Aerodynamic Design of a Reusable Booster Stage Flight Experiment

The DLR Project ReFEx is a flight experiment to gain experience for future HTVL reusable rocket stages. The focus of this paper lies on the aerodynamic properties and difficulties during the reentry flight. The stable flight envelope, regions with little and without aerodynamic stability and the analysis of various forms of stable and unstable motion are covered. The test flight is scheduled for 2022

Preliminary Aerodynamic Design of a Reusable Booster Flight Experiment

The Reusable Flight Experiment (ReFEx) is an experimental vehicle currently in development by the German Aerospace Center (DLR), which simulates the reentry of a winged reusable booster stage. The topic covered in this paper is the aerodynamic design through the Mach number range from 6.0 to 0.6, including the transonic regime, by CFD simulations using the DLR TAU-Code. For steering and lift generation the vehicle is equipped with multiple aerodynamic surfaces: canards, wings and a vertical fin. A VSB30 was chosen as the carrier rocket, leading to numerous limiting conditions that had to be fulfilled. The resulting tradeoffs are discussed. Also the process to achieve a configuration that meets all needs regarding stability during ascent and descent, controllability and energy management to autonomously follow a desired trajectory is explained. Since this vehicle is under development, the presented geometry is not necessarily the final shape. However, the completed design iterations strongly indicate that only details will differ between the presented state to the final and flyable ReFEx, scheduled to fly late 2021

Aerodynamic Data Set Generation for the Experimental Vehicle ReFEx

Aerodynamic characterization of vehicles is mandatory to identify their flight en-velope, their controllability behavior and ultimately their shape. During the design process one goal is to efficiently determine the aerodynamic properties for every possible state during the flight. Therefore, the aerodynamic force and moment co-efficients need to be known for all combinations that are expected to occur of ve-locity, orientation, altitude, control surface deflections and dynamic values such as rotation rates. The amount of conditions that need to be evaluated can be re-duced if an independence within these variation parameters is proven. For an aer-odynamic design process via CFD this paper purposes an additional method to reduce the amount of data points. Through the use of the DLR TAU code with an overlapping meshes feature, envelope datasets can be produced for the momen-tum free trimmed state in each flight point. With this starting set, several subsets with parameter variations can be computed. This reduces the amount of simula-tions needed by 65% for the investigated case, the flight experiment ReFEx

Contribution of Numerical and Experimental Flow Simulations to the Aerodynamic Data Base of the DLR Reusable Flight Experiment ReFEx

ReFEx is a Reusable Flight Experiment of the DLR. For the layout of the aerodynamic shape of the vehicle, the identification of a flight trajectory and finally the control systems, extensive data sets are necessary. The focus of this paper lays on the comparison of calculated versus measured aerodynamic coefficients. All simulations were carried out with the DRL TAU Code. The measurements were performed in the trisonic wind tunnel (TMK) of the DLR. One aerodynamic flight control element of ReFEx are the canards. The here presented analysis delivers a good agreement comparing the calculated and measured coefficients, looking at the symmetrical canard deflections. The occurred differences of the asymmetrical canard deflection are discussed in detail, including the numerical as well as experimental uncertainties

Hypersonic Flight Experiment ReFEx: Status and Future Perspectives

The hypersonic flight experiment ReFEx (Reusability Flight Experiment) under development at the German Aerospace Center (DLR) passed the preliminary design review in 2019 and several subsystem CDRs are to be completed this year. The paper summarizes the latest status of major characteristics of ReFEx, the planned reentry corridor, flight and range safety considerations and assessments on the vehicle’s controllability. Examples of the numerical and experimental aerodynamic configuration analyses are shown. The second part of the paper investigates potential next demonstration steps for winged RLV. Intermediate steps on larger and more powerful launch systems are evaluated with the aim of having a liquid-rocket powered demonstrator stage with multiple-flight reusability ready before the end of this decade. A preliminary version of the technology development roadmap will be presented

The Reusability Flight Experiment – ReFEx: From Design to Flight – Hardware

The hypersonic flight experiment ReFEx has been under development at the German Aerospace Center (DLR) for a number of years and passed CDR in September of 2021. It will be launched on a VSB-30 sounding rocket in 2023 from Koonibba Test Range (KTR) in Southern Australia. The sounding rocket will inject ReFEx into a trajectory typical of aerodynamically controlled RLV-booster stages, where it will test several key technologies required for future reusable aerodynamically controlled first stages. A key feature of ReFEx is its sole reliance on aerodynamic means for the return leg of the flight, including a heading change of more than 30°, providing valuable flight data at the other end of the spectrum for RLVs (Reusable Launch Vehicle) from current propulsive return concepts [1]. With its length of 2.7 m, a wingspan of 1.1 m, a mass of approx. 400 kg, ReFEx features a densely packed fuselage, containing systems critical for flight as well as sophisticated sensors for flight analysis. With the passage of CDR, the project is progressing into the flight hardware production and verification phase [1]. The paper summarizes the latest status of ReFEx and shows how key challenges such as trajectory optimization, aerodynamic control with control reversals of the aero surfaces, thermal loading, folding wind systems as well as operational issues such as flight safety and campaign planning where tackled to be able to freeze the design and reach CDR status