Patent ID: 12208928

DETAILED DESCRIPTION OF EMBODIMENTS

In general, this description describes a deployable spacecraft atmospheric-entry heat shield (herein, heat shield) which allows for protection and deceleration of a spacecraft during entry into an atmosphere. The spacecraft can be any type of space vehicle or flying body that is to enter or re-enter the atmosphere of the earth or another planet or a planetary moon at a high speed, for which thermal protection (and deceleration) of the spacecraft are needed.

An origami-like pattern is used to enable the heat shield to be deployed from a compact, stowed configuration to a deployed configuration before (and/or during) atmospheric-entry. Origami and similar folding techniques can efficiently pack large deployable space structures into sizes appropriate for launching into space. Traditional origami typically assumes that the thickness of folding material is negligible because in traditional origami, the material is typically paper and treating the thickness of paper as negligible is a valid assumption. However, in structural origami, the material's thickness needs to be accounted for to avoid any undesirable material deformations, and allowing for stronger structures.

FIG.1Ashows an origami pattern known as a flasher pattern1which assumes a negligible thickness. This style of origami pattern was originally coined as a ‘flasher’ by origami author 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 well understood and used within technical circles. A flasher pattern is a specific type of transformable polyhedral-surface having a plurality of sectors. A single sector2is shown inFIG.1B. Each sector has a plurality of mountain fold lines4,5, a plurality of valley fold lines6,7, and a plurality of rigid facets8lying between the fold lines. The flasher pattern1is shown to have a polygon centre region10from which mountain fold lines4, and valley fold lines6extend out to the periphery. In the case ofFIGS.1A and1B, the polygon centre region10is a pentagon.

Flasher patterns typically have major and minor fold lines, such that there are major mountain fold lines4, major valley fold lines6, minor mountain fold lines5, and minor valley fold lines7. The major mountain fold lines4are shown inFIGS.1A-2Bas heavy dotted lines. The major valley fold lines6are shown inFIGS.1A-2Bas heavy dashed lines. The minor mountain fold lines5are shown inFIGS.1A and2Aas light dotted lines. The minor valley fold lines7are shown inFIGS.1A and2Aas light dashed lines. Facets8bordering a major fold line substantially abut when the flasher pattern is in its stowed configuration. In contrast, minor fold lines can be considered as being ‘minor’ since they fold to a lesser degree, as their purpose is to allow the flasher pattern to roll up in the stowed configuration, as will be apparent from the transformations shown inFIGS.3A to6C. Consequently, the major fold lines4,6extend from the polygon central region10to an outside edge12of the flasher pattern. The minor fold lines5,7branch off from and run between the major fold lines4,6, thus creating a complex fold line pattern.

The outside edge12has a shape which generally corresponds with the shape of the polygon central region10; however, where there is a vertex in the polygon central region10there are at least two vertices13,14in a stepped configuration in the outside edge12. Each sector2of the flasher pattern1comprises at least two vertices13,14, such that one vertex13defines an angle of 90 degrees or less, and the other vertex14defines an obtuse angle (greater than 90 degrees). Within each sector2, the major fold lines4,6do not extend to at least one vertex13of the outside edge12.

Flasher patterns in general are designed to move from a stowed configuration to a deployed configuration and vice versa in a theoretical single degree of freedom. As the flasher pattern moves from a deployed configuration to a stowed configuration the sectors wrap around the longitudinal axis of the flasher pattern (for the flasher pattern1this axis is into the page ofFIG.1A, also shown by reference numeral32inFIGS.3C and5C). Flasher patterns typically have a deployed configuration which lies substantially normal to said axis of the polygon centre region. The flasher pattern's theoretical single degree of freedom is due to its intended fold line structure, although with enough force the flasher may deform due to material limitations in unintended ways. To put this another way, the fold line pattern of the flasher pattern restricts the expansion to the deployed configuration so that it can only occur in a single way/method (i.e., unwrap from the polygon centre region10), and any deviation/deformation from this single way/method of expansion may occur if a strong enough external force is applied to the flasher pattern (i.e., applying a force to bend the flasher pattern in its deployed configuration across its diameter—this is a deviation/deformation because it is unintended by the fold pattern). The flasher pattern can have a large difference in diameter between the stowed and deployed configurations, typically 1:5.

Beneficially, flasher patterns are mathematically definable. Therefore flasher patterns can be scaled in size and complexity. Flasher patterns can be defined by the parameters m, r and h:‘m’ is the rotational order of the flasher pattern, i.e., the number of sides of the polygon of the polygon centre region10(this is also equal to the number of sectors2).‘r’ is the number of rings of the flasher pattern, i.e., the number of layers in each section that will wrap around the polygon centre region10, equivalently the number of times the diagonal (the fold line(s) which extends from the polygon centre region10through the middle of each sector2) moves from bottom to top and vice versa. For example, as shown in flasher pattern1, the diagonal extends from the polygon centre region10firstly as a major mountain fold line4and secondly as a major valley fold line6. The bottom and top of the flasher pattern can be seen from the stowed configuration (seeFIGS.3A,5A, and6A) and are relative to the polygon centre region10such that the polygon centre region10can be at the top or bottom of the flasher pattern in its stowed configuration depending on orientation.‘h’ is the height of each ring of the flasher pattern. The height is in units of facets8defined by minor fold lines5,7, (i.e., before any minor fold lines5,7, are removed). For example, flasher pattern1inFIG.1Ais shown to have two rings (i.e., r=2) and extending between outside edge12and the adjacent ring are two facets8of unit height. Therefore, flasher pattern1has a height of 2. In another example, flasher pattern50inFIG.8Ais shown to have three rings (i.e., r=3) and extending between outside edge12and the closest adjacent ring is only one facet8of unit height. Therefore, flasher pattern50has a height of 1.

For example, the flasher pattern1ofFIG.1Ahas the parameters: m=5, r=2, and h=2.

To produce structural origami (that is, a flasher pattern with a finite thickness material), a flasher pattern is optimised to account for the thickness of the material. Optimisation can be performed using known thickness accommodating theories of origami, such as:Zirbel, S. A., Lang, R. J., Thomson, M. W., Sigel, D. A., Walkemeyer, P. E., Trease, B. P., Magleby, S. P., and Howell, L. L. (Oct. 3, 2013). “Accommodating Thickness in Origami-Based Deployable Arrays.” ASME. J. Mech. Des. November 2013; 135(11): 111005;Bowen, L., Trease, B., Frecker, M., & Simpson, T. (2016). “Dynamic modeling and analysis of an origami-inspired optical shield for the starshade spacecraft”. In Multifunctional Materials; Mechanics and Behavior of Active Materials; Integrated System Design and Implementation; Structural Health Monitoring [V001T01A012] (ASME 2016 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, SMASIS 2016; Vol. 1). American Society of Mechanical Engineers; and,Hossain Bhuiyan, M E, Semer, D, & Trease, B P. “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. Sep. 18-20, 2017. V001T08A016. ASME.
hereby incorporated by reference herein in their entirety.

Any material thickness can be used as long as the material can fold without breaking. It is understood that a thickness optimised flasher pattern still has all of the characteristics of a flasher pattern, thus, the term flasher pattern may also describe a thickness optimised flasher pattern. However, to avoid confusion herein the term ‘thickness accommodating flasher pattern’ is used to describe a flasher pattern which has been thickness optimised.

FIGS.2A and2Bshow a thickness accommodating flasher pattern20generated by optimising flasher pattern1ofFIG.1A(parameters m=5, r=2, h=2) for use as a deployable spacecraft atmospheric-entry heat shield. The thickness accommodating flasher pattern20maintains the same underlying characteristics as the flasher pattern1ofFIG.1A. Therefore, corresponding features have been given the same reference numerals. The thickness accommodating flasher pattern20can be described as a transformable polyhedral-surface.FIG.2Bshows the thickness accommodating flasher pattern20without the minor fold lines5,7. A configuration of the thickness accommodating flasher pattern20without the minor fold lines5,7can be used when the plurality of facets8are non-rigid/elastic. This is because the minor fold lines5,7are not required to allow the facets8to bend when the thickness accommodating flasher pattern20moves between the stowed configuration and the deployed configuration.

The thickness accommodating flasher pattern20is also an example of a fold pattern suitable for a heat shield30shown inFIGS.3A-6C. The characteristics of the thickness accommodating flasher pattern20enable the heat shield30to deploy from a stowed configuration shown inFIGS.3A,4A,5A, and6Ato a deployed configuration shown inFIGS.3C,4C,5C, and6C. “Stowed configuration” refers to when the heat shield30is folded such that the surface area/outer diameter is minimised. The “deployed configuration” is the disposition in which the shield naturally rests into a semi-folded equilibrium position without the application of any external forces. This state is known as the “no-load” shape and it is determined by a few parameters. The nature of the central polygon and the ratio between the flat outer diameter and the inscribed central polygon diameter will determine the swept-back angle that no-load shape rests in. Also, the rigidity of the shield materials and the joint stiffness will determine the angles in-between plates. The deployed configuration can also be the most stable configuration of the heat shield30, or the stable configuration of the heat shield30.

FIGS.3A-6Cshow a deployable heat shield30configured in the form of a flasher pattern, specifically, the thickness accommodating flasher pattern20.FIGS.3A-3Cshow the deployable heat shield30in an isometric view.FIG.3Ashows the deployable heat shield30in the stowed configuration.FIG.3Bshows the deployable heat shield30in a partially deployed configuration, which is a snap-shot of the deployable radiative heat shield30moving from the stowed configuration to a deployed configuration, or vice versa.FIG.3Cshows the deployable heat shield30in the deployed configuration and shows the longitudinal axis32as passing through the polygon (pentagon) central region10in the direction of intended travel of the deployable spacecraft atmospheric-entry heat shield30.

The deployable radiative heat shield30can be described as having a transformable polyhedral-surface with a plurality of sectors2, each sector2having a plurality of mountain fold lines4, a plurality of valley fold lines6, and a plurality of facets8lying between the fold lines. The transformable polyhedral-surface has only a single intended degree of freedom, and the heat shield30is configured to unfold from a stowed configuration to a deployed configuration in the single degree of freedom, as shown in the progression fromFIGS.3A to3C. The transformable polyhedral-surface can also have a polygon central region10from which fold lines4,6extend radially out to the outside or outer edge12of the heat shield30, similar to flasher pattern20. The transformable polyhedral-surface also has a radial symmetry about the polygon central region10, such that the plurality of sectors are radially symmetrical.

In the deployed configuration, the deployable heat shield30has an outer diameter of 1.3 m. For this diameter, the radiative heat shield30is designed to give a ballistic coefficient of <5 kg/m2and a mass-to-radiation area of 1 m2/kg, reducing the peak heat flux to <300 kW/m2and equilibrium temperature to ˜1300 K.

The deployable radiative heat shield30may be made from a rigid or semi-rigid material, in which case the flasher pattern of the heat shield may define minor mountain fold lines5and minor fold lines7to enable the heat shield to be deployable from a stowed configuration to a deployed configuration. Examples of such a rigid material may be certain metallic alloys such as steels, titanium alloys, nickle super-alloys and pure elemental metals such as those in the refractory group (or other materials typical to radiative heat shields) or ceramics such as silica based ceramics, and carbon-carbon (or other materials typical to ablative heat shields). Alternatively, the deployable radiative heat shield30may be made from an elastic material, in which case the deployable radiative heat shield30may not define any minor fold lines5,7, and the elastic properties of the material (of each of the facets8) can enable the deployable radiative heat shield30to be deployable from a stowed configuration to a deployed configuration. The material of the deployable radiative heat shield30can be a resilient material which can absorb energy when elastically deformed into the stowed configuration without permanent distortion, and released to a stable state upon unloading. Examples of such elastic material may be metals and metallic alloys.

The stowed configuration is shown byFIG.3A. The outside edge12of the deployable radiative heat shield30, which is apparent inFIGS.1A,2A and3B, is wrapped around the hub (i.e., the polygon (pentagon) centre region10) as the deployable radiative heat shield30is put into the stowed configuration. By stowing the deployable radiative heat shield30into the stowed configuration elastic energy can be stored in the fold lines and/or the material of the heat shield. The deployable radiative heat shield30can be retained in the stowed position by a retaining means. The heat shield can be configured to unfold from a stowed configuration to a deployed configuration (a stable state of the deployable radiative heat shield30) under at least the resilient energy of the fold lines and/or the material of the heat shield. By using a spiral wrapping of elastic material (e.g. metals/metallic alloys) stowed configuration of the flasher pattern, the deployable radiative heat shield30can be preloaded which simplifies deployment to the no-load shape (i.e. the deployed configuration/stable state) without the need for an active deployment system. In this manner the deployable heat shield30is arranged to spring outward once it is released from its deployed position.

The retaining means is used to retain the deployable heat shield30in the stowed configuration. The retaining means may be any suitable high tension string, cord, chain, binding, sheet, or the like. The retaining means can be released when an activation threshold is exceeded, such as a temperature, or altitude. The releasing process may take place automatically under certain conditions or may be microprocessor controlled based on the output of sensors, or pre-programmed. The retaining means can be released using a thermal knife system, pyro release system, or other suitable means. Once released the internal strain of the wound deployable radiative heat shield30causes rapid self-deployment to the deployed configuration.

FIG.4Ashows the deployable heat shield30in the stowed configuration from a top view.FIG.5Ashows the deployable heat shield30in the stowed configuration from a side view.FIG.6Ashows the deployable heat shield30in the stowed configuration in an isometric view when mounted on a spacecraft via the polygon central region10.

FIG.4Bshows the deployable heat shield30in the partially deployed configuration from a top view.FIG.5Bshows the deployable heat shield30in the partially deployed configuration from a side view.FIG.6Bshows the spacecraft mounted deployable heat shield30in the deployed configuration.

FIG.4Cshows the deployable radiative heat shield30in the deployed configuration from a top view.FIG.5Cshows the deployable radiative heat shield30in the partially deployed configuration from a side view.FIG.6Cshows the spacecraft mounted deployable radiative heat shield30in its fully deployed configuration.

Advantageously, flasher patterns can be designed with a large differential between the stowed and deployed diameter states (typically 1:5). That is, the diameter of the heat shield in the deployed configuration is greater than the diameter of the heat shield in the stowed configuration.

For the deployable radiative heat shield30, the ratio between the polygon central region10and outer flat-diameter of the flasher shape is 1:11. This enables the pre-deployed deployable radiative heat shield30to be compatible with a spacecraft36such as a cube format spacecraft (i.e. cubesat), nanosat or other small or large satellite which are typically subject to restricted launch volumes. As mentioned above, a ballistic coefficient of a body is a measure of its ability to overcome air resistance in flight and is equal to the mass divided by the drag coefficient per cross-sectional area. Thus, by using the deployable radiative heat shield30with a relatively large deployed diameter a lower ballistic coefficient can be achieved. The inventors have found that a lower ballistic coefficient can reduce the peak heating of a heat shield into the 100 s of kW/m2level. Therefore, the deployable radiative heat shield30can decrease the ballistic coefficient and increase the radiative area-to-mass ratio to a level where the equilibrium temperature during the peak heating of a low Earth orbit re-entry vehicle is lower than the melting point of many metals/metallic alloys that can also withstand the aerodynamic and deployment stresses during a flight. Examples of such metals/metallic alloys are steels, titanium alloys, nickle super-alloys and pure elemental metals such as those in the refractory group.

As shown inFIGS.6A-6C, when deployed the deployable radiative heat shield30is considerably larger in two dimensions than the attached spacecraft36and hence extends beyond the spacecraft's primary volume. This enables the deployable radiative heat shield30to radiate heat both forwards (into the direction of flight) and backwards, which significantly increases the useful radiative area per kilogram of heat shield material. The backward facing sections of the deployable radiative heat shield30are also radiating to a colder environment than the front facing sections (during atmospheric-entry), which further increases heat radiation efficiency.

Advantageously, the deployed configuration of the deployable radiative heat shield30leaves a non-flat pattern with significant mountain4and valley6ridges that increase the total radiative surface area of the deployable radiative heat shield30without affecting the total drag area, this allows these two parameters, i.e., total radiative surface area and drag area, to be controlled separately.

The deployable radiative heat shield30therefore benefits from increasing the radiative surface area-to-mass ratio and has twin advantages in lowering the peak heat flux (associated with the ballistic coefficient) and increasing the radiative area, which both lead to a lower equilibrium temperature that enables the use of less exotic materials (e.g. ablative materials such as, silica ceramics or carbon-carbon which are hard to produce and machine) for use in the deployable radiative heat shield30. A low equilibrium temperature during the peak heating of a low Earth orbit (LEO) re-entry of the radiative heat shield30can be lower than the melting point of many metals and metallic alloys.

Advantageously, with a low ballistic coefficient, the terminal velocity reduces in atmosphere to a level where a separate fabric parachute may not be required. This is a significant advantage as the deployment of fabric parachutes for atmospheric-entry spacecraft typically require mortar systems and there is significant risk of failure in parachute deployment. Fabric parachutes also reduce the accuracy of landing zone estimation due to the transient inflation and drag properties.

The transformable polyhedral-surface (e.g. flasher pattern) of the deployable radiative heat shield30can be formed as an integral sheet material, or with materials with substantially similar thermal conductivity. This allows thermal energy to easily distribute around the deployable radiative heat shield30and smooths out temperature hot spots, reducing the risk of uneven heating damaging the deployable radiative heat shield30. For example, mountain fold lines4naturally absorb more thermal energy during atmospheric-entry, however, this is distributed through the sheet material(s) to valley fold-lines6and areas which absorb less thermal energy. Metals/metal alloys generally have high thermal conductivity and are therefore suitable materials for the deployable radiative heat shield30. The overall shape of the deployable heat shield30can be etched as a single monolithic piece using a computer controlled metal working tool. This single monolithic piece may then be coated with a high emissivity (>0.8) and low absorptive coating (<0.1) to further reduce the peak heating temperature.

Radiative heat shields in general are more easily reused since they do not rely on surface vaporisation, as opposed to ablative heat shields, which rely on surface vaporisation. Beneficially, the deployable radiative heat shield30has a large deployed diameter state and therefore a relatively large radiative area in comparison to typical fixed sized (i.e., non-deployable) radiative heat shields. A larger radiative area enables a greater rate of heat to be radiated away from the system and hence the balance between incoming and outgoing heat occurs at a lower equilibrium temperature.

The transformable polyhedral-surface (e.g., flasher pattern) of the deployable radiative heat shield30adopts a swept back form in the deployed configuration as shown inFIG.5C. The swept back form is a result of the flasher pattern's m-r-h parameters. The swept back form shapes the deployable radiative heat shield30into a generally frusto-pyramidal shape as shown byFIG.5C.

This swept back angle is used to change the centre of pressure along the longitudinal axis32(i.e., the flight axis), so it is behind the polygon central region10and/or behind the centre of mass of the spacecraft36. This significantly improves the aerostability of the spacecraft36during all stages of atmospheric-entry. For example a ratio of 1:11 between the polygon central region10and no-load outer flat-diameter of the transformable polyhedral-surface gives a natural swept back angle of substantially 30 degrees, as shown inFIG.5C.FIG.5Cshows a swept back form of the deployable radiative heat shield30with an angle between the normal to the longitudinal axis and a mountain ridge at the outside edge of the heat shield of 30 degrees. This further enables passive aerostability which reduces requirements on the spacecraft36attitude control system to maintain safe pointing during atmospheric-entry (i.e., opposite to the direction of flow, which keeps the platform best protected from the heat). Advantageously, the non-flat pattern with significant mountain4and valley6ridges (formed via the mountain and valley fold lines) of the deployed configuration of the deployable radiative heat shield30also allows for improved passive aerostability.

The transformable polyhedral-surface (e.g., flasher pattern) of the deployable radiative heat shield30is configured such that the plurality of fold lines4,5,6,7of each sector substantially restrict angular rotation about a longitudinal axis32of the deployable radiative heat shield30. This prevents the deployable radiative heat shield30(and the spacecraft36) from experiencing a rotation during atmospheric-entry, which leads to a higher aerostability in the longitudinal axial direction and easier aerodynamic analysis. Put another way, the deployed configuration shape of the deployable radiative heat shield30is approximately axisymmetric. This provides a flight stabilising function and also resists collapsing back to the stowed position because the air pressure is distributed on opposite sides of the deployable radiative heat shield30due to the mountain4and valley6ridges. This contributes to the deployable radiative heat shield30being able to hold the deployed configuration shape without additional holding fixtures.

As mentioned above the material of the deployable radiative heat shield30can comprise metal and metal alloys (herein metals). These have many advantages, for example, metals can be worked and formed into customised shapes significantly easier than brittle silica tiles. Metals are not brittle and allow for thermal expansion without cracking. The plastic deformation of metals can also be used to define the desired deployed configuration (i.e., no-load shape) without additional holding fixtures, or additional minor fold lines5,7. Metals can be coated with a wider range of materials to improve the corrosion and radiation properties. Metals have a considerably lower sourcing cost and can be machined using more ubiquitous tools, leading to a significantly reduced cost per m2. Metals have predictable and highly linear stress-strain properties over temperature that aid in strength analysis.

The deployable radiative heat shield30can be mounted to the spacecraft36using the polygon central region10onto a custom shield mount that is connected to the forward facing panel of the spacecraft36. Other mounting methods are possible and would be apparent to the skilled person.

Turning now to alternative heat shields, a heat shield can be an ablative heat shield with many of the characteristics, configurations, and advantages of the deployable radiative heat shield30, as would be apparent to the skilled person. Ablation requires highly specialised heat shield materials that have a low vaporisation threshold and high thermal capacity. Ablation dominated heat shields are not typically reusable due to the significant erosion of the material that occurs during atmospheric-entry. The ablative heat shield may be made from a rigid material, in which case the flasher pattern of the heat shield may define minor mountain fold lines and minor fold lines to enable the heat shield to be deployable from a stowed configuration to a deployed configuration. Examples of such a rigid material may be ceramics, or other materials typical to ablative heat shields. By stowing the heat shield into the stowed position elastic energy can be stored in the fold lines materials which may be different to the ablative material. The ablative heat shield can also be retained in the stowed position by a retaining means. The ablative heat shield can be configured to unfold from a stowed configuration to a deployed configuration under at least the resilient energy of the fold lines of the heat shield, although additional holding fixtures may be used.

Fold lines of a deployable heat shield (radiative or ablative) can be achieved with surrogate folds, hinges, or any other suitable folding means, e.g., double layered panels with a thin flexible material between them.

The heat shields disclosed herein may additionally comprise holding fixtures, which may be used to support the deployed configuration shape of a deployable heat shield (radiative or ablative) during atmospheric-entry. Holding fixtures may be reinforcing ribs extending along fold lines.

The deployable heat shields disclosed herein may alternatively have a deployed configuration with a swept back form, with an angle between the normal to the longitudinal axis and a mountain ridge at the outside edge of the deployable heat shield between substantially 0-45 degrees, 20-40 degrees, 22-38 degrees, 25-35 degrees, 27-32 degrees. Alternatively, the swept back angle may be substantially 30 degrees.

Alternatively, the diameter ratio of the deployable heat shield to the spacecraft can be any ratio. In particular it may be greater than 2, this would be the case if there were a ratio of 1:11 between the polygon central region and outer flat-diameter of the transformable polyhedral-surface.

Although the transformable polyhedral-surface of the deployable heat shields disclosed herein are shown to be the same as mathematically defined (thickness accommodating) flasher patterns, the heat shields disclosed herein may vary from a strict mathematical definition while still performing substantially the same function, i.e., they are substantially mathematically defined. For example, the deployable heat shields may not have a polygon central region from which fold lines extend radially out. The deployable heat shields may not have a radial symmetry about the polygon central region, such that the plurality of sectors are radially symmetrical. For example, there may be intentional modifications which result in the deployable heat shields not having radial symmetry.

The deployable heat shield technology disclosed herein is scalable from pico (<1 kg) to large (>1000 kg) spacecraft and can be adapted by further adjusting the area-to-mass ratio for re-entry from higher orbits and other planetary bodies, including the Moon and Mars.

The deployable heat shields disclosed herein can also be used as an additional barrier whilst in space, and can consequently behave as a layer of protection against those threats. Differently from other space-deployable structures, the deployable heat shields disclosed herein can be made from resilient materials that can potentially protect a spacecraft from incoming particles, particularly in LEO/space. For example, the deployable heat shields disclosed herein may be used to protect a spacecraft from tail debris when used in comet exploration missions.

The deployable heat shields disclosed herein can also be used as a radiation shield.

The deployable heat shields disclosed herein can also be used as a wake shield to reduce the ambient pressure and atomic oxygen ingress for improved vacuum when in LEO. Simulation results have shown that a deployable heat shield suitable for surviving re-entry also reduces the ambient pressure behind that shield by two orders of magnitude when at altitudes between 400 km and 800 km. This is important for in-orbit manufacturing processes and scientific research that require ultra-high vacuum levels.

The deployable heat shields disclosed herein can also be used as a drag sail to passively decrease the altitude without the use of propellant. A deployable heat shield suitable for surviving re-entry would also lead to a passive reduction in the altitude of a LEO satellite by ˜10 km/month (dependent upon solar activity). This is useful for re-entry missions as it saves on the propellant required to manoeuvre into a low orbit to prepare for re-entry (where a lower starting point leads to a higher precision of landing zone).

The deployable heat shields disclosed herein can also be used as a flotation device, where the large relative water displacement of the swept back shield and the high centre of volume ensures static stability in light to moderate seas. This allows the heat shield to replace the need for a separate flotation device deployment system which would require additional resources and come with deployment risks.

The deployable heat shields disclosed herein function can be made based on any mathematically definable thickness accommodating flasher pattern/mathematically definable transformable polyhedral-surface. It will be understood that the parameters m=5, r=2, h=2 used forFIGS.1-6Cwas selected for illustrative purposes, and any type of flasher pattern/transformable polyhedral-surface which can be substantially defined by m-r-h parameters may be used to create a deployable heat shield as disclosed herein. Examples of other flasher patterns with alternative m-r-h parameters are shown with reference toFIGS.7A-9B.

FIGS.7A and7Bshow an alternative thickness accommodating flasher pattern40with parameters of m=5, r=1, h=2.FIG.7Ashows the thickness accommodating flasher pattern40with the minor fold lines shown, andFIG.7Bshows the thickness accommodating flasher pattern40without the minor fold lines shown.

FIGS.8A and8Bshow an alternative thickness accommodating flasher pattern50with parameters of m=4, r=3, h=1.FIG.8Ashows the thickness accommodating flasher pattern50with the minor fold lines shown, andFIG.8Bshows the thickness accommodating flasher pattern50without the minor fold lines shown.

FIGS.9A and9Bshow an alternative thickness accommodating flasher pattern60with parameters of m=10, r=2, h=5.FIG.9Ashows the thickness accommodating flasher pattern60with the minor fold lines shown, andFIG.9Bshows the thickness accommodating flasher pattern60without the minor fold lines shown.

FIGS.10A and10Bshow an alternative thickness accommodating flasher pattern70with the minor fold lines omitted, and defined by parameters m=6, r=3, h=2.FIG.10Ashows the flasher pattern70with an overlayed dashed circle80.FIG.10Bshows a thickness accommodating flasher pattern90which is the thickness accommodating flasher pattern70cut to the dashed circle80i.e., the thickness accommodating flasher pattern90is a ‘circularized’ thickness accommodating flasher pattern. The outside edge12of the thickness accommodating flasher pattern90corresponds to the dashed circle80. Therefore, the outside edge12of the thickness accommodating flasher pattern90corresponds to a circular shape (i.e., the outside edge12is circular). Specifically, if the transformable polyhedral-surface was forced into a single plane, i.e. flat, then the outside edge12would be a circle. This is preferably done in the design phase. The thickness accommodating flasher pattern90is dimensioned based on its radius such that the outer flat-diameter can be defined by the radius of the dashed circle80. The thickness accommodating flasher pattern90can provide improved aerostability over the thickness accommodating flasher pattern70. Any thickness accommodating flasher pattern may be modified to provide an outside edge12which substantially corresponds to a circle, and then benefit from improved aerostability.

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