Machine in-place tile thermal protection

A method for building an aerodynamic structure, an aerodynamic structure, and a vehicle that includes the aerodynamic structure are provided. The method includes providing a structure with at least one substantially-flat exterior surface. The method also includes attaching blocks of rigid fibrous insulation to the at least one substantially-flat outer surface of the structure. Outward-facing surfaces of the blocks of rigid fibrous insulation extend past a target outer mold line of a final aerodynamic shape. The method also includes machining the outward-facing surfaces of the attached blocks to the outer mold line.

BACKGROUND

Aspects described herein relate to thermal protection tiles, and more specifically, to shaping and installing thermal protection tiles.

SUMMARY

According to one aspect, a method for building an aerodynamic structure comprises providing a structure with at least one substantially-flat exterior surface. The method also comprises attaching blocks of rigid fibrous insulation to the at least one substantially-flat exterior surface of the structure. Outward-facing surfaces of the blocks of rigid fibrous insulation extend past an outer mold line of a final aerodynamic shape. The method also comprises machining the outward-facing surfaces of the attached blocks to the outer mold line.

According to one aspect, an aerodynamic surface comprises a structure that comprises a first substantially-flat exterior surface and a second substantially-flat exterior surface. The first and second substantially-flat exterior surfaces intersect at an angle. The aerodynamic surface also comprises a first plurality of blocks of rigid fibrous insulation attached to the first substantially-flat exterior surface. Outward-facing surfaces of the blocks form at least a first portion of an aerodynamic shape. The aerodynamic shape is continuous from an edge of a first one of the first plurality of blocks to an adjacent edge of a second one of the first plurality of blocks. The aerodynamic surface also comprises a second plurality of blocks of rigid fibrous insulation attached to the second substantially-flat exterior surface. One of inward-facing surfaces and sides of the at least one of the second plurality of blocks are in facing relationships with respective sides of at least one of the first plurality of blocks. Exterior surfaces of the second plurality of blocks form at least a second portion of the aerodynamic shape. The aerodynamic shape is continuous from an edge of a first one of the second plurality of blocks to an adjacent edge of a second one of the second plurality of blocks. The aerodynamic shape is continuous from the first plurality of blocks to adjacent ones of the second plurality of blocks.

According to one aspect, a vehicle comprises a structure that comprises a first substantially-flat exterior surface and a second substantially-flat exterior surface. The first and second substantially-flat exterior surfaces intersect at an angle. The vehicle also includes a first plurality of blocks of rigid fibrous insulation attached to the first substantially-flat exterior surface. Outward-facing surfaces of the blocks form at least a first portion of an aerodynamic shape for the vehicle. The aerodynamic shape is continuous from an edge of a first one of the first plurality of blocks to an adjacent edge of a second one of the first plurality of blocks. The vehicle also comprises a second plurality of blocks of rigid fibrous insulation attached to the second substantially-flat exterior surface. One of inward-facing surfaces and sides of the at least one of the second plurality of blocks are in facing relationships with respective sides of at least one of the first plurality of blocks. Exterior surfaces of the second plurality of blocks form at least a second portion of the aerodynamic shape. The aerodynamic shape is continuous from an edge of a first one of the second plurality of blocks to an adjacent edge of a second one of the second plurality of blocks, and wherein the aerodynamic shape is continuous from the first plurality of blocks to adjacent ones of the second plurality of blocks.

DETAILED DESCRIPTION

Spacecraft designed to reenter Earth's orbit and aircraft that travel at very high velocities typically cover exterior portions of the vehicles subject to air friction heating with ceramic thermal protection tiles. The ceramic thermal protection tiles are made of ceramic fibers fused together. The fused together ceramic fibers are referred to herein as “rigid fibrous insulation.” In at least one aspect, the rigid fibrous insulation is formed according to the processes described in U.S. Pat. No. 6,716,782, issued on Apr. 6, 2004, the contents of which are incorporated herein in their entirety. The ceramic thermal protection tiles insulate the underlying structure of the vehicle from the heat generated by air friction.

In typical applications, such as on the Space Shuttle or the Boeing X-37 Orbital Test Vehicle, the ceramic thermal protection tiles are installed on exterior surfaces of a vehicle structure that is substantially parallel to an aerodynamic exterior surface profile of the installed tiles (the exterior aerodynamic surface profile of the installed tiles is referred to herein as an outer mold line). As a result, the exterior surfaces of the structure typically include curved surfaces (e.g., at leading edges of airfoils, at wing-to-body fairings, and at the nose cone of the vehicle). The ceramic thermal protection tiles are shaped to fit in relation to each other as well as in relation to the aerodynamically-curved exterior surfaces of the structure. As a result, in many instances, each ceramic thermal protection tile is unique such that it can only be placed in a particular location on the vehicle. The manufacturing costs of making many uniquely-shaped ceramic thermal protection tiles, as well as the costs and logistics of tracking and storing the unique tiles, increases the cost of manufacturing and servicing such vehicles.

Additionally, the ceramic thermal protection tiles are typically installed on a strain isolation pad that is disposed on the exterior surface of the structure for the vehicle. The strain isolation pad may be a heat resistant Nomex felt fabric, or similar material, that cushions the ceramic thermal protection tiles from the exterior surface of the structure. The strain isolation pad allows the vehicle (including the exterior surface of the structure for the vehicle) to flex during the strain of vehicle operations (e.g., lift off, maneuvering, and reentry) without cracking the ceramic thermal protection tiles. One side of the strain isolation pad is typically glued or otherwise adhered to the exterior surface of the structure of the vehicle, and the ceramic thermal protection tiles are glued or otherwise adhered to the other side of the strain isolation pad. The strain isolation pad has a relatively large thickness tolerance. As a result, when the ceramic thermal protection tiles are installed on the strain isolation pad, there can be variations in height from one tile to the next tile, creating discontinuities in the aerodynamic profile of the outer mold line formed by the tiles. Such discontinuities, where an edge of the outward-facing surface of one tile is higher or lower than an adjacent edge of a neighboring tile, can reduce the aerodynamic performance of the vehicle by increasing drag and can increase heating along the surface. In some instances, high spots on certain tiles may be shaved after installation to mitigate some of these discontinuities. However, it may be impossible or impractical to completely eliminate all such discontinuities, and such shaving operations are time consuming and costly.

In aspects disclosed herein, the underlying structure of a vehicle includes flat exterior surfaces that intersect at an angle. Blocks of rigid fibrous insulation with a standardized shape (e.g., a rectangular cuboid or a trapezoidal cuboid) are glued or otherwise adhered to the flat exterior surfaces and/or, optionally, to strain isolation pads on the flat exterior surfaces. After the blocks of rigid fibrous insulation are adhered to the flat exterior surfaces, outward-facing surfaces of the blocks of rigid fibrous insulation are machined to form an outer mold line matching a desired aerodynamic profile. By using blocks of rigid fibrous insulation with standardized shapes, a relatively small number of block shapes may be used to cover the various exterior surfaces of the vehicle, thereby reducing part count and increasing interchangeability among the blocks. In addition, by machining the outward-facing surfaces of the blocks of rigid fibrous insulation after they are attached to the exterior surfaces of the structure of the vehicle, any variation caused by the use of a strain isolation pad may be mitigated. After the outward-facing surfaces of the blocks of rigid fibrous insulation have been machined to the outer mold line, a slurry (e.g., of ceramic powders in a colloidal solution) is applied to the outward-facing surface. The slurry cures at room temperature. In one aspect, room temperature is a temperature within a range between 68° F. and 77° F. In another aspect, room temperature may be within a range of between 60° F. and 100° F. In yet another aspect, room temperature may be within a range of between 60° F. and 90° F. In yet another embodiment, room temperature may be any temperature below temperatures that would cause damage and/or deformation to the structure on which blocks of rigid fibrous materials are attached or to other components attached to the structure. The cured slurry increases the hardness of the outward-facing surfaces of the blocks of rigid fibrous insulation, increases the impact protection of the blocks of rigid fibrous insulation, and improves the thermal emissivity of the blocks of rigid fibrous insulation. The blocks of rigid fibrous insulation with the cured slurry are ceramic thermal protection tiles. Since the slurry is applied after the blocks of rigid fibrous insulation after outward-facing surfaces of the blocks are machined to the outer mold line, the resulting ceramic thermal protection tiles may be uniformly coated with the cured slurry. By contrast, the above-described “shaving” of high spots on ceramic thermal protection tiles that are machined prior to installation on a structure may have a non-uniform coating due to this coating spots or dissimilar coatings applied at the shaving locations.

FIG. 1is a perspective view of a spacecraft100that includes a fuselage102, a nose cone110, and wings104. The wings104include leading edges106, and the wings104are attached to the fuselage102with a wing-to-body fairing108. The nose cone110, the leading edges106of the wings104, and the wing to body fairing108may all be subject to high temperatures due to air friction when the spacecraft100reenters the atmosphere. The nose cone110, the leading edges106of the wings104, and the wing-to-body fairing108are covered in ceramic thermal protection tiles, which insulate the underlying structure of the spacecraft100from the heat.

FIG. 2is a perspective cross-sectional view of an aerodynamic surface200for a vehicle, such as the spacecraft100. For example, the aerodynamic surface200could be a portion of the leading edge106of one of the wings104of the spacecraft100, according to one aspect. The aerodynamic surface200includes a structure202that comprises a first substantially-flat exterior surface204and a second substantially-flat exterior surface206. The first substantially-flat exterior surface204and the second substantially-flat exterior surface206intersect at an angle. The illustrated structure202includes a third substantially-flat exterior surface208, which intersects with the second substantially-flat exterior surface206at an angle. In various aspects, a structure could have more than three substantially-flat exterior surfaces. In at least one aspect, the substantially-flat exterior surfaces could form a faceted shape.

In the illustrated aspect, the first substantially-flat exterior surface204and the second substantially-flat exterior surface206are covered with a strain isolation pad210. As discussed above, the strain isolation pad210may be glued or otherwise adhered to the first substantially-flat exterior surface204and the second substantially-flat exterior surface206. The term “substantially-flat” refers to a surface that is flat but for manufacturing tolerances and/or part tolerances. For example, as discussed above, strain isolation pads210typically have a relatively high thickness variance. If such a strain isolation pad210were placed on a flat surface, the outward-facing surface of the strain isolation pad210would be considered a “substantially-flat” surface because any waviness to the outward-facing surface of the strain isolation pad210would be due to the part tolerances of the strain isolation pad210.

A first plurality of blocks of rigid fibrous insulation212are attached to the first substantially-flat exterior surface204. As discussed above, the first plurality of blocks of rigid fibrous insulation212are glued or otherwise adhered to the first substantially-flat exterior surface204. In at least one aspect, the adhesive is a room temperature vulcanizing (RTV) silicone. In at least one aspect, the RTV silicone is a two-part RTV silicone adhesive optimized for performance at elevated temperatures by adding fillers such as iron oxide. In aspects in which the first substantially-flat exterior surface204is covered with the strain isolation pad210, the first plurality of blocks of rigid fibrous insulation212are glued or otherwise adhered to the strain isolation pad210. In one aspect, the blocks of rigid fibrous insulation212are bonded to the strain isolation pad210before the strain isolation pad210is bonded to the first substantially-flat exterior surface204. In another aspect, the strain isolation pad210is bonded to the first substantially-flat exterior surface204and then the blocks of rigid fibrous insulation212are bonded to the strain isolation pad210.

As discussed above, the first plurality of blocks of rigid fibrous insulation212are made of ceramic fibers fused together. In at least one aspect, the ceramic fibers fused together resemble a bird's nest (if viewed through a microscope) or other porous structure. An adhesive applied to such a porous structure may be absorbed into the structure rather than stay on the surface of the blocks, thereby reducing the effectiveness of the adhesive when applied to the first substantially-flat exterior surface204and/or the strain isolation pad210. To mitigate absorption of the adhesive into the structure, a slurry is applied to the inward-facing surfaces of the first plurality of blocks of rigid fibrous insulation212(e.g., inward-facing surface216of block214and inward-facing surface224of block222). In one aspect, the slurry includes one or more types of ceramic powders in a colloidal solution. The colloidal solution may be an alcohol, water, or other liquid with oppositely charged polymers that adhere to particles of the ceramics. In one aspect, the slurry comprises between 60-80% colloidal silica solution, 20-40% silica powder, and 0-4% Silicon Hexaboride, by weight. The oppositely charged polymers prevent agglomeration of the ceramic particles. The coating may be cured at room temperature or at elevated temperatures (e.g., during firing in an autoclave or oven). In one aspect, the cured coating penetrates approximately one tenth of an inch into the surface of the blocks of rigid fibrous insulation, densifying the outermost one tenth of an inch of the blocks. Stated differently, the cured coating makes the inward-facing surfaces of the blocks of rigid fibrous insulation impermeable such that an adhesive applied to the inward-facing surfaces of the blocks remains on the surface. Additionally, the cured coatings strengthen the tiles and distributing the loads imparted at the interface between the blocks of rigid fibrous insulation212and the strain isolation pad210.

As shown inFIG. 2, the first plurality of blocks of rigid fibrous insulation212is attached to the first substantially-flat exterior surface204(or the strain isolation pad210). The first plurality of blocks of rigid fibrous insulation212is arranged on the first substantially-flat exterior surface204with gaps228and230therebetween. In one aspect, the gaps between blocks is between 0.01 and 0.20 inches. For example, blocks214and215of the first plurality of blocks of rigid fibrous insulation212are separated from blocks222and217of the first plurality of blocks of rigid fibrous insulation212by a gap228. Additionally, blocks214and222of the first plurality of blocks of rigid fibrous insulation212are separated from blocks215and217by the gap230.

InFIG. 2, the blocks of the first plurality of blocks of rigid fibrous insulation212have been machined to an outer mold line270such that the outward-facing surfaces of the blocks of rigid fibrous insulation form a continuous aerodynamic shape from one block to the next. For example, the aerodynamic shape defined by the outward-facing surface218of block214continues along the outward-facing surface226of block222across the gap228. Stated differently, the edge of the outward-facing surface218of block214to the adjacent edge of the outward-facing surface226of block222both lay on the outer mold line270. As another example, the aerodynamic shape defined by the outward-facing surface218of block214continues along the outward-facing surface220of block215across the gap230. The outer mold line270defines the aerodynamic shape of the outward-facing surfaces of the blocks of rigid fibrous material in all three dimensions (i.e., front-to-back relative to the spacecraft100, top-to-bottom relative to the spacecraft100, and side-to-side relative to the spacecraft100).

FIG. 2also shows a second plurality of blocks of rigid fibrous insulation240attached to the second substantially-flat exterior surface206(and/or to the strain isolation pad210). For example,FIG. 2shows blocks242,244,243, and245of the second plurality of blocks of rigid fibrous insulation240attached to the second substantially-flat exterior surface206and/or to the strain isolation pad210. As shown in the partial cross-sectional view, inward-facing surfaces248and250of blocks242and244, respectively, are attached to the strain isolation pad210(e.g., with glue or other adhesive). Additionally, the inward-facing surfaces248and250extend past the edges of the second substantially-flat exterior surface206(where the second substantially-flat exterior surface206intersects the first substantially-flat exterior surface204and the third substantially-flat exterior surface208, respectively). As a result, the inward-facing surface248of the block242is arranged in a facing relationship with a side surface234of the block214from the first plurality of blocks of rigid fibrous insulation212. A gap256is formed between the inward-facing surface248of the block242and the side surface234of the block214. Similarly, the inward-facing surface250of the block244is arranged in a facing relationship with a side surface266of a block262from a third plurality of blocks of rigid fibrous insulation260attached to the third substantially-flat exterior surface208. A gap268is formed between the inward-facing surface250of the block244and the side surface266of the block262.

The second plurality of blocks of rigid fibrous insulation240is arranged on the second substantially-flat exterior surface206with gaps246and230therebetween. For example, the block242and the block244of the second plurality of blocks of rigid fibrous insulation240are separated by a gap246. Additionally, the block243of the second plurality of blocks of rigid fibrous insulation240is separated from the block242by the gap230. As shown in the exemplary aspect ofFIG. 2, the blocks of the first plurality of blocks of rigid fibrous insulation212and the second plurality of blocks of rigid fibrous insulation240are aligned such that the gap230is continuous from the first plurality to the second plurality. In various other aspects, the first plurality of blocks of rigid fibrous insulation212and the second plurality of blocks of rigid fibrous insulation240may not be aligned such that the gap230would be positioned differently in the first plurality of blocks of rigid fibrous insulation212and the second plurality of blocks of rigid fibrous insulation240.

InFIG. 2, the blocks of the second plurality of blocks of rigid fibrous insulation240have been machined to the outer mold line270such that the outward-facing surfaces of the blocks of rigid fibrous insulation form a continuous aerodynamic shape from one block to the next. For example, the aerodynamic shape defined by the outward-facing surface252of block242continues along the outward-facing surface241of block244across the gap246. Stated differently, the edge of the outward-facing surface252of block242and the adjacent edge of the outward-facing surface241of block244lay along the outer mold line270. As another example, the aerodynamic shape defined by the outward-facing surface252of the block242continues along the outward-facing surface254of the block243across the gap230. Moreover, the aerodynamic shape defined by the outward-facing surfaces of the blocks is continuous from the blocks of the first plurality of blocks of rigid fibrous insulation212to the blocks of the second plurality of blocks of rigid fibrous insulation240. For example, the aerodynamic shape defined by the outward-facing surface252of block242continues along the outward-facing surface218of block214across the gap256. Likewise, the aerodynamic shape defined by the outward-facing surface254of block243continues along the outward-facing surface220of block215across the gap256. Similarly, the aerodynamic shape defined by the outward-facing surfaces of the blocks is continuous from the blocks of the second plurality of blocks of rigid fibrous insulation240to the blocks of the third plurality of blocks of rigid fibrous insulation260. For example, the aerodynamic shape defined by the outward-facing surface241of block244continues along the outward-facing surface264of block262across the gap268.

FIG. 3illustrates an exemplary block of rigid fibrous insulation300prior to installation onto a substantially-flat structure and prior to machining of an outward-facing surface to an outer mold line defining aerodynamic surface. For example, the illustrated block of rigid fibrous insulation300could be attached to the substantially-flat exterior surfaces204,206, and208of the structure202to form the first, second, and third pluralities of blocks of rigid fibrous insulation212,240, and260. Thereafter, outward-facing surfaces of the blocks of rigid fibrous insulation300could be machined to the outer mold line270to shape the first, second, and third pluralities of blocks of rigid fibrous insulation212,240, and260as illustrated inFIG. 2. The exemplary block of rigid fibrous insulation300has a rectangular cuboid shape, meaning that an inward-facing surface302and an outward-facing surface304are parallel to each other, and that sidewalls306and308extending between the inward-facing surface302and the outward-facing surface304are perpendicular to the inward-facing surface302, to the outward-facing surface304, and to each other. The block300may be a general block used for covering most of the flat surfaces of a structure. Where two flat or substantially-flat surfaces of the structure intersect at an angle, the block300may be modified to provide a block with surfaces specific for an intersection of blocks at that angle. For example, one or both of the sidewalls306and308could be arranged at a non-perpendicular angle relative to the inward-facing surface302, the outward-facing surface304, and/or each other. Such modifications to the block300could be performed by machining the block300(e.g., using a computer numerical control (CNC) mill) or by modifying a mold for forming the block300. Additionally, blocks300could be modified such that the inward-facing surface302and/or the outward-facing surface304has a non-rectangular shape for placement along an edge of a substantially-flat surface that is not linear or that will not align with edges of the unmodified block300.

In one aspect, the blocks of rigid fibrous insulation300are formed from a combination of silica (SiO2) and alumina (Al2O3) fibers, and boron-containing power (e.g., Boron Carbide) that are used as a sintering agent. The insulative material is composed of about 60 wt % to about 80 wt % silica fibers, about 20 wt % to about 40 wt % alumina fibers, and about 0.1 wt % to about 1.0 wt % boron-containing powder. During processing, the boron-containing powder provides boron-containing by-products which fuse and sinter the silica and alumina fibers when heated to elevated temperatures. Thus, no supplemental binder is required during production of the insulative material. The use of the boron-containing powder allows the use of lower amounts (relative to Nextel fibers used in AETB production) to form sufficient sintering between the fibers. This small amount of boron-containing powder is replacing a relatively large amount of Nextel fibers (12 to 15 wt %), which is one of the high cost components and is found to provide adverse effects on the thermal conductivity due to its larger diameter.

The tile material is produced by dispersing the ceramic fibers in an aqueous solution forming a slurry. The slurry is blended using the shear mixer, which disperses the fibers evenly throughout and chops them to a certain length. By using a shear mixer, the fibers tend to be oriented lengthwise in the direction of the radial flow of the slurry during mixing. In the finished tile, the fibers are substantially oriented in the direction perpendicular to the press direction of the slurry, making this material anisotropic. This arrangement of fibers results in much lower thermal conductivity along the press direction (through-the-thickness) relative to the direction perpendicular to the press direction (in-plane).

After mixing and chopping, the slurry is optionally classified through a separation means in order to remove undesirable solids, known as inclusions or shot, from the fiber slurry suspension. The insulative characteristic of the material stems from having small diameter ceramic fibers surrounded by large volumes of air. High-density ceramic shot or clumps are detrimental to the effectiveness of the insulation properties, and are therefore removed before the material is pressed.

After filtration of the shot and/or clumps, the slurry is pumped into the mold, otherwise known as the casting box, from which the fibers are drained and pressed. Water removal is accomplished via gravity drain through the porous bottom of the casting box. Acceleration of the draining step is done by the application of a vacuum at the bottom of the casting box. The slurry is pressed to produce a wet billet of ceramic fiber. The slurry is preferably pressed in the vertical direction, by moving a top surface downwards and pressing upon the fibers. The vertical press direction is also called “through-the-thickness” direction. The geometry of the top surface, otherwise known as the press plate, is preferably similar to that of the billet to reduce, if not eliminate, fiber layer separation caused by surface friction with the inner walls of the casting box.

After pressing, the wet billet is dried and fired. The drying step removes residual moisture from the billet. The firing step fuses the fibers to one another to produce a rigid body and to provide structural integrity. Drying occurs at approximately 200 to 500° F. for at least 24 hours. Firing occurs at a temperature between about 2,300° F. and about 2,600° F. for about 1 to about 5 hours.

The fused insulative material is machined into the shape of a tile, normally in the six-inch by six-inch planform and with thickness ranging from one to three inches. The tile is machined so that the top surface and the bottom surface of the tile are roughly parallel to the direction of the fiber alignment within the tile material. This arrangement provides an increase in tensile strength in the in-plane direction, which prevents the shrinkage and slumping that is problematic in the older generation tiles. For example, tensile strength of a new tile having a bulk density of 8 lbs/ft3is approximately 110-140 lbs/in2in the in-plane direction and approximately 35-55 lbs/in2in the through-the-thickness direction. The direction is termed as “in-plane” when it is perpendicular to the fiber press direction, while “through-the-thickness” direction is termed when it is parallel to the fiber press direction. The strength of the tile is sufficient to support a coating (e.g., a room-temperature curing slurry) applied on the outer surface of the tile without problems associated with slumping.

The insulative material exhibits very low thermal conductivity, particularly in the through-the-thickness direction.

FIGS. 4A-4Cillustrate steps for attaching blocks of rigid fibrous insulation (e.g., blocks300) on a structure400and then machining the blocks of rigid fibrous insulation to an outer mold line defining an aerodynamic shape. The exemplary structure400and outer mold line of the aerodynamic shape illustrated inFIGS. 4A-4Cis different from the structure202and outer mold line270of the aerodynamic shape illustrated inFIG. 2. Therefore, the blocks300of rigid fibrous insulation may be attached to the structure400in a different arrangement and/or outward-facing surfaces of the blocks300of rigid fibrous insulation may be machined differently to form the different outer mold line.FIG. 4Aillustrates a structure400that includes a first substantially-flat exterior surface402and a second substantially-flat exterior surface404meet at an angle at a line of intersection406. As shown inFIG. 4A, seven blocks300of rigid fibrous insulation have been attached to the first substantially-flat exterior surface402of the structure400, and an eighth block300of rigid fibrous insulation is being attached to the first substantially-flat exterior surface402of the structure400(as indicated by arrow A). As discussed above, prior to attaching the blocks300to the first substantially-flat exterior surface402, the inward-facing surfaces302of the blocks300have been coated with a slurry, and the slurry has been cured. Additional blocks300of rigid fibrous insulation have been attached to the second substantially-flat exterior surface404of the structure400. As shown best inFIGS. 4B and 4C, the second substantially-flat exterior surface404includes modified blocks300adisposed along the line of intersection406that have a side surface arranged at a non-orthogonal angle relative to the inward-facing surface302and the outward-facing surface304. The non-orthogonal side surfaces of the modified blocks300aare arranged at an angle such that the non-orthogonal side surfaces of the modified blocks300aare arranged in a parallel facing relationship with the orthogonal side surfaces of the blocks300attached to the first substantially-flat exterior surface402and disposed along the line of intersection406. As shown inFIG. 4A, the structure is covered by two types of blocks300and300a. Thus, for this exemplary structure, only two types of blocks kept in inventory.

Referring now toFIG. 4B, after the blocks300and modified blocks300aare attached to the first substantially-flat exterior surface402and the second substantially-flat exterior surface404of the structure400, outward-facing surfaces of the blocks300and300aare machined to an outer mold line410that defines an aerodynamic surface. For example, the structure400, with the blocks300and300aattached, may be placed in a CNC mill, which follows a computer program to use a cutting head to mechanically remove material from the outward-facing surfaces of the blocks300and300a. As another example, an etching agent may be selectively applied to chemically remove material from the outward-facing surfaces of the blocks300and300a. In yet another example, a laser or other radiation source may be applied to ablate the outward-facing surfaces of the blocks300and300a. InFIG. 4B, certain ones of the blocks300′ and300a′ have been partially machined to the outer mold line410, certain others of the blocks300″ have been fully machined to the outer mold line410, and the remainder of the blocks300and300ahave not been machined yet. InFIG. 4C, all of the blocks300″ and300a″ have been fully machined to the outer mold line410that defines a desired aerodynamic shape.

After the blocks300and300ahave been machined to the mold line defining the desired aerodynamic shape, the outward-facing surfaces of the blocks300and300aare coated with a slurry (e.g., ceramic powders in a colloidal solution). In one aspect, the slurry comprises about 60-80% colloidal silica solution, 20-40% silica powder, and 1-5% silicon hexaboride. The slurry may be sprayed on or brushed on. In at least one aspect, gaps between adjacent blocks300and300aare covered prior to applying the coating such that the slurry does not fill in the gaps. Here, the slurry cures at room temperature. The cured slurry densifies the outward-facing surface of the blocks300and300a, improving rigidity, impact protection, and thermal emissivity of the outward-facing surfaces of the blocks300and300a. After the coating has cured, the blocks300and300aof rigid fibrous insulation are ceramic thermal protection tiles for the structure400.

FIG. 5Ais a flow chart for a method500of providing ceramic thermal protection tiles on a structure. In block502of the method500, a structure is provided with at least one substantially-flat outer surface. In block504of the method500, blocks of rigid fibrous insulation are attached to the at least one substantially-flat outer surface of the structure. Outward-facing surfaces of the blocks of rigid fibrous insulation extend past a target outer mold line of a final aerodynamic shape for the structure. In block506of the method500, the outward-facing surfaces of the attached blocks are machined to the outer mold line to form the aerodynamic shape. In block508of the method500, a slurry is applied to the machined exterior surfaces of the attached blocks. The slurry cures at room temperature. Once the slurry cures, the blocks of fibrous rigid insulation are ceramic thermal protection tiles on the surface of the structure.

FIG. 5Bis a flow chart for block504of the method500. In block510, a slurry is applied to inward-facing surfaces of the blocks of rigid fibrous insulation that will abut a selected one of the at least one flat outer surface. After the slurry or coating has cured (at room temperature or after the application of heat, according to the composition of the slurry), an adhesive is applied to the inward-facing surfaces of the blocks. In block514, the blocks are adhered to the at least one flat outer surface of the structure.

In the above-described aspects, ceramic thermal protection tiles may be arranged on a structure in a manner that is less expensive and less time-consuming than previous methods for arranging tiles, in which individual tiles are custom shaped to fit into a particular location. Moreover, in the above-described aspects, the ceramic thermal protection tiles are formed such that outward-facing surfaces of the ceramic thermal protection tiles form a continuous aerodynamic surface, which is more aerodynamic than the previous methods for arranging tiles, which commonly result in aerodynamic discontinuities.

The above-described aspects for forming ceramic thermal protection tiles have been described with reference to aerodynamic surfaces of an aircraft or spacecraft. In various other aspects, the methods described above could be used to form ceramic thermal protection tiles for other applications, such as for a furnace.

The descriptions of the various aspects have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the aspects disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described aspects. The terminology used herein was chosen to best explain the principles of the aspects, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the aspects disclosed herein.

While the foregoing is directed to certain aspects, other and further aspects may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.