Skip to comments.The Space Shuttle Orbiter and Ceramic Tiles - Some History and Information
Posted on 02/02/2003 4:43:56 PM PST by NormsRevenge
Space Shuttle Tiles - A little history and some general information with links
Press Release from Lockheed , May 1, 1992
SPACE SHUTTLE TILES WERE JUST THE BEGINNING FOR LOCKHEED'S AEROSPACE CERAMIC SYSTEMS
SUNNYVALE, California, May 1, 1992 -- When the Space Shuttle Endeavour rockets into space on its maiden voyage, it will be protected by ceramic tiles manufactured by Lockheed Missiles & Space Company, Inc. of Sunnyvale, California. NASA's entire orbiter fleet -- Columbia, Challenger, Discovery, Atlantis, and now Endeavour -- is protected from the searing heat of reentry by Lockheed's Reusable Surface Insulation. Endeavour will be protected with over 26,000 tiles. Earlier orbiters used as many as 34,000 tiles, but as the knowledge base increased, tiles on surfaces that experienced moderate reentry temperatures, such as the upper fuselage, were eventually replaced with flexible insulating blankets.
As early as 1957, Lockheed began investigating a broad range of insulating materials, including zirconium compoutes. By 1961, work focused on finding a suitable all-silica material. By 1968, the basic shuttle tile material LI-900 (which stands for Lockheed Insulation/9 lbs per cubic foot) was developed and successfully tested during the reentry of NASA's Pacemaker spacecraft where surface temperatures reached 2300ûF.
Space shuttle tiles are made of high-purity amorphous silica fibers (2 to 4 microns in diameter, as long a 1/16th inch) derived from common sand. A water slurry containing silica fibers is frame cast to form soft, porous blocks to which a colloidal silica binder solution is added. The blocks are then dried, sintered at 2300ûF. to develop maximum strength, then quartered and machined to precise dimensions. Machined tiles then go to ovens for baked-on coatings. Tiles for areas of the orbiter that experience reentry heating up to 2300ûF. receive a black borosilicate glass coating. Those for lower temperature areas, from 600û to 1200ûF., are coated with a white silica compound which includes alumina to better reflect the heat of the Sun on-orbit. All tiles are treated with a waterproofing polymer.
An installed square foot of shuttle tile material, reusable for up to 100 missions, cost NASA about $10,000. The ablative heat shields used on Apollo command modules returning astronauts from the Moon were priced at $30,000 per square foot, and were used only once.
Once the shuttle tile production line was running smoothly, Lockheed used independent development funds to develop third generation tile material. Called, HTP, for High Thermal Performance, it surpasses shuttle tile material in strength by a factor of two and one-half, and coupled with the success of Lockheed's Reusable Surface Insulation for the space shuttle fleet, transformed Aerospace Ceramic Systems from a single- contract, single-customer group into a multiple-contract, multiple customer group in the space of a few years. The first non-shuttle contract came from the Lockheed Aeronautical Systems Company, builder of the F117 Stealth Fighter. The material is used for high temperature insulation. Similarly, Northrop turned to Lockheed's Aerospace Ceramic Systems for heat shield parts to be used on the B-2 Stealth Bomber. Between 1989 and 1991, Aerospace Ceramic Systems fulfilled 112 separate contracts. Typically, one new proposal a week now comes out of the office. "In the area of low-density, high- strength rigid fiber ceramics, Lockheed is really the only game in town" exclaims John Donaldson, Lockheed senior staff engineer, "And if you want manned spaceflight qualified rigid fibrous ceramics, you should come to us. As far as we know, nobody else in the industry makes it." In that regard, Lockheed has been approached by General Dynamics in Fort Worth, Texas to submit a bid to build heat shield test parts for the National Aerospace Plane. Structural ceramic composites represent another productive area for Aerospace Ceramic Systems. As silica-based tile material is quite fragile, Lockheed engineers devised a rigid skin to surround the material, thus reducing its fragility. These composites have been used to create missile nosecones and laser- hardened spacecraft antennas.
Lockheed's HTP material is also an outstanding acoustic attenuator, and that characteristic, coupled with excellent heat rejection capability make it ideal for use in the suppression of noise associated with engine exhausts. While modern means of transportation have brought increased mobility to millions, the introduction of noise into the environment remains a persistent concern. Lockheed's Aerospace Ceramic Systems is poised to address that problem.
One challenge for the future will be to produce ceramic insulation that can withstand reentry temperatures for spacecraft returning to Earth from the Moon and Mars. Current material can withstand temperatures of 2300ûF., but 3500ûF. reentry temperatures will not be unusual for astronauts venturing beyond Earth orbit. John Donaldson, and the Aerospace Ceramic Systems team are looking for solutions: "We're looking for exotic ceramic materials that can be made into fibres, and then we'll turn them into low density products. We'll figure it out. We always have."
From Kennedy Space Center re: Space Shuttle Orbiter Systems
The thermal protection system consists of various materials applied externally to the outer structural skin of the orbiter to maintain the skin within acceptable temperatures, primarily during the entry phase of the mission. The orbiter's outer structural skin is constructed primarily of aluminum and graphite epoxy.
During entry, the TPS materials protect the orbiter outer skin from temperatures above 350 F. In addition, they are reusable for 100 missions with refurbishment and maintenance. These materials perform in temperature ranges from minus 250 F in the cold soak of space to entry temperatures that reach nearly 3,000 F. The TPS also sustains the forces induced by deflections of the orbiter airframe as it responds to the various external environments. Because the thermal protection system is installed on the outside of the orbiter skin, it establishes the aerodynamics over the vehicle in addition to acting as the heat sink.
Orbiter interior temperatures also are controlled by internal insulation, heaters and purging techniques in the various phases of the mission.
The TPS is a passive system consisting of materials selected for stability at high temperatures and weight efficiency. These materials are as follows:
1. Reinforced carbon-carbon is used on the wing leading edges; the nose cap, including an area immediately aft of the nose cap on the lower surface (chine panel); and the immediate area around the forward orbiter/external tank structural attachment. RCC protects areas where temperatures exceed 2,300 F during entry.
2. Black high-temperature reusable surface insulation tiles are used in areas on the upper forward fuselage, including around the forward fuselage windows; the entire underside of the vehicle where RCC is not used; portions of the orbital maneuvering system and reaction control system pods; the leading and trailing edges of the vertical stabilizer; wing glove areas; elevon trailing edges; adjacent to the RCC on the upper wing surface; the base heat shield; the interface with wing leading edge RCC; and the upper body flap surface. The HRSI tiles protect areas where temperatures are below 2,300 F. These tiles have a black surface coating necessary for entry emittance.
3. Black tiles called fibrous refractory composite insulation were developed later in the thermal protection system program. FRCI tiles replace some of the HRSI tiles in selected areas of the orbiter.
4. Low-temperature reusable surface insulation white tiles are used in selected areas of the forward, mid-, and aft fuselages; vertical tail; upper wing; and OMS/RCS pods. These tiles protect areas where temperatures are below 1,200 F. These tiles have a white surface coating to provide better thermal characteristics on orbit.
5. After the initial delivery of Columbia from Rockwell International's Palmdale assembly facility, an advanced flexible reusable surface insulation was developed. This material consists of sewn composite quilted fabric insulation batting between two layers of white fabric that are sewn together to form a quilted blanket. AFRSI was used on Discovery and Atlantis to replace the vast majority of the LRSI tiles. Following its seventh flight, Columbia also was modified to replace most of the LRSI tiles with AFRSI. The AFRSI blankets provide improved producibility and durability, reduced fabrication and installation time and costs, and a weight reduction over that of the LRSI tiles. The AFRSI blankets protect areas where temperatures are below 1,200 F.
6. White blankets made of coated Nomex felt reusable surface insulation are used on the upper payload bay doors, portions of the midfuselage and aft fuselage sides, portions of the upper wing surface and a portion of the OMS/RCS pods. The FRSI blankets protect areas where temperatures are below 700 F.
7. Additional materials are used in other special areas. These materials are thermal panes for the windows; metal for the forward reaction control system fairings and elevon seal panels on the upper wing to elevon interface; a combination of white- and black-pigmented silica cloth for thermal barriers and gap fillers around operable penetrations, such as main and nose landing gear doors, egress and ingress flight crew side hatch, umbilical doors, elevon cove, forward RCS, RCS thrusters, midfuselage vent doors, payload bay doors, rudder/speed brake, OMS/RCS pods and gaps between TPS tiles in high differential pressure areas; and room-temperature vulcanizing material for the thick aluminum T-0 umbilicals on the sides of the orbiter aft fuselage.
RCC fabrication begins with a rayon cloth graphitized and impregnated with a phenolic resin. This impregnated cloth is layed up as a laminate and cured in an autoclave. After being cured, the laminate is pyrolized to convert the resin to carbon. This is then impregnated with furfural alcohol in a vacuum chamber, then cured and pyrolized again to convert the furfural alcohol to carbon. This process is repeated three times until the desired carbon-carbon properties are achieved.
To provide oxidation resistance for reuse capability, the outer layers of the RCC are converted to silicon carbide. The RCC is packed in a retort with a dry pack material made up of a mixture of alumina, silicon and silicon carbide. The retort is placed in a furnace, and the coating conversion process takes place in argon with a stepped-time-temperature cycle up to 3,200 F. A diffusion reaction occurs between the dry pack and carbon-carbon in which the outer layers of the carbon-carbon are converted to silicon carbide (whitish-gray color) with no thickness increase. It is this silicon-carbide coating that protects the carbon-carbon from oxidation. The silicon-carbide coating develops surface cracks caused by differential thermal expansion mismatch, requiring further oxidation resistance. That is provided by impregnation of a coated RCC part with tetraethyl orthosilicate. The part is then sealed with a glossy overcoat. The RCC laminate is superior to a sandwich design because it is light in weight and rugged; and it promotes internal cross-radiation from the hot stagnation region to cooler areas, thus reducing stagnation temperatures and thermal gradients around the leading edge. The operating range of RCC is from minus 250 F to about 3,000 F. The RCC is highly resistant to fatigue loading that is experienced during ascent and entry.
The RCC panels are mechanically attached to the wing with a series of floating joints to reduce loading on the panels caused by wing deflections. The seal between each wing leading edge panel is referred to as a T-seal. The T-seals allow for lateral motion and thermal expansion differences between the RCC and the orbiter wing. In addition, they prevent the direct flow of hot boundary layer gases into the wing leading edge cavity during entry. The T-seals are constructed of RCC.
Since carbon is a good thermal conductor, the adjacent aluminum and the metallic attachments must be protected from exceeding temperature limits by internal insulation. Inconel 718 and A-286 fittings are bolted to flanges on the RCC components and are attached to the aluminum wing spars and nose bulkhead. Inconel-covered cerachrome insulation protects the metallic attach fittings and spar from the heat radiated from the inside surface of the RCC wing panels.
The nose cap thermal insulation ues a blanket made from ceramic fibers and filled with silica fibers. HRSI or FRCI tiles are used to protect the forward fuselage from the heat radiated from the hot inside surface of the RCC.
During flight operations, damage has occurred in the area between the RCC nose cap and the nose landing gear doors from impact during ascent and excess heat during entry. The HRSI tiles in this area are to be replaced with RCC.
In the immediate area surrounding the forward orbiter/ET attach point, an AB312 ceramic cloth blanket is placed on the forward fuselage. RCC is placed over the blanket and is attached by metal standoffs for additional protection from the forward orbiter/ET attach point pyrotechnics.
The HRSI tiles are made of a low-density, high-purity silica 99.8-percent amorphous fiber (fibers derived from common sand, 1 to 2 mils thick) insulation that is made rigid by ceramic bonding. Because 90 percent of the tile is void and the remaining 10 percent is material, the tile weighs approximately 9 pounds per cubic foot. A slurry containing fibers mixed with water is frame-cast to form soft, porous blocks to which a collodial silica binder solution is added. When it is sintered, a rigid block is produced that is cut into quarters and then machined to the precise dimensions required for individual tiles.
HRSI tiles vary in thickness from 1 inch to 5 inches. The variable thickness is determined by the heat load encountered during entry. Generally, the HRSI tiles are thicker at the forward areas of the orbiter and thinner toward the aft end. Except for closeout areas, the HRSI tiles are nominally 6- by 6-inch squares. The HRSI tiles vary in sizes and shapes in the closeout areas on the orbiter. The HRSI tiles withstand on-orbit cold soak conditions, repeated heating and cooling thermal shock and extreme acoustic environments (165 decibels) at launch.
For example, an HRSI tile taken from a 2,300 F oven can be immersed in cold water without damage. Surface heat dissipates so quickly that an uncoated tile can be held by its edges with an ungloved hand seconds after removal from the oven while its interior still glows red.
The HRSI tiles are coated on the top and sides with a mixture of powdered tetrasilicide and borosilicate glass with a liquid carrier. This material is sprayed on the tile to coating thicknesses of 16 to 18 mils. The coated tiles then are placed in an oven and heated to a temperature of 2,300 F. This results in a black, waterproof glossy coating that has a surface emittance of 0.85 and a solar absorptance of about 0.85. After the ceramic coating heating process, the remaining silica fibers are treated with a silicon resin to provide bulk waterproofing.
Note that the tiles cannot withstand airframe load deformation; therefore, stress isolation is necessary between the tiles and the orbiter structure. This isolation is provided by a strain isolation pad. SIPs isolate the tiles from the orbiter's structural deflections, expansions and acoustic excitation, thereby preventing stress failure in the tiles. The SIPs are thermal isolators made of Nomex felt material supplied in thicknesses of 0.090, 0.115 or 0.160 inch. SIPs are bonded to the tiles, and the SIP and tile assembly is bonded to the orbiter structure by an RTV process.
Nomex felt is a basic aramid fiber. The fibers are 2 deniers in fineness, 3 inches long and crimped. They are loaded into a carding machine that untangles the clumps of fibers and combs them to make a tenuous mass of lengthwise-oriented, relatively parallel fibers called a web. The cross-lapped web is fed into a loom, where it is lightly needled into a batt. Generally, two such batts are placed face-to-face and needled together to form felt. The felt then is subjected to a multineedle pass process until the desired strength is reached. The needled felt is calendered to stabilize at a thickness of 0.16 inch to 0.40 inch by passing through heated rollers at selected pressures. The calendered material is heat-set at approximately 500 F to thermally stabilize the felt.
The RTV silicon adhesive is applied to the orbiter surface in a layer approximately 0.008 inch thick. The very thin bond line reduces weight and minimizes the thermal expansion at temperatures of 500 F during entry and temperatures below minus 170 F on orbit. The tile/SIP bond is cured at room temperature under pressure applied by vacuum bags.
Since the tiles thermally expand or contract very little compared to the orbiter structure, it is necessary to leave gaps of 25 to 65 mils between them to prevent tile-to-tile contact. Nomex felt material insulation is required in the bo
|Meteors burn up when they hit the Earth's atmosphere. Why doesn't the space shuttle?
| When a small meteor enters the Earth's atmosphere, it goes from traveling through a vacuum to traveling through air. Traveling through a vacuum is effortless -- it takes no energy. Traveling through air is another story.
A meteor moving through the vacuum of space typically travels at speeds reaching tens of thousands of miles per hour. When the meteor hits the atmosphere, the air in front of it compresses incredibly quickly. When a gas is compressed, its temperature rises. This causes the meteor to heat up so much that it glows. The air burns the meteor until there is nothing left. Re-entry temperatures can reach as high as 3,000 degrees F (1,650 degrees C)!
Obviously, it would not be good for a spacecraft to burn up when it re-enters the atmosphere! Two technologies are used to allow spacecraft to re-enter:
The space shuttles are protected by special silica tiles. Silica (SiO2) is an incredible insulator. It is possible to hold a space shuttle tile by the edge and then heat up the center of the tile with a blow torch. The tile insulates so well that no heat makes it out to the edges. This page discusses the tiles:
These tiles keep the heat of re-entry from ever reaching the body of the shuttle.
These links will help you learn more:
I can only post on Geocities and have little bandwidth to post, so perhaps someone can post it for me.
I inverted the photo on my computer and the writing reads:
-076 (or G) MN00
With these numbers, the tile should be traced to its exact location. It came from Kerens, Texas, 65 miles SE of Dallas and another tile is in Rice, Texas, 45 miles S of Dallas on I-45. If these tile came from under the left wing, that would place its failure at the top of the debris field.
Irwin Thompson / DMN
The tiles themselves would scare you...intuitively, they look insubstantial and too much like styrofoam. Kind of crumbly and brittle and unlike much of anything you'd trust. Amazing stuff.
Reentry sounds a lot like a kiln. Regular porcelain liquifies before hardening.
Would it be possible to coordinate launch schedules with the Russians so that they would have a Soyuz 24 hours or less from launchability when we do a shuttle mission, with the ability to retarget to the Shuttle's orbit should the need arise (with us possibly providing some reciprocal services)?
To be sure, the Soyuz would probably only be able to remove two of the astronauts, but it could also supply life-support supplies as well as such repair supplies as were determined to be necessary.
The most critical tiles are on the underbody of the shuttle. Those are not very likely to be either damaged or suspect, tho' they are replaced after missions frequently in small numbers and in a routine manner. But to look at them , "This is gonna get me home?".
Space Flight is the ultimate act of faith... but you better believe in your vehicle.
Anyway, just a throwaway, an idle curiosity. Did you know that there are ceramic knives far harder and sharper than the best steel?
He created a substance that which was in a liquid form, but could be poured into a mold and allowed to set as a solid. In either form it would not retain heat.
Since then I have never heard anymore about this and I often wonder what happened to the guy.
Yes, I heard of the ceramic knife not too long ago. Strange, but heck, the cavemen and native americans used certain rocks to make some pretty sharp cutting devices as well. Maybe, we are finally catching up technology-wise our ancient ancestors.
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