Object that can be stabilized while floating freely in a space and method for controlling the position of an object in weightlessness or in free fall

Abstract

An object that can be stabilized while freely floating in space, in particular a space object, with an object-side, first attitude control device (L1) for controlling the attitude of the object (1, 1', 1") having an object center of gravity (So) in weightlessness or in free fall, wherein the object (1, 1', 1") is coupled to an external object extension device (2) that can be moved independently in space, is characterized in that the external object extension device (2) is provided with a second attitude control device (L2) that can be moved relative to the object (1, 1', 1").

Description

The invention relates to an object which can be stabilized in a free-floating manner in a space, in particular a space object, according to the preamble of claim 1.The invention is thus concerned with an object which can be stabilized freely floating in a room, for example in space or under the influence of gravity in the free fall and which is coupled to an external object extension device (2) which can be moved independently in the room. Such an object can be, for example, a space station to which a robot arm as an object extension device is coupled on the outside. Such an object can also be, for example, a satellite to be maintained or repaired, to which a robot satellite is coupled as a service satellite. Furthermore, the invention relates to a method for the orientation control of objects in zero gravity (for example in WorldAll) or in free fall in a gravitational field by a position control system (Attitude Determination and Control System) and the mechanical construction of a device suitable for carrying out this method with an extended reaction wheel arrangement, a so-called extended reaction wheel assembly (EREW). In this context, the subject matter in particular is the use of reaction wheels, so-called reaction wheels (RWs), and "constrained gyros", so-called control torque gyros (CMGs), and their desaturation after the orientation of the object has been changed.Position control systems are implemented technically in various ways. Here, reaction wheels, active momentum gyroscopes or engines may be used. In the industrial implementation by reaction wheels, usually at least one reaction wheel is used for a spatial axis in order to regulate its orientation. The reaction wheels are rigidly connected to the object and form angular momentum exchange devices which are used for orientation control of space objects and which usually comprise actuated, i.e. drive-actuated, rotating disks.An object in the sense of the present application can be, for example, a satellite, a spacecraft, a space station, or else a non-technological space object, such as, for example, a rocket or rocket stage, a space scrap object, or it can even be an asteroid. However, the invention is not limited to the above space objects, but it can also be applied to "irdic" flying objects if they are located, for example, in a free fall in a gravitational field of a celestial body.The rotational speed of such reaction wheels is proportional to the orientation of the object about the rotational axis of a respective rotational wheel. However, the maximum rotational speed and rotational acceleration of a rotary wheel are subject to technical and physical restrictions, for example due to load limits of the rotary bearings and the centrifugal resistance of the rotary wheel and the motor output of a drive for the rotary wheel. Accordingly, the change in orientation of the object is also subject to corresponding limitations. Changes or corrections to the orientation of such an object can therefore only be carried out to a limited extent, namely so frequently and so intensively until the rotational wheel has reached its maximum rotational speed. A change in the rotational speed of a reaction wheel for a spatial axis, for example in order to reduce the rotational speed of the rotational wheel again, is associated with a usually undesirable change in orientation of the object and must therefore be compensated for by another position control system, such as position control engines. However, the great disadvantage of engines is the limited supply of fuel on the object and thus the limited useful life of an engine position control system.DE 10 2007 041 994 B4 shows and describes a mechanism provided on one satellite for launching a collision mass for deflecting another satellite. In this case, a collision mass is provided on a first robot arm of the first satellite, which is thrown against the other satellite by means of the robot arm. To compensate for the impulse occurring when the impact mass is thrown away, a countermass is simultaneously thrown away in the opposite direction by a further robot arm. For both ejection masses, i.e. both for the impact mass and for the counter mass, a compensating arm with a corresponding compensating mass is provided diametrically on the first satellite. The counter mass attached to the further robot arm serves to change the position and position of the firing auxiliary satellite as little as possible.It is an object of the present invention to provide an object which can be stabilized freely floating in a space and is coupled to an external object expansion device which can be moved independently in the space, with improved position control properties, and an improved method for position control of such a unit of object and object expansion device which also function over a long time independently of the fuel supplies.The object is achieved by the features of claim 1.An object which can be stabilized in a space in a freely floating manner, in particular a space object, is provided with an object-side, first position control device for position control of the object having an object center of gravity in the zero gravity or in the free fall, wherein the object is coupled to an external object expansion device which can be moved independently in the space and is in turn provided with a second position control device which can be moved relative to the object and has at least one expanded reaction wheel arrangement which is coupled to the object and in turn has a center of gravity. Such a reaction wheel arrangement is a proven position control means.Movements of an object extension device coupled to such an object, for example of a robot arm attached to a satellite, are conventionally compensated by the object-side position control device, as a result of which said position control device can reach its limits quickly. The inventors have recognized that a second position control device additionally provided on the object extension device can not only relieve the object-side, first position control device, but can even improve the position control properties thereof in cooperation with the first position control device.Further preferred and advantageous design features of the object according to the invention are the subject matter of the dependent claims 2 to 11.It is advantageous here if the extended reaction wheel arrangement is provided with at least one reaction wheel which can be rotated about an axis of rotation by means of a rotational drive.Preferably, the axis of rotation of the reaction wheel is displaceable relative to the object center of gravity by means of at least one actuator.In a preferred embodiment thereof, it is provided that the rotary drive and the at least one actuator can be controlled by a control device.A particularly preferred implementation of the invention is characterized in that the object is a space object.In a further particularly preferred embodiment, the object expansion device has a robot arm which can be moved in space or is formed by such a robot arm.Advantageously, the at least one reaction wheel is attached to the object via a lever mechanism, wherein the reaction wheel is provided with the rotation drive and the lever mechanism is provided with the at least one actuator, which is designed to subject at least one lever arm of the lever mechanism to a pivoting movement about an associated pivot axis, in order thus to execute the translatory movement of the center of gravity of the reaction wheel arrangement along the circular path about the object center of gravity.Preferably, the reaction wheel is rotatably mounted on the free end of a lever arm of the lever mechanism about its rotational wheel axis.It is also advantageous if the lever mechanism has two or more lever arms, which can each be pivoted about an associated pivot axis by means of an associated actuator. Particularly advantageous in this case is a lever mechanism having two lever arms which are articulatedly coupled to one another in series and the joints of which each have an actuator and the pivot axes of which run parallel to one another. The pivoting movement effected by the relevant actuator in the relevant lever joint is advantageously controlled by the control device in such a way that the center of gravity of the extended reaction wheel arrangement performs a linear translation movement away from the object center of gravity or towards the object center of gravity in the first and third steps.Preferably, the pivot axes of the lever arms extend parallel to one another and parallel to the axis of rotation of the reaction wheel.Preferably, three reaction wheel arrangements are provided for an object, wherein the pivot and rotation axes of a first rotation wheel arrangement run orthogonally to the pivot and rotation axes of a second rotation wheel arrangement, wherein the pivot and rotation axes of the second rotation wheel arrangement run orthogonally to the pivot and rotation axes of a third rotation wheel arrangement, and wherein the pivot and rotation axes of the third rotation wheel arrangement run orthogonally to the pivot and rotation axes of the first rotation wheel arrangement.The part of the object directed to the method is achieved by the features of claim 12.In such a method for the position control of an aforementioned object having an object center of gravity in the zero gravity or in the free fall, wherein the object has a first object-side position control system and is coupled to an external object expansion device which can be moved in regions relative to the object and has a second position control system which has at least one expanded reaction wheel arrangement which in turn has a center of gravity and which is provided with at least one reaction wheel which can be rotated about an axis of rotation by means of a rotational drive, wherein the axis of rotation can be displaced relative to the object center of gravity by means of at least one actuator, wherein the rotational drive and the at least one actuator can be controlled by a control device, characterized by the steps:determining a movement path curve associated with a predetermined movement of the expanded reaction wheel arrangement for the center of gravity of the expanded reaction wheel arrangement,moving the extended reaction wheel arrangement by means of the at least one actuator along the previously determined path of movement curve in such a way that the center of gravity of the extended reaction wheel arrangement moves about the object center of gravity on a path, in particular a circular path, wherein at the same time the rotational drive changes the rotational speed of the reaction wheel in such a way that the vectorial sum of the angular momentum of the reaction wheel rotating about the reaction wheel axis and the angular momentum of the extended reaction wheel arrangement moving about the object center of gravity axis along the path is constant.By means of this procedure according to the invention, the rotational speed of a reaction wheel in question can be denatured, for example, that is to say brought to zero, without inducing a change in orientation of the object.Further preferred and advantageous design features of the method according to the invention are the subject matter of the dependent claims 13 to 15.In a particularly advantageous embodiment of the method according to the invention, provision is made for,in a first step, the at least one actuator increases the distance of the reaction wheel from the object center of gravity, wherein the center of gravity of the extended reaction wheel arrangement moves away from the object center of gravity in a first translation movement along a straight line starting from the object center of gravity, and wherein the rotational speed of the reaction wheel does not change,in a second step, the at least one actuator moves the extended reaction wheel arrangement in such a way that the center of gravity of the extended reaction wheel arrangement on the path moves about the object center of gravity, wherein at the same time the rotation drive changes the rotation speed of the reaction wheel in such a way that the vectorial sum of the angular momentum of the reaction wheel rotating about the reaction wheel axis and the angular momentum of the extended reaction wheel arrangement moving about the object center of gravity axis along the path is constant, andin a third step, the at least one actuator reduces the distance of the reaction wheel from the object center of gravity, wherein the center of gravity of the extended reaction wheel arrangement moves in a second translation movement along a further straight line proceeding from the object center of gravity toward the object center of gravity, and wherein the rotational speed of the reaction wheel changed in the second step does not change any further.Although the actuator-controlled movement of the center of gravity of the expanded reaction wheel arrangement on a radially outer path, in particular a circular path, about the object center of gravity according to the second step in turn induces a rotational impulse on the object, this is compensated for by the synchronous braking of the rotational speed of the reaction wheel.Once the speed of rotation of the reaction wheel has reached the predefined target variable, for example zero, the movement of the reaction wheel on the path around the object center of gravity is stopped. In the third step, the reaction wheel is then moved again in translation towards the object center of gravity, in order to restore the original radial distance, for example. During the three steps of the method according to the invention, the rotational speed of the reaction wheel is thus changed, for example reduced, without a rotational impulse being induced on the object as a result; the object consequently maintains its position in space unchanged.Preferably, the changed rotational speed of the reaction wheel forms a target variable, according to which the translatory movement of the center of gravity of the expanded reaction wheel arrangement along the path, in particular the circular path, about the object center of gravity is determined in the control device. A computer provided in the control device or assigned to it consequently calculates, starting from the target variable of the desired rotational speed, the required trajectory of the reaction wheel when carrying out steps one to three and the speed of the radial movements and the movement of the center of gravity of the extended reaction wheel arrangement along the circular path and supplies corresponding control signals for the actuators and the rotational drive.It is particularly advantageous if the changed rotational speed of the reaction wheel, i.e. the target variable of the rotational speed of the reaction wheel, is equal to zero. This allows the full range of position control capability of the reaction wheel assembly to be restored.However, the target variable can also assume any desired positive or negative value, for example if a pulse applied externally to the object is expected, for example when docking a spacecraft to a space station, in order to prevent a permanent change in orientation of the object (for example the space station) after the docking maneuver. Ideally, the method according to the invention can be carried out synchronously therewith even during the docking maneuver, in order to minimize or even avoid any change in position of the object during docking.The core of the invention relating to the method thus consists in a method for regulating the position of an object having an object center of gravity in the zero gravity situation or in the free fall situation by means of at least one extended reaction wheel arrangement coupled to the object and is characterized in that, in a first step, the at least one actuator moves the distance of the center of gravity of the extended reaction wheel arrangement in a first translation movement along a straight line proceeding from the object center of gravity away from the object center of gravity, wherein the rotational speed of the reaction wheel does not change; in a second step, the at least one actuator moves the center of gravity of the extended reaction wheel arrangement on a circular path around the object center of gravity, wherein at the same time the rotational drive changes the rotational speed of the reaction wheel in such a way that the vectorial sum of the angular momentum of the reaction wheel rotating around the reaction wheel axis and the angular momentum of the extended reaction wheel arrangement moving around the object center of gravity axis along the circular path is constant, and in a third step, the at least one actuator moves the center of gravity of the extended reaction wheel arrangement in a second translatory movement along a further straight line proceeding from the object center of gravity towards the object center of gravity, wherein the rotational speed of the reaction wheel changed in the second step does not change any further.Preferred exemplary embodiments of the invention with additional design details and further advantages are described and explained in more detail below with reference to the attached drawing.It shows: FIG. 1 is a schematic diagram of an apparatus according to the invention; FIG. 2 shows a schematic illustration of the method sequence according to the invention; FIG. 3A shows a satellite arrangement without a device according to the invention; FIG. 3B shows the satellite arrangement from FIG. 3A with a device according to the invention, and FIG. 4 shows an application of the device according to the invention from FIG. 1 at a space station in a docking maneuver;FIG. 1 shows a schematic diagram of an apparatus according to the invention for regulating the position of an object formed by a satellite 1 in space or on an orbit under influence of zero gravity. A reaction wheel arrangement 2' is attached to a structure 10 of the satellite 1, which structure is only schematically illustrated here, which reaction wheel arrangement has a reaction wheel 20 and a lever mechanism 24.The reaction wheel 20 of the reaction wheel arrangement 2' is rotatable about a rotation wheel axis 20' by means of a rotation drive 21 and is rotatably mounted for this purpose on a first lever arm 23 of the lever mechanism 24 by means of a rotation bearing 22. The first lever arm 23 is mounted on a second lever arm 27 of the lever mechanism 24 so as to be pivotable about a first pivot axis 25' by means of a first pivot bearing 25. A first actuator 26 is provided in the region of the first pivot bearing 25 and is designed to pivot the first lever arm 23 relative to the second lever arm 27. The second lever arm 27 is mounted on the structure 10 of the satellite such that it can be pivoted about a second pivot axis 28' by means of a second pivot bearing 28. A second actuator 29 is provided in the region of the second pivot bearing 28 and is designed to pivot the second lever arm 27 relative to the structure 10 of the satellite 1. The rotary drive 21, the first actuator 26 and the second actuator 29 are supplied with control signals by a control device 3, as shown symbolically by thin lines in FIG. 1, in order to carry out the method according to the invention.Also shown schematically in FIG. 1 are the center of mass of the satellite 1 with its object center of gravity axis 13, referred to as object center of gravity So, and the center of mass of the reaction wheel arrangement 2' referred to as center of gravity S ERW as well as a circular path 4, on which the center of gravity S ERW of the reaction wheel arrangement 2' moves according to the method of the invention, as is explained below with reference to FIG. 2.The first pivot axis 25', the second pivot axis 28' and the rotational wheel axis 20' run parallel to one another and to the object centroid axis 13 and extend in FIG. 1 perpendicular to the plane of the drawing. Consequently, a pivoting movement of the lever arms 23 and 27 of the lever mechanism 24 takes place in one plane, namely in the plane of the drawing of FIG. 1.Figure 2 schematically shows the motion profile passing through the centre of gravity S ERW of the reaction wheel assembly 2' when carrying out the method of the invention. In a first step, the first actuator 26 and the second actuator 29 are synchronously actuated in such a way that the first lever arm 23 and the second lever arm 27 are pivoted in such a way that the center of gravity S ERW of the extended reaction wheel arrangement 2' moves away from the object center of gravity So in a first translatory movement along a straight line A proceeding from the object center of gravity So, whereby the distance of the center of gravity S ERW from the object center of gravity So increases, wherein the rotational speed of the reaction wheel 20 does not change and consequently the rotational pulses about the center of gravity S ERW of the extended reaction wheel arrangement 2' and about the object center of gravity So mutually compensate one another, that is to say no rotational pulse is induced in the object formed by the satellite 1.In a second method step, the two actuators 26, 29 are acted upon by the control device 3 with signals in such a way that they move the reaction wheel arrangement 2' in such a way that the center of gravity S ERW of the extended reaction wheel arrangement 2' moves along a curved trajectory B on a circular path 4 about the object center of gravity axis 13 of the object center of gravity So. At the same time, signals are applied to the rotary drive 21 by the control device 3 in such a way that the rotational speed of the reaction wheel 20 is gradually reduced. The sum of the angular momentum of the reaction wheel 20 rotating about the axis 20' of the rotational wheel and the angular momentum of the extended reaction wheel arrangement 2' moving about the axis of the center of gravity of the object along the circular path 4 remains constant. During the movement along the curved trajectory B, the rotational speed of the reaction wheel 20 is thus reduced-preferably down to zero-by appropriate actuation of the reaction wheel drive 21 without an additional angular momentum being induced on the object 1; the object 1 therefore maintains its orientation in space.In a third step, the actuators 26, 29 are controlled by the control device 3 in such a way that the distance of the reaction wheel 20 from the object center of gravity So decreases in such a way that the center of gravity S ERW of the extended reaction wheel arrangement 2' moves in a second translation movement along a further straight line C proceeding from the object center of gravity So toward the object center of gravity So. In this case, the reduced rotational speed of the reaction wheel 2' does not change, so that its angular momentum remains constant and the orientation of the object 1 in space does not change. Details are giventhe trajectory A for a movement of the center of gravity S ERW of the extended reaction wheel assembly 2' on a line connecting the centers of gravity of the reaction wheel assembly 2' and the object 1 away from the center of gravity So of the object 1 During this first phase, the rotational speed of the reaction wheel and the orientation of the object are not changed;the trajectory B for a movement of the center of gravity S ERW of the extended reaction wheel arrangement 2' on a circular path, the trajectory B. In this case, the direction of movement is always orthogonal to the line which connects the centers of gravity So and S ERW to one another. With the rotation speed of the reaction wheel remaining the same, this circular path movement would cause a change in the orientation of the object 1. However, this is prevented by the method according to the invention,the trajectory C for a movement of the center of gravity S ERW of the extended reaction wheel assembly 2' on a line connecting the centers of gravity of the reaction wheel assembly 2' and the object 1 to each other toward the center of gravity So of the object 1.FIGS. 3A and 3B show a case of application for desaturation of the reaction wheel with the same orientation of the object during execution of the trajectory optimized according to the invention. By "desaturation" is meant bringing the rotational speed of the reaction wheel 20 to zero.FIG. 3A shows a satellite arrangement 1' of conventional design, having a satellite body 11' and a solar panel 12' extended therefrom, which is illuminated by the sun H. The radiation pressure of the solar radiation W H emanating from the sun H causes the satellite arrangement 1' to gradually turn away from its desired orientation about its center of gravity So.In the modification shown in FIG. 3B, the satellite is equipped with a reaction wheel assembly 2' according to the invention. The reaction wheel 20 is required to compensate for the orientation disturbance caused by the irradiation pressure of the sun. Here, the rotational speed of the reaction wheel 20 must be continuously changed in one direction. This inevitably leads to reaching the technical limits of the reaction wheel assembly 2' (maximum rotational speed) at some time. This problem of reaching the limits is counteracted by the method according to the invention, since the reaction wheel can be denatured from time to time.FIG. 4 shows another application of the method according to the invention and of the device according to the invention, namely a targeted increase in the rotational speed of the reaction wheel 20 for prevention of planned events. A room station 1" with a solar panel 12, a docking module 14 provided with a docking port 15 and a location module 16 is equipped with the reaction wheel arrangement 2' according to the invention. A space transporter 5 moves toward the space stationThe rotational speed of the space station 1" is zero at the beginning. The space transporter 5 is docked to the docking port 15 by means of a docking interface 50.In the conventional case of the prior art, this induced rotational speed would be compensated for by rotational wheels starting with a rotational speed of the rotational wheels which depends on previous maneuvers. Once a rotary wheel has reached its maximum rotational speed, it can no longer contribute to the compensation of the induced angular momentum and the compensation must take place by position control engines.By virtue of the mechanical construction of the reaction wheel arrangement 2' according to the invention, the rotational speed of the reaction wheel can be changed independently of the orientation of the object, that is to say of the space station 1". Accordingly, the rotation speed of the reaction wheel concerned before docking can be adjusted in the opposite rotation direction to the rotation direction required after docking in order to stabilize space station 1". Due to this opposite initial direction of rotation, the respective reaction wheel can generate torque in the desired direction for a longer period of time than, for example, a reaction wheel which initially has a rotational speed of zero. This has the advantage that either the object, i.e. the space station, can be stabilized more quickly, or that the reaction wheels used can be dimensioned smaller.The mechanical structure of the device according to the invention thus has a concatenation of at least one actuator 26, 29 and at least one reaction wheel 20, wherein the reaction wheel 20 can be attached either at the end of a serial concatenation or decentrally on or on the object 1.The method according to the invention is controlled by a control device 3 with a computer, on which, for example, a program with an algorithm for coordinated actuation of the actuators 26, 29 and of the reaction wheel 20 runs with the aim of achieving a desired final rotational speed of the reaction wheel 20. It should be noted that the actuators 26, 29 are actuated in a manner which changes the overall orientation of the object 1 only in a desired manner by observing the angular pulse generation.For this purpose, trajectories can be found which allow an independent change in the reaction wheel speed and the object rotation speed. The principle of pulse conservation is utilized.The velocity vector of the entire unit, i.e. of the object 1 provided with the expanded reaction wheel arrangement 2' is determined according to the following formula: with the vector of the velocity of the object 1, i.e. of the spacecraft, in space (spatial velocity): with the vector of the velocity (spatial velocity) of the entire unit at the point of the center of mass S ERW of the expanded reaction wheel arrangement 2' in space: and with the resulting vector of the velocities of all driven reaction wheels 20 in space:The equation of motion is: with the forces F s acting on the spacecraft at the center of mass So of the object 1, i.e. in the example of the spacecraft, F a at the center of mass S ERW of the driven mechanism of the extended reaction wheel arrangement 2' and the resulting force F r of the driven reaction wheels:Assuming that during movement the systems are not driven from the outside by an external force, i.e. that the effects of gravity gradients, solar radiation pressure, magnetic effects or the use of engines are not taken into account, the maintenance of the impulse, expressed in the inertial system, results in: the corresponding entries of the first six rows of the matrix being M.The trajectory of the extended reaction wheel arrangement 2' is found, for example, by an optimization calculation which is based on equation (4). This makes use of the fact that the pulse h is constant on account of the pulse conservation. Accordingly, V_a and V_r are optimized such that V_s follows a desired setpoint trajectory (e.g., remains constant zero to induce no net rotation). As a further task in the optimization calculation, a cost function is formulated which results in the rotational speed of the reaction wheels 20 following a setpoint trajectory (for example zero, in order to denaturate the reaction wheel).The invention is not limited to the above embodiments, which serve merely to explain the core idea of the invention in general. Rather, within the scope of the invention, the device according to the invention can also assume embodiments other than those described above. The device can in particular have features which represent a combination of the respective individual features of the claims.Reference numerals in the claims, the description and the drawings are used merely for better understanding of the invention and are not intended to limit the scope of protection.List of reference characters1 Satellite 1' Satellite 1" Space station 2 Object expansion device 2' Reaction wheel arrangement 3 Control device 4 Movement path 5 Space transporter 10 Structure of the satellite 11' Satellite body 12 Solar panel 12' Solar panel 13 Object centroid axis 14 Docking module 15 Docking port 16 Stay module 20 Reaction wheel 20' Rotation wheel axis 21 Rotation drive 22 Rotation bearing 23 First lever arm 24 Lever mechanism 25 First pivot bearing 25' First pivot axis 26 First actuator 27 Second lever arm 28 Second pivot bearing 28' Second pivot axis 29 Second actuator 50 Docking interface A Straight B Curved trajectory C Straight Fs Force F r Resulting force H Sun L 1 First position control system L 2 Second position control system thus, the center of gravity of the object is S ERW the center of gravity of 2 W H solar radiation

Claims

Object which can be stabilized in a space in a freely floating manner, in particular a space object, having an object-side, first position control device (L 1) for controlling the position of the object (1, 1', 1") having an object centroid (So) in the zero gravity or in the free fall, wherein the object (1, 1', 1") is coupled to an external object expansion device (2) which can be moved independently in the space, characterized in that the external object expansion device (2) is provided with a second position control device (L 2) which can be moved relative to the object (1, 1', 1") and has at least one expanded reaction wheel arrangement (2') which is coupled to the object (1, 1', 1") and which in turn has a centroid (S ERW).Object according to claim 1, characterised in that the extended reaction wheel arrangement (2') is provided with at least one reaction wheel (20) rotatable about an axis of rotation (20') by means of a rotational drive (21).Object according to claim 2, characterised in that the axis of rotation (20') of the reaction wheel (20) is displaceable relative to the centre of gravity (So) of the object by means of at least one actuator (26, 29).Object according to claim 3, characterised in that the rotational drive (21) and the at least one actuator (26, 29) can be controlled by a control device (3).Object according to one of the preceding claims, characterized in that the object is a space object.Object according to one of the preceding claims, characterized in that the object expansion device (2) has a robot arm which can be moved in space or is formed by such a robot arm.Object according to one of Claims 2 to 6, characterized in that the at least one reaction wheel (20) is attached to the object (1, 1', 1") via a lever mechanism (24), wherein the reaction wheel (20) is provided with the rotational drive (21) and the lever mechanism (24) is provided with the at least one actuator (26, 29) which is designed to subject at least one lever arm (23, 27) of the lever mechanism (24) to a pivoting movement about an associated pivot axis (25', 28'), in order thus to carry out the translatory movement of the centre of gravity (S ERW) of the reaction wheel arrangement (2') along the circular path (4) about the object centre of gravity (So).Object according to claim 7, characterised in that the reaction wheel (20) is mounted on the free end of a lever arm (23) of the lever mechanism (24) so as to be rotatable about its axis of rotation wheel (20').Object according to claim 7 or 8, characterised in that the lever mechanism (24) has two or more lever arms (23, 27), which can each be pivoted about a pivot axis (25', 28') by means of an associated actuator (26, 29).Object according to claim 7, 8 or 9, characterised in that the pivot axes (25', 28') of the lever arms (23, 27) run parallel to one another and parallel to the axis of rotation (20') of the reaction wheel (20).Object according to one of the preceding claims, characterized in that three reaction wheel arrangements are provided, wherein the pivot and rotation axes of a first rotation wheel arrangement run orthogonally to the pivot and rotation axes of a second rotation wheel arrangement, wherein the pivot and rotation axes of the second rotation wheel arrangement run orthogonally to the pivot and rotation axes of a third rotation wheel arrangement, and wherein the pivot and rotation axes of the third rotation wheel arrangement run orthogonally to the pivot and rotation axes of the first rotation wheel arrangement.Method for the position control of an object (1, 1', 1") having an object centroid (So), in particular according to one of the preceding claims, in the absence of gravity or in the free fall, wherein the object (1, 1', 1") has a first object-side position control system (L 1) wherein the object (1, 1', 1") is coupled to an external object extension device (2) which can be moved in regions relative to the object (1, 1', 1") and has a second position control system (L 2) which has at least one extended reaction wheel arrangement (2'), which in turn has a centroid (S ERW) and which is provided with at least one reaction wheel (20) which can be rotated about an axis of rotation (20') by means of a rotational drive (21), wherein the rotational axis (20') can be displaced relative to the object center of gravity (So) by means of at least one actuator (26, 29), wherein the rotational drive (21) and the at least one actuator (26, 29) can be controlled by a control device (3), characterized bythe steps of - determining a movement path curve for the center of gravity (S ERW) of the extended reaction wheel arrangement (2') assigned to a predefined movement of the extended reaction wheel arrangement (2'), - moving the extended reaction wheel arrangement (2') by means of the at least one actuator (16, 29) along the previously determined movement path curve in such a way that the center of gravity (S ERW) of the extended reaction wheel arrangement (2') moves about the object center of gravity (So) on a path (4), in particular a circular path, wherein the rotational drive (21) simultaneously changes the rotational speed of the reaction wheel (20) such that the vectorial sum of the angular momentum of the reaction wheel (20) rotating about the reaction wheel axis (20') and the angular momentum of the extended reaction wheel arrangement (2') moving about the object center of gravity axis (13) along the path (4) is constant.Method according to Claim 12, characterized - in that, in a first step, the at least one actuator (16, 29) increases the distance of the reaction wheel (20) from the object centroid (So), wherein the centroid (S ERW) of the extended reaction wheel arrangement (2') moves away from the object centroid (So) in a first translation movement along a straight line (A) proceeding from the object centroid (So), and wherein the rotational speed of the reaction wheel (20) does not change, - in that, in a second step, the at least one actuator (26, 29) moves the extended reaction wheel arrangement (2') in such a way that the centroid (S ERW) of the extended reaction wheel arrangement (2') moves about the object centroid (So) on the path (4), wherein the rotational drive (21) simultaneously changes the rotational speed of the reaction wheel (20) in such a way that the vectorial sum of the angular momentum of the reaction wheel (20) rotating about the reaction wheel axis (20') and the angular momentum of the extended reaction wheel arrangement (2') moving about the object centroid axis (13) along the path (4) is constant, and - that in a third step the at least one actuator (26, 29) reduces the distance of the reaction wheel (20) from the object centroid (So), wherein the centroid (S ERW) of the extended reaction wheel arrangement (2') moves in a second translatory movement along a further straight line (C) originating from the object centroid (So) towards the object centroid (So), and wherein the rotational speed of the reaction wheel (20) changed in the second step does not change any further.Method according to Claim 12 or 13, characterized in that the changed rotational speed of the reaction wheel (20) is a target variable, according to which the translatory movement of the centre of gravity (S ERW) of the widened reaction wheel arrangement (2') along the path (4) about the object centre of gravity (So) is determined in the control device (3).Method according to claim 12, 13 or 14, characterised in that the changed rotational speed of the reaction wheel (20) is equal to zero.

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