Simulation and Analysis of Pull-Up Manoeuvre during In-Air Capturing of a Reusable Launch Vehicle
Creators: name:  S. SINGH 
name:   S. STAPPERT 
name:   M. SIPPEL 
name:   S. BUCKINGHAM 
name:   C. KUCUKOSMAN 
name:   L. BUSSLER 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: REUSABLE SYSTEMS
SPACE ACCESS
FALCON

description: Over the 21st century, the commercial interest in reusable launch technology has grown tremendously. Reusable Launch Vehicles (RLVs) reduce launch cost through recovery and reuse of parts of the launcher. The currently operational RLVs mostly land vertically using the engines from first stage to slow down. This method requires significant amount of fuel for deceleration and landing, thereby adding to the inert mass and causing a penalty on payload capacity. An innovative approach, called In-Air-Capturing (IAC), which eliminates these disadvantages has been patented by DLR [1]. The idea involves the winged stage being caught mid-air and towed back to the launch site without the need of additional propulsion system [2]. The operational cycle of IAC starts with the launcher lifting off vertically and ascending until Main Engine Cut-Off (MECO). At MECO, the winged first stage separates from the launch vehicle and re-enters the atmosphere in a ballistic trajectory, in the course of which it decelerates from supersonic velocity to a subsonic glide. Meanwhile, a capturing aircraft is waiting at the downrange rendezvous area, loitering until the RLV arrives. Between 8 km to 2 km altitude, the final IAC manoeuvre is performed [3]. First, the aircraft approaches the RLV such that both vehicles have similar velocities and flight path angles, separated by a safe distance [4]. Once a parallel formation is achieved, an Aerodynamically Controlled Capturing Device (ACCD) is released from the aircraft. This device autonomously navigates to the RLV and connects the two aircraft with a rope [5]. Next, the pull-up manoeuvre is performed. Here the mated configuration, pulls up from a descending flight to cruise at an optimal altitude. Finally, the RLV is towed back to launch site, where it is released to land horizontally on an airstrip. The focus of this study is to get a comprehensive understanding of the third phase of IAC, called the Pull-Up Manoeuvre. In this manoeuvre, the thrust from the aircraft should be able to counteract the drag from the RLV, thereby facilitating the mated configuration to gain altitude and eventually achieve cruise flight. Trajectory simulations are performed considering full-scale test cases. The towing aircraft is selected to be the four-engine commercial jetliner, Airbus A340-600 [3]. For the RLV, a 3-Stage-To-Orbit (3STO) launch vehicle with a folding wing (dubbed RLVC4) is proposed in [6]. For the current study, the two vehicles are assumed to be connected via a rigid link (rope) of fixed length. To get a more realistic definition, the aerodynamic datasets are generated using Reynolds-averaged NavierStokes (RANs) calculations. Additionally, the propulsion system is modelled with turbofan performance in consideration. The analysis also involves identification of an optimal guidance trajectory and control strategy for Pull-Up Manoeuvre. Some significant factors like thrust requirements, control surface limitations and environmental disturbances are also examined. The research is performed under the H2020 project - Formation flight for in-Air Launcher 1st stage Capturing demonstration (FALCon), aimed at the development and testing of the IAC technology.