Electrodynamic assembly for propelling a spacecraft in orbit around a star having a magnetic field

Abstract

An electrodynamic assembly for propelling a spacecraft in orbit around a celestial body having a magnetic field is disclosed. The assembly includes a plurality of coaxial cables for an electrodynamic assembly for propelling a spacecraft in orbit around a celestial body having a magnetic field. Each coaxial cable includes an electrically conductive core surrounded by a first electrically insulating sheath, and an electrically conductive current return circuit mounted outside the first electrically insulating sheath. The current return circuit includes a first end electrically connected to a first end of the core of the coaxial cable.

Claims

1. An electrodynamic assembly for propelling a spacecraft in orbit around a celestial body having a magnetic field, the electrodynamic assembly comprising: a plurality of coaxial cables, each coaxial cable comprising an electrically conductive core surrounded by a first electrically insulating sheath, wherein each coaxial cable further comprises an electrically conductive current return circuit mounted outside the first electrically insulating sheath, the current return circuit including a first end electrically connected to a first end of said core of the coaxial cable, wherein the coaxial cables are electrically coupled in series such that when a current circulates, the current return circuits see a same current direction and the cores all see a same direction opposite the current return circuits, and wherein the electrodynamic assembly extends between a first free end of the electrodynamic assembly and a second end fastened to the spacecraft.

2. The electrodynamic assembly according to claim 1, wherein each coaxial cable further comprises a coating made from a magnetically conductive material surrounding said first electrically insulating sheath.

3. The electrodynamic assembly according to claim 2, wherein the current return circuit comprises a layer of copper or silver arranged on the coating made from magnetically conductive material.

4. The electrodynamic assembly according to claim 1, wherein the current return circuit of each coaxial cable comprises an electrically conductive wire.

5. The electrodynamic assembly according to claim 2, wherein the current return circuit of each coaxial cable is formed by said coating made from magnetically conductive material surrounding said first electrically insulating sheath.

6. The electrodynamic assembly according to claim 1, wherein each coaxial cable further comprises a second electrically insulating sheath surrounding the current return circuit.

7. The electrodynamic assembly according to claim 1, wherein the coaxial cables are placed in bundles.

8. The electrodynamic assembly according to claim 1, further comprising an input terminal formed by a second free end of the core of a coaxial cable and an output terminal formed by a second free end of the current return circuit of another coaxial cable.

9. A spacecraft able to be orbited around a celestial body having a magnetic field comprising an electrodynamic assembly according to claim 1.

10. The electrodynamic assembly according to claim 1, wherein the plurality of coaxial cables are electrically insulated except for electrical connections between the current return circuit of a coaxial cable of the plurality of coaxial cables and the core of another coaxial cable of the plurality of coaxial cables.

11. The electrodynamic assembly according to claim 1, wherein a length of the electrodynamic assembly is 1000 m.

12. The electrodynamic assembly according to claim 1, wherein a diameter of the core of the plurality of coaxial cables is between 0.08 mm and 11.7 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood upon reading the following, for information but non-limitingly, in reference to the appended drawings, in which:

(2) FIG. 1 shows a schematic illustration of a spacecraft provided with an electrodynamic assembly according to the invention;

(3) FIGS. 2A, 2B, 2C and 2D each show a perspective view of an electrodynamic assembly according to a first and a second embodiment of the invention;

(4) FIG. 3 illustrates an electrical diagram of coupling of the coaxial cables of the electrodynamic assembly according to the first and second embodiments of the invention; and

(5) FIG. 4 illustrates an electrical diagram of coupling of the coaxial cables of the electrodynamic assembly according to a third embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

(6) FIG. 1 shows a schematic illustration of a spacecraft 1 provided with an electrodynamic assembly according to the invention.

(7) The spacecraft 1 comprises an artificial satellite 2 including an electric generator and able to include chemical or other directional propulsion means, the artificial satellite 2 further comprising an electrodynamic assembly 3 with a length of 1000 m and extending between a first free end 5 of the electrodynamic assembly 3 and a second end 6 fastened to the artificial satellite 2.

(8) As illustrated in FIGS. 2A, 2B, 2C and 2D, which each show a perspective view of an electrodynamic assembly 3 respectively according to a first, second, third and fourth embodiment of the invention, the electrodynamic assembly 3 comprises several coaxial cables 7 assembled in a bundle, each coaxial cable 7 having a tether corresponding to the length of the electrodynamic assembly 3.

(9) In the four embodiments illustrated in FIGS. 2A to 2D, each coaxial cable 7 comprises an electrically conductive central core 8 surrounded by a first electrically insulating sheath 9. The core 8 is made from copper or from another electrically conductive metal such as gold or silver, for example.

(10) The first sheath 9 is covered on its outer face by a coating 10 made from a magnetically conductive material, such as pmetal or soft iron, for example. The coating 10 made from magnetically conductive material makes it possible to make the inner part of the coaxial cable 7, where the inner conductor is located, that is to say the core 8, not particularly sensitive to the surrounding magnetic fields.

(11) In the four embodiments illustrated in FIGS. 2A to 2D, each coaxial cable 7 further comprises a an electrically conductive current return circuit 11. The current return circuit 11 has a first and a second end respectively denoted 111 and 112, and the core 8 has a first and a second end respectively denoted 81 and 82. The first end 81 and 111 of the core 8 and the current return circuit 11 are at a same first end of the bundle, and the second ends 82 and 112 of the core 8 and the current return circuit 11 are a same second end of the bundle. For each coaxial cable 7 of the bundle, the second end 82 of its core 8 is electrically connected to the second end 112 of its current return circuit 11.

(12) The coaxial cables 7 of the electrodynamic assembly 3 thus make it possible to perform a return not by the ambient plasma, but by the coaxial cable 7 itself by using a design where only the external element, i.e., the current return circuit 10, is subject to the Earth's magnetic field, since only the axis 8 inserted into the first sheath 9 is inside the magnetically conductive coating 10 forming a magnetic shielding.

(13) In the first embodiment illustrated in FIG. 2A, the current return circuit 11 is formed by a layer 12 of electrically conductive material, such as a layer of copper, arranged, by chemical deposition, on the coating 10 so as to cover the coating 10. Furthermore, each coaxial cable 7 further comprises a second electrically insulating sheath 13 covering the current return circuit 11. The second electrically insulating sheath 13 makes it possible to electrically insulate each of the coaxial cables 7 of the bundle from the other coaxial cables 7 of the bundle, and more particularly to insulate the current return circuit 11 of one coaxial cable 7 from the current return circuit 11 of another coaxial cable 7. The coaxial cables 7 of a bundle are electrically insulated with the exception of the electrical connections made between the current return circuit 11 of a coaxial cable 7 and the core 8 of another coaxial cable, as illustrated in FIGS. 2A to 2D, 3 and 4.

(14) The second embodiment illustrated in FIG. 2B differs from the first embodiment illustrated in FIG. 2A in that the electrical insulation of the current return circuits 11 of each coaxial cable 7 is done not using a second sheath 13 for each coaxial cable 7, but using a single sheath 130 in which each coaxial cable 7 is embedded in the ground.

(15) The third embodiment illustrated in FIG. 2C differs from the first embodiment illustrated in FIG. 2A in that the current return circuit 110 is formed by the coating 10, the material of the coating 10 being magnetically conductive and electrically conductive. The coating 10 can for example be made from soft iron. Soft iron is not as good an electrical conductor as copper, such that the current return circuit 110 has an electrical conduction comparable to that of the current return circuit 11 of the first embodiment, the thickness of the coating 10 in the third embodiment being better than that of the coating in the first embodiment.

(16) The fourth embodiment illustrated in FIG. 2D differs from the first embodiment illustrated in FIG. 2A in that the current return circuit 1100 comprises an electrically conductive wire 14 coated by an electrical insulation 15 instead of the layer of copper 12, the second electrically insulating sheath 13 being mounted directly on the magnetically conductive coating 10. The electrical wire 14 is kept outside the magnetic shielding and preferably on the outside of the bundle in order to stay in the space sensitive to the surrounding magnetic field.

(17) FIG. 3 shows an electrical coupling diagram of the coaxial cables 7 of the electrodynamic assembly 3 according to the first, second and third embodiments of the invention. As shown, the coaxial cables 7 of the electrodynamic assembly 3 are electrically coupled in series to form a circuit in series with an input terminal 16 connected to a first end 81 of the core 8 of the first coaxial cable 71 and an output terminal 17 connected to a first end 111 of the current return circuit 11 of a second coaxial cable 72.

(18) Each coaxial cable 73 between the first coaxial cable 71 and the second coaxial cable 72 comprises a second end 82 of its core 8 electrically coupled to a second end 112 of its current return circuit 11, the first end 111 of the current return circuit 11 of a coaxial cable 73 being electrically coupled to the first end 81 of the core 8 of a following coaxial cable and the first end 81 of the core 8 of a coaxial cable 73 being electrically coupled to the first end 111 of the current return circuit 11 of a preceding coaxial cable.

(19) The cores 8 and the current return circuits 11 of the coaxial cables 7 are thus electrically coupled in series such that if a current circulates, the current return circuits 11 all see the same current direction and the cores 8 all see the same direction opposite the current return circuits 11.

(20) In the first and second embodiments illustrated in FIGS. 2A and 2B, the current return circuit 11 of a coaxial cable 7 comprises an electrically conductive coating layer 12 covering the coating 10 with magnetically conductive material that covers the first insulating sheath 9 of the coaxial cable 7.

(21) In the third embodiment, the return circuit 110 of a coaxial cable 7 is formed directly by the coating 10, which is formed at least partially by an electrically conductive and magnetically conductive material.

(22) FIG. 4 shows an electrical coupling diagram of the coaxial cables 7 of the electrodynamic assembly 3 according to the fourth embodiment of the invention illustrated in FIG. 2D. In this fourth embodiment, the current return circuit 1100 of the coaxial cables 7 is done by the connected, nonprotected wire 14 of the ambient magnetic field.

(23) In all four embodiments, the diameter of the core 8 of the coaxial cables varies between 0.08 mm and 11.7 mm as a function of the current to be passed in the core 8, and the thickness of the first and second electrically insulating sheaths 9 and 13 is approximately 0.1 mm for a voltage of 1000 V.

(24) In the first and second embodiments, the coating 10 forming the magnetic barrier has a thickness on the order of 0.1 mm for a land application, i.e., for an electrodynamic assembly 3 intended to be mounted on a satellite 2 for use in the Earth's magnetic field, and the copper layer 12 has a thickness varying between less than 0.01 mm and 2.3 mm.

(25) The artificial satellite 2 being movable in the Earth's magnetic field, its speed v combined with the presence of a magnetic field B will create, on the return circuits 10, a voltage proportional to their length.

(26) Indeed, on the charge carriers with charge q, in particular the electrons, the Laplace equation applies: F=q (E+v×B), with F the Lorentz force exerted by a magnetic field B on a conductor traveled by charges q generating a current producing an electric field E, and v the speed of the artificial satellite 2.

(27) If the conductor is not connected to both sides, one has, at equilibrium: F=0 and E=−v×B.

(28) One also has E=−grad V=ϑV/ϑx.

(29) There is therefore a voltage across the terminals of the conductor depending on the length and maximum norm corresponding to the product of the norm of the magnetic field with the speed v of the artificial satellite 2 and the length of the electrodynamic assembly 3, or B*v*L. The voltage depends on the relative position of the movement directions of the artificial satellite 2, the magnetic field B, and the direction of the coaxial cables 7. For example, it will be nil if B is collinear to v and will be maximal if v and B are orthogonal.

(30) This voltage will generate current once the circuit is closed: the cores 8 ensure a current return toward the next coaxial cable 7 that is only very partially subject to the magnetic field B and therefore does not create a significant counter-electromotive force.

(31) The return current by the cores 8 is limited by the voltage of the electric resistance of the core 8.

(32) The coaxial cables 7 being numerous, this creates a direct current that also generates Laplace force opposing the speed v of the artificial satellite 2. This is a good way to create a force on the order of 1 to 100 mN continuously that can be used for the orbiting.

(33) When the circuit is open, a voltage is created. Measuring it makes it possible to determine the local magnetic field in the direction orthogonal to the cables-satellite speed plane.

(34) It is then possible, by grouping together 3 sets of orthogonal cables, to produce a braking propulsion that can be modulated as a function of the measurement (by acting on carefully positioned switches) and taking into account the relative speed.

(35) The invention thus provides an electrodynamic assembly configured to be placed on board a spacecraft and allowing a current return protected from ambient electric disturbances.