 kg/kW. At 1.5 AU from the Sun (on or near Mars), α=αPV+αconc=0.54 kg/kW+0.45 kg/kW=0.99 kg/kW. At 5.2 AU from the Sun (on or near Jupiter), α=αPV+αconc=0.54 kg/kW+5.3 kg/kW=5.84 kg/kW. The low specific mass space power system described in these examples may be used, for example, as a space power system for orbiting spacecraft or surface elements on or near Earth, the Moon, asteroids or comets, on or near Mars, or elsewhere in space. In one example for calculations involving combined concentrator and PV specific mass, the concentration factor is kept fixed for different operational environments. The graphs of 1030 depict the combined specific mass of low specific mass space power system examples operating at 1.0 AU, 1.5 AU, and 5.2 AU, showing that concentrator systems with areal mass densities less than 400 g/m2 and concentration factors of 10× correspond to higher specific power and lower specific mass than the standard PV power system without concentration or filtering. Operating the same system with higher concentration factors reduces the specific mass of the low specific mass system further as indicated by the narrower plot lines in 1030, as indicated in the figure legend. In the graphs of 1030, the photovoltaic conversion efficiency with filtered light is assumed to be fixed at ηPV=0.45, but there may be other examples where photovoltaic efficiency is driven by concentration factor.
When the low specific mass space power system is used in conjunction with an electric propulsion system, overall power and propulsion system performance for example missions may be assessed. By using the rocket equation and interplanetary trajectory characteristics from the literature, the space platform capabilities defined for a given specific mass αpp may be analyzed.
Table 2 shows an example technology roadmap for raising technology readiness levels and improving component-level and system-level technologies, methods and operations to ensure the reliability and performance for high power and heavy payload missions, for example missions involving human passengers. Each row of Table 2 corresponds to a mission example enabled by a low specific mass solar power system, with the final three rows corresponding to the three identified missions of
Based on these analyses for examples of low specific mass space power systems, rapid human and robotic mission transits to Mars may be feasible in the near future with transit times less than half of those currently proposed and with less initial mass required in low Earth orbit. Less IMLEO reduces mission costs and complexity, and shorter transit times, or higher payload fractions, increase the utility of missions, and may also reduce the overall mission time, further reducing mission complexity and cost.
In addition to an application to fast transits to Mars, a broad set of applications for the low specific mass space power system exists on, near, and far from Earth or the Moon for electrically powered applications, for example for applications including solar power systems. For example, a low specific mass space power system may be readily applied to Earth-based systems on the ground, at sea, and in the air, or to space missions in Earth orbit, cis-lunar orbit, on or near the Moon, on or near Mars, and elsewhere in the Solar System or beyond. In one example, surface-based operations would benefit from low specific mass space power systems to perform the following example functions: mine and process water for human consumption or other use; mine and process fuel including hydrogen, oxygen, methane, or other chemicals for use with robotic or human vehicles, for example for missions from the surface to orbiting platforms or transfer vehicles; mine and process regolith or local materials for consumables or building materials; or other in-situ resource utilization functions. Many in-situ resource utilization functions require high power, and delivering power sources to the lunar surface, the Martian surface, or to other bodies in our Solar System can be prohibitively expensive, providing an additional motivation to reduce the specific mass of power systems to reduce launch costs to support these surface missions.
Table 3 depicts examples of the low specific mass space power system as applied to operations near Saturn, Uranus, Neptune and Pluto. These examples are compared with the general purpose heat source radioisotope thermal generator (GPHS-RTG), a space power system currently used for deep space missions where sunlight intensity is low. A single GPHS-RTG unit provides roughly 300 W and has a mass of 56.4 kg. For example, the Cassini mission to Saturn used three GPHS-RTG units with a collective mass of roughly 169.2 kg for production of 889 W at beginning of life (BOL). A variety of low specific mass space power system examples are considered that produce the same power as the GPHS-RTG, but with reduced mass. Alternatively, for the same mass as the GPHS-RTG, a low specific mass space power system could provide deep space exploration platforms with higher power to enable more valuable science returns and higher utility missions.
Table 3 shows power system comparisons for deep space exploration missions. For missions to Saturn, operations are assumed to occur at 9.54 AU from the Sun, where the local sunlight intensity is estimated to be 14.96 W/m2. Operations at Uranus are assumed to occur at 19.18 AU, with a local sunlight intensity of 3.70 W/m2. Operations at Neptune are assumed to occur at 30.06 AU, with a local sunlight intensity of 1.51 W/m2. Operations at Pluto are assumed to occur at Pluto's average orbiting distance of 39.44 AU, with a local sunlight intensity of 0.87 W/m2. In Table 3, low specific mass (low-α) solar power system calculations assume examples with a filtered light concentration factor of 100×, and with ηopt=0.2, .ηsteer=0.85, and ηPV=0.45. The first two rows in Table 3 list examples for Saturn, comparing low specific mass space power system mass against the mass of three GPHS-RTG units (first row) and against the mass of one GPHS-RTG unit (second row). Examples of a low specific mass space power system are shown with concentrator areal mass densities ranging from 20 g/m2 to 100 g/m2. In each case, the low specific mass space power system example provides the same amount of power as the GPHS-RTG system with less mass allocated to the power system. The last rows of Table 3 depict the power delivered to missions at Uranus, Neptune, and Pluto for a single example of the low specific mass space power system of mass 15.7 kg, corresponding to a PV array area of 3.53 m2, effective concentrator area of 353 m2, and concentrator areal mass density of 20 g/m2. No GPHS-RTG space power system mass is used for comparison in this case, since these examples correspond to delivered power levels lower than the minimum GPHS-RTG power, and would be applicable, for example, to systems that required power units with lower mass than the GPHS-RTG.
The example of the 15.7 kg low specific mass space power system described in the final row of Table 3, which features a PV array area of 3.53 m2, effective concentrator area of 353 m2, and concentrator areal mass density of 20 g/m2 is considered in one example for use in other mission contexts. Assuming a filtered light concentration factor of 100× and ηopt=0.2, .ηsteer=0.85, and ηPV=0.45, example missions are considered elsewhere in the Solar System. For example, with this low specific mass space power system, 404 W can be generated at Saturn (at 9.54 AU) with a filtered, concentrated intensity of 254 W/m2, 1.36 kW at Jupiter (at 5.20 AU) with a filtered, concentrated intensity of 855 W/m2, 15.9 kW at Mars (at 1.52 AU) with a filtered, concentrated intensity of 9.97 kW/m2, and 36.8 kW at Earth or the Moon (at 1 AU) with a filtered, concentrated intensity of 23.1 kW/m2. Given the high intensity of filtered, concentrated light at 1 AU of this example system, another example involves the use of a smaller concentration factor to reduce the thermal dissipation requirements for the PV system. For example, the same example low specific mass space power system (PV array area of 3.53 m2, a concentrator areal mass density of 20 g/m2, with ηopt=0.2, .ηsteer=0.85, and ηPV=0.45) can be considered for use with a concentration factor of 43×, corresponding to an effective concentrator area of 152 m2. In this example, an estimated 15.8 kW could be produced on or near the Earth or Moon (at 1 AU) with a filtered, concentrated intensity of 9.95 kW/m2.
In one aspect, one or more of the steps for providing a low specific mass space power system may be executed by one or more processors which may include hardware, software, firmware, etc. The one or more processors, for example, may be used to execute software or firmware needed to perform the steps in the flow diagram of
The software may reside on a computer-readable medium. The computer-readable medium may be a non-transitory computer-readable medium. A non-transitory computer-readable medium includes, by way of example, a magnetic storage device (e.g., hard disk, floppy disk, magnetic strip), an optical disk (e.g., a compact disc (CD) or a digital versatile disc (DVD)), a smart card, a flash memory device (e.g., a card, a stick, or a key drive), a random access memory (RAM), a read only memory (ROM), a programmable ROM (PROM), an erasable PROM (EPROM), an electrically erasable PROM (EEPROM), a register, a removable disk, and any other suitable medium for storing software and/or instructions that may be accessed and read by a computer. The computer-readable medium may also include, by way of example, a carrier wave, a transmission line, and any other suitable medium for transmitting software and/or instructions that may be accessed and read by a computer. The computer-readable medium may reside in a processing system, external to the processing system, or distributed across multiple entities including the processing system. The computer-readable medium may be embodied in a computer program product. By way of example, a computer program product may include a computer-readable medium in packaging materials. The computer-readable medium may include software or firmware for providing a low specific mass space power system. Those skilled in the art will recognize how best to implement the described functionality presented throughout this disclosure depending on the particular application and the overall design constraints imposed on the overall system.
Any circuitry included in the processor(s) is merely provided as an example, and other means for carrying out the described functions may be included within various aspects of the present disclosure, including but not limited to the instructions stored in the computer-readable medium, or any other suitable apparatus or means described herein, and utilizing, for example, the processes and/or algorithms described herein in relation to the example flow diagram.
Within the present disclosure, the word “exemplary” is used to mean “serving as an example, instance, or illustration.” Any implementation or aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects of the disclosure. Likewise, the term “aspects” does not require that all aspects of the disclosure include the discussed feature, advantage or mode of operation. The term “coupled” is used herein to refer to the direct or indirect coupling between two objects. For example, if object A physically touches object B, and object B touches object C, then objects A and C may still be considered coupled to one another—even if they do not directly physically touch each other. For instance, a first die may be coupled to a second die in a package even though the first die is never directly physically in contact with the second die. The terms “circuit” and “circuitry” are used broadly, and intended to include both hardware implementations of electrical devices and conductors that, when connected and configured, enable the performance of the functions described in the present disclosure, without limitation as to the type of electronic circuits, as well as software implementations of information and instructions that, when executed by a processor, enable the performance of the functions described in the present disclosure.
One or more of the components, steps, features and/or functions illustrated in the figures may be rearranged and/or combined into a single component, step, feature or function or embodied in several components, steps, or functions. Additional elements, components, steps, and/or functions may also be added without departing from novel features disclosed herein. The apparatus, devices, and/or components illustrated in the figures may be configured to perform one or more of the methods, features, or steps described herein. The novel algorithms described herein may also be efficiently implemented in software and/or embedded in hardware.
It is to be understood that the specific order or hierarchy of steps in the methods disclosed is an illustration of exemplary processes. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the methods may be rearranged. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented unless specifically recited therein.
The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but are to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. A phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a; b; c; a and b; a and c; b and c; and a, b and c. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. § 112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.”
This application is a divisional application of patent application Ser. No. 16/988,674 filed Aug. 9, 2020, the entire contents of the prior application are incorporated herein by reference as if fully set forth below in its entirety and for all applicable purposes. The present divisional application and the pending patent application Ser. No. 16/988,674 claim priority to Provisional Application No. 62/885,870 entitled “Low Specific Mass Space Power System”, filed Aug. 13, 2019, and assigned to the assignee hereof and hereby expressly incorporated by reference herein.
Number | Date | Country | |
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62885870 | Aug 2019 | US |
Number | Date | Country | |
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Parent | 16988674 | Aug 2020 | US |
Child | 17866291 | US |