A Full-Scale Simulation and Analysis of Formation Flight during In-Air Capturing

Abstract

In the past two decades, the renewed interest in sustainable space transportation has fueled the development of many innovative reusable launch technologies. One such concept called ‘In-Air-Capturing (IAC)’ involves winged rocket stages captured mid-air and towed back to the launch site using an aircraft. The approach patented by German Aerospace Center (DLR), shows potential for substantial mass and cost reduction by eliminating the need for additional propulsion during the descent. A critical aspect of IAC requires the two involved vehicles to be in a formation flight with similar velocities, altitudes and flight path angles separated by a safe distance. The preliminary requirement is to maintain the formation for a minimum of 60 s, despite any external disturbances. This paper presents the modelling and simulation of a full-scale reusable launch vehicle and a towing aircraft attempting the formation flight for IAC. First, a suitable aircraft configuration is selected based on the aerodynamic performance of the selected test rocket stage. Important subsystems are also identified and modelled comprehensively. Then, trajectory simulations are performed to identify the best approach and initial conditions for the formation. Sensitivity of the formation flight to several factors like the idle thrust, wake turbulence and wind gusts are also analysed. The simulation yielded that the minimum duration of formation flight could be maintained, despite the external disturbances. Lastly, potential improvements and future simulations are discussed