BACKGROUND

[001] The present disclosure relates to Hall-effect thrusters (HETs) for on-orbit spacecraft propulsion, and more particularly to a magnetic field source and magnetic field flux guide arrangement for a HET.

SUMMARY OF THE INVENTION

[0001] The disclosure provides an assembly for a Hall-effect thruster including an inner guide member extending axially along a longitudinal axis to a discharge end. An outer guide member has a surface radially facing and radially spaced from the inner guide member and extends parallel to the longitudinal axis. The inner and outer guide members are formed of material with high magnetic relative permeability. A magnetic source subassembly extends between the inner guide member and the outer guide member such that during operation a magnetic moment extends in a direction from one of the inner guide member and the outer guide member through the magnetic source subassembly to the other of the inner guide member and the outer guide member.

[0002] The disclosure provides, in another aspect, an assembly for a Hall-effect thruster including an inner guide member extending axially along a longitudinal axis to a discharge end. An outer guide member is spaced radially from the inner guide member relative to the longitudinal axis. The outer guide member defines an outer wall. A cavity is within the outer wall such that the outer wall defines a volume therebetween. The inner and outer guide members are concentric with the longitudinal axis and radially separated from each other within the volume. A magnetic source subassembly including magnetic sources is positioned within the volume between the inner and outer guide members and configured to produce a magnetic field, at least a portion of which is radially directed within the magnetic sources.

[0003] The disclosure provides, in yet another aspect, a Hall-effect thruster assembly including an inner guide member extending axially along a longitudinal axis to a discharge end. Material with high magnetic relative permeability is spaced radially with respect to the inner guide member and oriented to direct a magnetic field. The material defines an outer wall. A magnetic source is positioned such that none of the material with high magnetic relative permeability extends continuously from the outer wall to the longitudinal axis.

[0004] The disclosure provides, in yet still another aspect, an assembly for a Hall-effect thruster including an inner guide member extending axially along a longitudinal axis to a discharge end, and a plurality of discrete outer guide member portions. Each discrete outer guide member portion has a surface radially facing and radially spaced from the inner guide member and extending parallel to the longitudinal axis. The inner guide member and the discrete outer guide member portions are formed of material with high magnetic relative permeability. The assembly further includes a magnetic source subassembly including a plurality of discrete magnetic sources. Each magnetic source extends between the inner guide member and one of the discrete outer guide member portions such that during operation a magnetic moment of each magnetic source extends in a direction from one of the inner guide member and the discrete outer guide member portion through the magnetic source subassembly to the other of the inner guide member and the discrete outer guide member portion.

[0005] Other aspects of the disclosure will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 is an external simplified perspective view of a portion of a conventional HET.

[0007] FIG. 2 is an exploded view of the portion of FIG. 1.

[0008] FIG. 3 is a cross-sectional schematic view of the portion of FIG. 1 taken along line 3-

3 and showing a conventional arrangement of magnetic field sources and magnetic field flux guides.

[0009] FIG. 4A is an external simplified perspective view of a portion of another

conventional HET.

[0010] FIG. 4B is a cross-sectional schematic view of the portion of FIG. 4A taken along line 4B-4B. [0011] FIG. 5 is an external simplified perspective view of a portion of a HET in accordance with the disclosure.

[0012] FIG. 6 is an exploded view of the portion of FIG. 5.

[0013] FIG. 7 is a cross-sectional schematic view of the portion of FIG. 5 taken along line 7- 7 and embodying an arrangement of magnetic field sources and magnetic field flux guides.

[0014] FIG. 8 is an end view of the portion of the HET of FIG. 5.

[0015] FIG. 9 is a perspective end view of a portion of a HET according to another embodiment.

[0016] FIG. 10 is a perspective end view of a portion of a HET according to another embodiment.

[0017] FIG. 11 is a perspective end view of a portion of a HET according to another embodiment.

[0018] FIG. 12 a perspective end view of a portion of a HET according to another embodiment.

[0019] FIG. 13 is a perspective end view of a portion of a HET according to another embodiment.

[0020] FIG. 14 is a perspective end view of a portion of a HET according to another embodiment.

[0021] FIG. 15 a cross-sectional schematic view of the portion of FIG. 14 taken along line 15-15.

[0022] FIG. 16 is a perspective end view of a portion of a HET according to another embodiment.

[0023] FIG. 17 is a perspective cross-sectional view of a portion of a HET according to another embodiment. [0024] FIG. 18 is a perspective view of a portion of a HET according to another embodiment.

[0025] FIG. 19 is a cross-sectional schematic view of the portion of FIG. 18 taken along line 19-19.

[0026] Before any embodiments of the disclosure are explained in detail, it is to be understood that the disclosure is not limited in its application to the details of the formation and arrangement of components set forth in the following description or illustrated in the accompanying drawings. The disclosure is capable of supporting other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

DETAILED DESCRIPTION

[0027] FIG. 1 illustrates a Hall-effect thruster 10 (HET) for spacecraft propulsion. The HET 10 includes a housing 20 having magnetic sources and material positioned therein for creating a magnetic circuit.

[0028] Referring to FIGS. 2 and 3, in a conventional concentric arrangement of magnetic field sources and magnetic field flux guides within the housing 20, a discharge chamber 50 is configured to receive propellant (e.g., Xenon, Krypton, Argon, etc.). More specifically, the propellant is introduced into the discharge chamber 50 through openings (not shown) in the housing 20 and/or the magnetic field flux guides. Voltage applied between a cathode (not shown) positioned at or near a first, discharge end 28 and an anode (not shown) positioned at or near a second end 24 forms an electric field extending axially relative to a longitudinal axis A within the discharge chamber 50. A magnetic circuit (i.e., arrows 56) including magnetic field sources 40A, 40B and magnetic field flux guide material 30 is configured to create a radially- oriented magnetic field at the first end 28. Electrons within the magnetic field are used to ionize the propellant. Subsequently, the propellant ions are accelerated by the electric field for generating a thrust at the first end 28. [0029] As shown in FIGS. 2 and 3, the magnetic field sources 40A, 40B (e.g., electromagnetic coils or permanent magnets) are oriented such that their magnetic moments are axial relative to the longitudinal axis A from proximate the first end 28 to proximate the second end 24. The illustrated magnetic field sources 40A, 40B form generally annular shapes about the longitudinal axis A, but in other embodiments such sources 40A, 40B may comprise a plurality of discrete sources (FIGS. 4A-4B). In other constructions, the magnetic circuit may only include one of the magnetic field sources 40 A, 40B. Additional magnetic field flux guide material 30 in the form of a plate 32 with high magnetic relative permeability positioned at the second end 24 extends radially from the longitudinal axis A outward to the housing 20 and completes the magnetic circuit.

[0030] FIGS. 4A-4B illustrate another conventional arrangement of a Hall-effect thruster 10’ (HET) for spacecraft propulsion in which the magnetic field sources are formed by

electromagnetic coils 40A’, 40B’ and like elements have been given the same reference numbers plus a prime (“‘“) symbol. The electromagnetic coils 40B’ extend axially between proximate a first end 28’ and proximate a second end 24’ at each corner of the HET 10’ (only three of which are shown in FIG. 4A). The electromagnetic coil 40 A’ extends axially between proximate the first end 28’ and proximate the second end 24’ along a center or longitudinal axis A’ (FIG. 4B). Specifically, the electromagnetic coils 40 A’, 40B’ create a magnetic flux that is directed axially between the first and second ends 28’, 24’. Magnetic field flux guide material 30’ is positioned at the first and second ends 28’, 24’ for creating a magnetic circuit 56’. The magnetic field flux guide material 30’ extends radially relative to the longitudinal axis A’ for completing the magnetic circuit 56’. In this construction of the HET 10’, an inner cylinder 74 is provided for defining the discharge chamber 50’, in which the inner cylinder 74 is formed of material that does not affect the magnetic circuit 56’.

[0031] FIGS. 5-8 illustrate an assembly of a HET 110 embodying the present disclosure, and like elements have been given the same reference numbers plus 100. The HET 110 includes magnetic field flux guide material 130 in the form of a first or inner guide member 134, a second or outer guide member 136, and end guide members 138. [0032] The inner guide member 134 is generally cylindrical in shape and extends along a longitudinal axis B. A first end 128 may be defined as the discharge end 128 (i.e., the end associated with the discharge of thrust by the HET 110), and the HET 110 further includes a second end 124 that is opposite the first end 128. The illustrated inner guide member 134 is centrally positioned with respect to the longitudinal axis B (FIG. 7) and extends from at or proximate the first end 128 to at or proximate the second end 124. In other embodiments, the inner guide member 134 may include other geometric shapes (for example, as shown in FIG. 12, to be further described). The longitudinal axis B may define a center C of the HET 110.

[0033] The annular outer guide member 136 surrounds the inner guide member 134 and also extends parallel to the longitudinal axis B from at or proximate the first end 128 to at or proximate the second end 124. In this orientation, the annular outer guide member 136 includes an inner wall or surface 146 spaced radially from the longitudinal axis B and facing the inner guide member 134 and an outer wall or surface 148 spaced radially from the longitudinal axis B (FIG. 7). In other words, the material of the outer guide member 136 is spaced radially from the material of the inner guide member 134. The outer guide member 136 as illustrated is circumferentially continuous relative to the longitudinal axis B. Alternatively, in other embodiments the outer guide member 136 may be formed by discrete portions (e.g., portions 136a, 136b, l36c, l36d, etc. in FIG. 18).

[0034] The HET 110 may additionally include a housing (not shown) in which the housing is configured to at least partially surround or enclose the outer guide member 136, or the HET 110 may not include a housing at all.

[0035] Referring again to FIGS. 5-8, the end guide members 138 are coupled to or formed with the inner and outer guide members 134, 136 at the first end 128.

[0036] The magnetic field flux guide members 130 may be formed of material with high magnetic relative permeability such as iron, nickel, cobalt, Hiperco 50, etc. The term“high” with respect to magnetic relative permeability may be defined as the magnetic field flux guide members 130 having a relative permeability of 1000 or more. For example, the magnetic field flux guide members 130 formed of Hiperco 50 may have a magnetic relative permeability of 15,000. In some embodiments, the material for the inner guide members 134, the outer guide members 136, and the end guide members 138 may be the same or of a different type or composition.

[0037] The HET 110 further defines a volume 152 (FIG. 7) contained radially inward of the outer wall or surface 148 between the first and second ends 128, 124. The illustrated inner and outer magnetic guide members 134, 136 are concentric with the longitudinal axis B and radially separated from each other within the volume 152.

[0038] With reference to FIGS. 6-7, the HET 110 includes a magnetic source subassembly 140 positioned at or near the second end 124. In the illustrated construction, the magnetic source subassembly 140 is positioned at the second end 124. In other constructions, the magnetic source subassembly 140 is positioned near the second end 124, wherein near means within ten percent of an axial length defined along the axis B and between the first and second ends 128,

124 of the HET 110. Still further, in other constructions the magnetic source subassembly 140 may be positioned at any axial location along the length between the first end 128 and the second end 124. For example, the magnetic source assembly 140 may be positioned near the first end 128.

[0039] The magnetic source subassembly 140 is positioned between the inner and outer guide members 134, 136 and as illustrated in the embodiment of FIG. 7, extends from the second end 124 and presents an axially-facing side 142 relative to the longitudinal axis B. The axially- facing side 142 is positioned intermediate the first and second ends 128, 124 within the volume 152. In the illustrated embodiment, the axially-facing side 142 is nearer to the second end 124 than to the first end 128.

[0040] The magnetic field flux guide members 130 (i.e., the inner and outer guide members 134, 136 and the end guide members 138) and the magnetic source subassembly 140 are connected together such that a magnetic connection forms between the magnetic field flux guide members 130 and the magnetic source subassembly 140. In other words, the magnetic field flux guide members 130 and the magnetic source subassembly 140 may be coupled together with or without fasteners (not shown) or may simply abut against each other. For example, as shown in FIG. 7, the magnetic source subassembly 140 abuts against the inner and outer guide members 134, 136. In other embodiments, one of the magnetic field flux guide members 130 (e.g., members 134, 136) and the magnetic source subassembly 140 may include a recess, depression, or the like, and the other of the magnetic field flux guide members 130 and the magnetic source subassembly 140 may at least partially extend into the recess or depression in an abutting or coupled relationship. In yet other embodiments, the magnetic field flux guide members 130 and the magnetic source subassembly 140 may only be positioned close to each other such that a gap (not shown) exists between the magnetic field flux guide members 130 and the magnetic source subassembly 140 small enough such that the magnetic flux is still sufficiently continuous and unaffected thereacross. Therefore, the magnetic connection between the magnetic field flux guide members 130 and the magnetic source subassembly 140 may include any or all of the aforesaid relationships. These relationships may also apply between magnetic field flux guide members and may also apply between magnetic sources of the magnetic source subassembly 140.

[0041] With reference to FIGS. 7 and 8, the magnetic source subassembly 140 extends radially relative to the longitudinal axis B (i.e., the center B) from the inner guide member 134 toward the outer guide member 136. As such, the magnetic field flux guide members 130 (i.e., the material with high magnetic relative permeability) are radially discontinuous from the outer wall or surface 148 of the outer guide member 136 to the longitudinal axis B, and the magnetic source subassembly 140 radially magnetically connects or is positioned between the inner guide member 134 and the outer guide member 136. More specifically, the high magnetic relative permeability material of the magnetic field flux guide members 130 (e.g., the inner and outer guide members 134, 136) is discontinuous in the radial direction relative to the longitudinal axis B such that none of the high magnetic relative permeable material extends continuously from the outer wall or surface 148 of the outer guide member 136 to the longitudinal axis B.

[0042] The magnetic source subassembly 140 is configured to occupy a portion of the volume 152 of the HET 110. Specifically, the magnetic source subassembly 140 is configured to take up a portion of the volume 152 of about twenty percent to about fifty percent. In the illustrated embodiment, the magnetic source subassembly 140 takes up a portion of the volume 152 of about twenty-five percent. In other embodiments, the magnetic source subassembly 140 comprises less than fifty percent of the volume 152. [0043] With reference again to FIG. 7, the previously identified volume 152 comprises the inner and outer guide members 134, 136, the magnetic source subassembly 140, and an annular space 150. The annular space 150 is defined between the inner and outer guide members 134, 136, and the magnetic source subassembly 140 (applicable to all embodiments previously described). Specifically, the space 150 is the remaining portion of the volume 152 of the HET 110 not taken up by the inner and outer guide members 134, 136 and the magnetic source subassembly 140. The space 150 forms the discharge chamber configured to receive the propellant (e.g., Xenon, etc.), as previously discussed above.

[0044] With reference to FIGS. 8-18, the magnetic source subassembly 140 includes a plurality of magnetic sources 144. The magnetic sources 144 may be formed by permanent magnets 160 (FIGS. 8-15 and 18) or a plurality of electromagnetic coils 180 (FIGS. 16-17) or some combination thereof. The plurality of magnetic sources 144 separates the inner guide member 134 from the outer guide member 136. Furthermore, the magnetic sources 144 are oriented such that their magnetic moments are radial relative to the longitudinal axis B. The magnetic sources 144 are configured to create a predetermined magnetic flux passing through the inner and outer guide members. Specifically, the magnetic source subassembly 140 magnetically connects the inner and outer guide members 134, 136 to create a magnetic circuit (i.e., arrows 156), which is configured to create a radially-oriented magnetic field at the discharge end 128.

[0045] With reference to FIG. 8, each magnetic source 144 forms a segment of the magnetic source subassembly 140 in which each segment has a field direction that is everywhere parallel within the segment, but is generally radially oriented. Specifically, a magnetic moment 168 of each segment is formed along a center 172 of each segment such that each magnetic moment 168 extends radially outward from the longitudinal axis B. These radial magnetic moments 168 represent portions of the magnetic circuit (arrows 156). As such, at least a portion of the magnetic field passes from the inner guide member 134 to the outer guide member 136 through the magnetic source subassembly 140.

[0046] With reference to FIGS. 8-14 and 16-18, the radial magnetic moments 168 illustrate the field direction for each of the magnetic sources 144. In other embodiments, the magnetic circuit 156 may be reversed such that the magnetic moments 168 are opposite in direction to the arrows shown. In this and all other embodiments, the direction of the magnetic moment 168 may be radially reversed, with a consequent reversal in the direction of the overall magnetic circuit (arrows 156). For example, as shown in FIGS. 9, 13, and 18, the field direction of the magnetic moments 168 extends from the outer guide member 136 radially inward toward the inner guide member 134. As such, at least a portion of the magnetic field passes from the outer guide member 136 to the inner guide member 134 through the magnetic source subassembly 140. As noted, the magnetic moments 168 must be either parallel or anti-parallel to those shown to create the radially oriented magnetic field (and remaining magnetic circuit illustrated by arrows 156).

[0047] With reference to FIGS. 8, 10-15, and 18, the plurality of magnetic sources 144 (e.g., magnets 160) may be in the form of permanent magnets and magnetically connect the inner and outer guide members 134, 136. Furthermore, the number of the magnetic sources 144 forming the magnetic source subassembly 140 is variable in different embodiments. For example, the number of magnetic sources 144 may be four (FIGS. 8, 11 and 18), six (FIG. 12), eight (FIG.

13), twelve (FIG. 10), etc. With reference to FIG. 9, the magnetic source subassembly 140 represents a theoretical magnetic source 144 connecting the inner and outer guide members 134, 136 and having everywhere a perfect radially-oriented magnetic field. Specifically, the magnetic source 144 of FIG. 9 is configured such that at every azimuthal position the resulting magnetic moment 168 is in a radial orientation.

[0048] The number and strength of magnetic sources 144 may be determined based on a predetermined magnetic flux required. In addition, the magnetic source subassembly 140 may include spaces or openings 164 (FIGS. 11, 12, and 18) between the magnetic sources 144, i.e., all magnets of the sources 144 need not abut each other.

[0049] With continued reference to FIGS. 8, 10-15, and 18, the magnetic sources 144 each form a generally pie shape (FIGS. 8, 10-11, 13, and 14) positioned radially around the inner guide member 134. In other constructions, the magnetic sources 144 may form any shape such as rectangular, annular, cylindrical, etc. For example, as shown in FIGS. 12 and 18, each magnetic source 144 forms a generally rectangular shape. The openings 164 may form a shape similar to the shape of the magnetic sources 144 (FIG. 10), or the openings 164 may form other shapes such as triangular, rectangular, etc. In addition, the inner guide member 134 may include a shape other than cylindrical to correspond to or cooperate with the shape of the sources 144.

For example, as shown in FIG. 12, the inner guide member 134 forms a generally hexagonal shape, and the rectangular magnets 160 extend from each side of the hexagonal shape towards the outer guide member 136.

[0050] With specific reference to FIGS. 18 and 19, the magnetic source subassembly 140 includes a plurality of discrete magnetic sources 144. In the illustrated embodiment, the magnetic sources 144 include four permanent magnets extending radially from a portion 134A of the inner guide member 134. In other embodiments, the number of magnetic sources 144 may include fewer or more than four permanent magnets. In addition, the portion 134A is formed of the material with high magnetic relative permeability and is axially continuous (FIG. 19) with the remaining portion of the inner guide member 134. As such, the inner guide member 134 may be formed by a plurality of portions 134, 134A having different shapes (e.g., cylindrical and square) extending between the first end 128 and the second end 124 such that the inner guide member 134, 134A need not be circumferentially continuous.

[0051] With continued reference to FIGS. 18 and 19, the illustrated outer guide member portions l36a, l36b, l36c, l36d are circumferentially spaced about the longitudinal axis B, and extend axially from at or proximate the second end 124 to at or proximate the first end 128. This circumferential spacing need not be even between adjacent outer guide member portions 136a,

136b, 136c, l36d. In addition, each outer member guide portion 136a, 136b, 136c, l36d has a surface radially facing and radially spaced from the inner guide member 134 and extending parallel to the longitudinal axis B between the second end 124 and the first end 128. In yet other embodiments, the portions 136a, 136b, 136c, etc., may themselves be differently shaped or oriented from at or near the second end 124 to at or near the first end 128, and there may be fewer or more than four outer guide member portions l36a, l36b, l36c, etc. Furthermore, in this construction of the HET 110, an inner containment boundary, illustrated as cylinder 174, is provided for defining the discharge chamber 150, in which the inner cylinder 174 is formed of material that does not affect the magnetic circuit 156.

[0052] With reference to FIGS. 14-15, the magnetic source subassembly 140 may include magnetic sources 144 having different magnetic orientations, shapes, and/or positions within the HET 110. For example, the magnetic source subassembly 140 may include both radially- oriented magnets 160 and axially-oriented magnets 160’. The illustrated radially-oriented magnets 160 include first radially-oriented magnets 160 A magnetically connecting the inner guide member 134 with the outer guide member 136 at or near the second end 124. The illustrated axially-oriented magnets 160’ include first axially-oriented magnet(s) 160A’ (FIG. 15) within the inner guide member 134 intermediate the first and second ends 128, 124, and second axially-oriented magnet(s) 160B’ within the outer guide member 136 intermediate the first and second ends 128, 124. The radially-oriented and axially-oriented magnets 160, 160’ have different shapes. In addition, the axially-oriented magnets 160A’, 160B’ may be at the same position relative to the longitudinal axis B and spaced radially apart. A combination of the different magnetic sources 144 is configured to create the predetermined magnetic flux for producing the desired magnetic field.

[0053] With reference to FIG. 16, the magnetic sources 144 may be electromagnetic coils 180. Each electromagnetic coil 180 includes windings that are circumferential with respect to a radial direction relative to the longitudinal axis B. As shown in FIG. 16, eight electromagnetic coils 180 extend radially from the inner guide member 134 to the outer guide member 136. The magnetic source subassembly 140 thereby includes openings 184 between the electromagnetic coils 180. As such, the magnetic source subassembly 140 may include spaces between the electromagnetic coils 180 proximate the second end 124 of the HET 110. The HET 110 may include any number of electromagnetic coils 180 extending radially for forming the radially oriented magnetic field.

[0054] In another embodiment, the magnetic sources 144 may be electromagnetic coils 180’ having windings that are circumferential with respect the longitudinal axis B (FIG. 17), as further discussed below. The electromagnetic coils 180, 180’ are positioned at or near the second end 124 and extend between the inner guide member 134 and the outer guide member 136.

Furthermore, the electromagnetic coils 180, 180’ magnetically connect the inner guide member 134 to the outer guide member 136 for forming the magnetic circuit. As shown in FIG. 17, the HET 110 includes first and second electromagnetic coils 180A’, 180B’ having windings wrapping circumferentially about the inner guide member 134 at the second end 124. A plate 188, forming a portion of the magnetic field flux guide members 130, separates the coils 180A’, 180B’.

[0055] In other embodiments, a combination of magnets 160 and electromagnetic coils 180 may be used to form the magnetic source subassembly 140. Specifically, the magnets 160 and electromagnetic coils 180 are configured to create a magnetic field that is radially oriented or directed from and within the magnetic sources 144.

[0056] In operation, with reference to FIGS. 7-13, the magnetic circuit 156 generated by the magnetic sources 144 extends radially from the longitudinal axis B through the magnetic source subassembly 140 (i.e., through each of the magnetic sources 144). Subsequently, the magnetic circuit 156 extends axially through the outer guide member 136 between the second end 124 and the first end 128. The magnetic circuit 156 then extends radially inward from the outer guide member 136 toward the inner guide member 134 along the end guide members 138, creating the radially oriented magnetic field. Finally, the magnetic circuit 156 extends axially through the inner guide member 134 from the first end 128 to the magnetic source assembly 140 to complete the magnetic circuit 156. As discussed, this pathway may be reversed as shown in FIGS. 9 and 13 if the magnetic moments 168 are flipped.

[0057] In operation, with reference to FIGS. 14-15, the magnetic circuit 156 extends radially from the outer guide member 136 toward the longitudinal axis B through the magnetic source assembly 140 (i.e., through each of the first radially oriented magnets 160A). Subsequently, the magnetic circuit 156 extends axially through the inner guide member 134 and through the axially-oriented magnets 160A’, between the second end 124 and the first end 128. The magnetic circuit 156 then extends radially outward from the inner guide member 134 toward the outer guide member 136 through the end guide members 138, creating the radially oriented magnetic field. Finally, the magnetic circuit 156 extends axially through the outer guide member 136 between the first end 128 and the magnetic source subassembly 140 to complete the magnetic circuit 156. The second axially-oriented magnets 160B’ further direct the magnetic circuit 156 through the axial direction of the outer guide member 136.

[0058] In operation, with reference to FIG. 16, current flows circumferentially about each of the coils 180 and, with a first direction of that current, generates a magnetic field radially outward from the inner guide member 134 to the outer guide member 136 to form a radially oriented magnetic moment 168. As such, the magnetic circuit 156 extends radially from the inner guide member 134 to the outer guide member 136. Subsequently, the magnetic circuit 156 extends axially through the outer guide member 136 between the second end 124 and the first end 128. The magnetic circuit 156 then extends radially inward from the outer guide member 136 toward the inner guide member 134 through the end guide members 138, creating the radially oriented magnetic field. Finally, the magnetic circuit 156 extends axially through the inner guide member 134 from the first end 128 to the electromagnetic coils 180 to complete the magnetic circuit 156. This pathway may be reversed by switching the direction of current flow in the coils 180, thereby flipping the direction of the magnetic moments 168.

[0059] In operation, with reference to FIG. 17, current flows circumferentially relative to the longitudinal axis B through coils 180A’, 180B7 In one embodiment, the current is clockwise in coil 180A’ and counter-clockwise in coil 180Έ (relative to an end view of second end 124), creating the magnetic moment 168 extending radially outward from the longitudinal axis B along the plate 188. As such, the magnetic circuit 156 extends radially from the inner guide member 134 to the outer guide member 136. Subsequently, the magnetic circuit 156 extends axially through the outer guide member 136 between the second end 124 and the first end 128. The magnetic circuit 156 then extends radially inward from the outer guide member 136 toward the inner guide member 134 through the end guide members 138, creating the radially oriented magnetic field. Finally, the magnetic circuit 156 extends axially through the inner guide member 134 from the first end 128 to the coils 180A’, 180B’ to complete the magnetic circuit 156. This pathway may be reversed by switching the direction of current flow in each of the coils 180A’, 180B’ (i.e., counter-clockwise in coil 180A’ and clockwise in coil 180Έ), thereby flipping the direction of the magnetic moments 168.

[0060] In operation, with reference to FIGS. 18 and 19, the magnetic circuit 156 generated by the magnetic sources 144 extends radially from the outer guide member 136 toward the longitudinal axis B through the magnetic source assembly 140 (i.e., through each of the magnetic sources 144). Subsequently, the magnetic circuit 156 extends axially through the inner guide member 134A, 134 between the second end 124 and the first end 128. The magnetic circuit 156 then extends radially outward from the inner guide member 134 toward the outer guide member 136 through the end guide members 138, creating the radially oriented magnetic field. Finally, the magnetic circuit 156 extends axially through the outer guide member 136 between the first end 128 and the magnetic source assembly 140 to complete the magnetic circuit 156. As discussed, this pathway may be reversed if the magnetic moments 168 are flipped.

[0061] Thus, the disclosure provides, among other things, a magnetic source subassembly 140 configured to create a sufficiently effective magnetic field during operation of the HET 110. Specifically, the magnetic source subassembly 140 is oriented with magnetization in the radial direction and configured to connect radially discontinuous magnetic flux guides (i.e., inner and outer flux guide members 134, 136). The magnetic source subassembly 140 may be constructed in a plurality of different configurations for creating the predetermined magnetic flux.

[0062] The magnetic source subassembly 140 is positioned axially with respect to the discharge chamber (i.e., space 150) and configured to fit within geometric constraints of the HET 110 away from the first, discharge end 128. Specifically, the magnetic source subassembly 140 may comprise a portion of the volume 152 of fifty percent or less proximate the end opposite the discharge end 128. As such, the HET 110 may be used for HETs that are smaller but require more magnetic flux to produce the desired magnetic field.

[0063] The position of the magnetic source subassembly 140 axially away from the discharge end 128 may prolong the life of the magnetic sources 144. The discharge end 128 has a higher temperature than other sections of the HET 110 during operation, and the position and orientation of magnetic source subassembly 140 as hereby disclosed exposes the magnetic source subassembly 140 to lower temperatures than a conventional orientation. As such, the position may inhibit degrading of the performance of the magnets 160 or may inhibit melting of insulation around the electromagnetic coils 180.

[0064] The following clauses list out various features of the disclosure as described.

[0065] Clause 1 : An assembly for a Hall-effect thruster, the assembly comprising an inner guide member extending axially along a longitudinal axis to a discharge end; an outer guide member having a surface radially facing and radially spaced from the inner guide member and extending parallel to the longitudinal axis, the inner and outer guide members formed of material with high magnetic relative permeability; and a magnetic source subassembly extending between the inner guide member and the outer guide member such that during operation a magnetic moment extends in a direction from one of the inner guide member and the outer guide member through the magnetic source subassembly to the other of the inner guide member and the outer guide member.

[0066] Clause 2: The assembly of clause 1, wherein the magnetic source subassembly includes a plurality of magnetic sources configured to create a predetermined magnetic flux passing through the inner and outer guide members.

[0067] Clause 3 : The assembly of clause 2, wherein the magnetic sources include a plurality of permanent magnets.

[0068] Clause 4: The assembly of clause 3, wherein the permanent magnets comprise four or more magnets.

[0069] Clause 5: The assembly of clause 3, wherein the permanent magnets are

circumferentially spaced from each other.

[0070] Clause 6: The assembly of clause 2, wherein the magnetic sources include

electromagnetic coils.

[0071] Clause 7: The assembly of clause 6, wherein windings of each coil are circumferential with respect to a radial direction relative to the longitudinal axis.

[0072] Clause 8: The assembly of clause 6, wherein windings of each coil are circumferential with respect to the longitudinal axis.

[0073] Clause 9: The assembly of clause 2, wherein the magnetic sources include at least one permanent magnet and at least one electromagnetic coil.

[0074] Clause 10: The assembly of clause 1, wherein the outer guide member is annular and concentric with the inner guide member. [0075] Clause 11 : The assembly of clause 2, wherein the plurality of magnetic sources radially separates the inner guide member from the outer guide member.

[0076] Clause 12: The assembly of clause 1, wherein the material with high magnetic relative permeability includes at least one selected from the group consisting of iron, nickel, cobalt, and Hiperco 50.

[0077] Clause 13: The assembly of clause 1, wherein the outer guide member is one of a plurality of outer guide members, each outer guide member having a surface radially facing and radially spaced from the inner guide member and extending parallel to the longitudinal axis.

[0078] Clause 14: An assembly for a Hall-effect thruster, the assembly comprising an inner guide member extending axially along a longitudinal axis to a discharge end; an outer guide member spaced radially from the inner guide member relative to the longitudinal axis, the outer guide member defining an outer wall; a volume contained radially inward of the outer wall, wherein the inner and outer guide members are concentric with the longitudinal axis and radially separated from each other within the volume; and a magnetic source subassembly including magnetic sources positioned within the volume between the inner and outer guide members and configured to produce a magnetic field, at least a portion of which is radially directed within the magnetic sources.

[0079] Clause 15: The assembly of clause 14, wherein the inner and outer guide members are formed of material with high magnetic relative permeability, and wherein the material with high magnetic relative permeability is discontinuous in the radial direction from the longitudinal axis to the outer wall.

[0080] Clause 16: The assembly of clause 14, wherein the discharge end is a first end of the assembly, and wherein the magnetic source subassembly is positioned nearer a second end of the assembly opposite the first end than to the first end.

[0081] Clause 17: The assembly of clause 14, wherein the magnetic sources are permanent magnets. [0082] Clause 18: The assembly of clause 14, further comprising a discharge chamber positioned between the inner and outer guide members, and wherein the magnetic source subassembly is positioned to one side of the discharge chamber relative to the longitudinal axis.

[0083] Clause 19: A Hall-effect thruster assembly comprising an inner guide member extending axially along a longitudinal axis to a discharge end; material with high magnetic relative permeability spaced radially with respect to the inner guide member and oriented to direct a magnetic field, the material defining an outer wall; and a magnetic source positioned such that none of the material with high magnetic relative permeability extends continuously from the outer wall to the longitudinal axis.

[0084] Clause 20: The Hall-effect thruster assembly of clause 19, further comprising a volume contained radially inward of the outer wall, and wherein the magnetic source comprises less than 50% of the volume.

[0085] Clause 21 : The Hall-effect thruster assembly of clause 20, wherein the inner and outer guide members are radially separated from each other within the volume, and wherein the magnetic source is positioned within the volume between the inner and outer guide members.

[0086] Clause 22: The Hall-effect thruster assembly of clause 19, wherein the magnetic source includes a plurality of permanent magnets.

[0087] Clause 23: An assembly for a Hall-effect thruster, the assembly comprising an inner guide member extending axially along a longitudinal axis to a discharge end; a plurality of discrete outer guide member portions, each discrete outer guide member portion having a surface radially facing and radially spaced from the inner guide member and extending parallel to the longitudinal axis, the inner guide member and the discrete outer guide member portions formed of material with high magnetic relative permeability; and a magnetic source subassembly including a plurality of discrete magnetic sources, wherein each magnetic source extends between the inner guide member and one of the discrete outer guide member portions such that during operation a magnetic moment of each magnetic source extends in a direction from one of the inner guide member and the discrete outer guide member portion through the magnetic source subassembly to the other of the inner guide member and the discrete outer guide member portion.

[0088] Clause 24: The assembly of clause 23, wherein each discrete magnetic source radially separates the inner guide member from one of the discrete outer guide member portions.

[0089] Clause 25: The assembly of clause 23, wherein the discrete outer guide member portions are circumferentially spaced about the longitudinal axis.

[0090] Clause 26: The assembly of clause 23, wherein the discrete outer guide member portions comprise four discrete outer guide member portions.

[0091] Although the disclosure has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the disclosure as described.

[0092] Various features of the disclosure are set forth in the following claims.