CN113623159A

CN113623159A - Propellant automatic supply device of coaxial vacuum arc propeller

Info

Publication number: CN113623159A
Application number: CN202111102047.5A
Authority: CN
Inventors: 史宗谦; 朱其杰; 徐鹏飞
Original assignee: Xian Jiaotong University
Current assignee: Xian Jiaotong University
Priority date: 2021-09-18
Filing date: 2021-09-18
Publication date: 2021-11-09

Abstract

The invention discloses an automatic propellant supply device of a coaxial vacuum arc propeller. The miniature stepping motor comprises a coaxially fixed anode, an axial insulating sleeve with internal threads, a cathode rod with external threads, a miniature stepping motor and a transmission mechanism thereof, wherein the transmission mechanism selects a pair of crossed-axis spiral straight gears and a threaded pipe. When the propellant needs to be supplied, a trigger pulse signal from the PPU drives the micro stepping motor to work, and the angular displacement of the micro stepping motor causes the rotation of the crossed shaft spiral straight gear and the threaded pipe, so that the spiral motion of the cathode rod is caused, and the purpose of supplying the propellant is achieved. The quality of the cathode for single propelling and supplying of the micro stepping motor is the same as the cathode loss in the current stage, so that the balance between consumption and supplying is achieved, and the service life of the propeller is prolonged. The vacuum arc thruster is simple in structure and easy to industrially apply, and can accurately supply the propellant so as to achieve the purpose of prolonging the service life of the vacuum arc thruster.

Description

Propellant automatic supply device of coaxial vacuum arc propeller

Technical Field

The invention relates to the technical field of satellite electric propulsion, in particular to a coaxial vacuum arc propeller.

Background

The method is limited by factors such as volume, weight and power, and the traditional propulsion system cannot meet the requirements of micro-nano satellite attitude control and orbit transfer. As a novel electric propulsion technology, a Vacuum Arc Thruster (VAT) has great technical advantages in the aspect of micro-nano satellite propulsion application due to the characteristics of miniaturization, low voltage, high specific impulse and the like.

The vacuum arc thruster can be divided into three types according to the difference of the structures of the discharge electrodes, namely a coaxial type structure, a circular ring type structure and a flat plate type structure. They share the same principle:

1) the arc discharge between the electrodes generates high-speed, high-energy and quasi-neutral plasma, and the plasma from the cathode spot escapes from the surface of the propeller at high speed under the action of the self pressure and the magnetic field, so that the propeller obtains thrust in the opposite direction.

2) VAT obtains thrust by directly ablating cathode material, mass loss of the cathode is mostly ejected at high speed in the form of plasma, a few parts are ejected at low speed of some neutral large particles or liquid drops, and ion parts contribute most of thrust. The greater the ion velocity, the more perpendicular the direction is to the exit surface, the greater the impulse obtained per unit weight of cathode fuel.

3) After the insulating medium is added between the electrodes, the electrodes do not break down the insulating medium to form electric arcs, but form flashover discharge on the surface of the insulating medium to trigger the electric arcs, and a layer of conductive coating is plated on the surface of the insulating medium by utilizing a vacuum coating technology, so that the breakdown voltage between the electrodes is further reduced. After the discharge is finished, part of the neutral large particles and liquid drops generated by cathode ablation are redeposited on the conductive film, and form dynamic balance with consumption in the discharge process, so that the effect of stable triggering is realized.

4) Under the action of the magnetic field, the rotating motion of the cathode spot can enable ablation to be more uniform, and the service life of the electrode is prolonged. Compared with a circular-ring-shaped VAT and a flat-plate-shaped VAT, the coaxial-type VAT can take the inner electrode as the cathode and the outer electrode as the anode, can better limit the movement range of cathode spots, and can maintain the shape to a greater extent to ensure the stability of arc discharge characteristics. In addition, the coaxial VAT has the advantages of good jet directionality and slightly higher plasma jet speed.

Due to the cathode itself acting as a propellant, ablation of the cathode surface material gradually increases the discharge path between the cathode and the anode, resulting in insufficient discharge voltage to form a vacuum arc plasma, shortening the useful life of the VAT. In order to expand the application of VAT as a micro-nano satellite propeller, an automatic supply mechanism needs to be designed to maintain propellant supply.

For the design of an inner anode and an outer cathode in a coaxial VAT, a scheme that a compressed spring stores force to provide a supply driving force is generally used, but a propeller under the scheme has poor jet flow directionality, so that supply failure caused by poor cathode ablation effect is easy to occur, and a shell shields the cathode, so that great energy loss can be generated. And the design scheme of the inner cathode of the outer anode in the coaxial VAT has good VAT jet directionality and high utilization rate of cathode materials, and the effective ablation of the cathode can bring higher use efficiency of the VAT. But currently there is a lack of practical and effective automatic propellant replenishment solutions in such designs.

Disclosure of Invention

The invention aims to provide a novel propellant replenishing design of a coaxial vacuum arc propeller, and effectively solves the problem of replenishing the coaxial vacuum arc propeller as a micro-nano satellite propeller.

The technical scheme of the invention is as follows: the rod-shaped cathode is spirally driven by the angular displacement of the micro stepping motor through a transmission mechanism so as to realize propellant replenishment of the coaxial VAT. In the scheme, an anode is coaxially sleeved outside a rod-shaped cathode, an axial insulating sleeve is arranged between the cathode and the anode, and the distance between the anode and the outer edge of the cathode is the wall width of the insulating sleeve. The rod-shaped cathode is provided with an external thread and the axial insulating sleeve is provided with an internal thread, and the rod-shaped cathode and the axial insulating sleeve are in threaded fit. At the outlet plane, the surfaces of the anode, the axial insulating sleeve and the cathode rod are basically flush, the surface of the axial insulating sleeve is covered with a conductive coating, and the cathode is ablated due to vacuum arc discharge. The ablated quality in the current stage can be known according to the ablation rate, single discharge energy and discharge frequency of the material, when the discharge path between the cathode and the anode is increased and the propellant needs to be replenished, the micro stepping motor is triggered to work, the cathode rod is driven to advance spirally through the transmission mechanism, and the propellant is replenished.

Wherein the amount of single supply of propellant must match the amount ablated during its current stage, otherwise too much or too little supply will result in arc failure.

The propellant supply amount of the micro stepping motor in single working can be adjusted by setting a trigger pulse signal, motor parameters and the transmission ratio of a transmission mechanism.

The invention is characterized in that:

the propellant of the coaxial vacuum arc propeller can be automatically supplied, and the supply amount can be accurately controlled by the micro stepping motor so as to achieve the balance of the supply amount and the ablation amount, thereby prolonging the service life of the propeller.

The angular displacement of the micro stepping motor can be controlled by a single chip microcomputer, the discharge is controlled by a semiconductor switch in a Power Processing Unit (PPU), and the pulse discharge frequency is counted by the single chip microcomputer. The ablation rate of the pusher's cathode material is fixed, on the order of tens of micrograms per coulomb. When the single chip microcomputer counts the number, a pulse driving signal is sent to the micro stepping motor to drive the transmission mechanism to supply the propellant with the same ablation quality.

The thread pitch of the external thread of the rod-shaped cathode and the internal thread of the axial insulating sleeve matched with the external thread of the rod-shaped cathode is required to be as small as possible, so that the supplying precision of the micro stepping motor is improved, and the service life of the propeller is prolonged.

The staggered shaft spiral straight gears are selected in the transmission mechanism, so that the complexity of the setting of the transmission mechanism can be reduced, and higher flexibility is provided for the space arrangement of the whole device.

The requirement on the axial insulating sleeve is made, the thickness of the axial insulating sleeve determines the electrode gap distance and further determines the size of the breakdown voltage required by discharge, the breakdown voltage required by overlarge distance is increased, and the distance is too short, so that the insulating medium can be irreversibly broken down to cause short circuit between electrodes. The materials such as boron nitride and aluminum oxide which have good thermal stability, can resist the corrosion of molten metal, and have lower relative dielectric constant, high breakdown strength and good processing performance can be selected.

Where the selection of the cathode material is required, the discharge cathode directly affects the vacuum arc characteristics and thus the performance parameters of the VAT. The melting point of the cathode material should not be too low, otherwise more neutral large particles and droplets are generated when the cathode is ablated, and the efficiency of the propeller is reduced. Materials with high ion velocity, melting point and ablation rate, such as titanium and copper, can be selected as the cathode material.

Compared with the prior art, the invention has the beneficial effects that: the propellant automatic supply of the coaxial vacuum arc propeller can be realized, and the purposes can be simply and effectively realized by utilizing the combined device of the micro stepping motor and the transmission mechanism.

Drawings

FIG. 1 is a schematic view of a coaxial type vacuum arc thruster including a power supply processing unit;

FIG. 2 is a schematic view of the outlet end face of a coaxial type vacuum arc thruster;

FIG. 3 is a schematic view showing the structure of an automatic propellant replenishing device of the coaxial vacuum arc thruster of the present invention;

fig. 4 is a side view of the automatic propellant supply apparatus of fig. 3 taken along a right-left diagonal axis.

Illustration of the drawings:

1-direct current power supply, 2-inductor, 3-semiconductor switch, optional MOSFET or IGBT, 4-current limiting resistor, 5-anode, 6-axial insulating sleeve, 7-rod-shaped cathode, 8-insulating base, 9-screwed pipe, 10-number 1 spiral straight gear, 11-number 2 spiral straight gear, 12-base support, 13-insulator, 14-micro stepping motor.

Detailed Description

The propellant automatic supply device of the coaxial vacuum arc thruster of the invention is explained in detail with reference to the attached drawings and the specific embodiment.

The PPU in fig. 1 comprises a 20-24V dc power supply 1, an inductor 2, a semiconductor switch 3 and a current limiting resistor 4, wherein the semiconductor switch 3 is typically selected from an IGBT or a MOSFET. The pulse signal generator is used for controlling the on-off working frequency and the pulse width of the semiconductor switch 3, the grid electrode of the semiconductor switch 3 receives a rectangular trigger pulse signal, when the trigger signal is at a high level, the source electrode and the drain electrode are conducted, the circuit is conducted, and at the moment, the PPU is in an energy storage state; when the trigger signal is at a low level, the circuit is disconnected, the PPU is in an energy release state, and the generated voltage is represented by the formula:

V＝L*dI/dt

fig. 2 is a discharge end face of the vacuum arc thruster, and a conductive film with impedance of 10 Ω to 10k Ω is plated on the surface of an axial insulating sleeve 6 between an anode 5 and a rod-shaped cathode 7, and a graphite film or a nano metal film with the same material as the cathode can be selected. The pulse voltage generated by the PPU is directly concentrated at two ends of a plurality of contact points of the conductive film and the cathode rod 7, the current density flowing through the contact points is very high, due to the Joule heat effect, the conductive film material and the cathode metal are gasified together, metal atom steam diffused in vacuum is ionized into micro-plasma, a low-impedance channel with impedance of about 10m omega between two electrodes is formed, the current is rapidly switched from the surface discharge of the initial electrode with high impedance to a plasma discharge path with low impedance, and finally the arc discharge between the electrodes is formed.

During multiple discharge ablations, the discharge path between the anode 5 and the cathode 7 increases, which can lead to failure of the trigger discharge. A value M may be set as the ablated mass when replenishment is required. When VAT is in a certain working condition, the total charge Q of a single pulse passing through the electrode is constant, and the ablation rate gamma of the cathode material is also constant. The ablation rate γ is determined from the mass loss Δ M and the total charge Q of the single-shot pulsed cathode:

γ＝ΔM/Q

the number N of pulse discharges required by the cathode consumption mass M can be calculated through the set ablated mass M, the cathode material ablation rate gamma and the single discharge energy Q:

N＝M/Qγ

the pulse signals of the semiconductor switch 3 in the PPU loop are counted by using the single chip microcomputer, and when the number of pulse discharges in the PPU reaches the value N obtained by the above calculation, in fig. 3, the single chip microcomputer applies the pulse signals to the micro stepping motor 14 to cause angular displacement, so as to drive the number 1 spiral spur gear 10 to rotate, because the number 1 spiral spur gear 10 and the number 2 spiral spur gear 11 are in a staggered shaft meshing configuration, and the number 2 spiral spur gear 11 rotates along with the rotation, so as to drive the coaxial threaded pipe 9 to rotate. And the external thread of the threaded pipe 9 is meshed with the external thread of the rod-shaped cathode 7 at the same pitch, so that the rod-shaped cathode 7 advances spirally to fulfill the aim of supplying the propellant. In the process, two ends of the rod-shaped cathode 7 are respectively restrained by the axial insulating sleeve 6 and the insulator 13, and the periphery of the anode 5 is fixed by the insulating base 8, so that the stability and smooth supply of all parts in the process of mechanical energy conversion are ensured.

It should be noted that the mass of propellant per charge of micro-stepper motor 14 should be the same as the mass M of ablated cathode when a charge is required as described above. The quality of the single replenishment can be adjusted by setting the trigger pulse signal, the motor parameter and the transmission ratio of the transmission mechanism of the micro stepping motor 14, so that the balance between consumption and replenishment is achieved, the stability of trigger discharge under long-time work is ensured, and the service life of the VAT is prolonged.

Claims

1. The propellant automatic supply device of the coaxial vacuum arc propeller comprises an insulating base, an insulator, a rod-shaped cathode, a jacket layer anode sleeved outside the cathode, a micro stepping motor and a transmission mechanism, and is characterized in that an axial insulating sleeve is arranged between the cathode and the jacket layer anode; the insulating base is arranged outside the anode and fixes the anode; the rod-shaped cathode is concentrically arranged in the axial insulating sleeve, and the far end of the rod-shaped cathode is flush with the surface of the anode and the surface of the axial insulating sleeve; the rod-shaped cathode can perform spiral advancing movement in the axial opening of the insulating sleeve;

the transmission mechanism comprises a pair of staggered shaft spiral straight gears and a threaded pipe and is used for transmitting mechanical energy of the miniature stepping motor and driving the rod-shaped cathode to spirally advance, so that the cathode rod rotates and moves to the far end in the axial insulating sleeve;

the insulator is used for fixing one end of the rod-shaped cathode, and the other end of the rod-shaped cathode is fixed in the axial insulating sleeve, so that the cathode rod is kept stable in the spiral propelling process.

2. The propellant automatic-supplying apparatus of the coaxial type vacuum arc thruster of claim 1, wherein the rod-shaped cathode has an external thread and the axial insulation sleeve has an internal thread.

3. The propellant automatic-supplying apparatus of the coaxial type vacuum arc thruster of claim 1, wherein the insulator has an internal thread matching with the external thread of the rod-shaped cathode.

4. The automatic propellant supply device for the coaxial vacuum arc thruster of claim 1, wherein the threaded pipe of the transmission mechanism has an external thread having the same pitch as the rod-shaped cathode and is engaged with the rod-shaped cathode.

5. The propellant automatic-supplying apparatus of the coaxial type vacuum arc thruster of claim 1, wherein a helical spur gear of the transmission mechanism is fixed to a transmission shaft of the micro stepping motor.

6. The automatic propellant replenishing device for the coaxial type vacuum arc thruster, according to claims 1 and 4, wherein a helical spur gear of the transmission mechanism is coaxially fixed with the threaded pipe, and the shaft is fixed to a base bracket.

7. The propellant automatic supply device of the coaxial type vacuum arc thruster of claim 1, 4 or 6, wherein both ends of the shaft of the fixed helical spur gear and the threaded pipe are rotatable relative to the base bracket.

8. The propellant automatic supply device of the coaxial vacuum arc thruster of claim 1, 5 or 6, wherein two helical spur gears in the transmission mechanism are in a staggered shaft meshing arrangement, and transmit the mechanical energy of the micro stepping motor to the threaded pipe.