Annotation: The main solid rocket motors of surface-to-air missiles and some short-range missiles have, as a rule, two operation modes – starting (augmented rating) and cruise (with decreased propellant consumption level). The methods to calculate intraballistic characteristics of such motors have a number of peculiarities, which set them apart from the methods of determining the characteristics of motors with constant propellant consumption level. The purpose of this article is to analyze such peculiarities, design methods, to find interrelation between the parameters of propellant consumption diagram, to determine the impact on the latter of motor design features and propellant characteristics. To achieve this goal, the method of analytical dependencies was developed. The equations obtained show that the required parameters of diagrams (including consumption-thrust characteristics difference between the starting and cruise modes) can be ensured due to varying either case diameter or propellant combustion rate or due to combined variation of these values. In practice, the cases are possible when for some reasons it does not seem possible to vary the case diameter or propellant combustion rate and the requirements to consumption diagram cannot be satisfied to the full extent. The task of motor developer in that case consists in determination of acceptable (alternative) propellant consumption diagrams that would be closest to required. The proposed method is based on calculation and construction of nomograms of dependencies of relative propellant consumption in cruse mode on relative time of starting leg at different propellant combustion rates and constant (required) case diameter and vice versa, at different values of case diameter and constant (available) propellant combustion rate. Using these nomograms, the rocket developer can determine the propellant consumption diagram acceptable for the rocket. In a number of cases, design limitations for separate main motor assemblies are imposed on consumption characteristic diagram that have an impact on its required parameters. The presented materials allow evaluating that impact and contain the proposals to remove it. The presented method allows quickly determining the conditions needed to fulfill required propellant combustion products consumption diagrams and in case of nonfulfillment of these conditions – allow presenting alternative options for selection of most acceptable one.

Annotation: This paper describes the firing rig test of the solid rocket motor, fastened to the rig in order to measure the thrust level. It is shown that when the motor enters the steady-state mode, the rig with solid rocket motor starts experiencing mechanical oscillations due to the sudden thrust build-up. Motion of the oscillating system is studied under the impact of the linearly or suddenly increasing impulse load. Mechanical oscillations damping is considered on the basis of the viscous friction model. Procedure of the analytical modeling of the damped oscillations is suggested for the complex pattern of the loading variations, based on the fundamental principle of superposition, according to which the motor displacement during the oscillating motion is considered as sum of displacements due to the impact of the impulsive, sudden and linearly increasing loadings. This procedure simulates different time variations of thrust as motor enters the steady-state mode. Oscillating motion with parameters of the oscillating system and thrust change with time option have been simulated as they were realized during the firing rig tests of one of the solid rocket motors. Simulated and experimental (thrust sensor readings) curves of the elastic force were compared, which showed the qualitative and quantitative conformity of the suggested model of oscillations to the actual oscillations of the solid rocket motor, installed in the rig during the firing rig test. Values of the initial thrust, initial impulse and other simulation parameters were updated, adjusting the simulated curve of the elastic force to the experimental one. It was concluded that simulation of the elastic oscillations of the solid rocket motor in the rig using the suggested analytical model will enable more reliable definition of the initial thrust of the motor and its time behavior, impulse loading due to the separation of the plug and used elements that separate with it. Application of the suggested procedure of motor oscillations simulation in the phase of rig design will enable more detailed prediction of the occurring processes as well as the estimation of parameters of the individual elements, units and rig as a whole.