FR2544919A1 - Guidance of large-size satellites with low density by electromagnetic effect - Google Patents

Abstract

Guidance system for large-size satellites of low density and for solar sails using the torque effect induced between the local magnetic field and a field created by an electromagnetic effect generated by loops of electrical conductors placed in different planes and traversed by currents whose direction, strength and duration are controlled as a function of the characteristics of the local magnetic field, the initial orientation of the satellite and the desired final orientation. This electromagnetic guidance torque can advantageously be strengthed by implanting along the conductors a material with high magnetic permeability.

Description

Control of large satellites and low specific mass by electromagnetic effect
The invention relates to piloting the orientation of satellites in space, and in particular satellites of low specific mass and large dimensions.

The satellites launched in recent years are characterized by
- Small or medium dimensions (order of magnitude ranging from one meter to ten meters).

- An average mass density (around 1 Kg / liter)
The device for controlling the orientation of these satellites in space generally uses a combination of flywheels, reaction wheels and small side nozzles which have great flexibility of use and allow rapid rotations around all axes. regardless of any external constraints.

The Earth's magnetic field was used in the early years of space weathering to control and command the directions of satellites. Magnetic coils with soft iron cores, the length of which went up to 80 cm and the number of ampere-turns up to 200, made it possible to create couples of a few hundredths of a Newton-meter.

However, this technology is no longer used because it creates large magnetic fields, disruptive for on-board experiences and cause significant consumption of electricity. The most conventional use of the magnetic field today is that of magnetic bars, passive bars fixed at various points on the satellite and responsible for causing it to lose its kinetic energy by hysteresis by playing the role of rotation damper.

Large satellites and low specific mass pose a particular piloting problem while offering increased possibilities of piloting torque due to their dimensions. They are by definition much more sensitive to the action of surface forces such as atmospheric braking and radiation pressure. It's here
this is why controlling their orientation with respect to these flows is fundamental for the control of their orbit. A solar sail with a surface density of 50 g per m2 can modify due to the solar flux, its orbit at the speed of a few kilometers per day for a low orbit, and this speed increases in proportion to the orbital period.

Two energy-efficient principles can be used to generate these steering torques. The first one, viewed by all the authors of solar sails projects, is based on the torque generated by the action of the radiative flux on a surface asymmetry created voluntarily by means of orientable flaps. The second proposed here uses the torque generated by the electromagnetic effect in reaction with the local magnetic field. The latter is considerably higher
(factor 100 to 10,000) and this results in much greater speed and precision of maneuver. This is how to maneuver a solar sail with a surface area of 200 m2 and an average surface density of 50 g / m2, is possible to generate from a current source with a power of
100 Watts in the vicinity of the Earth, tilting torques of the order of Newton-cm allowing changes of orientation of 900 in about ten minutes. The object of the invention is to provide a technologically simple and precise solution, suitable for controlling all large satellites and of low specific mass, used for example for the following applications
- Solar sails or photon powered vehicles.

 - Maintaining a satellite station by using radiation pressure on a maneuverable sail.

- Satellite mirror reflecting sunlight on a
given land area.

- Large stable radio antenna
read on a listening axis. Etc ...

 The system object of the invention consists of two or more loops of electrical conductors forming each of the maximum surface turns and placed in different planes so as to be able to generate a magnetic field vector of given value in all directions of space. Practically, in the example of a solar sail, a loop will be placed on the periphery of the sail, and two other loops will be placed in two planes orthogonal to the sail and orthogonal to each other. The three conductor loops thus formed allow the magnetic torque of the satellite to be oriented at will by sending the available electrical power in the proportions and directions determined on the three loops.

 The electrical conductors may preferably consist of aluminum foils or foils, a metal having the best resistivity-density ratio. An important improvement of the process consists in using strips of soft iron or magnetic oxides having high magnetic sealing characteristics, placed on the structure of the satellite near the electrical conductors. Their use considerably increases the value of the steering torque and makes it possible to reduce maneuver times.

 Furthermore, when designing the overall art of satellite architecture, it is necessary to eliminate parasitic sources of torque, on the one hand by constructing a completely symmetrical satellite so as to avoid couples due to differential pressure action radiation, and secondly by providing the satellite with a spherical inertia ellipsoid so as to avoid the torque generated by the gravity gradient.

The control chain by electromagnetic effect of such a satellite will generally consist
- A star pointer giving the satellite the absolute axis reference.

- A computer controlled by a navigation program, the inputs of which are as follows
ta The trajectory of the satellite possibly readjusted periodically from observations made on the ground.

 The position of the sun relative to this trajectory in the case of solar sails.

 The direction and amplitude of the local magnetic field recorded by a magnetometer installed on board.

 The law and the steering objectives given to the satellite.

- One or more current sources
Or by solar panels statically arranged on the satellite in several directions so as to be able to supply the installation in all configurations.

 . Either by one or more mobile panels.

 . Either by electrochemical generators.

 . Or by a combination of generator systems.

 - A multiplexer device allowing, from the orders received from the computer, to direct the electrical power available on the different magnetic field generation loops in the desired proportions and directions.

 The invention can be illustrated with the aid of the appended figures and the additional description which follows, which of course have no restrictive or limiting character.

 Figure A shows a possible architecture for a solar sail.

 Figure B shows a possible architecture for a radio telescope.

 In FIG. A, the solar sail of square plan, rep 1, carries at the crossing of its diagonals a central mast, rep 2, crossing it right through. A first conductor loop, rep 3, is fixed along the perimeter of the sail.

 The other two conductor loops, rep 4 and rep 5, are fixed between the ends of the mast and the tops of the sail so as to form three loops in orthonormal marks.

These conductors are either stretched or carried by transparent veils fixed on the mirror at the level of the diagonals as well as on the mast, materializing the orthonormal benchmark mentioned above.

 In FIG. B, the radio telescope is composed of a passive reflector, rep 6, on which is fixed coaxially to the focal axis a mast, rep 7. A first conductor loop, rep 8, is fixed on the outer perimeter of the reflector. The two other conductor loops, rep 9 and 10, are fixed on the intersections of two planes orthogonal to each other and passing through the focal axis of the reflector.

Claims (3)

Claims 1. Control system for large satellites and low specific mass and more particularly for solar sails using the effect of the induced torque between the local magnetic field and a field generated by electromagnetic effect, characterized by the fact that this electromagnetic field is generated by at least two loops of electrical conductors placed in different planes orthogonal or not and traversed by electric currents of direction, intensity and duration controlled according to the characteristics of the local magnetic field, the initial orientation of the satellite and the 'final orientation desired.  2. Piloting system for a solar sail or any device reflecting photonic or electromagnetic radiation according to claim 1 characterized in that a loop of electrical conductors is fixed at the edge in the plane of the sail or the reflector and that one or two other loops are placed in one or two planes orthogonal to this first plane and supported by a mast in the center and on the focal axis of the reflector. 3. Control system according to claims 1 or 2 characterized in that materials having high magnetic permeability characteristics such as for example iron oxides, are fixed to the structure of the satellite near the loops of electrical conductors amplifying the electromagnetic torque resulting from the passage of electric current through the corresponding loop.