Spacecraft heat shield

Abstract

An expandable atmospheric entry spacecraft heat shield (30, 40, 50, 60) is configured to have a flasher pattern of transformable polyhedral surfaces. The transformable polyhedral surfaces have a plurality of sectors (2), each sector (2) having a plurality of mountain fold lines (4, 5), a plurality of valley fold lines (6, 7), a plurality of faces (8) between the fold lines (4, 5, 6, 7), and an outer edge (12). The heat shield (30, 40, 50, 60) is expandable from a stowed configuration to a deployed configuration.

Description

Technical Field

[0001] This invention relates to a spacecraft heat shield, and more specifically, to a deployable atmospheric entry heat shield for spacecraft. A heat shield is a device used to thermally protect and decelerate a spacecraft as it enters the atmosphere from space. Background Technology

[0002] When a spacecraft re-enters the Earth's atmosphere from orbit or enters the atmosphere of other planets such as Mars or Venus (hereinafter referred to as atmospheric entry for simplicity), a spacecraft heat shield is required to prevent excessive heat from entering the spacecraft. There are two main methods for heat dissipation during atmospheric entry: ablation and radiation.

[0003] Ablation-dominant heat shields rely on ablation: the vaporization of the shield's surface material allows heat to be carried away with the escaping gas rather than deposited into the spacecraft. All currently operational or near-operational atmospheric entry manned spacecraft (such as Soyuz, Shenzhou, Dragon, and Starliner) use ablation-dominant heat shields because this type of heat shield has a long history and the underlying physics is well understood.

[0004] Radiative heat shields rely on electromagnetic radiation, particularly in the infrared range (i.e., thermal radiation), to remove heat from the shield. The energy emitted depends on the surface temperature and its ability to emit energy. Due to the extremely high temperatures reached during atmospheric reentry (typically exceeding 2000 K), the potential materials for radiative heat shields in space shuttle-type configurations are limited. The temperature reached by the heat shield depends on its area-to-mass ratio. Heat flux during atmospheric reentry (MW / m²) 2 The input rate of a heat shield is primarily determined by the ballistic coefficient. This is an indicator of the heat shield's ability to overcome air resistance during flight, and is equal to the drag coefficient (kg / m) calculated by dividing the mass by the unit cross-sectional area of ​​the heat shield. For simple geometries, the ballistic coefficient is a measure of the ratio of aerodynamic drag area to total mass.

[0005] For example, a commercial reentry vehicle currently in service has a ballistic coefficient of approximately 570 kg / m during reentry. 2 The US space shuttle had a relatively low ballistic coefficient, approximately 350 kg / m², due to its large wing area. 2 During reentry into the atmosphere from low Earth orbit (LEO), the heat flux of these two types of spacecraft typically reaches single digits of megawatts per square meter (MW / m²) for tens of seconds. 2 Furthermore, the heat shield radiation area of ​​a currently operational commercial reentry vehicle is approximately 0.002 square meters per kilogram of vehicle weight. 2 / kg), while the heat shield of the US Space Shuttle has a radiation area of ​​approximately 0.003 square meters per kilogram (m²).2 / kg).

[0006] Spacecraft may also require deceleration devices, such as parachutes, canopies, and / or heat shields protruding outwards from two dimensions of the spacecraft. However, these deceleration devices can be very bulky. This can be a disadvantage because the volume of the spacecraft's launch vehicle or cargo bay is limited. Summary of the Invention

[0007] Given the above, there is a need for a compact heat shield that can provide protection and deceleration for spacecraft.

[0008] The first aspect of this application provides a deployable atmospheric entry spacecraft heat shield with a variable polyhedral surface, comprising: multiple sectors, wherein each sector has multiple mountain folds, multiple valley folds, multiple faces located between the folds, and an outer edge. The heat shield is configured to deploy from a retracted structure to a deployable structure.

[0009] The heat shield is a radiation heat shield.

[0010] The transformable polyhedral surface includes a central region of an m-order polygon, from which polygonal lines extend radially outward. Mountain polygons include primary and secondary mountain polygons, and valley polygons include primary and secondary valley polygons. Primary mountain and valley polygons extend from the central region of the polygon. Secondary mountain and valley polygons extend between the primary mountain and valley polygons.

[0011] The transformable polyhedral surface exhibits radial symmetry about the central region of an m-order polygon. Multiple sectors are radially symmetric.

[0012] The surface of the heat shield is formed as a single piece of material.

[0013] The multiple zigzag lines in each sector are configured to substantially limit angular rotation around the longitudinal axis of the heat shield during use.

[0014] The ratio of the diameter of the polygonal central region to the outer flat diameter of the unfolded structure of the transformable polyhedron surface is 1:11. The outer flat diameter is the diameter when the transformable polyhedron surface is forcibly transformed into a single plane (i.e., flat).

[0015] The transformable polyhedral surface is configured to be swept back in the deployable structure. The deployable structure can be configured such that the center of mass of the heat shield (or the spacecraft containing the heat shield) is located behind the center of the polygon relative to the longitudinal axis of the heat shield.

[0016] The deployed structure is in a stable state, and the fixing device is configured to hold the heat shield in the retracted structure. The fixing device is configured to release when an activation threshold is exceeded.

[0017] The outer edge is rounded.

[0018] The second aspect of this application provides a deployable atmospheric entry spacecraft heat shield configured in a flasher pattern. All features of the first aspect can be combined with the second aspect.

[0019] The second aspect of this application provides a spacecraft including a heat shield as described in any of the preceding claims. All features of the first aspect can be combined with the third aspect.

[0020] Advantageously, the heat shield described above can be deployed in a variety of situations to perform various functions, including acting as a heat shield. The heat shield is compact when retracted. This compact size is ideal for space applications due to launch volume limitations. The heat shield can also be deployed to an unfolded structure to significantly increase its effective surface area. This allows the heat shield to not only effectively protect the spacecraft from excessive heat but also reduce the spacecraft's velocity during atmospheric reentry. This combination of characteristics allows for the efficient use of a wider range of materials in the manufacture of the heat shield. Other advantages are also apparent to engineers and will be highlighted in this article. Attached Figure Description

[0021] Embodiments of the present invention will now be described with reference to the accompanying drawings, in which:

[0022] Figure 1A It is an origami pattern called a flasher pattern, which is defined by parameters m=5, r=2, h=2, and assumes that the thickness is negligible.

[0023] Figure 1B yes Figure 1A A sector of the flasher pattern.

[0024] Figure 2A Through optimization Figure 1A Thickness-adaptive flasher patterns are generated from flasher patterns.

[0025] Figure 2B yes Figure 2A The thickness-adaptive flasher pattern with secondary zigzag lines is omitted.

[0026] Figure 3A Based on Figure 2A Isometric view of the unfoldable heat shield with a flasher pattern under the retracted structure.

[0027] Figure 3B yes Figure 3A Isometric view of the deployable heat shield in a partially deployable structure.

[0028] Figure 3C yes Figure 3A Isometric view of the deployable heat shield in its fully deployed structure.

[0029] Figure 4A yes Figure 3A A top view of the deployable heat shield under the retracted structure.

[0030] Figure 4B yes Figure 3A A top view of the deployable heat shield in its partially deployable structure.

[0031] Figure 4C yes Figure 3A A top view of the deployable heat shield in its fully deployed state.

[0032] Figure 5A yes Figure 3A Side view of the deployable heat shield under the retracted structure.

[0033] Figure 5B yes Figure 3A Side view of the deployable heat shield under the partially deployable structure.

[0034] Figure 5C yes Figure 3A Side view of the deployable heat shield in its fully deployed structure.

[0035] Figure 6A yes Figure 3A An isometric view of the deployable heat shield mounted on the spacecraft in its retracted configuration.

[0036] Figure 6B yes Figure 3A An isometric view of the deployable heat shield mounted on the spacecraft in a partially deployable structure.

[0037] Figure 6C yes Figure 3A An isometric view of the deployable heat shield mounted on the spacecraft in its fully deployed configuration.

[0038] Figure 7A It is another type of thickness-adaptive flasher pattern defined by parameters m=5, r=1, h=2, with secondary polylines.

[0039] Figure 7B Secondary broken lines were omitted. Figure 7A Thickness-adaptive flasher patterns.

[0040] Figure 8A It is another type of thickness-adaptive flasher pattern with secondary polylines, defined by parameters m=4, r=3, h=1.

[0041] Figure 8B Secondary broken lines were omitted. Figure 8A Thickness-adaptive flasher patterns.

[0042] Figure 9A It is another type of thickness-adaptive flasher pattern with secondary polylines, defined by parameters m=10, r=2, h=5.

[0043] Figure 9B Secondary broken lines were omitted. Figure 9A Thickness-adaptive flasher patterns.

[0044] Figure 10A It is another type of thickness-adaptive flasher pattern defined by parameters m=6, r=3, h=2, which omits secondary polylines and has superimposed dashed circular templates.

[0045] Figure 10B It has been cut into Figure 10A The dotted circle template is cut Figure 10A Thickness-adaptive flasher patterns. Detailed Implementation

[0046] In summary, this specification describes a deployable atmospheric entry spacecraft heat shield (hereinafter referred to as the heat shield) that can protect and decelerate a spacecraft during atmospheric reentry. The spacecraft can be any type of spacecraft or flying body that will enter or re-enter the atmosphere of Earth or another planet or satellite at high speed, thus requiring thermal protection (and deceleration).

[0047] Before (and / or during) atmospheric reentry, origami-like patterns can be used to unfold the heat shield from a compact, collapsed structure into an unfolded one. Origami and similar folding techniques can effectively package large, deployable space structures to a size suitable for launch into space. Traditional origami often assumes that the thickness of the folded material is negligible because the material is typically paper, so treating the paper's thickness as negligible is a valid assumption. However, in structural origami, the thickness of the material needs to be taken into account to avoid any undesirable material deformation, thus making the structure more robust.

[0048] Figure 1AThe image shown is an origami pattern known as "flasher pattern 1," with a hypothetical thickness that is negligible. This type of origami pattern was originally named "flasher" by origami artist Jeremy Shafer in his book *Origami to Astonish and Amuse* (St. Martin's Griffin, 2001, ISBN 0-312-25404-0). However, the term "flasher" is now widely understood and used in the technical community. A flasher pattern is a special type of deformable polyhedral surface with multiple sectors. Figure 1B A sector 2 is shown. Each sector has multiple mountain folds 4 and 5, multiple valley folds 6 and 7, and multiple rigid surfaces 8 located between the folds. As shown, the flasher pattern 1 has a polygonal central region 10, from which the mountain folds 4 and valley folds 6 extend outwards. Figure 1A and Figure 1B In the middle, the central region 10 of the polygon is a pentagon.

[0049] Flasher patterns typically feature primary and secondary zigzag lines, such as primary mountain zigzag 4, primary valley zigzag 6, secondary mountain zigzag 5, and secondary valley zigzag 7. Primary mountain zigzag 4... Figures 1A to 2B The main valley line is shown as a thick dashed line. Figures 1A to 2B The middle section shows a thick dashed line. The secondary mountain zigzag line 5 is shown in... Figure 1A and Figure 2A The secondary valley line is displayed as a light dashed line. (The second part, "7," appears to be a typo and should be removed.) Figure 1A and Figure 2A The lines are shown as light dashed lines. When the flasher pattern is in the rolled-up structure, the faces 8 adjacent to the main folds are essentially adjacent. Conversely, secondary folds are considered "secondary" because they have a smaller degree of folding, and their purpose is to allow the flasher pattern to curl up in the rolled-up structure, which is evident from... Figures 3A to 6C This is clearly visible in the transformation shown. Therefore, the main polylines 4 and 6 extend from the central region 10 of the polygon to the outer edge 12 of the flasher pattern. The secondary polylines 5 and 7 branch off from the main polylines 4 and 6 and travel between the main polylines 4 and 6, thus forming a complex polyline pattern.

[0050] The shape of the outer edge 12 is substantially the same as that of the polygonal central region 10. However, the polygonal central region 10 has only one vertex, while the outer edge 12 has at least two vertices 13 and 14 arranged in a stepped structure. Each sector 2 of the flasher pattern 1 includes at least two vertices 13 and 14, such that one vertex 13 defines an angle of 90 degrees or less, and the other vertex 14 defines an obtuse angle (greater than 90 degrees). In each sector 2, the main polylines 4 and 6 do not extend to at least one vertex 13 of the outer edge 12.

[0051] Generally, a flasher pattern is designed to theoretically transform from a collapsed structure to an expanded structure and vice versa within a single degree of freedom. When a flasher pattern transforms from an expanded structure to a collapsed structure, the sectors surround the longitudinal axis of the flasher pattern (for flasher pattern 1, this axis is located at...). Figure 1A On the page, Figure 3C and Figure 5C (Referring to Figure 32). Flasher patterns typically have an unfolded structure substantially perpendicular to the axis of the central region of the polygon. Although, due to material limitations, the flasher may deform in unintended ways under sufficient force, the flasher pattern theoretically has only one degree of freedom determined by the intended polygonal structure. In other words, the polygonal pattern of the flasher pattern restricts its expansion into the unfolded structure, and therefore this expansion can only occur in a single manner (i.e., unfolding from the central region 10 of the polygon). Any deviation from this single manner of expansion may occur if a sufficiently strong external force is applied to the flasher pattern (i.e., an external force is applied that causes the flasher pattern to bend across its diameter in its unfolded structure—a deviation / deformation since this bending is not intended by the polygonal pattern). The diameter of the flasher pattern can differ significantly between the collapsed and unfolded structures, typically by a ratio of 1:5.

[0052] Advantageously, flasher patterns are mathematically definable. Therefore, the size and complexity of a flasher pattern can be adjusted. A flasher pattern can be defined using parameters m, r, and h: • “m” represents the rotation order of the flasher pattern, which is the number of sides of the polygon in the central region 10 (also equal to the number of sectors 2). • “r” represents the number of rings in the flasher pattern, that is, the number of layers (10) surrounding the central polygon area in each part. This is equivalent to the number of times the diagonal (the broken line from the center region 10 of the polygon through the middle of each sector 2) moves from bottom to top, and vice versa. For example, as shown in flasher pattern 1, the diagonal extends from the center region 10 of the polygon first as a major mountain broken line 4, and then as a major valley broken line 6. From the collapsed structure (see...) Figure 3A , Figure 5A and Figure 6A The bottom and top of the flasher pattern can be seen, which are opposite to the center region 10 of the polygon. Therefore, the center region 10 of the polygon can be located at the top or bottom of the flasher pattern under the collapsed structure, depending on the orientation. • “h” is the height of each ring in the flasher pattern. The height is measured in units of face 8 defined by secondary polylines 5 and 7 (i.e., before any secondary polylines 5 and 7 are removed). For example, Figure 1A The flasher pattern 1 has two loops (i.e., r = 2), and between the outer edge 12 and the adjacent loop extends a face 8 of two unit height. Therefore, the height of flasher pattern 1 is 2. In another example, Figure 8A The flasher pattern 50 has three rings (i.e., r = 3), and there is only one unit height face 8 between the outer edge 2 and the nearest adjacent ring. Therefore, the height of the flasher pattern 50 is 1.

[0053] For example, Figure 1A The parameters of the flasher pattern 1 are: m = 5, r = 2, h = 2.

[0054] To create structural origami (i.e., a flasher pattern with material of finite thickness), the flasher pattern needs to be optimized to account for the material thickness. This optimization can be achieved using known origami thickness adaptation theories, for example: Zirbel, SA, Lang, RJ, Thomson, MW, Sigel, DA, Walkemeyer, PE, Trease, BP, Magleby, SP, and Howell, LL (October 3, 2013), “Accommodating Thickness in Origami-Based Deployable Arrays”. ASME. J. Mech. Des. 2013 Nov; 135(11):111005; Bowen, L., Trease, B., Frecker, M., & Simpson, T. (2016) “Dynamic modeling and analysis of anorigami-inspired optical shield for the starshade spacecraft”, In Multifunctional Materials; Mechanics and Behavior of Active Materials; Integrated System Design and Implementation; Structural HealthMonitoring [V001T01A012](ASME 2016Conference on Smart Materials,AdaptiveStructures and Intelligent Systems,SMASIS2016;Vol.1).American Society of Mechanical Engineers; and Hossain Bhuiyan, ME, Semer, D, & Trease, BP. “Parametric Studies of Geometric Design Factors on Static and Dynamic Loading of an Origami Flasher”, Proceedings of the ASME 2017 Conference on Smart Materials, Adaptive Structures and Intelligent Systems. Volume 1: Development and Characterization of Multifunctional Materials; Mechanics and Behavior of Active Materials; Bioinspired Smart Materials and Systems; Energy Harvesting; Emerging Technologies. Snowbird, Utah, USA. September 18–20, 2017. V001T08A016. ASME.

[0055] Its entire contents are incorporated herein by reference.

[0056] Materials of any thickness can be used as long as they can be folded without breaking. Understandably, thickness-optimized flasher patterns still retain all the characteristics of traditional flasher patterns; therefore, the term "flasher pattern" can also describe thickness-optimized flasher patterns. However, to avoid confusion, this article uses "thickness-adaptive flasher pattern" to describe thickness-optimized flasher patterns.

[0057] Figure 2A and Figure 2B It shows that by optimizing Figure 1A A thickness-adaptive flasher pattern 20 is generated from flasher pattern 1 (parameters m=5, r=2, h=2), which can be used as a heat shield for deployable atmospheric entry spacecraft. The thickness-adaptive flasher pattern 20 and... Figure 1A The flasher pattern 1 retains the same basic features. Therefore, the corresponding features are given the same reference numerals. The thickness-adaptive flasher pattern 20 is described as a transformable polyhedral surface. Figure 2B The image shown is a thickness-adaptive flasher pattern 20 without secondary fold lines 5 and 7. A thickness-adaptive flasher pattern 20 without secondary fold lines 5 and 7 can be used when multiple faces 8 are non-rigid / elastic. This is because when the thickness-adaptive flasher pattern 20 moves between the collapsed and unfolded structures, it is not necessary to bend the faces 8 via secondary fold lines 5 and 7.

[0058] Thickness-adaptable flasher pattern 20 is also suitable Figures 3A to 6C An example of the folding pattern of the heat shield 30 is shown. The thickness-adaptive flasher pattern 20 allows the heat shield 30 to... Figure 3A , Figure 4A , Figure 5A and Figure 6A The collapsed structure shown unfolds to Figure 3C , Figure 4C , Figure 5C and Figure 6C The diagram shows the unfolded structure. A "folded structure" refers to the heat shield 30 folded to minimize its surface area / outer diameter. An "unfolded structure" refers to the heat shield naturally being in a semi-folded equilibrium position without any external force applied. This state is called the "unloaded" shape and is determined by several parameters. The properties of the central polygon and the ratio between the flat outer diameter and the diameter of the inscribed central polygon will determine the sweep angle of the unloaded shape. Furthermore, the stiffness of the shield material and the connection stiffness will also determine the angle between the plates. The unfolded structure can also be the most stable structure of the heat shield 30, or a stable structure of the heat shield 30.

[0059] Figures 3A to 6C The deployable heat shield 30 is shown in a flasher pattern configuration, specifically a thickness-adaptive flasher pattern 20. Figures 3A to 3C An isometric view of the deployable heat shield 30 is shown. Figure 3A The deployable heat shield 30 under the retracted structure is shown. Figure 3B The image shows the deployable heat shield 30 in a partially deployed configuration. This is a snapshot of the deployable radiative heat shield 30 moving from a retracted configuration to a deployed configuration, and vice versa. Figure 3C The deployable heat shield 30 in its deployable structure is shown, along with the longitudinal axis 32 passing through the polygonal (pentagonal) central region 10 along the predetermined travel direction of the deployable atmospheric entry spacecraft heat shield 30.

[0060] The deployable radiative heat shield 30 is described as having a transformable polyhedral surface comprising multiple sectors 2, each sector 2 having multiple mountain folds 4, multiple valley folds 6, and multiple cross-sections 8 located between the folds. Figures 3A to 3CAs shown, the transformable polyhedral surface has only one predetermined degree of freedom, and the heat shield 30 is configured to unfold from a retracted structure to an unfolded structure within this single degree of freedom. The transformable polyhedral surface may also have a polygonal central region 10, from which broken lines 4 and 6 extend radially to the outer side or outer edge 12 of the heat shield 30, similar to the flasher pattern 20. The transformable polyhedral surface also exhibits radial symmetry about the polygonal central region 10, thereby making the multiple sectors also radially symmetrical.

[0061] In the deployable structure, the deployable heat shield 30 has an outer diameter of 1.3 meters. For this diameter, the radiation heat shield 30 is designed to achieve a ballistic coefficient of less than 5 kg / m. 2 Mass-radiation area is 1m 2 / kg, thereby reducing the peak heat flux to less than 300kW / m² 2 The equilibrium temperature drops to approximately 1300K.

[0062] The deployable radiative heat shield 30 can be made of a rigid or semi-rigid material, in which case the flasher pattern of the heat shield may define secondary fold lines 5 and 7 to allow the heat shield to unfold from a retracted structure to an unfolded structure. Examples of such rigid materials may be certain metallic alloys, such as steel, titanium alloys, nickel superalloys, and pure elemental metals, such as refractory metals (or other typical materials for radiative heat shields), or ceramics, such as silicon-based ceramics and carbon-carbon (or other typical materials for ablative heat shields). Alternatively, the deployable radiative heat shield 30 can be made of an elastic material, in which case the deployable radiative heat shield 30 may not define any secondary fold lines 5, 7, and the elastic properties of the material (of each face 8) may allow the deployable radiative heat shield 30 to unfold from a retracted structure to an unfolded state. The material of the deployable radiative heat shield 30 may be an elastic material, thereby absorbing energy without permanent deformation when the heat shield elastically deforms to a retracted structure and releasing it to a stable state upon unloading. Examples of such elastic materials may be metals and metal alloys.

[0063] Figure 3A The displayed structure is collapsed. Figure 1A , Figure 2A and Figure 3BIn this configuration, the outer edge 12 of the deployable radiative heat shield 30 wraps around the hub (i.e., the central region 10 of the polygonal (pentagonal) shape), at which point the deployable radiative heat shield 30 enters the retracted structure. By retracting the deployable radiative heat shield 30 into the retracted structure, elastic energy can be stored in the folded lines and / or the heat shield material. The deployable radiative heat shield 30 can be held in the retracted position by a fixing device. The heat shield can be configured to deploy from the retracted structure to the deployed structure (the stable state of the deployable radiative heat shield 30) at least under the action of the elastic energy of the folded lines and / or the heat shield material. By using a retracted structure with a helical winding of a flasher patterned elastic material (such as metal / metal alloy), the deployable radiative heat shield 30 can be preloaded, thereby simplifying the process of deploying to the unloaded shape (i.e., the deployed structure / stable state) without the need for an active deployment system. In this way, once released from the deployed position, the deployable heat shield 30 pops outward.

[0064] The securing device is used to attach the deployable heat shield 30 to the retractable structure. The securing device can be any suitable high-tensile rope, cord, chain, binding material, sheet, or similar material. The securing device can be released when an activation threshold (such as temperature or altitude) is exceeded. The release process can be automated under specific conditions or controlled by a microprocessor based on sensor output or pre-programmed. The securing device can be released using a thermal knife system, thermal release system, or other suitable methods. Once released, the internal strain of the wound-wound deployable radiation heat shield 30 will cause it to rapidly and automatically deploy into the deployed structure.

[0065] Figure 4A The top view shows the deployable heat shield 30 under the retracted structure. Figure 5A The side view shows the deployable heat shield 30 under the retracted structure. Figure 6A This shows an isometric view of the spacecraft when the deployable heat shield 30 under the retracted structure is mounted on the spacecraft through the polygonal central region 10.

[0066] Figure 4B The top view shows the deployable heat shield 30 under the partially deployable structure. Figure 5B The side view shows the deployable heat shield 30 under the partially deployable structure. Figure 6B The deployable heat shield 30 is shown under the deployable structure installed on the spacecraft.

[0067] Figure 4C The top view shows the deployable radiation heat shield 30 in its deployable structure. Figure 5C The side view shows the deployable radiation heat shield 30 under the partially deployable structure. Figure 6C The deployable radiation heat shield 30 is shown under the fully deployable structure installed on the spacecraft.

[0068] Advantageously, a flasher pattern with a large difference (typically 1:5) in diameter can be designed between the retracted and extended states. That is, the diameter of the heat shield in the extended state is larger than the diameter of the heat shield in the retracted state.

[0069] For the deployable radiative heat shield 30, the ratio of the vanisher-shaped polygonal central region 10 to the outer flat diameter is 1:11. This allows the pre-deployed deployable radiative heat shield 30 to be compatible with spacecraft 36, such as cubic-format spacecraft (i.e., CubeSats), microsatellites, or other small or large satellites limited by a finite launch capacity. As mentioned above, the ballistic coefficient of an object is a measure of its ability to overcome air resistance in flight, equal to its mass divided by the drag coefficient per unit cross-sectional area. Therefore, by using a deployable radiative heat shield 30 with a relatively large deployment diameter, a lower ballistic coefficient can be achieved. The inventors have found that a lower ballistic coefficient can reduce the peak heating of the heat shield to 100 kW / m². 2 Therefore, the deployable radiative heat shield 30 can reduce the ballistic coefficient and increase the radiative area to mass ratio, so that the equilibrium temperature during the peak heating period of the near-Earth orbit reentry vehicle is lower than the melting point of many metal / metal alloys that can also withstand aerodynamic and deployment stresses during flight. Examples of such metal / metal alloys include steel, titanium alloys, nickel superalloys, and pure elemental metals, such as refractory metals.

[0070] like Figures 6A to 6C As shown, when deployed, the deployable radiative heat shield 30 is significantly larger than the spacecraft 36 to which it is attached in two dimensions, thus exceeding the main volume of the spacecraft. This allows the deployable radiative heat shield 30 to radiate heat both forward (towards flight) and backward, thereby greatly increasing the useful radiating area per kilogram of heat shield material. The rearward portion of the deployable radiative heat shield 30 also radiates into the cooler environment (during atmospheric reentry) more than the frontal portion, further improving thermal radiation efficiency.

[0071] Advantageously, the deployable radiative heat shield 30 has a deployable structure that leaves a non-planar pattern with distinct mountain 4 and valley 6 ridges. These mountain 4 and valley 6 ridges increase the total radiative surface area of ​​the deployable radiative heat shield 30 without affecting the total drag area. This allows both parameters, namely the total radiative surface area and the drag area, to be controlled separately.

[0072] Therefore, the deployable radiative heat shield 30 benefits from an increased radiative surface area to mass ratio and has the dual advantages of reducing peak heat flux (related to the ballistic coefficient) and increasing radiative area, both of which result in a lower equilibrium temperature. This allows the use of less unusual materials (such as silicon ceramics or ablative materials that are difficult to produce and process, like carbon-carbon) in the deployable radiative heat shield 30. During the peak heating of the radiative heat shield 30 during reentry into Low Earth Orbit (LEO), the low equilibrium temperature may be below the melting point of many metals and metal alloys.

[0073] Advantageously, due to the low ballistic coefficient, the final velocity in the atmosphere will decrease to a level where a separate fabric parachute may not be necessary. This is a significant advantage because the deployment of fabric parachutes for spacecraft entering the atmosphere typically requires a mortar system, and the risk of parachute deployment failure is substantial. However, fabric parachutes also reduce the accuracy of landing zone estimation due to their instantaneous inflation and drag characteristics.

[0074] The adaptable polyhedral surface (such as a flasher pattern) of the deployable radiative heat shield 30 can be formed as a single sheet material or together with a material having substantially similar thermal conductivity. This allows heat energy to be easily distributed around the deployable radiative heat shield 30, eliminating temperature hotspots and reducing the risk of uneven heating damaging the shield 30. For example, during atmospheric reentry, the mountain fold 4 naturally absorbs more heat energy; however, this heat energy is distributed through the sheet to the valley fold 6 and areas that absorb less heat. Metal / metal alloys typically have high thermal conductivity and are therefore suitable materials for the deployable radiative heat shield 30. The overall shape of the deployable heat shield 30 can be etched into a single piece using computer-controlled metalworking tools. A high emissivity (>0.8) and low absorptivity (<0.1) coating can then be applied to this single integral piece to further reduce peak heating temperatures.

[0075] Generally, compared to ablative heat shields that rely on surface vaporization, radiative heat shields are more easily reused because they do not depend on surface vaporization. Advantageously, the deployable radiative heat shield 30 has a larger deployed diameter compared to typical fixed-size (i.e., non-deployable) radiative heat shields, and therefore also a relatively larger radiative area. The larger radiative area allows more heat to radiate out of the system, thus achieving a balance between incoming and outgoing heat at a lower equilibrium temperature.

[0076] like Figure 5C As shown, the transformable polyhedral surface (such as a flasher pattern) of the deployable radiative heat shield 30 adopts a swept-back form in the deployable structure. This swept-back form is a result of the flasher pattern form's mrh parameters. Figure 5CAs shown, the swept-back form shapes the deployable radiation heat shield 30 into a roughly truncated pyramidal shape.

[0077] This sweep angle is used to shift the center of pressure along the longitudinal axis 32 (i.e., the flight axis) so that it is located behind the polygonal center region 10 and / or the spacecraft's center of mass 36. This significantly improves the aerodynamic stability of the spacecraft 36 during all phases of atmospheric reentry. For example, as... Figure 5C As shown, the ratio of the central region 10 of the polygon to the unloaded outer flat diameter of the transformable polyhedron surface is 1:11, so the natural sweep angle is approximately 30 degrees. Figure 5C The swept-back form of the deployable radiative heat shield 30 is shown, with an angle of 30 degrees between its longitudinal axis normal and the ridge of the outer edge of the heat shield. This further enhances passive aerodynamic stability and reduces the requirements of the spacecraft's attitude control system 36 to maintain a safe orientation (i.e., opposite to the airflow direction, thus providing optimal protection of the platform from heat) during atmospheric reentry. Advantageously, the non-flat pattern of the deployable radiative heat shield 30's deployment structure, with its distinct mountain 4 and valley 6 ridges (formed by mountain and valley fold lines), also improves passive aerodynamic stability.

[0078] The transformable polyhedral surface (e.g., a flasher pattern) of the deployable heat shield 30 is configured such that multiple fold lines 4, 5, 6, 7 in each sector substantially limit angular rotation about the longitudinal axis 32 of the deployable heat shield 30. This prevents the deployable heat shield 30 (and spacecraft 36) from rotating during atmospheric reentry, thereby improving aerodynamic stability along the longitudinal axis and facilitating aerodynamic analysis. In other words, the deployed structural shape of the deployable heat shield 30 is approximately axisymmetric. Due to the action of ridges 4 and valleys 6, air pressure is distributed on opposite sides of the deployable heat shield 30, thus providing not only flight stabilization but also preventing collapse back to the retracted position. This helps the deployable heat shield 30 maintain its deployed structural shape without additional securing devices.

[0079] As described above, the materials for the deployable radiative heat shield 30 can include metals and metal alloys (metals in this case). These materials offer numerous advantages; for example, metals are easier to process and shape into custom forms than brittle silica bricks. Metals are not brittle and allow for thermal expansion without cracking. The plastic deformation of metals can also be used to determine the desired deployment structure (i.e., the unloaded shape) without additional fixing devices or additional secondary fold lines 5, 7. Metals can be coated with a variety of materials to improve corrosion and radiation properties. Metals have relatively low procurement costs and can be processed using more common tools, significantly reducing the cost per square meter. Metals exhibit predictable and highly linear stress-strain characteristics at different temperatures, which aids in strength analysis.

[0080] The deployable radiative heat shield 30 can be mounted onto a custom-designed heat shield bracket on spacecraft 36 using the polygonal central region 10, which is connected to the forward panel of spacecraft 36. Other mounting methods are also possible, which are obvious to technicians.

[0081] Now we turn to alternative heat shields, which can be ablative heat shields possessing many of the properties, structures, and advantages of deployable radiative heat shields 30, as is readily apparent to technicians. Ablation requires highly specialized heat shield materials with low vaporization thresholds and high heat capacities. Due to the severe erosion of materials during atmospheric reentry, ablative-dominant heat shields are generally not reusable. Ablation heat shields can be made of rigid materials, in which case the flasher pattern of the heat shield defines secondary and fold lines, allowing the heat shield to deploy from a retracted to an deployed position. Examples of such rigid materials could be ceramics or other typical ablative heat shield materials. By retracting the heat shield to the retracted position, elastic energy can be stored in the folded material, which may differ from the ablative material. The ablative heat shield can also be held in the retracted position by a retaining device. The ablative heat shield can be configured to deploy from the retracted to the deployed position at least under the action of the elastic energy of the heat shield's fold lines, and additional securing devices may also be used.

[0082] The fold lines of the deployable heat shield (radiation or ablation) can be achieved by alternatives to folding, hinges, or any other suitable folding method, such as using a double-layer panel of thin, flexible material between them.

[0083] The heat shield disclosed herein may also include a fixing device for supporting the deployment structural shape of the deployable heat shield (radiation or ablation) during atmospheric reentry. The fixing device may be a reinforcing rib extending along a zigzag line.

[0084] The deployable heat shield disclosed herein may alternatively have a deployable structure with a swept-back form, wherein the angle between the longitudinal axis normal of the deployable heat shield and the ridge of the outer edge is approximately between 0 and 45 degrees, 20 and 40 degrees, 22 and 38 degrees, 25 and 35 degrees, and 27 and 32 degrees. Alternatively, the swept-back angle may be approximately 30 degrees.

[0085] Furthermore, the ratio of the deployable heat shield to the spacecraft's diameter can be any ratio. In particular, if the ratio of the polygonal central region to the outer flat diameter of the transformable polyhedron surface is 1:11, then this ratio can be greater than 2.

[0086] Although the transformable polyhedral surface of the deployable heat shield disclosed herein is identical to the mathematically defined (thickness-adaptive) flasher pattern, the heat shield disclosed herein may differ from the strict mathematical definition, although it may still perform essentially the same function, i.e., they are essentially mathematically defined. For example, a deployable heat shield may not have a polygonal central region from which the polygonal lines extend radially outward. A deployable heat shield may not have radial symmetry about the polygonal central region, such that multiple sector regions are radially symmetrical. For example, there may be intentional modifications that result in the deployable heat shield lacking radial symmetry.

[0087] The deployable heat shield technology disclosed in this paper can be scaled up from micro (<1kg) spacecraft to large (>1000kg) spacecraft, and can be adapted to the needs of atmospheric reentry from higher orbits and other planetary bodies (including the Moon and Mars) by further adjusting the area-to-mass ratio.

[0088] The deployable heat shield disclosed in this paper can also serve as an additional barrier in space, thus becoming a protective layer against these threats. Unlike other deployable structures in space, the deployable heat shield disclosed in this paper is made of elastic materials that can protect spacecraft from particle intrusion, especially in low Earth orbit / space. For example, the deployable heat shield disclosed in this paper can be used to protect spacecraft from tail debris during comet exploration missions.

[0089] The deployable heat shield disclosed in this article can also be used as radiation shielding.

[0090] The deployable heat shield disclosed in this paper can also be used as a wake shield to reduce environmental pressure and the entry of atomic oxygen, thereby improving the vacuum level in low Earth orbit. Simulation results show that at altitudes between 400 and 800 kilometers, a deployable heat shield suitable for reentry can reduce the environmental pressure behind the heat shield by two orders of magnitude. This is crucial for on-orbit manufacturing processes and scientific research requiring ultra-high vacuum levels.

[0091] The deployable heat shield disclosed in this paper can also be used as a drag sail, thereby passively reducing altitude without the use of propellant. A deployable heat shield suitable for atmospheric reentry can also passively reduce the altitude of low Earth orbit satellites by approximately 10 kilometers per month (depending on solar activity). This is extremely useful for reentry missions because it saves the propellant needed for maneuvering into low Earth orbit to prepare for reentry (the lower the starting point, the higher the accuracy of the landing zone).

[0092] The deployable heat shield disclosed in this paper can also be used as a flotation device. The relatively large displacement and high center of mass of the swept-back heat shield ensure static stability in light to moderate sea conditions. In this way, the heat shield can replace a separate flotation device deployment system, which requires additional resources and carries deployment risks.

[0093] The deployable heat shield disclosed herein can be based on any mathematically defined thickness-adaptive flasher pattern / mathematically defined transformable polyhedral surface. It is understood that Figures 1 to... Figure 6C The parameters m=5, r=2, h=2 used are chosen for illustrative purposes. Any type of flasher pattern / transformable polyhedral surface (which can be roughly defined by the mrh parameters) can be used to manufacture the deployable heat shield disclosed herein. Figures 7A to 9B Examples of other flasher patterns with alternative mrh parameters are shown.

[0094] Figure 7A and Figure 7B Another thickness-adaptive flasher pattern 40 is shown, with parameters m=5, r=1, h=2. Figure 7A The display shows a thickness-adaptive flasher pattern 40 with secondary zigzag lines. Figure 7B The displayed image shows a thickness-adaptive flasher pattern 40 without secondary fold lines.

[0095] Figure 8A and Figure 8B Another thickness-adaptive flasher pattern 50 is shown, with parameters m=4, r=3, h=1. Figure 8A The display shows a thickness-adaptive flasher pattern 50 with secondary zigzag lines. Figure 8B The displayed image is a thickness-adaptive flasher pattern 50 without secondary fold lines.

[0096] Figure 9A and Figure 9B Another thickness-adaptive flasher pattern 60 is shown, with parameters m=10, r=2, h=5. Figure 9A The display shows a thickness-adaptive flasher pattern 60 with secondary zigzag lines. Figure 9B The displayed image is a thickness-adaptive flasher pattern 60 without secondary fold lines.

[0097] Figure 10A and Figure 10B Another thickness-adaptive flasher pattern 70 with secondary fold lines omitted is shown, with parameters m=6, r=3, h=2. Figure 10AA flasher pattern 70 with superimposed dashed circles 80 is shown. Figure 10B A thickness-adaptive flamer pattern 90 is shown, which is a thickness-adaptive flamer pattern 70 cut into a dashed circle 80; that is, the thickness-adaptive flamer pattern 90 is a "circularized" thickness-adaptive flamer pattern. The outer edge 12 of the thickness-adaptive flamer pattern 90 corresponds to the dashed circle 80. Therefore, the outer edge 12 of the thickness-adaptive flamer pattern 90 corresponds to a circle (i.e., the outer edge 12 is circular). Specifically, if the transformable polyhedral surface is forced into a single plane, i.e., flat, then the outer edge 12 will be circular. This is best done during the design phase. The dimensions of the thickness-adaptive flamer pattern 90 are determined by its radius, so the outer flat diameter can be determined by the radius of the dashed circle 80. Compared to the thickness-adaptive flamer pattern 70, the thickness-adaptive flamer pattern 90 provides better aerodynamic stability. Any thickness-adaptive flamer pattern can be modified to provide an outer edge 12 that substantially corresponds to a circle, thereby benefiting from improved aerodynamic stability.

[0098] Although the invention has been described above with reference to one or more preferred embodiments, it is understood that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. A deployable atmospheric entry spacecraft heat shield having a variable polyhedral surface, comprising: The central region of the polygon; Multiple sectors are arranged around the central region, wherein each sector has multiple mountain zigzag lines, multiple valley zigzag lines, multiple faces located between the zigzag lines, and an outer edge; in, The mountain break lines include primary mountain break lines and secondary mountain break lines; The valley zigzag lines include primary valley zigzag lines and secondary valley zigzag lines; The main mountain zigzag and the main valley zigzag extend from the central region of the polygon; The heat shield is configured to unfold from a folded structure to an unfolded structure, wherein the unfolded structure refers to the heat shield naturally being in a semi-folded equilibrium position without any external force being applied. The heat insulation cover is arranged in a non-flat pattern in the unfolded structure, the pattern having multiple ridges and multiple valley ridges, each ridge corresponding to each of the multiple mountain folds, and each valley ridge corresponding to one of the multiple valley folds; The transformable polyhedral surface is configured to adopt a swept-back form in the unfolded structure, the main zigzag line having a generally constant swept-back angle from the normal of the longitudinal axis of the polygon's central region to the ridge of the outer edge in the unfolded structure, and the unfolded structure is configured such that the center of mass of the heat shield is located behind the normal of the longitudinal axis of the heat shield relative to the central region of the polygon.

2. The heat insulation cover according to claim 1, characterized in that, The heat shield is a radiation heat shield.

3. The heat insulation cover according to claim 1, characterized in that, The secondary mountain zigzag and the secondary valley zigzag extend between the primary mountain zigzag and the primary valley zigzag.

4. The heat insulation cover according to claim 1, characterized in that, The transformable polyhedral surface includes radial symmetry about the central region of the polygon, wherein the plurality of sectors are radially symmetrical.

5. The heat insulation cover according to claim 1, characterized in that, The surface of the heat insulation cover is formed as a single piece of material.

6. The heat insulation cover according to claim 1, characterized in that, The multiple zigzag lines of each sector are configured to substantially limit angular rotation about the longitudinal axis of the heat shield during use.

7. The heat insulation cover according to claim 1, characterized in that, The ratio of the diameter of the polygonal central region to the diameter of the outer flat region of the unfolded structure of the transformable polyhedron surface is 1:

11.

8. The heat insulation cover according to claim 1, characterized in that, The unfolded structure is in a stable state, and the fixing device is configured to hold the heat shield in the retracted structure.

9. The heat insulation cover according to claim 8, characterized in that, The fixing device is configured to release when an activation threshold is exceeded.

10. The heat insulation cover according to claim 1, characterized in that, The outer edge is circular.

11. A spacecraft comprising a heat shield as described in any of the preceding claims.

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