RELATED APPLICATION DATA

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application Serial No. 63/331,938, filed April 18, 2022, and titled “Nonlinear-Flow Heat Exchangers for Heating Propellants, And Propulsion Systems Incorporating Same”, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

[0002] The present disclosure generally relates to the field of fluid heaters having integrated heat sources. In particular, the present disclosure is directed to integrated heaters having nonlinear passageways for heating fluids, and apparatuses incorporating same.

BACKGROUND

[0003] A resistojet is a well-known type of thrust generator for spacecraft propulsion.

Generally, a resistojet electrically heats a typically nonreactive fluid in a heating chamber to cause the fluid to expand and provide thrust as the expanding fluid exits a nozzle of the resistojet.

Resistojets can be desirable for certain applications, as they can provide a balance between the specific impulse provided by a hydrazine thruster and the safety of using a propellant that is not volatile like hydrazine. While resistojets have been around since at least 1965, improvements in size and efficiency are still desirable.

SUMMARY

[0004] In one implementation, the present disclosure is directed to a heater for heating a fluid. The heater includes a body comprising a heat-conducting material and having a longitudinal axis, a fluid-inlet end for receiving the fluid, and a fluid-outlet end for outputting the fluid, with the fluidoutlet end being spaced from the fluid-inlet end along the longitudinal axis, the body containing one or more nonlinear fluid-passageways formed therein and extending between the fluid-inlet end and the fluid-outlet end and being designed and configured to carry the fluid therethrough during use of the heater; and a component of a heating system integrated with the body, wherein during use of the heater, the component of the heating system provides heat to the heat-conducting material, which transfers the heat to the fluid along each nonlinear flow passageway so as to heat the fluid. [0005] In another implementation, the present disclosure is directed to a thruster, which includes a heater as described above; and a nozzle attached to the heater proximate to the fluid-outlet end.

[0006] In yet another implementation, the present disclosure is directed to a propulsion system designed and configured to provide thrust from a fluid-propellant. The propulsion system including a thruster as described immediately above; and a fluid-propellant source designed and configured to contain the fluid-propellant, wherein the fluid-propellant source is in fluid communication with the fluid-inlet end of the heater so as to provide the fluid-propellant to the heater during use of the thruster to provide the thrust; wherein the heating system includes an energy source in operative communication with the component of the heating system and configured to provide energy to the component so that the heating system provides heat to the fluid-propellant during operation of the propulsion system.

[0007] In still another implementation, the present disclosure is directed to a spacecraft, which includes a body structure; and one or more propulsion systems each in accordance with the propulsion system mentioned immediately above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] For the purpose of illustration, the accompanying drawings show aspects of one or more embodiments of the invention(s). However, it should be understood that the invention(s) of this disclosure is/are not limited to the precise arrangements and instrumentalities shown in the drawings, wherein:

[0009] FIG. 1 A is a perspective cross-sectional view of an example thruster made in accordance with the present disclosure, showing two internal fluid-passageways arranged in a double helix;

[0010] FIG. IB is a perspective view of fluid contained within the double-helix fluidpassageways of the example thruster of FIG. 1 A, with the physical structure of the thruster removed to highlight the fluid flow within the fluid-passageways;

[0011] FIG. 1C is an enlarged partial cross-sectional view of the example thruster of FIG. 1 A showing an internal geometry at the flow-outlet end of the body of the heater suitable for 3-D printing; [0012] FIG. 2 is a cross-sectional view of an example heater made in accordance with the present disclosure that includes a core and various placements of integrated electrically resistive heating elements;

[0013] FIG. 3 is a side view of an example heater made in accordance with the present disclosure that includes double-helix fluid-passageways having a long twist pitch;

[0014] FIG. 4 is a side view of an example heater made in accordance with the present disclosure that includes double-helix fluid-passageways having a short twist pitch; and

[0015] FIG. 5 is a high-level block diagram of a spacecraft made in accordance with the present disclosure.

DETAILED DESCRIPTION

[0016] GENERAL

[0017] In some aspects, the present disclosure is directed to heaters for heating a primary fluid, which can be either a gas or a liquid or a combination thereof. When the primary fluid is a gas, the heating of the primary fluid causes the gas to expand. When the primary fluid is a liquid, the heating of the primary liquid can, for example, cause the primary liquid to change phase from liquid to gas and perhaps also cause the resulting gas to expand, cause the fluid to decompose, and/or cause the fluid to ignite. Example primary fluids include, but are by no means limited to, nitrogen (liquid or gas), monopropellants (e.g., hydrogen peroxide, nitrous oxide, hydrazine), water (liquid or gas (steam)), and gases containing one or more atomized liquids and/or one or more materials in particular form, among others. A heater of the present disclosure can be used to heat a primary fluid for any suitable purpose, such as providing thrust to a spacecraft for propulsion, starting a combustion reaction, extending the lifetime of a catalyst reactor through a warm start, providing a stream of steam for cleaning surfaces, providing a stream of gas for driving a mechanism, or to provide a stream of gas for spraying a substance, among others. Fundamentally, there is no limitation on use of the primary fluid heated by a heater made in accordance with the present disclosure.

[0018] In some embodiments, for example in the context of a thruster, the heating of an inertgas propellant (e.g., nitrogen, argon, etc.) by a heater of the present disclosure may be to increase the efficiency of the propellant. In this scenario, any amount of heat into the flow will raise the temperature and therefore specific impulse. The properties of the inert-gas propellant determine how much the temperature will rise per joule of heat provided by the thruster. For example, room temperature nitrogen requires approximately 1.04 joules to raise 1 gram of flow 1 degree Celsius, whereas argon under the same conditions requires approximately 0.52 joules of heat.

[0019] In some embodiments, a heater of the present disclosure may be used for an endothermic or non-self-sustaining phase change. In this scenario, the benefits of the heater are only realized if the phase change is reached and is much more binary than the gas example immediately above. An example of this is using water as a primary fluid / propellant. The water must be raised to 100°C or higher (at a rate of 1 degree Celsius per gram per approximately 4.18 joules) to become steam and generate useful thrust, and the heat typically must be provided continually to make this phase change happen while firing. Once the phase change has occurred, the temperature of the steam can be raised further for added efficiency much like inert-gas example immediately above. As another example, ammonia decomposition is an endothermic reaction that would require continual heat input in a similar way.

[0020] In some embodiments, a heater of the present disclosure may be used for an exothermic reaction (exothermic phase change, exothermic decomposition, combustion). In this scenario, the temperature of the working fluid must be raised past a critical point like the endothermic example immediately above. However, once the reaction starts to take place, it releases its own heat to sustain the reaction and the heater can be turned off. An example of this would be isopropyl alcohol and oxygen being heated by the heater, for example, in a thruster. In this scenario, you need to raise the temperature of the isopropyl alcohol above about 200°C, at which point it will auto-ignite with the gaseous oxygen. A gram of isopropyl alcohol will require approximately 2.6 joules to raise its temperature 1°C. Once ignition has occurred and the combustion reaction has commenced, it will generate enough heat to maintain the reaction and the heater can be turned off.

[0021] A heater of the present disclosure may include a body that includes a fluid-inlet end, a fluid-outlet end, and at least one nonlinear fluid-passageway extending from the fluid-inlet end to the fluid-outlet end along a longitudinal axis of the heater for carrying the primary fluid. Each nonlinear fluid-passageway is provided to, for example: generate secondary fluid velocity components, for example, components tangential and/or radial to a local axis of the nonlinear fluid-passageway and/or to the longitudinal axis of the heater; provide more heated surface area of the heater in contact with the primary fluid than a conventional device (e.g., resistojet) having circular cross-section straight-through flow path would provide in the same envelope; provide a longer flow path than a conventional device (e.g., resistojet) having a conventional circular cross-section straight-through flow path, resulting in a longer residence time (i.e., the time that the primary fluid remains within the heater); and provide a decreased hydraulic diameter that, in effect, increases the coefficient of heat transfer, among others.

[0022] In some embodiments, each of the one or more nonlinear fluid-passageways is helical so as to have a central helix axis extending parallel to the longitudinal axis of the heater. In some embodiments, multiple interposed helixes (e.g., 2, 3, or 4 helixes) having a common central helix axis are provided to form a “plural helix”. In the case of two interposed helixes, such a plural helix is commonly referred to as a “double helix”. Several examples of heaters of the present disclosure having double-helix style nonlinear flow passageways are illustrated in the accompanying drawings and described below.

[0023] While multiple helixes can be interposed with one another, in some embodiments when multiple helixes (or other shape(s)) are used, the central axes of the helixes can be spaced from one another in a transverse cross-sectional view of the heater. In some embodiments, a combination of interposed helixes with spaced-apart central axes can be provided. As a nonlimiting example, a heater of the present disclosure may be provided with ten double helixes for the nonlinear fluidpassageways, with the corresponding ten central helix axes of the ten double helixes spaced from one another in a transverse cross-sectional view of the heat, such as nine double helixes evenly distributed at 40°-apart locations around a central tenth double helix located at the longitudinal axis of the heater. Many other embodiments can be provided, especially considering that shapes of nonlinear flow-passages other than helical can be provided. Some simple examples of non-helical shapes include, but are not limited to, serpentine and zig-zag, among others. In some embodiments, helical shapes and corkscrew shapes may be most desirable due to their lower negative impact on the flow of the primary fluid.

[0024] When at least some of the nonlinear flow-passages have spaced-apart entrances, such as in the double-helix and ten-double-helix examples above, a flow-distribution structure, such as an inlet manifold or a distribution chamber, can be provided at the inlet end of the heater to distribute a common inflow of the primary fluid to such nonlinear flow-passageways. In some embodiments, nonlinear flow-passageways having spaced-apart central axes may be fed by differing primary -fluid sources. When at least some of the nonlinear flow-passages have spaced-apart exits, a flowcollection structure, such as an outlet manifold or a flow-straightening chamber, can be provided at the outlet end of the heater to collect the flow output, for example, to provide it to a single outlet. [0025] It is noted that various geometric parameters of the one or more nonlinear fluidpassageways can be selected to suit particular applications and/or heating requirements. For example, for helical and similarly shaped fluid-passageways, geometric parameters that can be selected include, but are not limited to: the cross-sectional size and shape of the nonlinear fluidpassageways; the inner diameter of the helix (how much of a “core” within the helix / plural helix is present); the outer diameter of the helix / plural helix; and the longitudinal pitch, among others. Each of these and/or other geometrical parameters may be constant or variable, depending on the needs and/or design.

[0026] A heater of the present disclosure may include an integrated component of a heating system, such as an electric heating system or a heating-fluid-based heating system, or any combination thereof Tn some embodiments of an electric heating system, the component may be one or more heating elements, such as one or more electrically resistive heating elements. Any electrically resistive heating elements may be provided internally (e.g., as electrically resistive wires, regions of electrically resistive material, etc.) or externally (e.g., as electrically resistive heating tape or wire wrapping, etc.) to the heater, among others, or a combination of internally and externally. In some embodiments of a heating-fluid-based heating system, the heater may include one or more heating-fluid-passageways formed internally to the heater, such as formed within structure(s) (e.g., wall(s), septum(s), core(s), etc.) of the heater, or heating fluid-passageways provided externally to the heater, such as in external coils or an external fluid jacket, among others, or a combination thereof.

[0027] A heater of the present disclosure may be made at least partially of one or more heat- conducting materials that are good to excellent heat conductors, such as any one or more types of metals, any one or more types of ceramics, and any one or more types of polymers, among others, and any suitable combination thereof. In some embodiments, the entire body may be composed entirely or mostly of one or more heat-conducting materials. When composed mostly of one or more heat-conducting materials, the other portion(s) of the body may include one or more electrically- resistive heating elements, one or more heating-fluid-passageways, and/or a thermally insulating material. In some embodiments, the body may include only the heat-conducting materials between the heating element(s) or heating-fluid-passageways and the primary fluid contained within the body, with the balance of the body being made of one or more electrically-resistive heating elements and/or a thermally insulating material. Those skilled in the art will readily appreciate the variety of constructions and materials that can be used to construct a heater of the present disclosure. [0028] In some embodiments of a heater of the present disclosure that includes interposed plural helixes, the primary fluid-passageways of immediately adjacent ones of the helixes may be separated from one another via an intermediate separating wall, or septum, that may have any thickness desired to suit a particular design. In some embodiments, the body of a heater that includes interposed plural helix nonlinear fluid-passageways may include an exterior wall. In some embodiments, the exterior wall may define an open cylindrical chamber, with the plural helix being defined by a septum insert inserted into the cylindrical chamber. In such embodiments, the septum insert may have a core with the septums extending generally radially away from the core, but forming a helical shape. In some embodiments, the septum insert may form a press fit with the inside of the exterior wall of the body of the heater and/or may be secured to the exterior wall, for example, by welding or adhesive, among other things. In some embodiments, the septum(s) may be formed integrally with the exterior wall, for example, via any suitable additive manufacturing process, such as 3-D printing, among others, or subtractive manufacturing, such as electricaldischarge machining, among others.

[0029] In some embodiments, the heater may include a flow-straightener, for example, located downstream of the fluid outlet end of the body. In an example, the flow-straightener may comprise or be an open chamber formed within an exterior wall that may essentially be an extension of the wall of the body discussed above. In the context of an example in which a plurality of nonlinear flow passageways are provided by a plural helix, all of the nonlinear fluid-passageways may empty into the open chamber. In an example, the flow-straightener may comprise an additional transition fluid-passageway for each nonlinear fluid-passageway that transitions from the flow axis of the nonlinear flow-passageway that is not parallel to the longitudinal axis of the heater to a flow axis that is parallel or more parallel to the longitudinal axis of the heater. When multiple nonlinear flowpassageways are present, some or all of the transition fluid-passageways may exhaust into a common region, such as a region similar to the open-chamber-type flow- straightener mentioned above.

[0030] In some aspects, the present disclosure is directed to thrusters that each include a heater as discussed above or otherwise disclosed herein for heating a fluid-propellant so that the thruster provides thrust based on the expansion, including any phase change that may or may not be present, of the propellant. In addition to a heater of the present disclosure, a thruster of the present disclosure may also include a nozzle, such as a convergent-divergent (CD) nozzle, for controlling the thrust that the thruster generates from the fluid-propellant. Examples of fluid-propellants that can be used with a thruster of the present disclosure include suitable ones of the example primary fluids mentioned above.

[0031] In some aspects, the present disclosure is directed to propulsion systems that each include a thruster of the present disclosure, such as any thruster mentioned above and includes a heater for heating the fluid-propellant, a fluid-propellant source that contains the fluid-propellant, and a heating system that provides the heat to the fluid-propellant. The fluid-propellant source is in fluid communication with the fluid-inlet end of the heater so as to provide the fluid-propellant to the heater during use of the thruster to provide thrust. In some embodiments, the fluid-propellant source includes a gas-propellant source that contains a gas propellant. In some embodiments, the fluidpropellant source includes a liquid-propellant source that contains a liquid propellant. In some embodiments, more than one fluid-propellant source may be part of the propulsion system.

[0032] The heating system may include an energy source in operative communication with an integrated component of the heater and configured to provide energy to the integrated component so as to heat the fluid-propellant during operation of the propulsion system. In some embodiments, the integrated component of the heating system includes one or more electrically resistive heating elements, and the energy source includes an electrical energy source. Examples of electrical energy sources include, but are not limited to, batteries, electrical generators, solar cells, among others, and any combination thereof. In some embodiments, the integrated component of the heating system includes one or more heating-fluid-passageways, and the energy source includes a heating-fluid heater. Examples of heating-fluid heaters include, but are not limited to, electrically resistive type heating-fluid heaters, solar type heating-fluid heaters, and combustion type heating-fluid heaters, among others. Other embodiments may include another type of integrated component and/or another type of energy source.

[0033] In some aspects, the present disclosure is directed to spacecrafts that each include a body structure and one or more of the propulsion systems discussed above engaged with the body structure. In some embodiments, the body structure of the spacecraft may include a frame structure and/or a shell structure, among others. Examples of spacecrafts with which a propulsion system of the present disclosure may be used include, but are not limited to satellites (e.g., microsatellites), orbital transport vehicles (OTVs), on-orbit manufacturing plants, and space stations, among others. Thrusters made in accordance with the present disclosure typically provide low thrust and are particularly suited to small satellites due to their lower power. Thrusters made in accordance with the present disclosure can also be made to be more efficient that conventional resistojets and use less thrust and can therefore scale-up better than conventional resistojet designs. In some embodiments, each thruster of a spacecraft of the present disclosure may be associated with its own fluid-propellant source. In some embodiments, two or more thruster may be associated with the same fluidpropellant source. Those skilled in the art will understand how to configure satellites and their propulsion systems using propellant heaters of the present disclosure.

[0034] In addition to the foregoing aspects, embodiments, and examples, additional aspects, embodiments, and examples are described below.

[0035] EXAMPLES

[0036] Turning now to the drawings, FIGS. 1 A and IB illustrate an example thruster 100 made in accordance with aspects of the present disclosure. In this example and referring to FIG. 1 A unless noted otherwise, the thruster includes a heater 104 and a CD nozzle 108, here, formed integrally with the heater, for example, via a 3-D printing process, though in other embodiments the CD nozzle can be provided as a separate structure that is then secured to the heater.

[0037] The heater 104 includes a fluid-inlet end 1041 and a fluid-outlet end 1040 and a pair of fluid-passageways 104P(l) and 104P(2) extending from the fluid-inlet end to the fluid-outlet end along a longitudinal axis 104LA of the heater. In this example the fluid-passageways 104P(l) and 104P(2) are arranged in an interposed manner so as to form a double helix. For clarity, FIG. IB shows all of the physical structure of the thruster 100 of FIG. 1A removed and depicting a fluidpropellant 112 filling the fluid-passageways 104P(l) and 104P(2) of FIG. 1A and also a feed passageway 116 that provides the fluid-propellant to the fluid-passageways. The double-helix nature of the fluid-passageways 104P(l) and 104P(2) are more clearly represented in FIG. IB than in FIG. 1A.

[0038] Referring again to FIG. 1 A, the fluid-passageways 104P(l) and 104P(2) are contained in a body 120 that in this example includes an outer wall 120W and internal structure 120S that, together with the outer wall, define the fluid-passageways. While in this embodiment the outer wall 120W and the internal structure 120S are all formed integrally with one another, in other embodiments the outer wall and the internal structure can be separate components. In this example, the internal structure 120S includes a separating wall, or “septum” 124, that separates the two fluidpassageways 104P(l) and 104P(2) from one another. In this example, the entirety of the outer wall 120W and the internal structure 120S are made of a good heat conductor, such as a metal, ceramic, or certain polymer.

[0039] The example thruster 100 also includes an electrically resistive heating element 128, here, located in a heating-element receptacle 120R formed integrally with the body 120. In this example, the heating element 128 is a rod-type heating element that is inserted in the heatingelement receptacle 120R after the thruster 100 has been formed. However, in other embodiments, the heating element 128 can be formed integrally with the thruster 100, for example, using suitable 3-D printing techniques.

[0040] In this embodiment, the thruster 100 optionally includes a flow-straightener 132 located downstream of the fluid-outlet end 1040 of the heater 104 and upstream of the CD nozzle 108. The flow-straightener 132 may be provided to ensure that the thruster 100 outputs symmetric and even thrust. In this example, the flow-straightener 132 is generally an open chamber formed within an outer wall 136, which here may be considered an extension of the outer wall 120W. As discussed above in the previous section, the flow-straightener 132 straightens the flow of heated fluidpropellant 112 (FIG. IB) after it passes through the fluid-passageways 104P(l) and 104P(2) in which substantially all of the heating of the fluid-propellant 112 (FIG. IB) occurs before the heated fluid-propellant passes through the CD nozzle 108. While the flow-straightener 132 shown is of an open-chamber type, as noted in the previous section above, it may be of another type, such as a type that gradually transitions from the flow directions of the fluid-passageways 104P(l) and 104P(2) to a direction more in line with the longitudinal axis 104LA of the heater 104.

[0041] In the embodiment of FIG. 1A, the structure of the thruster 100 may be additively manufactured in a high heat-conductivity material, such as a copper alloy GRCop-42 material, via direct metal laser sintering 3-D printing technology. The result is a highly thermally conductive, monolithic heater 104. Additive manufacturing is a desirable method of making a heater of the present disclosure, such as the heater 104 of FIG. 1A, not only for being highly effective for relatively small form factors, but also because the structure(s) defining the flow-passages (e.g., structure 120S defining flow-passages 104P(l) and 104P(2)) can be formed integrally with the outer wall(s) (e.g., outer wall 120W) of the heater, thereby providing a continuous and definable heat-flow path through the structure of the heater. Flow paths on the scale of <50 mm ² can be difficult or impossible to assemble from multiple components, and metal-additive manufacturing has been demonstrated from sub-millimeter precision up to print areas of multiple square meters in size, making it a desirable manufacturing option for hard-to-manufacture use cases.

[0042] FIG. 1C illustrates an example configuration 140 of the fluid-outlet end 1040 to facilitate fabricating the thruster 100 by 3-D printing in a printing direction 144 that is parallel to the longitudinal axis 104LA from the CD nozzle 108 to the fluid-inlet end 1041 of the heater 104. In this example, the example configuration 140 includes surfaces 140S, here, surfaces exposed to the flowstraightener 132, that form an angle, a, relative to the printing direction of about 45° or less. This relatively low angle allows the flow-outlet end 1040, when no structure(s) of the heater 104 is/are present downstream of the flow-outlet end, to be 3-D printed without any temporary support structure(s). As can be readily appreciated, in the design shown in FIGS. 1 A and 1C, it would be unnecessarily challenging to remove any temporary support structure located within the flowstraightener 132 given the location between the narrow throat 108T of the CD nozzle 108 and the ends of the long, twisting fluid-passageways 104P(l) and 104P(2). In the embodiment shown and referring back to FIG. 1A, the thruster 100 includes an optional mounting bracket 148 that can be used for testing the thruster and/or mounting the thruster to a structure (not shown) aboard a spacecraft (not shown).

[0043] Computer-based analysis of the example helical design of FIGS. 1 A through 1C demonstrated a significant advantage over a conventional straight-tube flow path, with the advantage being confirmed through testing. Analysis of the thruster 100 of FIGS. 1A through 1C using computational fluid dynamics (CFD) showed up to a 74% improvement over a conventional straighttube design of the same diameter as measured by propellant temperature increase. Figure 4 of U.S. Provisional Patent Application Serial No. 63/331,938, filed April 18, 2022, and titled “Nonlinear- Flow Heat Exchangers for Heating Propellants, And Propulsion Systems Incorporating Same” in the names of Walton et al., which is incorporated herein by reference, shows an example of the CFD simulations.

[0044] Fluid-propellants can vary widely in their chemical and physical properties. A helical fluid-propellant heater of the present disclosure, such as any one of the heaters 104, 200, 300, and 400 of FIGS. 1A and 2 through 4, respectively, is applicable to both gas- and liquid-phase propellants. At small scales, the flow of the fluid-propellant is typically laminar and high velocity. These properties make heating the liquid propellant very difficult, and consequently a heater of the present disclosure having helical flow-passageways returns better performance gains in these flow regimes. There is no reason that such a design could not be used for heating any type of fluidpropellant, but it appears most applicable for fluid-propellants (more generally, primary fluids) having a Reynold number less than about 2000.

[0045] FIG. 2 shows an example heater 200 made in accordance with aspects of the present disclosure for heating a primary fluid, such as a fluid-propellant, among other things. The example heater 200 of this embodiment comprises a body 204 having a longitudinal axis 204LA, a central core 204C extending along the longitudinal axis, and an outer wall 204OW located at a constant radius from the longitudinal axis. The body 204 contains four nonlinear fluid-passageways 204P(l) through 204P(4) each having a helical shape having a corresponding central helix axis (not labeled) that is coincident with the longitudinal axis 204LA of the body so as to provide an inner double helix 204H(l) defined by fluid-passageways 204P(l) and 204P(2) and an outer double helix 204H(2) defined by fluid-passageways 204P(3) and 204P(4). In some constructions, the heater 200 may be formed by a substrative manufacturing process and/or an additive manufacturing process, such as 3- D printing and, therefore, be unitary monolithic.

[0046] The central core 204C may be defined by an inner wall 204IW (inner relative to the fluid-passageways 204P(l) through 204P(4)), the fluid-passageways 204P(l) and 204P(2) in the inner double helix 204H may be separated from one another by a first septum 204S(l), the fluidpassageways 204P(3) and 204P(4) may be separated from one another by a second septum 204S(2), and the adjacent ones of the fluid-passageways 204P(l) and 204P(2) of the inner double helix and the fluid-passageways 204P(3) and 204P(4) of the outer double helix may be separated from one another by, respectively, septums 204S(3) and 204S(4). In this example, the central core 204C contains an electrically resistive heating element 208 that may either be provided as a separate element or provided as a printed structure. The heating element 208 is electrically powered via a suitable electrical connector 210. Relative to the design of the heater 104 of FIG. 1A and making the outside diameter of the heater 200 the same as or similar to the outside diameter of the heater 104 of FIG. 1 A, the design of the heater 200 of FIG. 2 that provides helical fluid-passageways 204P(l) to 204P(4) around a central core 204C further increases heat transfer from the body 204 to the primary fluid (not shown) within the fluid-passageways into a high flow rate. By decreasing the transverse cross-sectional sizes of the fluid-passageways 204P(l) to 204P(4) in this way, flow velocities of the primary fluid increase and thereby lead to higher turbulence and convective coefficients that enhance mixing even further. In another example compared to the heater 104 of FIG. 1A, if the scale of the fluid-passageways 204P(l) to 204P(4) of the heater 200 of FIG. 2 is the same as or similar to the scale of the fluid-passageways 104P( 1 ) and 104P(2) of the heater 104 of FIG. 1 A, then the flow rate of the heater 200 of FIG. 200 can be increased while maintaining the fluid and thermal properties of the heater 104 of FIG. 1A. Those skilled in the art will appreciate that these are merely nonlimiting examples for context.

[0047] Still referring to FIG. 2, the heater 200 may additionally or alternatively include one or more heating elements 212 (only a few labeled to avoid clutter) located within the structure 216 between the inner and outer walls 204IW and 204OW that contains the septums 204S(l) to 204S(4) that define the fluid-passageways 204P(l) through 204P(4) along with the inner and outer walls. In some embodiments, each heating element 212 may be, for example, a heating-fluid passageway or an electrically resistive heating element, such as an electrically resistive wire or wire equivalent formed in place, such as by 3-D printing. When formed in place with a heater made of an electrically conductive material, an electrically insulating layer made of a material, such as a ceramic, having a suitable dielectric constant, may be used between the heat-conducting material of the heater 200 and the electrically resistive material of the heating element(s) 212. While the heating element(s) 212 are shown as being located within the thickened regions of the structure 216 formed at the intersections of the septums 204S(l) to 204S(4), they may alternatively or additionally be located elsewhere, such as within the septums themselves and/or within either or both of the inner and outer walls 204IW and 204OW.

[0048] The heater 200 may additionally or alternatively include an external heating element 220 (only a few locations labeled to avoid clutter) located on the outside of the outer wall 204OW. Such an external heating element 220 may be, for example, of a wrap, a sleeve / jacket, or a coil, among others. Example types for the heating element 220 include, but are not limited to, electrically resistive types (e.g., electrically resistive heating tape) and heating-fluid types (e.g., a water / steam jacket), among others. As alluded to above, heating elements that are the same or similar to the heating elements 212 can be used in other heaters disclosed herein, including the heaters 104, 300, and 400 of FIGS. 1A, 3, and 4, respectively.

[0049] FIGS. 3 and 4 illustrate, respectively, example heaters 300 and 400 made in accordance with the present disclosure that each include a body 304 and 404 having corresponding nonlinear passageways 304P(l) and 304P(2) (FIG. 3) and 404P(l) and 404P(2) (FIG. 4) provided in double helixes 304H (FIG. 3) and 404H (FIG. 4) having differing twist pitches 304TP (FIG. 3) and 404TP (FIG. 4). For the sake of comparison, the vertical scales of FIGS. 3 and 4 relative to the sheet containing FIGS. 3 and 4 are identical to one another. Consequently, the twist pitch 304TP of the double helix 304H of FIG. 3 is about 4.3 times greater than the twist pitch 404TP of the double helix 404H of FIG. 4. The relatively lower twist pitch 304TP of the heater 300 of FIG. 3 can be ideal for primary fluids that are gases and/or have low heat capacities. In contrast, the relatively higher twist pitch 404TP of the heater 400 of FIG. 4, all other things being equal relative to the heater 300 of FIG. 3, provides a larger area for the surfaces of the heater 400 in contact with the primary fluid (not shown) within the fluid-passageways 404P(l) and 404P(2), increase the residence time of the primary fluid within the heater 400, and induce greater mixing to create more heat transfer into the primary fluid for primary fluids that require it. Water is an example of a primary fluid that requires greater heat input for its temperature to be raised by the same amount as some other primary fluids. For example, water requires roughly four times as much heat as nitrogen requires to increase the temperature of each by the same amount. It is noted that the twist pitches 304TP and 404TP illustrated in FIGS. 3 and 4 are constant throughout the lengths of the heaters 300 and 400, respectively. However, as noted above, each of the twist pitches 304TP and 404TP of FIGS. 3 and 4, respectively, may be variable. For example, either twist pitch 304TP or 404TP may start at a low value and end at a high value (including at or near infinity so as to act as a flow-straightener), or may start at a high value and end at a low value, or transition two or more times between high and low values or low and high values. Many possibilities exist for variable twist pitch designs.

[0050] FIG. 5 illustrates an example spacecraft 500 made using aspects of the present disclosure. The spacecraft 500 may be any spacecraft that would benefit from a thruster made in accordance with the present disclosure, such as the thruster 100 of FIGS. 1A through 1C or any variation taught or otherwise disclosed in this disclosure, including variations that include any one of the heaters 200, 300, and 400 of FIGS. 2 through 4, respectively, and any other heater disclosed herein. Example types of the spacecraft 500 include, but are not limited to, satellites (e.g., microsatellites), OTVs, on-orbit manufacturing plants, and space stations, among others. In this connection, the spacecraft 500 includes one or more propulsion systems (singly and collectively represented at element 504) that each includes at least one thruster (singly and collectively represented at element 508), at least one heating system (singly and collectively represented at element 512), and at least one fluid-propellant source (singly and collectively represented at element 516) for providing a fluid-propellant 520 to the thruster(s). Each of the thruster(s) 508 includes a heater 524, which may be any heater disclosed herein or apparent to one of ordinary skill in the art after reading this disclosure, including any one of the heaters 200, 300, and 400 of FIGS. 2 through 4, respectively, and any other heater disclosed herein.

[0051] Each heating system 512 includes one or more heating elements (singly and collectively represented at element 528) integrated with each heater 524 in any manner disclosed herein, such as internally within the heater or externally to the heater, for example, as discussed relative to heating elements 208, 212, and 220 of the heater 200 of FIG. 2, among others. Each heating element may be, for example, an electrically resistive heating element or a heating-fluid heating element. Each heating system 512 also includes an energy source 532 for providing energy to the heating element(s) 528. Each energy source 532 may be any energy source compatible with the type of the corresponding heating element(s) 528. Examples of types of energy sources include, but are not limited to batteries, electrical generators, solar cells, among others, any combination thereof, electrically resistive type heating-fluid heaters, solar type heating-fluid heaters, and combustion type heating-fluid heaters, among others.

[0052] Each fluid-propellant source 516 may be, for example, any suitable storage tank for storing the corresponding fluid-propellant 520 in its storage form, for example, either gas or liquid, or a combination thereof. The liquid propellant 520 may be any type suitable for a particular mission, including any of the primary liquids mentioned above. Those skilled in the art will readily understand how to design and construct each propellant source 516 according to the chosen liquid propellant 520 and mission conditions.

[0053] The spacecraft 500 includes a structure 536 that physically supports and/or contains each propulsion system 504 and components thereof, as well as any other components (not shown) needed to complete the spacecraft. Those skilled in the art will readily understand that the structure 536 may include any suitable physical structure, such as framework, shells, skins, etc., that provide the usual structural functions for spacecraft of the relevant type.

[0054] Various modifications and additions can be made without departing from the spirit and scope of this disclosure. Features of each of the various embodiments described above may be combined with features of other described embodiments as appropriate in order to provide a multiplicity of feature combinations in associated new embodiments. Furthermore, while the foregoing describes a number of separate embodiments, what has been described herein is merely illustrative of the application of the principles of the present invention. Additionally, although particular methods herein may be illustrated and/or described as being performed in a specific order, the ordering is highly variable within ordinary skill to achieve aspects of the present disclosure. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this disclosure.

[0055] Exemplary embodiments have been disclosed above and illustrated in the accompanying drawings. It will be understood by those skilled in the art that various changes, omissions and additions may be made to that which is specifically disclosed herein without departing from the spirit and scope of the present disclosure.