Shuttle material

3 Shuttle aterlul. Some of the characteristics of an ideal shuttle material are (1) low-actiration cross section, (2) low density, (3) high thermal conductivity, (4) stability to radiation, and (5) structural strength. 

The first property is desirable to prevent the carrier s becoming active enough to require shielding during the unloading operation. Materials that satisfy this requirement are electrolytic iron, beryllium, zirconium, carbon, polystyrene, and bakelite. 

The use of beryllium or zirconium would permit a larger wall thickness for a given weight carrier. The activity of these elements is controlled by the impurities aluminum and hafnium. 

Some of the plastics are promising, but the inherent low thermal conductivity makes cooling of the sample difficult. Information on the effects of radiation on plastics is rather incomplete at this time. However, from experiments made with low neutron fluxes, it appears feasible to use bakelite and polystyrene as shuttle materials. 

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Leger, L. Oxygen Atom Reaction with Space Shuttle Materials at Orbital Altitudes, NASA Technical Memorandum 58246, May 1982... 

Hoggatt, J. T. (1971). Paper presented at 1971 National SAMPE Technical Conf. on Space Shuttle Materials, Huntsville, Alabama, Oct. 5. 

In most instances, plants receiving resin via railcar have a rail siding on site, but this is not always the case. In some instances, the rail-car is held at a local railyard and material is transferred out of the railcar and into a bulk truck by means of a portable railcar unloader. These units are typically mounted on trailers and powered by diesel engines. The truck shuttles material to the plant where it self-unloads into the silos. This method adds a cost to the operation, thereby reducing savings, but it is an option where on-site sidings are not available. 

Evidence examined in the review of space shuttle material, manufacturing, assembly, quality control, and processing of nonconformance reports found no flight hardware shipped to the launch site that fell outside the limits of shuttle design specifications. 

Beryllium is used as an alloying agent in producing beryllium copper, which is extensively used for springs, electrical contacts, spot-welding electrodes, and non-sparking tools. It is applied as a structural material for high-speed aircraft, missiles, spacecraft, and communication satellites. Other uses include windshield frame, brake discs, support beams, and other structural components of the space shuttle. 

The practice of employing reusable thermal protection systems for reentry is becoming more common. These are essentially ablative materials exposed to environments where veryHtde ablation actually occurs. Examples iuclude the space shuttle tiles and leading edges, exhaust no22le flaps for advanced engines, and the proposed stmctural surface skin for the National Aerospace plane. 

Polyimides (PI) were among the eadiest candidates in the field of thermally stable polymers. In addition to high temperature property retention, these materials also exhibit chemical resistance and relative ease of synthesis and use. This has led to numerous innovations in the chemistry of synthesis and cure mechanisms, stmcture variations, and ultimately products and appHcations. Polyimides (qv) are available as films, fibers, enamels or varnishes, adhesives, matrix resins for composites, and mol ding powders. They are used in numerous commercial and military aircraft as stmctural composites, eg, over a ton of polyimide film is presently used on the NASA shuttle orbiter. Work continues on these materials, including the more recent electronic apphcations. 

Solids. Increasing use of bulk cars, especially of covered hopper cars, has accompanied the expansion of the tank-car fleet. The principal drawback of bulk cars is the requirement for limited use, specialized cars, which necessitates a large investment. However, if such investment can be justified, the cost of transportation for dry bulk materials ia hopper cars usually is less than those for goods ia shipping containers. In many instances, such cars are used in closed-loop service that is, they shuttle in unit trains between filling and discharge points. Similar equipment is also used in specialized highway vehicles whose tmck bodies can incorporate dump hoppers and built-in conveyors. 

In bulk coating processes, bulk materials are joined to the substrate either by a surface melt process or by attachment of the soHd material. An example of the latter is the appHcation of heat-resistant tiles of sHica-type material to the aluminum alloy skin of a space shuttle vehicle, enabling the vehicle to withstand the reentry heat. 

Originally developed for tyre cords, Kevlar-type materials have also become widely used in composites. Uses include filament-wound rocket motors and pressure vessels, metal-lined Kevlar-overwrapped vessels in the space shuttle, boat and kayak hulls, Kevlar-epoxy helmets for the US military, and as one of the reinforcements in composite lorry cabs. 

The potential weight savings in a variety of structures are displayed in Figure 1-27, There, the savings range from a modest 25/lb ( 55/kg), barely justifying the use of some composite materials, to the enormous 15,000/lb ( 33,000/kg) in the Space Shuttle. In the case of the Space Shuttle, use of composite materials fairly shouts for attention. In between those two extremes, composite materials have very strong justification for use. 

Historically, polymer-matrix composite materials such as boron-epoxy and graphite-epoxy first found favor in applications, followed by metal-matrix materials such as boron-aluminum. Ceramic-matrix and carbon-matrix materials are still under development at this writing, but carbon-matrix materials have been applied in the relatively limited areas of reentry vehicle nosetips, rocket nozzles, and the Space Shuttle since the early 1970s. 

In order to evaluate one of the issues that is very pertinent to this material selection, the cost to get the truss elements up into space must be known. In 1985, a Shuttle flight cost 90 million. If the Shuttle is capable of carrying a payload of 60,000 lb (27,000 kg), then for every... 

First, achieving lower raw material cost than at present is always an important economic factor. When the price for one material comes down relative to another, the point at which we trade-off between the two materials changes because cost is a factor in most designs. That statement is not meant to imply that engineers are not concerned about cost in some designs, but we must emphasize that some particular structures have functional requirements as the most important issue. Can they or can they not do the job Cost is not the primary issue in that case. We would naturally like to have a less-expensive Space Shuttle, but can we do the job that the Space Shuttle is now doing with a lower-cost structure We could use less-expensive materials, but would they be able to hold up, would they survive reentry, and would the astronauts be able to survive If the astronauts would not be able to survive, then clearly you would acknowledge that we must pay the added cost to get the job done, i.e., to ensure their safety. 

Boron itself has been used for over two decades in filament form in various composites BO3/H2 is reacted at 1300° on the surface of a continuously moving tungsten fibre 12/tm in diameter. US production capacity is about 20 tonnes pa and the price in about 80(. The primary use so far has been in military aircraft and space shuttles, but boron fibre composites are also being studied as reinforcement materials for commercial aircraft. At the domestic level they are finding increasing application in golf shafts, tennis rackets and bicycle frames. 

Over-molding Over-molding is also called in-mold assembly, two-color rotary, or two-color shuttle. Two materials are molded so that the first molded shot is over-molded by the second molded shot first molded part is positioned so the second material can be molded around, over, sections, or through it. The two materials can be the same or different and they can be molded to bond together or not bond together. If materials... 

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