A modeling system for use in modeling a gas turbine engine including a pulse detonation system having detonation tubes and a detonation chamber, said modeling system comprising: a computer comprising a processor; and, characterized by: at least one database coupled to said computer, said processor programmed to predict characteristics of the pulse detonation system by; using engine parameter data input to the computer, calculating the history in time and space from an instant and location of the initiation of detonation, of temperatures and pressures generated within the detonation tubes and the detonation chamber during pulsing of the engine; determining, for each pulse, a first length of time within the detonation tubes and the detonation chamber elapsed between the detonation of a pulse and a return of pressure within the detonation tubes to a pressure that existed within the detonation tubes before detonation; using thermodynamic properties of gases stored within the database, calculating for each pulse a second length of time necessary to fill the detonation tubes with fuel and air prior to detonation; and determining a desired size of the detonation tubes accounting for the first and second lengths of elapsed time; the processor further programmed to predict characteristics of the gas turbine engine using the first length of time, second length of time and the desired size of the detonation tubes of the pulse detonation system for engine cycle design and off-design performance mapping. a computer comprising a processor; and, characterized by: at least one database coupled to said computer, said processor programmed to predict characteristics of the pulse detonation system by; using engine parameter data input to the computer, calculating the history in time and space from an instant and location of the initiation of detonation, of temperatures and pressures generated within the detonation tubes and the detonation chamber during pulsing of the engine; determining, for each pulse, a first length of time within the detonation tubes and the detonation chamber elapsed between the detonation of a pulse and a return of pressure within the detonation tubes to a pressure that existed within the detonation tubes before detonation; using thermodynamic properties of gases stored within the database, calculating for each pulse a second length of time necessary to fill the detonation tubes with fuel and air prior to detonation; and determining a desired size of the detonation tubes accounting for the first and second lengths of elapsed time; the processor further programmed to predict characteristics of the gas turbine engine using the first length of time, second length of time and the desired size of the detonation tubes of the pulse detonation system for engine cycle design and off-design performance mapping. at least one database coupled to said computer, said processor programmed to predict characteristics of the pulse detonation system by; using engine parameter data input to the computer, calculating the history in time and space from an instant and location of the initiation of detonation, of temperatures and pressures generated within the detonation tubes and the detonation chamber during pulsing of the engine; determining, for each pulse, a first length of time within the detonation tubes and the detonation chamber elapsed between the detonation of a pulse and a return of pressure within the detonation tubes to a pressure that existed within the detonation tubes before detonation; using thermodynamic properties of gases stored within the database, calculating for each pulse a second length of time necessary to fill the detonation tubes with fuel and air prior to detonation; and determining a desired size of the detonation tubes accounting for the first and second lengths of elapsed time; the processor further programmed to predict characteristics of the gas turbine engine using the first length of time, second length of time and the desired size of the detonation tubes of the pulse detonation system for engine cycle design and off-design performance mapping.