Preliminary Design of Solid Propellant Rocket Motors

The Solid Propellant Rocket Motor Performance Prediction Computer Program (SPPMEF) is Standard computer program for the prediction of nozzle and motor performance of solid propellant rocket motors.

SPPMEF consists of a series of modules that are integrated to provide a method to predict the average delivered performance:

  • Calculation of theoretical performances of rocket motors - module TCPSP 
  • Design of nozzle and estimate loss in rocket motor - module NOZZLE
  • Grain Design, module GEOM
  • Module for prediction of interior ballistic performances of rocket motors - module ROCKET

Nozzle module

Performs the following functions:

  • Estimates combustion efficiency and Estimates performance losses in nozle
  • Calculate delived specific impulse
  • Sizes the throat area and exit area

The NOZZLE module analyzes and summarizes the performance loss mechanisms into six categories:

  • Divergence loss,
  • Kinetics loss,
  • Boundary Layer loss,
  • Two Phase Flow loss,
  • Submergence loss and
  • Throat Erosion

For estimation of the performance losses, a set of empirical formulas suggested by the Propulsion and Energetics Panel of AGARD (Advisory Group for Aerospace Research and Development) in AGARD-AR-230. The empirical formulas are valid for alluminized propellants. 

Material for nozzle

  • Steel
  • Ordinary nozzles (composite material or nozzle with insulation)
  • Nozzle with or with out Graphite throat


Nozzle Types

Grain Design modules

Grain Design modules contains three standard grain design shapes:

  • CP Grain (cylinder with internal burning surface, cylinder with internal-external burning surfaces),
  • Cluster CP Grain (multiple cylinders with internal-external burning surfaces),
  • Star Grain.
  • For 3D grain we prefer using database obtained modelling the grain in AutoCAD.


This module is consisted of two parts:

  • a part for designing the propellant grain and
  • a part for regression of burning surface

The computer program OPTIM, which insure to choose optimal geometry of star by variation seven independent geometric variables of propellant with assumptive intervals of volumetric loading, relative rest of propellant which is not burned (sliver) and degree of neutrality burning area of propellant, has been developed.

Comparative analyses of results from OPTIM computer code with referring code SPP (Solid Performance Program) have been carried out and very good agreement has obtained. 

Regression analyses of burning area 


Internal ballistic code ROCKET is one-dimensional motor ballistics modules. This module provide predict the average delivered performance, as well as mass flow, pressure, thrust, and impulse as functions of time (see figure).

Internal ballistic analysis computer program

Pressure-time curve for the test rocket motor 128 mm, RM-2