Overview:

Commercial solid rocket motors use various grain geometries that differ from what we employ on the MIT Rocket Team. This page is meant to describe the grain geometries of different industry rockets and their effects on flight performance in order to learn and adapt to our own designs.

Space Shuttle Booster:

The forward segment of the motor employs an 11-point star shape along with a domed closure at the front. The middle segments use a straight-walled cylinder shape (BATES). The aft segment is mostly BATES, but tapers outward to surround the booster's submerged nozzle. As seen in the thrust curve, this combination was designed to create a boost to get off the launch pad before decreasing thrust to handle maximum dynamic pressure. The domed closure and submerged nozzle were likely designed for a structural reason rather than pure grain shape, with the grain serving to fill up the otherwise empty space (as opposed to MIT Rocket Team's normal cylindrical tube).

Ariane 5 P-230 Booster:

The forward segment of the booster has a 15-point star grain geometry along with a domed forward closure. The forward segment also includes faster burning fuel than the rest of the motor to alter the thrust curve. The center segments are straight-walled (BATES) grain. In the aft segment, the BATES tapers outward to enclose a submerged nozzle. The thrust of the motor is as follows: it increases with the expanding area of the BATES and star shapes, it decreases substantially when the forward segment burns out, and finally it increases with the BATES until it also burns out.

Vega P80 Motor:

The