ION THRUSTER FOR THRUST VECTORED PROPULSION OF A SPACECRAFT

Abstract

The disclosed subject matter relates to an ion thruster for thrust vectored propulsion of a spacecraft, comprising a reservoir for a propellant, an emitter having a base and, on one side of the base, at least one outlet for emitting ions of the propellant, wherein the base is connected to the reservoir for providing flow of propellant from the reservoir to said at least one outlet, and an extractor facing said one side of the emitter for extracting and accelerating the ions from the emitter, wherein the extractor is split into sectors about an axis which orthogonally runs through said one side of the emitter, wherein said sectors are electrically insulated from one another.

Claims

1. An ion thruster for thrust vectored propulsion of a spacecraft, comprising: a reservoir for a propellant, an emitter having a base and, on one side of the base, at least one outlet for emitting ions of the propellant, wherein the base is connected to the reservoir for providing flow of propellant from the reservoir to said at least one outlet, and an extractor facing said one side of the emitter for extracting and accelerating the ions from the emitter, wherein the emitter and the extractor form a common acceleration chamber with all outlets therein, which extractor is split into sectors about an axis which orthogonally runs through said one side of the emitter, wherein said sectors are electrically insulated from one another.

2. The ion thruster according to claim 1, wherein the extractor is split into three sectors.

3. The ion thruster according to claim 1, wherein two or more outlets are arranged in a circular symmetry about said axis and all sectors about said axis.

4. The ion thruster according to claim 3, wherein the emitter has a multitude of outlets arranged in a single circle on the base about said axis.

5. The ion thruster according to claim 1, wherein said at least one outlet is a projection on said one side of the base.

6. The ion thruster according to claim 5, wherein the projection is needle-shaped.

7. The ion thruster according to claim 1, wherein the emitter is made of a porous material which is wetting in respect to the propellant.

Description

[0017] The invention shall now be explained in more detail below on the basis of exemplary embodiments thereof with reference to the accompanying drawings, in which:

[0018] FIGS. 1a and 1b show a first embodiment of the ion thruster according to the present invention in a top view (FIG. 1a) and in a detail of a longitudinal section along line A-A of FIG. 1a (FIG. 1b), respectively; and

[0019] FIGS. 2a to 2c show a second embodiment of the ion thruster according to the present invention in a top view (FIG. 2a), in a detail of a longitudinal section along line B-B of FIG. 2a (FIG. 2b), and in a detail C of FIG. 2b (FIG. 2c), respectively.

[0020] Both examples, the one of FIGS. 1a and 1b and the one of FIGS. 2a to 2c, show an ion thruster 1 for propulsion of a spacecraft, particularly a satellite. The ion thruster 1 comprises a reservoir 2 for a propellant 3 (FIG. 2c). The ion thruster 1 further comprises an emitter 4 for emitting ions 3.sup.+ of the propellant 3 and an extractor 5 for extracting and accelerating the ions 3.sup.+ from the emitter 4. The extractor 5 is, therefore, permeable to the propellant 3, e.g., by means of apertures P.

[0021] The depicted ion thruster 1 is of field-emission electric propulsion (FEEP) type. Ion thrusters 1 of this type use liquid metal as propellant 3, e.g. caesium, indium, gallium or mercury, which is heated above the liquefaction temperature in the reservoir 2, fed from the reservoir 2 towards the emitter 4 and ionized by field-emission as will be explained in greater detail below. The extractor 5 extracts and accelerates the generated (here: positive) ions 3.sup.+ of the propellant 3, thereby generating thrust for propulsion of the spacecraft. Moreover, the ion thruster 1 also optionally comprises one or more (in the examples of FIGS. 1a and 2a: two and four, respectively) electron sources 6 (also known in the art as “neutralizers”) to the sides of the emitter 4 for balancing a charging of the ion thruster 1 and thus of the spacecraft due to emission of positively charged ions 3.sup.+.

[0022] Alternatively, the ion thruster 1 may be of colloid type using ionic liquid, e.g. room temperature molten salts, as propellant 3. In this case, the electron sources 6 may not be necessary, as colloid thrusters usually change polarity periodically so that a continued self-charging of the ion thruster 1 and the spacecraft does not occur. In a further alternative, the ion thruster 1 can use gas, e.g. xenon, as propellant 3, which is again ionized by extracting electrons from the atoms.

[0023] The emitter 4 has a base 7 and one or more outlets for propellant 3 on one side 7.sub.1 of the base 7 of the emitter 4, said one side 7.sub.1 being faced by the extractor 5. In the present example the outlets are projections 8 projecting from the side 7.sub.1. Alternatively, the outlets could just be channels such as bores or capillary channels in the base 7 opening to said one side 7.sub.1. Therefore, all said for projections in the following applies to outlets in the form of channels in the base as well.

[0024] As will be explicated in greater detail with reference to FIG. 2c below, the ions 3.sup.+ are emitted from said projections 8 of the emitter 4. For this purpose, each projection 8 has the shape of a cone, a pyramid, a triangular prism, or the like and has a sharp tip 9 or edge, respectively, opposite the base 7. In the present examples, each projection 8 is needle-shaped, i.e. a narrow, pointed cone.

[0025] Moreover, the base 7 is connected to the reservoir 2 for providing passive flow of propellant 3 from the reservoir 2 to the projections 8. Alternatively, the flow could be an active flow by pressurizing the propellant 3 in the reservoir 2.

[0026] In the present examples, the base 7 is made of porous material which is wettable by the propellant, thereby providing passive flow of the propellant 3 by means of capillary forces, i.e., by a combination of surface tension, (pore) geometry and wettability of the respective surface, through the base 7 to the projections 8. Therefore, the base 7 has another side 7.sub.2 which is, e.g., opposite to said one side 7.sub.1 and is connected to the reservoir 2 (FIG. 2b). In an alternative embodiment, the base 7 may be impermeable by the propellant 3 except for channels (not shown) providing flow of propellant 3 from said other side 7.sub.2 to the projections 8. In yet another embodiment, the flow of propellant 3 can be provided on a surface of the base 7, which is wettable by the propellant 3; in this case, the base 7 can be connected to the reservoir 2, e.g., on a lateral side.

[0027] For providing flow of the propellant 3 from the thusly porous, channeled and/or wettable base 7 to the tip 9 of the projection 8, each projection 8 is either made of porous material or has a central channel utilizing said capillary forces, or the projection 8 has a surface wettable by the propellant 3 for providing flow of the propellant 3 on the surface. In one optional embodiment, the emitter 4, i.e., both the base 7 and the projections 8, is made of porous material which is wetting in respect to the propellant 3.

[0028] Between the projection 8 of the emitter 4 and the extractor 5, a strong electric field in the range from several hundred to several thousand Volt is applied by means of electrodes E.sup.+, E.sup.−, one of which is connected to the emitter 4, the other one to the extractor 5. By applying the electric field, the propellant 3 forms a so-called Taylor cone 10 on the tip 9 of the projection 8 (FIG. 2c). In the strong electric field on top of the Tailor cone 10, one or more electrons tunnel back to the surface of the projection 8 due to field-emission in FEEP-type ion thrusters 1, changing the formerly neutral atom to a positively charged ion 3.sup.+. In case of colloid ion thrusters 1 with ionic propellant 3, this ionization is not necessary.

[0029] As shown in FIG. 2c, a further consequence of the strong electric field is that a jet 11 is formed on the apex of the Tailor cone 10, from which the ions 3.sup.+ of the propellant 3 are extracted and then accelerated by the extractor 5 generating thrust. New propellant 3 is replenished by the aforementioned passive or active forces from downstream. Due to the precision at which the voltage between the needle 3 and the extraction electrode E.sup.− can be controlled, the strength of the generated thrust can be controlled with high accuracy.

[0030] Generally, the thrust provided by the ion thruster 1, symbolized by a thrust vector V, is parallel to an axis T which orthogonally runs through said one side 7.sub.1 of the base 7 where the projections 8 face the extractor 5, when the arrangement is perfectly symmetrical around that axis T. Strictly speaking, while each individual ion beam exiting from a projection 8 of the emitter 4 is slightly bent outward towards the extractor 5, the summed thrust vector V of all ion beams is parallel to the axis T in a perfect arrangement. However, due to irregularities in the nature and composition of ion thrusters 1 the summed thrust vector V of the ions 3.sup.+ extracted from the emitter 4 may vary temporally and/or deviate permanently from the intended direction.

In order to compensate for such unintended irregularities and/or to intentionally deflect the thrust vector V from said axis T, i.e. for “thrust vectoring”, the extractor 5 is split into sectors 5.sub.1, 5.sub.2, . . . , generally 5.sub.i, about the axis T. Said sectors 5.sub.i are electrically insulated from one another, e.g., by an insulating material or simply by gaps 12 between neighboring sectors 5.sub.i. Thereby, each sector 5.sub.i can be separately voltage-supplied and electric fields of individual strength can be applied.

[0031] Each sector 5.sub.i is allocated to (here: by being close to) at least one projection 8 as shown. Consequently, those sectors 5.sub.i of the extractor 5, where a stronger electrical field is applied, will extract and accelerate more ions 3.sup.+ from the projections 8 allocated thereto than others; thus, the resulting thrust vector V′ is deflected, e.g., by an angle δ, to or from said axis T, e.g., to or from the original thrust vector V.

[0032] The emitter 4 shown in the example of FIGS. 1a and 1b has a multitude of needle-shaped projections 8 which are arranged symmetrically about the axis T in a single circle (FIG. 1a) on said one side 7.sub.1 of the base 7. Also the base 7 is ring-shaped such that a crown-shaped emitter 4 is formed. Moreover, the extractor 5 has a single aperture P for emission of the ions 3.sup.+ of the propellant 3 from all projection 8 of the crown-shaped emitter 4. Thereby, a common acceleration chamber 13 for the ions 3.sup.+ is formed between the emitter 4 and the extractor 5.

[0033] The extractor 5 of this example is split into three (here: ring-)sectors 5.sub.i about the axis T. Each sector 5.sub.i is allocated to the respectively closest projections 8. The sectors 5.sub.i can either be symmetrical, i.e. each sector 5.sub.i spanning the same angle α about the axis T (as in the example of FIG. 1a) or differ from each other, i.e., each or some of the sectors 5.sub.i span a different angle α.

[0034] As shown in the example of FIGS. 1a and 1b, said other side 7.sub.2 of the base 7 which is connected to the reservoir 2 can optionally be a lateral side of the base 7 of the (here: crown-shaped) emitter 4.

[0035] In the example of FIGS. 2a and 2b, the shape of the emitter 4 and the extractor 5 as well as the arrangement of the projections 8 are different: The projections 8 are arranged on the base 7 in straight rows and columns. Hence, the projections 8 in this example are symmetric about the axis T. Specifically, the projections 8 could be arranged in a circular symmetry about the axis T (not shown). However, a symmetry is not necessary. All sectors 5.sub.i of the extractor 5 optionally span the same angle α about the axis T, as explained above with respect to the example of FIG. 1a.

[0036] Furthermore, the extractor 5 in the example of FIGS. 2a and 2b has a separate aperture P for each projection 8 which aperture P is penetrated by the ions 3.sup.+ extracted and accelerated from this projection 8. Nevertheless, a common acceleration chamber 13 for the ions 3.sup.+ without intermediate walls or segmenting is formed by the emitter 4 and the extractor 5. The extractor 5 in this example is split orthogonally into four equal sectors 5.sub.i each of which being allocated to the same number of (here: nine) projections 8.

[0037] It is, however, understood that the extractors 5 in the examples of FIGS. 1a and 2a (and in any other embodiment) can alternatively be split into two or more than three or four sectors 5.sub.i, respectively, and/or the sectors 5.sub.i of the extractors 5 could optionally be allocated to different numbers of projections 8, e.g., by spanning different angles α.

[0038] The invention is not restricted to these specific embodiments described in detail herein but encompasses all variants, combinations, and modifications thereof that fall within the frame of the appended claims.