Patent Application
20120175467
The present disclosure relates to micrometeoroid and orbital debris shielding and thermal management of exposed equipment surfaces associated with space missions.
For space and low Earth orbit (LEO) missions, micrometeoroid and orbital debris (MMOD) protection for exposed equipment surfaces associated with spacecraft, space-borne instruments, space stations and orbiting fuel depots is critical to mission safety and success. There are numerous documented cases of MMOD damage causing critical equipment mission impairment or failure in space. Moreover, the risk of damage to equipment from orbital debris (OD) steadily increases with the ever-increasing amount of orbital debris resulting from space missions and space defense operations.
A number of existing MMOD protective shields have a Whipple-type design that include an exposed aluminum front bumper shield and an aluminum rear wall held at a fixed spacing by rigid standoffs. These shields, which may further include layers of KEVLAR and/or NEXTEL material, are referred to as Stuffed Whipple Shields. The effectiveness of the Whipple-type shields, as well as other multi-layer shield designs, is sensitive to the separation distance between the exposed bumper shield and the rear wall of the MMOD shield. Additionally, the rigid metal standoffs necessary to maintain separation between the bumper shield and the rear wall are thermally conductive and add additional weight to the Whipple-type shields. Further, the heavy materials of standoffs may introduce undesired additional debris ejecta as a result of particle impact on the standoff due to the spalling of the underside of the front bumper or due to damage to one of the shield's metal structural standoffs.
Another category of existing MMOD protective shield designs, the multishock shield design, replaces the aluminum front bumper of the Whipple-type shield with a series of NEXTEL bumpers as well as a single or multiple internal aluminum bumpers and a Whipple-type aluminum rear wall. Although the weight and damaging secondary ejecta associated with particle impacts to the multishock shield design are reduced relative to the Whipple-type shields, the multishock shields also require heavy and thermally conductive structural standoffs to maintain separation between layers. None of the Whipple-type shield, Stuffed Whipple Shield, or multishock shield designs provides the thermal insulation required for many spacecraft, satellite and space-borne instrument applications.
Multilayer insulation (MLI) blankets have also been used to provide some measure of protection against micrometeoroid and orbital debris impacts in addition to the MLI blanket's primary function of providing a barrier against thermal radiation and conduction. MLI blankets typically include multiple layers of thin KAPTON or MYLAR material and may further include one or more outer layers of a reinforcing material, such as NEXTEL, to enhance the MLI blanket's ability to shield the underlying structure against micrometeoroid and orbital debris impacts. Despite having a relatively low areal density (i.e. mass per unit area of shielding material), MLI blankets provide limited protection against micrometeoroid and orbital debris impacts. However, this low areal density also limits the MLI blanket's ability to stop heavier orbital debris, thus precluding the use of MLI blankets as the sole MMOD shield for an orbiting device or vehicle. In addition, because MLI blankets typically lack rigid structural standoffs to maintain a precise separation distance between layers, the separation between layers may vary considerably, resulting in relatively unpredictable layer spacing, which may influence the MLI blanket's effectiveness as a MMOD shield.
A need exists for a structure that integrates the elements of a MMOD shield, while inhibiting the transfer of thermal energy between the equipment to be protected by the structure and the surrounding volume. In addition, the need exists for an integrated MMOD shield and thermal radiation barrier that is relatively lightweight and compressible to facilitate transport, and that may be deployed into a structure having predictable and controlled separation between layers using simple tools.
The foregoing examples of the related art and limitations read therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.
The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other improvements.
In one aspect of the present invention, a micrometeoroid and orbital debris/integrated multi-layer insulation (MMOD/IMLI) structure is provided. The MMOD/IMLI structure includes a first ballistic layer, a plurality of first spacers supporting the first ballistic layer, and an IMLI sub-assembly. The IMLI sub-assembly includes a first thermal radiative barrier layer, a plurality of second spacers supporting the first thermal radiative barrier layer, a second thermal radiative barrier layer adjacent to the plurality of second spacers opposite to the first thermal radiative barrier layer and a plurality of third spacers supporting the second thermal radiative barrier layer. The MMOD/IMLI structure simultaneously provides shielding against high-velocity projectiles and thermal insulation to the equipment surface.
In another aspect, a method for simultaneously insulating an equipment item that includes an equipment surface as well as shielding the equipment surface against high-velocity projectiles is provided. The method includes providing an MMOD/IMLI structure and situating the MMOD/IMLI structure over the equipment surface. The MMOD/IMLI structure includes a ballistic layer and an IMLI sub-assembly. The IMLI sub-assembly includes a lower IMLI surface and a plurality of spacers supporting the lower IMLI surface; the plurality of spacers are arranged in a grid pattern.
In an additional aspect, a micrometeoroid and orbital debris/integrated multi-layer insulation (MMOD/IMLI) structure is provided that includes at least one flexible ballistic layer and at least one flexible thermal insulation layer. The at least one flexible ballistic layer and the at least one flexible thermal insulation layer are separated by a plurality of spacers. The plurality of spacers define at least one leg extending obliquely between the at least one flexible ballistic layer and the at least one flexible thermal insulation layer.
In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following descriptions.
Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than limiting.
Corresponding reference characters and labels indicate corresponding elements among the view of the drawings. The headings used in the figures should not be interpreted to limit the scope of the claims.
A Micrometeoroid Orbital Debris Integrated Multi layer Insulation (MMOD/IMLI) structure is provided that overcomes many of the existing MMOD shield limitations and provides both MMOD protection and thermal management not achievable by any single conventional shield or insulation structure. The MMOD/IMLI structure provides a multifunctional MMOD/protective and thermal management structure for use on spacecraft, orbital fuel depots, space-borne instruments, space laboratories or habitats, satellites, as well as terrestrial applications including ballistic shields and insulation. The MMOD/IMLI structures may be used to protect equipment operating within the Earth's atmosphere, in low Earth orbit, in lunar orbit, and in any other terrestrial or space-based environment. The MMOD/IMLI structure includes one or more IMLI layers or sub-assemblies and one or more ballistic layers arranged in an interspersed and layered pattern. Each IMLI sub-assembly may include one or more layers of thermal radiant barriers including, but not limited to, metalized MYLAR sheets. Each ballistic layer may include one or more layers of high-strength ballistic material including, but not limited to, KEVLAR and/or NEXTEL.
In addition, the adjacent layers of material within the MMOD/IMLI structure may be physically attached to one another or otherwise separated and supported by way of discrete spacers. These spacers also maintain a separation distance between the adjacent layers of the MMOD/IMLI structure to provide controlled, repeatable, layer-to-layer spacing in a robust self-supporting structure. The spacers are typically constructed of a lightweight and high strength material and are situated in a predetermined pattern to reduce thermal conduction from layer to layer and to enhance structural integrity.
In use, the IMLI subassemblies of the MMOD/IMLI structure may be configured to inhibit the gains and losses of thermal energy to and from the equipment to be protected by the structure, and the ballistic layers are configured to provide impact protection against projectiles including, but not limited to, micrometeoroids and/or orbiting debris. However, the IMLI sub-assemblies may further provide limited protection against projectiles, and the ballistic layers may further provide limited insulative properties. The MMOD/IMLI structure derives a synergistic benefit as a result of the incorporation of the IMLI sub-assemblies and ballistic layers in a single integrated structure. This synergistic benefit further results in enhanced performance, reduced weight, and reduced volume of the MMOD/IMLI structure relative to existing separate MMOD shields and thermal protection structures.
The IMLI sub-assemblies and ballistic layers of the MMOD/IMLI structure are modular by design and may be arranged in virtually any configuration according to need. The MMOD/IMLI structure may be configured to fulfill mission-specific requirements for both thermal and impact protection requirements, among other requirements. These mission-specific requirements may be based on any one or more of at least several factors, including but not limited to: the duration of the mission, the characteristics of the equipment to be protected by the MMOD/IMLI structure, the altitude and inclination of the equipment in orbit, the MMOD fluence (i.e. debris flux) at the given altitude and inclination of the equipment, the probability of no penetration (PNP) requirement for the mission, the critical particle diameter to be protected against, other relevant characteristics of the mission environment such as solar flares, and any combination thereof.
Typically, thermal performance criteria will govern the design and arrangement of the IMLI sub-assemblies in the MMOD/IMLI structure. Similarly, impact protection requirements including, but not limited to, PNP requirements may govern the design and arrangement of the ballistic layers in the MMOD/IMLI structure. The ballistic layers and IMLI sub-assemblies may be configured in any order, number or thickness to meet application requirements.
For example, the mission-specific requirements for cryogenic applications including, but not limited to, orbiting cryogenic propellant tanks may include: the probability of penetration by projectiles over its mission duration, current MMOD fluence for the mission location, and the thermal requirements to minimize cryogenic propellant boil-off from the tank over the duration of the mission. The MMOD fluence may be combined with characteristics of the equipment including, but not limited to, the spacecraft area and geometric factors to estimate the probability of projectile impacts. The controlled inter-layer spacing and repeatable configuration of the MMOD/IMLI structure enhances the accuracy of the modeling of ballistic and thermal performance, thereby facilitating the process of designing the MMOD/IMLI structure.
An embodiment of a MMOD/IMLI structure 100 is illustrated in
A plurality of discrete spacers 108A-108Z separate and support each of the adjacent layers, including the thermal radiant barrier layers 106A-106J and ballistic layers 104A-104C. Each of the plurality of discrete spacers 108A-108Z is attached to the layers situated immediately above and below of each spacer 108A-108Z, resulting in the attachment of all layers of the MMOD/IMLI structure 100 to form a single integrated structure. In addition, the discrete spacers 108A-108Z maintain the adjacent layers at a predetermined distance, forming interlayer volumes 110A-110M bounded by the corresponding layers situated immediately above and below the interlayer volumes 110A-110M.
In one aspect, the lowermost spacers 108M and 108Z may be attached to both the lowermost layer 106J and to the underlying equipment surface 112, thereby attaching the MMOD/IMLI structure 100 to the equipment to be protected and insulated, as illustrated in
Aspects of the MMOD/IMLI structure, including the ballistic layers, IMLI sub-assemblies, and spacers, as well as methods of producing the MMOD/IMLI structure are described in detail below.
The MMOD protection imparted by the MMOD/IMLI structure is influenced by the distribution of the ballistic layers throughout the structure. The MMOD/IMLI structure may be designed to stop high-velocity projectiles within the layers of the MMOD/IMLI structure or prior to full penetration of the underlying equipment surface. Non-limiting examples of high-velocity projectiles for which the MMOD/IMLI structure may be designed to stop include micrometeoroids and orbital debris. In some cases, limited damage to the protected equipment may be tolerated without compromising the function of the equipment. In these cases, the MMOD/IMLI structure may be designed to reduce the impact of high-velocity projectiles to within allowable ranges.
Without being limited to any particular theory, in one aspect the ballistic layers and the IMLI sub-assemblies are designed to break up the incoming particle or change the particle's state, thus generating smaller particles, a debris cloud, and/or a plasma.
Due to the momentum of the impact, a primary debris cloud 206 formed from the combination of particle fragments and ballistic layer fragments may pass into the interlayer volume 110A. The fragments within the primary debris cloud 206 may include fragments with a variety of sizes and masses, and individual fragments may be in a solid phase, liquid phase, and/or plasma phase. Because a significant amount of energy is absorbed by the ballistic layer 104A at impact and the mass of the fragments is reduced relative to the original projectile 202, the fragments within the primary debris cloud 206 travel at a velocity that may be significantly slower than the impact velocity of the original projectile 202. As a result, the impact of the fragments within the primary debris cloud 206 is less likely to penetrate the underlying ballistic layer 104B.
In some cases, one of more of the fragments within the primary debris cloud 206 may possess sufficient mass and velocity to perforate the underlying ballistic layer 104B in one or more regions. In this case, secondary debris clouds 208 and 210 may pass through the ballistic layer 104B into the interlayer volume 110B. The radiant barrier layer 106A beneath ballistic layer 104B may stop all particles of the secondary debris cloud 208, as illustrated in
Although the penetration of three layers of the MMOD/IMLI structure 100 are illustrated in
The primary stopping power of the MMOD/IMLI structure may be influenced by factors including, but not limited to, layer spacing and the strength and tenacity of the materials of the ballistic layers. In addition, the radiant barrier layers of the IMLI sub-assemblies may enhance the stopping power of the MMOD/IMLI structure. Clearly, the size, velocity and angle of impact of the projectile may further affect the stopping power of the MMOD/IMLI structure.
In an aspect, the materials and dimensions of the ballistic layers may be selected in order to enhance the stopping power of the MMOD/IMLI structure. For example, the upper ballistic layers (those nearer the impact surface 104A) of the MMOD/IMLI structure may be formed from a more rigid or layered material in order to induce the fragmentation and/or phase change of an incoming projectile upon impact. In addition, the lower ballistic layers (those nearer the equipment surface to be protected and insulated) may be formed from a more resilient material capable of absorbing energy through deformation of the ballistic layer in order to enhance the stopping power of the lower ballistic layers against lower kinetic energy debris cloud particles.
a. Outer Ballistic Layers
In an aspect, the outer ballistic layers are configured to break up an incoming projectile upon impact into smaller fragments, to change the phase of the projectile and/or fragments from a solid phase into a liquid (molten) phase and/or plasma phase, and any combination thereof. In addition, the materials of the ballistic layers, in particular the outer ballistic layers, may resist spalling and/or may readily convert to a plasma phase, thereby limiting the kinetic energy of any debris ejecta formed during the impact of a projectile with a ballistic layer. To this end, the materials used to construct the outer ballistic layers may be selected based on one or more of at least several desired characteristics, including but not limited to: light weight, high yield stress, high hardness, and high Young's modulus. In addition, because all ballistic layers may function as radiant barrier layers in conjunction with the IMLI sub-assemblies, the materials of the ballistic layers may be selected based on one or more additional thermal characteristics, including, but not limited to, low thermal conductivity and low thermal emissivity. Alternatively, the outer ballistic layer may be high density, whereas other layers and the overall structure may be low density.
Non-limiting examples of materials suitable for the outer ballistic layers include: ceramic cloths such as NEXTEL; fiberglass; aluminum plating; ceramic panels; ballistic armor panels, and other laminate armor materials comprising layers of metal, ceramic, and/or plastic materials. In addition, the outer ballistic layer materials may include energy-absorbing materials, including but not limited to KEVLAR and SPECTRA fiber.
The outer ballistic layers may be of any thickness depending on one or more of at least several factors including, but not limited to, the properties of the materials within the ballistic layer, the position of the ballistic layer within the MMOD/IMLI structure, the spacing of layers, the total number of layers in the MMOD/IMLI structure, the desired performance of the MMOD/IMLI structure, the desired weight of the MMOD/IMLI structure, and any combination thereof. In one aspect, if the outer ballistic layer is a NEXTEL layer, the thickness of the outer ballistic layer may range from about 0.25 mm to about 6.0 mm.
Each outer ballistic layer may include a single layer of a single material, or each outer ballistic layer may include two or more layers of a single material or multiple materials. The materials may either be situated immediately adjacent to one another, or the materials may be bonded into a single sheet with no space between the two or more attached layers. For example, an outer ballistic layer may include a NEXTEL sheet immediately adjacent to a KEVLAR sheet.
In another aspect, the materials of the outer ballistic layers may be modified to enhance the performance of these layers. For example, the materials of the outer ballistic layers may be metalized to reduce their thermal emissivity. Additionally, the various layers and/or spacers may be metalized such that the structure may provide electrical grounding, electromagnetic interference (EMI) shielding, shielding from static electricity, and the like, improving over conventional grounding techniques that involve a bolt which may both reduce thermal performance through high thermal conduction, and compromise the structure's MMOD shielding effectiveness by spalling when impacted by a projectile.
b. Inner Ballistic Layers
In an aspect, the inner ballistic layers are configured to absorb the energy of impinging debris clouds and ejecta generated by the multiple impacts of the projectile and subsequent primary, secondary, and subsequent debris clouds and ejecta with the ballistic layers and/or IMLI sub-assemblies situated above the inner ballistic layers. To this end, the materials used to construct the inner ballistic layers may be selected based on one or more of at least several desired characteristics, including but not limited to: light weight, high yield stress, lower Young's modulus relative to the materials of the outer ballistic layers, and any combination thereof. In addition, the materials of the inner ballistic layers may be selected based on one or more additional thermal characteristics, including, but not limited to, low thermal conductivity and low thermal emissivity.
Non-limiting examples of materials suitable for the inner ballistic layers include: cloths of aramid fibers such as KEVLAR, SPECTRA fiber, and TECHNORA. In addition, the inner ballistic layer materials may include any of the outer ballistic layer materials described herein above.
The inner ballistic layers may be of any thickness depending on one or more of at least several factors including, but not limited to, the properties of the materials within the ballistic layer, the position of the layer within the MMOD/IMLI structure, the spacing of layers, the total number of layers in the MMOD/IMLI structure, the desired performance of the MMOD/IMLI structure, the desired weight of the MMOD/IMLI structure, and any combination thereof. In one aspect, if the inner ballistic layer is a KEVLAR layer, the thickness of the inner ballistic layer may range from about 0.25 mm to about 6.0 mm.
Each inner ballistic layer may include a single layer of a single material, or each inner ballistic layer may include two or more layers of a single material or multiple materials. The layers may be situated immediately adjacent to each other, or the layers may be bonded into a single sheet with no space between the two or more attached layers. For example, an inner ballistic layer may include a NEXTEL sheet and a KEVLAR sheet.
In another aspect, the materials of the inner ballistic layers may be modified to enhance the performance of these layers. For example, the materials of the inner ballistic layers may be metalized to reduce their thermal emissivity or provide for an electrically grounded MMOD/IMLI structure.
In an aspect, the MMOD/IMLI structure incorporates the discrete spacer design and the insulation structures of the Integrated Multilayer Insulation (IMLI) and Load Responsive Integrated Multilayer Insulation (LRMLI) disclosed in U.S. Pat. No. 7,954,301, Published U.S. patent application Ser. No. 12/493,852 (CIP), and Published PCT application PCT/US/2010/039352, all of which are hereby incorporated by reference in their entirety.
The thermal performance of the MMOD/IMLI structure is enhanced by the inclusion of one or more IMLI sub-assemblies including one or more low emissivity thermal radiant barrier layers separated by a plurality of spacers. The spacers may provide a controlled separation between the thermal radiant barrier layers to prevent thermal shorting, while also reducing the thermal conduction from layer to layer. The IMLI sub-assembly may be designed such that the insulation performance is relatively unaffected by compression effects due to gravity. As a result, the low-gravity performance of the IMLI sub-assembly may be better predicted from ground testing, and the regular gravity and low gravity performance of the IMLI sub-assembly may be more consistent and less sensitive to labor and assembly variations. The use of the spacers to support the thermal radiant barrier layers may also facilitate the automation of the IMLI sub-assembly fabrication and handling.
Referring again to
In addition, the number of IMLI sub-assemblies 102A and 102B may vary depending on the desired performance of the MMOD-IMLI structure 100 as well as the number of layers in each IMLI sub-assembly. In an aspect, the number of IMLI sub-assemblies incorporated into an MMOD/IMLI structure 100 may range from about 1 to about 10 or more sub-assemblies, resulting in a total number of thermal radiant barrier layers within the ranges described herein above. The number of IMLI sub-assemblies included in the MMOD/IMLI structure 100 may also be affected by the number of intervening ballistic layers 104C.
The IMLI sub-assemblies incorporated into an MMOD/IMLI structure may be identical to each other in design, or may vary in design between individual IMLI sub-assemblies. For example, design elements including, but not limited to the number of layers, the layer thickness and constituent material of the thermal radiant barrier layers, the spacing between adjacent thermal radiant barrier layers, the arrangement of spacers such as the arrangement of spacers within each level or the offset of support arrangements between successive levels, the intervening ballistic layers, and any combination thereof may vary between individual IMLI sub-assemblies incorporated into an MMOD/IMLI structure.
In another aspect, the sequencing of the one or more IMLI sub-assemblies incorporated into a MMOD/IMLI structure may further vary depending upon the desired performance of the MMOD/IMLI structure. For example, the MMOD/IMLI structure may include one or more single IMLI sub-assemblies alternating with one or more ballistic layers. In another example, the MMOD/IMLI structure may include a layer of IMLI sub-assemblies that include two or more consecutive IMLI sub-assemblies alternating with one or more ballistic layers.
a. Thermal Radiant Barrier Layer Materials
The thermal radiant barrier layers comprise thin sheets of material designed to inhibit the thermal radiation flux from/to the equipment situated beneath the MMOD/IMLI structure. The materials used to form the thermal radiant barrier layers are selected based on one or more of at least several factors including, but not limited to: light weight, low thermal conductance, low emissivity, resistance to damage during fabrication, transport, and subsequent use, and any combination thereof. Non-limiting examples of materials suitable for use as thermal radiant barrier layers include metalized polymers with a low emissivity surface, such as silverized, goldized, and/or aluminized MYLAR (polyethylene terephthalate polyester film) or KAPTON (polyimide film); polymers with a non-metallic coating such as vanadium oxide; layers with associated quantum dots; thin, low emissivity metal foils such as aluminum foil or tungsten foil; and any combination thereof.
b. Thermal Radiant Barrier Layer Thickness
The thickness of each thermal radiant barrier layer may be selected based on any one or more of at least several factors including, but not limited to: material used to construct the thermal radiant barrier layer; light weight; reduction of thermal conduction pathways within the MMOD/IMLI structure; reduction of layer emissivity; resistance to tearing; location within the IMLI sub-assembly; and any combination thereof. In addition, any one or more of at least several factors related to MMOD protection may be used to select the thickness of the thermal radiant barrier layer, including but not limited the ultimate stress and/or energy absorbing abilities of the layer's material.
The thickness of each thermal radiant barrier layer may range from about 0.1 mils to about 20 mils. In an aspect, the IMLI sub-assembly may include a bottom (innermost) layer that may comprise a sheet of metal or polymer ranging from about 1 mil to about 20 mils in thickness to provide a relatively sturdy structural base for the IMLI sub-assembly. This structural base may be situated directly against the surface of the underlying equipment to be protected in one aspect. In another aspect, this structural base may be situated exterior to the equipment such that the MMOD/IMLI structure does not directly contact the equipment. In addition, a layer of spacers may be attached to the base layer. In another aspect, the interior layers of the IMLI sub-assembly may range from about 0.1 mils to about 5 mils in thickness. In yet another aspect, the IMLI sub-assembly may include a top (outermost) layer ranging from about 1 mil to about 20 mils in thickness.
c. Separation Distance Between Adjacent Barrier Layers
The separation distance between adjacent thermal radiant barrier layers may influence the thermal performance of the IMLI sub-assemblies as well as other characteristics including but not limited to weight and structural integrity. In one aspect, the separation distance between adjacent thermal radiant barrier layers may range from about 40 mils to about 80 mils (i.e. about 1 mm to about 2 mm). In another aspect, the thermal radiant barrier layers may have a layer spacing of about 10 layers per cm. The separation distance between adjacent thermal radiant barrier layers may be governed by the height of the spacers situated between the adjacent layers of the IMLI sub-assembly.
In an aspect, the MMOD/IMLI structure includes a plurality of spacers situated between adjacent layers within the MMOD/IMLI structure including, but not limited to, between adjacent thermal radiation barrier layers within each IMLI sub-assembly, between a ballistic layer and an adjacent IMLI sub-assembly, between adjacent ballistic layers, and between an IMLI sub-assembly and a surface of the underlying equipment to be protected by the MMOD/IMLI structure. The spacers may support the layers and maintain a space or separation distance between adjacent layers within the MMOD/IMLI structure. Various aspects of the spacer pattern including, but not limited to, the number, distance between adjacent spacers within the same layer, and the spatial arrangement of the spacers may influence one or more characteristics of the MMOD/IMLI structure. Non-limiting examples of MMOD/IMLI structural characteristics that may be influenced by the spacer pattern include structural support of the layers within the MMOD/IMLI structure, controlled and repeatable inter-layer spacing, reduction of thermal conduction pathways, light weight, and overall structural integrity. In addition, the incorporation of discrete spacers made of a light weight material significantly reduces the vulnerability of the spacers to fragmentation and formation of high-velocity or high density debris ejecta relative to existing MMOD shield designs that include more substantial and massive rigid metal standoffs to maintain the separation of shield layers.
a. Attachment of Spacers to Layers of MMOD/IMLI Structure
In an aspect, each spacer may be attached to the adjacent layers situated above and below the spacer. In another aspect, each spacer may be attached to one of the adjacent layers situated either above or below the spacer. Referring back to
In another aspect, each of the spacers may be securely attached to the exposed upper and lower surfaces of the corresponding adjacent layers situated immediately above and below each spacer without perforating or otherwise penetrating the material of the corresponding adjacent layers. In this aspect, each layer remains intact, with no discontinuities in the material, which may degrade the bi-directional thermal management of the MMOD/IMLI structure due to the transmission of thermal radiation through the discontinuities in the material of the layer.
b. Arrangement of Spacers within MMOD/IMLI Structure
The spacers may be arranged in any spatial arrangement that results in acceptable structural integrity, thermal performance, and MMOD protection for the MMOD/IMLI structure. In an aspect, the spacers within a layer may be arranged in a grid pattern, with vertical alignment of the corresponding spacers within layers above and below each spacer in the grid, as illustrated in
In an aspect, each spacer within a layer may be interconnected to one or more adjacent spacers by beams or webbing attached to each of the interconnected spacers, as illustrated in
The interconnecting webbing or beams may be fabricated from the same material as the spacers as described herein below in one aspect. In another aspect, the interconnecting beams or webbing may be provided as part of an integrated spacer/webbing support structure situated between the adjacent layers of the MMOD/IMLI structure. In yet another aspect, the interconnecting webbing or beams may be fabricated from different material than the spacers. In this aspect, any of the suitable spacer materials described herein below may be used.
The beams or webbing may enhance the ease of handling and alignment of the spacers during assembly, and may further reinforce the buckling strength of the spacers. The beams may be arranged to connect all the spacers in a layer in a two-dimensional grid in one aspect. In another aspect, the beams may be arranged so there are gaps in the two-dimensional grid pattern to reduce the overall mass of the grid layer, to provide flexibility to the MMOD/IMLI structure, and to provide regions through which the MMOD-IMLI structure may be more easily cut. Other arrangements or combinations of beams and spacers are possible.
In an additional aspect, the spacers may be arranged in a grid pattern with staggering of the patterns between adjacent layers, as illustrated in
In another additional aspect, the spacers may be designed such that the conductive thermal pathway between vertically-aligned spacers within adjacent layers is disrupted independent of the degree of vertical alignment of the grids of spacers on between adjoining levels. A detailed description of aspects of the spacer design is presented in more detail herein below.
c. Spacer Materials
In an aspect, the spacers may be fabricated from a molded polymer with low thermal conductivity, high compressive strength and hardness and low vacuum outgassing. Non-limiting examples of suitable molded polymers include polyetherimide, polyimide, polyamide-imide, polyethyl ketone or wholly aromatic copolyesters. Other examples of suitable spacer materials include high-temperature spacer materials such as alumina or ceramic materials. For example, the spacers may be formed from ULTEM (polyetherimide) or PEEK (polyetheretherketone). The upper and lower surfaces of a spacer that contact adjacent layers may include a rough surface texture, including, but not limited to grooves, to minimize the contact conductance between the spacer and the adjacent layer and/or the vertically aligned and adjacent spacers.
In another aspect, a thin layer of aluminum, gold, silver or other low-emissivity material may be deposited on the surface of the spacers to reduce the infrared absorption of the metalized spacer as compared to an un-metalized spacer. The metalized spacers may further function as conductive elements in an electrically grounded MMOD/IMLI structure in an aspect.
Reducing the infrared absorption of the spacers through metalizing the spacer surface may enhance the thermal insulation performance of the MMOD/IMLI structure in one aspect. In another aspect, the spacer material may be coated with any metallic or non-metallic material having a suitably low emissivity. The metalizing of the spacer surface may comprise the formation or provision of a metal layer that covers all or substantially the entire exposed surface of the spacers. As used herein, substantially the entire exposed surface of a spacer comprises at least most of the surface of the spacer that is not adhered to or in contact with an adjacent layer. The metalizing of the spacer surface may be patterned, such that gaps are formed in the metal layer, thereby disrupting the thermal conductive path along the metalized surface of the spacers. The inclusion of these gaps may ameliorate any degradation in the insulation performance of the MMOD/IMLI structure due to thermal conduction paths along the metal layers on the spacers. The metal layer may be deposited on the spacer using any existing method, including but not limited to vapor deposition, electroplating or any other known metal deposition technique. Gaps in the metal layer may be formed by masking the spacers during metal deposition or by removing portions of the metal layer by etching or mechanical processes.
d. Spacer Design
The design of the spacer may be based on any one or more of at least several criteria including, but not limited to: structural strength, maintenance of constant and reliable distance between adjacent sheets, light weight, low thermal conductivity, low thermal emissivity, compatibility with layer materials and methods of attaching the spacers to the layer materials, and any combination thereof. Various aspects of the spacer design were previously provided herein above.
In an aspect, the spacer design may also incorporate compressible elements to facilitate the compressing of the MMOD/IMLI structure into a compressed state for transport and installation at any stage of mission preparation or at any stage of the mission itself, and to further implement the reversion of the MMOD/IMLI structure prior to use or once on orbit. In these aspects, the spacer may incorporate flexible, resilient elements sized and dimensioned to provide the desired degree of compressibility without compromising the integrity of the MMOD/IMLI structure in use. Any spacer design that incorporates compressible elements may be used in the MMOD/IMLI structure, including any of the spacer designs of the Integrated Multilayer Insulation (IMLI) and Load Responsive Integrated Multilayer Insulation (LRMLI) disclosed in U.S. Pat. No. 7,954,301, Published US patent application Ser. No. 12/493,852 (CIP), and Published PCT application PCT/US/2010/039352, all of which are hereby incorporated by reference in their entirety.
In an aspect, the spacers 400 may be designed to reversibly compress under loading for reduction in volume during mission preparation and during various stages of the mission, and to self-deploy as needed during mission preparation and during various stages of the mission. For example, the spacer 400 may be constructed from a resilient material such that the support arms 406A-406C may deform under a compressive load, as illustrated in
Once in orbit, a self-deployment feature may be actuated to remove the compressed state and allow the structure to return to its natural uncompressed state as illustrated in
Depending on the degree of compressing, the base structure 408 and top structure 404 of a particular spacer 400 may be situated in close proximity to the base structures and top structures of corresponding spacers situated immediately above and below the particular spacer 400, separated only by the intervening material of the layers above and below the particular spacer 400. This close proximity of the top structures and base structures forms a pathway having a significantly lower resistance to thermal conduction than exists when the MMOD/IMLI structure is in an uncompressed state. As a result, the thermal insulation performance of the MMOD/IMLI structure that includes spacers of the design illustrated in
To reduce the reduction in thermal insulation performance in the compressed state due to the creation of low-resistance thermally conductive pathways due to the close proximity of vertically adjacent spacers, a modified spacer design, illustrated in
The spacer 700 includes a base structure 702 and a top structure 704 connected by resilient support arms 706A-706C. Upper support arms 710A-710C project radially from the top structure 704, forming a stable tripod for contact with the layer immediately above the spacer 700. The upper support arms 710A-710C may be arranged in any alignment. For example the upper support arms 710A-710C may be aligned vertically with the resilient support arms 706A-706C. Alternatively, the upper support arms 710A-710C may be rotated with respect to the resilient support arms 706A-706C so that each upper support arm is situated between two adjacent resilient support arms, as illustrated in
The design features of the spacer 700 may result in enhanced support during compression of the spacer 700, as illustrated in
When the spacer is in an uncompressed state, as shown in
In other aspects, the support beam 708 may incorporate additional cross-sectional shapes and/or orientations. For example, the support beam 708 may be a solid cylinder or an open (hollow) cylinder in an aspect.
In an aspect, a method of producing an MMOD/IMLI structure is provided. This method includes attaching successive layers of thermal radiative barrier materials and/or ballistic materials in succession to build up the MMOD/IMLI structure. Referring back to
Adhesive may then be applied to the top surface of the spacers 108M and 108Z, and the first thermal radiative barrier layer 106J may be placed on top of spacers 108M and 108Z, thereby attaching the first thermal radiative barrier layer 106J to the top surface of the spacers 108M and 108Z. In another aspect, a ballistic layer (not shown) may be attached or situated over the underlying equipment surface 112. The bottom surfaces of a second layer of spacers 108L and 108Y may then be attached to the upper surface of the first thermal radiative barrier layer 106J. Similarly, an adhesive may be applied to the top surfaces of spacers 108L and 108Y and the second thermal radiative barrier layer 1061 may then be attached to the top surfaces of spacers 108L and 108Y. In a similar manner, the spacers 108K and 108X may be attached to the second thermal radiative barrier layer 1061, followed by the attachment of the third thermal radiative barrier layer 106H to the top surfaces of spacers 108K and 108X and so on. Each array of spacers may be arranged in vertical alignment with the array of spacers in the previous layer, as illustrated in
The layering process may be continued until the desired arrangement and number of layers in the MMOD/IMLI structure are achieved. Each of the layers may be securely attached to its corresponding adjacent layers, and the adjacent layers may be uniformly spaced relative to each other at a distance governed by the height of the spacers. Dispersed within the MMOD/IMLI structure are a number of radiation barrier layers as well as a number of ballistic layers in any order as needed.
In another aspect, the MMOD/IMLI structure may include at least one lateral edge defining the perimeter of the structure. In this aspect, the MMOD/IMLI structure may be assembled over the underlying equipment surface by seaming the adjoining lateral edges of adjacent modular panels together. The seaming of the adjoining lateral edges may be accomplished using any known joining technique including, but not limited to, sewing, bonding, taping, snapping, interleaving or by other means such that the seamed lateral edges form a continuous MMOD/IMLI structural surface capable of providing full thermal insulation and MMOD protection. In this aspect, the layers of one lateral edge may be overlapped and/or interleaved with the layers of the adjacent lateral edge of the seamed lateral edges. This aspect overcomes a limitation of previous panel designs, in that the joining of heavier, stiff existing panels such as Whipple Shields or Stuffed Whipple Shields results in a discontinuous abutment of panels that may either include small unprotected regions or overlapping regions that result in additional mass and an increased risk of debris generation due to spalling due to the impact of a projectile on an overlapping seam.
The following examples illustrate various aspects of the present disclosure.
To demonstrate the feasibility of constructing an MMOD/IMLI structure as described herein above, the following experiments were conducted.
Ballistic coupons were assembled for use in Projectile Impact Testing. Each ballistic coupon included a total of 120 layers of material, including twelve ballistic layers and 108 layers associated with IMLI sub-assemblies. Each coupon included the IMLI sub-assemblies situated in between each of six inner KEVLAR ballistic layers and six outer NEXTEL ballistic layers. Neighboring individual layers were separated by ULTEM tripod spacers similar to the spacer illustrated in
Each of the 12 ballistic layers were constructed by securing a layer of KEVLAR or NEXTEL within a stainless steel support frame for additional support during high-velocity impact (HVI) testing, as shown in
Each of the IMLI sub-assemblies was constructed by layering 9 MYLAR sheets, and neighboring MYLAR sheets were separated at a fixed distance using ULTEM tripod spacers, as shown in
The coupon was assembled by alternating ballistic layers and IMLI sub-assemblies. Initially, the first IMLI sub-assembly was attached to a base plate as shown in
In a similar manner, the second KEVLAR sub-assembly was attached to the upper surface of the second IMLI sub-assembly, and so on until all six KEVLAR ballistic layers, followed by all six NEXTEL ballistic sublayers, each separated by an IMLI sub-assembly, were stacked and attached, as shown in
The results of this experiment demonstrated the feasibility of assembling an MMOD/IMLI structure that included alternating ballistic layers and IMLI sub-assemblies.
To assess the ability of an MMOD/IMLI structure to withstand the impact of high velocity projectiles such as micrometeoroids or orbital debris, the following experiments were conducted.
The ballistic coupon described in Example 1 was mounted to a HVIT light gas gun (LGG) at the White Sands Test Facility (WSTF) in Las Cruces, N. Mex., USA. The test coupon was impacted by a 5.4 mm projectile traveling at a velocity of 6.63 km/s, as fired from the 0.50 cal LGG. The projectile was previously predicted to penetrate to the lowest KEVLAR ballistic layer, i.e. the 12th ballistic layer counting from the outermost layer (analysis not included).
As summarized in
The results of this experiment demonstrated the ability of the MMOD/IMLI structure to withstand the impact of high velocity projectiles.
To demonstrate the feasibility of constructing an MMOD/IMLI thermal test article suitable for thermal testing, the following experiments were conducted.
The thermal test article representing a subset of the ballistic coupon described in Examples 1 and 2 was designed and fabricated to allow small scale thermal performance testing. The resulting MMOD/IMLI thermal test article was sized to fit a 20 L test calorimeter. The MMOD/IMLI thermal test article included IMLI and ballistic layers sequentially wrapped over the test calorimeter: 1) a lower 4-layer IMLI sub-assembly layer, 2) a KEVLAR ballistic layer, 3) a second 4-layer IMLI sub-assembly layer, and 4) an exposed outer NEXTEL ballistic layer. Each of the layers was maintained at a constant layer separation distance by a grid of ULTEM tripod spacers arranged as described below.
The IMLI sub-assembly layers included four MYLAR layers separated by ULTEM tripod spacers spaced in a radial pattern. Each IMLI sub-assembly layer was fabricated as a continuous sheet designed to fit the contour of the lateral wall of the calorimeter, as well as a pair of end caps. The inner IMLI sub-assembly layer wrapped around the lateral wall of the 20 L calorimeter is shown in
After applying adhesive to each of the exposed ULTEM tripod spacers on the surface of the inner IMLI sub-assembly layer, a KEVLAR ballistic layer was attached to the inner IMLI sub-assembly layer as shown in
The results of the experiment demonstrated the feasibility of constructing an MMOD/IMLI thermal structure suitable for thermal testing by covering a 20 L calorimeter with an MMOD/IMLI structure.
To assess the thermal performance of an MMOD/IMLI structure, the following experiments were conducted.
The thermal structure described in Example 3 was used for the thermal testing. The thermal structure included a 20 L cylindrical tank covered with the MMOD/IMLI structure as described in Example 3. The tank was suspended by a 0.5 inch OD fill/vent tube within a Janis cylindrical vacuum chamber. The tank pressure in the thermal structure was regulated using an MKS 640 absolute pressure controller (MKS Instruments, Andover, Mass., USA). The rate of nitrogen gas boil-off was measured using a 1 L/rev wet test meter (Elster American Meter). The liquid level in the 20 L tank was also measured by observing the frost line on a black rod placed down the fill/vent tube.
The thermal structure was placed in the vacuum chamber and the chamber was evacuated to a vacuum pressure of 2.0×10−6 torr. The tank was filled with liquid nitrogen (LN2) through a 0.25 inch tube inserted into the fill/vent tube of the thermal structure. The 20 L tank was then allowed to vent until the flow rate slowed to approximately steady flow rate. The pressure controller was then installed on the vent line along with the WTM. The pressure controller was set initially at 650 torr and later at 660 torr. Flow rate data was then obtained until a steady state flow rate was achieved with the tank close to full and with the MKS 640 maintaining a steady pressure.
The average steady flow rate as measured by the WTM was 0.249 grams/min, corresponding to an average steady heat flux of about 1.58 W/m2, assuming a 0.53 m2 log mean surface area.
The results of this experiment indicated that the prototype MMOD/IMLI structure that included two four-layer IMLI sub-assemblies, a KEVLAR ballistic layer, and a NEXTEL ballistic layer limited the steady heat flux to about 1.58 W/m2.
While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub combinations thereof. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.
This application is a continuation-in-part of U.S. patent application Ser. No. 12/493,852 entitled “Integrated Multilayer Insulation” filed on Jun. 29, 2009, which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12493852 | Jun 2009 | US |
| Child | 13313723 | US |
