Ascent Trajectory Optimization for a Hybrid Propulsion Mini Launcher

In the last years the Small Satellites Market is taking more and more ground as well as the Small Launcher Market. Small satellites are generally delivered as piggyback payloads on rockets commissioned for larger spacecraft. In this situation the primary payload takes priority, and extra payloads have to be adapted to the launch schedule and orbit. This has led to the need to start developing launchers dedicated to small satellites, in this way, the latter are the main payload and do not have to adapt to the mission specifications of large payloads and medium or heavy launch-vehicles. In this context HyImpulse was born. HyImpulse is a newly founded company located in Hardthausen with the aim to develop a small satellite launch vehicle based on the hybrid propulsion and turbopump technology developed at the DLR Instituteof Space Propulsion. The main goal of the work presented in this thesis has been to use Astos Software for the study and the optimization of a three stages mini launcher’s ascent trajectory capable to insert the maximum possible payload mass in a 500 km sun synchronous orbit. One of the missing feature of the software is related to the fact that during the definition of the rocket’s model it does not allow to model hybrid engines. For this reason the first part of the work has dealt with the writing of a C code able to simulate the hybrid engine’s working by computing its performances parameters. This code is recalled in each instant of time of simulation and the main output is the thrust’s value in the instant of time considered that is used by Astos in the equations of motion for the trajectory’s computation. The second part of the work has dealt with the trajectory’s optimization. Optimization means to find the trajectory that allows to maximize the payload by respecting the mission requirements and satisfying all the constraints imposed (Maximum dynamic pressure reached, maximum heat flow before the release of the fairing, etc).