The various physical and chemical processes that occur in an actual rocket motor during operation are highly complex. These processes include the complex chemical reactions that occur during combustion; the manner in which "consumption" of the propellant grain occurs during burning; the behaviour of the flow of exhaust gases as they form at the burning surface, travel through the chamber, and exit through the nozzle; the interaction between the exhaust gases and condensed particles (smoke).
The theoretical analysis of a solid rocket motor necessitates certain simplifications, that is, the assumption is of an ideal rocket motor. An ideal rocket motor assumes the following:

• The propellant combustion is complete and does not vary from that assumed by the combustion equation.
• The combustion products obey the perfect gas law.
• There is no friction impeding the flow of exhaust products.
• The combustion and flow in the motor and nozzle is adiabatic, that is, no heat loss occurs to the surroundings.
• Unless noted otherwise, steady-state conditions exist during operation of the motor. This means that the conditions or processes that occur do not change with time (for a given geometric conditions) during burning.
• Expansion of the working fluid (exhaust products) occurs in a uniform manner without shock or discontinuites.
• Flow through the nozzle is one-dimensional and non-rotational.
• The flow velocity, pressure, and density is uniform across any cross-section normal to the nozzle axis.
• Chemical equilibrium is established in the combustion chamber and does not shift during flow through the nozzle. This is known as "frozen equilibrium" conditions.
• Burning of the propellant grain always progresses normal (perpendicular) to the burning surface, and occurs in a uniform manner over the entire surface area exposed to combustion.