Debris clearance system and method

Abstract

A system 20 for decreasing the velocity of orbital space debris, the system comprising a plurality of framed nets 10 each comprising a frame (7, fig. 1) and a netting 2 comprising a plurality of strip

Description

Field The present invention relates to systems and methods for the slowing down and collection of objects in low earth orbit, in particular for the clearing of orbital debris. Background It is estimated that there are about 500,000 pieces of 1cm3 orbital debris in low earth orbit (LEO) which poses a huge risk to space infrastructure. This is due to the extreme speeds at which the debris orbits the earth, which is many times faster than a bullet. A collision between a piece of orbital debris and a satellite can therefore cause immense damage. This danger is getting increasing worse as the number of pieces of orbital debris in LEO continues to rise. Furthermore, as time goes by, the risk of Kessler Syndrome increases. This is also known as collisional cascading, which is when one collision causes more space debris to be generated. Each new piece, in turn, goes on to collide with further infrastructure producing an exponential spiral of collisions. This has a variety of drastic consequences such as making many orbits unusable and potentially destroying infrastructure such as satellite constellations. As a consequence, weather predictions, scientific research and satellite communications would be disrupted. Due to the threat of this phenomenon occurring, satellite companies must pay increased insurance rates due to the high risk of damage to satellites. Currently, there are a number of solutions for the problem of orbital debris. However these solutions almost exclusively tackle large pieces of orbital debris e.g. whole defunct satellites. While there are some solutions for small pieces of orbital debris, many of these solutions fail to meet the future needs of the industry because they aim to deorbit the pieces of debris instead of capturing them and retaining them so that they can be recycled and used further in space. Other solutions attempt to use Whipple Shields, i.e barriers or armour to protect satellites from debris impact. Although these solutions do manage to slow down the orbital debris enough so that it does not damage the satellites, they do not meet industry standards since as they work sacrificially and are destroyed or at least significantly damaged by the impact of high speed debris. There is therefore a need for an improved method to slow down small pieces of orbital debris. A system for orbital debris removal comprising layers of netting is disclosed in US2012097799A1. The system uses an arrangement of wires to break up pieces of orbital debris. Summary of invention According to a first aspect there is provided a system for decreasing the velocity of orbital space debris, the system comprising: a plurality of spaced layers of framed nets each comprising a frame and a netting comprising a plurality of strips arranged as a lattice structure and attached to the frame; and at least one support member rigidly attached to the plurality of framed nets to maintain the spacing between the plurality of framed nets; wherein the lattice structure of each respective frame is oriented diagonally relative to the frame. Optionally, each of the plurality of strips have a width and thickness, wherein the width is greater than the thickness. Optionally, each of plurality of strips are formed of a material with a yield strength greater than 327.2MPa. Optionally, each of the plurality of strips are formed of one or more metal alloys, preferably one or more aluminium alloys. Optionally, each of the plurality of strips is formed of Aluminium 7475-T61. Optionally, a subset of the plurality of strips located closest to the centre point of each respective framed net are formed of a material with a yield strength greater than the yield strength of the material forming the plurality of strips located towards the periphery the respective framed net. Optionally, each of the plurality of framed nets further comprises at least one fastening configured to connect respective pairs of strips of the plurality of strips at a location where the respective pair of strips overlap. Optionally, the frame of each of the plurality of framed nets is rectangular-shaped along an x-y plane perpendicular to the direction of the spacing between the plurality of framed nets. Optionally, each of the frames of the plurality of framed nets has dimensions between 0.4mx0.4m and 0.5mx0.5m along the x-y plane. Optionally, a plurality of holes are formed by the lattice structure wherein each of the plurality of holes have an area between 9mm2 and 81mm2 Optionally, each of the plurality of strips of each of the plurality of framed nets has a thickness greater than 1.2 mm, preferably greater than 1.3mm. Optionally, wherein the spacing between each of the plurality of framed nets is between 0.2m and 0.25mm. Optionally, the frame of each successive framed net of the plurality of framed nets has smaller dimensions than the frame of the previous framed net of the plurality of framed nets along the x-y plane perpendicular to the direction of the spacing of the plurality of framed nets. According to second aspect there is provided a spacecraft comprising: a main chamber with an opening leading to outside the spacecraft; and the system of framed nets, wherein the netting of each of the plurality of framed nets faces the opening. Optionally, the spacecraft further comprises a storage chamber connected to the main chamber for storing collected orbital debris. According to a third aspect there is provided a method of slowing down orbital debris, the method comprising: guiding the spacecraft towards orbital debris; and positioning the opening of the main chamber towards the incoming path of orbital debris. According to a fourth aspect there is provided a method of manufacturing a system for decreasing the velocity of orbital space debris, the method comprising: providing a plurality of frames; attaching a netting formed of a plurality of strips arranged as a lattice structure to each of the plurality of frames to form a plurality of framed nets; and rigidly attaching at least one support member to each of the plurality of framed nets to provide a spacing between each of the plurality of framed nets, wherein the plurality of framed nets are arranged in layers; and wherein the lattice structure is arranged diagonally relative to each respective frame. Brief description of the drawings Embodiments are now described, byway of non-limiting example, and are illustrated in the following figures, in which: Figure 1A illustrates a framed net for decreasing the velocity of orbital debris; Figure 1B illustrates an enlarged view of a subsection of the plurality of strips forming the framed net of Figure 1A. Figures 2A-2D illustrates an enlarged view of a portion of the framed net of Figure 1A in A) a relaxed state, B) upon contact with a piece of orbital debris, C) in a stretched state allowing piece of orbital debris can pass, and D) in a relaxed state; Figures 3A-3B illustrate the framed net of Figure 1A in A) a diagonal (left panel) and square (right panel) lattice configuration and B) with the strips of the netting unconnected (left panel) and connected (right panel); and Figure 4 illustrates a system comprising multiple layers of the framed net of Figure 1 A. Description The nested netting system described herein is able to slow down orbital debris so that it no longer poses a risk to space infrastructure. The nested netting system works by using a series of framed nets with a netting formed of a plurality strips arranged as a lattice structure. The lattice structure is orientated diagonally relative to the respective frame. When a piece of debris impacts the netting of a framed net, the netting absorbs the kinetic energy of the piece of the debris and stretches until a hole between the strips of the net is big enough to allow the debris to pass through and impact a subsequent net. This process repeats until the debris slows down or comes to a stop. The nested netting system will now be described in further detail with reference to Figure 1A, which illustrates a framed net 10. The net 10 comprises a netting 2 and frame 7. The netting 2 comprises of a plurality of strips 1 arranged as a lattice structure. Each of the plurality of strips 1 are spaced apart from one another such that a plurality of holes 5 are formed by the lattice structure. The frame 7 provides a support for the plurality of strips 1 and each of the plurality of strips 1 are rigidly attached to the frame 7. The frame 7 may be formed of metal such as aluminium or any other material suitable material for withstanding the impact of orbit debris. The plurality of strips 1 may be formed of an elastic metal. As can be seen in Figure 1B, which shows a sub-section of the netting 2 of Figure 1A, each of the plurality of strips 1 have a width and a thickness, wherein the width greater than the thickness. The plurality of strips 1 are arranged so that the wide faces of the strips 1 overlap each other. In some embodiments, the width of each of the plurality of strips may be at least three times greater than the thickness. In one embodiment, each of the plurality of strips have a width of 4.5mm and a thickness of 1.3 mm. An embodiment suitable for slowing down orbit debris travelling in LEO with a diameter between 0.5 cm and 1cm and a maximum mass of 4.515g, will now be described. The maximum mass is calculated based on the assumption that the orbital debris is made of titanium, which is the material commonly used in spacecraft with the highest mass. Each of the plurality of strips 1 of the framed net 10 have a width between 4mm and 5mm and a thickness greater than 1.1.2mm, and preferably greater than 1.3mm. The frame 7 has dimensions between O.m x O.m and 0.5m x 0.5m. When the netting 2 is in a relaxed state, each of the plurality of holes 5 has an area between 9mm2 and 81mm2. In one embodiment, the netting 2 comprises 68 strips 1 in total, with each of the plurality of strips 1 having a width of 4.5mm and a thickness of 1.3mm. The netting 2 has dimensions of 0.45m x 0.45m x 0.0013m and the frame 7 is square-shaped. The four strips 1 closest to the diagonal of the net 10 have a length of 0.63m. The remaining strips 1 vary in length depending on where in the netting 2 they are located. When the netting 2 is in a relaxed state, each of the plurality of holes 5 has an area of 9mm2. In some embodiments, the netting 2 is formed of a material with a yield strength greater than 327.2MPa. The yield strength determines the limit of elastic behaviour of a material and therefore corresponds to a maximum pressure that can be exerted on the netting 2 to allow the netting 2 to return to its original dimensions. A yield strength greater than 327.2MPa is derived as follows: for a piece of orbital debris with a mass of 4.151g, the maximum kinetic energy in LEO is 2257.5J. If an area of 1cm2 of the orbital debris impacts the netting 2, the pressure exerted on the netting 2 is 327.2MPa.. As a consequence, impact of a piece of orbital debris with a kinetic energy of up to 2257.5J will cause the plurality of strips 1 to stretch without breaking. This causes the holes 5 between the plurality of strips 1 to enlarge such that the piece of orbital debris can pass through the framed net with decreased velocity or be stopped. In some embodiments, each of the plurality of strips 2 is formed of a metal alloy such as an alloy of aluminium, such as aluminium 2024-T4. Aluminium 2024-T4 has a high strength to weight ratio and good fatigue resistance and is widely used in aircraft. The yield strength of Aluminium 2024-T4 is 372.6MPa. In other embodiments, each of the plurality of strips 2 is formed of Aluminium 7475-T61 which has a yield strength of 565 MPa. In other embodiments, it is envisaged that the framed net 10 may have other dimensions and be made of other materials suitable for collecting orbital debris of different volume, mass and velocity. In these embodiments, it would be straightforward for the skilled person to calculate the required dimensions and properties of the framed net 10 based on the volume, mass and velocity of the pieces of orbital debris that the framed net 10 is intended to slow down. In one embodiment, each of the plurality of strips 1 are formed of the same material. In other embodiments, each of the plurality of strips 1 may be formed of a variety of different materials. For example, the strips 1 towards the centre of the netting 2 may be formed of a material with a higher yield strength than material forming the strips located towards the periphery of the netting 2. In use, the centre of the framed net 10 can be directed towards oncoming orbital debris. Advantageously, since a metal with a high yield strength material can be more expensive than a metal with a lower yield strength, manufacturing costs can be saved by utilising the higher yield strength metal for the central strips 1 which are directed to the oncoming orbital debris. In the present embodiment, the spacing between each of the plurality of strips 1 is equal. In other embodiments, the spacing between each of the plurality of strips in a respective framed net 10 may vary so that the netting 2 comprises holes 5 of a variety of different sizes. In the present embodiment, both the netting 2 and frame 7 are rectangular in form. In other embodiments, it is envisaged that the netting 2 and frame 7 may be any other suitable shape, such as a triangle. As shown in Figure 2A, a plurality of fastenings 4 are provided to connect each of the strips 1 to each of the respective other strips 1 that it overlaps with. The fastenings 4 are provided at the points of intersection of each of the plurality of strips 1. The fastenings 4 may be welding such as gas tungsten arc welding. Alternatively, any other suitable form of fastening may be provided such as an adhesive. In the present embodiment, fastenings 4 are provided at all of the points of overlap of the strips 1. In other embodiments, fastenings 4 may be provided at only some of the points of overlap, or no fastenings 4 may be provided at all. Turning to Figures 2A to 2D, the use of the net 10 to slow down a piece of orbital debris will now be described. Figure 2A illustrates a central portion of netting 2 with the strips 1 in a relaxed state. Figure 2B shows the instance that a piece of orbital debris 30 collides with the central portion of the netting 2. A typical piece of orbital debris 30 in LEO has a volume of approximately 1cm3 and has a kinetic energy of around 2257.5J. Since the hole 5 has area of 9mm2 the piece of orbital debris is too large to pass through the hole 5. Due to the high yield strength of the central portion of the netting 2, the netting 2 can withstand the impact with the piece of orbital debris 30. The kinetic energy from the piece of orbital debris 30 is transferred to the netting 2 to stretch it, causing the hole 5 to enlarge. As illustrated in Figure 2C, eventually the hole 5 will enlarge until the piece of orbital debris 30 is large enough to pass through it. A transfer of % of the kinetic energy of the piece of orbital debris 30 to the central portion of netting 2 results in hole 5 expanding to have an area of 100mm2. Subsequent to the piece of orbital debris 30 passing through the net, the netting 2 recoils back to an relaxed state as shown in Figure 2D. Turning now to Figures 3A and 3B, the effect of energy transfer from the piece of orbital debris 30 to a central portion of the netting 2 will now be considered with regard to various configurations of the netting 2. The left panel of Figure 3A illustrates the strips 1 of the netting 2 of the present embodiment arranged as a diagonal lattice with respect to the sides of the frame 7. When a piece of orbital debris 30 hits a central portion of the netting 2 a force will be exerted on the corners of the netting 2 which will pull on the corners of the frame 7. The shaded portions of the net 1 show where the forces are exerted on the net 1 by the piece of orbital debris. Since the corners of the frame 7 have the greatest structural integrity, the framed net 10 will be able to withstand the impact. Furthermore, by directing the forces to all of the corners of the frame 7, the forces on the frame 7 are well distributed which reduces the chance of structural damage to the net 1. The right panel of Figure 3A illustrates the strips 1 of the netting 2 arranged parallel and perpendicular to the sides of the frame 7, which is not part of the present embodiment. When a piece of orbital debris hits the center of the net 1 in the right panel, a force is exerted to the mid-points of all four sides of the frame 7. These midpoints are structurally the weakest points of the frame as they are the furthest points from the corners. As a consequence, the impact of orbit debris 30 with the net 1 can cause the sides of the net 1 to cave in. A further advantage of the diagonal configuration is that for a piece of orbital debris with a 1cm2 square surface hitting the centre of the net 1, there will be a greater area of contact between the strips 1 and the debris when the strips are in a diagonal configuration compared to the square configuration in the right panel of Figure 3A. The deceleration of the orbital debris will be more effective. Figure 3B illustrates one embodiment where the strips 1 are unconnected (left panel) and another embodiment where the strips 1 are connected (right panel). In the configuration in the left panel the strips 1 overlap one other similar to the weaving pattern of a basket. During impact of the net 1 with a piece of orbital debris 10, the force is mainly transmitted to the strips 1 that are closest to the diagonal of the net 1. As a consequence, most of the force is transmitted to the corners of the frame 7. In the embodiment shown in the right panel of Figure 3B, the strips 1 are connected by a fastening such as welding, which gives the netting a structure analogous to a tennis net. During impact of the net 1 with a piece of orbital debris 10, the force is directed along many more strips than when the strips 1 are unconnected, and therefore the force is distributed more evenly along the frame 7. As a result, the longevity of the frame 7 is increased. In one embodiment, all of the points of overlap between each of the respective pairs of strips 1 are connected with a fastening. In another embodiment, a portion of the points of overlap between each of the respective pairs of strips 1 are connected with a fastening. An example nested netting system 20 for slowing down orbital debris is illustrated in Figure 4. The system comprises a plurality of nets 1 positioned in series and spaced apart from each other by a distance d between 0.2m and 0.25m, and preferably 0.22m. The plurality of nets 1 are arranged such that the center point of each of the nets is located along a z-axis perpendicular to the x-y plane defined by the netting 2. Since in this embodiment each strip 1 has a thickness of 1.3mm, the overall dimensions of the system 20, excluding the frame, is 0.45 x 0.45 0 x.68m. Each of the nets 1 is held relative to the other nets by a plurality of support members 17, which may be bars made of metal or any other material suitable for withstanding the impact of orbit debris. In the embodiment shown in Figure 4, the system comprises four framed nets 10. In embodiments where the plurality of strips 1 are formed of Aluminium 2024-T4, the total elastic potential energy of the strips is 656.8J. In these embodiments, four framed nets are sufficient to bring a piece of orbital debris of 1cm3 with a kinetic energy of 2257.5J to a stop. In other embodiments, the system 2 may comprise any number of framed nets 10. In other embodiments, any other suitable support may be used to hold the nets 1 at a distance to the other nets 1. In addition, in other embodiments the nets 1 may be held at any suitable distance away from each other. In other embodiments, each of the nets 1 may be a different size, e.g. each successive net 1 may have a smaller area than the previous net 1. In use, the system 20 is provided inside a main chamber of a drone-like spacecraft and accessible through an opening in the drone-like spacecraft. The drone-like spacecraft can be transported into the path of fast moving orbital debris in order to slow and collect them. Orbital debris which enters through the opening of the spacecraft towards the main chamber will be deaccelerated by the system 20 by transferring its kinetic energy to each of the nets 1 in turn until it is unable to pass through any further net 1. The main chamber of the drone-like spacecraft leads to a storage chamber where the debris is kept during operation of the drone-like spacecraft until the chamber is full. In other embodiments, the system 20 may be provided as part of a lightweight defensive system for a space station such as the International Space Station. The system 20 disclosed herein is unique when compared with other known devices because it is directed to slowing down and collecting extremely small pieces of orbital debris traveling at high velocities and it slows these pieces down without being damaged in any way itself. This is achieved through a series of nets that absorb the kinetic energy of the orbital debris so that it is fully stopped or slowed down enough so that it no longer poses a risk to space infrastructure. This system is especially suitable for collecting orbital debris between 0.5 and 1.5cm in diameter, preferably 0.75 to 1.25, and more preferably 0.8 to 1.2cm. The system can be integrated into a drone-like spacecraft operating in Low Earth Orbit. When integrated into a spacecraft, the pieces of orbital debris can be captured and transported until they can be deposited instead of simply deorbiting them like other solutions. Whilst certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. Indeed the novel methods and systems described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the invention. The accompanying claims and their equivalents are intended to cover such forms and modifications as would fall within the scope of the invention.

Claims

1. A system for decreasing the velocity of orbital space debris, the system comprising:a plurality of spaced layers of framed nets each comprising a frame and a netting comprising a plurality of strips arranged as a lattice structure and attached to the frame; andat least one support member rigidly attached to the plurality of framed nets to maintain the spacing between the plurality of framed nets;wherein the lattice structure of each respective frame is oriented diagonally relative to the frame.

2. The system of claim 1, wherein each of the plurality of strips have a width and thickness, wherein the width is greater than the thickness.

3. The system of claim 1 or 2, wherein each of plurality of strips are formed of a material with a yield strength greater than 327.2MPa.

4. The system of any one or more of claims 1 to 3, wherein each of the plurality of strips is formed of one or more metal alloys, preferably one or more aluminium alloys.

5. The system of any one or more of claims 1 to 4, each of the plurality of strips is formed of Aluminium 7475-T61.

6. The system of any one or more of claims 1 to 5, wherein a subset of the plurality of strips located closest to the centre point of each respective framed net are formed of a material with a yield strength greater than the yield strength of the material forming the plurality of strips located towards the periphery of the respective framed net.

7. The system of any one or more of claims 1 to 6, wherein each of the plurality of framed nets further comprises at least one fastening configured to connect respective pairs of strips of the plurality of strips at a location where the respective pair of strips overlap.

8. The system of any one or more of claims 1 to 7, wherein the frame of each of the plurality of framed nets is rectangular-shaped along an x-y plane perpendicular to the direction of the spacing between the plurality of framed nets and optionally, wherein each of the frames of the plurality of framed nets has dimensions between 0.4mx0.4m and 0.5mx0.5m along the x-y plane.

9. The system of any one or more of claims 1 to 8, wherein a plurality of holes are formed by the lattice structure, wherein each of the plurality of holes have an area between 9mm2 and 81mm2.

10. The system of any one or more of claims 1 to 9, wherein each of the plurality of strips of each of the plurality of framed nets has a thickness greater than 1.2mm, preferably greater than 1.3mm, and optionally, wherein the spacing between each of the plurality of framed nets is between 0.2m and 0.25m.

11. The system of any one or more of claims 1 to 10, wherein the frame of each successive framed net of the plurality of framed nets has smaller dimensions than the frame of the previous framed net of the plurality of framed nets along the x-y plane perpendicular to the direction of the spacing of the plurality of framed nets.

12. A spacecraft comprising:a main chamber with an opening leading to outside the spacecraft; and the system of any one or more of claims 1 to 11 disposed in the main chamber, wherein the netting of each of the plurality of framed nets faces the opening.

13. The spacecraft of claim 12, further comprising:a storage chamber connected to the main chamber for storing collected orbital debris.

14. A method of slowing down orbital debris, the method comprising:guiding the spacecraft of claims 12 or 13 towards orbital debris; andpositioning the opening of the main chamber towards the incoming path of orbital debris.

15. A method of manufacturing a system for decreasing the velocity of orbital space debris, the method comprising:providing a plurality of frames;attaching a netting formed of a plurality of strips arranged as a lattice structure to each of the plurality of frames to form a plurality of framed nets; andrigidly attaching at least one support member to each of the plurality of framed nets to provide a spacing between each of the plurality of framed nets,wherein the plurality of framed nets are arranged in layers; andwherein the lattice structure is arranged diagonally relative to each respective frame.

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