Abstract:
Methods and systems for passively slowing the spin rate of an uncontrolled object in space are presented. A damper mechanism is provided that includes a magnet that is free to rotate in any direction about a central point with respect to a carrier or outer housing. The magnet can be carried within an inner element or sphere, that is in turn mounted within an outer sphere. The inner and outer spheres can be separated by a viscous fluid or other mechanism in which damping can be introduced. The damper mechanism can be associated with an attachment mechanism, that secures the resulting damper or despin system to a target object. A method of neutralizing the magnetic field is also included to enable the system to be launched in a passive state.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/707,368, filed Sep. 28, 2012, the entire disclosure of which is hereby incorporated herein by reference. 
    
    
     FIELD 
     Methods and systems for passively slowing the spin rate of an object in space are presented. More particularly, passive despin systems that include a magnet interconnected to a carrier and methods for utilizing such systems to cause an object in orbit to slow its spin rate to match that of the rotation rate of the Earth&#39;s magnetic field in the orbit frame are provided. 
     BACKGROUND 
     Uncontrolled satellites and debris in orbit about the Earth are an increasingly serious problem. In particular, such objects pose a risk of collision with other satellites and spacecraft. According to studies by NASA&#39;s debris office, controlling the propagation of the on-orbit debris environment can be accomplished by actively removing at least five large debris objects such as rocket bodies, boosters and derelict spacecraft per year. However, such objects are difficult to capture and move, either out of orbit or into orbits considered safe. One difficulty is that some percentage of these objects remain spinning in orbit at relatively high rates, or acquire a spin, as a result of disturbance torques which act on the object. 
     In order to actively remove these objects from orbit, many studies have considered using a secondary spacecraft to approach, rendezvous and dock with the target and, using an applied thrust, change their combined orbit so that the object will reenter Earth&#39;s atmosphere within 25 years or less. The difficulty of proximity operations increases dramatically as the spin rate of the target object increases. Decreasing the spin rate of the target object would allow more time for sensor data processing, which would significantly decrease the processing requirements for the active spacecraft and also dramatically decrease its propulsion requirements. However, the ability to decrease the spin rate of objects in space has been limited. 
     SUMMARY 
     In accordance with embodiments of the present disclosure, a passive despin system includes a damper mechanism and an attachment mechanism. The damper mechanism includes a first element or carrier to which a magnet or set of magnets is mounted. An interconnection allows the magnet to rotate independently of the carrier. As a result, the magnet can remain aligned with an external magnetic field, such as the magnetic field of the Earth, while the carrier can rotate, for example with a spinning satellite to which the despin system is connected. In accordance with still other embodiments of the present disclosure, the rotation of the magnet relative to the carrier is damped. 
     Embodiments of the disclosed passive despin system can include a passive despin or damper mechanism or device consisting of a large magnet or set of magnets held within a sphere (hereinafter referred to as the “inner sphere”). This sphere is suspended within a carrier comprising a second sphere (herein after referred to as the “outer sphere”) that is slightly larger than the inner sphere. The interconnection between the magnet and the carrier includes the outer surface of the inner sphere, the inner surface of the outer sphere, and a layer of a viscous fluid suspended between the two spheres. The cooperating surfaces of the spheres need not be continuous. For example, one or both of the spheres can include a spherical surface that is a partial or discontinuous surface. In accordance with still other embodiments, the magnet assembly is connected to the carrier by an interconnection comprising a three axis gimbal. 
     The despin system can additionally include an attachment mechanism. The attachment mechanism is configured to secure the despin system to a satellite or other object. As examples, but without limitation, the attachment mechanism can comprise a grapple, a piercing element, a chemical adhesive, or a structure configured to mate with or attach to a structure of the object. 
     Methods in accordance with embodiments of the present disclosure can include operably associating the despin mechanism with an object in orbit. For example, a despin assembly that includes an attachment mechanism can be brought into the proximity of an object while the object is in orbit. The despin assembly can then be attached to the object using the features of the attachment mechanism. Examples of attachment methods include but are not limited to piercing an outer shell of an object and expanding an element within an interior of the object, grasping or grappling an exterior of the object, fixing an element or elements to an exterior of the object using an adhesive, or attaching to a mounting surface on the object. As a further example, a despin system can be deployed with or as part of an object. During launch, while placing the object in the desired orbit, and/or during normal operation, the despin system can be deactivated. The despin mechanism can then be enabled, for example at or around a time at which attitude control of the object is otherwise lost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts aspects of an example passive despin system attached to an orbiting body in accordance with embodiments of the present disclosure; 
         FIG. 2A  is a cross-section of a damper mechanism in accordance with embodiments of the present disclosure; 
         FIG. 2B  is a cross-section of a damper mechanism in accordance with other embodiments of the present disclosure; 
         FIG. 2C  is a cross-section of a damper mechanism in accordance with other embodiments of the present disclosure; 
         FIG. 2D  is a cross-section of a damper mechanism in accordance with other embodiments of the present disclosure; 
         FIG. 2E  is a cross-section of a damper mechanism in accordance with embodiments of the present disclosure, with a magnetic field neutralizing element; 
         FIG. 3  depicts aspects of another example passive despin system attached to an orbiting body in accordance with embodiments of the present disclosure; and 
         FIG. 4  is a flowchart depicting aspects of a method for passively despinning an object. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  depicts a passive despin system  100  as disclosed herein attached to an object or target object  104  in orbit about a body  108  having a magnetic field  110 . The despin system  100  generally includes a damper or despin mechanism  112 , and an attachment mechanism  116 . The damper mechanism  112 , shown in cross-section, includes a magnet or set of magnets  120  connected to an inner element  124 . Where the magnet  120  comprises a plurality of magnets, the magnetic fields of the individual magnets are aligned with one another. The inner element  124  is in turn joined to an outer element or carrier  128  by an interconnection  132 . The interconnection  132  allows the inner element  124 , and in turn the magnet or magnets  120  to rotate in any direction about a central point C relative to the outer element or carrier  128 . Accordingly, when the damper mechanism  112  is connected to a target object  104 , the carrier  128  rotates with the object  104 , while the magnet  120  and inner element  124  can rotate independently of the object. 
     As can be appreciated by one of skill in the art, a magnet floating in space will align itself with an external magnetic field, such as is present about the Earth, and if it is in orbit, it will rotate on average at twice orbit rate. As can also be appreciated by one of skill in the art after consideration of the present disclosure, with the damper mechanism  112  attached to an object  104  in orbit, the magnet  120  will align itself with the external magnetic field  110  and will remain aligned with the external magnetic field  110  while the carrier  128  rotates with the object  104 . The resulting relative movement between the inner element  124  to which the magnet  120  is attached and the carrier  128  can be dampened by friction in the interconnection  132  between the inner element  124  and the carrier  128 . Accordingly, rotational energy in the object  104  can be dissipated as heat. 
     The attachment mechanism  116  is fixed to the carrier  128 , and provides a mechanism by which the damper mechanism  112  can be attached to the target object  104 . In the example of  FIG. 1 , the attachment mechanism  116  includes a plurality of grapples or arms  136 , to provide a mechanical interconnection between the damper mechanism  112  and the object  104 . However, as discussed elsewhere herein, other means for attachment, including but not limited to adhesives, mating fixtures, or the like can be provided. Moreover, an object  104  to which the damper mechanism  112  can be attached includes but is not limited to a satellite or debris. 
       FIGS. 2A-2D  depict different exemplary configurations of a damper mechanism  112  in accordance with embodiments of the present disclosure in cross section. In general, the damper mechanism  112  includes a magnet or set of magnets  120  comprising or provided as part of an inner element  124 . The inner element  124  is in turn joined to a carrier or outer element  128  by an interconnection  132 . The interconnection  132  permits rotation of the magnet  120  in any direction about a center point C relative to the carrier  128 . 
     In the exemplary embodiment illustrated in  FIG. 2A , the inner element  124  has a spherical outer surface  204  that faces a spherical inner surface  208  of the outer element or carrier  128 . As shown, the diameter of the outer surface  204  of the inner element  124  is smaller than the diameter of the inner surface  208  of the carrier  128 , creating a volume  212  there between. In the figure, the difference in diameter between the opposing surfaces  204  and  208  is exaggerated for purposes of illustration. However, in a typical implementation, the difference is small. For example, but without limitation, for an inner surface  204  with a diameter of about 20 cm the gap between the surfaces  204  and  208  is about 2 cm or less. A viscous fluid  216  is placed in the volume  212 . As an example, but without limitation, the viscous fluid  216  may comprise a synthetic oil, or other fluid that maintains a desired viscosity over an expected range of operating temperatures. Alternatively or in addition, the damper mechanism  112  can incorporate a heating element to maintain a desired fluid  216  viscosity. 
     As can be appreciated by one of skill in the art after consideration of the present disclosure, the inner element  124  can be constructed from two or more elements formed from a nonmagnetic material that together form the spherical outer surface  204 , and an interior volume to which the magnet or magnets  120  can be secured. Examples of suitable nonmagnetic materials include but are not limited to titanium, aluminum, stainless steel, copper, fiberglass, and glass. The carrier  128  can likewise be constructed from two or more elements formed from a nonmagnetic material that together form the spherical inner surface  208 , and that can be secured around the spherical outer surface  204 . Prior to sealing the carrier  128  about the inner element  124 , the viscous fluid  216  can be injected into the volume  212 . Alternatively or in addition, a port can be provided in the carrier  128  for injecting the viscous fluid  216  into the volume  212  before the volume  212  is sealed. 
     The magnet or magnets  120  can be in the form of a permanent magnet or set of permanent magnets. Where a plurality of magnets are utilized, their poles are aligned with one another. In general, by providing a magnet  120  that is relatively strong, the time required to dampen the rotation of the target object  104  relative to the external magnetic field will be shorter than for a magnet  120  that is relatively weak. The dampening effect of the damper mechanism  112  can also be enhanced by providing a more viscous fluid  216 . 
     In the example illustrated in  FIG. 2B , the interconnection  132  between the inner element  124  and the carrier  128  incorporates a plurality of bearings  220  located within the volume  212 . As in the previous example, the inner element  124  and the carrier  128  include facing, spherical surfaces  204  and  208 . In a typical implementation, both of the surfaces  204  and  208  are complete spherical surfaces. In accordance with other embodiments, one of the surfaces can include voids or discontinuities. For example, one of the surfaces can include a plurality of surfaces that have relative locations defining points on a spherical surface. The bearings  220  can be in the form of pucks, dots, rings, races or other shapes disposed between the spherical surface  204  of the inner element  124  and the spherical surface  208  of the carrier or outer element  128 , such that a spacing is maintained between the opposing spherical surfaces  204  and  208 . The bearings  220  can incorporate or be associated with elements that maintain a desired spacing between individual bearings  220 . Alternatively or in addition, the bearings  220  can be fixed to one of the surfaces  204  or  208 . In accordance with at least some embodiments, the bearings can comprise ridges, hemispheres or other shapes that are integral to and that extend from one of the elements  124  or  128 . A viscous fluid  216  can be included in the volume  212  with the bearings  220 . In accordance with still other embodiments, the bearings  220  can be formed from a self lubricating material, and therefore a viscous fluid  216  need not be provided. 
     In the example of  FIG. 2C , the damper mechanism  112  includes an inner element  124  that includes a discontinuous spherical surface  204 . In particular, the example shows an inner element  124  that includes a pair of equatorial bands  224 . The outer surfaces of the equatorial bands  224  generally lie on a spherical surface  204  that is centered at point C and that is concentric with a facing spherical surface  208  defined by the carrier  128 . The outer surfaces of the equatorial bands  224  and the facing spherical surface  208  can function as opposed bearing surfaces. Moreover, bearing surfaces can be coated by a viscous fluid. Alternatively or in addition, bearings  220  can be fixed to the equatorial bands  224 . In alternate embodiments, the carrier  128  can incorporate equatorial bands or other discontinuous spherical surface  208  elements in cooperation with an inner element  204  that provides a continuous spherical surface. 
     In the example damper mechanism  112  of  FIG. 2D , the interconnection  132  comprises a gimbal structure that allows rotation of the magnet  120  relative to the carrier  128  in any direction about a center point C. More particularly, the interconnection  132  can include an intermediate equatorial ring  228  and sets of orthogonally aligned bearings  232 . In accordance with still other embodiments, the bearings  232  may incorporate or be associated with braking mechanisms to dissipate rotational energy as heat. 
     In the example damper mechanism  112  of  FIG. 2E , a magnetic field neutralizing element or mechanism  236  is provided. The magnetic field neutralizing element  236  may comprise a permanent magnet, electromagnet, or combination thereof. Moreover, the poles of the neutralizing element  236  are aligned such that they are opposite those of the magnet  120 . The relative strengths of the magnetic fields of the magnet  120  and the magnetic field neutralizing element  236  can be selected so that the combined magnetic field is negligible with respect to the operation of a vehicle or other system carrying or associated with the damper mechanism. For example, where a despin system  100  is deployed as part of an object  104 , the magnetic field neutralizing element  236  may be in place during launch and normal operation of the object  104 . The magnetic field neutralizing element  236  can then be removed or otherwise deactivated to allow operation of the damper mechanism  112 . Although depicted as a horseshoe type element, the magnetic field neutralizing mechanism  236  can be configured in different ways. For example, the magnet  120  can be formed from a plurality of magnets, with individual magnets oppositely aligned, so that the overall magnetic field of the magnet  120  is neutralized. In such an embodiment, the damper mechanism  112  can be activated by moving the individual magnets so that their magnetic fields are aligned with one another. 
       FIG. 3  depicts a despin system  100  that includes the damper or despin mechanism  112 , and an attachment mechanism  116 . More particularly, the damper mechanism  112  is fixed to the attachment mechanism  116 . The attachment mechanism  116  is generally configured to facilitate a secure attachment of the despin system  100  to an orbiting object  104 , including but not limited to a satellite, or debris. In the exemplary embodiment illustrated in  FIG. 3 , the attachment mechanism  116  includes a central strut  308  that is fixed to the damper mechanism  112  at a first end. The central strut  308  can extend through a trigger plate  312 . The trigger plate  312  is biased away from the despin mechanism  112  by a coil spring  316 . The trigger plate  312  includes a sleeve  320  that receives spring loaded arms  324 . The spring loaded arms  324  are mounted at or proximate to a second end of the central strut  308 . The attachment mechanism  116  in the example also generally includes a penetrating tip  328 . 
     With reference now to  FIG. 4 , aspects of a method for passively despinning or reducing a spin rate of an orbiting object  104  are depicted. Initially, at step  404 , the passive despin system  100  is brought into the proximity of the target object  104 . For example, the passive despin system  100  can be deployed from a rocket, shuttle, or other vehicle while the vehicle is itself in orbit. The despin system  100  is then attached to the target object  104  (step  408 ). Various techniques may be utilized for attaching the despin system  100  to the target object  104 , depending on the features and capabilities of the associated attachment mechanism  116 . For example, but without limitation, the target object  104  can be mechanically grappled, an attachment mechanism  116  with a flexible element and an adhesive can be affixed to the target object  104 , a member or receiver provided by the attachment mechanism  116  can be mated with a corresponding structure on the target object  104 , or an exterior of the target object  104  can be pierced by an attachment mechanism  116  with an expanding element. 
     As a specific example, where the attachment mechanism  116  includes a central strut  308  with a penetrating tip  328 , the inertia of the despin system  100  can be used to force the penetrating tip  328  through a surface or structure of the target object  104 . As the penetrating tip moves further through the surface or structure, the trigger plate  312  contacts the surface or structure. Moreover, as the despin system  100  continues moving relative to the target object, the trigger plate  312  moves against the spring  316 , increasing the distance between the sleeve  320  and the second end of the central strut  308 . Once the sleeve  320  has moved a distance sufficient for the spring loaded arms  324  to clear the sleeve  320 , the spring loaded arms  324  extend, securing the despin system  100  to the target object. As can be appreciated by one of skill in the art from the present disclosure, other configurations of attachment mechanism  116  secure the despin system  100  as described herein to a target object  104  by grappling, adhering, fixing, or otherwise joining the despin system  100  to the target object  104 . 
     After the despin system  100  has been attached to the target object  104 , the despin system  100  will spin or otherwise move with the target object  104 . Over some period of time, the magnet  120 , which is free to rotate in any direction relative to the carrier  128 , will align its magnetic field with the external magnetic field  110  of the body  108  about which the target object  104  is orbiting (step  412 ). As can be appreciated by one of skill in the art after consideration of the present disclosure, a relatively stronger magnet  120  will tend to align itself with the external magnetic field  110  more quickly than a relatively weaker magnet  120 . Once the magnet  120  has aligned itself with the external magnetic field  110 , the inner element  124  to which the magnet  120  is fixed will move relative to the carrier  128  (step  416 ). This relative movement will tend to decrease (i.e. it will be damped) by friction in the interconnection  132  between the inner element  124  and the carrier  128 , and the relative rotational energy will be dissipated as heat (step  420 ). This will in turn slow the spin rate of the target object  104  relative to the magnetic field  110  of the body  108  (step  424 ). After the spin rate of the target object has slowed by a sufficient amount, further operations can be performed on the target object  104  (step  428 ). For example, but without limitation, the target object  104  can be more easily approached for rendezvous, capture, and/or deorbit operations, and/or the despin system  100  can be disconnected from the target object  104 , for example to be used to slow the spin rate of another target object  104 . 
     In accordance with still other embodiments of the present disclosure, a damper mechanism  112  can be deployed as part of an object  104 . More particularly, while the object  104  is placed into orbit about a body  108 , the magnetic field of the damper mechanism  112  can be neutralized. For example, a neutralizing element  236  can be provided. As a further example, an additional magnet, with its poles aligned oppositely the polls of the magnet  120 , can be used to neutralize the magnetic field of the magnet  120 . In this configuration, the effect of the magnetic field associated with the damper mechanism  112  is reduced or eliminated. The magnetic field of the magnet  120  can thus be activated when desired by removing the neutralizing element  236  or by switching the orientation of the additional magnet. For example, when the object  104  has reached its end of life, the damper mechanism  112  can be activated, to maintain the object  104  in a static or relatively static configuration relative to the magnetic field  110  of the body  108 , or in order to bring the object  104  into a static or relatively static configuration relative to the magnetic field  110  of the body  108 . 
     As can be appreciated by one of skill in the art after consideration of the present disclosure, a damper mechanism  112  operates by converting the spinning energy of a target object  104  to which the damper mechanism  112  is attached into heat. Accordingly, the rotation of the target object  104  relative to an external magnetic field  110  can be reduced or eliminated, without requiring an external power source or propulsive force. 
     The foregoing discussion of the invention has been presented for purposes of illustration and description. Further, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, within the skill or knowledge of the relevant art, are within the scope of the present invention. The embodiments described hereinabove are further intended to explain the best mode presently known of practicing the invention and to enable others skilled in the art to utilize the invention in such or in other embodiments and with various modifications required by the particular application or use of the invention. It is intended that the appended claims be construed to include alternative embodiments to the extent permitted by the prior art.