GB1570529A - Nutation neutralising devices for spacecraft - Google Patents

Description

(54) IMPROVEMENTS RELATING TO NUTATION NEUTRALISING DEVICES FOR SPACECRAFT (71) We, BRITISH AIRCRAFT CORPORATION LIMITED, a British Company, of 100 Pall Mall, London, S.W.1., do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to nutation neutralising devices for those spacecraft at least part of which in use spin about a predetermined axis.

Such spacecraft can tend to wobble about this axis as they spin (that is to say they have a nutational movement) and may eventually tumble into an unstable condition. Accordingly nutation neutralising devices are provided to oppose and reduce (that is to say, damp) this wobbling or nutational movement and thus maintain the craft in a stable condition.

British patent number 1,304,867 discloses such a nutation neutralising device. Claim 1 of that patent states : - "1. A satellite capable of inherent rotation about a spin axis wherein a drive motor has an output shaft disposed along the spin axis, the motor being fixed with respect to the body of the satellite, and the shaft being drivingly connected to a flywheel by a universal connection for rotation of the flywheel about the spin axis, the flywheel rotation being such as to damp any incipient nutation of the satellite." The specification discloses a shaft driven by a motor, and a flywheel drivably mounted on the shaft by a universal joint arrangement, the flywheel rotation being such as to damp any incipient nutation of a spacecraft on which the device is carried.In this specification a simple fricrional arrangement is provided to transmit damping torque between the flywheel and the shaft as the flywheel tilts relatively to the shaft. It is found that this arrangement has an inherent dis advanrage in use in some circumstances the damping torque is insufficient to overcome the friction between the flywheel and the shaft and no relative tilting movement can occur therebetween. In other words a certain threshold level of torque between the flywheel and the shaft must be reached before nutation neutralising can take place.

An object of the present invention is to provide a nutational damper in which there is no such threshold level of torque required and rhe torque is thus always a monotonic function of tilting velocity, being zero tilt velocity, and rising with tilt velocity in a direction to oppose said tilt velocity.

According to the present invention a nutation neutralising device, for a spacecraft at least part of which spins about a predetermined axis, includes shaft means, driving means for effecting rotation of the shaft means, flywheel means, flywheel mounting means on the shaft means for carrying the flywheel means such that the flywheel means rotates with the shaft means but can tilt relatively thereto in any direction, spaced noncontacting regions movable with the flywheel means and the shaft means respectively, and torque transmitting means effecting transmission between said regions of a torque being a monotonic function of the velocity of tilt between the flywheel means and the shaft means.

The said non-contacting spaced regions may form part of the flywheel mounting means or they may be carried separately therefrom.

The torque transmitting means may be a viscous fluid held between the said regions.

Alternatively said means may comprise an eddy current generating arrangement.

Some preferred embodiments of nutation neutralising devices are described with reference to the accompanying drawings in which: Figure 1 is a cross-sectional view of one embodiment with the cross-section taken upon the rotational axis of the shaft.

Figure 2 is a cross-sectional view of the gimbal system with the cross-section taken upon line II--II of Figure 1, Figure 3 is a similar cross-secuonal view to that of Figure 1 but illustrating an alternative embodiment, Figure 4 is an enlarged cross-sectional view of the flywheel means, shaft means and the flywheel mounting means of yet a further embodiment, Figure 5 is an enlarged cross-sectional view of a cruciform leaf spring assembly, and, Figure 6 is a cross-sectional view on Arrows VI-VI of Figure 5.

Referring initially to Figures 1 and 2, a nutation damper includes a shaft 1, which is mounted for rotation in a housing 2 by spaced bearing assemblies 3 and 4. The shaft is driven by an electric motor 5 itself mounted on the housing coaxially with the shaft. The housing 2 is capable of being evacuated and refilled with a substantially inert gas mixture at a small fraction of atmospheric pressure.

Carried for rotation with the shaft 1 by means of a mounting arrangement is a flywheel 6. The mounting arrangement is such to allow tilting of the flywheel 6 in any direction as it rotates within the housing. In Figures 1 and 2, the flywheel mounting arrangement comprises a gimbal system 7 and to accom modate this the shaft 1 has a flattened inter mediate region la with an aperture ib formed through it. The gimbal pivots are formed as follows. Pressed into the sides of this inter mediate region are co-axial cups 8 and 9, the walls of which match spaced cylindrical co-axial surfaces 10 and 11 respectively, formed upon spigots which are part of a cruciform gimbal member 12.The cruciform member 12 has further spigots upon which spaced cylindrical co-axial surfaces 13 and 14, respectively, are arranged about an axis per pendicular to the axis of the surfaces 10 and 11. The surfaces 13 and 14 match further co-axial cups 15 and 16, respectively, carried by the flywheel 6. The surfaces 10, 11 and 13, 14 of the spigots on the cruciform mem ber are of such a length to protrude deeply into each cup but not allow their end faces 10a, 11a, 13a and 14e to contact the base surfaces 8a, 9a, 15a, and 16a of the respective cups. Thus a cavity 17 is formed in each cup. These cavities are in communication with a port on the exterior of the cruciform mem ber by means of ducts 18.Through this port a viscous fluid is admitted which is passed centrifugally as the flywheel is rotated through the ducts 18 into the cavities 17 where it remains permanently.

As the flywheel tilts a relative rotary move ment occurs between the end faces and the base surfaces and the viscous fluid serves to transmit a torque between them being a mono tonic function of the velocity of the rotation due to tilting. This torque is passed by the shaft to the spacecraft to oppose nutation.

The housing is provided with an annular seating surface 19 and tapped holes 20 for attachment to a spacecraft with the axis of the shaft 1 coincident or parallel to the axis of spin of the spacecraft. The direction of flywheel rotation is always opposite to that of the spacecraft.

Referring now to Figure 3 in which like components have like reference numerals to the embodiment of Figures 1 and 2, a nutation damper of generally similar construction to that described with reference to Figures 1 and 2, has an alternative arrangement for mounting the flywheel 6 on the shaft 1. Similarly, the mounting allows for rotation with the shaft and also allows tilting of the flywheel in any direction within the housing 2. Basically the gimbal system 7 of Figures 1 and 2 is replaced by a part-spherical bearing assembly 20 comprising a convex bearing surface 21 fixedly mounted on an intermediate region of the shaft 1 and a mating but not contacting concave bearing surface 22 mounted upon the flywheel 6.A viscous fluid is placed between the two spherical bearing surfaces to maintain them apart and is found to remain there since the concave portion forms an annular cup region into which the centrifugal action of flywheel rotation tends to urge the fluid. In this case the fluid acts again to transmit a torque being a monotonic function of the velocity of the relative tilting movement when the flywheel 6 tilts relatively to the shaft 1 and as a non positive drive medium to effect rotation of the flywheel as the shaft rotates. In this case the flywheel may rotate somewhat more slowly than the shaft 1.

Referring now to Figure 4, a nutation neutralising device includes a driven shaft 25 again adapted to be mounted on a spacecraft with its axis coincident with or parallel to the axis of spin of the spacecraft and for rotation in an opposite direction to that of the spacecraft. The shaft carries a flywheel 26 on a mounting means, comprising mating convex and concave part-spherical surfaces 27 and 28, respectively, which is such that the flywheel rotates with the shaft but can tilt in any direction with respect to it To the shaft is anchored a permanent bar magnet 29 having two spaced annular pole pieces 30 and 31 extending one from each end of the magnet. Between the pole pieces is defined an annular slot 32 through which protrudes in non-contacting relationship an annular conductor member 33. The latter member is anchored to the flywheel 26 and tilts with it, the tilting movement causing eddy currents which produce a torque being a monotonic function of the velocity of tilting movement which is transmitted into the shaft and hence to the spacecraft to oppose nutation.

Although described with reference to an embodiment in which the flywheel mounting means is a part-spherical joint this arrangement is also applicable to other embodiments such as a gimbal system.

In each of the embodiments described any inertia in the flywheel mounting means can be countered by the incorporation of a spring arrangement which also tends to enhance the nutation damping properties of the device.

Such a spring arrangement of known design is described with reference to Figures 2, 5 and 6. In Figure 2 one of the spigots carrying the surfaces 13 or 14 are replaced by a leafspring assembly of the type illustrated in Figures 5 and 6. This allows pivotal movement of the gimbal assembly, i.e. rotational movement of the spigots within their cups, but any such movement effects flexing of the springs. Each spring assembly comprises two caxially disposed cylindrical members 35, 36, one of which is anchored to a spigot member and the other of which is anchored to a cup member. Each cylindrical member has an axially protruding member 37, 38 respectively which extends from its respective cylindrical member into the adjacent cylindrical member.Between each protruding member and the wall of the cylindrical' mem ber into which it protrudes extends a leaf spring 39, the arrangement being such that the two leaf springs lie generally at right angles to one another.

WHAT WE CLAIM IS:- 1. A nutation neutralising device, for a spacecraft at least part of which spins about a predetermined axis of spin, including shaft means, driving means for effecting rotation of the shaft means, flywheel means, flywheel mounting means on the shaft means for carry ing the flywheel means such that the flywheel means rotates with the shaft means but can tilt relatively thereto in any direction, spaced non-contacting regions movable with the fly wheel means and the shaft means respectively and torque transmitting means effecting transmission between said regions of a torque being a monotonic function of the velocity of tilt between the flywheel means and the shaft means.

2. A nutation neutralising device according to claim 1 wherein the torque transmitting means comprises a viscous fluid held between said spaced noncontacting regions.

3. A nutation neutralising device according to claim 1 wherein the torque transmitting means comprises means for generating electromagnetic forces between said spaced noncontacting regions.

4. A nutation neutralising device according to any one of the previous claims wherein the flywheel mounting means comprises a gimbal assembly.

5. A nutation neutralising device according to any one of claims 1 to 3 wherein the flywheel mounting means comprises a part spherical bearing assembly.

6. A nutation neutralising device according to claim 4 when dependant upon claim 2 wherein each pivot of the gimbal assembly includes a spigot member having a cylindrical external bearing surface and an end face, and a cup member having a cylindrical internal bearing surface, within which the said external bearing surface engages, and an internal face on its base which lies spaced from the said end face to form a space within which the viscous fluid is housed.

7. A nutation neutralising device according to claim 5 when dependant upon claim 2 wherein the bearing assembly includes spaced convex and concave matching surfaces between which the viscous fluid is housed.

8. A nutation neutralising device according to claim 3 wherein the means for generating eleotro-magnetic forces comprises a magnet having pole pieces defining an annular gap and an annular conductor member extending through said gap for relative tilting movement as the flywheel means tilts with respect to the shaft means.

9. A nutation neutralising device according to any one of the previous claims in which a spring member lies between the flywheel means and the shaft means for deflection as relative tilting movement takes place.

10. A spacecraft, at least part of which in flight spins about a predetermined axis of spin, including a nutation neutralising device according to any one of the previous claims mounted upon a part of the spacecraft which spins such that the shaft means lies coincident with or generally parallel to the axis of spin for rotation in a direction opposite to the direction of spin.

11. A nutation neutralising device substantially as described with reference to the accomanying Figures.

12. A spacecraft including a nutation neutralising device substantially as described with reference to the accompanying Figures.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. be countered by the incorporation of a spring arrangement which also tends to enhance the nutation damping properties of the device. Such a spring arrangement of known design is described with reference to Figures 2, 5 and 6. In Figure 2 one of the spigots carrying the surfaces 13 or 14 are replaced by a leafspring assembly of the type illustrated in Figures 5 and 6. This allows pivotal movement of the gimbal assembly, i.e. rotational movement of the spigots within their cups, but any such movement effects flexing of the springs. Each spring assembly comprises two caxially disposed cylindrical members 35, 36, one of which is anchored to a spigot member and the other of which is anchored to a cup member. Each cylindrical member has an axially protruding member 37, 38 respectively which extends from its respective cylindrical member into the adjacent cylindrical member.Between each protruding member and the wall of the cylindrical' mem ber into which it protrudes extends a leaf spring 39, the arrangement being such that the two leaf springs lie generally at right angles to one another. WHAT WE CLAIM IS:-

1. A nutation neutralising device, for a spacecraft at least part of which spins about a predetermined axis of spin, including shaft means, driving means for effecting rotation of the shaft means, flywheel means, flywheel mounting means on the shaft means for carry ing the flywheel means such that the flywheel means rotates with the shaft means but can tilt relatively thereto in any direction, spaced non-contacting regions movable with the fly wheel means and the shaft means respectively and torque transmitting means effecting transmission between said regions of a torque being a monotonic function of the velocity of tilt between the flywheel means and the shaft means.

2. A nutation neutralising device according to claim 1 wherein the torque transmitting means comprises a viscous fluid held between said spaced noncontacting regions.

3. A nutation neutralising device according to claim 1 wherein the torque transmitting means comprises means for generating electromagnetic forces between said spaced noncontacting regions.

4. A nutation neutralising device according to any one of the previous claims wherein the flywheel mounting means comprises a gimbal assembly.

5. A nutation neutralising device according to any one of claims 1 to 3 wherein the flywheel mounting means comprises a part spherical bearing assembly.

6. A nutation neutralising device according to claim 4 when dependant upon claim 2 wherein each pivot of the gimbal assembly includes a spigot member having a cylindrical external bearing surface and an end face, and a cup member having a cylindrical internal bearing surface, within which the said external bearing surface engages, and an internal face on its base which lies spaced from the said end face to form a space within which the viscous fluid is housed.

7. A nutation neutralising device according to claim 5 when dependant upon claim 2 wherein the bearing assembly includes spaced convex and concave matching surfaces between which the viscous fluid is housed.

8. A nutation neutralising device according to claim 3 wherein the means for generating eleotro-magnetic forces comprises a magnet having pole pieces defining an annular gap and an annular conductor member extending through said gap for relative tilting movement as the flywheel means tilts with respect to the shaft means.

9. A nutation neutralising device according to any one of the previous claims in which a spring member lies between the flywheel means and the shaft means for deflection as relative tilting movement takes place.

10. A spacecraft, at least part of which in flight spins about a predetermined axis of spin, including a nutation neutralising device according to any one of the previous claims mounted upon a part of the spacecraft which spins such that the shaft means lies coincident with or generally parallel to the axis of spin for rotation in a direction opposite to the direction of spin.

11. A nutation neutralising device substantially as described with reference to the accomanying Figures.

12. A spacecraft including a nutation neutralising device substantially as described with reference to the accompanying Figures.