Simulation and Analysis of Pull-Up Manoeuvre during In-Air Capturing of a Reusable Launch Vehicle

Kurzfassung

The innovative "In-Air-Capturing (IAC)" recovery method involves winged rocket stages being captured mid-air and towed back to the launch site. This patented approach by German Aerospace Center (DLR), shows potential for substantial cost reduction by eliminating the need for an additional propulsion system during descent. A critical operation in IAC involves the Towing Aircraft (TA) and Reusable Launch Vehicle (RLV) performing a coordinated pull-up, such that the configuration transitions from a descending glide to a powered ascending flight. During this maneouvre, the two vehicles are connected to each other by a rope, allowing the TA to use its propulsion system to tow the RLV and gain altitude. The final goal at the end of this maneouvre is to reach a suitable cruise altitude for the tow-back to the launch site. This paper presents the modelling and simulation of a full-scale RLV and TA performing the Pull-Up Maneouvre of IAC. Important subsystems like aerodynamics, propulsion, guidance and control, as well as external disturbances from the wake of the aircraft are discussed in detail. The RLV and TA are assumed to be connected by a simplified rope, modelled as a rigid link. An analysis is performed to determine the optimal cruise flight conditions for the mated configuration. Trajectory simulations are then performed to identify the challenges and additional requirements for the system. From the simulations, it could be concluded that the configuration could reach the commanded cruise conditions despite external disturbances from the wake. To sum up, the potential improvements and future simulations are discussed.