Editing Solid-propellant rocket (section)

==Grain geometry==
Solid rocket fuel [[deflagrates]] from the surface of exposed propellant in the combustion chamber. In this fashion, the geometry of the propellant inside the rocket motor plays an important role in the overall motor performance. As the surface of the propellant burns, the shape evolves (a subject of study in internal ballistics), most often changing the propellant surface area exposed to the combustion gases. Since the propellant volume is equal to the [[cross sectional area]] <math>A_s</math> times the fuel length, the [[volumetric]] propellant consumption rate is the cross section area times the linear burn rate <math>\dot{b}</math>, and the [[instantaneous]] [[mass flow rate]] of combustion gases generated is equal to the volumetric rate times the fuel density <math>\rho</math>:

:<math>\dot{m} = \rho \cdot A_s \cdot \dot{b}</math>

Several geometric configurations are often used depending on the application and desired [[thrust curve]]:

<gallery>
Image:circ ex.jpg|Circular bore simulation
Image:cslot ex.jpg|C-slot simulation
Image:moon ex.jpg|Moon burner simulation
Image:fino ex.jpg|5-point finocyl simulation
</gallery>

* Circular bore: if in [[BATES]] configuration, produces progressive-regressive thrust curve.
* End burner: propellant burns from one axial end to other producing steady long burn, though has thermal difficulties, center of gravity (CG) shift.
* C-slot: propellant with large wedge cut out of side (along axial direction), producing fairly long regressive thrust, though has thermal difficulties and asymmetric CG characteristics.
* Moon burner: off-center circular bore produces progressive-regressive long burn, though has slight asymmetric CG characteristics
* Finocyl: usually a 5- or 6-legged star-like shape that can produce very level thrust, with a bit quicker burn than circular bore due to increased surface area.