Design aspects of launch vehicle sizing including air-breathing propulsion

Abstract The overall sizing of launch vehicles is of interest, especially when air-breathing is also included. The sizing of a launch vehicle is dictated by the State of Art technologies present and the need to match the challenging demands of high-payload fraction, low cost, and also ensure reliability. This paper presents some of the important design requirements. An ideal velocity approach, which assumes various velocity losses, is generally followed for initial vehicle sizing. However, as this approach is approximate and sometimes incorrect, a new concept of accounting the drag and thrust losses during the atmospheric phase for conventional rockets and air-breathing launch vehicles using scramjet propulsion is evolved complementing the ideal velocity sizing approach. A simplistic two-dimensional trajectory simulation program with graphics for quick interactive design was developed for this purpose. The air-breathing launch vehicle trajectory is split into three flight phases. The sizing of the vehicle considering, especially, the intermediate air-breathing regime is also dealt with. A method to determine the maximum-load envelope expressed in terms of the product of flight dynamic pressure and angle of attack, namely Q-alpha, for all weather launches useful for initial design purposes is also suggested. The design program meant for initial design sizing purposes gives a quick insight on the vehicle performance prior to detailed design with minimum basic vehicle data for conventional rockets and also for air-breathing scramjet vehicles. The various design factors, such as optimum velocity requirement for two stage to orbit vehicles and the sizing requirement of the orbital stage after end of air-breathing phase, are also discussed through representative typical values highlighting the design sensitivities.