The thrust of a solid propellant rocket depends directly upon the burning surface area of the solid grain. Therefore we try to modify the shape of the solid propellant grain to get the maximum surface area. This can be done by using a mathematical curve better known as a fractal curve.
Fractals are said to possess infinite detail. Thus theoretically, we could increase the inner burn surface area of the solid propellant to an infinite value. Thus for the first few seconds of burn, we could directly affect the burn rate of the solid propellant.
Take the example of the Koch snowflake. The Koch snowflake can be constructed by starting with an equilateral triangle, then recursively altering each line segment as follows:
1. Divide the line segment into three segments of equal length.
2. Draw an equilateral triangle that has the middle segment from as its base and points outward.
3. Remove the line segment that is the base of the triangle from step 2.
Thus after a single iteration you would have a hexagram. The Koch snowflake is the limit approached as the above steps are followed over and over again.
Using the newly developed techniques and methods like 3-D Printing and nanotechnology, we can print the mold out in the required fractal shape and mold the modified solid propellant.