13. Stage Auxiliary Systems

The launch vehicles are generally configured with multiple stages to achieve the required orbital velocity. To achieve the required orbital conditions, the burnt-out stages are to be separated from the vehicle immediately after meeting their intended functional requirements. These separation processes are mission-critical functions as the inadvertent collision during separation can lead to vehicle failure. All these systems are generally termed as stage auxiliary systems (SAS) and carry out the mission critical separation processes in the vehicle as per the specified requirements, thus ensuring the vehicle safety and successful mission. The stage auxiliary systems are configured with high-energy systems and they are built with pyro-elements, which, once assembled in the flight systems, are not amenable for ground tests. Thus, the stage auxiliary systems have only one chance to operate, that too directly in the flight after its manufacturing and these systems have to operate successfully in the first attempt itself. Therefore, these systems have to be highly reliable. They have to be necessarily robust with suitable built-in redundancy to achieve the safer and successful mission. The design of SAS is closely linked with all other subsystems of the vehicle. The high-energy pyro-systems during their operation induce severe environment to the vehicle systems. Design of the SAS is based on the vehicle systems inertial properties, vehicle subsystems, performance parameters and the vehicle operating environment. Therefore, integrated design approach is essential to achieve the robust and highly reliable designs for the complex, high-energy stage auxiliary systems. During the vehicle flight from lift-off till satellite injection, the vehicle can deviate from its nominal path due to abnormal behaviour or due to failure of any of the subsystems onboard. In such cases where the deviation is beyond the safe allowable corridor, the flight has to be terminated using vehicle destruct system. Additional care should be taken to avoid the inadvertent activation of the vehicle destruct system during normal flight. The stage auxiliary systems’ requirements of a launch vehicle, their functional aspects, integrated design aspects of SAS and the various elements involved in the SAS design process are explained in this chapter. The details of the actuators used in these systems based on pyro-mechanical devices, the jettisoning and destruct systems, their performance in a typical vehicle and the validation strategy of these important subsystems are also presented. Detailed analysis of the separated body dynamics with respect to the ongoing vehicle is very vital in the separation system design. The various aspects of system analysis are included.