The re-entry of Space Vehicles into the atmosphere after completing missions in orbit around the earth or the moon has been accomplished many times in the past two decades. Past man rated vehicles like Mercury, Gemini, and Apollo carried from one to three astronauts and were quite small and compact in size compared to the Space Shuttle Vehicle and required much less of an area to have re-entry insulation to protect the capsule and its occupants from the heat during re-entry. Insulation on past vehicles was an ablative type that actually charred and peeled away the dynamic heating of re-entry carrying the heat away from the capsule. These vehicles were used for only one mission. SEE FIGURE 4. Tiles manufactured by the Lockheed Missiles and Space Company, Space Systems Division, Thermal Protection System for use on the Space Shuttle Orbiter as a Thermal Protection System are designed to last up to 100 missions. The tile will keep the outer structure from melting and the internal compartments cool enough to enable human occupants to perform their duties comfortably during re-entry through the atmosphere. Since each tile is equally important as another, the need to dimension them accurately to determine the best fit and relationship to surrounding tile is very important. With the Space Shuttle Orbiter being larger in size than a Boeing 737 twin jet airliner, this gives one some idea of the area to be covered with tile. The Space Shuttle Orbiter cargo compartment is large enough (15′×15′×60″) to carry the Mercury, Gemini and Apollo all at one time. Since the Manufacturing process cycle is of key importance to maintaining the dimensional tolerance and strength requirements, a short review of these processes will be presented prior to the dimensional part of the lecture material. In the conclusion portion of the presentation, several photographs of the vehicle tile Thermal Protection System will be shown after mission return to show the effects of dynamic heating and tile integrity. The basic raw material is a short staple 99.7% pure amorphous silica fiber. The fibers are derived from common sand. Basic fibers are mixed into a slurry and cast into a Production Unit. From the production unit, the tile shapes arenumerically control machined. The tile are then coated on the designated area with a silica frit coating and kilned at 2300 degree fahrenheit to fuse the coating to the tile basic material. Identification of the tile is then applied and they are forwarded for inspection. The dimensional relationship of one tile to the other is equally important to achieve the proper spacing for any movement and a breather path to the atmosphere. Master Dimensional Data is analyzed and transformed into N/C machining and dimensional standard computer tapes which are used to machine and measure the completed tiles.
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