N-Prize Lower Stage

Modern rebuildable high power rocket motors are powerful, they can be the same formula as the Shuttles SRBs, but the reusable casings are heavy. The idea is a redesign to reduce weight and add the possibility of thrust vector control. Per the link the reusable casings usually weigh about the same as the propellant they are surrounding and to have any hope of reaching space, every gram must be saved and drag must be reduced wherever possible.

Rebuildable cases need to perform 3 functions, contain the pressure of the burning fuel, contain the heat from the burning fuel and provide the appropriate nozzle for directing thrust. Present cases do this with an aluminum outer tube with internal threads at each end and two O-ringed end caps, one is just a plug and the other has the nozzle.

Replace the aluminum tube with radial wrapped carbon fiber (thickness based calculated hoop stress * safety factor) with only the outer layer being a single layer of longitudinal fibers spaced out leaving ten longitudinal grooves between the runs. The ends on the carbon would be slotted with a convex slice which will be explained later. The end caps are replaced with cylindrical aluminum tubes with a semi-spherical ends. The basic idea is an aluminum can with the top cut off and then bottom pushed out to be semispherical. Each of the end caps are capped by a ceramic “bobbin” with one spherical side to match the end cap. One bobbin will have a solid center and the other will have hollow center with a SS cylinder inserted to support radial compression on the bobbin. On the nozzle end (the side with the hollow bobbin) a hole is drilled in the aluminum end cap which is the same size as the hole in the bobbin. This needs to be large enough for both the nozzle and to allow slight nozzle deflection. On the inside of the nozzle end cap goes quarter semi-spherical Teflon washer and a ceramic nozzle with a quarter semi-spherical base. A ceramic cap with a small spring is C-cliped around the nozzle to keep the nozzle assembly in contact with the aluminum end cap, but will still allow slight radial sliding deflections. Cover exposed aluminum surfaces with a thin ceramic insulator sheets (McMaster 93615K14). Create an aluminum tube and ceramic insulator spacer to go between the two end caps.

Now assemble the motor by stacking the motor grains inside the end cap and then another ceramic sheet and aluminum cap the ends so that the aluminum and ceramic butt against each other and slide the carbon fiber tube around the assembly. Take a Kevlar thread that has loops spliced onto each of its ends and thread around the assembly by wrapping first the bobbin then pass along the longitudinal gaps to the other bobbin. If this works, it should use the aluminum as a gas envelope, the ceramic as the thermal barrier, the carbon fiber as the hoop stress support and the Kevlar as the longitudinal stress support. Small piezoelectric actuators could be added to slightly deflect the nozzle for steering.