Rocket motors materials requirements

The combustion performance of a rocket motor is dependent on various physicochemical processes that occur during propellant burning. Since the free volume of a rocket motor is limited for practical reasons, the residence time of the reactive materials that produce the high temperature and high pressure for propulsion is too short to allow completion of the reaction within the limited volume of the motor as a reactor. Though rocket motor performance is increased by the addition of energetic materials such as nitramine particles or azide polymers, sufficient reaction time for the main oxidizer and fuel components is required. 

The volume of solid and liquid wastes other than metal rocket motor casing and fin fragments is expected to be low about 0.9 kg of filter dust and 0.2 m of condensate water and cooler blowdown per shot. Again, the dust from the filter will contain lead and could be defined as a RCRA hazardous waste. Although agent contamination is not an issue, the offgases will require treatment. Their volume and constituents will depend on the materials that are detonated and combusted in the DAVINCH vessel—that is, rocket propellant and, possibly, overpacking materials. 

Rocket motors are constructed of composite materials with each component material performing a specific function depending on its location. This type of construction is optimum, since the environmental conditions and hence the materials requirements vary greatly with motor position. 

In addition to the ablative materials employed in the primary propulsion systems, specialty purpose ablators are also required in the launching area of rocket motors. During ignition and takeoff of the solid propelled vehicle, the launch equipment may be immersed in the... 

Rocket motors last only for periods of a few minutes and their requirements are very different from those for supersonic or subsonic aircraft. Space re-entry vehicles can reach temperatures as high as 450-500°C, or even higher, for a period of 5-10 min. Black box flight recorders used in civil aircraft have to be able to withstand fires, with temperatures exceeding 1000°C for several minutes. Each of these materials has a different design specification and composition. 

Results of ablation tests show that the nanocomposites perform comparably to current state-of-the-art insulation materials with only 2 wt % addition of nanoscale filler (17). Table 1 shows the erosion rates for two state-of-the-art internal solid rocket motor insulation materials versus neat Nylon 6 and nanocomposites derived from Nylon 6 at two mass fluxes. As expected, neat Nylon 6 does not survive this extreme environment, completely being removed within the timescale of the test. In stark contrast, the erosion rates for the nanocomposites with as little as 2 wt% filler content are comparable to the rates for the current materials. The reduction in required filler content will offer a reduction in weight, an increase in reliability because the material can be manufactured as one single part, and ultimately, a drastic reduction in cost. 

Some applications are closed shapes or have a local reduction, like some pressure vessel types or rocket motor cases. If the products have no liner the core must be dissolvable. For dissolvable materials the following are usable sand (soluble, water soluble),plaster (soluble,breakout), salt (meltable, eutectic) and alloy (with a low melting temperature). All dissolvable cores are precast in an extra process step before the winding process starts. After the winding process the core is nearly complete covered with filaments. Depending on the dissolvable material used, different techniques to dissolve the core are required such as rinsing with water or heating up to a certain temperature. All dissolvable cores are non-heated. 

In the manufacture of the casings of solid rocket motor (SRM), the material requirements are bifunctional. They have to have high hoop strength on one side and high ablation resistance on the other. In order to prepare such materials, the technology of coextrusion is utilized. In a twin-screw extruder, both the materials are coextruded together. During the residence time of the polymers in the extruder, the interdiffusion of either material in the other occurs. Calculate the interlayer thickness as a function of the extruder residence time and diffusivities of the two materials. 

Structural analysis of the solid rocket case-grain system using experimentally determined propellant response properties may permit a complete description of the combined stresses and resultant deformations, but a statement expressing the ability of the propellant to withstand these stresses is also required. Such a statement, which relates the physical state at which failure occurs to some material parameters, is called a failure criterion. The criterion for failure permits a prediction of safety margins expected under motor operation and handling and defines the loading regimes where abnormal operations will occur with intolerable frequency. 

Solid-propellant rocket engines are attractive because of their simple propulsion principle, which avoids alimentation systems needed to produce combustion. Both oxidizer and fuel elements are present in a chemically stable material (the propellant), which is shaped to fit the motor itself. This feature, in particular, represents an obvious advantage for military applications such as nuclear ballistic missiles, which require a long-term storage capability and high service safety (3). 

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