Device and method for measuring the thrust of an ion engine of a rocket or satellite.

Abstract

The present invention (Fig. 1) relates to a device and a method for measuring thrust. More particularly, the present invention relates to a device for measuring the thrust of an ion engine of a rocket or satellite.

Description

Title of the invention: Device and method for measuring the thrust of an ion engine of a rocket or satellite.

[0001] The present invention relates to a device and a method for measuring thrust. More particularly, the present invention relates to a device for measuring the thrust of a rocket or satellite ion engine. State of the art

[0002] To design, develop, and test rocket or satellite engines that produce force, it is necessary to accurately measure the thrust produced during testing. In particular, with small engines such as ion or plasma engines, in addition to measuring the steady-state thrust provided by the engine, it is also necessary to accurately track the rapid rise and fall of the engine's thrust. The thrust measurement device must be capable of providing an accurate response based on an expected thrust-time curve profile. Such devices use a balance such as, for example, the one described in French patent FR1532374.

[0003] There are many books and many patents (US, FR, CN, RU) in the literature; however, this type of device is difficult to calibrate, and is generally very expensive.

[0004] Patent FR2511509 presents an accelerometer in which the test mass has a cruciform structure and is formed of three flat rectangular plates whose planes are orthogonal in pairs.

[0005] Patent FR2541775 describes a test mass comprising flat surface elements, two by two opposite and parallel, forming three pairs of surface elements, the directions normal to these elements corresponding to the sensitive axes of the accelerometer.

[0006] French patent FR2544865 describes another configuration of the test mass and the suspension electrode systems. The arrangement makes it possible to obtain a rigid test mass with a high surface area to mass ratio and to use flat electrode systems produced by vacuum metallization on an insulating substrate.

[0007] Moreover, the appearance of small rocket or satellite engines (with a thrust close to a few kg) which produce rapid start-up transient phenomena (with durations close to a few milliseconds to go from 10% to 90% of full thrust) have severe requirements for transient phenomena.

[0008] Indeed, the use of plasma thrusters for satellite propulsion has been steadily increasing for several years because of their performance and reliability, are pushing more and more satellite operators to use all-electric platforms.

[0009] All this increased activity means increased needs in terms of ground characterization of these propulsion systems.

[0010] It therefore becomes necessary to obtain very stable and very precise thrust measurements.

[0011] The present invention therefore aims to remedy the shortcomings of the prior art. Summary of the invention

[0012] In its simplest embodiment, the present invention proposes to measure the force or thrust provided by a rocket ion engine or a satellite engine with an electronic device that includes at least one integrated accelerometer. A microelectromechanical system (MEMS) component is a microsystem made from semiconductor materials. It generally comprises one or more mechanical elements and uses electricity to perform a sensor function, with a structure that has micrometric dimensions.

[0013] The accelerometers of the MEMS component accurately measure the transient phenomena of stopping and starting, while a position sensor measures the static thrust. The present invention aims to provide a method for measuring, with very high accuracy, rapid transient phenomena, as well as steady-state thrust levels. Brief description of the drawings

[0014] The present invention will be better understood with drawings.

[0015] [Fig.1] Fig.1 is a schematic drawing of the device according to the present invention.

[0016] [Fig.2] Fig.2 is a simulation of the movement of the measuring arm as a function time. Description of the invention

[0017] The present invention according to the device (1000) makes it possible to measure the thrust of an ion engine of a rocket or satellite whose thrust curve profile as a function of time is to be measured.

[0018] When the motor (100) to be tested is switched on, it produces a thrust or force in the axial direction and directed horizontally in the case described here. This thrust is exerted on a measuring arm which is supported by supports that allow it to move axially but prevent any lateral movement, torsion, or any movement in a direction other than the axial direction.

[0019] The measuring arm (200) is mobile along the axial direction.

[0020] The measuring arm (200) has an initial position notch (a marker).

[0021] The measuring arm (200) has end stops.

[0022] The measuring arm (200) includes a ferromagnetic part.

[0023] The supports (300) allow the measuring arm to be held in a position such that there is only one degree of freedom along the axial direction of measurements.

[0024] The supports (300) include bearings with a low coefficient of friction.

[0025] The supports (300) allow the measuring arm to slide easily within it.

[0026] The position sensor (400), for example a laser sighting sensor, makes it possible to measure with very high precision the position of the notch (of the marker) which is located on the measuring arm.

[0027] The solenoid (500) is placed along the measurement axis around the measuring arm (200).

[0028] The solenoid (500) includes a magnetic circuit which makes it possible to generate a magnetic field B.

[0029] When an electric current flows in the magnetic circuit, a magnetic field B is created along the axial direction of the measuring arm (200).

[0030] The value of this magnetic field is given for a solenoid of small diameter compared to its length by B = po NI / L, in which po is the magnetic permeability of free space, N is the number of juxtaposed turns constituting the solenoid, I is the intensity of the current flowing in one turn of the solenoid and L is the length of the solenoid.

[0031] The ferromagnetic part of the measuring arm (200) is inserted into a solenoid (500). The ferromagnetic part is constructed such that it has a magnetic component perpendicular to the magnetic field generated by the solenoid. This ensures that the measuring arm moves along the axial direction with a force F proportional to the field B.

[0032] A MEMS component (600) is attached to the side of the measuring arm (200). The MEMS component generates, via integrated accelerometers, an electrical current proportional to the acceleration of the measuring arm. The characteristics of the MEMS component, for measuring very small accelerations, are such that the measurement range of the accelerometers is ± 100 grams, with a nonlinear error of less than 50 ppm and noise on the order of micrograms.

[0033] A balancing mass (700) is fixed either to the end of the measuring arm or distributed over it to balance the mechanical forces on the measuring arm when it is loaded with the motor.

[0034] To calibrate the entire device, the measuring arm must be statically loaded with known weights and the device adjusted to obtain a very precise initial position. Indeed, the device calibration must be performed in situ to compensate for any drift and bias and thus increase the measurement accuracy. Furthermore, the ca Libration must guarantee a certain consistency when the device is subjected to variable ambient conditions, such as temperature, or electromagnetic effects, or vibrations.

[0035] The calibration operation requires time, equipment, and expertise. It should be noted that the calibration process may indeed involve the intervention of a third-party service provider to make adjustments to the device so that it can be certified as conforming to the expected specifications.

[0036] When a thrust is exerted along the axial direction of the measuring arm, the initial position of the measuring arm moves.

[0037] The position sensor measures the difference between the initial position and the new position. This value is acquired by an electronic measurement chain. This electronic measurement chain generates an electric current that is sent to the solenoid's magnetic circuit. This causes the measuring arm to move in the opposite direction to the thrust and to a stable position close to the initial position.

[0038] The value of the electric current flowing in the magnetic circuit of the solenoid allows the value of the static thrust to be obtained.

[0039] The measurement chain includes a PID (Proportional Integral Derivative) type control loop.

[0040] The electronic measurement chain can also acquire an electrical image of the thrust setpoint requested from the ion engine to be tested.

[0041] The instantaneous value of the thrust is given by one of the accelerometers of the MEMS component.

[0042] According to the present invention, the device (1000) for measuring a force exerted by rocket or satellite ion engines, characterized by the following points, separately or in combination, comprises a measuring arm intended to produce electrical signals in response to the loads applied to it, a MEMS component fixed to this measuring arm and intended to produce electrical signals in response to the accelerations applied to the measuring arm, a static position sensor, and a means intended to receive the electrical signals from the measuring arm and the MEMS component, optionally from the thrust setpoint requested from the ion engine to be tested, and to add / subtract the electrical signals to give electrical signals which are sent to a means capable of generating a magnetic field and thus of generating a force (for example, using a solenoid).

[0043] According to the present invention, the device (1000) used to measure a force exerted by rocket or satellite ion engines, when a thrust is applied, the electrical signals generated by the device compensate for the acceleration deviations that may exist in the electrical signals from the measuring arm.

[0044] According to the present invention, the device (1000) used to measure an exerted force by rocket or satellite ion engines, includes mounting means for holding the thrust measurement device and allowing it only one degree of freedom of movement.

[0045] According to the present invention, the method for measuring the force of a rocket or satellite ion engine consists of mounting this engine securely to a measuring arm in order to receive a thrust from it, starting the engine, receiving electrical signals from an electronic measurement chain and recording said electrical signals.

[0046] The present invention has been described with reference to various embodiments. Where possible, one or more elements, components, constituents, structures, or modules of the described embodiments may be combined, separated, interchanged, or rearranged with one or more other elements, components, constituents, structures, or modules of the embodiments without departing from the scope of the disclosed invention. The present invention is not limited by the description of the various embodiments. Those skilled in the art may derive other implementations from the technical solutions of the present invention.

Claims

1. Claims , device (1000), makes it possible to measure the thrust of a rocket or satellite ion engine whose profile of the thrust curve as a function of time is to be measured and comprising, the motor (100) to be tested is switched on, produces a thrust or force in the axial direction and directed horizontally and this thrust is exerted on a measuring arm, the measuring arm (200) is movable in the axial direction, has a notch (a mark) for the initial position, end-of-travel stops, a ferromagnetic part, the supports (300) allow the measuring arm to be held in a position such that there is only one degree of freedom along the axial measurement direction, and for the measuring arm to slide easily, the position sensor (400) with laser aiming makes it possible to measure with very high precision the position of the notch (of the marker) which is located on the measuring arm, the solenoid (500) is placed along the measurement axis around the measurement arm (200), comprises a magnetic circuit which makes it possible to generate a magnetic field B along the axial direction of the measurement arm (200), and makes it possible to ensure that the measurement arm moves along the axial direction with a force F proportional to the field B, the MEMS component (600) is fixed on the side of the measurement arm (200) and generates, thanks to the integrated accelerometers, an electric current proportional to the acceleration of the measurement arm (200), a balancing mass (700) is distributed on the measurement arm to balance the mechanical forces when it is loaded with the motor, and in such a way that when a thrust is exerted along the axial direction of the measurement arm, the initial position of the measurement arm moves, the position sensor measures the difference between the initial position and the new position, this value is acquired by an electronic measurement chain,this electronic measurement chain generates an electric current which is sent to the magnetic circuit of the solenoid, this has the consequence of moving the measuring arm in the opposite direction to the thrust and in a stable position close to the initial position, the value of the electric current circulating in the magnetic circuit of the solenoid makes it possible to obtain the value of the static thrust, the value, instantaneous thrust is given by one of the accelerometers of the MEMS component (600).

2. , device (1000) according to claim 1, such that the measuring range The accuracy of the integrated MEMS accelerometers (600) is ± 100 grams, with a nonlinear error of less than 50 ppm and noise in the microgram range.

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