Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
  • F03H—PRODUCING A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
  • F03H1/00—Using plasma to produce a reactive propulsive thrust
  • F03H1/0006—Details applicable to different types of plasma thrusters
  • F03H1/0012—Means for supplying the propellant
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
  • F03H—PRODUCING A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
  • F03H1/00—Using plasma to produce a reactive propulsive thrust
  • F03H1/0087—Electro-dynamic thrusters, e.g. pulsed plasma thrusters

Definitions

• the invention relates to a supply method for space arc vacuum propulsion, called VAT - acronym for "Vacuum Arc Thruster” in English terminology - and to a space vehicle propulsion module ( still called “satellite” in the present text) intended to implement such a method.
• VAT - acronym for "Vacuum Arc Thruster” in English terminology
• space vehicle propulsion module still called “satellite” in the present text
• the invention relates to the field of satellite propulsion with a storage of the propellant in solid form.
• plasma propulsion modules operate using a gas (usually xenon) stored in tanks, the engines having the role of ionizing and accelerating this gas to create the thrust needed to put the satellite in motion.
• the gas storage propulsion module has been replaced by a solid storage propulsion module.
• the solid storage propulsion systems can be classified according to several types: the pulsed plasma propulsion systems or PPT, acronym for “Pulsed Plasma Thruster”, the vacuum arc systems known as VAT, acronym for “Vacuum Arc Thruster”, and PLT laser ablation systems, the acronym for “Photonic Laser Thruster”, which uses a solid material (PTFE or metal) as a propellant. Ablation of this material is achieved by the impact of a high power density laser on the surface of the propellant solid.
• a PPT propulsion system consists of conductive electrodes - anode and a cathode - separated by an insulator serving as a propellant material, usually PTFE (acronym for "poly-tetrafluoroethylene").
• the electrodes are connected via a high voltage circuit. When the voltage at the terminals of a capacitor of this circuit is sufficient to form an intense current on the surface of the insulator, the latter vaporizes. This vaporization resulting in an increase in the number of neutral particles available in the vacuum, the electronic avalanche can then occur between the electrodes.
• the high temperature of the plasma thus causes the Laplace force to cause the acceleration of the plasma in the direction of thrust.
• the ionized plasma thus formed is engaged at high speed through a channelized outlet to produce a pulsed propulsive reaction force.
• This type of PPT propulsion has the advantage of being able to consume large amounts of PTFE, namely several kilograms, which ensures a long thrust period for the propulsion module.
• this technology offers a low propulsive efficiency, of the order of a few percent, and a specific impulse level (less than 800s) much lower than that obtained by the propulsion technology VAT, which provides a much higher level of impulse. high (greater than 1400s).
• the VAT type propulsion uses the material of the cathode and not the insulator as a propellant.
• electrical energy is stored in a high voltage circuit and released during the implementation of an arc initiation system.
• This arc initiation system is based on the creation of an initial plasma between the electrodes. This plasma generates an electronic discharge between the cathode and the anode.
• the electronic current takes place between the anode and the cathode and warms it locally by Joule effect to create a cathode spot.
• This cathode spot generates a temperature sufficient to emit by evaporation neutral metal particles which are then ionized and accelerated near the cathode surface by substantially faster electrons.
• each plasma pulse corresponds to a push pulse.
• the repetition frequency of the pulses as well as their durations and intensities are determined by a power electronics.
• the amount of material ejected at each pulse is substantially the same.
• propulsion VAT examples include US Pat. No. 7,053,333. These systems generally comprise a hollow tube-shaped cathode and a coaxial central (or the opposite) cylindrical anode, separated by an electrical insulator. in aluminum silicate over substantially their entire length. The insulation is covered with a metal film to promote the formation of micro-plasmas that extend along the propulsion initiator plasma. The superheated and consumed metal film is replaced by redeposition of the cathode material through the plasma arc. A magnetic core coupled to a coil creates a magnetic field to orient the particles in the same direction to provide effective propulsion.
• a spring - arranged in the propulsion module against the rear end face of the cathode - exerts pressure on the cathode to bring its other end facing a anode end that is not separated by insulation.
• This spring advance mechanism allows to consume only a few grams of cathode, which greatly limits the duration of thrust and is still insufficient to perform missions typically dedicated to space vehicles.
• the invention aims to achieve a consumption of several kilograms of cathode, or tens of kilograms or more, in the context of a propulsion type VAT, without degrading the performance of this type of propulsion.
• the invention provides for driving the cathode in an optimized helical movement so as to allow the consumption of substantially all the usable cathode material.
• the subject of the present invention is a supply method for vacuum electric arc propulsion of the VAT type, consisting in guiding an annular cathode along a helical path around a central axis, to arrange - in the immediate proximity and radially with respect to the cathode - several regularly distributed anodes in a plane perpendicular to the central axis, to adjust the pitch of the helical trajectory of the cathode, as well as the advance of the cathode on its trajectory helical and the intensity of the electronic discharge impact cycles between the cathode and the anodes, so that the helices formed by the electronic discharges between the cathode and each of the anodes are juxtaposed, and to straighten the plasma jet formed by the electronic discharges along the central axis to form a plasma that generates a propulsive reaction force parallel to this axis (X'X).
• the consumption of cathode material is optimized by an abrasion of substantially the entire surface of the cathode can be used.
• the increase in the number of anodes makes it possible to better parallelize the arcs and thus to increase the intensity of the thrust.
• This method allows an excellent vectorization of the thrust thanks to the possibility of choosing the location of the site of creation of the arc by powering up the anode corresponding to this site.
• the thrust can be pulsed with a variable frequency.
• a pre-plasma is generated in the immediate vicinity of the cathode in order to trigger a main electronic avalanche amplified by the electronic discharges;
• the pitch of the helical trajectory of the cathode is determined as a function of the size of crucibles successively formed by each cycle of impacts of arcs coming from the nearest anode, the succession of adjacent crucibles combined with the helical movement of the cathode then forming for each anode a helical groove and the formed helices being contiguous;
• the invention also relates to a satellite propulsion module for implementing the method defined above.
• a satellite propulsion module for implementing the method defined above.
• Such a module comprises a generally annular frame having a central axis and wherein is arranged an annular metal cathode guided by threading / tapping in helical connection with this frame, and a central hollow shaft and coaxial with the frame.
• On a transverse wall of this central shaft is fixed a circular support consisting of an insulating material and equipped with metal anodes regularly distributed in circumference.
• energy storage capacitors connect each anode to the cathode to provide, after the formation of a pre-plasma, the energy to generate electronic discharge cycles.
• a rotational drive mechanism is connected to the cathode to impart to it a movement of step-by-step movement in connection with the helical guide formed between the frame and the cathode.
• This module has in particular robustness and simplification qualities of the cathode lift mechanism and the integration of its constituent elements in the same frame.
• the central shaft integrates a discharge initiation system, composed in particular of optical fibers respectively coupled to optical terminals positioned in close proximity to the anodes and capable of transmitting ionizing electromagnetic radiation originating in the direction of the cathode from minus a source of electromagnetic radiation favoring the initialization of the plasma jet formation from an arc generation;
• the source of ionizing electromagnetic radiation is constituted by a laser
• an electromagnetic coil is also integrated in the frame to create an induced magnetic field in order to axially rectify the plasma formed by the successive electronic discharges;
• the rotation drive mechanism is constituted by a support ring of the cathode in connection with an electric motor step by step via a worm.
• FIG. 1 an overall perspective view of an exemplary satellite propulsion module according to the invention
• FIGS. 2a and 2b a perspective view intersected by a longitudinal plane and a front sectional view of the exemplary module according to FIG. 1, and
• a circular support 10 - in the form of disk - is equipped with eight anodes 1, fixed by screws 1 1 on its circumference.
• the anodes 1 are distributed regularly in a radial symmetry.
• An annular cathode 2 surrounds the circular support 10 at a small distance from the anodes 1, approximately 10 mm in the example illustrated, so that a circular end edge 2b of the cathode 2 is substantially in close proximity to the anodes 1.
• the cathode 2 extends along a longitudinal axis coinciding with the central axis X'X of the support 10 which extends transversely with respect to the cathode 2, perpendicularly to the central axis X'X.
• the cathode 2 is coupled to a frame 20 which encompasses it longitudinally.
• the circular support 10 has radial stiffening ribs 12, terminated by connecting rivets 13, via spacing pins 14, to a plate 30 also circular and disposed inside the frame 20.
• An electromagnetic coil 3 of cylindrical shape is integrated on the outer cylindrical face 20e of the frame 20, parallel to the cathode 2, so that the end edge 3b of the electromagnetic coil 3 is at the level of the anodes 1.
• FIG. 1 The views of the module 100 of Figures 2a and 2b, respectively in perspective cut along a longitudinal plane passing through the axis X'X ( Figure 2a) and in frontal section ( Figure 2b), show more precisely the interior of the frame 20.
• This frame 20 has a longitudinal hollow central shaft 2A X'X axis which extends at its ends to form transverse walls 21A and 21 B.
• the transverse wall 21A serves as a base for the circular support 10 and the other transverse wall 21 B forms an end wall of the frame 20.
• Figures 2a and 2b also shows the circular plate 30 on which are fixed capacitors 4 for storing energy between the anodes 1 and the cathode 2, and optical terminals 5 in the immediate vicinity of each anode 2.
• the potential difference between each anode 1 and the cathode 2 (connected to the ground) is 500V. In the vacuum, no discharge occurs with a voltage of this order.
• the optical terminations 5 are coupled to optical fiber ends 6 integrated in the longitudinal central shaft 2A of the frame 20.
• the other ends of the optical fibers are coupled to lasers (not shown) intended to emit high radiation.
• power density for example 10 8 W / m 2 .
• a helical guide system of the annular cathode 2 is made from a 2L thread type connection / tapping between the inner cylindrical face 20i of the frame 20 and the outer cylindrical face 2e of the cathode 2.
• This helical guidance is set in motion by a mechanism comprising a ring gear 7 arranged under the cathode 2 and driven in rotation by a worm 8 mounted on the axis of an electric motor 9.
• the annular cathode 2 thus describes a helical path around the central axis X'X according to the pitch of the helical link 2L.
• the cathode 2 is driven step by step by the helical guidance system with a frequency to pull a few million arcs between two advances corresponding to a 1 ⁇ 4 of degree in rotation.
• the electric drive motor 9 ( Figures 2a and 2b) rotates the cathode intermittently all these few million cycles.
• An arc trigger is generated in the immediate vicinity of each anode 1 by the cone of laser radiation 1 p focused by each optical termination 5 on the cathode 2.
• An initial plasma 2p is formed by a local heating and amplified during successive electronic discharges between the cathode 2 and each of the anodes 1.
• the shots in this same zone form a crater of diameter equal to 1 d and which will form a helix 1 H as the helical advance of the cathode 2.
• Each cycle of impacts of arcs corresponds to a few hundred thousand arches.
• the cathode 2 is set in motion on the helical guide path 2T. This movement is only a few degrees and allows each anode to begin the formation of a new crucible adjacent to the preceding one.
• the crucibles formed by the cycles of impacts of successive arcs from two adjacent anodes 1 then describe parallel helices 1 H.
• the value of the pitch " ⁇ " of the guide path 2T of the cathode 2 is predetermined so that the adjacent helices 1 H of width 1 d are juxtaposed because of the arc firing frequency used.
• all consumable cathodic material is used, which can represent several tens to several hundred kilograms depending on the thickness and height of the cathode.
• the initial plasma jet or pre-plasma 2p formed in the transverse plane of the support 10 by tearing of the cathode material 2 ( Figures 2a and 2b) and amplified by the successive electronic discharges, is straightened and accelerated along the central axis X'X to form a plasma 3p that generates a propulsive reaction force.
• the recovery and acceleration are produced axially by the application of a magnetic field "B" induced by the electromagnetic coil 3.
• the invention is not limited to the embodiments described and shown.
• the arcing between the cathode and each anode can be caused by the establishment of a high voltage between these electrodes, for example greater than 1000V, or by spark plugs adapted.
• the cathode can be rotated by indexing spring blades or by any type of rotary actuator that can be indexed (paddle, rack, etc.).
• the number of anodes is advantageously adapted to the dimensions of the propulsion module and can reach for example 12 or 16 or more.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Physics & Mathematics (AREA)
• Plasma & Fusion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Plasma Technology (AREA)

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• 2015
  • 2015-09-18 FR FR1558809A patent/FR3041390B1/fr not_active Expired - Fee Related
• 2016
  • 2016-09-14 EP EP16778690.4A patent/EP3350441B1/de active Active
  • 2016-09-14 WO PCT/EP2016/071617 patent/WO2017046115A1/fr active Application Filing

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