Reusable Launchers: Challenges for the prediction of aerodynamic characteristics and thermal loads

Kurzfassung

Retro-propulsion is a technique which involves the firing of rocket engines opposite to the direction of travel and has emerged as a transformative technology in the design and operation of reusable launch systems. Traditionally associated with spacecraft descent and landing on celestial bodies, retro-propulsion has found renewed interest and expanded applications in the realm of re-usable launch vehicles for earth orbit missions. One of the notable implementations of retro-propulsion in re-usable launch systems is the controlled descent of the first stage of a rocket. After propelling the payload to a certain altitude, the first stage initiates a controlled descent back to Earth. Retro-propulsion engines are activated to counteract the vehicle's forward momentum and shield critical components from the harsh conditions of re-entry, allowing for a precise and targeted return to the landing site or a recovery platform. SpaceX's Falcon 9, with its successful landings on drone ships and ground-based landing zones, stands as a prominent example of the practical implementation of retro-propulsion in reusable launch systems. The recent surge in interest in retro-propulsion technologies can be directly attributed to the success of Falcon 9, as well as the economic and environmental factors which play an important role in the sustainability of future space exploration. Reusable launchers incorporating retro-propulsion strategies have demonstrated a dramatic reduction in launch costs while achieving launch frequencies 10 to 20 times higher than expendable launchers. Despite these well-known advantages, the use of retro-propulsion introduces a set of complex engineering challenges. During the return to earth phase of flight, the booster is subjected to a wide spectrum of freestream conditions ranging from low Mach number incompressible flows to high Mach number compressible flows with thermo-chemical effects. Predicting the vehicle aerodynamic characteristics and thermal loads presents a distinct set of challenges for ground-based facilities, as well as numerical simulations. Aerodynamic considerations, such as the interaction of retro-propulsion plumes with the vehicle structure and control surfaces, demand careful analysis to ensure stability and controllability during descent. Moreover, the thermal loads generated during the retro-propulsion and aerodynamic glide phases require a thorough understanding of the heating distributions so that suitable thermal management systems can be designed to protect the critical components of the vehicle. This presentation will give an overview of the current challenges for the prediction of aerodynamic characteristics and thermal loads from both a numerical and experimental point of view. There will be a particular focus on results stemming from European based projects where DLR Göttingen has been a project partner.